EPS 2019

8 Jul 2019, 09:00 → 12 Jul 2019, 18:30 Europe/Rome

Building U6 (University of Milano-Bicocca UNIMIB)

Caterina Riconda (LULI, Sorbonne University - FRANCE)

Dear colleagues,

the 46th European Physical Society Conference on Plasma Physics (EPS 2019) will be held in Milan (Italy), July 8 to 12, 2019. Organized by the European Physical Society (EPS) Plasma Physics Division, this annual conference covers the wide field of plasma physics ranging from nuclear fusion to low temperature, astrophysical and laser plasmas.

The EPS2019 conference is co-organized by the Institute for Plasma Science and Technology of the National Research Council (ISTP Milano – CNR, former IFP-CNR), the University of Milano – Bicocca (UNIMIB) and the International Center Piero Caldirola (ISPP).

We are looking forward to meeting you in Milan.

The Local Organizing Committee

 

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Monday, 8 July

Opening Ceremony

EPS 2019 Opening Ceremony

Maria Cristina Messa, Rector, University Milano-Bicocca
Massimo Inguscio, President, National Research Council of Italy
Caterina Riconda, Programme Committee Chair
Daniela Farina, Local Organising Committee Chair
Richard Dendy, EPS Plasma Physics Division Chair

Convener: R. Dendy

Alfvén Prize Lecture

Convener: R. Dendy (Culham Centre for Fusion Energy)

1 I1.001 Laser plasma accelerators

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.001.pdf

The concept of laser plasma accelerators has been proposed by T. Tajima and Dawson in 1979. Through nonlinear theory and PIC simulations it was shown than GV/cm accelerating field should be produced when intense laser pulse interacts with an underdense plasma in the laser wakefield or in laser beat-wave regime. Since then many schemes have been proposed and demonstrated with fields exceeding TV/m peak accelerating field reached in the non-linear regime demonstrated by V. Malka et al. [2]. This talk reports on 4 decades of discoveries on laser plasma accelerators.

Reference
[1] T. Tajima and J. Dawson, Phys. Rev. Lett. 43, 267 (1979).
[2] V. Malka et al., Science 298, 1596 (2002).

Speakers: T. Tajima, V. Malka (EPS 2019)

10:20 Coffee Break

Plenary Session

Convener: C. Riconda

2 I1.002 Progress and challenges in understanding core transport in tokamaks in support to ITER operations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.002.pdf

Fusion performance in tokamaks depends on the core and edge regions as well as on their nonlinear feedbacks. The achievable degree of edge confinement under the constraints of power handling in presence of a metallic wall is still an open question. Therefore, any improvement in the core temperature and density peaking is crucial for achieving target performance. This has motivated further progress in understanding core transport mechanisms, to help scenario development in present devices and improve predictive tools for ITER operations. In the last decade, detailed experiments and their interpretation via the gyrokinetic theory of turbulent transport have led to a satisfactory level of understanding of the heat, particle, and momentum transport channels and of their mutual interactions. This talk will present some highlights of the progress, which stems from joint work of several devices and theory groups, in Europe and worldwide within the ITPA (International Tokamak Physics Activities) framework. The remaining challenges concern mostly the achievement of predictive capabilities of plasma profiles via integrated modeling, which best accounts for the nonlinear interactions inherent to the multi-channel nature of transport. However, this requires faster, reduced models, and the extent to which they capture the complex physics described by nonlinear gyrokinetics must be carefully evaluated. In a longer term the use of neural networks and high power computers will allow to achieve the best compromise between accuracy and speed.
Amongst the recent developments in transport understanding, particular emphasis will be given to: the importance of nonlinear electromagnetic effects and fast ion populations on the stabilization of ion-scale turbulence, potentially leading to a boost in neutron production; the role of multi-scale interactions between ion- and electron-scale turbulence, which may limit performance in electron heated machines such as ITER; the dependence of core transport on the isotope mass of the main gas, of relevance for reactor Deuterium-Tritium operations; the control of heavy impurity accumulation, impacting scenario development in metallic wall devices. For each topic, a brief survey will be given of present understanding, based on experiments and their interpretation using neoclassical and gyrokinetic theory, and of the capabilities of reduced models to correctly describe the physics needed for reliable integrated modeling and projections to future devices, pointing out where further work is still required.

Speaker: P. Mantica (EPS 2019)

3 I1.003 Exploring driven collisionless reconnection in the Terrestrial Reconnection Experiment (TREX)

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.003.pdf

The newly developed Terrestrial Reconnection Experiment (TREX) [1] in the Wisconsin Plasma Physics Laboratory (WiPPL) [2] is optimized to study magnetic reconnection in a regime where Coulomb collisions between electrons and ions are sufficiently infrequent that kinetic effects in the electron dynamics are retained (see Fig. 1).
In this fully collisionless regime electron pressure anisotropy develops and is fundamental to the structure of the electron diffusion region. The observed signatures of reconnection include narrow electron jets and current layers with widths down to the scale length of the electron skin depth, confirming previous results from fully kinetic simulations. Meanwhile, the experimental rate of reconnection is surprisingly large, with inflow speeds to the reconnection region being similar to the Alfvenic outflow speeds observed in the reconnection exhaust. Consequently, the normalized reconnection rate, on the order of unity, is about an order of magnitude larger than those typically observed in undriven systems. Driven reconnection scenarios are important to a range of systems including the interaction of stellar winds with planetary magnetospheres. The large rate of reconnection observed in TREX may also be helpful to explain burst of radiations from energetic electrons generated in supernova remnants.

References
[1] J. Olson, et al., Phys. Rev. Lett 116, 255001 (2016)
[2] C.B. Forest, et al., Jour. Plasma Phys., 81, 345810501 (2015)

Speaker: J. Egedal (EPS 2019)

4 I1.004 Mass spectrometry and plasma chemistry of atmospheric pressure plasma jets

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.004.pdf

Atmospheric pressure non-equilibrium plasmas are effective source of large densities of reactive radicals, metastables and ions and also high fluxes of photons with wavelengths down to the vacuum UV range. The resulting high reactivity of these APPs can be used in many surface treatment applications such as activation of polymer surfaces, treatment of living tissues (decontamination, acceleration of wound healing) or in deposition of thin films or nanostructured materials. However, the complexity of plasma-chemical processes in the discharge requires combined experimental and theoretical approach in plasma analysis, where quantitative and qualitative plasma diagnostics are compared with theoretical plasma simulations. In this contribution, molecular beam mass spectrometry (MBMS) for detection of neutral reactive and stable species and positive and negative ions will be introduced and discussed in detail. The advantage of mass spectrometry is that it measures the directly at the surface, the place of interest for any surface treatment, and it is not limited by existence of accessible optical transitions. Additionally, mass spectrometry provides absolute densities of the measured species when properly designed and carefully calibrated. It can even provide information about vibrational excitation of the detected species or about electronically excited metastables. The ion mass spectrometry can provides information about the formation of positive and negative ions (and ion clusters) in the effluent and provides supporting information about the influence of variety of species (including impurities) on plasma chemistry. These experimental results serve for validation of plasma-chemistry models and rate-equation calculations, which can provide deep insight into the whole plasma and plasma-surface interaction. Several examples of investigation of plasma chemistry processes in gas mixtures and at the surface relevant for plasma medicine applications and growth of thin films will be discussed.

Speaker: J. Benedikt (EPS 2019)

12:30 Lunch

Poster P1

5 P1.1001 Spectral structure and isotopic dependence of NBI ICE in the TUMAN-3M tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1001.pdf

Ion cyclotron emission (ICE) in tokamak plasmas has recently become a subject of enhanced interest due to their potent capability to be used as a diagnostic tool for fast ion and charged fusion product confinement characterization. At the TUMAN-3M tokamak, ICE is observed both in ohmic and NBI heated plasma. In former experiments on the TUMAN-3M with NBI plasma, the heating beam composed of approx. 40% hydrogen and 60% deuterium. The ICE was found to originate in central plasma region, with frequency corresponding to IC resonance for fast minority ion (i.e. deuterium (hydrogen) in hydrogen (deuterium) target plasma). Recently, thank to improvement in beam ion source fueling system, nearly pure hydrogen or deuterium beams are routinely available on the tokamak. The paper report on last observation of spectral characteristics of the ICE made with pure H or D beams injected in plasma with different isotope composition.
In the shots with D-beam injected into D-plasma with negligible hydrogen concentration, the ICE frequency was found to correspond to second harmonic of IC resonance frequency for deuterium, in NBI power (or energy) is bellow some threshold value. If this threshold is overcome, fundamental deuterium IC frequency appears. Thus, the observed ICE frequency matches not a minority IC but the main ion IC frequency. Symmetrical situation (H-beam injection into H-plasma) is currently under investigation.
The spectral lines of ICE were found to have a fine structure, which may be attributed to several effects, such as mixed beam composition or excitation of different spatial modes. Experiments with pure hydrogen and deuterium beams make it possible to discriminate between possible mechanisms of splitting of the spectral line.

References
1. Askinazi L.G. et al 2018 Nucl. Fusion 58 082003
2. Askinazi L.G. et al 2018 Proc. 45th EPS Conf. on Plasma Phys. P5.1084
3. Askinazi L.G. et al 2018 Technical Physics Letters 44 1020

Speaker: L. Askinazi (EPS 2019)

Abstract

6 P1.1002 Assessment of the current density evolution during an ELM cycle using beam emission polarimetry at ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1002.pdf

The knowledge of the current density in the pedestal region of H-mode plasmas is important to understand the stability of the pedestal with respect to edge localised modes (ELMs). The current density is connected to the poloidal magnetic field Bp via AmpËres law, which can be determined by an accurate measurement of the field line angle gamma = arctan (Bp/Bt) where Bt is the toroidal magnetic field. The D alpha line of fast neutral beam atoms is split due to an electric field in the rest frame of the atoms (motional Stark effect) and the multiplet contains in the centre sigma-lines, which are polarised perpendicular to the electric field, and pi-lines, which are polarised parallel to the electric field. The beam emission polarimetry diagnostic at ASDEX Ugrade [1] determines their polarisation direction at 5 spatial locations across the pedestal region. Three independent observations of each spatial location are used, where each optical head includes a polariser, which is roughly oriented at 0Deg, 45Deg, and 90Deg with respect to the electric field. The full multiplet is measured with a spectrometer with 3 ms time resolution. The 0Deg/90Deg channel serves as a reference for the strength of the pi-/ sigma-lines, while the 45Deg channel yields via radiance variations of the pi- and sigma-lines information about changes of the electric field direction. Changes in the design of the optical head, which resolved straylight issues mentioned in [1], and major improvements of the calibration and the spectra fitting analysis were established.
In an H-mode dicharge with Ip=1 MA and low frequency type-I ELMs with W(ELM)=50 kJ, the measured difference of Bp between pedestal top and separatrix was 25 mT before the ELMs. The Bp profile flattens during the ELMs with a stronger decrease at the separatrix and steepens again up to the next ELM. The interpretation of the Bp profile in terms of current density models and pressure constrained equilibria will be discussed and the recovery after the crash will be compared to the evolution of density and temperature of the electrons and the ion temperature.

[1] E. Viezzer, R. Dux, et. al, Rev. Sci. Instr, 87 11E528 (2016).

Speaker: R. Dux (EPS 2019)

7 P1.1003 Status of neutron emission spectroscopy diagnostics at the EAST tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1003.pdf

Measurements of fusion neutron spectrometry is one of the important diagnostics in EAST, with DD neutron yield from 10^9 to 10^15 n/s for deuterium plasma discharges with neutral beam injection, lower hybrid waves, ion cyclotron resonance frequency heating and their combination. A suite of compact neutron spectrometers, based on liquid scintillators (LSs) and a stilbene crystal detector has been installed and implemented on EAST for lower yield neutron measurements. The liquid scintillation and stilbene neutron spectrometers have been for the first time applied to successfully measure the neutron spectra for the low neutron yields and the ion temperature values were obtained from the deduced neutron spectra by a forward fitting method applied to the measured pulse height spectra. The neutron time-of-flight enhanced diagnostics (TOFED) spectrometer has been installed at the J port of EAST in order to study the behaviour of fast ions produced by the injection of external auxiliary power. The new design, where the ring of second plastic scintillators (S2) is split into two spherical zones, is shown to enhance the discrimination capability and will provide fusion neutron spectra with reduced admixture of multiple scattering events, which is essential for increasing the sensitivity to weak components in the neutron emission. This system includes a total of 80 S2 plastic scintillators and a five-layered detector (S1) assembly coupled to photomultiplier tubes. A new fully digital data acquisition system with on-board CFD timing function has been adopted and can provide a time resolution <500 ps, compatible with high count rate capability up to about 1 MHz/channel of the spectrometer. The energy resolution and detection efficiency of TOFED are about 6.6% and 1.8%, respectively. During the EAST 2017 and 2018 summer campaigns, synergized diagnostics from the TOFED and LS spectral measurements were performed for the first time, and the different components of neutron spectra and the velocity distributions of fast ions are successfully obtained at EAST plasmas with NBI heating.

Speaker: T. Fan (EPS 2019)

8 P1.1004 The role of the plasma diagnostics in compacttraps: from ion sources to nuclear astrophysics research

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1004.pdf

Axis-symmetric magnetic traps have been used for decades asion sourcesfor accelerators. Recent searches, however, revealed that plasma generated in compact traps is also a surprising environment for studies of nuclear astrophysics, includingnuclear beta-decays andplasma instabilities connected to solar flares. Either if used as an ion source or for astrophysics studies, the diagnostics of the magneto-plasma generated in compact traps is a key issue. In both cases, thekey goal of plasma diagnostics is the volumetric knowledge of the electron energy distribution function (EEDF) and the on-line measurementof the charge state distribution (CSD) within the plasma volume. These goals can be achieved by means of the simultaneous use of different diagnostics operating in different energy domains. The developed setup includes an interfero-polarimeter for total plasma density measurements(a back scattering profiling is in a development phase), a multi-X-ray detectors system for X-ray spectroscopy (including time resolved spectroscopy), a X-ray pin-hole camera for high-resolution 2D space resolved spectroscopy and different spectrometers for the plasma-emitted visible light characterization. The development of time resolved diagnostics is being allowed to attain precious information about the non-stationary phases ECRIS plasmas can undergo. Its full development will allow the investigation of plasma ignition, after-glow and Cyclotron-Maser instabilities and it is expected to allow the overcoming the current limitations of existing ion sources. A description of recent results about plasma parameters characterization in quiescent and turbulent Electron Cyclotron Resonance-heated plasmas will be also given. A complete characterization allowed thestudy, in particular, of the time evolution of X-ray spectra. Finally, the experimental setup is going to be further upgraded in order to allow measurements of nuclear decays in magnetoplasmas.

References
[1] G. Haas, J. Gernhardt, M. Keilhacker, E. B. Meservey and the ASDEX Team, J. Nucl. Mat. 121, 151 (1984)
[2] G. Haas and H.-S. Bosch, Vacuum 51, 39 (1998)
[3] U. Wenzel, T. Kremeyer, G. Schlisio, M. Marquardt, T. S. Pedersen, O. Schmitz, B. Mackie, J. Maisano-
Brown and the W7-X team, J. Instrum. 12, C09008 (2017)
[4] U. Wenzel, T. S. Pedersen, M. Marquardt and M. Singer, Rev. Sci. Inst. 89, 033503 (2018)

Speaker: G. Castro (EPS 2019)

9 P1.1005 Impurity transport studies using TESPEL in W7-X stellarator

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1005.pdf

The tracer-encapsulated solid pellet (TESPEL), which can be considered as an impurity-embedded hollow pellet, was developed at NIFS, Japan to promote detailed impurity transport studies in magnetically-confined high-temperature plasmas [1]. Recently, a TESPEL injection system has been commissioned on the Wendelstein 7-X (W7-X) stellarator at IPPGreifswald, Germany through on a collaboration between NIFS, IPP and Ciemat [2]. This has been prompted by the need to identify W7-X operation scenarios that avoid the impurity accumulation predicted for high-density steady-state discharges of this optimized stellarator [3]. Since its plasma volume is similar to that of the Large Helical Device (LHD), similar sized TESPELs are used for W7-X and LHD: the outer diameter is about 700/900 µm. One advantage of TESPEL is that it produces a 3-dimensionally isolated extrinsic impurity source inside the magnetically confined plasma. Such a local deposition of the tracer impurity embedded in the TESPEL has been confirmed in W7-X plasmas by signals from filtered PMTs, which view the light emissions from the ablation cloud from its injection port. The temporal evolution of various emission lines from highly-ionized tracer impurities has been observed clearly by other diagnostics installed in the W7-X, e.g., HEXOS, PHA, XICS, HR-XIS [4]. In particular, HEXOS clearly observed a local maximum in the temporal behaviour of some spectral lines emitted by tracer impurity ions. This is primarily attributed to the processes of outward transport and recombination of the impurity ions that come from inside the plasma where the tracers are deposited. Thus, this result clearly emphasizes the usefulness of the TESPEL for precise (local) studies of impurity transport. The temporal evolution of the line emissions observed by these various diagnostics is also compared with 1-D modelling by the STRAHL code for estimating impurity transport coefficients. In the W7-X, a laser blow-off (LBO) system is also installed as a complementary impurity injection method [5]. Therefore, the impact of impurity source location (at the core by TESPEL and at the edge by LBO) on impurity transport can be uniquely investigated in the W7-X. In this contribution, initial assessments of results from the TESPEL injection experiments in the operational phase OP1.2b of W7-X will be reported and discussed.

[1] S. Sudo, J. Plasma Fusion Res. 69, 1349 (1993).
[2] R. Bussiahn et al., Rev. Sci. Instrum. 89 10K112 (2018).
[3] R. Burhenn et al, Nucl. Fusion 49 (2009) 065005
[4] H. Thomsen et al., JINST 10 P10015 (2015).
[5] Th. Wegner et al., Rev. Sci. Instrum. 89, 073505 (2018)

Speaker: N. Tamura (EPS 2019)

10 P1.1006 Local measurements of the radial plasma velocity fluctuations in the FT-2 tokamak core plasmas by equatorial enhanced scattering

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1006.pdf

Considerable interest in radial fluctuations of plasma velocity is associated with their significant role in the formation of turbulent radial flows. In this paper we implement the new microwave technique - the equatorial enhanced scattering (EES) [1], possessing the submillimetre spatial radial resolution and demonstrate its feasibility for diagnosing the radial plasma velocity fluctuations temporal and spatial characteristics. The developed diagnostics utilizes the equatorial microwave X-mode probing by a narrow beam from the high field side and measurements of backscattering off small-scale density fluctuations in the upper hybrid resonance (UHR) vicinity. The radial propagation of the density fluctuations at a radial velocity associated with the plasma motion leads to the Doppler frequency shift in the EES spectrum. The random nature of the plasma radial motion leads to the broadening of the frequency spectrum at long-term measurements of the backscattered signal. An analysis of alternative mechanisms of the EES signal spectral broadening associated with poloidal plasma rotation (including GAM) or with a small-angle scattering of the probing/scattering wave in the UHR [2, 3] allowed to find the limits of applicability of the method. The dual-frequency probing provides the possibility to measure the radial correlation length of the velocity fluctuations in the equatorial plane. The local correlations between fluctuations of the EES Doppler frequency shift and oscillations of the scattered power of the X-mode reflectometer with the low field side equatorial probing were revealed. This effect, indicating the presence of correlation between the radial velocity fluctuations and the level of density fluctuations, possesses a potential for experimental investigation of the radial turbulent particle flux in the plasma. The experimental measurements data were compared to results of numerical gyrokinetic simulation by the global full-f nonlinear code ELMFIRE in the FT-2 tokamak regimes where the detailed validation was performed for the multi-scale turbulence [4].

[1] A.D. Gurchenko, E.Z. Gusakov, 2018 Technical Physics Letters 44, 337.
[2] A.D. Gurchenko, et al. 2004 Plasma Phys. Reports 30, 807.
[3] E.Z. Gusakov, A.V. Surkov, 2002 Plasma Phys. Reports 28, 827.
[4] P. Niskala, et al., 2018 Nuclear Fusion 58, 112006.

Speaker: A. Gurchenko (EPS 2019)

11 P1.1007 Tomographic reconstruction of COMPASS tokamak edge turbulence from single visible camera data and automatic turbulence structure tracking

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1007.pdf

The growing capabilities (speed, sensitivity, dynamic range) of fast visible cameras make this tool more and more interesting for diagnosing turbulence in plasma devices, and in particular,
in fusion ones. Especially, cameras' speed is approaching probe acquisition frequencies while they usually reach higher spatial resolution. On the other hand, light emission from a plasma
is usually not local and makes the data interpretation difficult. To overcome this 3D problem, imaging of a poloidal gas-puff jet has become a common method. However, this method is
known to locally perturb the plasma and to have effect on the probed turbulence [1].
In this contribution, we present tomographic inversion of edge turbulence recorded by a single visible camera observing the interaction between the edge plasma and the neutral gas naturally present in the vacuum vessel (i.e. no extra gas-puff) [2] - therefore a fully passive observation. Since the observed turbulent structures (filaments) are 3D and their images on the camera chip 2D, an assumption has to be taken to avoid ill-posed problems. As velocities of charged particles along field lines are very high, it is possible to assume that light emissivity is constant along that direction and then to reconstruct any poloidal plane in the field of view of the camera. Within this assumption, the method has been carefully checked using synthetic data from the TOKAM3X code [3] and then further validated by comparing experimental camera and Langmuir probe data. Using a recently developed detection and tracking software [4], it is then possible to study the position, size and velocity of the turbulent structures in the reconstructed poloidal plane and to obtain reliable statistics. Examples illustrating the benefits of the method for the characterization of edge plasma turbulence will be presented.

References:
[1] S. Zweben et al., Plasma Physics and Controlled Fusion, 49 (S1-S23), 2007.
[2] J. Cavalier et al., Nuclear Fusion, submitted (November 2018).
[3] P. Tamain et al. Journal of Computational Physics, 321 (606-623), 2016.
[4] R. Baude and M. Desecures. Track software. http://www.aprex-solutions.com/, 2018.

Speaker: N. Lemoine (EPS 2019)

12 P1.1008 Fundamental O-mode ECRH assisted low-loop voltage plasma start-up in tokamak ADITYA-U

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1008.pdf

The EC assisted low-loop voltage plasma start-up experiments have been carried in Tokamak ADITYA-U. The 42GHz ECRH system is used for off-axis breakdown in tokamak, which is operated at a toroidal magnetic field of ~ 1.2T. The EC power in fundamental O-mode is launched from low field side of the tokamak. The EC power and duration for breakdown are varied from 75kW to 150kW and from 50 ms to 100 ms respectively. The ECRH power is launched around 25ms before the start of the loop voltage and successful plasma start-up is achieved with 30-35% reduction in the peak loop voltage. In ADITYA-U, the gas breakdown and successful plasma start-up is normally achieved atpeak loop-voltage of ~20V (Electric field ~ 4.5V/m). In these EC-assisted low-loop voltage plasma start-up experiments, the peak loop voltage is reduced to 30–35% (~13V) by reducing the resistance values in the ohmic circuit. Without the EC assisted pre-ionization, no successful plasma start-up has beenachieved at this loop voltage. However, when EC-power launched around 30ms before the start of the loop voltage andpre-ionization is created with the help of EC, successful plasma start-up and current ramp-up has been achieved similar to those obtained at higher peak loop voltages without the EC pulse. Successful EC-assisted plasma discharges with plasma current ~115kA and discharge duration of ~250ms has been achieved with low (~13V) peak loop-voltage. The hydrogen fill pressure is ~1x10^-4mbar and the pre-ionized plasma density is ~ 1x10^18m^-3. As the pre-ionized plasma breakdown is obtained through fundamental harmonic of EC, the Halpha emission appears almost simultaneously with the start of EC-power pulse. It shows no delay in breakdown at fundamental harmonic. The EC-assisted low-loop voltage experiments arecontinuingfurther to obtain plasma discharges with peak loop voltage <10V in ADITYA-U. The paper will discuss the technical and physics details on fundamental harmonic EC assisted breakdown and successful low peak-loop-voltage plasma start-up in ADITYA-U.

Speaker: B. Shukla (EPS 2019)

13 P1.1009 Feasibility study and physics performance of a fast-ion loss diagnostics for the JT-60SA tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1009.pdf

The JT-60SA tokamak will be able to operate in scenarios with large fraction of fast-ion pressure. The fast-ion population with supra-alfvenic velocities is expected to play an important role in the stability of magnetohydrodynamic (MHD) fluctuations, in particular of the Alfven Eigenmodes (AEs). Direct wave-particle interaction between fast-ions and AEs may lead to enhanced fast-ion transport and eventual losses. In this context, scintillator based fast-ion loss detectors (FILDs) are diagnostics with unique capabilities for the investigation of the mechanisms underlying the wave-particle interaction. FILDs are charged particle collectors that work as magnetic spectrometers making use of the magnetic field of the tokamak and a collimator to disperse the escaping ions onto a scintillator plate. The impinging position of the ions in the scintillator plate depends on their energy and pitch-angle, thus giving complete information on the velocity-space of the escaping ions. The use of fast scintillator materials provides high temporal resolution, making possible the identification of MHD fluctuations responsible for the fast-ion losses. In this work, relevant aspects regarding the conceptual design of a FILD detector for JT60SA are presented. According to the location of the diagnostic within the machine, full orbit simulations allow estimating the expected signal. Furthermore, finite element simulations are used to assess the structural integrity of the detector, considering different effects such as the plasma thermal load and the magnetic field variations during disruptions.

Speaker: J. Ayllon-Guerola (EPS 2019)

14 P1.1010 Conceptual design of DTT magnetic diagnostics

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1010.pdf

The Divertor Tokamak Test (DTT) is a new tokamak device whose main mission is to explore innovative divertor concepts for DEMO and test them in heat loads conditions on plasma facing components relevant to a fusion reactor. The device is presently going through a detailed design process, and the tendering process has started for some of the components. Magnetic diagnostics for plasma current and shape control, and vertical position stabilization are essential diagnostics for tokamak operation, and are the first diagnostic components that will need to be ready for installation and commissioning when DTT vacuum vessel and magnets are assembled. The DTT operational conditions for in-vessel and ex-vessel magnetic diagnostics resemble those that will be encountered in ITER (high heat flux, long pulses, large Electromagnetic stresses), except for the 14MeV neutron effects. Furthermore the compact machine assembly implies a very tight space for High Field Side sensors, both in-vessel and ex-vessel, therefore a dedicated thin sensors design is mandatory. In this work the conceptual design of DTT magnetic diagnostics will be presented, including Mirnov Coils, LTCC coils, saddle loops, flux loops and diamagnetic loops, Hall probes and optic fibre plasma current measurements. The constraints that have been taken into account in choosing the sensors technology will be outlined, motivating the different design choices. Sensors number and sensitivity have been determined with a model-based optimization procedure: the error in the reconstruction of plasma current and current centroid position has been iteratively estimated by varying the placement of a current filament on a grid spanning the vacuum vessel volume. The maximum reconstruction error has been evaluated for different sensors number, position and effective area (NA). The optimal sensors setup will be discussed, in order to keep the error in plasma current less than 1%, and the error on the current centroid position less than 1cm. Finally the difficult task of integrating the sensors design with the machine first wall and vacuum vessel design will be discussed.

Speaker: M. Baruzzo (EPS 2019)

15 P1.1011 Runaway electrons expulsion during tokamak instabilities

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1011.pdf

The expulsion of runaway electrons (REs) in the presence of magnetic islands is studied for different island dynamics and different RE population fraction. Clear correlations are found between magnetic island size and RE diagnostics, in particular hard x-ray emission and a single-channel Cherenkov probe placed in the limiter shadow. The Cherenkov probe permits the detection of fast electrons expulsion with a high level of detail, presenting waveforms with 100% signal contrast during tearing mode growth and rotation, which implies strongly non-axisymmetric RE flux in the limiter shadow. Correlations between Cherenkov signal, hard x-ray emission and electron cyclotron emission also reveal the impulsive transfer of RE momentum from parallel to perpendicular degrees of freedom, which is likely due to pitch angle scattering on plasma waves, i.e., the so-called anomalous Doppler instability. The Cherenkov signal response to magnetic islands rotation changes dramatically as the RE pitch angle increases, in particular the peak amplitude increases and the phase shift with respect to the magnetic signal changes. These experimental observations provide both ideas and benchmark data to challenge the modelling of RE interaction with non-axisymmetric perturbations. For example, the ratio between Cherenkov and hard x-ray signals, which is indicative of the RE halo thickness in the limiter shadow, increases markedly with magnetic perturbation amplitude, and pulses of the same type but with different RE content (see figure) follow a common, non-linear trend.

Speaker: F. Causa (EPS 2019)

16 P1.1012 Physics requirements for the VUV survey spectrometer intended for the divertor radiation monitoring on JT-60SA

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1012.pdf

JT-60SA is a fusion experiment designed to support the operation of ITER and to investigate how best to optimize the operation of future fusion power plants. For the safe operation of the device, a survey spectrometer observing the plasma from an equatorial port is foreseen to monitor light impurities such as carbon and oxygen, metal impurities and extrinsic impurities injected ad hoc to mitigate the power exhaust problem. A second survey spectrometer, to be designed and constructed within the presented work, positioned on an upper port with a vertical line of sight, will complement the monitoring activity of the first system by measuring the relative contribution of the various impurities to the radiation losses in the divertor region and by studying the physics of the plasma-divertor detachment mechanism. It is aimed at up to 1 ms time resolution, 20-130 nm wavelength range and, when in imaging mode, a space resolution of about 5 cm. This contribution will highlight the details of the spectrometer-divertor plasma optical coupling, designed in order to optimize the inspection of the divertor region, the two dimensional detector to be used and the alignment procedure. The zero order of the spectrometer is planned to be fed into a visible spectrometer via fiber optics for the absolute calibration of the VUV spectrometer and also to provide monitoring of high n transitions of various C or Ne ionization states. The spectrometer, jointly designed by an EU-Japan team, will be procured by Eurofusion and installed on JT60-SA in late 2022.

Speaker: M. Chernyshova (EPS 2019)

17 P1.1013 Tangential phase-contrast imaging for fluctuation measurements in JT-60SA: a conceptual study

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1013.pdf

This contribution will present a feasibility study and conceptual design of a tangential phasecontrast imaging (PCI) diagnostic for the new JT60SA tokamak. PCI is a well known technique for measuring density fluctuations. Tangential launching, combined with an appropriate spatial filtering technique, affords the measurement highly improved spatial localization, as demonstrated in particular on the TCV tokamak. Tangential ports of 20cm diameter are envisioned to be used on JT60SA, obviating the need to mount steering optics on the vessel, which would be likely to introduce strong mechanical vibrations that would complicate the setup. The tangency point would be at a major radius 1.755 m, which is close to the inner wall; this is less advantageous than a tangency point on the magnetic axis or at midradius, but neither of these options is currently available. Still, a spatial resolution of approximately 10 to 20% of the minor radius can be achieved both in the core and in the pedestal region for k~10 cm^-1, which is near the highwavenumber limit of the ITGTEM spectral region, in both the noninductive highN and the inductive fullpower doublenull scenario. At longer wavelengths, e.g., k~2 cm^-1, the resolution becomes coarser, though it can still approach 20% of the minor radius in the inductive scenario. In the electronscale (ETG) region of the spectrum, the resolution becomes considerably better. The preliminary design presented here will illustrate the possible options regarding spectral access in both frequency and wave number, and will include hardware specifics such as the requirements for neutron and gamma shielding. The presentation will also discuss turbulence simulations with the fluxtube version of the gyrokinetic code GENE that have been performed to assist the design. It is envisioned that, at such time as the diagnostic becomes operational, this modeling machinery will be coupled with a synthetic diagnostic for meaningful theoryexperiment comparison.

Speaker: S. Coda (EPS 2019)

18 P1.1014 Plasma operation and electric field measurements in IShTAR

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1014.pdf

The overall goal of the IShTAR (Ion Cyclotron Sheath Test ARrangement) project is studying antenna near-fields in the presence of a plasma and magnetic field to assess theoretical predictions on RF sheaths and to guide theoretical modelling [1]. For antenna studies it is favourable to operate at tokamak edge-like conditions for density and temperature. Plasma characterisation has been done in a systematic way in order to obtain reproducible density profiles in front of the ICRF antenna. An extensive exploration of the discharge parameters (such as the neutral gas pressure, the gas type, the helicon antenna power and the magnetic field topology) was performed. Resulting density profiles will be presented. They have been obtained by an array of langmuir probes. The profiles have been documented in a database, which can be directly used for future operations. Furthermore, progress will be reported on electric (E) field measurements using helium spectroscopy. A new gas injection system has been implemented, which allows for a local gas puff of helium in the vicinity of the ICRF antenna. The goal is to increase the emission intensity of the spectral lines at the location of the sheath. In that way argon can be used as main gas, which creates plasmas in IShTAR with densities that are 10 times than for pure helium. The system is operational and first results will be presented. Also, a fibre bundle has recently been installed to complement the single fibre observation point, which was reported in [2]. The array focuses 7 fibres onto a 1 cm spot at the edge of the ICRF antenna. The fibres are stacked on top of each other at the entrance slit of a high-resolution spectrometer. For high E-fields (above 1 kV) Stark effects can be observed on the helium spectra (typically He I at 474.1 nm is selected). The fibre array will give information on the evolution of the electric field inside the sheath.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The work received support from the Research Foundation Flanders (G0B3115N).

[1] K. Crombé et al., "IShTAR: a helicon plasma source to characterize the interactions between ICRF and plasma", 26th IAEA Fusion Energy Conference (2016), EXP6_48.
[2] A. Kostic et al., "Development of a Spectroscopic Diagnostic Tool for Electric Field Measurements in IShTAR (Ion Cyclotron Sheath Test ARrangement)", Review of Scientific Instruments (2018) 89 (10), 10D115.

Speaker: K. Crombe (EPS 2019)

19 P1.1015 Development of gamma-ray spectrometers optimized for runaway electrons bremsstrahlung emission in fusion devices

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1015.pdf

The production of relativistic runaway electrons during disruptions can potentially compromise the integrity of plasma-facing-components in large tokamaks. In ITER up to 70% of the initial plasma current can be converted into relativistic runaway current. The energy content of such runaway electron beam can reach several tens of Megajoules. If untamed, a runaway electron beam colliding with the first wall can melt several kilograms of material in a single event, posing a significant threat to the machine [1]. Runaway electron production, control and mitigation is therefore currently one of the main topics studied in midsize and large-scale tokamaks.
A variety of diagnostic techniques are employed to characterize the runaway electron population. If the runaway electron beam remains well confined during the disruption, information on the runaway electron energy distribution can be extracted by measuring the bremsstrahlung radiation emitted by the interaction between the beam and the post disruption plasma. In order to do this, it is necessary to build a custom high counting rate (> 1MHz) gamma-ray spectrometer that can reliably measure the bremsstrahlung spectrum up to tens of MeV and a suitable deconvolution code that can retrieve the runway electron distribution from the measured spectrum.
In this work, we discuss the design of a new gamma-ray spectrometer optimized for runaway electrons bremsstrahlung emission. The detector is made of a LaBr3:Ce scintillator crystal coupled to a photomultiplier tube. An improved acquisition system allows for continuous data collection. This device was used to measure the gamma-ray emission during the 2019 runaway electron experiments at Asdex Upgrade. Results achieved are promising for inferring information on the high energy component of the runaway electron distribution in tokamaks.

[1] Hender TC, Wesley JC et al., Nuclear Fusion 47 (2007) S128-S202.

Speaker: A. Dal Molin (EPS 2019)

20 P1.1016 Design and development of probe for the measurements of runaway electrons inside the GOLEM tokamak plasma edge

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1016.pdf

Repeatable discharges with high loop voltage and low-density in GOLEM tokamak [1] present good experimental conditions for the study of runaway electrons (RE). A probe is being designed and developed for the spectral measurement [2] of RE energy inside and near the GOLEM tokamak plasma edge. Probe design is based on simulation results of FLUKA code [3] that estimates the energy absorbed by the filters of high-density materials and scintillating crystals. Simulations performed for the electron beams of energy 1-10MeV suggest that runaways may have energy much higher than 1MeV in the GOLEM tokamak. In the simulations, graphite, stainless steel, molybdenum and tungsten were tested to filter the suprathermal electrons. Since having low-Z and being sensitive to gamma radiations and electrons, (Y2SiO5:Ce) [2] scintillation crystal is chosen for the probe. However, flexible design of the probe allows different scintillating crystal and filter materials inside it. In the conference, design, development and preliminary results of the RE measurements by the probe will be presented.

References
[1] V. Svoboda, et al., Fusion Engineering and Design 86(6-8) 1310 (2011)
[2] T. Kudyakov et al., Review of Scientific Instruments 79 10F126 (2008)
[3] A. Ferrari, et al., FLUKA: A multi-particle transport code (Program version 2005). No. INFN-TC-05-11 (2005)

Speaker: P. Dhyani (EPS 2019)

21 P1.1017 An imaging heavy ion beam probe diagnostic for the ASDEX Upgrade tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1017.pdf

A new diagnostic - the imaging heavy ion beam probe (i-HIBP) [1] - for the simultaneous measurement of plasma potential, magnetic field and density fluctuations is being developed at the ASDEX Upgrade tokamak. A neutral beam of heavy atoms is injected into the plasma at energies around 70 keV. As the neutral primary beam penetrates the plasma, it ionizes leading to the generation of a fan of secondary beams which are deflected by the magnetic field of the tokamak and collected by a scintillator plate placed behind the limiter shadow of the machine. The light emitted by the scintillator plate is imaged by a fast-camera which provides high spatial and temporal resolution. The light pattern measured at the scintillator plate contains radially resolved information about the density, potential and magnetic field in the edge and scrape-off layer regions of the plasma. Detailed modelling of the beam trajectories has been carried out in order to find the optimum setup within the machine spatial constraints. The modelling includes the 3D magnetic field of the tokamak, to take into account effects such as the toroidal field ripple, as well as beam attenuation effects for Caesium and Rubidium atoms, in which electron impact ionization and charge exchange processes have been considered. Based on this modelling, a sensitivity study has been carried out to determine which physics phenomena can be investigated with the i-HIBP at ASDEX Upgrade. The hardware design will be presented, including the arrangement of the injector out-vessel and the scintillator and optics in-vessel. The results of laboratory tests for the characterization of the injector will be discussed.

[1] J. Galdon-Quiroga et al, JINST 12 C08023 (2017)

Speaker: J. Galdon-Quiroga (EPS 2019)

22 P1.1018 A plug-probe diagnostics for the measurement of electric field fluctuations in the turbulent state of the simply magnetised toroidal plasma device THORELLO

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1018.pdf

Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as well as in basic plasma physics toroidal devices. In particular the understanding of turbulent transport mechanisms has a great interest for the improvement of the magnetic confinement. Here we discuss the use of plug-probes, a suitable modification of traditional Langmuir electrostatic probes, for an experimental investigation of plasma parameters fluctuations of a turbulent, low beta, low temperature plasma in a simply magnetised toroidal configuration. The experiments have been executed on the Thorello device, operating at the University of Milano-Bicocca [1]. In this device, a low temperature, high density plasma can be produced in a steady configuration by driving a hot cathode discharge in low pressure hydrogen gas. In particular, in toroidal magnetised plasmas a large fraction of anomalous particles and energy transport is attributed to the propagation of coherent structures [2]. These are isolated and intermittent structures, with density and temperature above the surrounding plasma, extending along field lines and propagating away from the bulk. In simply magnetized toroidal devices, like Thorello, the propagation is controlled mainly by the ExB drift velocity. The local electric field is determined by the overall discharge conditions as well as by the electrical potential fluctuations, in particular the contribution of the coherent structures themselves. In our presentation we discuss the use of a plug-probe diagnostics for a better reconstruction of the properties of electric field fluctuations. Besides a characterization and optimization of the probe performances, some properties related to the plasma structures that develops and propagates in the edge region are presented too.

[1] R. Barni, C. Riccardi, Plasma Phys. & Contr. Fusion 51 (2009) 085010.
[2] G.R. Tynan, A. Fujisawa, G. McKee, Plasma Phys. & Contr. Fusion 51 (2009) 113001.

Speaker: E. Ghorbanpour (EPS 2019)

23 P1.1019 Doppler coherence imaging of puffed nitrogen SOL flows

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1019.pdf

The new Doppler Coherence Imaging Spectroscopy (CIS) system from Wendelstein 7-X (W7X) [1] is temporarily installed at ASDEX Upgrade (AUG) for a first extensive investigation of puffed nitrogen flows in the SOL and divertor. CIS is a powerful tool to measure 2D images of line-integrated, emission-weighted impurity ion and neutral flows in plasma regions that emit visible spectral lines [2]. It is a camera-based, passive optical diagnostic that detects the emission of a selected spectral line, for which an interferometric pattern is produced by a set of birefringent crystals. By the Fourier analysis of this pattern and comparison with a reference image of known wavelength, spectral information such as the Doppler shift can be determined. This work will present the CIS diagnostic set-up on AUG, that comes with the new addition of a tunable laser (called C-Wave [3]) as calibration source, which was successfully implemented and tested for the first time on W7-X [4]. With C-wave, direct calibration for several spectral N lines becomes possible, significantly simplyfing the N flow analysis.

CIS has been successfully tested on AUG already, and flows of intrinsic carbon and helium as well as neutral deuterium flows could be investigated in cases of attached regimes [5]. By the puffing of nitrogen, fully detached regimes can be reliably achieved in the tungsten divertor of AUG [6]. Assisted with the data of other diagnostics, the line-integrated SOL flow data from CIS allows a detailed characterization of an H-mode power exhaust scenario to further constrain numerical modeling of power exhaust in AUG by codes such as SOLPS. This work will present the diagnostic preparation and set-up for first N flow measurents with CIS on AUG.

References
[1] V. Perseo et al., 44th EPS Conf. on Plasma Phys. 41F, 5.103 (2017)
[2] J. Howard, J. Phys. B: At. Mol. Opt. Phys. 43, 144010 (2010)
[3] J. Sperling and K. Hens, Optik und Photonik 13 (Issue 3), Best of Applications, 22-24 (2018)
[4] D. Gradic, V. Perseo, R. Konig et al., Fus. Eng. Des. (accepted) (2019)
[5] D. Gradic, O.P. Ford, A. Burckhart et al., Plasma Phys. Control. Fusion 60, 084007 (2018)
[6] A. Kallenbach, M. Bernert, M. Beurskens et al., Nucl. Fusion 55, 053026 (8pp) (2015)

Speaker: D. Gradic (EPS 2019)

24 P1.1020 Study of statistical ELM properties by lithium beam emission spectroscopy on COMPASS

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1020.pdf

Recently, the Lithium Beam Emission Spectroscopy (Li-BES) system [1,2] on the COMPASS tokamak has reached its full diagnostic capabilities. It is used for routine automatic measurements in a majority of COMPASS discharges and serves as a standard tool for reconstruction of fast (up to 2 s) density profiles in the edge plasma region [3]. During the course of recent few years, an extensive database of COMPASS Li-BES measurements has been established. One way to utilize this set of data is to study statistical properties of relevant physics phenomena over a large number of discharges and a wide range of plasma parameters.
Here we report on such a study of statistical properties of ELMs in H-mode COMPASS plasmas [4]. Analysis of the ELM's filamentary structure, waiting time and duration distributions and their radial variations in dependence on the main plasma parameters were performed. One of the main aims was to attempt to statistically characterize and distinguish different ELM types and provide a way for their simple and automated classification. The usability of generalized sequential probability ratio test (gSPRT) [5] for automatic ELM event detection in Li-BES data is also demonstrated.

[1] G. Anda et al., Fusion Engineering and Design 108, 1-6 (2016)
[2] M. Berta et al., Fusion Engineering and Design 96-97, 795 (2015)
[3] J. Krbec et al., Review of Scientific Instruments 89, 113504 (2018)
[4] R. P·nek et al., Plasma Physics and Controlled Fusion 58, 014015 (2016)
[5] M. Berta et al., Fusion Engineering and Design 123, 950 (2017)

Speaker: P. Hacek (EPS 2019)

25 P1.1021 First results from the Thomson scattering diagnostics on Globus-M2

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1021.pdf

This work discusses first results of ne and Te measurements on Globus-M2 obtained with the upgraded Thomson scattering (TS) diagnostics. Globus-M2 is spherical tokamak with the following parameters R = 0.36m, r = 0.24m, Ip < 500 kA which differs from Globus-M by a two times higher magnetic field reaching 1 T. The upgrade Thomson scattering hardware consists of 12 TS digital polychromators representing a new generation of TS real-time spectral analytical equipment [1] based on 5GHz 14Bit ADC, ultra-low noise amplifiers and in-build computer with optical Gigabit Ethernet. The upgraded TS probing laser system consists of two lasers: Nd:Glass lasing at 1055 nm with pulse duration of 30 ns and Nd:YAG at 1064 nm with 3 ns duration. Nd:YAG laser is a prototype of the laser developed for ITER divertor Thomson scattering with shortening pulse duration (compare with common 10-15 ns) providing reduction of the accumulated plasma background and separating in time TS signal from stray light sources arranged at distances 0.5 m and more. Two probing laser wavelengths are planned to be used for self-calibration of relative sensitivity in two spectral channels closest to the laser lines. Signal processing as well as methods and instrumentation to reduce measurement errors are also under discussion.

[1] V. Solokha et al (2018). Digital filter polychromator for Thomson scattering applications. Journal of Physics: Conference Series. 982. 012003. 10.1088/1742-6596/982/1/012003.

Speaker: I.A. Khodunov (EPS 2019)

26 P1.1022 Intense and short bursts of whistler-frequency waves during the pedestal collapse in KSTAR H-mode plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1022.pdf

A high-speed broad-band (0.1-5 GHz) RF spectroscopy system has been developed to study the wave phenomena associated with the collapse of edge confinement barrier (called pedestal) in the KSTAR tokamak. In the early measurements using the dipole-type antennas (<1 GHz), the collapse always coincided with intense and short (~100 μs) broadband (<800 MHz) RF bursts [1-2], which was conjectured as a result of fast localized magnetic reconnection (MRX). To better understand the origin of the RF emissions, higher frequency range (up to 5 GHz) has been measured in 2018 KSTAR campaign by resolving the modulation the electron cyclotron emission (ECE), which can provide local measurement unlike the dipole antennas. During the pedestal collapse, narrow-band intense emissions with rapid frequency up/down chirps in the whistler frequency range (~ 3 GHz) appeared for tens of s, suggesting collisionless fast MRX [3]. Bicoherence analysis shows that the GHz emissions have substantial nonlinear interaction with the sub-GHz ion cyclotron harmonic waves, implying that both waves are generated at the same spatial location. The local nature of the wave emissions is consistent with the existence of solitary filament and its localized burst at the pedestal collapse measured by ECE imaging diagnostics [4-5]. This work is supported by R&D program of "KSTAR Experimental Collaboration and Fusion plasma research" (NFRI-EN1801-9), the National Research Foundation of Korea under contract No. NRF-2017M1A7A1A03064231 and BK21+ program.

References:
[1] S. G. Thatipamula et al, Plasma Phys. Control. Fusion 58, 065003 (2016).
[2] M.H. Kim et al., Nucl. Fusion 58, 096034 (2018)
[3] Y.D. Yoon et al., Phys. Plasmas 25, 055704 (2018)
[4] G.S. Yun et al, Phys. Rev. Lett. 107, 045004 (2011)
[5] J.E. Lee et al, Sci. Report 7, 45075 (2017)

Speaker: M. Kim (EPS 2019)

27 P1.1023 The impact of nonlinear scattering effects on Doppler reflectometry and radial correlation Doppler reflectometry

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1023.pdf

Turbulent transport plays a key role in plasma confinement, which makes understanding and control of plasma turbulence one of the major goals of fusion research. The tools for turbulence characterization include Doppler reflectometry (DR) and radial correlation Doppler reflectometry (RCDR) [1], latter of which utilizes simultaneous probing with two microwaves at different frequencies incident obliquely onto magnetic surface in the presence of the cutoff. By performing correlation analysis of reflected signals, the information about turbulence properties, such as radial correlation length can be extracted.
However, for both RCDR and conventional DR, analytical theory can only describe measured quantities and their relation to turbulence characteristics in the linear regime of scattering [2], corresponding to low turbulence amplitude. Some analytical results, such as the criteria for onset on nonlinearity [3] and transition to fully nonlinear regime [4] were obtained, but the main tools to analyze experimental data for nonlinear effects distorting the measurements at the moment are full-wave calculations.
In the present paper full-wave modeling with the use of IPF-FD3D code [5] is applied to the results of gyrokinetic modeling of FT-2 tokamak discharge to observe the effects of nonlinear scattering on the measurements of DR and RCDR. Scanning the amplitude of density fluctuations provided by ELMFIRE permits to identify nonlinear effects such as multiple scattering, strong phase modulation of the probing wave and nonlinear saturation of scattered signal power. Their impact on experimental data is also discussed.

[1] Schirmer J et al. 2007 Plasma Phys. Control. Fusion 49 1019.
[2] E Z Gusakov and A Yu Popov 2004 Plasma Phys. Control. Fusion 46 1393
[3] O.L. Krutkin et al 2019 Plasma Phys. Control. Fusion https://doi.org/10.1088/1361-6587/ab0236
[4] E.Z. Gusakov, A.Yu. Popov 2002 Plasma Phys. and Control. Fusion 44 2327
[5] Lechte et al. 2017 Plasma Phys. Control. Fusion 59, 07500

Speaker: O.L. Krutkin (EPS 2019)

28 P1.1024 Long range frequency sweeping of global Alfven eigenmodes

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1024.pdf

In magnetic fusion devices, unstable Alfvén eigenmodes (AEs) may lead to frequency sweeping events and enhanced particle transport. Refs. [1, 2] explain the frequency sweeping events in terms of evolution of coherent structures, namely holes and clumps, in the energetic particles (EPs) phase-space using a perturbative approach. This approach implies small deviations of frequency from the initially unstable linear mode, as the spatial structure of the mode is fixed. A nonperturbative adiabatic model was then developed in Ref. [3] to study the long range frequency chirping [4, 5] of a plasma wave whose spatial structure is notably affected by EPs. The model was subsequently extended to describe the effects of EPs collisions [6, 7] and equilibrium drift orbits [8].
In the present work, we use a Lagrangian formalism and finite element method to study the hard nonlinear frequency sweeping of a Global Alfvén eigenmode (GAE). We focus on the evolution of the radial structure of the eigenfunction. The eigenfunction is represented by a single poloidal and toroidal mode number. Toroidal effects are retained on EPs dynamics in a high aspect ratio tokamak limit. We track the evolution of frequency using the balance between the energy extracted from the EPs distribution function and the energy deposited into the bulk plasma. The model can be used to study the adiabatic frequency chirping of the Alfvén gap modes observed in experiments.

References
[1] Berk H, Breizman B, Petviashvili N, Physics Letters A 234, 213-218 (1997)
[2] Berk H L et al, Physics of Plasmas 6, 3102-3113 (1999)
[3] Breizman B N, Nuclear Fusion 50, 084014 (2010)
[4] Gryaznevich M, Sharapov S, Nuclear Fusion 40, 907 (2000)
[5] Maslovsky D, Levitt B, Mauel M E, Phys. Rev. Lett. 90(18), 185001 (2003)
[6] Nyqvist R, Lilley M, Breizman B, Nuclear Fusion 52, 094020 (2012)
[7] Nyqvist R M, Breizman B N, Physics of Plasmas 20, 042106 (2013)
[8] Hezaveh H, Qu Z, Layden B, Hole M, Nuclear Fusion 57, 126010 (2017)

Speaker: H. Hezaveh Hesar Maskan (EPS 2019)

29 P1.1025 Nonlinear Dynamics of Toroidal Alfvén Eigenmode in HL-2A H-mode Plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1025.pdf

The nonlinear dynamics of shear Alfvénic wave fluctuations have become a major concern in magnetically confined fusion, since they can be driven unstable by energetic particles (EPs). There are two routes for the Alfvénic fluctuation nonlinear dynamic evolution, with one corresponding to wave-particle phase space nonlinear dynamics dominated by resonant particles, while the other, dubbed as nonlinear wave-wave interactions, describing nonlinear spectrum evolution due to the nonlinear couplings among modes. The former route can be described by the bump-on-tail paradigm or fishbone paradigm. The latter route may take place via Compton scattering of the bulk ions and magnetohydrodynamic (MHD) nonlinearities effects as well as zonal structure generation. Those theoretical predictions had been shown to be relevant in realistic fusion plasmas. On experiments, many nonlinear dynamics phenomena of shear Alfvénic wave fluctuations occur and are identified in laboratory and space plasmas.
In the present paper, the nonlinear dynamics of toroidal Alfvén eigenmodes (TAEs), including nonlinear wave-particle and wave-wave interactions, have been observed in the HL-2A NBI H-mode plasmas. It is found that there are strong nonlinear mode couplings between TAEs with n=3 and low frequency MHD mode (kink or fishbone) with n=1. The pitch-fork phenomena of TAEs can grow explosively and become an explosive instability. The explosive events have two kind fine structures, i.e., multi-modes and pitch-fork. The two kind structures can coexist, but the strong nonlinear mode coupling induces that the pitch-fork weakens or vanishes and the modes blow-up in finite-time, and this indicates that the nonlinear mode coupling may redistribute energetic-ions, destroy hole-clump pairs in the phase-space, and induce three-wave mixing nonlinearly. As a consequence, the TAE nonlinear dynamics can trigger the onset of ELMs and pedestal collapse within several hundred Alfvén times. Following the continuous appearances of rich nonlinear dynamics phenomena, more attentions should be paid to understand the underlying mechanisms, as experimental verification of numerical simulations and analytical theory, that are developed for the predictive ability for future burning plasma scenarios.

Speaker: W. Chen (EPS 2019)

30 P1.1026 Reconstructing the fast-ion velocity distribution in the DIII-D tokamak during Alfven eigenmode activity

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1026.pdf

Fast-ion velocity-space tomography enables reconstruction of the 2D fast-ion velocity distribution from a set of 1D measurements. Here, we reconstruct for the first time the fast-ion velocity distribution for plasmas with high and low Alfvén eigenmode (AE) activity using the 4-view fast-ion D-alpha (FIDA) diagnostics in the DIII-D tokamak. We find that the fast-ion losses due to high AE activity are selective in velocity-space with a particularly strong density decrease in the population of co-going fast-ions with pitches greater than 0.2.

Speaker: B. Madsen (EPS 2019)

31 P1.1027 Optimal conditions for alpha channelling in burning plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1027.pdf

Alpha channelling is a mechanism to transfer the power associated with the fusion-generated alpha particles to the thermal ions through the interaction with an externally excited Ion Bernstein Wave (IBW) that absorbs the alpha particle energy associated with the perpendicular motion. The extraction of energy is associated with a radial diffusion towards the plasma edge. However, such extraction cannot be accomplished by the IBW alone, unless unrealistically high values for the injected IBW toroidal number are considered. Thus, alpha channelling schemes have included a second, low-frequency Alfvén wave to facilitate the extraction of the alphas that have already transferred most of their energy to the IBW. In this paper, the optimal conditions for alpha channelling are investigated for burning plasmas. In [1] the alpha particle distribution function has been determined by solving the Fokker-Planck equation in slab geometry. The model includes the effects of classical slowing down on the electron population and diffusion in the constant of motion space due to the interaction with the IBW. The low frequency wave is modeled via a boundary condition of outward particle flux Q at the boundary in phase space where the high-frequency wave induced diffusion vanishes. This approach has been generalized to arbitrary magnetic equilibria to quantify the amount of power transferred to the IBW and the energy spectrum of the alpha particles crossing the magnetic separatrix. The resulting flux depends on the toroidal IBW wave number and it can be made compatible with the condition of limited losses of high-energy particles under very general conditions. The possibility of alpha channelling relies on the excitation of IBW that are absorbed by the thermal ions and have negligible damping on the electrons. In order to determine the optimal excitation conditions, the propagation of IBW between the mode conversion layer and the resonance has been analytically studied using a generalization of the approach proposed in [2]. The ray trajectories and the wave amplitude have been determined including the effect of alpha channelling that acts as a volumetric source term in the wave amplitude equation. A comparison with the ray propagation obtained by the RAYIBW code has been performed. Using this solution it has been possible to determine the condition of maximum transfer from the IBW to the thermal ions. In parallel, the dynamics of the Alfvénic wave has been investigated in the frame of hybrid MHD-particle simulations performed by the XHMGC code. Alpha particles are described by yielding as initial (equilibrium) distribution function the analytic solution of the Fokker-Planck equation mentioned above. The distribution function is then let to evolve, according to the Vlasov equation, with the electromagnetic fields produced by the plasma response. The value of the flux at the boundary of the region where the quasilinear term is dominant are evaluated. When such a value matches the value used to obtain the analytic form of the equilibrium distribution function, the solution can be considered self-consistent.

[1] F. Cianfrani and F. Romanelli Nucl. Fusion 58 076013 (2018)
[2] A. Cardinali and F. Romanelli Phys. of Fluids B4 504 (1992).

Speaker: F. Cianfrani (EPS 2019)

32 P1.1028 Quantitative investigation of the neutron production in ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1028.pdf

Accurate measurements of the neutron emission in fusion plasmas are a prerequisite for the performance of present and future fusion devices mainly due to the role neutrons play in the fusion rate estimation. In addition, neutrons serve as an imprint of the fast ions content and dynamics, which can be detrimental to the plasma facing components.
Recent comparisons between the experimental neutron rate in JET and the neutron rate expected from TRANSP show discrepancies referred to as "neutron deficit", interpretation of which is still a challenging task. Based on this study, the deficit is concluded to originate from more than one process in the plasma [1]. Given the importance of accurate measurements, the physical understanding and minimization of these discrepancies is necessary for reliable fast ion studies.
In this work the absolute calibration technique of the neutron detectors is proposed as an additional candidate affecting the "neutron deficit". Thereby, a new calibration procedure has been performed in ASDEX Upgrade. A toy train carrying a radioactive source was run over two poloidal positions inside the tokamak vessel, thus allowing longer calibration time, better reproducibility and improved spatial precision than previous calibrations at ASDEX Upgrade. The calibration results are compared with the calculations of Serpent, a Monte Carlo particle transport code developed at the VTT Technical Research Centre of Finland [2].
The code allows the description of two- and three-dimensional reactor configurations and has the advantage of allowing the direct import of CAD geometries in the form of STL files. This gives a lot of freedom to manipulate the geometry inside any CAD-based program. Cross sections can be both taken from standard data libraries or generated by the user which broadens the scope of reliable neutron analysis. Moreover, the material compositions can be easily exchanged leaving some space for the investigation of possible physics scenarios.
Future goal of this work is the installation of a new scintillating detector designed to have better statistics, time resolution and therefore less uncertainty, which will contribute to the analysis of fast ion physics as a part of this research activity. Last but not least, the simulation of fusion reactions using Serpent will make further fusion related studies available in this project.

References
[1] H. Weisen, Hyun-Tae Kim, J. Strachan, S. Scott, Y. Baranov et al., The 'neutron deficit' in the JET tokamak, Nuclear Fusion (2017)
[2] J. Leppanen, M. Pusa, T. Viitanen, V. Valtavirta, and T. Kaltiaisenaho. "The Serpent Monte Carlo code: Status, development and applications in 2013." Ann. Nucl. Energy, 82 (2015) 142-150

Speaker: M. Koleva (EPS 2019)

33 P1.1029 Verification of neoclassical toroidal viscosity due to energetic particles

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1029.pdf

The strength of neoclassical toroidal viscosity (NTV) induced by energetic particles (EPs) is investigated with DIII-D experiments and MARS-K simulations [1]. Tokamak plasma confinement is sensitive to a low level of intrinsically existing or externally applied threedimensional (3-D) magnetic field perturbations. These 3-D fields generate toroidal NTV torque which can greatly affect the plasma momentum confinement. This NTV is a result of drift kinetic non-ambipolar transport in the presence of 3D fields [2], where both thermal particles (the focus of most current research [3]) and EPs can play a contributing role. In present day tokamaks, the EP population from NBI and ICRH can contribute up to half the stored energy, and in future fusion reactors the alpha particles will take up ~15% of the plasma energy, which motivated new experiments on DIII-D to validate the NTV torque due to trapped EPs. In theory and modeling, the NTV torque due to trapped EPs is derived and computed based on the equivalence between NTV and the imaginary part of the drift kinetic energy perturbation [4]. A sophisticated DIII-D experiment, utilizing the full duty cycle neutral beam with varying injection angle and beam energy in the presence of the n=2 magnetic perturbations, measured the induced NTV from these EPs. The plasma response [5] and NTV torque are compared between the experimental measurements and MARS-K kinetic simulation, to carefully verify the existence and parametric dependence of EP induced NTV. This proof of principle experiment and model validation is the first step towards predicting the EP NTV for future devices such as ITER, where the NTV is expected to play an important role in the momentum balance. This work is supported by US DOE under DE-FC02-04ER54698, DE-AC02-09CH11466.

[1] Y.Q. Liu et al., Phys. Plasmas 15, 112503 (2008).
[2] J.-K. Park, Phy. Plasmas 18, 110702 (2011).
[3] J.-K. Park, A.H. Boozer and J. E. Menard, Phy. Rev. Lett. 102, 065002 (2009).
[4] Z.R. Wang et al., Phys. Plasmas 21, 042502 (2014).
[5] Z.R. Wang et al., Phy. Rev. Lett. 114, 145005 (2015).

Speaker: Z. Wang (EPS 2019)

34 P1.1030 Simulation of fast ion loss induced by magnetic islands in the EAST tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1030.pdf

The neoclassical tearing mode (NTM) can result in a large amount of fast ion loss. A correlation between the frequency and the phase of the mode and those of the losses was observed with the diagnosis systems, i.e. the Mirnov coils and the fast ion losses detector (FILD), which explicitly showed that the NTM could lead to fast ion loss [1, 2]. The measurements of the noninductive current by use of neutral beam current drive (NBCD) were reduced significantly in the core region compared with the predictions during NTM, which implied that the NTM could transport fast ions [3, 4]. The fast ion loss induced by magnetic islands has been studied extensively with regard to numerical simulations. There were many codes to use, such as the guiding center drift code ORBIT [5]. The validation of ORBIT for computing the NTM-induced fast ion loss had been confirmed. The results of the simulation well reproduced the observations in the AUG tokamak and the DIII-D tokamak, respectively [6, 7]. In the EAST tokamak, the interaction between NTM and fast ions was observed [8]. Thus, it is interesting to study the beam ion loss due to magnetic islands in the EAST tokamak. In this work, based on ORBIT, we focus on the action of the n = 1, m = 2 mode on fast ions generated by neutral beam injection, where n is the toroidal mode number and m is the poloidal mode number. We scan the q-profile, the strength of toroidal magnetic field, the magnitude and structure as well as rotation of islands to investigate the effects of the NTM on fast ion loss in the EAST tokamak. We demonstrate the mechanisms of the loss due to drift islands, including the convective wave-induced prompt loss and the stochastic loss with the modulation by the magnetic islands.

References
[1] M. Garcia-Munoz et al, Nucl. Fusion 47, L10 (2007)
[2] J. Galdon-Quiroga et al, Nucl. Fusion 58, 036005 (2018)
[3] C. B. Forest et al, Phys. Rev. Lett. 79, 427 (1997)
[4] W. W. Heidbrink et al, Nucl. Fusion 58, 082027 (2018)
[5] R. B. White and M. S. Chance, Phys. Fluids 27, 2455 (1984)
[6] M. Gobbin et al, Nucl. Fusion 49, 095021 ( 2009)
[7] E. M. Carolipio et al, Nucl. Fusion 42, 853 (2002)
[8] E. Li et al, Plasma Phys. Control. Fusion 58, 045012 (2016)

Speaker: L. Yu (EPS 2019)

35 P1.1031 Theory of external-infernal modes in high performance quiescent tokamak regimes

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1031.pdf

Tokamak high-confinement regimes are normally affected by the presence of often violent edge localised modes (ELMs). ELMs deposit unacceptable peak heat loads causing a severe deterioration of the plasma facing components. Thus a vivid interest has arisen on the development of naturally ELM-free regimes. One of the most promising ELM-free regimes is the quiescent high-confinement (QH) mode. In QH plasmas, ELM activity is replaced by dominantly low-n steady mild rotating MHD edge harmonic oscillations (EHOs) pedestal localised. EHOs have been observed in DIII-D, ASDEX-U, JET, JT60 and NSTX. Particle transport is enhanced by EHOs allowing density and pedestal gradient control and potentially removal of fusion ash without the impulsive heat load problem. Extensive numerical modelling and dedicated experiments on DIII-D identify the E x B shearing rate as the key parameter for the QH accessibility with EHOs. A successful access to and control of this favourable regime, still requires a deeper understanding of its mechanisms in terms of basic stability concept. Within the ideal drift-MHD linear stability framework, we give a novel interpretation for the onset mechanism of these instabilities. Provided the possibility of edge infernal-type instabilities in QH plasmas, we show that the interplay of poloidal flows (MHD and diamagnetic) allows the suppression of short wavelength modes so that low-n oscillations, namely EHOs, can emerge. Our model retrieves several features measured experimentally such as mode rotation frequencies, radial struture, amplitude of the critical E x B shearing rate. The theoretical results are then applied to the interpretation of JET-C discharges exhibiting edge MHD activity in an ELM-free regime. In outlook these results can suggest improved diagnostics approaches and control tools for reactor grade tokamaks.

Speaker: D. Brunetti (EPS 2019)

36 P1.1032 ELMFIRE Gyrokinetic study of turbulence and equilibrium asymmetries at the FT-2 tokamak edge

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1032.pdf

The tokamak boundary is of central importance for controlled magnetic fusion. It regroups critical technological and scientific challenges that hold the key to achieving and sustaining ignition [1-4]. This includes plasma-surface interaction which submits the material wall to extreme fluence during long pulses, heat and particle transport and exhaust, the physics of edge transport barrier (ETB) formation and edge-localised modes (ELM), to name a few. Here, we use the global, full-f gyrokinetic code ELMFIRE [5] to investigate turbulence at the edge of the FT-2 tokamak. ELMFIRE has been upgraded to include the scrape-off layer in the simulation domain [6,7]. The FT-2 tokamak, which has been extensively studied with ELMFIRE, allows for a detailed study of the edge region thanks to comprehensive diagnostics, in particular a set of Langmuir probes covering most of the poloidal range. Recently, poloidal asymmetries on a flux surface have been reported, both in ELMFIRE in the confined region [8] and in fluid simulations of the edge and SOL [9]. In the current study, a comprehensive investigation of the edge region of dedicated FT-2 discharges is carried out, and compared to ELMFIRE gyrokinetic simulations, to validate the model and provide further insight in the dynamics of turbulence and blobs.

[1] Progress in the ITER Physics Basis, Nucl. Fusion 47 (2007) S1-S414
[2] P. C. Stangeby, The Plasma Boundary of Magnetic Fusion Devices, IOP, 2000
[3] F. Wagner, Plasma Phys. Control. Fusion 49 (2007) B1
[4] F. Ryter et al., Nucl. Fusion 54 (2014) 083003
[5] J. A. Heikkinen et al., J. Comput. Phys. 227 (2008) 55825609
[6] L. Chôné et al., Contrib. Plasma Phys. 58 (2018) 534-539
[7] L. Chôné et al., proceedings of the 45th EPS conference on Plasma Physics (2018)
[8] P. Niskala, PhD Thesis, Aalto University publication series (2018)
[9] B. Zhu et al., Nucl. Fusion 58 (2018) 106039

Speaker: L. Chôné (EPS 2019)

37 P1.1033 Sawtooth activities in EAST neutral beam injection plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1033.pdf

Neutral beam injection (NBI) system has been proved to affect sawtooth activities through both producing energetic particles and supplying torque applied to the plasma. The impact of NBI on sawtooth crashes has been studied in the EAST tokamak, which is equipped with co- and counter NBIs. Statistical analysis shows that both strong co- and counter-NBI yield stronger sawtooth activities than cases when heating power is weak. A minimum sawtooth period is observed at a counter-NBI power of 0.2 MW. This is linked to zero-plasma rotation and a non-rotating precursor mode of the sawtooth instability. This indicates that the sawtooth instability is stabilized by plasma rotation as previously suggested. The fast-ion content differs between co- and counter-NBI, so energetic particles might additionally contribute to the sawtooth activities.

Speaker: Y. Chao (EPS 2019)

38 P1.1034 Observation of radiation asymmetry during EAST mitigated plasma disruption by massive gas injection

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1004.pdf

In tokamak plasma, disruptions are dangerous events for device safety due to the large energy loss in very short time. Plasma disruption mitigation by massive gas injection (MGI) is an effective heat dissipation method through high radiation [1-3]. The MGI disruption experiments are researched with noble Helium (He) and Argon (Ar) gas injection on EAST. About 45% of plasma thermal energy lost by radiation in Ar gas injection experiments and the value is lower in He gas injection experiments [4]. The first radiation peaking are usually found near the gas injection location. The radiation asymmetries both in toroidal direction and in poloidal direction are observed, which are serious during pre-thermal quench and become weak gradually. The behaviour of radiation asymmetries with He gas injection is different from that with Ar gas injection. In addition, MHD are the general phenomena during the disruption process and the changes of MHD mode structures can affect the radiation peaking. The radiation distribution and radiation peaking are compared for different injected particle quantities. In the coming EAST experimental campaign, one new scattered Lithium pellet injection (SPI) system driven by high pressure gas will be run and some new experiments results will be presented.

References
[1] D. G. Whyte, et al., Phys. Rev. Lett. 89 (2002) 055001.
[2] G. Pautasso, et al., Nucl. Fusion 58 (2018) 036011.
[3] N. W. Eidietis, et al., Physics of Plasmas 24 (2017) 102504.
[4] D. L. Chen, et al., Nucl. Fusion 58 (2018) 036003.

Speaker: Y.M. Duan (EPS 2019)

39 P1.1035 Non-linear MHD simulations of pellet triggered ELMs in JET

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1035.pdf

Non-linear MHD simulations of pellet-triggered ELMs in JET plasma have been carried out with the JOREK code [1, 2, 3]. The pellet particle fueling efficiency and the power flux at the divertor target during the pellet-triggered ELM have been studied. The understanding of the ELM mitigation is more important in the "local" power load onto the divertor target. The JOREK simulations show the good agreement with the experiment observation in terms of the similar heat flux onto the divertor target, 60 MW/m^2. The spontaneous ELM shows small toroidal variations ( ± 15%) of the time-averaged heat flux, 60 MW/m^2. In this work, the toroidal angle of 90 where the location of the infra-red (IR) camera and the angle of 270 which is the toroidally opposite side of the camera location are estimated. The pellet triggered ELM shows a toroidally asymmetric in the energy deposition, the heat flux of 60 MW/m^2 at the IR camera location. On the other hand, the toroidally opposite side shows up to 120 MW/m^2, a factor 2 larger than the observation of IR camera which cannot see this toroidal location. The JOREK analysis suggests that the IR camera in the experiment might not be focussed onto the most damaging toroidal location for the pellet triggered ELM.

References
[1] Huysmans GTA and Czarny O, Nuclear Fusion 47 659 (2007)
[2] Czarny O and Huysmans G, JCP 227, 7423 (2008)
[3] Futatani et al., Nuclear Fusion 54, 073008 (2014)

Speaker: S. Futatani (EPS 2019)

40 P1.1036 Numerical studies of nonlinear growth of double tearing modes in cylindrical geometry

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1036.pdf

Double tearing mode (DTM) is an important kind of magnetohydrodynamics (MHD) instability that often occurs with reversed central magnetic shear configuration in tokamak discharges. A 5th order Weighted Essentially Non-Oscillatory (WENO) scheme is applied to build up a new numerical nonlinear MHD code based on a conservative perturbed MHD model in cylindrical geometry. After careful benchmark between the new initial value code with eigenvalue codethe new code is successfully applied to the nonlinear study of double tearing mode in cylindrical geometry. The formation of plasmoids is found in high Lundquist number regime in such configurations for the first time. Long and thin Sweet-Parker (SP) current sheets are formed near the original inner and outer rational surfaces and become tearing unstable for a large enough Lundquist number. The system can eventually saturate at a quasi-stationary state with small island pairs. The details will be presented.

This work is supported by the National Key R&D Program of China under Grant No. 2017YFE0300402 and the National Natural Science Foundation of China under Grant Nos. 11475219, 11775268.

Speaker: W. Guo (EPS 2019)

41 P1.1037 The Ideal Evolution Equationand Fast Magnetic Reconnection

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1037.pdf

The ideal evolution equation, ∂B/∂t =curl×(u⊥×B),implies magnetic field lines move with a velocity u⊥and cannot change their connections. Nevertheless, for an electric field that is arbitrarily close to the ideal form, E +u⊥×B= -grad Φ,magnetic connections will in general break on a time scale τ, where 1/τ≈|grad u⊥|, times the logarithm of the magnetic Reynolds number ℜm, which is |u⊥×B| divided by the deviation of the parallel electric field from the ideal form. The connections breaking part of the magnetic field is proportional to exp(t/τ)/ℜm. This mathematical theorem is proven [1] using Lagrangian coordinates, ∂x(x0,t)/∂t=u⊥(x,t), which provide an explicit solution for an ideally evolving magnetic field BI(x,t). The exact electric field defines the evolution of the Clebsch potential sinB=gradα×gradβ. This evolution can be solved an alytically for the deviation of a magnetic field from its ideal form, B -BI, while that deviation is small. The generic behavior of anear-ideal evolution provides answers to four fundamental questions on magnetic reconnection: (1) Why does the near-ideal evolution of natural and laboratory magnetic fields robustly lead to states of fast magnetic reconnection independent of the drive and of the initial state? (2)What is the characteristic time required to reach a state of fast magnetic reconnection? (3)What is the explanation of the effects produced by fast magnetic reconnection, which are primarily associated with magnetic helicity conservation and an energy transfer from the magnetic field to the plasma? (4) Why does the Alfvén speed define the time scale during which the effects produced by fast magnetic reconnection occur? A middle singular value of the Singular Value Decomposition of the Jacobian matrix ∂x/∂x0of Lagrangian coordinates is required for an exponential growth of the connections-breaking field while having a small, non-exponential, change inthemagneticfield strength. The two-dimensional assumption of traditional reconnection theories effectively excludes exponentiation. Traditional theories are inapplicable to the fast reconnection that occurs during tokamak disruptions and of problematic applicability to the astrophysical problems for which they were developed.

Work supported by U.S. Department of Energyawards DE-FG02-95ER54333, DE-FG02-03ER54696, DE-SC0018424, and DE-SC0019479.

[1] A. H. Boozer, Phys. Plasmas 26, 042104 (2019).

Speaker: A. H. Boozer (EPS 2019)

42 P1.1038 Turbulence in open field-line helical plasmas: Fluid v. gyrokinetic

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1038 .pdf

Helical magnetic field devices, such as the Helimak (University of Texas) and TORPEX (EPFL), provide a useful environment for refining our understanding of open fieldline toroidal systems and testing both new and old codes. These devices have important ingredients of tokamak scrape-off-layer turbulence: parallel transport onto sheaths, turbulent cross-field transport, curvature and ∇B drifts, and interaction with plasma-facing materials. The Helimak has been simulated using full-f fluid models for many years [1], and despite the simplified geometry and relatively high collisionality of its plasmas, predictive capability is still unattained and interesting open questions remain. We direct newer tools to these longstanding objectives. The two-fluid turbulence code GDB [2] and the continuum gyrokinetic code Gkeyll [3] have both been employed to simulate low ion temperature Helimak plasmas. In this work we offer complementary descriptions of the blobby, interchage and drift-resistive fluctuations existing in the Helimak. A first of its kind comparison between fluid and gyrokinetic turbulence calculations in open field lines is presented, as well as the experimental data for corresponding experiments. This dual GDB-Gkeyllanalysis offers insight into what additional kinetic effects, if any, can be discerned in a low temperature plasma. By comparing against GDB we also identify improvements to the gyrokinetic model in order to converge to correct collisional results, an important aspect of tokamak modeling already underway with Gkeyll [4].

[1] B. Li, et. al., Phys. Plasmas 16, 082510 (2009).
[2] B. Zhu, et al., Comp. Phys. Comm. 232, 46­58 (2017).
[3] T. Bernard, et. al., Gyrokinetic continuum simulations of plasma turbulence in the Texas Helimak, submitted to Phys. Plasmas (arXiv:1812.05703).
[4] E. L. Shi, et. al., Phys. Plasmas 26, 012307 (2019).

Speaker: M. Francisquez (EPS 2019)

43 P1.1039 Gyrokinetic theory of the nonlinear saturation of toroidal Alfvén eigenmode

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1039.pdf

Shear Alfvén wave instabilities such as toroidal Alfvén eigenmode (TAE) are expected to play important roles in magnetic confinement fusion devices as energetic particles (EPs) contribute significantly to the total power density. TAE can be driven unstable by EPs, and in turn, induce EP transport and degrade overall plasma confinement.
Nonlinear saturation of TAE via ion induced scatterings [1] is investigated in the shortwavelength gyrokinetic regime [2]. It is found that the nonlinear evolution depends on the thermal ion value. Here, is the plasma thermal to magnetic pressure ratio. Both the saturation levels and associated energetic-particle transport coefficients are derived and estimated correspondingly [3].

References
[1] Hahm T S and Chen L 1995 Phys. Rev. Lett. 74(2) 266-269
[2] Chen L and Zonca F 2013 Phys. Plasmas 20 055402
[3] Qiu Z, Chen L and Zonca F, "Gyrokinetic theory of the nonlinear saturation of toroidal Alfvén eigenmode" 2019 Nucl. Fusion submitted

Speaker: Z. Qiu (EPS 2019)

44 P1.1040 A local equilibrium model for tokamak plasmas: theory and applications.

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1040.pdf

Magnetic equilibria are fundamental to almost every phenomena in tokamak plasmas, but accurate numerical solutions of the Grad-Shafranov (GS) equation are not always the best tool to gain insight into such complex processes. Simplified local descriptions, like the s - alpha model with circular magnetic surfaces [1] or Miller's model for shaped plasmas [2], are often preferable and have seen a wide range of applications. However, local models presently available for shaped plasmas cannot provide tractable expressions for the magnetic-field components, having thus a very limited ability to assess plasma-shaping effects in analytically driven work.
A local magnetic equilibrium model is here presented, with finite aspect ratio and up-down asymmetrically shaped cross section [3]. In contrast with other local equilibria, which provide simple magnetic-surface parametrisations at the cost of complex poloidal-field flux descriptions, the proposed model is intentionally built to afford analytically tractable magnetic-field components. Its analytical abilities are used next to address the effects of plasma shaping in three different applications: a) transformation to straight-field coordinates, where previous results in the circular limit [4] are generalised to finite magnetic shear; b) geodesic-curvature induced coupling between shear-Alfvén and slow-acoustic continuous spectra, where the threemode model for low frequency -induced Alfvén-acoustic eigenmodes [5] is extended to more than two sidebands; c) guiding-centre orbits of charged particles in tokamaks, for which some orbital characteristics of interest [6] are written for non-circular equilibria.

References
[1] J. W. Connor, R. J. Hastie, and J. B. Taylor, Phys. Rev. Lett. 40, 396 (1978).
[2] R. L. Miller et al, Phys. Plasmas 5, 973 (1998).
[3] P. Rodrigues and A. Coroado, Nucl. Fusion 58, 106040 (2018).
[4] X. Lapillonne et al, Phys. Plasmas 16, 032308 (2009).
[5] B. van der Holst, A. Belien, and J. Goedbloed, Phys. Plasmas 7, 4208 (2000).
[6] A. Brizard, Phys. Plasmas 18, 022508 (2011).
IPFN activities were supported by "Fundação para a Ciência e Tecnologia" (FCT) project UID/FIS/50010/2013; FC was supported by a FuseNet master internship grant.

Speaker: P. Rodrigues (EPS 2019)

45 P1.1041 Progress on disruption event characterization and forecasting in tokamaks and supporting physics analysis

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1041.pdf

Disruption prediction and avoidance is critical in ITER and reactor-scale tokamaks to maintain steady plasma operation and to avoid damage to device components. The present status and results from the physics-based disruption event characterization and forecasting (DECAF) research effort are shown for multiple tokamak devices. Present analysis of KSTAR, MAST, and NSTX databases shows low disruptivity paths to high beta operation. The DECAF code applied to a database of ~104 plasmas with only 5 DECAF events predicts disruptions with 91.2% true positives and 8.7% false negatives. Increasing the number of events will improve the latter value. Automated analysis of rotating magnetohydrodynamic (MHD) modes now allows the identification of disruption event chains for several devices including coupling, bifurcation, locking, and potential triggering by other MHD activity. DECAF can now provide an early disruption forecast (on transport timescales) allowing the potential for disruption avoidance through profile control. Hardware to allow real-time evaluation of this activity on KSTAR is now being configured for installation in 2019. New analysis of the MAST database has uncovered global MHD events at high normalized beta, N, with characteristics identifying them as resistive wall modes (RWMs). The MAST RWM eigenfunction shape and growth rate appear significantly altered by the location of conducting structure compared to results from NSTX. The conducting wall stabilizing effect on the kink mode is computed to be relatively small in MAST and primarily due to the vacuum vessel, but will be increased for MAST-U by changes to the divertor plates. Analysis of high performance KSTAR experiments using TRANSP shows that the non-inductive current fraction has reached 75%. Regions of weak safety factor q shear can form in different parts of these plasmas dependent upon the broadness of the bootstrap current profile. Resistive stability including ' calculation by the Resistive DCON code is evaluated for these plasmas using kinetic equilibrium reconstructions with magnetic field pitch angle data to determine capability for instability forecasting. TRANSP code predictive capability is used to examine the impact of the second (off-axis) KSTAR neutral beam injection (NBI) system determining plasma parameters important for stability. Predictive analyses are used to design experiments using as few as 4 (of 6) NBI sources yielding solutions with N~4.5 and 100% non-inductive current drive, adding a novel regime for disruption prediction studies.

Supported by US DOE Grants DE-SC0016614 and DE-SC0018623.

Speaker: S.A. Sabbagh (EPS 2019)

46 P1.1042 Arc discharges at the plasma periphery during disruption in tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1042.pdf

Development of the arc discharges in the peripheral plasma is considered as a possible mechanism determining transition from relatively slow growth of the large-scale MHD perturbations to thermal quench (minor disruption) and subsequent transition to a major disruption (current collapse). Development of the arc discharges can lead to a sharp increase in the interaction of the plasma with the first wall and limiters, accompanied by entry of impurities and neutral gas into the bulk plasma and formation of the unstable plasma configuration. This mechanism could be especially strong in experiments with all-metal (tungsten) first wall considered as baseline plasma-facing component in ITER.
Arc discharges are studied in the T-10 tokamak with tungsten limiters in plasma with relatively high density. Effects of the arc discharges are generally evaluated by postoperational inspection of the vessel components. Installation of the movable magnetic and electrical probes located near the plasma boundary at multiple positions inside the vacuum vessel (far and in the vicinity of the limiters, at the high and low field side of the torus) allowed identification of the fast-scale (0.5-2.0 MHz) electromagnetic perturbations attributed to the arc discharges. Simultaneous measurements of the x-ray intensity and analysis of the visible light images by fast-frame camera confirmed strong plasma-wall interaction during bursts of the fast-scale electromagnetic perturbations. Essential new feature of the T-10 experiments is installation of the new "ARC" probe with castellated surface stimulating arc discharges directly at the location of the electric probe with simultaneous measurements of the magnetic perturbations in the immediate vicinity of the arc zone. Experiments indicated that transition to major disruption is generally associated with enhanced currents to the "ARC" probe. In addition to the "passive" measurements of the arc perturbations, "active" experiments were conducted in the T-10 tokamak, with initiation of the currents in the peripheral plasma using biasing (U~0-400V) between different in-vessel components (vacuum chamber, limiters, and special movable electrode). Experiments indicated that critical surface current density is required for the arcs initiation. Parameters of electromagnetic perturbations measured in the experiments on T-10 tokamak are compared with the characteristics of oscillations during arc discharges on a laboratory bench.

The work is supported by ROSATOM (Contract T-10 2019).

Speaker: P. Savrukhin (EPS 2019)

47 P1.1043 A new instability and a new nonlinear MHD simulation pattern for rapid sawtooth crash

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1043.pdf

The rapid sawtooth crash without magnetic reconnection during crash phase is a longdebated issue in fusion plasma. In relatively high central beta plasma, nonlinear simulation with the extended MHD code predicted that it is unstable to a new type of instability over q=1, a nonlinear ideal-MHD unstable mode with coupled n=1 and 2 harmonics, that grows to an internal-kink-like sawtooth crash. A perturbation with n=1 and m=2/n=2 remains over q=1 and couples to other harmonics across the entire plasma radius, consistent with observations of annular hot belt in many tokamaks like JET and TFTR [1,2]. No large 2/1 magnetic island after fast collapse is seen in simulation. Large axis-symmetric flow can be produced after rapid sawtooth crash.

[1] A W Edwards et al PRL 57 (1986) 211
[2] Zhang C et al PRL 77 (1996) 3553

Speaker: L. Xu (EPS 2019)

48 P1.1044 Operation in the quiescent regime with a high runaway electron current fraction on the EAST tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1044.pdf

Plasmas with a high runaway electron (RE) current fraction, fRE > 0.5, have been achieved during the flat-top of EAST Ohmic discharges with both a circular limited and an X-point diverted configuration. The RE current fraction and the energy distribution are characterized stably and independent of plasma current and density. Operation in the quiescent regime including accurate measurement of all key parameters related to REs provides a suitable experimental platform for RE excitation and dissipation, which could potentially have beneficial implications to the post-disruption RE regime [1-3]. Extremely low density operation (ne<41018m^-3) free of error field penetration supports the excitation of fruitful quiescent RE populations. By slowly letting the density ramp down during the flattop, REs are firstly confirmed by visible hard X-rays (HXRs) and electron cyclotron emission (ECE) and then the signals of HXRs and ECE grow fast, indicating that amount of REs are generated. At a lower density, a transition from growth of HXRs and ECE to saturation are simultaneously observed. Meanwhile, a large drop of the surface loop voltage (down to <50% of the loop voltage value before this transition) is found, indicating the replacement of the resistive plasma current by that carried by the REs. After the transition, continuing to ramp down the density does not raise the toroidal electric field (Eloop) and the amplitude of HXRs and ECE keeps constant, supporting that the stable characterizations of the RE current fraction and the energy distribution in the regime. Also, the saturated electric field is ~8 times above the theoretical critical electric field for avalanche growth (EC) but lower than the threshold electric field for Dreicer generation (12-20 EC).

References
[1] T. C. Hender et al Nucl. Fusion 47, S128 (2007)
[2] P. Aleynikov and B. Breizmann, Phys. Rev. Lett. 114, 155001 (2015)
[3] L. Zeng et al, 43rd EPS conference on Plasma Physics, Leuven, Belgium, O4.112 (2016)

Speaker: L. Zeng (EPS 2019)

49 P1.1045 High-resolution measurements of the internal kink eigenfunction during sawtooth-free (1/1) bursts and long-lived saturated modes

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1045.pdf

Detailed properties of the 3D structure of (1/1) internal kinks can be accessed using a modern suite of spectroscopic imaging diagnostics. A combination of high time- and space-resolved 1D measurements of electron density and temperature fluctuations together with local 2D soft x-ray (SXR) radiated power density profiles can shed light on the spatial structure of the ideal internal kink eigenfunction during sawtooth-free (1,1) fishbone bursts and early phase of longlived saturated modes. Particularly useful are the SXR reconstruction routines based on a Bessel formalism to extract the lowest order component and fit the data with a Bessel function of order one which can constrain the ideal-kink eigenfunction. SXR signatures of the (1,1) and midplane J1(lr) fit for an ideal kink. solution (y1~J1). Soft x-ray (SXR) emissivity profiles of electron fishbones in Alcator C-Mod [1,2] show for example that the mode forms and grows as a small amplitude (1/1) kink with a nearly circular cross section. The perturbation has a characteristic eigenfunction of the form J1(lr)cosq which is adequate for the 1/1 internal kink in a cylindrical plasma; lrq=13.83 is the first zero of J1(x) and rq=1 is the location of q=1 which in this case is 5 cm away from the magnetic axis (rq=1/a~20%). In comparison, the inversion radius is at 2.5 cm. Combining this functional form with data from a two-color interferometer is possible to infer an electron density perturbation of the order of 4% which peaks at the same location of the SXR intensity. An additional constraint can be obtained using a 1D ECE radiometer which also provides additional evidence that LHCD fast electrons are connected to the mode onset and evolution. Radiation at the second harmonic of the electron cyclotron frequency produced by fast electrons in the central region are often detected in a frequency channel assigned at the low-field edge nearly 20 cm away from the magnetic axis and only while the mode is active. This apparent mismatch in the location of the ECE emission is due to the strong downshift of electron gyro-frequency introduced by relativistic effects. Nonetheless, assuming a 1/R dependence for the toroidal magnetic field and a perturbation of the ECE signals that maximizes/minimizes at a midplane position at opposite sides of the kink (e.g. ±rk), it is thus possible to obtain a simple solution of the downshift profile leading to rk=1.53 cm; not surprisingly, rk is also at the peak of the J1(lr) perturbation inside the q=1 radius. These high resolution tools are also being used to study the early phase of long-lived saturated (1,1) kink modes before their resistive phase [3-6].
Work supported by the US DOE under contract DEAC05-00OR22725 at ORNL and DE-AC02-09CH11466 at PPPL.

[1] L. Delgado-Aparicio, et al., PoP, 22, 050701, (2015)
[2] L. Sugiyama, et al., 25, 082120, (2018)
[3] L. Delgado-Aparicio, et al., PRL, 110, 065006, (2013)
[4] L. Delgado-Aparicio, et al., NF, 53, 043019, (2013)
[5] A. Wingen, et al., NF, 58, 036004, (2018)
[6] A. Wingen, et al., PoP, 58, 022501, (2019).

Speaker: L. Delgado-Aparicio (EPS 2019)

50 P1.1046 Dynamics and spectral properties of Turbulence-Driven Magnetic Islands

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1046.pdf

Neoclassical tearing modes (NTM) are metastable magnetic islands in tokamaks; however, they appear frequently in experiments without any noticeable triggering event. In order to understand this, it has been numerically shown that turbulence can create a seed island by mode coupling [1, 2, 3], even remotely [4] ; such a seed island can indeed be large enough to further grow from the NTM mechanism [5].
However, this amplification only happens for islands larger than a critical size. Therefore, the definition and determination of the size of turbulence-driven magnetic islands is of crucial importance.
First, the definition of island size is more ambiguous in a turbulent context than in a quiescent, tearing mode context. Different definitions of the island size are discussed, as well as the associated diagnostics that can be implemented in numerical codes.
Next, we use 3D reduced-MHD simulations of flux-driven ballooning turbulence to study the seed island creation in regimes where the classical tearing mode is linearly stable. A localized pressure source is used to control the radial position and strength of the turbulence, and allows to radially separate turbulent region from q = 2 island resonant surface.
We show that the onset of the magnetic island on the q = 2 surface follows complex dynamics that can be split into several distinct phases: as a first step the nonlinearly dominant mode in the turbulent region drives a weak harmonic island on the q = 2 surface. Subsequently the spectrum on the q = 2 surface evolves towards larger scales. The final dominant island mode depends on the power source that feeds the turbulent region; this can lead to an oscillating behaviour when the peak of the final island spectrum lies between integer harmonics.

References
[1] A. Ishizawa et al, Phys. Plasmas 14, 040702 (2007)
[2] W. A. Hornsby et al, EPL 91 45001 (2010)
[3] M. Muraglia et al, Phys. Rev. Lett., 107, 095003 (2011)
[4] A. Poye et al, Physics of Plasmas 22, 030704 (2015)
[5] M. Muraglia et al, Nuclear Fusion 57 (7), 072010 (2017)

Speaker: N. Dubuit (EPS 2019)

51 P1.1047 Non-linear MHD modelling of 3-D plasma edge with Resonant Magnetic Perturbations in DIII-D and ITER.

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1047.pdf

At present, the intensive experimental and theoretical studies of Edge Localized Modes (ELMs) physics are particularly oriented towards finding the methods of their control in ITER. ELMs potentially represent an issue for ITER divertor lifetime due to large transient heat and particle losses released in each ELM relaxation [1]. The application of small Resonant Magnetic Perturbations (RMPs) generated by specific coils demonstrated the possibility of total ELMs suppression or strong mitigation of their size [2], motivating the use of such method in ITER. The important drawback of RMP application is the complex magnetic topology at the edge and formation of 3D Scrape of Layer (SOL) leading to the splitting of the separatrix seen in experiment as helical "lobes" at the X-point. When crossing the divertor plates they form fingerlike structures ("footprints") and non-axisymmetric heat and particle fluxes observed in many RMP experiments [3]. The 3D SOL and non-axisymmetric divertor fluxes with RMPs can represent an issue in ITER leading to local high heat fluxes ("hot spots") in the unprotected areas, additional material erosion and fatigue stress on the divertor components.
In this work the characterisation of 3D plasma edge and divertor footprints with RMPs was done using the non-linear MHD code JOREK [4] including two fluid diamagnetic effects, toroidal plasma rotation and neoclassical poloidal friction in the model which was shown to contain essential elements for the self-consistent modelling of the non-linear plasma response to RMPs [5]. Firstly, the benchmarking of RMP model implemented in JOREK was done comparing simulation results with ELM suppression experiment on DIII-D. The divertor magnetic 3D footprints structure obtained in modelling taking into account plasma response to the realistic RMP spectrum with dominant toroidal modes N=1 and N=3 demonstrated rather good agreement with FASTCAM measurements of the divertor particle flux splitting observed in DIII-D pulse #166439 [3]. It will be shown that non-linear plasma response to RMPs can be very different compared to the vacuum fields due to the screening by rotating plasma or amplification via so called external kink/peeling response. In particular, self-consistent interplay between RMP penetration, evolution of radial electric field and electron poloidal plasma rotation taken in to account seems to be necessary elements for successful benchmarking with experiment. Secondly, the results of JOREK modelling of ITER divertor magnetic footprints and divertor fluxes with RMPs generated by In Vessel Coils (IVC) will be presented for standard H-mode scenario 15MA/5.3T. Some of the potentially possible methods of asymmetry reduction of the RMP divertor footprints such as rigid rotation or optimisation of RMP spectrum will be discussed.
Ackowledgements: This work has been is supported by EUROFUSION Enabling Research project CfP-WP19ENR-01/MPG-03 and US DOE under DE-FC02-04ER54698,DE-FG02-05ER54809 and DE-SC0018030. The views and opinions expressed herein do not necessarily reflect those of the European Commission, DOE or ITER.

[1] A Loarte A et al Nucl Fusion 54 033007(2014)
[2] T E Evans et al Phys Rev Lett 92(2004) 235003(2004)
[3] R A Moyer et al Rev of Scientific Instruments 89, 10E106 (2018)
[4] G T A Huysmans et al Nucl. Fusion 47 (2007) 659
[5] F Orain et al Phys. Plasmas 20 102510 (2013)

Speaker: M. Becoulet (EPS 2019)

52 P1.1048 High-n tearing mode dynamics in fast rotating RFP plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1048.pdf

The Reversed Field Pinch (RFP) configuration is often characterized by a wide spectrum of unstable tearing modes (TMs) involved in the generation and sustainment of the magnetic field in the plasma. This dynamo process is heavily influenced also by other processes or parameters like intrinsic plasma flow (no external torque sources are normally present), wall resistivity and interaction with external non axi-symmetric magnetic fields provided by active coils. The transition between fast-slow rotation branches under the application of magnetic feedback boundary conditions was studied in [1] for the case of RFX-mod, a medium size (a = 0.459 m, R0 = 2m) flexible toroidal magnetic confinement device. In particular, RFXmod is equipped with an advanced and sophisticated feedback system realized by a grid of independently controlled 48 (toroidal) x4 (poloidal) active saddle coils. In this contribution the interaction of the m=1, n>9 tearing modes with the bulk plasma close to the fast-slow transition threshold is investigated with the help of a systematic set of experiments where the active feedback control is selectively switched on and off on specific modes during the discharge dynamics. The peculiar result found is that also in fast rotating discharges, although the radial component at the wall of high n tearing modes is almost zero, in the absence of active feedback control a gradual modification (growth) of the total mode amplitude is measured, leading potentially to wall locking of that mode and to the back transition to the slow rotation branch. Data showing the mode-mode and mode-wall interaction will be presented for several combinations of non-controlled TMs. The process is discussed also in function of the dynamics of the plasma flow, following the lines presented in [2], and showing the clear correlation between active control, MHD dynamics and plasma flow.

[1] P. Innocente et al., Nucl. Fusion 54 (2014) 122001
[2] B. Zaniol et al., P4.153, 42nd EPS Conference on Plasma Physics (2015)

Speaker: T. Bolzonella (EPS 2019)

53 P1.1049 Effect of a realistic boundary on the helical self-organization of the RFP

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1049.pdf

The reversed-field pinch (RFP) is a configuration for the magnetic confinement of fusion plasmas, in which most of the toroidal field is generated by the plasma itself through a self-organized dynamo process, instead of being produced by external coils as in the tokamak. In the RFP, the nonlinear saturation of resistive-kink/tearing modes brings to the spontaneous emergence of helical states with improved confinement. This is observed both in nonlinear magnetohydrodynamics (MHD) modelling [1] and in RFP devices, especially at high current [2]. A major advance in the predictive capability of nonlinear MHD modelling for RFP plasmas was made possible by allowing helical perturbations of the radial magnetic field at the plasma boundary [3]. A proper use of helical magnetic perturbations (MPs) in MHD modelling allowed to obtain experimental-like helical states [4] and to predict new helical states with chosen helical twist, successfully produced in RFX-mod [5]. Here, we describe a further refinement of the magnetic boundary modelling. Instead of applying fixed helical MPs, we study the helical self-organization in the presence of a thin resistive shell and a vacuum layer between the plasma and the ideal shell. Two main results are discussed. On the one hand, by varying the distance between the plasma and the ideal wall it is possible to provide a nonlinear estimate for the decrease of secondary modes by increased shell-plasma proximity. This is of interest in view of the upgraded RFX-mod2 device (starting operation in 2020), in which the shell-plasma proximity will change from b/a=1.11 to b/a=1.04 [6]. On the other hand, it is observed that with a proper choice for the resistivity of the conducting shell at the plasma boundary, experimental-like helical states do emerge in a self-consistent way, as in the experiment, without the need to impose a fixed helical MP. Finally, further extensions of the realistic boundary implementation, in order to take into account a double resistive shell and a feedback control system, will be discussed.

[1] S. Cappello and D.F. Escande, Phys. Rev. Lett 85, 3838 (2000)
[2] R. Lorenzini, et al., Nature Physics 5, 570 (2009); J.S. Sarff, et al., Nucl. Fusion 53, 104017 (2013)
[3] D. Bonfiglio, D.F. Escande, P. Zanca and S. Cappello, Nucl. Fusion 51, 063016 (2011)
[4] D. Bonfiglio, M. Veranda, S. Cappello, et al., Phys. Rev. Lett 111, 085002 (2013)
[5] M. Veranda, D. Bonfiglio, S. Cappello, et al., Nucl. Fusion 57, 116029 (2017)
[6] L. Marrelli, R. Cavazzana, et al., submitted to Nucl. Fusion (2019)

Speaker: D. Bonfiglio (EPS 2019)

54 P1.1050 Cross phase of edge-plasma fluctuations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1050.pdf

Knowledge of the cross phases between the fluctuations is crucial in the turbulent transport of the plasma particles and the thermal energy. The cross phase plays an important role in the determination of the turbulence level because the fluctuations in the drift plasma turbulence are driven by the turbulent fluxes across the plasma profiles. In the presentation the cross phase between the electrostatic potential and the electron density is analyzed based on the numerical simulations of the two-dimensional Hasegawa-Wakatani model. In the presence of the zonal flow V (ZF) the cross phase is strongly distorted by the ZF. Where the flow curvature V (the gradient of the zonal vorticity) is positive, is reduced at the saturated state if the electron response is nearly adiabatic. Turbulence is localized where V is in the direction of the electron diamagnetic drift and V > 0. The cross phase is found negative where the turbulence is weak. Results of two separate numerical simulations of ZF being either sinusoidally imposed or dynamically generated will be discussed at the presentation.

Speaker: C. B. Kim (EPS 2019)

55 P1.1051 Modelling of non-linear edge harmonic oscillations and the effect of non-axisymmetric magnetic coils

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1051.pdf

Quiescent H-mode (QH-mode) operation is highly desirable relative to the well known Hmode operation because it allows for high energy density in the core as well as potentially improved confinement of energy and particles. A feature of QH-mode is that the Edge Localized Mode (ELM) instabilities are replaced with continuous Edge Harmonic Oscillations (EHO) [1]. Control and reproduction of robust QH-mode regimes could be crucial for future fusion operation. In some cases it may be useful to modify the main characteristics of QH-mode discharges while keeping constant the key elements needed to achieve QH-mode (such as applied torque, edge current density, pedestal pressure, etc.). With that in mind, the effect of global toroidal mode seeding in the vacuum magnetic field on the amplitude of EHO is investigated. Previous numerical simulations have shown that free boundary equilibrium calculations are able to recover non-linear saturated 3D equilibria with edge corrugations associated with EHO in QHmode [2, 3]. Here we use the VMEC free boundary code to do a proof of principle investigation of the coupling between EHO and global toroidal mode seeding. This is done by first producing a QH-mode plasma using the vacuum magnetic field modeled by JET-like toroidal and poloidal field coils. Then, a global toroidal mode n=1,2 is seeded numerically by perturbing the vacuum field using a set of non-axisymmetric external coils associated with the Error Field Correction Coils (EFCC's) in JET and the plasma response is studied. Due to the EFCC's geometry, it is crucial to account for up-down asymmetry in the VMEC code. Spectral decomposition of the 3D plasma displacement with respect to the equivalent 2D axisymmetric equilibrium is performed and compared with linear numerical simulations using the KINX code. A study that effectively isolates the coupling of global n=1,2 toroidal modes with current driven and pressure driven EHO is presented, and the impact of external coils and associated plasma response clearly determined.

References
[1] K. H. Burrell et al., Physics of Plasmas 8, 2153 (2001).
[2] A. Kleiner, submitted for publication to Plasma Phys. Control. Fusion. "Current and pressure gradient trig-
gering and non-linear saturation of edge harmonic oscillations in tokamaks"
[3] D. Brunetti et al., Journal of Plasma Physics, 84 (2), 745840201 (2018).

Speaker: G. Bustos Ramirez (EPS 2019)

56 P1.1052 Electromagnetic modelling of the reversed field pinch configuration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1052.pdf

A four-terminal electrical network formulation for the Reversed Field Pinch (RFP) is derived, fixing the flaws of the similar models available in the past literature [1][2]. The approach used in those papers starts from a specific plasma description, and the four electrical quantities of interest (toroidal loop voltage, plasma current, poloidal loop voltage, toroidal magnetic field) along with their governing equations are derived a posteriori. The final results, although appealing, raised a number of misleading or even wrong results and interpretations.
Here the modelling takes the steps from a rather general electromagnetic formulation, independent from the specific underlying physics of the plasma considered, which has to be specified at a later stage.
This approach highlights the effective boundary condition of the RFP, which turns out to be the same used in the stability studies of the screw pinch [3]: the ratio between the toroidal and poloidal fields (Bt/Bp) at the plasma boundary (or equivalently to the edge safety factor q(a) = a/R·Bt/Bp), with the plasma current acting as a scale parameter. On the other hand the total toroidal flux becomes a "free variable", determined by the physical description used for the plasma: by the stability criteria for the mentioned case of the screw pinch or by the specific processes of the RFP (e.g. those ruled by visco-resistive or by two fluid MHD equations).
In this view the toroidal field reversal is not a property of the plasma itself, but the result of a process guided from outside the plasma by the externally imposed boundary conditions. Moreover the traditional RFP derivation with global helicity and toroidal flux conservation [4] is a particular choice among the many possible underlying plasma physics descriptions.
As a sample application of the proposed modelling approach, the correct expression of the resistive component of the toroidal loop voltage for the RFP is finally given.

[1] Sprott, J.C. Electrical circuit modeling of reversed field pinches. The Physics of fluids, 31(8), 2266-2275, (1988).
[2] Schoenberg, K.F., Gribble, R.F. and Baker, D.A. Oscillating field current drive for reversed field pinch discharges. Journal of applied physics, 56(9), 2519-2529, (1984).
[3] Glasstone, S, and Lovberg R.H. "Controlled thermonuclear reactions: an introduction to theory and experiment." pp. 493-495, D. Van Nostrand Co., Princeton NJ (1960).
[4] Taylor, J.B. Relaxation of toroidal plasma and generation of reverse magnetic fields. Physical Review Letters, 33(19), 1139 (1974).

Speaker: R. Cavazzana (EPS 2019)

57 P1.1053 Shaping effects on the interaction of shear Alfvén and slow sonic continua

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1053.pdf

Experimentally it is observed that modes at frequency lower than toroidicity-induced Alfvén eigenmodes (TAEs) could enhance the loss of circulating ions injected in the plasma by the heating system, degrading the plasma confinement [1]. These low frequency modes can be identified with beta-induced Alfvén-acoustic eigenmodes (BAAEs), that exist in a frequency gap generated by the interaction between the Alfvénic continnum and the sound branches that differ from it in one poloidal mode number. In a compressible plasma the geodesic curvature (kG) [2] couples a Alfvén harmonic with poloidal number mA with a sound harmonic with mS = mA ± delta, with delta an integer number. An equilibrium model with circular magnetic surfaces provides an harmonic content to the geodesic curvature that is able to couple only branches with delta = 1.
In this work a non circular equilibrium is considered, thanks to which the geodesic curvature can be expanded in further harmonics of the poloidal angle. This increased spectral content allows the Alfvénic continuum to interact with sonic displacements corresponding to a higher poloidal mode number difference delta, which results in extra frequency gaps in the continuum induced by the plasma shaping. Inside these gaps discrete eigenmodes were computed with the MHD code CASTOR (Complex Alfvén Spectrum in TORoidal geometry) [3], whose frequencies, assuming values between BAAEs and TAEs ones, make them good candidates to interact with fast ions. A critical value of the safety factor, that if exceeded suppresses the Alvénic-sonic coupling, is set and other conditions to access the existence of shaping-induced gaps are discussed.

This work is supported by a FuseNet Master internship grant.

References
[1] W. W. Heidbrink, E. Ruskov, E. M. Carolipio, J. Fang, M. A. van Zeeland, and R. A. James, Physics of Plasmas 6, 1147 (1999)
[2] C. Z. Cheng, M.S. Change, The Physics of Fluids 29, 3695 (1986)
[3] W. Kerner, J. P. Goedbloed, G. T. A. Huysmans, S. Poedts,y and E. Schwarzz, Journal of computational
Physics 142, 271-303 (1998)

Speaker: F. Cella (EPS 2019)

58 P1.1055 Utilizing M3D-C1 to understand triggering of ELMs in pellet pacing experiments in DIII-D ITER-like plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1055.pdf

M3D-C1, a code for solving the linear and non-linear extended-MHD equations in toroidal geometry, is currently being used to model pellet ELM triggering in DIII-D ITER-like plasmas. Large edge localized modes (ELMs) in magnetically confined plasmas can lead to the sudden release of thermal and magnetic stored energy and can potentially cause damage to plasma facing components, especially as stored energy increases in larger devices. ELM pacing via injection of hydrogenic pellets can trigger small ELMs at a rate exceeding the natural ELM frequency and has been shown to be a successful method to mitigate effects of large ELMs. Understanding of the physical mechanisms of ELM triggering and improved modeling are required for confident extrapolation to ITER and beyond. A feature of M3D-C1 is that an unstructured triangular mesh provides sufficient resolution to capture the sharp gradients present in the pellet deposition layer. Additionally, the code provides high toroidal resolution that is important for investigating the ballooning mode physics of ELM triggering by pellets. M3D-C1 results run in 2D linear mode show that the localized perturbation is due to the pellet destabilizing peeling-ballooning modes. Calculations of linear peeling-ballooning stability as a function of pellet size suggest that a 2D pellet density ring underestimates the effects of the pellet. Linear simulations also suggest that the destabilization seems to be a resistive effect. Recent M3D-C1 modeling efforts have focused on 3D nonlinear, timedependent simulations incorporating a pellet ablation model. Simulations are focused on pellets injected at a speed of 150 m/s and are focused on studying how the pellet size and ablation location affect ELM triggering in DIII-D ITER-like plasmas. Initial 3D results show toroidally localized perturbations in the pressure and current profiles due to the presence of the pellet.

Work supported in part by the US DOE under contracts DE-AC05-00Or22725, DEAC02-09CH11466, and DE-FC02-04ER54698.

Speaker: S. Diem (EPS 2019)

59 P1.1056 Locked mode and disruption in JET-ILW

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1056.pdf

An n = 1 locked, or slowly rotating, mode has been observed in most pulses prior to JET disruptions. However, a small fraction of non-disruptive pulses has a locked mode which eventually vanishes without disruption. Despite these exceptions the locked mode amplitude is routinely used as a trigger for the JET disruption protection system. There are two threshold levels of locked mode: (i) if locked mode amplitude exceeds the "low" threshold level, the emergency pulse shutdown is activated; (ii) if the locked mode amplitude exceeds the "high" threshold level, the massive gas injection (MGI) is triggered to terminate the pulse because the plasma is at high risk of disruption, and so it is necessary to mitigate disruption damage to the vessel and the Plasma Facing Component (PFC). On JET, four vessel octant data consisting of 18 pick-up coils and 14 saddle loops can be used to calculate the locked mode amplitude and phase. The coils measure tangential to the vessel poloidal magnetic field (Bp) and saddles normal to the vessel field (Bn). The n = 1 locked mode amplitude and phase are calculated either from a subset of the four pick-up coils or the four saddle loops located in the identical poloidal location. An n = 2 locked mode was observed in a few exceptional pulses prior to disruption, in that case the amplitude and phase are calculated from 8 octant saddle measurements in the middle plane at the low toroidal field side. For the monotonic plasma current profile, the O-point of the tearing mode island corresponds to a reduction of the measured tangential poloidal field. ECE data, when they are valid, are used to study a locked mode evolution during 2011-16 JET-ILW operation. The O-point of the locked mode has a preferred toroidal phase dwelling mainly in octants 4 and 5, which manifest in the machine toroidal asymmetries. The fact the locked mode exists for a long time prior to disruptions suggests other physics could be involved in finally triggering the disruption.

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053 and from the RCUK Energy Programme [EP/P012450/1]. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: S.N. Gerasimov (EPS 2019)

60 P1.1057 Runaway electron mitigation by n=1 and n=2 magnetic perturbations in COMPASS

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1057.pdf

The application of 3D fields might help in preventing and mitigating the avalanche generation of runaway electrons (RE) during disruption events in controlled fusion devices [1, 2]. The
successful results recently obtained in ASDEX Upgrade [3] have motivated new experiments with this technique also in the COMPASS tokamak [4].
The resonant magnetic perturbation (RMP) coil system in COMPASS has been used to apply 3D fields with different amplitude and toroidal mode number (n=1 and n=2) to mitigate
the RE beams generated during disruptions induced by impurity massive injection (Argon or Neon). Like in ASDEX Upgrade, the application of RMP results in a significantly higher decay
rate and reduced lifetime of the generated RE beam. The strength of the observed effects strongly depends on the upper-to-lower coil phasing, i.e. on the poloidal spectrum of the applied
perturbation, which has been reconstructed including the plasma response by the code MARS-F [5]. The RMP coils were powered both before and after the impurity gas puff, demonstrating that the RE deconfinement due to perturbation appears in the RE dominated disruption independently of the same effect on the hot plasma. The enhanced deconfinement of
the RE seed population was observed as an increase of HXR signal immediately after energizing the RMP coils in the pre-disruption scenario. RMPs have a different impact in disruptions
induced by Argon or Neon, indeed in the latter case a stronger reduction of the RE beam lifetime (down to -80%) has been observed. External perturbations also destabilize the RE radial beam position, increase the level of radial fluctuations and are correlated with the appearance of sudden HXR bursts for those coils phasing which maximize the predicted plasma response.
Moreover, the configuration with n=2 RMP odd parity induces a MHD instability accompanied by a significant increase of the radial fluctuations resulting in a faster current decay rate.

[1] M. Lehnen et al., Phys. Rev. Lett. 100 255003 (2008)
[2] E.M. Hollmann et al. Phys. Plasmas 17 056117 (2010)
[3] M. Gobbin et al, Plasma Phys. Control. Fusion 60 014036 (2018)
[4] J. Mlynar et al, Plasma Phys. Control. Fusion 61 014010 (2019)
[5] Y. Liu et al., Phys. Plasmas 7 3681 (2000)

Speaker: M. Gobbin (EPS 2019)

61 P1.1058 Phase relation between phase locked (2,1) and (3,1) tearing modes in ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1058.pdf

Tearing modes (TMs) are a major concern for tokamak operation. Especially a (m = 2, n = 1) TM (with m poloidal and n toroidal mode number) can cause strong confinement reduction and also initiate a disruption.
When modes with the same toroidal but different poloidal mode numbers are phase locked, the local phase relation inevitably varies in space. In a tokamak with its toroidal symmetry, coupled modes are usually observed to rotate as a rigid body in toroidal direction. Thus, the phase relation varies with poloidal angle only. A (2,1) mode is mostly coupled to a (1,1) core mode when q0 < 1, while coupling to (m > 2, n = 1) TMs is not a general observation. Several publications that report on observed mode coupling or predict the phase relation between n = 1 TMs indicate that the modes are in phase on the low field side (LFS). E.g. in [1] this is observed prior to a density limit disruption for the (3,1) and (2,1) TMs.
Recent observations in ASDEX Upgrade with local electron temperature measurements by electron cyclotron emission diagnostics show that (2,1) and (3,1) TMs can couple with different phase relations on the LFS, reaching up to antiphase (i.e. the O-point of one island is next to the X-point of the other). The dependence on several parameters is discussed. Especially plasma rotation and plasma beta are strongly correlated with the phase between the modes.
Knowledge of the local phase can be of importance, e.g. when an island should be stabilised by current drive in the island's O-point using modulated electron cyclotron current drive (ECCD). An important tool for detecting and analysing TMs in real time are magnetic pick-up coils, which measure the perturbation field outside the plasma. In order to determine the correct ECCD timing from magnetic measurements in case of coupled modes, the phase relation between the modes has to be considered.

References
[1] W. Suttrop et al, Nuclear Fusion 37, 119 (1997)

Speaker: A. Gude (EPS 2019)

62 P1.1059 Non-linear MHD Simulations of ELMs in a Detached Divertor

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1059.pdf

ITER plasmas will be characterized by a high density plasma (i.e. Greenwald fraction) at low collisionality inside the separatrix, a high density in the scrape-off layer combined with a high recycling detached divertor. ELMs in ITER are expected to be tolerable at low plasma current but need to be controlled at the full 15MA current. Whether ELMs are tolerable depends in part on the interaction of the ELM energy and density losses with the detached divertor, i.e. do (very) small ELMs burn through the detached divertor plasma. Since the ITER regime cannot be obtained in current experiments, i.e. numerical simulations of ELMs are required for the extrapolation to ITER.
To improve the modelling of the divertor in the non-linear MHD code JOREK, a description of neutrals and impurities have been implemented. Previously, the neutrals have been modelled as a fluid. Recently, the JOREK code has been extended to include a kinetic (i.e. particle) description of neutrals and impurities [1]. Both neutrals and impurities are followed as discrete particles in the JOREK finite element grid. Ionisation and recombination lead to sources and sinks for plasma density and neutrals and to changes in charge state of the impurities. Radiation is included for both neutrals and impurities. Using the binary collision model for the impurities, the thermal force, leading to a flow of impurities up the temperature gradient, is taken into account. Multiple species of impurities, of arbitrary (time varying) charge state, can be included. The sputtering of impurities, by the main plasma, by self-sputtering or by other impurities has been implemented and verified. The sputtering model includes the prompt redeposition, particularly important for heavy impurities such as Tungsten. As a first application, ELMs are simulated in ITER plasmas on a domain extending up to ITER first wall panels and the divertor.

[1] D.C. van Vugt, Kinetic modelling of ELM-induced tungsten transport in a tokamak plasma, submitted

Speaker: G. Huijsmans (EPS 2019)

63 P1.1060 Drift kinetic effects on the neoclassical tearing mode threshold

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1060.pdf

For successful operation of future tokamaks such as ITER, it is paramount that we control neoclassical tearing modes (NTMs): plasma instabilities characterised by the evolution of magnetic islands. Experimentally, a sufficiently small island (comparable in width to the ion banana width, rho_bi) can heal itself and shrink away. An NTM control system could be deployed effectively by shrinking the seed islands to below the "threshold" level. The key questions to ask are: what is the threshold island width, w_c, and what are the essential pieces of physics?
We have developed a drift kinetic approach valid for small island cases, which we solve numerically for the perturbed ion distribution function [1]. One significant consequence of the finite orbit width effect, when rho_bi ~ w (rho_bi ~ epsilon^1/2 rho_theta_i, rho_theta_i is the ion poloidal Larmor radius and w is the island half-width), is the "drift island" structure in the perturbed distribution function: the contours of constant distribution function resemble those for the magnetic island flux surfaces, but shifted radially by an amount comparable to rho_theta_i. Consequently the flat-gradient regions of the distribution function no longer align with the magnetic island, the effect of which is to partially restore the density gradient across the island width, thus reducing the NTM drive.
Numerical solutions for the contribution to the island evolution, Delta'_loc, exhibits a clear threshold behaviour (see figure). For small island widths, w ~ rho_theta_i, the curves start to deviate from the analytic limit of Ref.[2]. The threshold width w_c, for which Delta'_loc = 0, scales linearly with rho_theta_i: w_c ~ 2.7 rho_theta_i, which is in qualitative agreement with experimental measurements [3]. This arises from the electron response to the electrostatic potential required for quasineutrality, motivating our future work to further improve our treatment of the electrons.

References
[1] K. Imada et al, Phys. Rev. Lett. 121, 175001 (2018)
[2] H.R. Wilson et al, Phys. Plasmas 3, 248 (1996)
[3] R.J. La Haye et al, Nucl. Fusion 46, 451 (2006)

Speaker: K. Imada (EPS 2019)

64 P1.1061 Rotation coupling of magnetic islands with different toroidal wave-numbers due to plasma viscosity in tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1061.pdf

The rotation of a magnetic island chain in tokamak plasma can be affected by both the electromagnetic and viscous torques applied to the resonant plasma layer that is occupied by the magnetic islands. In the presence of a static Resonant Magnetic Perturbation (RMP), in particular an Error Field, the rotation is irregular that appears as cyclical time variations of the mode Instantaneous Angular Velocity (IAV) [1]. The IAV is defined as time derivative of the mode angular phase. In the case of a single mode, the period of IAV variations in time is equal to the period of the mode oscillations. This sort of rotation irregularity is attributed to oscillations of the electromagnetic torque, applied to the resonant plasma layer from the RMP, along with the island rotation.
The electromagnetic coupling of the tearing-modes (see [2]) with different poloidal, m, and equal toroidal, n, numbers occurs because in toroidal geometry each mode has sideband components that differ by the m numbers. On the contrary, the tearing-mode does not have side-band n-harmonics because of the axisymmetric tokamak geometry with respect to the main vertical toroidal axis. Therefore, the electromagnetic coupling of tearing-modes with different toroidal, n, numbers seems impossible. However, rotation of these different-n modes can be coupled via viscous radial transfer of angular momentum in plasma (see [3]).
The simulation and its experimental validation of the rotation coupling between m/n = 2/1 and 3/2 modes in T-10 tokamak are presented. In the specially chosen T-10 regime, the m/n = 2/1 mode and the m/n = 3/2 mode are observed simultaneously. The rotation irregularity (IAV oscillations) of each mode due to the Error Field effect is used as a marker to distinguish this mode presence in the IAV oscillations of the other mode. The admixture of 4 kHz component to the natural 2 kHz oscillations of the m/n = 2/1 mode IAV and the admixture of 2 kHz component to the natural 4 kHz oscillations of the m/n = 3/2 mode IAV are observed in the experiment (see Fig.1).
The nonlinear visco-resistive TEAR-code [1, 4] is used for simulation. The comparison of the simulation results with experimental data confirms the assumption that the observed coupling between m/n = 2/1 and 3/2 modes is attributed to plasma viscosity.

[1] Eliseev L.G., et al. Physics of Plasmas 22 (2015) 052504
[2] Nave M.F.F., et al. Eur. Phys. J. D 8 (2000) 287
[3] Kakurin A.M., Orlovskiy I.I. Plasma Physics Reports 35 (2009) 93
[4] Ivanov N.V., Kakurin A.M. Nucl. Fusion 57 (2017) 016021

Speaker: N. Ivanov (EPS 2019)

65 P1.1062 Rotational instabilities of liquid metal droplets in tokamaks

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1062.pdf

Safely achieving the goal of stable power production in magnetic confinement fusion devices is critically dependent on controlling the mobilization and accumulation of dust[1]. The aggregation of high Z impurities in the core plasma from the ablation of metal dust grains causes strong bremstrahhlung losses[2] and can destabilise the plasma[3] which must be avoided to maintain acceptable fusion yield. The retention of dust causes a biological hazard due to the toxicity of beryllium and radioactivity of tritiated carbon dust[4] with the possiblity for inhalation and contamination of local environment in a loss of vacuum event[5]. This will be a key issue for ITER where operational time scales may be limited by radioactive dust inventories.
Impurity transport is greatly enhanced by dust breakup. A model for the rotational instability of liquid metals in tokamak plasmas is presented as the probable explanation for the observation of forking trajectories, characterised by consistent and repeatable splitting into pairs of sub-droplets. Inferred rotational speeds are consistent with longstanding theories of particle spinning in magnetized plasmas[6] but are two orders of magnitude greater than previous measurements of rotating particles in plasmas. Analysis with the Dust in TOKamakS (DTOKS) Figure 1: Liquid breakup event in code yields statistical predictions for fast-camera observations and predictions for droplet behaviour in current and next-generation tokamaks, see figure 1.

References
[1] A. Malizia, L. A. Poggi, J. F. Ciparisse, R. Rossi, C. Bellecci, and P. Gaudio, Energies 9, (2016).
[2] T. Pütterich, R. Neu, R. Dux, A. D. Whiteford, M. G. O'Mullane, and H. P. Summers, Nucl. Fusion 50,
(2010).
[3] P. C. De Vries, M. F. Johnson, B. Alper, P. Buratti, T. C. Hender, H. R. Koslowski, and V. Riccardo, Nucl.
Fusion 51, (2011).
[4] G. R. Longhurst and L. L. Snead, (2004).
[5] J. Roth, E. Tsitrone, T. Loarer, V. Philipps, S. Brezinsek, A. Loarte, G. F. Counsell, R. P. Doerner, K. Schmid,
O. V Ogorodnikova, and R. A. Causey, Plasma Phys. Control. Fusion 50, 103001 (2008).
[6] S. I. Krasheninnikov, Phys. Plasmas 13, 2004 (2006).

Speaker: L. Simons (EPS 2019)

66 P1.1063 Plasma confinement by moving multiple mirrors

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1063.pdf

The achievable gain in magnetic mirrors fusion machines is limited by particles and energy flux through the mirrors. The moving multiple mirrors (MMM) concept is based on many mirror coils at each end of the trap, synchronized in sequence to generate magnetic mirror that moves towards the centre of the trap. Particles escaping from the main cell are scattered out of the loss-cone in the MMM sections and propelled back inside by the magnetic wave. Analytical optimization of the MMM parameters for a conceptual fusion mirror machine, suggests that gain >>1 can be obtained with reasonable voltage, current and power dissipation in the MMM driving system. We present the design of an experimental system aiming to explore the MMM concept and demonstrate orders of magnitude reduction in axial plasma flux.

Speaker: I. Be'ery (EPS 2019)

67 P1.1064 Analysis of Gyrokinetic Model Collision Operator and Comparison with Braginskii Fluid Simulations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1064.pdf

It is highly desirable to find a common regime of validity for gyrokinetic and Braginskii fluid codes, which would give us a handle to extend the regime of validity of either to the very edge and H-mode transition conditions. Up to now the highly nonlinear conditions there are more naturally the domain of fluid codes, while the short scale lengths and collisionless effects are the expertise of gyrokinetics.
In this vein, the gyrokinetic code CGYRO [1] implementing the Sugama model-collisionoperator [2] and the non-local Braginskii two-fluid code NLET [3] have both been applied to the highly collisional, resistive ballooning turbulence scenarios relevant to the edge of a tokamak, which approach the fluid limit. These comparisons yielded a good match for the collisional regime for dominant density perturbations. However, significant temperature fluctuations (due to temperature gradients) systematically gave differing transport and turbulence intensity. (Surprisingly, completely collisionless scenarios in the high gradient ITG regime also agree.)
The reason for the remaining mismatch in the highly-collisional fluid regime are inaccuracies in the gyrokinetic model collision operator. That collision operator uses an ad-hoc field operator with the purpose of restoring energy and momentum balance while maintaining Onsager symmetry, Galilean and temperature shift invariance.
The transport coefficients produced by the model collision operator in CGYRO have been compared to the predicted Braginskii values [4, 5]. Terms which depend only on the test particle component of the operator, such as the frictional heat flux, perpendicular resistivity, are exactly right, while like-particle collision dependent terms, such as the parallel resistivity or the perpendicular heat flux are overestimated.
A way to improvement, are corrections to the collision operator taking into account higher moments of the "field" collision operator, or a (costly) transition to the full Landau operator, which is complicated in gyrokinetics by the necessary pull-back operation.

[1] J. Candy, E.A. Belli, R.V. Bravenec, J. Comput. Phys. 324, 73 (2016)
[2] H. Sugama, T.-H. Watanabe, M. Nunami, Phys. Plasmas 16 (2009) 112503.
[3] K. Hallatschek, A. Zeiler, Phys. Plasmas 7, (2000) 2554
[4] S. I. Braginskii, in Reviews of Plasma Physics, ed. M. A. Leontovich (New York, 1965), Vol. I, 205
[5] Hinton, Fred L. Handbook of Plasma Physics 1, 147 (1983).

Speaker: K. Hallatschek (EPS 2019)

68 P1.1065 Anti-symmetric plasma fluid models with exact discrete conservation

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1065.pdf

We construct fluid plasma models that combine physical consistency and numerical stability with a simple and flexible implementation [1]. This is achieved by exploiting the anti-symmetric property of the plasma flow operator, ∫dVφ(∇·v+v·∇)ψ=−∫dVψ(∇·v+v·∇)φ, which results in exact conservation. Since this expression has an equivalent discrete analog, computer implementations of fluid models using our representation automatically inherit the conservation properties of the continuous system. Additionally, it can be shown that the plasma velocity generates infinitesimal rotations of the fluid element, implying local time reversibility, e.g. existence of a discrete inverse. The anti-symmetric equations are written using generalized moments √n,√nv,√p, related to conserved quantities n,K= (1/2)mv2,U= (3/2)p, n, nv, p, related to conserved quantities n, K=

(1/2)mv2,

U

=

(3/2) p,

that ensure mass and energy positivity. Altogether, these properties lead to an intrinsically stable code implementation, provided that a few restrictions on the choice of numerical scheme are satisfied. We demonstrate this by applying our methodology to the Braginskii two-fluid model, the magnetohydrodynamics (MHD) equations, and also more computationally efficient drift-ordered models. The conservation properties are verified using representative cases such as single seeded blob dynamics and the Orzsag-Tang vortex, obtaining high-fidelity simulation results with negligible dissipation.

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, Theory Program, under Award no. DE-FG02-95ER54309.

References
[1] F.D. Halpern and R.E. Waltz, Phys. Plasmas 25, 060703 (2018); F.D. Halpern and R.E. Waltz, A family of consistent and numerically stable fluid plasma models (to be submitted).

Speaker: F.D. Halpern (EPS 2019)

69 P1.1066 Statistical modeling of heavy ions quasicontinuum in thermonuclear plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1066.pdf

The heavy ions quasicontinuum (in the 4-8 nm spectral range) presently was observed on many modern thermonuclear installations. In particular it could be used for monitoring the tungsten transport. The statistical modeling of heavy ions is proposed to describe general features of these spectra. It considers the ions excitations in terms of the collective oscillations with plasma frequencies, determined by the local atomic electron density [1]. The electron density distribution of the outer ion shells is approximated by the Slater-type functions n(r) n_Sl (r) = Ar^2 e^-2 r . As this distribution has a maximum, it results in a sharp cut of the spectra at the specific short wave length for a given shell of a given ion within the local plasma frequency model. Just this general feature is observed in the experimental spectra on different installations [2-5]. Fig. 1 demonstrates the correspondence of the observed quasicontinuum of tungsten ions with the statistical modeling.

References
[1] Brandt W., Lindquist S. Phys. Rev. 139 3A (1965) 612
[2] Hinnov E., Mattioli M. Phys. Lett. A 66 (1978) 109
[3] Johnson B.M., et al. Phys. Lett. 70A(4) (1979) 320
[4] Isler R.C. et al. Phys. Lett. 63A(3) (1977) 295
[5] Harte C. S. et al. J. Phys. B: At. Mol. Opt. Phys. 43 (2010) 205004

Speaker: D.S. Leontyev (EPS 2019)

70 P1.1067 A comparison of experimental and theoretical electron energy distribution functions in an argon GyM plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1067.pdf

A joint experimental/theoretical investigation on the characteristics of plasmas produced in GyM magnetic linear device [1] has been carried out, comparing the measured electron energy distribution function (EEDF) with the distribution resulting from a self-consistent state-to-state kinetic model coupling the chemistry of inelastic and reactive collisional processes with the Boltzmann equation for free electrons [2]. The simulations are performed feeding the code with discharge parameters (pressure, power, intensity of magnetic field) derived from experimental conditions. The level kinetics includes an extended collisional radiative model with electron excitation (deexcitation) and ionization from the ground and excited states, in order to estimate radiation emission. Three body recombination and radiative recombination have also been included. EEDF has been experimentally determined by Langmuir probe measurements in argon plasmas. A preliminary comparison between the theoretically simulated and experimentally measured ionization degree shows a reasonable agreement. The experimental EEDF presents a peak region around 10 eV, a hint of the presence of non-maxwellian distribution. This peak corresponds to the superelastic collisions of electrons with neutral argon excited in its metastable state. This activity represents the first attempt to model the plasma produced in GyM, and in the future it will be extended to molecular plasmas such as hydrogen and nitrogen.

[1] D. Iraji et al. Fusion science and technology (Online) 62 , 428 (2012)
[2] G. Colonna et al. Chemical Physics, Volume 398, 4 April 2012, Pages 37-45

Speaker: L. Laguardia (EPS 2019)

71 P1.1068 Tokamak GOLEM for fusion education - chapter 10

See the full abstract:
here http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1068.pdf

The GOLEM tokamak is the oldest still operational experimental device in the high temperature tokamak plasma physics. Currently its main mission is to be an educational device to train future thermonuclear fusion specialists. The GOLEM is unique thanks to its remote-control system [1], which allows to carry out the discharge and instantly process experimental data remotely. This contribution is devoted to the current experimental projects of the students:
- Calibration of the ball-pen probe [2] and measurements of plasma parameters in H and He plasma, based on a shot-to-shot method using movable combined probe head composed of the ball-pen and Langmuir probes. Configuration allows measuring profiles of el. temperature, floating and plasma potentials. In the case of He plasma, it is the first measurement of this kind.
- Mass spectrometer PrismaPlus. Integrating of the spectrometer to the system will make the automatic data collection possible, with applications, e.g., calibration of the pressure gauge and improvement of wall conditioning methods.
- The parallel Mach number is measured using the double tunnel probe. It is found that the confined plasma rotates opposite to the plasma current with M~0,1-0,5 and the rotation direction tends to reverse toward the plasma edge.
- Double rake probe for studying plasma turbulence. Edge plasma potential biasing is a way to induce shear flows that suppress the turbulence. Double rake probe is used as main diagnostics to measure particle flux in poloidal and radial directions.
- Research on runaway electrons (RE) is focused on two topics: i) segmented semiconductor detector placed in vacuum chamber for various measurements and ii) probe based on scintillating materials alternating with heavy absorbers able to measure RE energy.

[1] Tokamak GOLEM, Czech Technical University in Prague, http://golem.fjfi.cvut.cz/wiki/ [online]
[2] J. Adamek,, J. Stockel, J. Hron, A novel approach to direct measurement of the plasma potential (2004).

Speaker: P. Macha (EPS 2019)

72 P1.1069 Advances Towards Modeling a Simplified Lithium Vapor Box Design

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1069.pdf

The surface heat flux in a fusion Demonstration power reactor operating under attached conditions has been predicted to reach values far beyond the capabilities of any solid surface [1]. The injection of gaseous impurities to cause divertor detachment can result in strong radiation at the X-point [3], causing the pedestal temperature to decrease. This can have detrimental effects on plasma confinement. The lithium vapor box is a divertor design that aims to radiate a large fraction of the loss power volumetrically via lithium line radiation, while localizing the lithium vapor to the divertor region. Even in a simple divertor configuration without special-purpose baffles, [2], local evaporation and condensation can create a strong differential pumping effect, minimizing lithium vapor near the X-point while keeping a high enough lithium density to detach the plasma [4, 5]. This system is resilient to changes in power loss, because the lithium ionization increases as the divertor leg extends towards the target. Due to the presence of regions with high neutral fractions, self-consistent investigation of lithium-plasma interactions in this configuration necessitates the use of a coupled fluid plasma - kinetic neutrals code. SOLPSITER is capable of modeling both the neutral-dominated regions near the lithium evaporator and the plasma-dominated regions further upstream. Here, SOLPS-ITER is used along with relevant PFC geometries and EFIT equilibria to simulate a simplified lithium vapor box divertor within the Experimental Advanced Superconducting Tokamak (EAST). SOLPS-ITER neutral transport results are benchmarked against the SPARTA Direct Simulation Monte Carlo code. Lithium fractions, electron densities and temperatures, and radiation distributions are presented for detached cases in EAST.

References
[1] R.J. Goldston, Theoretical aspects and practical implications of the heuristic drift SOL model, Journal of Nuclear Materials 463 (2015) 397-400, http://dx.doi.org/10.1016/j.jnucmat.2014.10.080
[2] L.G. Golubchikov et al., Development of a liquid-metal fusion reactor divertor with a capillary-pore system, Journal of Nuclear Materials 233-237 (1996) 667-672
[3] S. Potzel et al., A new experimental classification of divertor detachment in ASDEX Upgrade (2014) Nucl. Fusion 54 013001
[4] E.D. Emdee et al., Study of Lithium Vapor Flow In a Detached Divertor using DSMC code, Nuclear Materials and Energy (2019) accepted for publication
[5] T.D. Rognlien et al., Simulations of a high-density, highly-radiating lithium divertor, Nuclear Materials and Energy (2019) accepted for publication

Speaker: E. Emdee (EPS 2019)

73 P1.1070 Nonlinear growth of ELMs driven by divertor currents

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1070.pdf

Type I-ELM heat loads are of great concern for ITER and future power plants as they can lead to divertor erosion and melting. Investigation of the nonlinear ELM phase and its dynamics is indispensable for progress on ELM control and understanding. An additional driver providing explosive growth in the nonlinear ELM phase has been identified in DIII-D in the form of stochasticity enhancing thermoelectric currents flowing through the confined plasma. Before a significant increase in divertor ELM heat flux occurs, rapidly oscillating currents to divertor tiles are measured in DIII-D with an array of shunted tiles. Extrapolation of measurement results in peak tile currents of 5-20 kA flowing in a concentric circle near the strike point, which is on the order of the loss of bootstrap current. Toroidal analysis of these currents is consistent with a low n mode composition which will affect stability and transport in the nonlinear phase. An ELM current model (ECM) is developed based on thermoelectric origin of the tile currents and found consistent with the current measurements. Field line tracing and resistance calculations using thermoelectric current models suggest partial current flow through flux tubes in the confined plasma within the separatrix. In this model, these currents produce further flux tubes in a self-amplifying process. Ultimately this process leads to stochasticity enhancement and provides additional transport in the initial nonlinear ELM phase (<0.3 ms). A validation of the model is provided through Double Null plasma analysis, where the increase of ELM currents is measured simultaneously on high and low field side. Pure current flow in the SOL cannot explain the instant rise on the high field side as it would take finite time for the perturbation to spread there; hence currents are flowing through the confined plasma. These measurements encourage implementing tile current modules into nonlinear simulations and considering non-axisymmetric divertor biasing for ELM mitigation. This mechanism could provide the explosive nonlinear growth that has been sought in computational ELM simulations in order to provide the measured fast heat flux rise in the divertor1,2.

Work supported in part by U.S. DOE under DE-AC05-00OR22725, DE-AC02-09CH11466, and DE-FC02-04ER54698.

1 L.E. Sugiyama and H.R. Strauss, Phys. Plasmas 17, (2010).
2 S. Pamela, T. Eich, L. Frassinetti, B. Sieglin, S. Saarelma, G. Huijsmans, M. Hoelzl, M. Becoulet, F. Orain, S. Devaux, I. Chapman, I. Lupelli, E. Solano, and J.E.T. Contributors, Plasma Phys. Control. Fusion 58, (2015).

Speaker: M. Knolker (EPS 2019)

74 P1.1071 From a reflectrometry code to a standard EC code to investigate the impact of the edge density fluctuations on the EC waves propagation

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1071.pdf

Recent modelling and experimental studies [1-4] show that the edge density fluctuations can affect the electron cyclotron (EC) wave propagation in a tokamak plasma. In particular, the presence of density fluctuations in the scrape-off layer (SOL) can modify the EC beam propagation causing a power deposition broadening at the EC resonance location. This aspect could play a major role in the efficiency of the EC waves in stabilizing/suppressing the neoclassical tearing modes (NTMs). In this work, we show a new numerical tool originally developed for reflectometer simulations [5, 6] to address the points described above. This code was commonly used for reflectometer antenna-plasma coupling calculations that include density fluctuations [7]. The main capabilities of the codes are: (i) it solves the Maxwell equations in both 2D and 3D geometries; (ii) the numerical domain can be divided in three regions: a vacuum region, a paraxial region, and a full-wave region, each with the appropriate wave solving strategy for high computation efficiency. A description of the code will be presented together with a comparison between the paraxial and the full-wave solutions with and without edge density fluctuations in both 2D and 3D geometries. A scan in the amplitude of edge density fluctuations will be presented together with the evaluation of the 3D electric field pattern at the location of the EC resonance. Moreover, the impact of a time variation of the SOL density fluctuations to the EC beam will be explored. Finally, future applications with realistic fluctuations from experiment measurements and/or from turbulence codes will be discussed.

[1] A. Snicker et al., Nucl. Fusion 58, 016002 (2018).
[2] A. Snicker et al., Plasma Phys. Control. Fusion 60, 014020 (2018).
[3] A Köhn et al., Plasma Phys. Control. Fusion 60, 075006 (2018).
[4] O. Chellaï et al., Phys. Rev. Letters 120, 105001 (2018).
[5] E. J. Valeo et al., Plasma Phys. Control. Fusion 44, L1 (2002).
[6] E. J. Valeo et al., AIP Conf. Proc. 1187, 649 (2009).
[7] G. J. Kramer et al., Nucl. Fusion 58, 126014 (2018).
*Work supported by US DOE Contract DE-AC02-09CH11466.

Speaker: N. Bertelli (EPS 2019)

75 P1.1072 Interaction between high-power ICRF waves and drift-wave turbulence in LAPD

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1072.pdf

The Basic Plasma Science Facility (BaPSF) at UCLA is a US national user facility for studies of fundamental processes in magnetized plasmas. The centerpiece of the facility is the Large Plasma Device (LAPD), a 20m long, magnetized linear plasma device [1]. This LAPD has been utilized to study a number of fundamental processes, including: dispersion and damping of kinetic and inertial Alfvén waves, flux ropes and magnetic reconnection, three-wave interactions and parametric instabilities of Alfvén waves, turbulence and transport and interactions of energetic ions and electrons with plasma waves. An experimental campaign on the physics of ICRF waves has recently begun using LAPD.
The LAPD has typical plasma parameters ne ~ 1.0 10^12 - 10^13cm^-3, Te ~ 1 - 10eV and B ~ 1000G. A new high-power (~150 kW) RF system and antenna 0.8 have been developed for excitation of large amplitude fast waves in LAPD. The source runs at a frequency of 1-5 MHz, corresponding to 1 - 10 fci, depending on plasma parameters. Recent work has focused on the structure and scaling of RF sheaths and convection cells near the antenna[2]. In these same experiments, strong low-frequency modulation of coupled fast wave power is observed via direct measurement of the magnetic signals associated with the fast waves in the core plasma. This modulation is well correlated with low-frequency edge density fluctuations associated with drift waves. Suprisingly, the amplitude of the RF modulation and the amplitude of edge density fluctuations in the drift wave frenquency range both grow with increasing RF power, as shown in Fig. 1, suggesting some nonlinear coupling between the edge drift waves and large amplitude fast waves in the core region.

References
[1] W. Gekelman, et al., Rev. Sci. Inst. 87, 025105 (2016).
[2] M. Martin, et al., Phys. Rev. Lett. 119, 205002 (2017).

Speaker: T. Carter (EPS 2019)

76 P1.1073 Experiments on negative ion sources at the NIO1 installation

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1073.pdf

Negative ion sources are a critical component of neutral beam injectors NBI (used for stellarator and tokamak heating and current drive), due to the stringent requirement current density, beam divergence and operational stability. In support to the NBI development, a relatively compact 9 beamlet H- source (named NIO1, for negative ion optimization phase 1) was developed in close collaboration between Consorzio RFX and INFN, and is operated since 2014, for studying the influence of magnetic field configuration and other conditions on extracted beam. A robust rf system (amplifier can tolerate the load mismatch at plasma onset) and strong water cooling of the ion source and accelerator allow CW operation of the beam, well over the one hour pulse length required by ITER. A dedicated Cs oven (including a hot closure valve) was verified in separated test stand, where final calibrations are in progress, for installation in NIO1. Effects of several magnetic field configurations were studied in NIO1 in pure volume production conditions, which in principle should guarantee long term stability of extracted beam; spontaneous and unexpected fluctuations of plasma regime (with time scale in the order of minutes, or tens of minutes) were sometimes observed, and partly related to several changes in operational procedures (history of pressure changes). As a general trend, the typical source perfomances improve with strength of the magnetic field filter (with collected data spanning from 1 to 12 mT), which also helps to reduce the coextracted electron current. Evolution of diagnostic and simulation development is also summarized in this contribution: the beam images taken by two orthogonal cameras and the beam optics simulation are in fair agreement. Some development of energy recovery system and related full power beam calorimeter are also noted. More detailed modelling of source plasma will benefit from data of Cavity Ring Down Spectrometer whose installation, nearly finished, is also described.

Speaker: M. Cavenago (EPS 2019)

77 P1.1074 Approaching the ion source parameters for ITER's NBI systems with the test facility ELISE

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1074.pdf

The test facility ELISE represents a 1/2-size scaled experiment for the development of the RF-driven negative hydrogen ion source of the ITER neutral beam injection (NBI) systems. ELISE is dedicated to demonstrate the ITER requirements in terms of extracted negative hydrogen current densities (329 A/m^2 H-, 286 A/m^2 D-) with an electron-to-ion ratio of less than one at a source pressure of 0.3 Pa for durations of up to one hour. Taking into account the stripping losses in the accelerator, accelerated current densities of 230 A/m^2 H and 200 A/m^2 D are targeted at ITER NBI whereas at ELISE less stripping losses are expected due to its three stage acceleration system (about 15% max. instead of 30% at ITER). The beam can be extracted and accelerated up to total energies of 60 keV with the constrain of having a pulsed power supply available, leading to beam blips of 10 s every ~150 s while having continuous plasma operation. In order to achieve high ion and low electron current densities, caesium is seeded into the low temperature hydrogen plasma, imposing the complexity of a strong temporal dynamics. Another challenging requirement concerns beam homogeneity: deviations in the uniformity of the large beam (about 1x1 m^2 composed of 640 beamlets) of less than 10% are allowed only. ELISE went into operation in 2013 and made remarkable progress since then, starting from short pulse operation (10 s) to the ITER target of 1000 s for H- and 3600 s for D-. Recently the target parameters for hydrogen were demonstrated representing a milestone for the success of ITER NBI. Beside the challenge to control the high temporal dynamics of the co-extracted electron current, the caesium management in the source and the beam uniformity turned out to be very sensitive on the ion source parameters. As for deuterium the amount of co-extracted electrons is higher with stronger temporal dynamic than in hydrogen and as deuterium operation requires higher caesium amounts the current activities are focussing on improved suppression and control of co-extracted electrons together with the supply of sufficient caesium for the 1 hour pulses, both mandatory to achieve the targets for deuterium beams.

Speaker: U. Fantz (EPS 2019)

78 P1.1075 Parametric decay instabilities during electron cyclotron resonance heating at ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1075.pdf

Parametric decay instabilities (PDIs) are phenomena in which a large-amplitude pump wave decays to two lower-frequency daughter waves once its amplitude exceeds a nonlinear threshold. PDIs are ubiquitous in situations where plasmas interact with strong waves, including ionospheric modification experiments and wave heating of laboratory plasmas, and may lead to a significantly different wave response than the one expected from linear theories [1]. Here, we focus on PDIs occurring during electron cyclotron resonance heating (ECRH) at the ASDEX Upgrade tokamak; particularly, PDIs near the 2nd-harmonic upper hybrid resonance (UHR). For these PDIs, trapping of the daughter waves is necessary to reduce the threshold to a level accessible with ECRH [1]. Such trapping may occur near a local maximum of the electron density, e.g. in connection with magnetic islands and edge localised modes (ELMs). We demonstrate the occurrence of these PDIs during ELMs at high electron densities through measurements Figure 1: Wave trapping near the 2nd-harmonic with the collective Thomson scattering sys- UHR during an ELM crash, simulated with tem. Further, in Fig. 1, we show the first con- JOREK [2]. A PDI with an absolute ECRH firmation of the existence of wave trapping beam power threshold of approximately 2 kW and excess of the PDI threshold during such and a convective ECRH beam power threshold ELMs for electron density and temperature of approximately 300 kW exists in this case [1]. profiles simulated using the JOREK code [2].

References
[1] A.Yu. Popov and E.Z. Gusakov, Plasma Phys. Control. Fusion 57, 025022 (2015)
[2] M. Hoelzl et al., Contrib. Plasma Phys. 58, 518 (2018)

Speaker: S.K. Hansen (EPS 2019)

79 P1.1076 Frist time neutral beam heating on Wendelstein 7-X

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1076.pdf

In the recent experimental campaign of W7-X, a neutral beam injection (NBI) system was put into operation for the first time. This system is in many parts identical to the system on AUG. It consists of two injectors, NI21 and NI20, that can accommodate up to four radio-frequency driven ion sources. The acceleration grid spacing of each source is optimized for 55 kV hydrogen or 60 kV deuterium injection with a neutral beam power at the plasma of 1.7 and 2.5 MW, respectively. The pulse length is limited to 6.5 sec in hydrogen, at a repetition rate of one pulse every three to five minutes. Both injectors are located symmetrically w.r.t. the magnetic field configuration of W7-X. NI21, so far, has been operated with two sources in hydrogen. The technical commissioning involved operating the beams onto an internal calorimeter. This confirmed the expected neutralization efficiency, beam divergence and species fraction. Validation of the safety interlocks involved NBI pulses into the empty plasma vessel. The impact of NBI generated fast ions on plasma vessel components during injection into plasmas was carefully assessed. For certain magnetic field configurations it was possible to heat and sustain the plasma with NBI as the only heating source for close to the technical limit of 4.8 sec. The beam attenuation in the plasma approximately agrees with predictions. About 300 plasma discharges involved NI injection and, overall, the system performed reliably in single pulses or pulse trains up to about 100 Hz.

Speaker: D.A. Hartmann (EPS 2019)

80 P1.1077 Adaptation and benchmarking of the pellet simulation code HPI2 for the stellarators TJ-II and W7-X

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1077.pdf

An efficient fuelling capability is mandatory for large fusion devices; this being of primary importance for helical devices [1]. The injection of cryogenic pellets is the best candidate to refuel the plasma core in large devices. During the past decades pellet injection (PI) technologies have become well developed while advancement in the understanding of pellet ablation, and subsequent particle deposition, has been substantial. Moreover, PI simulation codes, such as HPI2 [2-4], have been developed in order to aid experimental analysis and to design PI systems for new large devices, e.g., W7-X. Despite such advances, further effort in pellet physics studies is needed since a complete comprehension of experimental observations, e.g., related to pellet particle deposition, remains outstanding, in particular for stellarators. In parallel, it is necessary to incorporate new insights into the underlying physics of pellet ablation, drift, and diffusion into simulation codes in order to improve predictions.
Cryogenic PI is used for low-field side fuelling of the TJ-II heliac, a medium-sized stellarator, characterized by high flexibility [5,6]. Its PI database has been used to benchmark a new stellarator version of the HPI2 code [7] that would allow predictions for the new stellarator W7-X. In general, good agreement with experiment has been found for TJ-II injections, thus providing confidence for W7-X simulations. However, under certain experimental conditions in TJ-II, deposition profiles deviate significantly from predictions. For instance, when suprathermal electrons are present in the plasma core, particle deposition is significantly deeper than predicted and fuelling efficiency is improved [7,8]. In order to understand this, an upgraded fast imaging camera follows plasmoid drift during dedicated experiments. This has provided input for developing new algorithms for the stellarator versions of HPI2.

[1] H. Maaßberg, C.D. Beidler, E.E. Simmet, Plasma Phys. Control. Fusion 41 (1999) 1135-1153.
[2] B. Pégourié et al., Plasma Phys. Control. Fusion 47 (2005) 17-35.
[3] B. Pegourie, V. Waller, H. Nehme, L. Garzotti, A. Geraud, Nucl. Fusion 47 (2007) 44-56.
[4] F. Köchl et al., Prepr. EFDA-JET-PR(12)57 (2012) 82.
[5] J.L. Velasco et al., Plasma Phys. Control. Fusion 58 (2016) 084004.
[6] K.J. McCarthy et al., Nucl. Fusion 57 (2017) 056039.
[7] N. Panadero et al., Nucl. Fusion 58 (2018) 026025.
[8] K.J. McCarthy et al., Plasma Phys. Control. Fusion 61 (2019) 014013.

Speaker: J.L. Velasco (EPS 2019)

81 P1.1078 Enhanced accessibility and absorption of helicon and lower hybrid waves in tokamak plasmas via n|| upshift from poloidal inhomogeneity

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1078.pdf

Two high-power systems for non-inductive current drive in the mid-radius region with waves in the lower hybrid range of frequencies (LHRF) are under construction for the DIII-D tokamak. One system will launch fast waves at 0.48 GHz ('helicons') from a 30-element traveling wave antenna of the comb-line type mounted above the mid-plane on the outboard side of the torus, while the other system will launch slow waves at 4.6 GHz from a grill mounted near the midplane on the high-field side of the torus. In each case, the aim is to couple ~1 MW of power to DIII-D plasmas at a launched value of the parallel index of refraction of approximately n|| 3. The reason for requiring this relatively high value of n||, with its consequent challenge for efficient coupling, is to obtain accessibility to the core plasma at high density in the low toroidal field of DIII-D (BT(0)<2.2 T) for the 4.6 GHz slow wave, while in the case of the 0.48 GHz helicon, a value of n|| at least this high is needed to yield strong first-pass Landau damping at attainable electron pressures in DIII-D. Analysis with the ray-tracing code GENRAY verifies that the evolution of n|| along the ray is decisively affected by poloidal inhomogeneity for both the slow lower hybrid wave [1] and for the fast wave in the lower hybrid range of frequencies [2]. We show that this similarity in behavior can be traced to the essentially geometric origin of the effect, and that the propagation properties of the two modes in simple geometries are qualitatively similar in this frequency range. The consequences for wave accessibility to the core and the location of strong damping are analyzed for the conditions of the upcoming DIII-D experiments. We quantify the degree of sensitivity of the deposition location to variations in the plasma equilibrium. The highpower helicon experiments will commence in 2020, while the installation of the equipment for the high-field-side launch lower hybrid experiment is scheduled to occur between the 2020 and 2021 campaigns. Progress on hardware construction and installation will be reported.

[1] P.T. Bonoli and E. Ott, Phys. Fluids 25, 359 (1982) [2] D.L. Grekov, V.E. D'Yakov and K.N. Stepanov, Nucl. Fusion 23, 1402 (1983)

Work supported in part by the US Department of Energy under DE-FC02-04ER54698 and the Science Undergraduate Laboratory Internship (SULI).

Speaker: R.I. Pinsker (EPS 2019)

82 P1.1079 Possibility of strong anomalous absorption in electron cyclotron resonance heating experiments

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1079.pdf

The electron cyclotron resonance heating (ECRH) is widely used in the toroidal devices and planned for application in ITER. Its concept is based on the linear theory. However, during the last decade the anomalous scattering of pump microwaves was discovered in presence of a non-monotonic density profile in the X2-mode ECRH experiments [1]. This effect was explained in [2] by excitation of low-threshold two-plasmon parametric decay instability (PDI) possible due to a localization of upper hybrid (UH) daughter waves at the local maximum of the density profile. On the basis of the proposed mechanism the PDI was analyzed and the level of its saturation due to a cascade of UH waves decays was determined. The theory explains quantitatively the anomalous backscattering observed in [1] as a result of a nonlinear coupling of different daughter waves. The proposed scenario predicts a substantial anomalous absorption of pump power (5%-20%), which is however far from been total.
In this paper the effect of strong anomalous absorption of microwaves in the ECRH experiments in toroidal devices is reported. It was discovered in the course of detailed investigation of the low-power-threshold two-plasmon PDI saturation. It is shown that there are two most important mechanisms, the cascade of low-threshold secondary decays and the pump depletion, leading to the transition of primary instability to the saturation regime. The cascade of secondary decays giving rise to the secondary UH and ion Bernstein waves continues until the generated UH wave remains trapped at the local maximum of the density profile. The power threshold of parametric excitation of the non-trapped UH wave appears not to be overcome. Under the experimental conditions when the number of secondary decays is odd this effect dominates over the pump depletion and is responsible for the saturation of primary instability at a lower level [2]. As it is disclosed in the present paper, in the opposite case of the even number of secondary decays the pump depletion turns to be mostly responsible for the saturation of primary instability at much higher level than in the case of the odd number of secondary decays. In this case the efficiency of anomalous absorption jumps up to the level bigger than 60% and strongly modifies the power deposition profile.

[1] S. K. Nielsen, M. Salewski, et al., Plasma Phys. Controlled Fusion 55, 115003 (2013).
[2] E. Z. Gusakov, A. Yu. Popov, Physics of Plasmas 23, 082503 (2016).

Speaker: A. Popov (EPS 2019)

83 P1.1080 DIII-D high field side lower hybrid current drive: experiment overview

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1080.pdf

High field side lower hybrid current drive (HFS LHCD) has potential to provide efficient off-axis current drive consistent with advanced tokamak (AT) scenarios via improved wave accessibility and penetration.[1] Due to the quiescent HFS scrape off layer, HFS LHCD has potentially dramatically reduced plasma material interaction (PMI) issues and improved coupling.[1] DIII-D AT discharges provide an opportunity to validate HFS RF wave physics and LHCD physics models and to demonstrate PMI and coupling challenges are mitigated.
In DIII-D AT discharges, HFS launch below mid-plane allows LH waves to penetrate and single pass damp in region rho~0.6-0.8 with driven current up to 140 kA/MW coupled sufficient for current profile control. In addition, an optimized discharge based on QH-mode has been identified where up to 250 kA/MW coupled is predicted.
To accommodate a HFS coupler in DIII-D, the center post tile thickness is planned to be increased by 2.5 cm while keeping the divertor floor height unmodified. Within this physical envelope, a compact coupler where the expected power density is ~32 MW/m^2 has been designed using a cold plasma model load in COMSOL. The coupler distributes power poloidally utilizing a traveling wave, 4-way splitter and a six way multi-junction to split and set the wave spectrum.[2] For the coupler and in-vessel waveguide, copper cannot be utilized as structural material due to the 380°C machine bake (anneals copper) and disruption loads. The primary material options include copper plated Inconel, copper plated stainless and GRCop-84(Cu-8%Cr-4%Nb)[3]. To facilitate assembly, an RF/vacuum flange has been have designed and tested. The latest simulations, design and system status will be presented.

Work supported by the U.S. DoE, Office of Science, Office of Fusion Energy Sciences, using User Facility DIII-D, DE-FC02-04ER54698, and by Scientific Discovery through Advanced Computing Initiative, DE-FC02-01ER54648.

[1] P.T. Bonoli, et al, "High Field Side Lower Hybrid Wave Launch for Steady State Plasma Sustainment," Nucl. Fusion 58, 126032, (2018)
[2] A. Seltzman et al., "A High Field Side Multijunction Launcher with Aperture Impedance Matching for Lower Hybrid Current Drive in DIII-D Advanced Tokamak Plasmas," Nucl. Fusion (submitted 2018).
[3] D. L. Ellis, "GRCop-84: A High-Temperature Copper Alloy for High-Heat-Flux Applications," Vols. NASA/TM - 2005-213566, 2005.

Speaker: S.J. Wukitch (EPS 2019)

84 P1.1081 Multi-machine analysis of EU experiments using the EUROfusion Integrated Modelling (EU-IM) framework

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1081.pdf

Multi-tokamak analysis and modelling is performed within the EUROfusion Integrated Modelling (EU-IM) framework [1], backbone to the Integrated Modelling and Analysis Suite (IMAS)[2], which offer unique capabilities by providing device agnostic integrated simulation workflows, encompassing interchangeable physics modules spanning from high-fidelity to (fast) simplified models. EU-IM/IMAS workflows are now mature and are being prepared for full exploitation on a wide variety of devices, as JET, MST tokamaks, JT-60SA, ITER, DEMO, WEST. In particular, the impact of MSE or polarimetry measurements constraints on improving equilibrium reconstructions has been investigated on JET, MST and WEST plasmas, via an arbitrary device IMAS workflow. Analysis of JET mixed isotopes scenarios, has been enabled by self-consistent simulation of multi-species plasmas with the European Transport Simulator (ETS) [3], recently enhanced to meet the requirements for DT predictive modelling [4]. ETS offers the capability for separate modelling of hydrogen isotopes, as well as light and heavy impurities in all their charge states; further, a set of advanced heating and current drive modules, can valuably account for proper modelling of fast particle species and mixed isotope heating schemes, as well as for the synergy between ICRH and NBI heating. Validation of ETS multi-species simulations was achieved on JET L-mode H and D plasmas, assessing the impact on effective diffusivities of the quasilinear versus multi-fluid transport models therein (TGLF, QuaLiKiz or EDWM). Novel results on modelling of JET H and 3He minority hybrid discharges heated by waves and beams highlight the key role of the interplay of the various particle populations. Self-consistent modelling of NBI and ICRH synergy in JET D hybrid discharges, shows a resulting enhancement of the DD fusion reaction neutron rate (depending on H minority concentration), in good agreement with the measurements.

References
[1] G.L. Falchetto, et al., Nucl. Fusion, 54, 043018 (2014)
[2] F. Imbeaux, et al. Nucl. Fusion 55, 123006 (2015)
[3] D. Kalupin, et al., Nucl. Fusion 53, 123007 (2013)
[4] P. Strand, et al., 27th IAEA FEC 2018

Speaker: G.L. Falchetto (EPS 2019)

85 P1.1082 The operational space of the first divertor experiments in Wendelstein 7-X

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1082.pdf

One of the main goals of Wendelstein 7-X is to show that stellarators can sustain fusion-relevant plasma conditions in steady-state. It is envisaged to demonstrate plasma operation with a density well above 10^20/m^3, central electron and ion temperatures around 3 keV and a pulse length of half an hour. Finding a suitable target scenario is one of the key issues of the initial experimental campaigns. In this contribution we present the operational space (density and heating power) that has been mapped out already and report on operational limits that have been observed.
At the moment, steady-state heating is only provided by ECRH. The minimum and maximum heating power are determined by the technical capabilities of the heating system. Increasing the power is not a fundamental problem and is planned for future upgrades. However, there are two operational density limits that have been observed so far: One is the occurrence of radiative collapses at a power-dependent critical density and the other is related to the absorbed ECRH power at high densities: The absorption of the microwaves in O2-polarization used for ECR heating above the X2-cutoff at 1.2·10^20 m^-3 depends strongly on the electron temperature and, hence, at fixed power on the density. In contrast to the radiative collapse, the latter does not lead to plasma termination, but prohibits effective heating and poses risks to the machine safety due to stray radiation. At the highest heating powers (up to 7.5 MW), the O2 absorption efficiency drops at densities lower than the radiadtive density limit. Stable plasma operation has been achieved at a line-averaged density of 1.5·10^20 m^-3. At lower heating powers, the critical density for radiative collapses decreases and denies access to such high densities. Close to the critical density, however, stable plasma operation is possible despite a high radiated power fraction. At lower densities, the global confinement benefits slightly (relative to empirical scalings) from the reduced radiation. However, so far detachment, which is considered a prerequisite for high-performance long-pulse operation, has only been observed at high density and heating power. These observations show that stable plasma operation is possible over a large parameter range with the most promising conditions for long-pulse operation at high densities and heating powers. This suggests that planned upgrades to increase the heating power are indeed necessary.

Speaker: G. Fuchert (EPS 2019)

86 P1.1083 Integrated code framework for operation scenario development with the global-optimizer-based iterative solver GOTRESS

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1083.pdf

The steady-state transport equation solver, GOTRESS, has been developed, which directly finds the solution where a transport flux matches an integrated source using global optimization techniques such as a genetic algorithm and Nelder-Mead method [M. Honda, Comput. Phys. Commun. 231 (2018) 94.], given an equilibrium and source profiles in advance. Very recently a novel integrated model with GOTRESS as a kernel of the model, GOTRESS+, has been developed, mainly consisting of the equilibrium and current profile solver ACCOME and the neutral beam (NB) heating code OFMC. A workflow of GOTRESS+ is in the following, as summarized in fig. 1. The prescribed density and temperature profiles are given to ACCOME as a first step. After the iterative calculations in ACCOME, a consistent solution is obtained between an equilibrium and a current profile according to the given kinetic profiles. Then OFMC estimates the NB heating and current drive profiles. GOTRESS in turn predicts the temperature profiles based on the data computed by ACCOME and OFMC. The first iteration of GOTRESS+ is now completed and the second iteration commences at the same time as the predicted temperature profiles are sent to ACCOME. This iteration continues until the profiles are well converged. GOTRESS+ results have been successfully compared to those by the integrated code TOPICS.

Speaker: M. Honda (EPS 2019)

87 P1.1084 Tritium-concentration requirements in the fueling lines for high-Q operation in ITER

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1084.pdf

One of the most fundamental control problems arising in ITER and future burning-plasma tokamaks is the regulation of the plasma temperature and density to produce a determined amount of fusion power while avoiding undesired transients. ITER is designed to achieve a ratio of fusion power to auxiliary power, Q, of 10. The reactor's high plasma density (> 1x10^20m^-3) and low burn fraction ( 1%) will require high deuterium (D) and tritium (T) fueling rates. Gas puffing will have a low fueling efficiency (< 1%) due to poor neutral penetration [1]. Therefore, the initial phase of ITER will rely on two pellet injectors located on its magnetic high-field-side (HFS) for deep core fueling. The D pellet injector (with pellets of 100% D nominal concentration) and the D-T pellet injector (with pellets of 10%D-90%T nominal concentration) are planned to have maximum throughputs of 120 Pa m3/s and 111 Pa m3/s, respectively [2]. However, limitations in the tritium plant subsystems could result in a lower T concentration. Even if the nominal concentration could be initially achieved, it might not be possible to sustain it for the total duration of long pulses. This not only imposes burn-control challenges [3] but also raises serious concerns over having sufficient concentration of T in the fueling lines to sustain long-pulse high-Q operation. In this work, a volume-averaged model of ITER's burning plasma is used to assess the feasibility of accessing Q = 10 operation for different levels of T concentration. Operation points characterized by Q = 10 are sought within ITER's limits for fueling rates and auxiliary heating powers. The results are presented in the form of Plasma Operation CONtour (POPCON) plots that span the density-temperature space. The minimum tritium concentration that can maintain the plasma at Q = 10 is determined for different particle-recycling assumptions. Although this work is concerned with the design parameters of ITER, the analysis can be extended to other future burning-plasma reactors such as DEMO.

References
[1] S. K. Combs, L. R. Baylor and others, "Overview of recent developments in pellet injection for ITER," Fusion Engineering and Design, vol. 87, pp. 634-640, 2012.
[2] J.A. Snipes, D. Beltran and others, "Actuator and diagnostic requirements of the ITER Plasma Control System," Fusion Engineering and Design, vol. 87, no. 12, pp. 1900-1906, 2012.
[3] A. Pajares and E. Schuster, "Robust Burn Control in ITER Under Deuterium-Tritium Concentration Variations in the Fueling Lines," 27th IAEA Fusion Energy Conference, Gandhinagar, India, October 22-27, 2018.

Speaker: E. Schuster (EPS 2019)

88 P1.1085 Intermittent plasma fluctuations in the Alcator C-Mod scrape-off layer in L H and I-modes

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1085.pdf

Fluctuations in the scrape-off layer of Alcator C-Mod have been investigated by gas puff imaging and mirror Langmuir probe measurements, including L, H and I-mode plasmas. In all cases, the time series from the far scrape-off layer region are dominated by large-amplitude bursts attributed to the radially outwards motion of blob-like filament structures [1]. This results in significant skewness and kurtosis moments and thus strong intermittency of the fluctuations. There is a striking similarity between L- and H-mode plasmas, the latter comprising both quiet/ELM-free H-modes and EDA H-modes [2].
The average burst wave form is well described by a two-sided exponential function, and the time scale is the same for all plasmas investigated [1, 2]. It is shown that both burst amplitudes and the waiting times between them are exponentially distributed. Moreover, there is a universal shape of the frequency power spectrum for all radial positions in the scrape-off layer and for all confinement modes. It is demonstrated that both gas puff imaging and Langmuir probe measurements give the same statistical properties for the fluctuations.
These properties of the fluctuations are shown to be in excellent agreement with predictions of a stochastic model based on a super-position of uncorrelated exponential pulses [1, 2]. This suggests that the power spectrum is determined solely by the exponential pulse shape, while the radial variation of intermittency as quantified by the skewness and kurtosis moments depend on the degree of pulse overlap [1, 2]. A new deconvolution method is applied, demonstrating for the first time that the bursts are uncorrelated and appear in accordance with a homogeneous Poisson process.
Finally, a set of I-mode plasmas are analyzed, showing that in some cases the bursts in the far scrape-off layer appear quasi-periodically and that the blob structures may be associated with geodesic acoustic modes in the edge region.

References
[1] A. Theodorsen et al., Nucl. Fusion 57, 114004 (2017); Phys. Plasmas 25, 122309 (2018)
[2] O.E. Garcia et al., Phys. Plasmas 20 055901 (2013); 25, 056103 (2018)

Speaker: R. Kube (EPS 2019)

89 P1.1086 Stability of microtearing modes

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1086.pdf

In H-mode plasmas, the modelling of the pedestal dynamics is an important issue to predict temperature and density profiles in the tokamak edge and therefore in the core. The model EPED [1] , based on the stability of large and small scales MagnetoHydroDynamic (MHD) modes, is most commonly used to characterize the pedestal region. The EPED model has been quite successful until now. However some recent analysis of JET plasmas [2] suggest that another class of instabilities, called microtearing modes, may be responsible for electron heat transport in the pedestal, and thereby play some role in determining the pedestal characteristics. Microtearing modes belong to a class of instabilities where a modification of the magnetic field line topology is induced at the ion Larmor radius scale. This leads to the formation of magnetic islands, which can enhance the electron heat transport. The past analytical work predicted peaked growth rate of MTM at a finite value of collisionality and decreases down to negative value in collisionless regime[3]. However, recent gyrokinetic simulations in toroidal geometry found unstable MTMs [4], even at low collisionality. The purpose of our work is to progressively include missing physical mechanisms (magnetic drift, electric potential, collsions,...) in the analytical model and compare it with the numerical simulations to improve the understanding of MTM destabilization mechanisms.
Numerically, the modelling of MTMs is challenging. The width of the current layer and the sensitivity of magnetic reconnection to dissipation imply having a very high numerical resolution and a very weak numerical dissipation, especially at low collisionality. The improvement of the analytical model is crucial, first to better understand the role played by the different physical parameters, but also because it is free of these problems. As a first step, linear theory of a slab microtearing mode using a kinetic approach has been established and compared with linear gyrokinetic simulations [5]. The linear stability of the collisionless MTMs predicted by the theory is found consistent with numerical simulations using the gyrokinetic code GKW [6]. Starting with this simple model the magnetic drift and the electric potential are included progressively in the analytical calculation. The full expression of the current inside the resistive layer is rather complex. Without the electric potential, the magnetic drift has been found to be destabilising, but only in conjunction with a finite collisionality[7]. Then, with both electric potential and magnetic drift, the evaluation of the current inside the resistive layer is obtained from a system of two equations linking the vector potential( as the consequence the current) and the electric potential. This system of equations have been solved numerically using an eigenvalue code. A good agreement between the analytical calculation and GKW simulations has been found. It appears that the magnetic drift velocity and electric field fluctuations are destabilizing when combined with collisions. However, this destabilization effect disappears at low collisionality and no unstable MTM is found so far in collisionless plasmas. The magnetic drift and electric potential cannot explain the destabilization of MTMs at low collisional frequency observed in recent gyrokinetic simulations [4]. The effect of trapped particle is now under investigation. It is found numerically that depending on the collisionality, trapped particles can increase or decrease the MTM growth rate. The next step of this study is investigate the properties of MTM turbulence and evaluate the corresponding electron heat transport in particular in the JET-ILW pedestal.

References
[1] P.B. Snyder, T.H. Osborne and K.H. Burrel, Phys. Plasmas, 19: 056115 (2012).
[2] D.R. Hatch and M. Kotschenreuther et al., Nucl. Fusion 56: 104003 (2016).
[3] R. D. Hazeltine, D. Dobrott and T.S. Wang, Phys. Fluids 18: 1778 (1975).
[4] D. Dickinson et al, Phys. Rev. Let., 108, 135002 (2012).
[5] M. Hamed, M. Muraglia, Y. Camenen and X. Garbet, Contrib. Plas. Phys., 58: 529-533 (2018).
[6] A.G. Peeters et al., Comput. Phys. Commun. 180, 2650 (2009).
[7] M. Hamed, M. Muraglia, Y. Camenen and X. Garbet, J. Phys. Conf. Ser. 1125: 012012.

Speaker: M. Hamed (EPS 2019)

90 P1.1087 Dynamics of cold pulses induced by super-sonic molecular beam injection in the EAST tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1087.pdf

One of the most provocative phenomenons in plasma transport is the so called non-local heat transport: the core temperature increases in response to edge cooling. This was observed for the first time in the TEXT experiment in 1995, and was reproduced in many tokamaks (TFTR, Tore Supra, RTP, ASDEX-U, JET, HL-2A, Alcator C-Mod, KSTAR, J-TEXT) and helical devices (LHD).
In EAST non-local heat transport has been observed recently during plasma edge cooling induced by super-sonic molecular beam injection (SMBI) [1]. The non-local heat transport occurs for discharges with plasma current Ip = 450 kA (q95~5.55), and electron density ne0 below a critical value of (1.35 ± 0.25) x 10^19 m^-3. In contrary to the response of core electron temperature and electron density (roughly 10 ms after SMBI), the electron density fluctuation in the plasma core increases promptly after SMBI and reaches its maximum around 15 ms after SMBI. The electron density fluctuation in the plasma core begins to decrease before the core electron temperature reaches its maximum (roughly 30 ms). It was also observed that the turbulence perpendicular
velocity close to the inversion point of the temperature perturbation changes sign after SMBI.

[1] Y. Liu et al., Nucl. Fusion (2019) accepted

This work was supported by the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology, and the National Natural Science Foundation of China under Grant Nos. 11405211, 11575248. This work was also partly supported by National Magnetic Confinement Fusion Science Program of China under Contract Nos. 2015GB101003 and 2015GB103002, Basic Science Research Program through the National Research Foundation (NRF) funded by the Ministry of Science and ICT of Republic of Korea (No. 2018R1A2B2008692).

Speaker: Y. Liu (EPS 2019)

91 P1.1088 Edge stochastization and collisionality dependence of the L-H transition power threshold with applied n=3 resonant magnetic perturbations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1088.pdf

It is shown that stochastic edge magnetic field topology with applied resonant magnetic perturbations can explain the increased L-H power threshold with applied n=2 resonant magnetic perturbations (RMP) in low rotation, ITER-similar-shape plasmas in DIII-D (<ne>=1.5-5x10^19m^-3, Bt=1.9-2T, Ip=1.5 MA, q95~3.6). With RMP, the normalized L-H transition power threshold scales inversely with edge collisionality as PLH/PLH-08 ~ e*(=0.95)-0.5, where PLH-08 is the 2008 ITPA power threshold scaling (Martin scaling) [1]. The pertinent signatures of stochastic electron transport are a diminished L-mode Er well and E◊B shear, and increased edge toroidal rotation.
Spontaneous reversal (bifurcation) to a positive edge electric field can occur at high RMP strength. TRIP3D fieldline tracing calculations show a stochastic field line loss fraction of ~50% for > 0.97. A simple fluid theory [2], balancing stochastic radial electron flow and neoclassical ion flow, explains quantitatively the observed Er modifications, including the sign reversal at high RMP field, and the increased edge toroidal rotation (figure 1). This theory also predicts a more pronounced reduction of the Er well at low collisionality, consistent with experimental results. With RMP, increased turbulence levels are observed by BES, including modes propagating in electron diamagnetic drift direction (0.92<=rho<=0.97) and lower wavenumber ion-direction modes.
Matching the power balance ion thermal flux with TGLF/TGYRO requires 50-80% increase in a/LTi compared to a/LTi Carbon measured via impurity (Carbon) CER for > 0.85, but consistent within error margins with the main ion a/LTi from main ion CER [3]. Power balance electron thermal fluxes in the plasma edge are substantially under-predicted by TGLF within error limits for the measured a/LTe. These observations suggest that the increase in PLH with applied RMP results from increased L-mode electron and ion thermal power loss across the separatrix with simultaneously reduced E◊B shear due to stochastic radial electron flow and increased toroidal edge rotation.

This work was supported by the US Department of Energy under DE-FG02-08ER54984, DE-FG02-08ER 54999, DE-AC05-00OR22725, and DE-FC02-04ER54698.

[1] Martin Y.R., Takizuka T. et al. 2008 J. Physics: Conf. Series 123 012033.
[2] Kaganovich I. and Rozhansky V. 1998 Phys. Plasmas 5 3901.
[3] Haskey S, Grierson B., Chrystal C. et al. 2018 Plasma Phys Control. Fusion 60 105001.

Speaker: L. Schmitz (EPS 2019)

92 P1.1089 Near-realtime tokamak scenario simulation with neural networks

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1089.pdf

Accurate prediction of turbulent transport is essential for interpretation of current-day fusion experiments, designing future devices, and optimization of plasma scenarios. Turbulent transport in the core of the plasma is well-described by quasilinear theory, which can be leveraged to create reduced models. These are then applied within flux driven integrated modelling to predict time evolution of temperature, density, and rotation profiles in fusion devices. Recent developments in the QuaLiKiz gyrokinetic quasilinear transport model [1, 2] within the JINTRAC integrated modelling suite [3] has provided validated prediction of JET and AUG scenarios, with 1s of plasma evolution predicted in 24 hours using 10 cores [4, 5].
We provide further significant speedup of first-principle-based turbulent transport modelling sufficient for large scale reactor optimization and control oriented applications. We apply feedforward neural networks (FFNNs) for regression of a pre-generated QuaLiKiz database consisting of 108 flux calculations. The resultant neural network surrogate model is 5 orders of magnitude faster than QuaLiKiz itself. Generic neural network training is not sufficient to correctly capture known physical features of tokamak turbulence, such as sharp instability thresholds common to all transport channels. We show how we can incorporate these features directly in the training process.
The surrogate turbulent transport model is applied within the rapid plasma transport simulator RAPTOR [6, 7] and JINTRAC. We show that the predictions of temperature and density evolution of JET plasmas are in excellent agreement with the original QuaLiKiz model, yet orders of magnitude faster. This allows us to simulate one second of plasma evolution in less than 10 seconds, a speed that is unprecedented for first-principle based transport simulations, opening up new avenues for tokamak scenario optimization and realtime control applications.

References
[1] Bourdelle, C. et al. 2016 Plasma Physics and Controlled Fusion 58 014036
[2] Citrin, J. et al. 2017 Plasma Physics and Controlled Fusion 59 12400
[3] Romanelli, M. et al. 2014 Plasma and Fusion research 9 3403023
[4] Ho, A. et al. 2019 Nuclear Fusion
[5] Linder, O. et al. 2018 Nuclear Fusion 59 016003
[6] Felici, F. et al. 2012 Plasma Physics and Controlled Fusion 54 025002
[7] Felici, F. et al. 2018 Nuclear Fusion 58 096006

Speaker: K.L. van de Plassche (EPS 2019)

93 P1.1090 Enhancement of Nonlinear Regulation Dynamics in SMBI-stimulated L-H transition of HL-2A

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1090.pdf

For future fusion devices, like ITER, controllable L-H transition and reducing the power threshold are highly desirable when the available heating power is marginal for accessing the H-mode. Theoretic models have predicted that the L-H transition can be triggered by particle injection below the threshold (P < Pth) [1]. In the HL-2A tokamak, the L-H transition can be triggered by supersonic molecular beam injection (SMBI), a plasma fueling tool, which was first proposed in the HL-1 tokamak, then applied on several tokamaks and stellarator [2]. Figure 1 shows the dynamics of turbulence, geodesic acoustic mode (GAM) and limit cycle oscillations (LCOs) in the SMBI-triggered transition. It has been found that nonlinear interactions are enhanced by SMBI.
These enhanced processes quench the turbulence and maintain the turbulence collapse. Finally, the turbulent transport is reduced and the L-H transition is triggered. Statistic result indicates that SMBI can reduce the H-mode threshold. It suggests that SMBI can be an external method for realization of a controllable L-H transition.

References
[1] K. Miki et al., Phys. Rev. Lett. 110, 195002 (2013). [2] L.H. Yao et al., Nucl. Fusion 47, 1399 (2007)

Speaker: W. Zhong (EPS 2019)

94 P1.1091 Effect of relativistically intense laser pulses on magnetically confined fusion plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1091.pdf

Existing methods for diagnostics and control are still insufficient to deal with the various kinds of instabilities and collective dynamics that occur in magnetically confined fusion plasmas, which may impact the missions of the ITER and DEMO projects. Using small-scale laser experiments on the J-KAREN-P laser at KPSI, numerical simulations on the JFRS-1 supercomputer at IFERC-CSC, and theoretical analyses, we are investigating whether short pulses (ps-fs) of a high power laser (TW-PW) may be used to address some of these issues. The object of interest is the electron-free positively charged plasma wake channel that is carved out by a laser pulse with relativistic intensity (normalized amplitude a0 1) [1]. Using the relativistic PIC codes EPOCH [2] and REMP [3], we simulate the long-time evolution of such wake channels in the presence of a strong magnetic field ( 2 T) as is typical for present-day tokamaks.
We demonstrate that there exists a parameter window where the after-glow dynamics of the magnetized wake channels are effectively independent of the laser wavelength under tokamak conditions; namely, for highly subcritical electron density n_e/n_crit w_pe^2/W_laser^2<<1. This justifies scaled simulations with artificially increased wavelengths, which reduces the computational expenses (memory and time) to the point where long-time 3D simulations become feasible.
We compare the results of recently performed 2D and 3D simulations and examine the effects of the plasma density and magnetic field strength via parameter scans. In particular, we will report our observations regarding particle acceleration, charge separation and the generation of magnetic vortices. First insights concerning the role of thermal motion will be discussed along with possible implications for tokamak plasma control and diagnostics [4].

This research is supported by QST Director Fund for Creative Scientific Research (No. 16).

References
[1] G.A. Mourou, T. Tajima and S.V. Bulanov, Rev. Mod. Phys. 78 309 (2006)
[2] T.D. Arber et al., Plasma Phys. Control. Fusion 57 113001 (2015)
[3] T.Zh. Esirkepov, Comp. Phys. Comm. 135 144 (2001)
[4] A. Bierwage et al, 2nd QST Intl. Symp.: "Frontier of Quantum Beam Science with High Power Lasers", Nara, Japan, Nov. 2018, invited.

Speaker: A. Bierwage (EPS 2019)

95 P1.1092 Full exploitation of the HYMAGYC code for a shaped cross section scenario

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1092.pdf

HYMAGYC [1] is a HYbrid MAgnetohydrodynamycs GYrokinetic Code suitable to study the interaction between energetic particles (EPs) and Alfvénic modes. Thermal plasma is described as a single fluid by fully resistive linear MHD equations, while EPs are described by nonlinear gyrokinetic Vlasov equations [2]. In this work all the code capabilities have been fully exploited: a realistic shaped cross section AUG model scenario [3], finite magnetic compression, Finite Larmor Radius (FLR) effects. The proposed model scenario has been analyzed by CHEASE in order to compute the equilibrium quantities required by HYMAGYC. Running first the MHD linear stability eigenvalue code MARS, the shear Alfvén continua have been identified for low toroidal mode numbers (n=1,2,3). Then, a Maxwellian energetic particle population of deuterium is introduced and unstable modes appear. Frequencies and growth rates are reported for different simulation parameters. Finally the FLR and magnetic compression effects are retained and analyzed, showing a slight stabilazing effect on unstable modes. Note that CHEASE and MARS are already fully compliant with IMAS/EU-IM frameworks, while HYMAGYC is currently updating to the most up-to-date framework versions.

References
[1] G. Fogaccia, G. Vlad, S. Briguglio, Nucl. Fusion 56 (2016) 112004
[2] Brizard A.J. and Hahm T.S. 2007 Rev. Mod. Phys. 79 421-68
[3] (Ph.Lauber et al., NLED-AUG reference case, http://www2.ipp.mpg.de/~pwl/NLED_AUG/data.html)

Acknowledgments. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Part of the computing resources and the related technical support used for this work has been provided in part by the CRESCO/ENEAGRID High Performance Computing infrastructure and its staff.

Speaker: G. Fogaccia (EPS 2019)

96 P1.1093 Impact of shape and plasma physics constraints on performance of a tokamak fusion system

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1093.pdf

An optimal radial build and system parameters of a tokamak reactor were found by utilizing a new simulation method which couples a conventional tokamak plasma analysis and a radiation transport analysis. Neutron impacts on shielding and tritium breeding capability were self-consistently incorporated, together with plasma physics and tokamak engineering constraints, which were moderately extrapolated from the ITER model. In a low-aspect ratio tokamak reactor, the minimum major radius to produce a desired fusion power was mainly determined by the shielding requirements, while in a normal aspect ratio tokamak reactor, it was determined not only by the requirements on the shielding, but also by the requirements on the tritium breeding and the magnetic flux density at the toroidal field (TF) coil. As the aspect ratio increased, the minimum major radius and the system size decreased as long as the tritium self-sufficiency was satisfied with only an outboard blanket, but they began to increase as the inboard blanket thickness increased to meet the requirements for tritium self-sufficiency and the TF coil bore radius increased to meet the requirements for the magnetic flux density at the TF coil. The fusion energy gain Q increased as the fusion power increased and as the confinement characteristics improved. For the aspect ratio A = 1.5, Q > 20 was possible for fusion power levels > 1,500 MW with the confinement enhancement factor H = 1.4. For A = 2.0, Q > 20 was not possible with fusion power < 2,000 MW. When A = 3.0, Q > 20 was possible for fusion power > 1,900 MW with H = 1.3, and fusion power > 1,500 MW with H = 1.4. When A = 4.0, it was not possible to have Q > 20.

Speaker: B. Hong (EPS 2019)

97 P1.1094 The Role of Resonant Magnetic Field Penetration in Edge Localized Mode Suppression in the DIII-D Tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1094.pdf

Measurements and modeling of DIII-D low collisionality (v*e~0.1-0.3) plasmas reveal pedestal-top locked modes as the probable trigger for Edge-Localized-Mode (ELM) suppression by n=2 and n=3 Resonant Magnetic Perturbations (RMPs) in a range of plasma conditions including neutral beam torque 3 - 6 Nm, plasma average triangularity delta=0.6-0.3 and edge safety factor q95=3.1-4.1. At the onset of ELM suppression in all these conditions, a rapid (< 1 ms) increase is observed in the high-field-side magnetic response concomitant with an increase in the co-Ip ExB rotation at the top of the pedestal. The nonlinear two-fluid MHD code TM1 [1] is used to simulate the onset of edge locked modes driven by RMPs for experimentally relevant profiles and transport parameters. The simulations reproduce the observed magnitude and time scale for changes in the pedestal ExB rotation and magnetic response of the plasma, strongly supporting the conjecture that ELM suppression is triggered by edge locked mode onset. Further evidence for magnetic island generation at the onset of ELM suppression comes from experiments designed to the hover near the threshold of ELM suppression. Near threshold conditions we observe cyclic magnetic pulsations with a slow toroidal rotation of the plasma magnetic response to the RMP [2], consistent with recent theoretical predictions of the limit cycle behavior of partially penetrated resonant fields [3]. The ELMs are suppressed cyclically in phase with the magnetic pulsations, consistent with the role of finite size magnetic islands in ELM suppression.

This work was supported in part by the US Department of Energy under DE-AC02-09CH11466, DE-FC02-04ER54698, DEAC05-06OR23100 and DE-FG02-04ER54761. DIII-D data shown in this paper can be obtained in digital format by following the links at https://fusion.gat.com/global/D3D_DMP. Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

[1] Hu, Q. et al. Nucl. Fusion 59, 016005 (2019),
[2] R. Nazikian et al Nucl. Fusion 58 106010 (2018)
[3] R. Fitzpatrick, Physics of Plasmas 25, 112505 (2018)

Speaker: R. Nazikian (EPS 2019)

98 P1.1095 Studies of Alfvén eigenmodes on JET with both experimental measurements with the AEAD and modelling with GTC

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1095.pdf

The resonant detection and measurement of the damping rates of Alfvén Eigenmodes (AEs) is of critical importance to the design of experiments and development of models of AE stability [1]. With the Alfvén Eigenmodes Active Diagnostic (AEAD) on JET, weakly-damped Toroidal AEs (TAEs) have been probed. Theoretical modeling using the Gyrokinetic Toroidal Code (GTC) has been made to simulate both stable and unstable TAEs, a good agreement was obtained between experiments and modeling [1]. With GTC we also identified and quantified modes' individual drive and damping mechanisms.
The AEAD has undergone a major upgrade with new amplifiers, filters and digital control system [2], which allow us to perform new study and damping rate measurements of low frequency modes such as GAMs, BAEs/BAAEs and RSAEs. These modes along with TAEs are expected to be probed during next JET isotope experiments and the DT campaign. Those new experimental results will be compared with modeling using state of the art MHD and gyrokinetic (GTC) codes. JET counts now more than twenty newly installed magnetic probes which will give more accuracy to the AEAD real-time detection system and our analyses. These will improve further predictions for next-step burning plasma, including ITER.

[1] V. Aslanyan et al., Nucl. Fusion 59, 026008 (2019).
[2] P. Puglia et al., Nucl. Fusion 56, 112020 (2016).
Support for MIT was provided by the US DOE / DE-FG02-99ER54563, and for the Swiss group in part by the Swiss NSF.

*See the author list of "Overview of the JET preparation for Deuterium-Tritium Operation" by E. Joffrin et al., to be published in Nuclear Fusion Special issue for the 27th Fusion Energy Conference.

Speaker: M. Porkolab (EPS 2019)

99 P1.1096 Sideways forces on the wall during early disruption phase in tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1096.pdf

The sideways forces acting on the conducting wall due to the n=1 kink instability are investigated. During the early phase of the disruption the plasma is considered to be isolated from the wall and halo currents do not appear. The plasma with minor radius of 1 m and almost circular shape with a large current (> 5 MA) and the safety factor of q ~ 1 close enough to the top of the ITER vacuum chamber is considered, so that the ideal n=1 kink mode is wall stabilized [1], but instead the resistive wall mode (RWM) develops. RWM growth rates, plasma displacement structure and the n=1 surface currents induced in the wall are calculated with the KINX stability code [2]. Sideways forces acting on the wall are determined as the Ampere force from the perturbed surface currents and the equilibrium magnetic field.
In [1] sideways forces produced by the equilibrium toroidal field and RWM induced currents in the wall were found to reach maximum in the ideal wall limit gamma tao w tends to infinity. The seeming disagreement with zero sideways force in the ideal wall limit for the considered inertia-less plasma model [3] is resolved by taking into account the force on the conductors inside the wall (the only possibility to make the equilibrium poloidal field at the wall vanish) balancing the force on the wall instead of the balance from the equilibrium poloidal field in case with external currents outside the wall.
The magnitudes of the sideways force for ITER early disruption plasmas are computed for several cases of free-boundary equilibria obtained with the SPIDER code [4] under plasma current variation. For inertia-less plasma the total force on the wall reaches its maximum for low values of RWM growth rate gamma tao w : 1 and vanishes in the ideal wall limit in accordance with [3]. This asymptotic behavior is attained for any inertia-less RWM perturbation once the consistent equilibrium field is used. The right balance of the toroidal and poloidal equilibrium field induced forces leads to lower magnitudes of sideways forces as compared to [1]. For m=1 dominated RWM characteristic for q<1 the sideways force is close to the estimates [3], but several times lower for the ITER-like cases with q>1 and toroidally coupled m=1 mode generating the force. All the considered models strongly suggest that possibilities of larger sideways force should be connected with plasma-wall interaction at the next stages of disruptions or with realistic 3D wall models.

[1] S.Yu. Medvedev et al. 45th EPS Conference on Plasma Physics, 2018, ECA Vol. 42A, P4.1060.
[2] L. Degtyarev et al. Computer Phys. Commun. 103 (1997) 10-27.
[3] D.V. Mironov, V.D. Pustovitov. Physics of Plasmas 24 (2017) 092508.
[4] A.A. Ivanov et al. 32nd EPS Conference on Plasma Physics 2005, ECA Vol. 29C, P-5.063

Speaker: A. A. Martynov (EPS 2019)

100 P1.1097 High density hydrogen plasma for negative hydrogen ion production in HELicon Experiment for Negative ion source (HELEN-I)

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1097.pdf

Large-scale fusion reactors like ITER are going to require very high-energy neutral beams (>1MeV) for plasma heating purposes as well as diagnostic neutral beams. To realize this, negative ion sources are a better alternative to the conventional positive ion sources because of their higher efficiency of neutralization. The helicon plasma sources are yet another advancement on the conventional inductively coupled plasma sources to produce high-density plasma for the production of negative hydrogen ions (H-). HELicon Experiment for Negative ion source (HELEN-I) is developed with a focus on the volume production of negative hydrogen ions. In the Helicon wave heated plasmas very high plasma densities can be attained in the source region. The plasma expands in a diverging field into the expansion chamber where the electron temperature is low and the plasma conditions are conducive to the high production rate and low destruction rate of negative hydrogen ions without the use of a low function material like Caesium in the chamber. The low electron temperature is achieved in the expansion chamber with the magnetic and geometric expansion of the plasma without the use of filter fields. The present helicon source using permanent magnets is a cost effective and incredibly convenient alternative in terms of handling and maintenance as compared to the conventional caesium based negative hydrogen ion sources. In HELEN device at IPR, a Hydrogen gas helicon plasma is produced in a diverging magnetic field inside the source volume by applying RF Power of 13.56 MHz at 800-1000W using a Nagoya-III antenna for exciting m = ±1 azimuthal mode in the plasma. The plasma diffuses into the expansion volume where it is confined by a multiline cusp field. The characteristic density jump from inductively coupled mode to Helicon mode is observed at Prf ~ 800W with plasma density ~ 10^18 m^-3 and electron temperature ~ 1-2 eV. The negative hydrogen ion density is measured in the expansion volume by Spectroscopy and Cavity Ring Down Spectroscopic technique and lies in the order of 10^16 m^-3.

Speaker: A. Pandey (EPS 2019)

101 P1.1098 Prospects for fuel ion ratio measurements in DT plasmas with compact neutron spectrometers

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1098.pdf

In a DT plasma the T/D fuel ion ratio represents an important parameter which is difficult to measure. In principle, it is possible to infer the T/D ratio from a direct simultaneous measurement of the neutron spectra of 2.5 MeV neutrons from D+D->He3+n and 14 MeV neutrons from the D+T->He4+n reactions, respectively. However, the main challenges in this measurement arise from the background contribution in the 2.5 MeV neutron energy range produced by backscattered 14 MeV neutrons and from the experimental difficulties in measuring 2.5 MeV neutron spectra in a high 14 MeV neutron field. For ITER the method proposed is instead based on high-resolution spectroscopy of the 14 MeV neutrons whereby the D/T ratio is inferred from an accurate separation of suprathermal beam component from thermal emission. This requires a dedicated suite of high-resolution neutron spectrometers to cover the T/D range from 0.001 up to 0.9. CVD diamond is a high-resolution neutron spectrometer capable of measuring 14 MeV neutrons by exploiting the peak due to the 12C(n,)9Be reaction, and 2.5 MeV neutrons via elastic scattering with carbon atoms. Further, the recently developed CLYC inorganic scintillator detector is a capable of a direct spectroscopic measurement of 2.5 MeV neutron on the basis of 35Cl(n,p)35S nuclear reactions, while on the other hand 14 MeV neutron spectroscopy is prevented by the opening of other inelastic reactions. The synthetic data presented in this work shows the methodology identified to determine the T/D ratio from measurements obtained with a system combining CVD diamond and CLYC spectrometers, either by measuring 2.5 and 14 MeV neutron spectra (T/D ratio <0.1), or by high-resolution 14 MeV neutron spectroscopy (T/D>0.1). The work consists in Monte Carlo simulations of the neutron emission spectra for different DT plasma scenarios in order to predict the measured spectra along a specific line of sight. From the analysis of the synthetic data it is possible to evaluate the capability to infer back the T/D ratio.

Speaker: M. Rebai (EPS 2019)

102 P1.1099 Evaluation of tritium burn-up fraction for CFETR advanced scenario with the integrated simulations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1099.pdf

The next-step fusion facility China Fusion Engineering Test Reactor (CFETR) has been proposed to bridge the gaps between ITER and DEMO [1]. One of the most important missions for CFETR operation is tritium self-sufficiency, which is mainly determined by tritium burn-up fraction (fb) and the design of blanket and tritium reprocessing systems. Therefore, precise evaluation of tritium burn-up fraction is essential to physics and engineering design of CFETR.
The self-consistent core-SOL coupling COREDIV code [2] has been used to evaluate tritium burn-up fraction of CFETR advanced scenario with 1 GW fusion power. Simulations are firstly performed without consideration of impurities other than the fusion products, helium (He) impurity. The simulations indicated that higher He recycling will reduce tritium burn-up fraction due to the core plasma dilution by He impurity. But the influence is such slight that with increasing He concentration in the core from 0.9% to 4.5%, the corresponding fb is only reduced by about 13%. Higher fuel recycling can strongly increase tritium burn-up fraction due to the reduction of fuelling source. However, in order to obtain the minimal requirement of tritium burn-up fraction fb=3% for CFETR, fuel recycling needs to be higher than 0.996. Simulations also illustrate that tritium burn-up fraction can be effectively increased by reducing the ratio between particle and heat transport in the core ξ=Di/χe. The previous results are performed with ξ=0.35. For a lower ξ= 0.1, f_b can be higher than 3% when fuel recycling is higher than 0.96.
The existence of impurities in plasma is unavoidable during CFETR operations. The influence of both intrisic (W) and extrisic (Ne, Ar, Kr) impurities on tritium burn-up fration has been studied. As the first step, all of the considered impurities are assumed to be puffed from the wall. The preliminary results indicate that Ne mainly reduce tritium burn-up fracion due to plsama dilution. On the contrary, higher Kr and W source can increased tritium burn-up fracion by about a factor of 2, due to the reduction of transport with a fixed plasma confinement. In the case of Ar, there is almonst no change on the tritium burn-up fracion. More complicated situations such as different impurity seeding in a full W wall environment will also be presented. The results can provide important suggestions and implications for the optimization of tritium burn-up fracion for CFETR scenarios.

[1] V.S. Chan, A.E. Costley, B.N. Wan, et al., Nuclear Fusion 55(2015) 023017
[2] R. Zagorski, I. Ivanova-Stanik and R. Stankiewicz, Nuclear Fusion 53 (2013) 073030.

Speaker: R. Ding (EPS 2019)

103 P1.1100 Current profile tailoring with the upgraded ECRH system at ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1100.pdf

Adjustable current and q-profile shapes are of particular interest for the development of advanced scenarios, e.g., non-inductive tokamak operation, and for testing and refining of transport models for predictive capabilities. The current profile is tailored at ASDEX Upgrade using improved heating and current-drive actuators with an upgraded ECRH system with 8 MW for 10 s. The adjustable localised current drive capability of this flexible ECRH environment allows dedicated variations of the shape of the q-profile.
To resolve the highly-shaped current distribution an integration of all available measurement and modelling information is necessary. The equilibrium reconstruction is based on the coupling of a Grad-Shafranov (GS) solver with the current diffusion (CD) equation employing a physical coupling of neighbouring time points [1]. This coupling improves the estimated equilibrium current profile if neo-classical current diffusion can be assumed. Further ingredients are given by reliable electron and ion temperature and density profiles from an integrated data analysis approach, fast-ion pressure and driven current profiles from the RABBIT code, the electroncyclotron driven current from the TORBEAM code, bootstrap-current evaluation, all magnetic data of an extended set of poloidal-field and diamagnetic-loop measurements, internal current measurements from imaging MSE and polarimetry, and a sawtooth detection algorithm [2].
A recently developed fast reconstruction of the current distribution between plasma discharges allows for an educated and efficient scenario development. The equilibrium code IDE is parallelized using an OpenMP scheme within the Grad-Shafranov solver, within the RABBIT code of up to 8 NI-beams and within the TORBEAM code. On top of this, an MPI (Message Passing Interface)-based approach is applied for parallel calculations of the GS-solver response matrix and for parallel TORBEAM evaluations of up to 8 EC-beams for the CD-integration.
Various settings of localised counter- and co-, on-axis and off-axis current drive and heating allow for large flexibility in the q-profiles. Recent current and q-profiles obtained with the upgraded ECRH system will be presented.

[1] R. Fischer et al., Fusion Sci. Technol., 69:526-536, 2016
[2] R. Fischer et al., Nucl. Fusion, 2019, accepted

Speaker: R. Fischer (EPS 2019)

104 P1.1101 Pellet cloud expansion in hot plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1101.pdf

It has recently been demonstrated that the injection of cryogenic pellets into a magnetically confined plasma is accompanied by a considerable transfer of thermal energy from the electrons of the background plasma to the ions [1]. This is the result of the ambipolar expansion along the magnetic field line of the cold and dense plasma cloud left behind by the ablated pellet. During this expansion, the cloud is constantly heated by the hot background plasma. Ref. [1] suggested a self-similar solution for the system of hydrodynamic equations (continuity equation, momentum equation and power-balance equation), which describes such one-dimensional (along x) heated plasma expansion:

n(x,t) = n0 sqrt(3 mi / 8 pi tau t^3) exp(-3m_ix^2 / 8 tau t^3),
u(x,t) = 3x/2t
T(t) = t,

where n is the plasma cloud density (assumed to be much greater than the background plasma density), u denotes the ion velocity, m_i the mass of the ions, and tau =1/3n_0 integral Qdx
the heating power (assumed to be uniform and constant in time). A notable feature of this solution is that the cloud electron temperature is half of what it would have been if the pellet cloud were stationary.
Therefore, half the heating power goes into the ion kinetic energy associated with the expansion of the cloud, significantly affecting the energy balance of the pellet-fuelled plasma.
In the present work, we compare predictions of this simplified analytical model with more complete numerical simulations in which the finite temperature for the cloud ions, cloud viscosity and heat conductivity are retained and the collisional transfer of momentum and energy from the background plasma are calculated kinetically. The applicability conditions for the analytical result are discussed. In addition, the effects of radiative energy losses from the pellet cloud are also investigated.

References
[1] Pavel Aleynikov, Boris N. Breizman, Per Helander and Yuriy Turkin, J. Plasma Phys. 85 (2019)

Speaker: P. Aleynikov (EPS 2019)

105 P1.1102 Simulation of ablation of Ne pellets and SPI in tokamaks

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1102.pdf

Detailed numerical studies of single neon pellets and multiple pellet fragments have been performed in support of the shattered pellet injection (SPI) concept for the plasma disruption mitigation system [1].
Two codes have been developed to study details of the evolution and properties of ablation clouds in the tokamak plasma based on the physics models and algorithms developed in [2] for deuterium pellets. Simulations of the single pellet ablation in spherically symmetric (SS) and axisymmetric 2D approximations have been performed using the hybrid Eulerian-Lagragian code FronTier [3] and 3D simulations of single pellets and multiple pellet fragments have been performed based on the Lagrangian particle (LP) code [4]. These are in excellent agreement in the SS approximation with the semi-analyticial model of Parks [5]. The LP code optimally resolves large changes in the cloud density and avoids numerical difficulties associated with the background plasma. Both codes while different in their numerical approaches, include the same set of physics models: pellet surface ablation, kinetic models for the energy deposition of hot plasma electrons into the ablation cloud, ionization in the cloud, radiation, and the low magnetic Reynolds number approximation for the ionized cloud channeling along the magnetic field lines. Effective ablation channel lengths were estimated based on the B-drift model [6].
Using FronTier and the LP code, we computed single pellet ablation rates for a range of plasma densities, temperatures, magnetic field strengths, and pellet radii. In addition, the Lagrangian particle code was used to compute ablation rates of several pellet fragments by resolving partial screening and cooling of the hot electrons penetrating the cluster cloud formed by the ablated sacrificial front. The present work focuses on the multiscale coupling of the Lagrangian particle SPI code to global tokamak MHD codes such as M3D-C1 and NIMROD.

References
[1] D. Shiraki et al., Physics of Plasmas 23, 6 (2016)
[2] R. Samulyak, T. Lu, P.B. Parks, Nuclear Fusion 47, 2 (2007)
[3] J. Glimm, J. Grove, Y. Zhang, SIAM Journal on Scientific Computing 24, 1 (2002)
[4] R. Samulyak, X. Wang, H.C Chen, Journal of Computational Physics 362, (2018)
[5] P.B Parks, submitted to Physics of Plasma
[6] P.B. Parks, L.R. Baylor, PRL 94, 125002 (2005)

Speaker: N. Bosviel (EPS 2019)

106 P1.1103 Channeling of neutral beam injection power into radio frequency waves

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1103.pdf

The concept of alpha power channeling has been proposed by N. Fisch and collaborators as an efficient tool to improve the performance of fusion reactors, delivering the fusion alpha power into radio frequency waves, which are absorbed by ion species [1]. Alpha channeling by Doppler-shifted inverse nonlinear Landau damping at half-integer cyclotron resonance has been recently discussed [2], suggesting that Deuterium neutral beam (NB) injection power can be also channeled into ion Bernstein wave (IBW) power. NB channeling into IBW has been indeed recently observed [3]. We discuss here a possible effect of channeling into radiofrequency waves of Deuterium NB power injected in D-T tokamak plasma of ITER with 7Li or 9Be minority. We consider fast magnetosonic waves (FW) launched from the low field side at operating frequency suitable to locate the fundamental cyclotron resonant layer of minority species near the magnetic axis. Depending on the concentrations of the ion species and the launched spectra vs. the parallel refractive index, the three-ion heating scheme by FW proposed by E. Kazakov [4], or the IBW ion heating in mode conversion regime [5] occur, both providing efficient ion heating. Inverse Landau damping at the Doppler shifted fundamental ion cyclotron resonance of Deuterium ions might then provide NB power channeling into radiofrequency waves, due to the inversion of the D+ population in the velocity space perpendicular to the static magnetic field. Numerical and analytical solutions of the relevant Fokker-Planck equation, here discussed, indicate that such inversion can occur in steady state conditions if the space diffusion rate of the deuterons produced by the NB ionization is sufficient large compared with the slowing down rate. Similar condition for channeling has been suggested in previous theoretical [2] and experimental works [3].

[1] N.J. Fisch, The alpha channeling effect, AIP Conf. Proc. 2015, 020001 (2015)
[2] C. Castaldo, A. Cardinali, Alpha channeling by inverse nonlinear damping of ion Bernstein waves, EPS (2018), http://ocs.ciemat.es/EPS2018PAP/pdf/P1.1066.pdf, submitted to Plasma Physics and Controlled Fusion
[3] R.M. Magee, et al., Nature Physics (2019) 1-6
[4] E. Kazakov, et al., Nature Physics 13 (2017) 973
[5] C. Castaldo, A. Cardinali, Phys. Plasmas 17 (2010) 072513

Speaker: C. Castaldo (EPS 2019)

107 P1.1104 First-principles simulation of plasma fuelling in a tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1104.pdf

We study tokamak fuelling by using a first-principles approach, based on turbulent numerical simulations of the plasma periphery. These simulations are carried out by using the GBS code [1, 2]. GBS is a 3D flux-driven turbulence code that advances the drift-reduced two-fluid Braginskii equations, while solving a kinetic equation that describes the neutral dynamics. Neutral and plasma models are coupled via ionization, charge exchange and recombination processes. GBS simulates both the SOL and the edge, the most external region with closed magnetic flux surfaces. For a proper description of the plasma fuelling, a mass-conserving model was recently implemented. This required: a) to take into account the toroidal geometry consistently by including the radial variation of the tokamak aspect ratio; b) to include contributions of gradients parallel to the magnetic field previously neglected in comparison to the perpendicular gradients; c) to implement proper boundary conditions ensuring mass conservation for the plasma recycling occurring at the walls.
Since the plasma continuity equation is exactly satisfied and the simulations conserve the total number of ions and neutrals both globally and locally, GBS now provides a tool for a quantitative assessment of the mechanisms behind tokamak plasma fuelling. Based on our simulation results, we developed a 1D radial model that describes the balance between plasma and neutrals. The first results show that, while the plasma radial flux in the SOL is dominated by an ExB outward-pointing turbulent flow, the radial flux in the edge is determined by the competition between equilibrium ExB and diamagnetic flows. Understanding the physics behind these radial fluxes in the context of the neutral-plasma interplay is a first step to study the fuelling and improve our understanding of the mechanisms determining plasma transport in the edge and SOL.

References
[1] F. D. Halpern, P. Ricci, S. Jolliet, J. Loizu J. Morales, A. Mosetto, F. Musil, F. Riva, T.M. Tran and C. Wersal, Journal of Computational Physics 315, 388-408 (2016).
[2] C. Wersal and P. Ricci, Nuclear Fusion 55, 123014 (2015).

Speaker: A.C. Coroado (EPS 2019)

108 P1.2001 Self-Similar Multimode Evolution of the Ablative Rayleigh-Taylor Instability and Its Application in Inertial Confinement Fusion

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2001.pdf

The self-similar nonlinear evolution of the multimode ablative Rayleigh-Taylor instability (RTI) is studied numerically. It is shown that the nonlinear multimode bubble-front penetration follows the gt2 scaling law with dependent on the initial conditions and ablation velocity. It is shown that mass ablation reduces with respect to its classical value for the same initial perturbation amplitude. The value of can be described by the bubble competition theory and is not significantly affected by the vorticity acceleration of the bubble-front velocity. It is also shown that ablation effect prevents the transition of the RTI from the bubble competition to the bubble-merger regime at large initial amplitudes, leading to higher values of than in the classical case. The bubble competition theory of the ablative RTI is further applied to access the hydrodynamic stability boundary and compared with the experimental observations in laser direct-drive implosion experiments. It is indicated that the experimental hydrodynamic stability boundary could be caused by the nonlinear ablative RTI in the acceleration phase of the implosion.

This work was supported by the DOE Office of Fusion Energy Sciences Grant DE-SC0014318, the DOE National Nuclear Security Administration under Award DE-NA0001944, NSF Grant OCE-1259794 and LANL LDRD program through Project Number 20150568ER.

Speaker: H. Zhang (EPS 2019)

109 P1.2002 Progress on weakly nonlinear hydrodynamic instabilities in spherical geometry

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2002.pdf

In the ICF central ignition implosion, a spherical target is uniformly irradiated and ablatively compressed, creating the temperature and density conditions (i.e., the stagnation pressure) necessary to achieve thermonuclear ignition. Throughout the entire ICF implosions, the integrity of the compressed shell is of critical importance. The final fuel assembly must consist of a low-density, high-temperature core surrounded by a high-density, low-temperature shell to maximize the number of fusion reactions that can occur while the fuel is inertially confined. To create the fusion hot-spot, the shell must maintain its integrity throughout the implosion to prevent significant shell deformation, ablator material mixing into the central region, and thermal mixing between the hot core and cold fuel. Hydrodynamic instabilities are of significant concern when trying to achieve the highest integrity of the compressed shell possible in ICF implosions, which can compromise the shell's integrity throughout the implosion, rupturing the shell or quenching the hot-spot before the target maximum gain is achieved. In this report, we summarize the progress of theoretical research of hydrodynamic instabilities in spherical geometry in our group over the past several years.

References
[1] J. Zhang, L. F. Wang, W. H. Ye, et al. Weakly nonlinear multi-mode Rayleigh-Taylor instability in two-dimensional spherical geometry. Phys. Plasmas, 2018, 25:082713
[2] J. Zhang, L. F. Wang, W. H. Ye, et al. Weakly nonlinear incompressible Rayleigh-Taylor instability in spherical and planar geometries. Phys. Plasmas, 2018, 25:022701
[3] J. Zhang, L. F. Wang, W. H. Ye, et al. Weakly nonlinear incompressible Rayleigh-Taylor instability in spherical geometry. Phys. Plasmas, 2017, 24:062703
[4] K. G. Zhao, C. Xue, L. F. Wang, et al. Two-dimensional thin shell model for the
Rayleigh-Taylor instability in spherical geometry. Phys. Plasmas (to be publised)
[5] K. G. Zhao, C. Xue, L. F. Wang, et al. Thin shell model for the nonlinear fluid instability of cylindrical shells. Phys. Plasmas, 2018, 25:092703
[6] K. G. Zhao, L. F. Wang, C. Xue, et al. Thin layer model for nonlinear evolution of the Rayleigh-Taylor instability. Phys. Plasmas, 2018, 25:032708

Speaker: L. Wang (EPS 2019)

110 P1.2004 Estimates of the radio isotope production from laser driven proton acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2004.pdf

Laser-driven ion acceleration is an attractive way to realize compact and affordable ion sources for many exciting applications including cancer therapy, proton radiography, and inertial confinement fusion. Many of these applications require high energy ion beams with narrow energy spread as well as high flux.
Several new acceleration mechanisms have been explored by varying laser conditions and target states. So when a near critical (or rather overdense) target is irradiated by a laser pulse, ions are compressed to form a density spike, which in turn launches electrostatic shocks in the target. These shocks can reflect upstream ions and yield ion beams with monoenergetic peaks of a few MeV [1].
Currently, laser driven ion acceleration does not allow to reach the energies required for protontherapy (E > 200MeV ). In this study, we propose to estimate the use of protons to induce reactions in secondary targets to produce radioisotopes of relevance to the nuclear medecine community ( beta+ emitters), like 11C , 13N or 18F via (p,n) or (p,alpha) reactions. Indeed, these radioisotopes can be produced with lower proton energy, below 35MeV, energy achievable by laser acceleration. Laser ion acceleration is therefore promising to replace cyclotrons by a more flexible devices : laser systems.
In this work, we present the numerical chain formed by PIC [2] and MONTE CARLO [3] codes. First results of radiosiotope production are analysed, as a function of ion acceleration mechanisms and of targets properties.

References
[1] Fiuza et al Phys. Rev. Lett. 109 215001 (2012)
[2] J. Derouillat, A. Beck, F. Pérez, T. Vinci, M. Chiaramello, A. Grassi, M. Flé, G. Bouchard, I. Plotnikov, N.
Aunai, J. Dargent, C. Riconda, M. Grech, SMILEI : a collaborative, open-source, multi-purpose particle-incell code for plasma simulation, Comput. Phys. Commun. 222, 351-373 (2018)
[3] A. Ferrari, P.R. Sala, A. Fasso, and J. Ranft, FLUKA : a multi-particle transport code, CERN-2005-10 (2005)

Speaker: J. Bonvalet (EPS 2019)

111 P1.2005 3D numerical simulation of magnetically-driven plasma fluxes generated in nested wire arrays

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2005.pdf

We study short-lived plasma flows during sub-microsecond Z-pinch implosion by high current facility. To fulfil multiparametric numerical simulations we use radiativemagnetohydrodynamics (RMHD) code MARPLE-3D developed in Keldysh Institute of Applied Mathematics. MARPLE is designed as an expandable full-scale multiphysics research platform using the state-of-the-art physics, mathematics and numerics as well as the up-to-date high performance computing functionality. MARPLE main physics includes: - one-fluid two-temperature MHD model with electron-ion energy relaxation and general Ohm's law, - anisotropic resistivity and heat conductivity in the magnetic field, radiative energy diffusion with multigroup spectral model, - prolonged plasma ablation model, - widerange datatables including equations of state, transport and kinetic coefficients, - opacity and emissivity datatables taking into account non-LTE effects. Multiwire array implosion at Angara-5-1 facility (TRINITI, Troitsk) is studied in a series of numerical experiments. We consider different configurations of wire arrays: cylindrical and quasispherical arrays, single and nested arrays, metal wires and polymer fibers. As it is found the two-cascade nested array design allows a stable compact compression. A shock wave is formed between the cascades, which damps the inhomogeneities of the plasma jets. The effect is also observed when the external and internal cascades are of the same material. The decrease in the trailing mass is more significant in the case of a quasi-spherical array. We show a quite good qualitative and quantitative agreement of the simulation results with experimental data and theoretical estimates.
This work is carried out with the partial financial support of the Russian Foundation for Basic Research under grants No. 18-29-21005, No. 18-02-00170. The simulations are done using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University and supercomputers at Joint Supercomputer Center of the Russian Academy of Sciences (JSCC RAS).

Speaker: O. Olkhovskaya (EPS 2019)

112 P1.2006 Pulse-periodic laser-driven hard x-ray source

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2006.pdf

Laser electron accelerators are considered as a novel high brightness x-ray source with unprecedented features such as small size and narrow divergence. These advantages make this source a promising diagnostic for variety of applications especially in radiography. For the most future applications it is necessary to enhance total charge of electron bunch.
Most laser plasma electron acceleration experiments are performed at irradiation of low density targets (gas-filled capillaries, gas cells etc.). Highly collimated quasimonochromatic electron bunches with energies up to several GeV are produced [1,2]. Typical charges of these bunches are of the order of tens of picoCoulombs. Several approaches were examined [3,4] to increase the charge, but up to data these regimes haven't been investigated completely.
We report on experiments on electron acceleration from high density gas jets (ne~10^20cm^-3) which were performed on 100 TW femtosecond laser facility (800 nm, 25 fs, 10 Hz). Gas jet parameters were measured using interferometry method.
Relativistic electron bunch spectra were obtained in experiments with various gas jet parameters and the total charge of the electron bunches were estimated.
Generated electron beams were converted into hard x-ray bremsstrahlung radiation via Ta slab placed few centimeters after gas target. Yield of hard x-rays and their spectrum temperature were measured. Hard x-ray doze on the axis for a distance of 2 m from the source is evaluated to be ~2.5 mrad/shot.

[1] X. Wang, R. Zgadjai, N. Fazel et al., Nature Communications V.4, No. 1988 (2013)
[2] W.P. Leemans, A.J. Gonsalves, H.-S. Mao et al., Phys. Rev. Lett. 113, 245002 (2014)
[3] V. Malka, J. Faure, J.R. Marques et al., Phys. Plasmas, Vol. 8, No. 6, 2605-2608 (2001)
[4] M.I.K. Santala, Z. Najmudin, E.L. Clark et al., Phys. Rev. Lett. 86, 1227 (2001)

Speaker: V.A. Flegentov (EPS 2019)

113 P1.2007 Double layer target with interface modulations for laser acceleration of collimated ion beams

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2007.pdf

With the advent of multi-petawatt laser systems like the ELI-Beamlines (Czech Republic), APOLLON (France) and SEL (China) the laser-driven ion accelerators will enter the acceleration regimes dominated by radiation pressure [1]. High quality ion beams with low emittance and narrow energy spectrum will be generated when these lasers irradiate tailored targets.
Below we present the results of studying the effects of the interface modulations in double layer targets. The numerical particle-in-cell simulations with the code EPOCH [2] are used. We show that the pre-modulated targets can undergo relativistic Rayleigh-Taylor [3] and RichtmyerMeshkov instabilities. Their use can improve the properties of generated ion beams [4].
It is shown that small perturbations originated from the interface modulation grow during the laser-target interaction. This leads to the formation of low-density regions and high-density ion bunches between them at the positions determined by the pre-modulation geometry. The ion bunches are then accelerated by the laser radiation pressure. The collimated central bunch of proton beam has the average energy in the multi-GeV range with narrow energy spread. The laser accelerated ion beams from composite targets will find applications in nuclear physics research [5].

Our work is supported by projects High Field Initiative (CZ.02.1.01/0.0/0.0/15 003/0000449) and Extreme Light Infrastructure Tools for Advanced Simulation (CZ.02.1.01/0.0/0.0/16_013/0001793) from the European Regional Development Fund and by Czech Science Foundation (18-09560S).

References
[1] T. Esirkepov, M. Borghesi, S. V. Bulanov et al., Phys. Rev. Lett. 92, 175003 (2004)
[2] T. D. Arber, K. Bennett, C. S. Brady et al., Plasma Phys. Control. Fusion 57, 113001 (2015)
[3] F. Pegoraro and S. V. Bulanov, Phys. Rev. Lett. 99, 065002 (2007)
[4] S. V. Bulanov, E. Y. Echkina, T. Z. Esirkepov et al, Phys. Rev. Lett. 104, 135003 (2010)
[5] M. Nishiuchi, H. Sakaki, T. Z. Esirkepov et al, Plasma Phys. Rep. 42, 327 (2016)

Speaker: M. Matys (EPS 2019)

114 P1.2008 Relativistic polarized electron generation via plasma wakefield acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2008.pdf

Spin-polarized electron beams are extensively used for spin-dependent high energy physics and material science. Here we propose a new approach based on plasma wakefield acceleration (PWFA) for generating high-energy polarized electron beams. In a pre-polarized gas target, we found the restrictions to preserve the electron beam polarization for beam-driven PWFA and further proposed to use a new structure of laser pulse to resolve the depolarization issue of injected electrons in LWFA. The theoretical predictions for PWFA and LWFA to generate relativistic polarized electron beams are confirmed in full three-dimensional particle-in-cell simulations incorporating spin dynamics (the Thomas-Bargmann Michel Telegdi equation), where the latter preserves the electron spin polarity by more than 80% at high beam charge and flux. The proposed method releases the limit on beam flux for polarized electron acceleration and promises more than an order of magnitude boost in peak flux, as compared to ordinary Gaussian beams. These results suggest a promising table-top all-optical method to produce energetic polarized electron beams.

Speaker: L. Ji (EPS 2019)

115 P1.2009 Physics of the chromatic focusing and post-acceleration of laser-driven protons by the target discharge current

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2009.pdf

The production of laser driven protons has attracted a large number of studies thanks to their potential applications such as isochoric heating, proton radiography, isotope production or proton therapy [1]. The Target Normal Sheath Acceleration (TNSA) is the most robust and well-known generating process but it produces proton bunches suffering from a broad energy spectrum and large beam divergence. To optimize the properties of the proton beam, a new scheme of post-acceleration and chromatic focusing of TNSA-produced protons [2,3] proposes to add a helical coil connected at the rear side of the target foil. After the laserplasma interaction, the discharge current induced by the electron charge ejection propagates through this helix and generates an electromagnetic pulse which collimates, post-accelerates and energy selects the protons emitted from the rear side of the target. A highly collimated, propagating along the helix axis and quasi-monoenergetic proton bunch is then produced.
We present the results of the experimental campaign carried out at the LULI 2000 facility where 100 TW laser pulses were irradiating gold foils attached to helixes of different diameters, lengths or pitches. The goal of the campaign was to demonstrate how the control of the propagation of the discharge current through the helical coil can influence the proton chromatic focusing. The experimental data will be compared to the results of numerical simulations carried out with the home-made code SOPHIE. This massively parallelized Particle-In-Cell code models the generation and propagation of the discharge current through the helix by using realistic boundary conditions as well as the proton energy selection, focusing and acceleration, in a self-consistent manner between fields and particles.

Acknowledgements: This work was partly supported by the exploratory program Bottom-Up lead by the Commissariat à l'Énergie Atomique et aux Energies Alternatives (CEA).

[1] A. Macchi et al., Rev. Mod. Phys. 85, 751 (2013)
[2] S. Kar et al., Nature Com. 7, 10792 (2016)
[3] H. Ahmed et al., Scientific Reports 7, 10891 (2017)

Speaker: J.G. Moreau (EPS 2019)

116 P1.2010 Effects of Coulomb collisions in solid-density laser plasma shocks

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2010.pdf

Kinetic shocks in laser-plasmas provide a promising acceleration scheme to produce highly mono-energetic ion beams [1, 2, 3]. The modeling of such setups often neglects Coulomb collisions due to the short time scales of the kinetic processes involved. However, previous results suggest at that collisions might qualitatively affect the behavior of shocks in solid density targets [4], even though the dynamics remains largely governed by collisionless physics.
We investigate the effect of Coulomb collisions on laser-plasma shocks in solid density targets. In particular, we study how collisions affect the laser energy absorption and the ion acceleration. We use the PIC code Smilei [5], which has a relativistic binary collision module [6]. We mainly consider targets containing protons and a heavier ion species in comparable concentration.
In the cases considered, we find that collisions can increase the laser energy absorption by up to 40 % compared to the same setup without collisions. We analyze how a significant collisional scattering of electrons modify previously studied collisionless absorption processes, such as standing wave acceleration [7], leading to higher absorption. The additional absorbed energy leads to a significant increase in the electron temperature, providing a boost to the shock wave amplitude and the propagation speed. The energy of the shock accelerated protons increases by 50-70 % while the accelerated proton yield is not reduced. As expected from the strong charge dependence of collisions with high-charge ions, the ion composition has a major impact on the collisional processes. Besides the increased collisionality, the presence of heavy ions also increase the fraction of reflected ions in accordance with previous results [8].

References
[1] D. Haberberger et al., Nat. Phys. 8 95-99 (2012).
[2] A. Pak et al., Phys. Rev. Accel. Beams 21 103401 (2018).
[3] L. O. Silva et al., Phys. Rev. Lett. 92 015002 (2004).
[4] A. E. Turrell, M. Sherlock, and S. J. Rose, Nat. Commun. 6 8905 (2015).
[5] J. Derouillat et al., Comput. Phys. Commun. 222 351-373 (2018).
[6] F. Pérez et al., Phys. of Plasmas 19 083104 (2012).
[7] J. May et al., Phys. Rev. E 84 025401 (2011).
[8] I. Pusztai et al., Plasma Phys. Control. Fusion 60 035004 (2018).

Speaker: A. Sundström (EPS 2019)

117 P1.2011 Inertial electrostatic confinement fusion neutron source with an externally applied magnetic field

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2011.pdf

The purpose of this research is to develop a compact neutron source. Neutron can be generated by a nuclear fusion reaction. Inertia electrostatic confinement fusion (IECF) is one of the compact neutron sources by using a nuclear fusion reaction. Characteristics of the IECF are compact, monochromatic energy (2.45 MeV for D-D nuclear fusion reaction) and high controllability. In this research, a compact neutron source by a high voltage ring cathode discharge has been developed. Schematic drawing of the neutron source is shown in figure below. The used gas is deuterium. Deuterons in the discharge around the ring cathode are accelerated to the centre of the ring cathode and are converged by the high voltage. Such deuterons collide each other and the fusion reaction occurs around the centre of the ring cathode. The estimated neutron fluence rate is approximately 5 cm^-2 s^-1 at the distance of 350 mm under the condition that the cathode voltage is -30 kV and discharge current is 8 mA. As new experimental results, the increase of the neutron fluence rate by a applying a magnetic field will be reported in this presentation.

Speaker: M. Watanabe (EPS 2019)

118 P1.2012 Helical light modes in the emitted spectrum of the laser plasma undulator

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2012.pdf

The laser plasma undulator is a tunable device which utilizes laser plasma interaction to function as a short period undulator. Such an undulator could provide a table top solution for the production of X-ray beams which could be utilized in laboratories and medicine. In the regime of linear laser plasma interaction, the propagation of a beam in plasma can be modeled using the wave equation applied to the beam's vector potential function.. An underdense, parabolic plasma channel can essentially function as a waveguide for the injected beam, however, the propagation of the beam is highly dependent on the injection conditions. If the beam is injected off of the channel's axis of symmetry, the beam's centroid will oscillate about the channel's central axis. In this case, the amplitude and other characteristics of the beam are conserved during propagation. Through utilizing the solutions of an electron under the influence of a plane wave, one can model the trajectories of electrons copropagating with the beam in the plasma channel. The electron velocities follow the vector potential and subsequently the electrons also oscillate about the plasma channel's axis of symmetry producing undulator motion[1]. From the motion of the electron in such a channel, one can calculate the spectrum of the emitted radiation through Lienard-Wiechert potentials.
In this work, we utilized Crank-Nicolson schemes to model the propagation of the beam within the channel. This vector potential is then used to compute the trajectories of electrons. We then numerically integrate the intensity equation. We also analytically solved the intensity integral for this synchrotron motion. We found that the emitted spectrum of this device displays interesting features as shown in figure 1.
First, the short undulator wavelength results in a strong fundamental harmonic of 10keV X-rays. Second, off-axis, we find integer spaced harmonics corresponding to angular momentum quanta as indicated by the analytical solution of the intensity integral. The solution describes a helically distributed field similar to optical vortices.

References
[1] S. G. Rykovanov et al, Phys. Rev. Accel. Beams strong fundamental and harmonics in the 19,090703 (2016)

Speaker: T.C. Teter (EPS 2019)

119 P1.2013 Numerical simulations of the electromagnetic field shielding in petawatt regime using Finite-Difference Time-Domain method

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2013.pdf

The recent progresses made in the development of high intensity lasers open new perspectives of fundamental physics and also impacts applications from laboratory astrophysics and inertial confinement fusion to laser matter interaction in ultra-intense regimes. The interaction of high power laser pulses with a solid target generates intense broadband electromagnetic pulses in a wide frequency regime, from radio frequency to x-rays. In the petwatt regime, these intense laser pulses are expected to be emitted in the Giga to Tera-Hertz domain, being also called Giant Electro-Magnetic Pulses (GEMP) [1].
Starting from the cells response on particular wavelengths and respectively during petawatt irradiation experiments and considering the GEMP spectra generated during real experiments, we had performed 3D numerical simulations to investigate the behavior of different shielding materials by using a scaled configuration setup. The main objective is to compare the performances of these materials at some different frequencies, considered as relevant both for the generated frequencies and for the cell's absorbed wavelengths under the conditions imposed by high energy experiments planned to be performed at CETAL PW facility. The 3D numerical simulations of the electromagnetic field shielding have been made using FiniteDifference Time-Domain (FDTD) method using FullWave, a package of the commercial software RSoft (by Synopsys Optical Solution Group) which solves Maxwell equations. Lately, a plenty of FDTD studies had been elaborated in order to determine the optimum conditions for extreme electric field generation [2-4]. A detailed study concerning the electromagnetic field shielding under petawatt irradiation conditions has been elaborated using different structures both as metallic foil or mesh in order to measure its efficiency in a wide frequency regime (100-4000 MHz). The results obtained by this method will be presented and discussed.

This work has been financed by the national project: PN III 5/5.1/ELI-RO, Project 17-ELI/2016 ("BIOSAFE"), under the financial support of Institute for Atomic Physics - IFA.

[1] M. J. Mead, D. Neely, J. Gauoin, R. Heathcote, P. Patel, Rev. Sci. Instrum. 75, 4225 (2004)
[2] L. Ionel, D. Ursescu, Opt. Express 24(7) 7046-7054 (2016)
[3] L. Ionel, D. Ursescu, , Laser Part. Beams 32(1), 89-97 (2014)
[4] Z. Lin, X. Chen, P. Ding, W. Qiu, J. Pu, Opt. Express, 25(7) 8440-8449 (2017)

Speaker: L. Ionel (EPS 2019)

120 P1.2014 A paradigm model for studying the nonstationary behavior of gyrotron backward wave oscillators

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2014.pdf

A paradigm model is proposed for the study of the nonstationary behavior of gyrotron backward wave oscillators. The model is first examined by comparisons with the PIC simulation, large signal theory and the linear theory for retaining the basic ingredient of formulations about the mechanism of electron cyclotron resonance maser. The physical reason for the alternating appearance of the nonstationary behaviors of gyrotron backward wave oscillators [1] - [3] with the increase of beam current at different interaction lengths is thus possibly explored by the theoretical analysis on the basis of the paradigm model.

[1] T. H. Chang, S. H. Chen, L. R. Barnett, and K. R. Chu, Physical Review Letters Physical Review Letters 87, 064802 (2001).
[2] S. H. Chen, T. H. Chang, K. F. Pao, C. D. Fang, and K. R. Chu, Physical Review Letters 89, 268303 (2003).
[3] S. H. Chen and L. Chen, Physics of Plasmas 20, 123108 (2013).

Speaker: S. Chen (EPS 2019)

121 P1.2015 Generation of few- and subcycle radiation at combination frequencies of ultrashort multicolor ionizing laser pulse

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2015.pdf

We discuss a new method to generate few-cycle pulses from ionization of a medium by twocolor (or, more generally, multicolor) femtosecond fields [1, 2]. The method is based on the parametric excitation of a free-electron nonlinear current at the combination frequencies of ionizing pulses. In contrast to the common parametric frequency mixers using nonlinear crystals, the varying parameter here is the plasma density, and the ionization dominates over other nonlinearities. Since the effect is caused by the motion of free electrons, it may be strong enough even if the particle number and density are small compared to the case of condensed media, so the ionized gases may be used for generation. This significantly expands the range of pump intensities and the frequency range (compared to the wave mixing in nonlinear crystals where dispersion and absorption are generally essential around the numerous resonant frequencies). Moreover, using ambient air provides the possibility for the remote generation of few-cycle pulses since the ionization region may be placed in the immediate vicinity of a target to be irradiated by obtained few-cycle pulses (as realized for the remote laser-plasma terahertz generation in air [3]). Thus, one can avoid the transportation of generated pulses over long distances with inevitable diffraction and dispersion. The highorder nature of nonlinear ionization results in a very short duration of the generated pulse at combination frequencies. This duration coincides with the duration of ionization (i.e., with the characteristic time scale of the plasma density buildup) and is commonly much shorter than the duration of the ionizing pump [4]. The resulting pulse can easily be a few-cycle, or even subcycle, one with the carrier-envelope phase determined by the phase shift between onecolor components of the ionizing pulse.

[1] V.A. Kostin, N.V. Vvedenskii, Phys. Rev. Lett. 120, 065002 (2018).
[2] A.A. Silaev, V.A. Kostin, I.D. Laryushin, N.V. Vvedenskii, JETP Lett. 107, 151 (2018).
[3] C. D'Amico, A. Houard, M. Franco, B. Prade, A. Mysyrowicz, A. Couairon, V.T. Tikhonchuk, Phys. Rev. Lett. 98, 235002 (2007).
[4] V.A. Kostin, I.D. Laryushin, A.A. Silaev, N.V. Vvedenskii, Phys. Rev. Lett. 117, 035003 (2016).

Speaker: N. Vvedenskii (EPS 2019)

122 P1.2016 High-order harmonic generation in an electron-positron-ion plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2016.pdf

We show that high-order harmonic generation (HHG) in a solid-density target is significantly changed after an electron-positron pair plasma is produced [1], with strong and well-defined signals at harmonics of the plasma frequency (i.e., npe) present in the spectrum. The peradiation comes from the plasma wave excited by the laser-accelerated dense positron beam via the beam-plasma instability [2, 3]. The subsequent reflux of the positrons induces a counterpropagating plasma wave. The inverse two-plasmon decay between these counterpropagating waves will radiate harmonics at 2pe [4]. Furthermore, 3pe-radiation is also observed due to the higher-order plasma coalescence [5]. Particle-in-cell (PIC) simulations with OSIRIS 4.0 show that these signals are prominent and robust with different target density, pair density, and temperature [1]. For example, the 2pe-radiation is enhanced by more than 150 times (compared with the same electron-ion target without pair plasma generation) after a pair plasma is produced with a density fraction of just 0.05%. Therefore, these signals can be used as an in situ diagnostic for the pair plasma generation mechanism. In addition, the radiation enhancement at is up to be 3.9 ◊ 104 times, paving a way to the bright and compact extreme ultraviolet (XUV) radiation source.

References
[1] W. L. Zhang, T. Grismayer, R. A. Fonseca, L. O. Silva, Submitted, 2019.
[2] R. G. Greaves and C. M. Surko, Phys. Rev. Lett. 75, 3846 (1995).
[3] T. J. M. Boyd and J. J. Sanderson, The Physics of Plasmas, Cambridge University Press, 2003.
[4] T. Kunzl, R. Lichters, and J. Meyer-Ter-Vehn, Laser and Particle Beams 21, 583 (2003).
[5] T. J. M. Boyd and R. Ondarza-Rovira, Phys. Rev. Lett. 85, 1440 (2000).

Speaker: W. Zhang (EPS 2019)

123 P1.2017 Dissipative shock structures in dispersive systems – application in multicomponent plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2017.pdf

A generalized "hybrid" Korteweg - de Vries/Burgers (hKdVB) type partial-differential equation is considered. Although the model equation is known to arise in multi-fluid plasma models treated by multiscale (so called reductive perturbation) techniques [1], its generic form is considered in this work, carrying a broader focus and ambition for applicability in different models of dispersive systems (dynamics). The combined effect of nonlinearity and dispersion, in addition to diffusivity and dissipation, included via effective ad hoc terms, is taken into account.
An approximate analytical solution is obtained via a perturbative approach based on the hyperbolic tangent (tanh) method. Explicit shock-type solutions are obtained and analyzed, for different values of the relevant parameters. Various limiting cases are discussed.
A series of computational simulations based on an original numerical algorithm are then carried out, to test our analytical predictions. A critical comparison between analytical and numerical results reveals a very good agreement in the time-dependent shock amplitude, although the analytical method fails to reproduce the shock front steepening in time; it is argued that this is due to intrinsic limitations of the analytical method adopted. A train of soliton-like pulses, superposed over the shock-wave structure, also appears in computational simulations, when a large amplitude initial condition is considered.

References
[1] I. S. Elkamash and I. Kourakis, Physics of Plasmas, 25 (6), 062104 (2018); DOI: 10.1063/1.5029322.

Speaker: I. Kourakis (EPS 2019)

124 P1.2018 High-order harmonic generation from the relativistic plasma resonance in an inhomogeneous plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2018.pdf

Analytical theory of harmonic generation in an inhomogeneous laser-produced plasma based on the relativistic plasma resonance mechanism [1] is presented. This theory applies renormgroup symmetries method and advances known approaches beyond their applicability conditions. Relativistically strong electric fields and electron velocities in the vicinity of the critical plasma density are found. Nonlinear current, considered as a source of radiation in a vacuum, is calculated. The spectral and angular characteristics of the radiation field, which includes highorder harmonics are revealed. It is shown that relativistic nonlinearity of the plasma wave leads to a phase modulation of the electron oscillations that determines a flattening and modulation of the spectral curve. The applicability condition of our theory is given by the plasma wave breaking condition in the vicinity of the critical plasma, that enables higher laser intensities than all previous theories. A comparison with the perturbation theory [2, 3] is performed. Smooth power-law emission spectra of high-order harmonics is demonstrated.

References
[1] I.I. Metelskii, V.F. Kovalev, V.Yu. Bychenkov, Plasma Physics Reports 43, (2017)
[2] N.S. Erochin, S.S. Moiseev, V.V. Mukhin, Nuclear Fusion 14, 3, (1974)
[3] A.B. Vladimirskii and V.P. Silin, Sov. J. Plasma Phys. 6, (1980)

Speaker: I.I. Metelskii (EPS 2019)

125 P1.2019 Betatron radiation of high brightness from electron acceleration in the regime of laser bullet

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2019.pdf

Short laser pulse interaction with a rather dense gas plasma target may result in pulse propagation regime which maximize the charge of the high-energy electron bunches. This regime corresponds to laser pulse propagation in a self-trapping mode, where the diffraction divergence is balanced by the relativistic nonlinearity, so that the laser beam radius stays unchanged during pulse propagation over many Rayleigh lengths. Such regime occurs for near critical density where the pulse length exceeds both the plasma wavelength and the pulse width. Electron acceleration occurs in a travelling cavity with a high-frequency laser field filling and a longitudinal electrostatic single-cycle field ("light bullet"). High charge of accelerated electrons enables efficiently produce X-rays through betatron oscillations. This was demonstrated by using the 3D PIC simulation results for electron characteristics. It has been shown that 100 TW laser pulse is able to produce over 4.5x10^10 photons per shot with the photon energy over 5 keV.

Speaker: M.G. Lobok (EPS 2019)

126 P1.2020 Feasibility studies for all-optical and compact gamma-ray blaster by PetaWatt-class laser pulse and its application

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2020.pdf

The all-optical Compton backscattering setup by using laser pulses becomes a promising method in building a compact gamma-ray source [1]. Nevertheless, this method only produces a single gamma-ray flash and other sources are suppressed. In this work, we study the feasibility of producing double gamma-rays flashes by using one 1 PW laser pulse. This method utilises the alloptical setup with a structured solid target as a reflecting foil. The laser pulse is reflected by this foil after propagating a few millimetres into the underdense plasma. The reflected laser intensity is boosted strong enough to invoke radiation reaction as nonlinear Compton backscattering. After that, the electron bunch passes the foil for bremsstrahlung. Our simulation result shows that a collimated -ray beam from the nonlinear Compton backscattering (NCBS) with peak brilliance of 6.7 x 10^20 photons/s/mm^2/mrad^2/0 1%BW at 15 MeV is obtained. At the same energy, bremsstrahlung process provided another collimated gamma-ray beam with 2.1 x 10^16 photons/s/mm^2/mrad^2/0 1%BW. The double gamma-rays beams can find application for the pump-probe experiment down to the nuclear structure [2].

References
[1] K. Ta Phuoc, S. Corde, C. Thaury, V. Malka, A. Tafzi, J. P. Goddet, R. C. Shah, S. Sebban and A. Rousse, Nature Photonics 6, 308 (2012).
[2] J. F. Ong, A. C. Berceanu, K. Seto, S. Aogaki and L. Neagu, submitted

Speaker: J. Ong (EPS 2019)

127 P1.2021 X-ray absorption in plasma by one-photon stimulated bremsstrahlung with the exact consideration of Coulomb potential

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2021.pdf

With the appearance of recent X-ray free electron lasers (FEL) [1], the stimulated bremsstrahlung (SB) process of electrons on plasma ions' scattering centres may provide a sufficient energy for plasma heating at the absorption even one-two photons [2], which makes the SB as one of the effective mechanisms for laser heating of a plasma with X-ray FELs.
In the present work the absorption process of X-ray quanta with energies above 5-10 keV (~Å wavelengths) in high temperature plasma with the high nuclear charge is investigated beyond the Born approximation. The coherent electromagnetic radiation field is considered by the perturbation theory. The quantum dynamics of X-ray absorption process at the electron-ion SB in maxwellian plasma is studied by the fourth-order adaptive Runge-Kutta method for absorption coefficient via inverse-bremsstrahlung mechanism with the exact consideration of the Coulomb field. The temperature dependence of the absorption coefficient is investigated numerically.
The present work extends the known analytical results of the paper [3] with the help of numerical simulations and evaluation of the bulk formulas containing, in particular, complex special (hypergeometric) functions. The obtained results can have practical significance for plasma heating, taking into account that XUV/X-ray laser beams of necessary frequencies at present are available at the Stanford and DESY Accelerator Centres.

This work was supported by State Committee of Science of RA.

References
[1] H. Mimura et al., Nat. Commun. 5, 3539 (2014).
[2] F. V. Bunkin, A. E. Kazakov, and M. V. Fedorov, Sov. Phys. Usp. 15, 416 (1973); Y. Shuma, H. Yatom, Phys. Rev. A 12, 2106 (1975).
[3] H. K. Avetissian, A. K. Avetissian, K. Z. Hatsagortsian, and S. V. Movsissian, J. Phys. B 23, 4207 (1990).

Speaker: A.G. Ghazaryan (EPS 2019)

128 P1.2022 A novel approach to the study of electron dynamics in colliding laser fields

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2022.pdf

We show that the proper choice of canonical variables and effective time, such that the new Hamiltonian is conserved for electrons in a dominant laser field, greatly simplifies analytical treatment of the problem. For example, for the case of counter propagating planar laser beams and dominant laser with relativistic intensity, a>1, such approach allows an exhaustive analytic analysis of electron dynamics. We find that for the amplitude a1 of a weaker laser (a_1 <a) exceeding the threshold value a_th, a_th~a^-3<<a, stochastic acceleration of electrons becomes possible within some range of electron kinetic energy. Maximum electron kinetic energy, which could be gained under stochastic acceleration, significantly exceeds the ponderomotive scaling for the dominant laser when the ratio, k1, of perturbative to dominant laser frequencies is relatively small, k1\<a (in this case, energetic electrons move in the direction of the propagation of the dominant laser beam) and for large k_1, such that k_1>a^2>1, providing that (a^2/k1 )4/3 < a_1/a < 1 (where energetic electrons move in the direction of the propagation of the perturbative laser beam). The results of numerical solutions of the governing equations are in a very good agreement with the findings from our analytic theory. We notice that the approach presented in this work could be applied to many other cases including electron dynamics in the laser and quasi-stationary electromagnetic fields, in intense laser and Langmuir waves, etc.

This work was supported by the University of California Office of the President Lab Fee grant number LFR-17-449059.

Speaker: S. Krasheninnikov (EPS 2019)

129 P1.2023 Electromagnetic pulses generated from ultra-thin targets irradiated by the Vulcan Petawatt laser

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2023.pdf

One of the effects accompanying laser-target interactions at high laser intensities is the generation of strong electromagnetic pulses (EMP) with frequencies in the range of tens of MHz to few GHz. Such pulses may interfere with the electronics of the data acquisition systems and pose a threat to the safe and reliable operation of high-intensity laser facilities. Recently, EMP measurements were performed at several laser facilities, including the Vulcan PW laser [1,2]. In this contribution, we report on a ride-along measurement of EMP generated at the Vulcan PW laser facility from ultra-thin (tens to hundreds of nanometers thick) metal and plastic targets. Such targets undergo substantial deformation during the interaction, with the possibility of forming particle jets, resulting in conditions for which EMP generation had been rarely studied so far.. Proper conditions were created to capture the multi-GHz component of the resulting electromagnetic pulses. Measurements were performed using conductive B-dot and D-dot probes placed inside and outside the experimental chamber. High-bandwidth double-shielded coaxial cables were used to connect the probes to an oscilloscope with a 13 GHz bandwidth and 4x40 GSa/s sampling rate. The oscilloscope was enclosed in a Faraday cage to protect it from any electromagnetic disturbances propagating directly through the air. It was found that the spectrum of the generated pulses is quite wide and the multi-GHz component constitutes the bulk of the signal. It was also observed that despite having a random and chaotic appearance such pulses are reproducible from shot to shot to a surprising degree. Electric fields on the order of 250 kV/m were measured inside the experimental chamber.

References
1. T.S. Robinson et al., Sci. Rep. 7, 983 (2017).
2. P. Bradford et al., High Power Laser Science and Engineering 6, e21 (2018).

Speaker: P. Raczka (EPS 2019)

130 P1.2024 Magnetic field generation of kinetic plasma waves carrying orbital angular momentum

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2024.pdf

Electromagnetic waves, while propagating through a vacuum, can carry orbital angular momentum [1] this is used in a variety of applications[2, 3]. In this study Langmuir waves carrying finite orbital angular moment are examined within a revised paraxial optics approximation. While Laguerre-Gaussian modes appear to be eigenfunctions of the plasma wave in the fluid description[4], theoretical analysis shows that LG Modes are not eigenfunctions of the electron kinetic equation[5]. Here we find a revised coupling term in the dispersion relation for LG modes as well as an additional term for Landau damping, important at tight focus. A second part of this work is the 2nd order magnetic fields generated by the rotating plasmon structure. Two structures are described (see fig. 1), the first structure is that of a single mode plasma wave, the second structure that of two counter propagating plasma waves.

References
[1] L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, J. P. Woerd-
man, Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes, Phys. Rev. A 45, 8185 (1992).
[2] Q. Zhan, Cylindrical vector beams: from mathematical concepts to applications, Advances Opt. Photonics 1, 1 (2009).
[3] J. Vieira, J. T. Mendonça, Nonlinear laser driven donut wakefields for positron and electron acceleration, Phys. Rev. Lett. 112, 215001 (2014).
[4] J. T. Mendonça, S. Ali, B. Thidé, Plasmons with orbital angular momentum, Phys. Plasmas 16, 112103 (2009).
[5] J. T. Mendonça, Kinetic description of electron plasma waves with orbital angular momentum, Phys. Plasmas 19, 112113 (2012).

Speaker: D.R. Blackman (EPS 2019)

131 P1.2025 Diagnostic of forward fast electrons in femtosecond laser-foil interactions using terahertz radiation

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2025.pdf

Fast electrons are important for laser-driven x-ray sources, proton acceleration and fast ignition of the inertial confinement fusion. Fast electrons in a solid target can be diagnosed with x-ray emission, proton acceleration and optical transition radiation. However, it is quite challenge to measure their temporal evolution. Recently Terahertz (THz) emission from intense-laser-produced plasmas has attracted much interest since such an emitter could not only be a potential tabletop brilliant THz source, but also a noninvasive diagnostic for fast electrons. We have systematically studied THz radiation from solid targets driven by relativistic laser pulses and found that THz can be generated due to coherent transition radiation (CTR) of the forward fast electrons when they pass the solid-vacuum boundary. We will show using the THz CTR to characterize the temporal history, charge, and divergence angle of the fast forward fast electron beam in a solid target in this presentation.

Speaker: Y. Li (EPS 2019)

132 P1.2026 Enhancement of fast electrons and energetic protons by intense short laser interactions with structured targets

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.2026.pdf

Some kinds of tailored structured targets were proposed to enhance laser-target coupling and improve the qualities of fast electrons. When an intense propagates in a vacuum capillary, its profile is reshaped due to laser-plasma interaction near the entrance of capillary. Only the relatively low-intensity periphery of the reshaped pulse interacts with the capillary-wall plasma, so that the high-intensity center of the pulse can propagate in the narrow vacuum channel over a distance much larger than the Rayleigh length.
A hollow cone with two opens may be used for attaining extremely high light intensities since it can focus an intense laser to a tiny and highly localized spot. When a thin foil is attached to the tip of the cone, the cone-focused light pulse compresses and accelerates the ions in its path and can punch through the thin target, creating highly localized energetic ion bunches of high density.
A novel copper nanobrush target has been proposed to achieve brighter Ka X ray. Compared to a regular planar target, the simulations show that the laser absorption efficiency by the particular target is remarkably enhanced to near 80%. The depth of laser energy penetration is larger than the skin length and more fast electrons are generated, so the laser coupling efficiency is greatly increased. The physics on the enhancement of Ka photon yield and conversion efficiency from laser to Ka x-ray is studied by combining Monte Carlo simulations and previous particle-in-cell simulation results. Subsequently, the conical nanolayered, cone-nanolayered and tailored cone-nanolayered targets are proposed to enhance coupling efficiency and control the emission angles of fast electrons. They are very promising in designing high brightness X-ray or Ka sources.
Recently, some recent research on laser interactions on solid target with external magnetic fields has been carried out. When the external magnetic field normalized by the laser magnetic field is larger than the relativistic factor, the right-hand (RH-) circularly polarized (CP) lasers will keep on propagating till the laser energy is depleted. Two-dimensional particle-incell simulation results show that in the presence of external longitudinal magnetic field, the energies and yields of fast electrons are greatly enhanced for RH-CP laser. Furthermore, the proton acceleration driven by an RH-CP laser interaction with a pre-magnetized cone target filled with a preformed plasma has also been investigated under the mechanism of target normal sheath acceleration (TNSA). The two-dimensional particle-in-cell simulation results show that with an external longitudinal magnetic field, both the energy and yield of protons accelerated by the sheath electric field at the rear of the target are remarkably increased because of the higher coupling efficiency from RH-CP laser energy to electrons and the more efficient electron acceleration. The maximum cut-off energy of protons with an imposed longitudinal magnetic field can be promoted to be as high as 82MeV.

1. J. X. Gong, Lihua Cao et al., Phys. Plasmas 26, 014502 (2019); 24, 033103(2017); 24, 053109(2017).
2. J. C. Zhao, Lihua Cao et al., Phys. Plasmas 25, 033104(2018).
3. Jincui Zhao, Jianhua Zheng, Lihua Cao et al., Phys. Plasmas 23,022705(2016).
4. Lihua Cao et al., Phys. Plasmas 18, 054501 (2011); 17, 043103 (2010); 17,103106(2010); 16, 093109(2009).
5. Lihua Cao et al., Phys. Rev. E 78,036405(2008).

Speaker: L. Cao (EPS 2019)

133 P1.3001 2d-hybrid model for plasma accelerator with open walls and closed electron drift

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3001.pdf

The original approach to use Hall-type plasma accelerators with closed electron drift and open walls for production converging towards axis accelerating ion beam describes here. The model in which a generalization condition of self-sustained discharge in crossed ExH fields with taking into consideration both electron and ion dynamic peculiarity is obtained is created. Two-dimensional hybrid model (in cylindrical coordinate r-z) for accelerator was created for which a kinetic approximation was used for ions and neutral description and a hydrodynamic - for electrons description. The performed computer modeling showed that in high-current mode the ions moving toward the system center and then along the axis in both directions. In the center of system they are able to create space charge which can be used for negative charge particle beam control. The simulation results show that potential drop along the axis arises which can be used for ion beam accelerating. The calculation results are in good agreement with obtained experimental data.
Note that the presented plasma device is attractive for many different high-tech practical applications, for example, like plasma lens with positive space cloud for focusing negative intense charge particles beams (electrons and negative ions) and for potential devises small rocket engines.

Speaker: I.V. Litovko (EPS 2019)

134 P1.3002 A new analytic solution to the collision free plasma equation with warm ions

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3002.pdf

Speaker: L. Kos (EPS 2019)

135 P1.3003 Analysis of initial stage of capillary discharge using numerical simulation

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3003.pdf

Nowadays capillary discharge is considered as the main way to create compact sources of EUV and soft X-ray radiation. Radiation in this range with such discharge is generated at the stage of magnetic plasma compression, when the current flowing through the system reaches values of the order of several kiloamperes. The initial conditions for the flow of such current are created by the so-called sliding discharge. In addition to pre-ionization, the role of such discharge is in stabilization during compression stage [1] and potential X-ray generation during the transition from a sliding discharge to a high-current one [2]. A complete picture of the physical processes that accompany the transition is not yet available. Consistent numerical modeling can significantly clarify the situation. We present the results of a numerical study of a sliding discharge at low pressures and applied voltages with nanosecond durations and amplitudes of several kilovolts in a long dielectric tube of small radius. The propagation dynamics of the sliding discharge along the capillary tube was reproduced, the role of the transverse field on the dynamics of the whole capillary discharge was evaluated, the values of propagation speed and degree of ionization were analyzed depending on different pressures and pulse parameters.

[1] J. Szasz, M. Kiss, I. Santa, S. Szatmari, S. V. Kukhlevsky, "Magnetoelectric Confinement and stabilization of Z Pinch in a Soft≠x-Ray Ar+8 Laser", Phys. Rev. Lett. ,110, 2013.
[2] V. A. Burtsev, V. V. Zabrodskii, N. V. Kalinin, E. P. Bol'shakov, "Electromagnetic radiation sources based on a low-inductive extended z-discharge," Technical Physics, 58(2), 192-199, 2013.

Speaker: M. Timshina (EPS 2019)

136 P1.3004 Characterization of aluminum oxide nanoparticle clouds in a rf discharge

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3004.pdf

Dusty plasmas with nanoparticles have attracted increased attention in the last few years. In comparison to the existing experimental setups with nanoparticles grown in the rf discharge, we present the insertion of industrial, nanoscaled Al2O3 dust with a gas jet injection setup. Beside the insertion, the characterization of the nanodusty plasma is of scattering angle particular interest.
The confined particles are being investigated in terms of size by a Mie scattering setup. The angular dependent scattering intensity of particles allows to determine their size, see Fig. 1. Using a telecentric lens, we are able to obtain the size distribution of the nanoparticle cloud, see Fig. 2a).
The density distribution has been measured with an absorption spectroscopy setup. Recording the transmission of light emitted by a white LED panel through the particle cloud gives the line integrated particle density. Under the assumption of a cylindrical symmetry of the cloud, an Abel inversion is performed to obtain the spatially resolved particle density, see Fig. 2b) [1].
Furthermore, theoretical calculations predict a charge dependent shift of the absorption in the infrared spectral range of the particles [2]. A measurement of this shift could lead to a non-invasive measurement of the charge of the nanoparticles. Existing experiments have measured the absorption in-situ, but did not show a charge variation due to a low resolution of the FTIR spectrometer yet. Therefore, new experiments with a higher resolution have been carried out.

This work was financially supported by the DFG via SFB-TR24 Project A3 and ME 1534/8-1.

References
[1] H Kr¸ger, C. Killer, S. Sch¸tt and A. Melzer, Plasma Sources Sci. Technol. 27 025004 (2018)
[2] R. L. Heinisch, F.X. Bronold and H. Fehske, Phys. Rev. Lett. 109, 243903 (2012)

Speaker: H. Krüger (EPS 2019)

137 P1.3005 Charging of microparticles in a dc discharge in ground-based and microgravity experiments

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3005.pdf

The charge of microparticles immersed into the dc discharge of PK-4 experimental facility was estimated using the particle velocities from the experiments performed on Earth and under microgravity conditions on the International Space Station (ISS). PK-4 is an experimental laboratory developed to provide a range of various complex plasma experiments in the direct current (dc) and/or radiofrequency (rf) low temperature gas discharge [1]. It was installed in the Columbus module of the International Space Station (ISS) in November 2014. The experiments were performed in the flight model (FM) onboard ISS as well as in science reference model 1 (SRM 1) of PK-4 in a ground-based laboratory, which is functionally identical to the FM. The gas pressure was varied from 20 to 100 Pa and the discharge current from 0.5 to 1.5 mA for argon and neon gases. The microparticles of three different diameters 1.3, 2.5 and 3.4 m were injected into the chamber. They were illuminated by a laser beam and their motion was recorded by video cameras with 35 fps and 14,3 m/pixel resolution. The velocities were estimated by measuring the front velocity of the whole particle cloud while entering and leaving the field of view within several consecutive frames. Another method is the method of the so-called space-time diagrams, where the averaged frame intensity in y direction is plotted within the certain time for every x coordinate, since the particles are mainly moving in x direction. The particle velocity was estimated from the slope of intensity distribution on this diagram. The experimental data from ISS showed that under microgravity conditions the velocities of microparticles are systematically lower than those measured on the ground, as it was already observed in parabolic flight experiments [2]. The difference is more pronounced in the lower pressure range (20-30 Pa). Using the analytical model of particle charging which takes into account the radial variation of the discharge parameters within the discharge tube and different values of electron reflection coefficient [3] we compared experimentally measured particle velocities with the results of the model. Both the experimentally measured and theoretically estimated particle velocities as well as the particle charge show different behaviour for argon and neon discharges with respect to the pressure. Also the quantitative values of the charge differ for these two gases. All authors greatly acknowledge the joint ESA-Roscosmos "Experiment Plasmakristall-4" onboard the International Space Station.

This work was also partially supported by DLR Grants Nos. 50WM1441 and 50WM1442.

[1] M. Y. Pustylnik, M. A. Fink, V. Nosenko et al., Rev. Sci. Instrum. 87, 093505 (2016)
[2] S. A. Khrapak, M. H. Thoma, M. Chaudhuri et al. Phys. Rev. E 87, 063109 (2013)
[3] A. V. Zobnin, A. D. Usachev, O. F. Petrov, V. E. Fortov, M. H. Thoma, and M. A. Fink, Phys. Plasmas 25,
033702 (2018)

Speaker: T. Antonova (EPS 2019)

138 P1.3006 Computer simulation for an array based on capillary discharge

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3006.pdf

Pulsed plasma jets are often used in various technical and scientific applications and can be formed by using a capillary discharge with an evaporating wall (CDEW) [1-10]. The CDEW is a powerful pulsed plasma-dynamic discharge whose plasma is created in a dielectric cylindrical channel filled to facilitate electrical breakdown by a metallized powder. In this case, the pulsed electric current flows through the cylindrical channel and forms a dense hot plasma in it, which flows through the output section of the CDEW, having a high emissivity. We modelled a two dimensional plasma array based on series connected capillary discharge. Each capillary device is composed a CDEW. Numerical simulation is performed and spatial distributions of pressure, temperature, velocity and Mach number in a pulsed capillary discharge jet and a system of pulsed jets at different instants of time are obtained. The structure of an underexpanded supersonic jet that expires from the working channel of the CDEW is investigated.

This research is supported by the Russian Minobrnauki (Project No. 13.5240.2017/8.9).

References
[1]. Pashchina, A.S., Efimov, A.V., Chinnov, V.F. and Ageev, A.G., "Specific features of the radial distributions of plasma parameters in the initial segment of a supersonic jet generated by a pulsed capillary discharge," Plasma Phys. Rep. 43, 796-800 (2017)
[2]. Varaksin A.Yu., High Temperature 56, 275-295 (2018)
[3]. V.V. Kuzenov and S.V. Ryzhkov, Bull. Russ. Acad. Sci.: Phys. 80, 598 (2016)
[4]. V. V. Kuzenov, T.N. Polozova and S. V. Ryzhkov, Problems of Atomic Science and Technology No. 4 (98), 12 (2015)
[5]. V.V. Kuzenov, S.V. Ryzhkov, A.Yu. Gavrilova and E.P. Skorokhod, "Computer simulation of plasmadynamic processes in capillary discharges", High Temperature Material Processes 18, 119 (2014)
[6]. V.V. Kuzenov and S.V. Ryzhkov, Problems of Atomic Science and Technology 1, 12 (2013)
[7]. V.V. Kuzenov and S.V. Ryzhkov, Problems of Atomic Science and Technology 4 (86), 103 (2013)
[8]. S.V. Ryzhkov, Proc. 35th EPS Conf. on Plasma Physics and Contr. Fusion, EA Vol. 32D, P1.114 (2008)
[9]. V.V. Kuzenov and S.V. Ryzhkov, Journal of Physics: Conference Series 830, 012124 (2017)
[10]. Varaksin A.Yu., High Temperature 54, 409-427 (2016)

Speaker: S.V. Ryzhkov (EPS 2019)

139 P1.3008 Configurational temperature: Temperature and charge measurements in dusty plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3008.pdf

Speaker: M. Himpel (EPS 2019)

140 P1.3009 Determination of electron density in microwave plasma torch by microwave interferometry

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3009.pdf

The microwave plasma torch represents a class of plasma generators, important for their applications. In cases, where ethanol (typical carbon structures growth precursor) is admixed to the working gas, the environment becomes dusty, which brings known problems with plasma diagnostics (e.g. electron density cannot be determined from Stark broadening of H). This contribution presents the numerically enhanced microwave interferometry for electron density measurement in such discharges, with the plasma electron density and experimentally observed phase shifts connected via the complex plasma permittivity [1].
The 2.45 GHz atmospheric pressure plasma torch enclosed in quasi-cylindrical reactor chamber (150 mm i.d., 400 mm height) is sustained in argon atmosphere with varying
admixtures of ethanol and molecular gas (O2, H2). For diagnostics, the Mach-Zehnder configuration of 34.5 GHz interferometer (with its probing arm extending inside the reactor chamber) is used, as depicted in Fig. 1. This setting of the interferometer is noteworthy for the absence of the discharge tube walls combined with close proximity to the discharge. Despite this, the small dimension of plasma channel dictates the use of numerical model (COMSOL Multiphysics). Typical results for varying discharge power are shown in Fig. 2.

This work was supported by The Czech Science Foundation (GA CR) under grant 18-08520S and by Ministry of Education, Youth and Sports of Czech Republic by the project LO1411 (NPU I)

References
[1] Heald M A, Wharton C B, Plasma diagnostics with microwaves, Wiley, 1965

Speaker: J. Faltynek (EPS 2019)

141 P1.3010 Development of triple probe diagnostics for laboratory pulsed plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3010.pdf

Speaker: P.K. Srivastava (EPS 2019)

142 P1.3011 Distinctive characteristics of electromagnetic force distributions in compressed plasma flows

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3011.pdf

High-density compressed plasma flows have many applications in the field of plasma-surface interaction [1, 2]. Additionally, magnetoplasma compressors (MPCs) are among the most commonly investigated types of possible technological sources of extreme ultraviolet (EUV) radiation [3]. Previous experimental findings have revealed that electromagnetic force distributions, as well as initial concentrations of working gases, interrelate closely with the main parameters of the compressed plasma stream, such as density and temperature, and, as a result, affect a spatial position of a compression zone. Nonetheless, a comprehensive study on the characteristics of spatial distributions of the electromagnetic forces and the output currents under various initial experimental conditions is still needful.
We have investigated the distinctive features of the MPC plasma flows for three gases at different initial pressures: argon (133.3 Pa), nitrogen (40 Pa and 80 Pa), and helium (266.6 Pa and 1.33 kPa). The experiments were carried out under the mode of operation with residual gas in the MPC facility. Spatial structures of the output currents (including fun-like configurations and induced toroidal current vortexes) have been plotted by using the data retrieved from the magnetic probe measurements. Overall, the results have clearly shown that the peculiarities of the compressive structures where the electromagnetic forces are directed mainly to the near-axis region or/and opposite to the plasma flow are intrinsically related to a particular operational mode. The plasma velocity and the density measurements, which illustrate dynamics of plasma stream deceleration and formation of compression zone with average electron density above 10^18 cm^-3, are in agreement with obtained distributions of the local electromagnetic forces.

[1] M.S. Ladygina et al. 2016 Phys.Scr. 91 (2016) 074006
[2] D.G. Solyakov et al. 2013 Plasma Phys. Rep. 39 986-92 [3] I.E. Garkusha et al. 2014 Phys. Scr. 161 014037

Speaker: Y. Volkova (EPS 2019)

143 P1.3012 Dust ion-cyclotron surface waves in semi-bounded (r q) distribution dusty plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3012.pdf

The effects of magnetic field strength, ion mass, and non-thermal character on the dispersion properties of dust ion-cyclotron surface wave are investigated in a semi-bounded (r, q) distribution dusty plasma. In the limit of short wave number, the dispersion relation is derived by employing the specular reflection boundary condition and the effective screening distance in (r, q) distribution dusty plasma. It is found that the stronger magnetic field strength suppresses the wave speed, but the heavier ions will enhance the wave propagation. The result would reduce to the case of Maxwellian plasma for r -> 0 and q -> infinity .

Speaker: Y. Jung (EPS 2019)

144 P1.3013 Effect of applied frequency on the number of micro-discharge in dielectric barriers discharge

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3013.pdf

Dielectric plasma discharge is used as a plasma reactor for surface modification, sterilization, germination, and ozone generation. The importance thing is plasma power controlling that is done by several ways such as voltage, frequency and pulse density of applying signal for plasma electrodes. This research is focus on the number of micro-discharge at difference frequency of applying signal. The measured resistor is installed between the electrode and negative port of power supply for measuring the signal of micro-discharge. The frequency is adjusted for 5 kHz, 8 kHz, 10 kHz, 12 kHz and 14 kHz and the number of microdischarge are 75.75, 60.50, 110.25, 270.25 and 297.25, respectively.

Speaker: K. Nilgumhang (EPS 2019)

145 P1.3014 Effect of electrode temperature on the generation of reactive gases and surface modification of polyimide film in an atmospheric dielectric barrier discharge plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3014.pdf

Atmospheric dielectric barrier discharge (DBD) plasma has been widely utilized in plasma bio-medicine due to generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), etc. These produced species would affect the dielectric materials by etching of dielectric surface. Polyimide (PI) is widely used as an electrode of DBD plasma source because of flexibility, good thermal resistance and permittivity.
To analyze the composition of the plasma and investigate the etched surface of PI, flexible copper clad laminates (FCCL) of Kapton ENC have been utilized, where plasma discharge conditions are the following: discharge voltage =10 kV, frequency = 5 kHz, duty = 5-10% working pressure = 760 mTorr in various electrode temperature, gas composition has been analyzed by two different spectroscopies: optical emission spectroscopy (OES) and Fourier Transform ≠ Infrared Spectroscopy (FT-IR). Various species such as O3, NO2, CO2 was generated as result of plasma-PI interaction. Etching surface of PI film was also observed by Scanning Electron Microscope (SEM).

Speaker: M. Lee (EPS 2019)

146 P1.3015 Effect of size of charged object on the propagation characteristics of precursor solitons

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3015.pdf

We address, the modifications in the propagation characteristics of precursor solitons due to the different sizes of the charged object. The experiments are performed in a -shaped Dusty Plasma Experimental (DPEx) [1] device where dusty plasma is created in a DC glow discharge Ar plasma using kaolin particles. A floating copper wire, is installed radially on midway of a long tray shaped cathode, acts as a charged object in the plasma environment. The flow on the dust fluid is initiated by suddenly lowering the potential of the charged object and as a result steady streaming solitons (precursor) radiates opposite to the flow. The size (height and width) of the potential hill is then varied by connecting a variable resistance in series with the wire to investigate the effect of propagations characteristics of these precursor solitons [2]. The amplitude, velocity and number of these precursor solitons decrease whereas the width increases with the decrease in height of the potential hill. All the experimental observations are qualitatively compared with the numerical solution of forced-Korteweg de Vries (f-KdV) model equation and it agrees quite well with the experimental findings.

1. S. Jaiswal, P. Bandyopadhyay, and A. Sen, Rev. Sci. Instrum. 86, 113503 (2015).
2. S. Jaiswal, P. Bandyopadhyay and A. Sen, Phys. Rev. E. 93, 041201 (2016).

Speaker: G. Arora (EPS 2019)

147 P1.3016 Electron capture by the exited hydrogen atom in the dense semiclassical partially ionized plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3016.pdf

The elementary processes in plasma have received considerable attention in many areas of physics such as astrophysics, atmospheric science, atomic physics, molecular physics, plasma physics, and surface sciences since the excitation and ionization of atoms and molecules have provided useful structural information on the collision systems as well as the physical information on environments of the collision systems. Especially, the electronimpact excitation of atoms in plasmas has been of a great interest since the emission spectra related to the excited atomic states would provide the useful information on plasma parameters, such as plasma density and temperature. Recently, the physical characteristics and properties of quantum plasmas have been extensively explored since the dense quantum plasmas are ubiquitous and have been found in nano-scale objects in modern science and technology, such as nano-devices, nano-wires, quantum dots, and semiconductor devices as well as astrophysical compact objects. One of the elementary processes in plasma is the electron capture process. In this work, the electron capture processes by the exited hydrogen atom was investigated. Here we took into account the polarization of the exited atom in different quantum-mechanical states. The motion of the electron in the field of the motionless atom was considered on the basis of the perturbation theory and the solving of the equation of motion. The interaction potentials between the electron and the hydrogen atom, taking into account the quantum-mechanical effect of diffraction and plasma screening effects, were presented in works [1-4]. In this work, the electron capture radius, which was determined by equating the kinetic energy of impacting electron and the interaction energy between the electron and the hydrogen atom, was presented. The trajectory of the electron in the field of the atom was simulated [4]. Using the electron capture probability, the electron capture cross section was calculated.

References
[1] T. S. Ramazanov, K. N. Dzhumagulova, Y. A. Omarbakiyeva, Physics of Plasmas 2005, 12, 092702.
[2] E.O. Shalenov et. al., Contrib. Plasma Physics 2017, 57, 486.
[3] E. O. Shalenov et. al., Physics of Plasmas 2018, 25, 082706.
[4] M. M. Seisembayeva, K. N. Dzhumagulova and T. S. Ramazanov, Nukleonika 2016, 61, 201.

Speaker: K. Dzhumagulova (EPS 2019)

148 P1.3017 Toroidal plasmoid generation via extreme hydrodynamic shear

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3017.pdf

Saint Elmo's fire and lightning are two known forms of naturally occurring atmospheric pressure plasmas. As a technology, non-thermal plasmas are induced from artificially created electromagnetic or electrostatic fields. Here we report the observation of arguably a new case of a naturally formed such plasma, created in air at room temperature without external electromagnetic action, by impinging a high-speed microjet of de-ionized water on a dielectric solid surface. We demonstrate that tribo-electrification from extreme and focused hydrodynamic shear is the driving mechanism for the generation of energetic free electrons. Air ionization results in a plasma that, unlike the general family, is topologically well-defined in the form of a coherent toroidal structure. Possibly confined through its self-induced electromagnetic field, this plasmoid is shown to emit strong luminescence and discrete-frequency radio waves. Our experimental study suggests the discovery of a novel platform to support new experimentation in low-temperature plasma science.

References
[1] Gharib M, Mendoza S, Rosenfeld M, Bezai M, Alves Pereira F (2017). Toroidal Plasmoid Generation Via Extreme Hydrodynamic Shear. Proceedings of the National Academy of Sciences, 114(48): 12657-12662.

Speaker: F. Alves Pereira (EPS 2019)

149 P1.3018 First experiments on dusty plasmas in the D-Mag magnet

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3018.pdf

In the past years the study of dusty plasmas under strong magnetic fields has gained increased interest. Dusty plasmas consist of nanometer to micrometer sized particles that acquire high negative charges due to the inflow of plasma electrons and ions. To reveal magnetization effects of the dust species high magnetic field strengths are required. In Greifswald, recently, the DMag magnet has been installed that allows to generate homogeneous magnetic fields up to 6 T.
Experiments at these field strengths have been performed using micrometer-sized dust particles immersed in an argon rf discharge plasma. Despite the strong field, magnetization of the dust species is not expected due to its large mass. However, electrons and ions will be magnetized and the influence of these magnetized plasma species on the dust will be investigated.
Our first results of dust systems under strong magnetic fields will be presented. This includes investigations of the dynamics of finite dust clusters as well as the dynamics of dust-density waves.

Speaker: A. Melzer (EPS 2019)

150 P1.3019 Discharge initiation by a laser pulse in a vacuum gap

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3019.pdf

Laser-induced discharge within a vacuum gap of few millimeters between electrodes is experimentally studied. The discharge is triggered by 1064 nm Nd:YAG laser pulses with intensities varied from 10^7 W/cm^2 to 10^9 W/cm^2 on the surface of titanium target electrode. The current formation time dependences from both the gap length and the residual gas pressure at a fixed electrode voltage were determined. Residual gas pressure varied from 10^-6 to 10^-2 torr, and voltage varied from 100 V to 5 kV. The dependences of current formation time on the laser pulse intensity and the voltage difference on the electrodes of different polarity are presented. The laser intensity thresholds for discharge are determined in our experimental conditions. In addition, we conducted the probe diagnostic of the laser plasma induced on the titanium target surface and inferred about the process of the discharge initiation by a laser pulse in a vacuum gap.

Speaker: A. Katorov (EPS 2019)

151 P1.3020 Microwave pulse compression based on laser-induced breakdown

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3020.pdf

Microwave Pulse Compressor (MPC) is an high power microwave device designed for generation of 100's of MW's thru amplification. The amplification is based upon time compression of an initial Microwave (RF) pulse characterized by a long (µsec) duration to a short (ns) output pulse, ideally increasing the RF power by the duration ratio of the pulses.
In order to accumulate RF power and radiate it outside a pressurized RF resonator we use a Qswitch method based on laser induced plasma channel. The RF pulse initiate a discharge in the gas, pre-ionization using microwave pulse, where a short (ns) laser pulse induce breakdown by a thin plasma channel which switch the resonator from a storage phase to a release phase, i.e. sufficient to reduce the Q factor of the resonator.
We demonstrate experimentally an efficient way to cause a discharge in the pressurized gas by focusing a short 2ns laser pulse inside the MPC volume. We have investigated the evolution of the plasma channel by means of gated MCP intensified CCD framing camera of ~1.5ns exposure time (4quikE camera). We found that as the accumulated energy inside the resonator increases, the time delay between lasing and switching decreases. Furthermore, stronger initiative RF pulse results in a stronger and spatially larger luminesce of the plasma channel. Using a spatialtemporal processing of the plasma luminesce imaging we were able to simulate this phenomenon by 2D-Lsp hybrid PIC modeling where we assume that the resonator is pressurized with gas, uniformly distributed background electron density of 10^3cm^-3 and seed electrons density occupying the laser focal region. Electron impact ionization develops self consistently with the oscillating RF field which eventually creates a plasma channel sufficient for the MPC switching. We fitted the seed electron density and the volume of the focal region to match the experimental results.

Speaker: E. Maguid (EPS 2019)

152 P1.3021 Diffusion coefficient of tungsten atoms in argon

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.3021.pdf

We present an experiment, based on laser induced fluorescence spectroscopy, developed to register small concentrations of atomic Tungsten and to determine its transport properties (diffu- sion coefficients) in various buffer gases. A pulsed tunable dye laser is routed through a hollow cathode where tungsten atoms are sputtered in a pulsed-mode gas discharge. The laser is tuned to a preselected resonance line and its pulses are triggered with a delay after the end the dis- charge pulse. The resulting fluorescence of the atoms is registered by varying the time delay, thus observing the decay of the concentration of particles. The completed experimental setup, the results acquired so far and future plans will be presented. The method is still to be developed to diagnose the absolute concentration of Tungsten atoms, which would be helpful to evaluate the contamination in the working volume of plasma devices.
This work was supported by the National Science Fund of Bulgaria through project No. DN 18/12 2017.

Speaker: A. Georgiev

153 P1.4001 Gyrokinetics of electron-positron plasmas in a magnetic Z-pinch: towards a turbulence free plasma?

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4001.pdf

Gyrokinetic stability of plasmas in a Z-pinch magnetic geometry is studied numerically using the GENE code [1] with a particular focus on the behaviour of "pair plasmas" consisting of positrons and electrons. Importantly, the simulations presented here are potentially applicable to dipole systems such as the upcoming APEX experiments investigating pair plasma confinement [2]. The numerical analysis is performed using a local flux-tube approximation with both plasma species being treated kinetically in a regime dominated by electrostatic fluctuations driven by spatial gradients in the density and temperature profiles. We first examine the linear stability of such plasmas, varying the mass ratio between the positive and negative charge carriers, from conventional hydrogen plasma through to electron-positron plasma. We provide the first numerical support of analytic theory predicting that electron-positron plasmas can be absolutely stable in certain regions of parameter space which may be accessible during the APEX experiments. We also study the stability of electron-positron plasmas in a standard model tokamak configuration to elucidate the favourable peculiarities of the Z-pinch geometry for pair plasma confinement. The insight gleaned from these linear simulations is then used to undertake a comprehensive study on the nonlinear behaviour of two different pair plasma scenarios: (i) an unstable plasma with an outwards heat flux and an inwards particle flux - the so called "inward pinch" known to exist in conventional plasmas which we report on here for the first time in pair plasmas. (ii) an unstable plasma without the inward pinch feature.

References
[1] F. Jenko, W. Dorland, M. Kotschenreuther and B. N. Rogers, Physics of Plamsas 7, 5 (2000)
[2] T. S. Pedersen, A. H. Boozer, W. Dorland, J. P. Kremer and R. Schmitt, Journal of Physics B: Atomic, Molecular and Optical Physics 36, 5 (2003)

Speaker: D. Kennedy (EPS 2019)

154 P1.4002 Do we know how to simulate fusion plasma?

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4002.pdf

Since more than three decades, numerical simulations of fusion plasmas have undergone significant development. Nowadays, access to the High-Performance Computing facilities allows one to model realistic plasma scenarios. The questions perhaps remain open about verification and validity of the results obtained from the numerical simulations.
It has been proved that the gyrokinetic models accurately predict violent, turbulent transport in the core region of a tokamak [1]. However, understanding of the processes in the edge of fusion devices, e.g. transition towards the high confinement mode with drastically increased plasma confinement, still be lacking. Several groups undertake the gyrokinetic simulations of the edge region across the world [2, 3, 4]. However, the codes models suitable for the core of the tokamak are unsuitable for simulations of the edge region. Indeed, the models for the edge should include electromagnetic effects and be fully non-linear. There exist no gyrokinetic code nowadays, possessing a self-consistent, energy conserving electromagnetic full-f model.
In this talk the two fold theoretical framework [5] for gyrokinetic models verification suitable for large spectrum of gyrokinetic codes will be presented for the edge modelling. It will be shown how the use of Hamiltonian and Lagrangian tools helps to prevent all the bottlenecks related to the models implemented in gyrokinetic simulations. Examples of test cases and simulations allowing to identify limits of currently implemented gyrokinetic models applications will be given for ORB5 code.

References
[1] X. Garbet, Y. Idomura, L. Villard, and T. H. Watanabe, Nuclear Fusion, 50, 043002 (2010)
[2] D. R. Hatch et al , Nucl. Fusion, 57, 036020 (2017)
[3] Q. Pan and D. Told and F. Jenko, Physics of Plasmas, 23, 102302 (2016)
[4] L. Villard and B. F. McMillan, E. Lanti et al, PPCF, 6, 3 (2019)
[5] N. Tronko, A. Bottino, T. Goerler, et al, Physics of Plasmas, 24, (2017)

Speaker: T. Natalia (EPS 2019)

155 P1.4003 Excitation of a plasma wakefield by incoherent radiation via Compton scattering

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4003.pdf

We show from first principles that an incoherent photon pulse traversing a plasma can excite a plasma wake via Compton scattering. We distinguish two regimes: i) the non-relativistic regime, where the incoherent photons have energy below the electron rest mass, and ii) the relativistic regime, where the incoherent photons have energy larger that the electron rest mass. In the first regime, the displacement of the plasma electrons due to the photon-electron scattering events is smaller than the electron inertial length and the wake is established likewise the ponderomotive force of a laser would do. In the second regime, the displacement of the plasma electrons due to the photon-electron scattering events is larger than the electron inertial length, this loads over time a relativistic electron beam that almost co-propagates with the incoherent photon pulse. Here the wake is driven by the loaded electron beam which grows in charge as the photon driver propagates. This fundamental mechanism may have implications both in wakefield accelerator technology, where an incoherent pulse of photons could replace a laser (coherent driver), and in astrophysics as an acceleration engine of particles alongside already known processes (e.g. magnetic reconnection, shock acceleration, etc ...). We illustrate these processes via the recently implemented Compton scattering module into the PIC code OSIRIS 4.0 [1], following the pioneer numerical work of Frederiksen [2]. This enables us to couple self-consistently and from first principles the interaction of the incoherent photons with the plasma. We have also derived from linear perturbation theory the average momentum transfer from the photon pulse to the plasma electrons, the amplitude of the perturbed electron density and the accelerating field strength. Our simulations show excellent agreement with the analytical estimates.

References
[1] R. Fonseca et al., Lecture Notes in Comput. Sci. 2331, 342 (2002)
[2] J. T. Frederiksen, The Astrophysical Journal 680 , L5 (2008)

Speaker: F. Del Gaudio (EPS 2019)

156 P1.4004 Effects of involved laser photons on radiation and electron-positron pair production in one coherence interval in ultra intense lasers

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4004.pdf

Electron radiation and gamma photon annihilation are two of the major processes in ultra-intense lasers (UIL). Understanding their behaviour in one coherence interval (CI) is the basis for UIL-matter interaction researches. However, most existing analytic formulae only give the average over many CIs. Present understanding of these two multi-photon processes in one CI usually assume that they emit forward and their spectra have a cutoff at the energy of the electron/. Such assumptions ignore the effects of involved laser photons (EILP). We deduced the formulae for these two processes in one CI with EILP included and give the conditions for the EILP to be significant. Strong EILP introduces new behaviours into these two processes in one CI, such as large angle emission and emit particles above the usually assumed cutoff. Simulations show that the EILP would be significant when laser intensity reaches 2x10^22W/cm^2, which is within the reach of state-of-art lasers.

Speaker: B. Zhang (EPS 2019)

157 P1.4005 Design and progress toward realization of a high Tc superconducting levitated dipole experiment for electron-positron plasma studies

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4005.pdf

Theory predicts that a magnetically confined electron-positron plasma with short Debye length will be remarkably stable and exhibit unique wave physics. The APEX (A PositronElectron eXperiment) project is progressing toward an experimental realization of such a system to test some of those predictions. In this contribution, we report on the design and progress toward realization of, what will be the world's smallest levitated dipole experiment to date. It will employ a magnetically levitated high-Tc superconducting coil with a radius of 7.5 cm and a mass of 1.6 kg. With field strengths approaching 1 T on the inboard region of the dipole, well-confined positronelectron plasma with temperatures in the range of 5 eV and densities of order 10^7 cm^-3 with short Debye lengths compared to the system size (minor radius of 5 cm) are targeted. Positrons from a reactor-based source will be accumulated in a buffer-gas trap, injected into the dipole trap in pulses where an electron plasma will be prepared in advance. Diagnostics that take advantage of 511 keV annihilation gamma rays are in the design stage. Experiments with a prototype permanent magnet trap have demonstrated successful positron injection using ExB drifts and well-confined single-particle orbits, giving us confidence that the levitated dipole experiment concept is sound.

Speaker: M.R. Stoneking (EPS 2019)

158 P1.4006 Hidden momentum and conservation laws in relativistic spin-1/2 plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4006.pdf

In both high-intensity laser-matter interactions [1-3] and astrophysical environments with very strong magnetic fields [4], it may be necessary to consider both relativistic effects and the electron spin. To this end, a kinetic model was developed recently [5], based on the FoldyWouthuysen transformation [6, 7] that separates positive and negative energy states of the Dirac equation.
We show [8] that this model conserves electric charge, energy, linear momentum, and angular momentum. In doing so, we find "hidden momentum" [9, 10], a general feature of systems with magnetic moments. We also find that the stress-energy tensor is non-symmetric, common to systems with spin angular momentum. We discuss the non-symmetry of the stress-energy tensor, how to find a symmetric alternative; and touch on the Abraham-Minkowski dilemma.

References
1 D. D. Sorbo, D. Seipt, A. G. R. Thomas, and C. P. Ridgers, Plasma Physics and Controlled Fusion 60, 064003 (2018).
2 M. W. Walser, D. J. Urbach, K. Z. Hatsagortsyan, S. X. Hu, and C. H. Keitel, Phys. Rev. A 65, 043410 (2002).
3 M. Wen, H. Bauke, and C. H. Keitel, Sci. Rep. 6, 31624 (2016).
4 A. K. Harding and D. Lai, Rep. Prog. Phys. 69, 2631 (2006).
5 R. Ekman, F. A. Asenjo, and J. Zamanian, Phys. Rev. E 96, 023207 (2017).
6 L. L. Foldy and S. A. Wouthuysen, Phys. Rev. 78, 29 (1950).
7 A. J. Silenko, Phys. Rev. A 77, 012116 (2008).
8 R. Ekman, H. Al-Naseri, G. Brodin, and J. Zamanian, (in preparation).
9 W. Shockley and R. P. James, Phys. Rev. Lett. 18, 876 (1967).
10 D. Babson, S. P. Reynolds, R. Bjorkquist, and D. J. Griffiths, Am. J. Phys. 77, 826 (2009).

Speaker: R. Ekman (EPS 2019)

159 P1.4007 3-dimensional modelling of lightning strike waveform C

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4007.pdf

It is estimated that a commercial aircraft will experience a lightning strike event once per year. This poses a significant risk to poorly conducting, carbon-fibre composite aircraft structures. The most widely adopted approach of providing lightning strike protection, on composite aerostructures, is through the embedding of a metallic mesh on the aircraft's aerodynamic surfaces. This adds weight and maintenance costs and the aerospace industry is seeking alternative solutions. The objective of this research is to develop the computational tools required to simulate the physics and environment of the thermal plasma channel formed during a lighting strike. This will yield accurate boundary conditions for the virtual testing of composite structures subjected to a lightning strike, enabling a more accurate assessment of potential damage arising.
A numerical approach using OpenFOAM for the modelling of atmospheric thermal plasma was undertaken. The custom built solver couples Maxwell's equations to the Navierstokes equations through the Lorentz body force, before solving the energy equation with thermal contributions from resistive heating in the air gap. The solver is capable of both steadystate and transient simulation of 3-dimensional, incompressible, laminar flows. The model replicates the experimental configuration for laboratory strike testing and uses the Society of Automotive Engineers (SAE) standard current waveform C as the basis for the simulation.
Temperature dependent properties for the air mixture is calculated up to a maximum temperature of 24,000 K and integrated into the solver. The air composition for 11 different species is equilibrated for a range of temperatures and pressures through the open-source software package Cantera [1]. Electron swarm parameters are then calculated through a Boltzmann equation solver, BOLSIG+[2], from the composition fractions.
The solver's capability is benchmarked against electromagnetic problems from literature and presented are the surface profiles generated by a waveform C strike test.

[1] D. G. Goodwin, H. K. Moffat, and R. L. Speth, "Cantera: An object-oriented software toolkit for chemical kinetics, thermodynamics, and transport properties." 2017.
[2] G. J. M. Hagelaar and L. C. Pitchford, "Solving the Boltzmann equation to obtain electron transport coefficients and rate coefficients for fluid models," Plasma Sources Sci. Technol., vol. 14, no. 4, pp. 722-733, 2005.

Speaker: J. Campbell (EPS 2019)

160 P1.4008 Optimizing injection of positrons into a magnetic dipole trap

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4008.pdf

In a pair plasma, the two oppositely charged particle species have a mass ratio of one. This property is predicted to have significant influence on the behavior of such a plasma including extraordinary stability characteristics [1]. APEX (A Positron-Electron Experiment) aims to create this kind of plasma in a magnetic dipole trap. Because the number of available positrons is the limiting factor to reach plasma densities, it is essential to be able to inject positrons as efficiently as possible into the confinement volume. Unfortunately, the physics that confines charged particles in the dipole also makes their injection from the outside challenging. Recently, lossless injection [2] of the steady positron beam of NEPOMUC [3] into the confinement volume of the magnetic field of a supported permanent magnet was achieved by utilizing the E◊B guiding-center drift and optimizing the electrostatic potentials of the surrounding electrodes. Moreover, confinement times exceeding 1s were observed [4]. These findings were accompanied and reproduced by single-particle simulations. On this basis, numerical studies for the next-generation experiments were carried out. The results promise improved confinement times and suggest that the accumulation of positrons from multiple pulses is potentially feasible in the dipole.

1. P. Helander, Microstability of Magnetically Confined Electron-Positron Plasmas, Phys. Rev. Lett. 113, 135003 (2014).
2. E.V. Stenson, S. Nifll, U. Hergenhahn, J. Horn-Stanja, M. Singer, H. Saitoh, T. Sunn Pedersen, J.R. Danielson, M.R. Stoneking, M. Dickmann, and C. Hugenschmidt, Lossless Positron Injection into a Magnetic Dipole Trap, Phys. Rev. Lett. 121, 235005 (2018).
3. C. Hugenschmidt, C. Piochacz, M. Reiner, and K. Schreckenbach, The NEPOMUC upgrade and advanced positron beam experiments, New J. Phys. 14, 055027 (2012).
4. J. Horn-Stanja, S. Nifll, U. Hergenhahn, T. Sunn Pedersen, H. Saitoh, E.V. Stenson, M. Dickmann, C. Hugenschmidt, M. Singer, M.R. Stoneking, and J.R. Danielson, Confinement of Positrons Exceeding 1 s in a Supported Magnetic Dipole Trap, Phys. Rev. Lett. 121, 235003 (2018).

Speaker: S. Nißl (EPS 2019)

161 P1.4009 Predicting the topology of self-organization in plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4009.pdf

Complex braided magnetic structures are known to self-organize in plasmas. Through often violent reconnection events, an elaborate braid can detangle itself to form straight flux tubes. Despite our advanced knowledge of plasma physics today, it remains unclear how to predict the topology of the magnetic structure after self-organization. Although it has been conjectured [1] that ultimately the topology is described by only two flux tubes with opposite helicity, recent studies [2, 3] have identified additional constraints. In this study, we simulate the self-organization process with prescribed magnetic braids as initial states. We use a measure called the field line helicity to trace the time-dependent topology in the model. We find that the magnetic relaxation (i.e. re-arrangement) happens in discrete stages. Resistivity and boundary conditions both affect the reconnection events and the resulting topology. Also, the topological evolution in 3D can be described qualitatively by a 2D analogous model with different timescales.

References
[1] E. N. Parker, Ap. J., 264:635-641 (1983).
[2] A. R. Yeates, G. Hornig and A. L. Wilmot-Smith, PRL105, 085002 (2010).
[3] A. R. Yeates, A. J. B. Russell and G. Hornig, Proc. R. Soc. A 471, 20150012 (2015).

Speaker: L. Chen (EPS 2019)

162 P1.4010 Laser-driven shock compression of water ammonia and water-ethanol-ammonia mixtures to probe the interiors of icy giant planets

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4010.pdf

Water, methane, and ammonia are amongst the key components of Uranus and Neptune. Knowing their equation of state, conductivity, and transport properties at planetary interiors conditions (pressures of several megabar and temperatures of a few thousand Kelvin) is required for developing precise models of the two planets, with the aim of explaining their puzzling structures, magnetic fields, and luminosities [1]. The physical and chemical behaviour of such mixtures at extreme pressures and temperatures is not only important for planetology but also interesting on its own, since those conditions are characterised by the coexistence of dissociated atoms, atomic clusters and chains. This regime is very difficult to study via ab initio simulations and experimental verifications are thus required.
Using laser-driven shocks, we compressed up to 3 Mbar pure water, pure liquid ammonia, and a C:H:N:O mixture composed by water, ethanol, and ammonia. Their principal Hugoniot curves have been explored using the decaying shock technique. Moreover, off-Hugoniot states have been reached via a double-shock technique and through the coupling of dynamic and static compression in diamond anvil cells. The experiments were performed at the LULI2000 laser facility employing standard rear-side optical diagnostics (Doppler velocimetry, optical pyrometry). The equation of state and the shock-front reflectivity have been measured, allowing an estimation of the electrical conductivity.
Our results show that water and the C:H:N:O mixture share similar Hugoniot curves with a trivial density scaling, while the reflectivity behaves differently in both the onset pressure and the saturation value. The experimental study of the structural and optical properties of shockcompressed ammonia essentially confirms the predictions of recent ab initio simulations [2]. The consequences for the modelling of the interiors of the icy giant planets will be discussed.

References
[1] T. Guillot, Annu. Rev. Earth Planet. Sci. 33, 493 (2005)
[2] D. Li, P. Zang, and J. Yan, The Journal of Chemical Physics 139, 134505 (2013)

Speaker: M. Guarguaglini (EPS 2019)

163 P1.4011 Generation of gravitational waves using high-power lasers

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4011.pdf

Gravitationnal waves have been predicted from Einstein's equations since he wrote his theory on General Relativity [1]. A century later, the LIGO [2] and VIRGO interferometers were at last able to pick up a gravitationnal wave from the merging of extremely massive astrophysical objects. The existence of gravitationnal waves now being proved, there is a need to study these waves to better understand how gravitation works, and fondamentally how does the geometry of space-time exactly affects physical phenomenons.
However, observations still rely on the occurrence of a rare and intense astrophysical phenomenon, as if, as a comparison, the only reliable source of observation for high energy photons were gamma-ray bursts. An interesting possibility would be to generate and detect gravitationnal waves in laboratory, which would allow for a more controlled environment for the observation of gravitationnal waves. Unfortunately, deplacements of matter generated in laboratory do not seem to have a big enough yield to allow any detection [3].
Continuing on the path led in 1962 by Gertsenshtein [4] and more recently in a study by Kolosnitsyn and Rudenko [5], we will here evaluate if the generation of gravitationnal waves by light only is a good alternative to the deplacement of mass. We will then discuss on the possibilities of an experiment making use of the peculiar aspects of light only gravitational waves generation and bring more details on what could be a new interesting way to look for gravitationnal waves in the laboratory, but also in the universe. High-power lasers present themselves as an interesting answer for the needs of a source for gravitational wave generation, as they can provide coherent ultra high intensity light beams.

[1] A. Einstein. Sitz. Preuss. Akad. Wiss. Berlin, (1918)
[2] B.P. Abbott et al. Phys. Rev. X 6, (2016)
[3] X. Ribeyre, V. T. Tikhonchuk. WSPC, (2010); E. G. Gelfer et al., Physics of Plasmas, 23, (2016)
[4] M. E. Gertsenshtein. Soviet Phys. JETP, (1962)
[5] N. I. Kolosnitsyn, V. N. Rudenko. Phys. Scr., 90, (2015)

Speaker: P. Lageyre (EPS 2019)

164 P1.4012 Characteristics of uphill diffusion with low frequency fluctuation in dipole magnetic field

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4012.pdf

The Ring Trap 1 (RT-1) device creates a laboratory magnetosphere that is realized by a levitated superconducting ring magnet in vacuum [1]. The RT-1 experiment has demonstrated the self-organization of a plasma clump with a steep density gradient; a peaked density distribution is spontaneously created through 'uphill diffusion' [2, 3]. Understandings of particle transport are essential element of confinement physics in the high-performance plasmas. The main purpose of our study is to reveal particle transport characteristics in the RT-1 magnetospheric plasmas.
The dynamical process of the uphill particle transport has been analyzed by injecting tracer gas into helium plasmas. At t = 1.1 sec, the helium gas is puffed during 5 msec. For the spacial profile of electron density, the line-integrated electron densities measured in one horizontal (r =0.45 m) and two vertical (r = 0.62 and 0.70 m) chords are reconstructed by a model function of magnetic flux surfaces [3, 4]. The spacial profiles reveal that the increase in electron density is clearly appeared at r = 0.55 m after the gas injection from t = 1.1 sec to t = 1.4 sec. We observe simultaneous excitation of low frequency (about 1.0 kHz) fluctuations in both electron density and magnetic measurements. The low frequency fluctuations are localized in the peripheral region of the peaked density profile, which suggests the localized fluctuations drive the uphill diffusion. Furthermore, magnetic proves in a toroidal array show the spatiotemporal structure of the low frequency fluctuations in the direction of magnetic field line. The magnetic probe array identified that (1) the toroidal mode number of the fluctuation is m = 5 in the plasma whose local electron beta e = 0.02 0.18, (2) the phase velocity of the fluctuation is 1100 m/s in the electron diamagnetic direction, and (3) both the amplitude and the frequency of the fluctuation increase as the increase of the local e value. We will report the characteristics of uphill diffusion considering the simultaneous fluctuations in the dipole magnetic field.

References
[1] Z. Yoshida et al. Phys. Plasmas 17, 112507 (2010)
[2] M. Nishiura et al. Nucl. Fusion 55, 053019 (2015)
[3] M. Nishiura et al. Nucl. Fusion 57, 086038 (2017)
[4] H. Saitoh et al. Phys. Plasmas 22, 024503 (2015)

Speaker: N. Kenmochi (EPS 2019)

165 P1.4013 Different dynamic regimes of stimulated electron-cyclotron emission from mirror-confined non-equilibrium plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4013.pdf

Electron cyclotron instabilities caused by resonant interaction between energetic electrons and electromagnetic waves are typical for plasma confined in open magnetic configurations. Studies of the cyclotron instabilities of non-equilibrium plasmas have led to the plasma cyclotron maser paradigm, which explains a rich class of phenomena of coherent radio emission from the Earth's magnetosphere, from other astrophysical objects, and from laboratory magnetic traps. In the present communication, we discuss the laboratory experiment on a controlled transition from the generation of periodic bursts of electromagnetic radiation into continuous-wave regime of a cyclotron maser [1]. The kinetic cyclotron instability of weakly inhomogeneous magnetized plasma is driven by the anisotropic electron population resulting from the electron cyclotron plasma heating in MHD-stable minimum-B open magnetic trap. The observed non-trivial dynamics may be caused by the temporal modulation of the electron distribution function due to excitation of unstable kinetic modes [2]. Within this theoretical frame, the transition between the burst and cw regimes of the electron cyclotron instability is related to the Poincae-AndronovHopf bifurcation, i.e., a stationary point attributed to cw generation becomes unstable through the birth of a stable limit cycle. In this paper, basing on new experimental data, we discuss new, more complicated, regimes of instability. Similar systems have been previously studied in the context of space cyclotron masers in planet magnetospheres [3,4]. However, a laboratory experiment is characterized by a very different mechanism providing a source of non-equilibrium electrons, and thus the existing theory needs to be reconsidered.

The work is supported by RFBR (project no. 19-02-00767).

[1] Shalashov A. G. et al., Phys. Rev. Lett., 114 205001 (2018)
[2] Shalashov A.G. et al., Eur. Phys. Lett., 124 (3) 35001 (2018)
[3] Bespalov P. A., Phys. Scripta, T2/2 576 (1982)
[4] Trakhtengerts V. Yu. and Rycroft M. J., Whistler and Alfven mode cyclotron masers in space. Cambridge University Press, NewYork, 2008

Speaker: E.D. Gospodchikov (EPS 2019)

166 P1.4014 Magnetosonic shocks in laboratory astrophysics experiments at the Prague Asterix Laser System

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4014.pdf

Shock formation through the interaction of supersonic plasma jets with ambient plasma is ubiquitous in astrophysics. Since magnetic fields often play a role in these systems, it is of particular interest to understand how they affect the formation and evolution of shocks. An investigation of magnetized shocks has been carried out using the iodine laser at the Prague Asterix Laser System (PALS) facility. Collimated supersonic plasma jets have previously been observed at PALS, and it has been shown that when such jets interact with a gas target, supersonic shocks can be generated [1]. The present work builds on these experiments by including a perpendicular ambient magnetic field of B 10 T, with particular focus on the effect on the shock compression ratio, and magnetic field enhancement in the interaction region. The third harmonic (lambda = 0.438 µm) of the laser was used for the main beam, with pulse duration tao = 250 ps, energy on target E_L= 15-100 J, intensity I_L ~ 10^14 Wcm^-2, and a focal spot radius of rL= 300 µm. Solid copper targets were used for the plasma jet formation, and argon/helium with pressure of P= 1040 bar for the gas target. The temporal evolution of the shock was observed using three frame shadowgraphy/interferometry, an X-ray streak camera, and a four frame XUV pinhole camera. The optical diagnostics could alternatively be set up for single-frame interferometry and polarimetry, thereby providing simultaneous measurements of density and magnetic field. The experiment has been simulated with a radiation magnetohydrodynamic code including laser energy deposition. The data concerning compression of the plasma and magnetic field in the bow shock are compared with the experiment, thus providing scaling to astrophysical conditions.

References
[1] Ph. Nicolaï, C. Stenz, A. Kasperczuk et al, Physics of Plasmas 15, 082701 (2008)

Speaker: H. Bohlin (EPS 2019)

167 P1.4015 Transition to collisionality, magnetic fields generated by the Biermann battery and the Weibel instability

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4015.pdf

In recent years, experiments with laser-target interactions create plasma with extremely strong magnetic fields (~ MGauss). With these conditions, and the unprecedented resolution that these experiments can now operate, we are able to probe physics that also occurs in astrophysical systems. In particular, the generation of these magnetic fields via the Biermann battery and the Weibel instability. Although intense short pulse lasers are capable of creating plasmas that are so hot that the particles are essentially collisionless, and kinetic physics is essential, the transition between such collisionless and collisional systems is not fully understood.
We have investigated the generation of magnetic fields in an expanding plasma bubble with misaligned density and temperature gradients, using a Monte-Carlo collision module integrated with particle-in-cell simulations. In addition to magnetic fields generated by the Biermann battery, temperature gradients lead to temperature anisotropies that drive the Weibel instability. This mechanism is only expected in collisionless plasmas, as the temperature anisotropies are washed away by collisions. We show how collisional the plasma must be to suppress the Weibel instability. The growth rate of the Weibel instability is itself modified by the collision rate for a constant anisotropy, verified by particle-in-cell simulations. However, the reduced anisotropy is the major cause of measured reduction of growth rate. In collisional systems, the anisotropy grows at a slower rate than a collisionless system, leading to a weaker anisotropy when the Weibel instability begins to develop. We confirm that the Weibel instability is suppressed when the collision rate approaches the rate of anisotropy growth in a collisionless system (i.e. the thermal crossing time), which leaves the Biermann battery as the dominant source of magnetic fields.

Speaker: K.M. Schoeffler (EPS 2019)

168 P1.4016 Magnetized Rayleigh-Taylor instability driving particle acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.4016.pdf

MegaGausslevel magnetic fields applied to laser produced plasmas are opening the door to a range of new studies in inertial confinement fusion and laboratory astrophysics. Our experiments and related theoretical work have addressed the physics of magnetized accretion flows [1], jet collimation [2, 3] and variability [4], and more recently, iondriven streaming instabilities and particle acceleration. In this paper we shall discuss the acceleration of charged particles in colliding plasma flows generated by irradiating with a nslaser, two oppositely facing solid targets. The expanding plumes are collimated into jets by an externally imposed 20 T magnetic field and the collision of the two jets generates a region of strong shocks and turbulence. Measurements using a Thomson parabola indicate particles with energies up to ~1MeV. To understand the mechanisms leading to the acceleration of the particles, simulations are performed with the 3D resistive MHD code GORGON coupled with a testparticles solver. The dynamics of the plasma and how the particles get their energy will be presented. Notably we find that the magnetized RayleighTaylor instability can drive expanding plasma spikes that energize particles by a Fermitype acceleration mechanism. Possible implications for astrophysical systems will be discussed.

References
[1] Revet et al., Science Advances, Vol. 3, no. 11, e1700982 (2017)
[2] Ciardi et al., Physical Review Letters, 110, 025002 (2013)
[3] Albertazzi et al., Science, Vol, 346, Issue 6207, pp. 325328 (2014)
[4] Higginson et al., Physical Review Letters, 119, 255002 (2007)

Speaker: J. Capitaine (EPS 2019)

16:00 Coffee Break

BPIF

Convener: K. Lancaster

169 I1.201 Relativistic nanophotonics: creating extreme plasma conditions from nanostructures with ultrafast lasers

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.201.pdf

The trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays can volumetrically heat dense matter into a new ultra-hot plasma regime [1]. Electron densities more than 100 times greater than the critical density with multi-keV temperatures are achieved using ultrashort laser pulses of only one Joule energy. Extraordinarily high degrees of ionization (e.g. 52 times ionized Au) are observed with gigabar pressures only exceeded in the laboratory in the central hot-spot of highly compressed thermonuclear fusion plasmas. The fundamental physics of relativistic laser pulse interactions with nanostructures and their promising applications will be reviewed. The large electron density, which shortens the radiative lifetime\combined with the large plasma volume that increases the hydrodynamic cooling time allow for greatly increased conversion into x-rays. Recent experiments in which gold nanowire arrays were heated by ultra-high contrast pulses at intensities of ~ 4 x 10^19 W cm^-2 produced record 20 percent conversion efficiency into picosecond x-ray pulses [2]. In a different set of experiments the acceleration of deuterons from a dense deuterated nanowire array to MeV energies resulted in a record number of monochromatic fusion neutrons per Joule for a compact laser. The neutron production was 500 times larger than that obtained irradiating flat solid targets of the same material (CD2) with the same laser pulses [3]. Results of the first experiments conducted at an increased intensity of ~ 5 x 10^21 W cm^-2 with ultra-high contrast pulses from a frequency-doubled petawatt-class laser will be presented and compared with 3-D relativistic particle-in-cell simulations.
Work supported by the U.S. Department of Energy, Fusion Science program of the Office of Science and by the Air Force Office of Scientific Research.

1. M.A. Purvis, et al., "Relativistic plasma nano-photonics for ultra-high energy density physics," Nature Photonics 7, 796, (2013).
2. R. Hollinger et al., "Efficient picosecond x-ray pulse generation from plasmas in the radiation dominated regime". Optica. 4, 1344, (2017).
3. A. Curtis, et al. , "Micro-scale fusion in dense relativistic nanowire array plasmas". Nature Communications. 9, 1077, (2018).

Speaker: J.J. Rocca (EPS 2019)

170 I1.202 Advanced laser-driven ion sources and their applications in materials and nuclear science

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.202.pdf

The investigation of superintense laser-driven ion sources and their potential applications offer unique opportunities of multisciplinary research [1]. Plasma physics can be combined with materials and nuclear science, radiation detection and advanced laser technology, leading to novel research challenges of great fundamental and applicative interest. In this contribution, the main results obtained so-far within the framework of the ERC ENSURE project will be presented. Numerical simulations and experimental activities carried out at 100s TW and PW-class laser facilities [2,3] have shown that targets consisting in a solid foil coated with a nanostructured low-density (near critical) foam can lead to an enhancement of the ion acceleration process. Thanks to a deep understanding of the foam growth process via Pulsed Laser Deposition technique [4] and to the complementary capabilities of the High-Power Impulse Magnetron Sputtering, advanced multi-layer targets based on near-critical films with carefully controlled properties (e.g. density gradients over few microns length scales) can now be manufactured, with applications outreaching the field of laser-driven ion acceleration. This also stimulated a thorough numerical investigation of superintense laser-interaction with nanostructured plasmas [5-7]. In addition, a comprehensive numerical and theoretical work has allowed to design a realistic table-top apparatus for laser-driven Ion Beam Analysis and neutron generation, that exploits a double-layer target to reduce the requirements for the laser system [8].

References
[1] A. Macchi, M. Borghesi, M. Passoni, Reviews of Modern Physics, 85, 2013
[2] I. Prencipe et al. Plasma Physics and Controlled Fusion, 58(3), 2016
[3] M. Passoni et al. Physical Review Accelerators and Beams, 19(6), 2016
[4] A. Maffini et al,, submitted to Physical Review Materials, 2019
[5] L. Cialfi, L. Fedeli, and M. Passoni, Physical Review E, 94, 2016
[6] L. Fedeli et al. Eur. Phys. J. D, 71, 202 ,2017;
[7] L. Fedeli et al. Scientific Reports 8, 3834, 2018
[8] M. Passoni et al. Scientific Reports, under review, 2019

Speaker: M. Passoni (EPS 2019)

171 I1.203 Magnetized high energy-density physics

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.203.pdf

Generation of laser-driven quasi-static magnetic fields (B-fields), in the range of the kTesla, paves the ground for novel high energy-density physics (HEDP) investigations.
I will review results and physical understanding in driving such strong B-fields. At LULI [Santos2015] and Gekko-XII [Law2016] laser facilities, ns-scale B-field pulses, above 500 T at the centre of coils connected to laser-driven diodes, were spatially and temporally characterized by a multiple diagnostic platform. The mechanisms yielding the looping superAlfvenic current-discharge are understood in terms of fast electron ejection from the laserirradiated surface and the background plasma magnetization and current-neutralization. Optimization parameters were identified [Tikhonchuk2017].
We successfully applied these B-fields to magnetise solid-density [Bailly-Grandvaux2018] or laser-compressed targets [Sakata2018], and therein radially confine and guide relativistic electron beams over distances of the order of 100 µm. The magnetised transport yielded impressive enhancements on the energy-density flux into matter, isochoric heating and energy coupling efficiency into the core of the compressed spheres. This platform will be further applied to enhance proton beam acceleration from magnetised thin foils [Santos2018].
I will conclude by discussing experimental projects related to magnetohydrodynamics, magnetised atomic physics and magnetised inertial confinement fusion [Santos2018].

[Bailly-Grandvaux2018] M. Bailly-Grandvaux et al., Nat. Comm. 9, 102 (2018).
[Law2016] K.F.F. Law et al., Appl. Phys. Lett. 108, 091104 (2016).
[Sakata2018] S. Sakata et al., Nat. Comm. 9, 3937 (2018).
[Santos2015] J.J. Santos et al., New J. Phys. 17, 083051 (2015).
[Santos2018] J.J. Santos et al., Phys. Plasmas 25, 056705 (2018).
[Tikhonchuk2017] V.T. Tikhonchuk et al., Phys. Rev. E 96, 023202 (2017).

Speaker: J.J. Santos (EPS 2019)

172 I1.204 Multi-PW laser driven electron acceleration and applications

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I1.204.pdf

Laser wakefield acceleration (LWFA) can realize compact electron accelerators using significantly higher acceleration field than that of conventional rf accelerators. The progress of laser technologies reached PW peak power [1] and advanced the energy of laser electron accelerators to several GeV energy range [2,3]. Recently, we accomplished upgrading one of our PW beamlines to 4 PW peak power [4] and started applying it to LWFA experiments. In the recent experiments, we obtained 4.5 GeV electron beam by applying a 2.5 PW laser pulse to a 7-cm helium gas cell target. In the experiment, we observed the charge of the electron beam was noticeably enhanced through the ionization injection scheme implemented by adding 1 % neon to the helium gas. Here, we present the recent progress in LWFA research with multi-PW lasers. In addition, we will discuss new LWFA schemes for improving beam quality. These developments of high energy electron beam with multi-PW lasers will open gateways to investigate nonlinear QED phenomena and nuclear processes.

Reference
[1] J. H. Sung et al., Opt. Lett. 35, 3021 (2010).
[2] H. T. Kim et al., Phys. Rev. Lett. 111, 165002 (2013).
[3] H. T. Kim et al., Sci. Rep. 7,10203 (2017).
[4] J. H. Sun et al., Opt. Lett. 42, 2058 (2017).

Speaker: H.T. Kim (EPS 2019)

BSAP

Convener: D. Burgess

173 I1.401 Beam generated Langmuir turbulence in plasmas with density fluctuations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.401.pdf

In the source regions of the Type III solar bursts, energetic electron beams are accelerated in the low solar corona during flares. Observations show that such beams can propagate in the solar wind up to distances around 1 AU and beyond, generating Langmuir turbulence that emits specific electromagnetic radiation. The solar wind has been revealed to be a inhomogeneous plasma with an average level of random density fluctuations reaching several percents of the background density. This circumstance allows explaining many observations performed by spacecraft which could not be predicted by the existing turbulence theories and remained unsolved during decades. Numerical simulations based on a new modelling and a novel approach show that the plasma density inhomogeneities crucially influence on the characteristics of the Langmuir wave turbulence and the beams' dynamics. Indeed, they allowed studying in details several physical processes: waves' growth and saturation, beam relaxation, slowing down and reabsorption, wave-wave coupling and wave decay cascades, particle diffusion processes, electron acceleration, transformation of waves on density fluctuations (scattering, refraction, reflection, tunnelling), modulations of waveforms, statistics of Langmuir field emission, mechanisms of electromagnetic emissions, etc...[1]-[5] Simulation results were successfully compared with recent observations by the Stereo and Wind spacecraft, and will be used to interpret forthcoming data from the Parker Solar Probe and the Solar Orbiter international missions.

[1] Krafft C., Volokitin A., Krasnoselskikh V., Astrophys. J., 778, 111, 2013.
[2] Krafft C., Volokitin A., Krasnoselskikh V., Astrophys. J., 809, 176, 2015.
[3] Volokitin A., Krafft C., Astrophys. J., 833, 166, 2016.
[4] Krafft C., Volokitin A., Astrophys. J., 821, 99, 2016.
[5] Volokitin A., Krafft C., Astrophys. J., 868, 104, 2018.

Speaker: C. Krafft (EPS 2019)

174 I1.402 Efficient non-thermal particle acceleration mediated by the kink instability in jets

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.402.pdf

Jets emanating from active galaxies are among the most powerful particle accelerators in the universe. They shine across the entire electromagnetic spectrum, and are candidate sources of ultrahigh-energy cosmic rays. Yet, the dominant mechanisms responsible for particle acceleration in these systems are not well understood. Global magnetohydrodynamic simulations suggest that the development of the current-driven kink instability (KI) can play an important role in the dissipation of the jet's internal magnetic field near recollimation regions, but it remains unclear if such process could lead to efficient non-thermal particle acceleration. We have performed large-scale 3D particle-incell simulations to investigate the self-consistent particle acceleration dynamics associated with the development of the KI in conditions relevant to magnetized relativistic jets. We find that the development of the KI mediates the efficient conversion of the magnetic energy into high-energy particles. We show that non-thermal particles are accelerated by a large-scale inductive electric field that develops throughout the unstable region during the nonlinear stage of the KI. The acceleration process is made efficient by the highly tangled magnetic field structure that arises in the nonlinear phase, which enables rapid curvature drifts across magnetic field lines and along the inductive electric field. This results in the development of a power-law energy tail that contains 50% of the initial magnetic energy, and that extends to the confinement energy of the jet. By scaling our results to the conditions of bright knots in AGN jets, such as HST-1 and Knot A in M87, we show that this mechanism can account for the spectrum of synchrotron radiating particles, and offers a viable means for accelerating ultra-high energy cosmic rays.

This work was supported by the U.S. DOE SLAC Contract No. DE-AC02-76SF00515, by the U.S. DOE Office of Science, Fusion Energy Sciences under FWP 100237, and by the U.S. DOE Early Career Research Program under FWP 100331.

Speaker: E. Alves (EPS 2019)

175 I1.403 Collisionless shock formation and particle acceleration in conditions relevant for NIF experiments.

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I1.403.pdf

Collisionless shocks are ubiquitous in the Universe and play an important role in the slow down of plasma flows, magnetic field generation/amplification, and particle acceleration. Depending on the plasma conditions, different plasma processes are believed to mediate shock formation and particle injection, however, these are not yet fully understood. Kinetic plasma simulations and high-energy-density (HED) laser-plasma experiments can help probe different plasma conditions and identify the dominant processes at play. I will present recent large-scale particle-in-cell (PIC) simulations of counter-streaming plasma flows for conditions relevant to ongoing collisionless shock experiments at the National Ignition Facility (NIF). The simulations take into account the time-dependent density and velocity profiles of the flows, that are inferred from hydrodynamical simulations. This study demonstrates that inhomogeneous ablation plasma profiles increase coherent length of magnetic field structures and make shock formation more efficient. I will show the comparison of the simulation results with recent experimental measurements on NIF, which suggest the characterization of electromagnetic collisionless shock formation for the first time in the laboratory. Finally, I will discuss the expected signatures of particle acceleration and the role of collisional effects.

Speaker: A. Grassi (EPS 2019)

176 I1.404 Interacting magnetized plasma flows in pulsed-power driven experiments

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I1.404.pdf

The interactions of fast-streaming, magnetized plasmas can result in a wide range of fundamental plasma physics processes such as the formation of MHD shocks, magnetic turbulence, reconnection and wave-particle interactions. We present experiments from a versatile platform, where supersonic plasma flows generated by the ablation of pulsed-power driven wire arrays are used to study a wide range of fundamental magnetized plasma interactions. The setup allows a control over the global system parameters, including the drive strength, magnetization, magnetic field topology and interaction geometry. The plasma composition (wire material) can also be chosen to vary the collisionality of the plasma and introduce dynamically significant radiative cooling. The detailed structure of the interactions is measured using optical Thomson scattering, multi-colour laser interferometry and Faraday rotation diagnostics, providing measurements of the flow velocities, plasma temperature, electron density and magnetic field distributions of the plasma.
Acknowledgements: The experiments are carried out at the MAGPIE pulsed-power generator at Imperial College London. The research is supported by EPSRC Grant No. EP/N013379/1 and by the NNSA Stewardship Sciences Academic Programs under DOE Cooperative Agreement DE-NA0003764.

[1] L.G. Suttle, J.D. Hare et al., Phys. Plasmas 25, 042108 (2018)
[2] J.D. Hare, L.G. Suttle et al., Phys. Plasmas 25, 055703 (2018)
[3] G.C. Burdiak, S.V. Lebedev et al., Phys. Plasmas 24, 072713 (2017)

Speaker: L.G. Suttle (EPS 2019)

LTPD

Convener: A. Milella (Asociaci__n EURATOM-CIEMAT)

177 I1.301 Effects of charge fluctuation on aerosol dynamics and thermal behavior of nanoparticles in dusty plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.301.pdf

Particles immersed in a plasma undergo charge fluctuation due to collisions with ions and electrons which has a strong bearing on their aerosol dynamics and thermal balance. As a matter of fact, a significant fraction of nm-sized particles can be non-negatively charged which enhances the coagulation kinetics and as a consequence, affects the particle size distribution. Also the collisions with ions and electrons is accompanied by large amounts of energy deposition on the particle. Especially the small nm-sized particles can undergo temperature fluctuations with high peak values that determine the crystallinity of the Nps.
In this presentation, we analyze the particles behavior in plasmas using detailed aerosol modeling in DC discharge combined with theoretical models for charge and thermal fluctuations. We showed that taking into account the discrete nature of the charge distribution is of prime importance to estimate the fraction of non-negatively charged particles. This results in the appearance of several particle generations, i.e. modes, and lower density and slightly larger diameter of the core distribution.
We also showed that for carbon nps in a typical processing discharges, the particles of size <5 nm diameter can attain peak temperatures as high as 2000 K, which explains the fact that small particles are usually crystalline while large particles are amorphous in nature [1].

[1] C. Arnas, and A. Mouberi, "Thermal balance of carbon nanoparticles in sputtering discharges," Journal of Applied Physics, vol. 105, no. 6, pp. 063301, 2009.

Speaker: A. Michau (EPS 2019)

178 I1.302 Strongly coupled plasma in refractory metals near the liquid-gas coexistence curve and critical point: first-principle study

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.302.pdf

Dense metallic plasma is a complicated object for both theoretical and experimental study. Due to very high coupling and degeneracy parameters traditional chemical picture and perturbation approaches are of questionable applicability for such plasma. Strong correlation effects hamper the usage of average atom models. Expanded states of a liquid metal can be obtained in shock-wave experiments with porous samples. In this case a porous sample unloads into some obstacle after the shock-wave compression and the expansion velocity can be registered. Such experiments are quite complicated and rare. Another example is an isobaric expansion (IEX) of wires under heating by a powerful current pulse. IEX experiments are also sparse and contradictory. The challenge of the current work is to describe both isobaric and isentropic expansion experiments for a number of metals by one and the same theory. Also it is of importance to estimate the liquid-gas phase transition boundary and critical point. A very important question - a probable existence of metal-tononmetal transition predicted in liquid iron - is also discussed.
We use quantum molecular dynamics to calculate thermodynamic properties and electrical conductivity of expanded liquid aluminum, molybdenum, tungsten, iron and uranium. Various shock-compression experiments are reproduced for porous tungsten [1] and molybdenum as well as subsequent isentropic expansion. Special attention is paid to available isobaric expansion experimental data for theoretical estimations of critical points. We succeeded in reconciliation of several types of experiments for refractory metals. Thorough analysis of experimental data will be presented. A special Monte Carlo procedure is applied for the estimation of the liquid≠gas coexistence curve and critical point parameters of tungsten and molybdenum. The result is close to an estimation obtained with Likalter's similarity relation. Also we apply a new criterion of mean ion charge estimation in strongly coupled plasmas. This work is supported by RSF grant No. 18-79-00346.

1. Minakov, D. V., Paramonov, M. A., & Levashov, P. R. Phys. Rev. B 97, 024205 (2018).

Speaker: P.R. Levashov (EPS 2019)

179 I1.303 Industrial applications of highly non-equilibrium low-pressure oxygen plasma

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I1.303.pdf

ow pressure gaseous plasma is a suitable medium for tailoring surface properties of solid materials on industrial scale. Treated materials are subjected to positively charged atomic and molecular ions, neutral radicals and ultraviolet as well as vacuum ultraviolet radiation. The penetration depth of ultraviolet radiation in organic materials is around a micrometre so it is suitable for modification of rather thick surface layers and triggering structural modifications such as cross-linking [1]. Vacuum ultraviolet radiation has penetration depth of around 10 nm, so it is particularly suitable for breaking bonds between atoms in the surface layer. The neutral radicals usually do not penetrate the solid material so they affect the surface only. In most cases, synergistic effects of radiation and neutral radicals are beneficial. Plasma rich in neutral radicals is usually sustained by electrodeless radiofrequency discharges. The coupling of powerful generators with plasma in industrial-size reactors is not trivial at frequencies around 10 MHz due to prohibitively large impedances so innovative solutions that supress the peak voltages such as [2] are beneficial. Oxygen plasma is particularly suitable for improving wettability of carbon-containing materials. The surface is often saturated with polar functional groups after receiving the fluence of O-atoms around 1x10^22 m-^2, what is achieved in milliseconds providing the reactor is properly designed. Prolonged treatment causes etching which is often inhomogeneous enough to cause nanostructuring and thus super-wettability of processed materials. Such a surface finish enables excellent adhesion of different coatings, even electrodeposited metallic films [4]. Several other industrial applications of highly non-equilibrium low-pressure oxygen plasma will be presented

[1] M. Lehocky et al, Device and method for producing UV radiation: patent EP3168860B1 (2018).
[2] A, Vesel et al, Device for high-frequency gas plasma excitation: DE 112012000015B4 (2016).
[3] A. Vesel et al, Initial stages in functionalization of polystyrene upon treatment with oxygen plasma late flowing afterglow. Plasma Sour. Sci. Technol. 27 (2018), 094005-1-9.
[4] U. Cvelbar et al, Method for improving the electrical connection properties of the surface of a product made from a polymer-matrix composite: patent EP 1828434B1 (2008).

Speaker: M. Mozetič (EPS 2019)

180 I1.304 Influence of the atmospheric pressure plasma source configurations on the properties of treated liquid samples

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I1.304.pdf

In recent years, expansion of non-equilibrium plasma applications is directed towards plasma sources operating at atmospheric pressure that are used for treatment of liquids. Usually, different applications involving liquid targets have different aims and, as precondition for all these applications, it is important to make the plasma processes as efficient as possible in every specific case. Therefore, these tasks are demanding due to the complexity of plasma chemistry, which depends on the type of plasma source and is further tangled by the presence of liquid target. Here we will present results of a laboratory-scale study aiming to make comparison between different plasma source configurations and to reveal their influence on treated pure and contaminated water samples. Two-level approach is necessary: on one side one should characterize the plasma used for treatments while, on the other side, properties of the liquid samples should be obtained. Detailed discharge diagnostics involving optical emission spectroscopy and electrical characterisation will provide information on plasma conditions for particular source. Emission spectrum provide information on excited species produced in the gas phase. Measurement of electrical signals allow to calculate power input provided to the system and thus establish a parameter describing the plasma. Additionally, certain physicochemical properties of the treated liquids (pH, dissolved Oxygen content, conductivity, total organic carbon content in contaminated samples etc.) will be obtained allowing to cross reference data with plasma characterization and give an insight into interaction chemistry of the specific plasma source used for liquid treatment. Results regarding the influence of different plasma source configurations to the treated liquid will be presented in the context of possibility of applications in the field of plasma agriculture (PAW, water decontamination etc.).

Speaker: N. Škoro (EPS 2019)

MCF

Convener: G. Granucci (ISTP Milano - CNR)

181 I1.101 Exploring Fusion-Reactor Physics with High-Power Electron-Cyclotron- Resonance Heating (ECRH) on ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.101.pdf

The ECRH system of ASDEX Upgrade has been upgraded over the last 15 years from a 2 MW, 2 s, 140 GHz system to an 8 MW, 10 s, dual frequency system (105/140 GHz). The power exceeds the L/H power threshold at least by a factor of two even for high densities and roughly equals the installed ICRF power. The power of both RF heating systems together (> 10 MW in the plasma) is about half of the available NBI power, allowing significant variations of torque input, shape of the heating profile and Qe/Qi even at high heating power. For applications at low magnetic field an X3 heating scheme is routinely in use as it is now foreseen also for ITER to study the first H-modes at one third of the full field. This versatile system allows addressing important issues fundamental to a fusion reactor: Hmode operation with dominant electron heating, accessing low collisionalities in full metal devices (also related to ELM suppression with resonant magnetic perturbations), influence of Te/Ti and rotational shear on transport, dependence of impurity accumulation on heating profiles. Experiments on all these subjects have been carried out over the last years and will be presented in this contribution. The adjustable localized current drive capability of ECRH allows dedicated variations of the shape of the q-profile and studying their influence on noninductive tokamak operation (so far at q95 > 5.3). The ultimate goal of these experiments is to use the experimental findings to refine theoretical models such that they allow a reliable design of operational schemes for reactor size devices. In this context, recent results comparing a quasi-linear approach (TGLF [1]) with fully non-linear modelling (GENE) of noninductive high beta plasmas will be presented.

[1] Staebler G.M. et al., 2016 Phys. Plasmas 23 062518

Speaker: J. Stober (EPS 2019)

182 I1.102 Advances in the physics studies for the JT-60SA tokamak exploitation and research plan

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.102.pdf

JT-60SA is a large fully superconducting new tokamak device being built jointly by Europe and Japan, and due to start operation in 2020 [1]. In this prospect, a broad set of preparation activities [2] has been carried out for years, involving the elaboration of the JT-60SA Research Plan [3], and is now focusing on the forthcoming experiments. The physics results obtained are not only relevant to the future JT-60SA experiments, but often constitute original contributions to plasma physics and fusion research. In particular, results have been obtained and research is further progressing on the following subjects:
- test and selection of models for transport, pedestal, H&CD, combined into integrated modelling simulations, and validated on JET and JT-60U selected sets of discharges [4-6]
- gyrokinetic modelling of impact of fast ions and electromagnetic effects on turbulent transport in high-beta regimes
- non-linear studies of ELM stability with the JOREK code
- core/SOL/divertor and impurity seeding simulations for C and W PFC configurations
- non-linear 3D kinetic modelling of RWM and their control
- MHD instabilities associated with fast ion distributions produced by NBI
- experimental validation of wall conditioning methods by EC waves
- advanced modelling of EC-assisted breakdown and magnetic control
- first results of a new simulator combining plasma model and free-boundary equilibria.
An overview of the main results achieved by these studies will be presented. The highlights of the scientific programme that will be carried out, as described in the final version of the Research Plan, will be discussed, with particular focus on the first experimental campaigns.

[1] H. Shirai et al., Nucl. Fusion 57 (2017) 102002.
[2] G. Giruzzi et al., Nucl. Fusion 57 (2017) 085001.
[3] JT-60SA Research Plan - Version 4.0, Sept. 2018, http://www.jt60sa.org/pdfs/JT-60SA_Res_Plan.pdf
[4] J. Garcia et al., Nucl. Fusion 54 (2014) 093010.
[5] N. Hayashi et al., Nucl. Fusion 57 (2017) 126037.
[6] L. Garzotti et al., Nucl. Fusion 58 (2018) 026029.

Speaker: G. Giruzzi (EPS 2019)

183 I1.103 MeV range particle physics studies in tokamak plasmas using gamma-ray spectroscopy

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/I1.103.pdf

Energetic particles in the MeV range are ubiquitous in fusion devices [1]. On one hand, they can be suprathermal ions born from the fusion reactions or accelerated by ion cyclotron resonance heating. On the other hand, they can be runaway electrons (REs) that are spontaneously generated, for example, during a disruption. Both species lead to gamma-ray emission by different means. Fast ions interact with impurities naturally found in the plasma and result in nuclear reactions where a heavy nucleus in an excited state is born. This in turn decays instantaneously, leading to the emission of gamma-rays at several discrete energies and whose detailed properties embed information on the fast ions that triggered the reactions. Confined suprathermal electrons, instead, emit gamma-rays by bremsstrahlung as they collide with ions or extrinsic impurities along their orbit in the tokamak. The resulting gamma-ray spectrum extends over a broad energy range and is continuous, with a detailed shape that reflects the RE distribution function and its temporal dynamics. In this presentation, we show how fast particle physics is studied using gamma-ray spectrometry [2]. In radio-frequency heating experiments at the Joint European Torus (JET), gamma-ray measurements reveal the acceleration of ions to the MeV range by the exploitation of finite Larmor radius effects in schemes that rely on resonances at multiple harmonics of the ion cyclotron frequency and determine the maximum fast ion energy [3]. In novel, so called 3 ion radio-frequency heating scenarios, gammaray spectra prove the existence of a multi MeV fast ion population [4]. Images of the gamma-ray emission from the plasma demonstrate the existence of a pinch effect, which squeezes the ions towards the core depending on the applied antenna phasing. The same images help at determining the spatial redistribution of the energetic ions, whenever their pressure is sufficient to drive instabilities. In RE physics experiments, the inversion of time resolved bremsstrahlung spectra in the gamma-ray energy range yield the evolution of the RE current and maximum energy in a disruption, which is used to understand the effect of the external actuators on the RE velocity space. An example is a recent DIII-D experiment, where gamma-ray measurements during the current quench shed light on the correlation between the presence of a high-energy RE population, the power of RE-driven kinetic instabilities and the likelihood of a post-disruption RE beam formation [5]. We finally address the prospects for particle measurements in plasmas with tritium, both at JET and ITER. Here gamma-ray measurements have a unique role, as they can in principle provide both the profile and the distribution function of the particles. In the latter case, the combination of a radial and tangential gamma-ray view is predicted to reveal pitch angle asymmetries of the distribution function, which are of interest to disentangle the effect of the Alfvenic instabilities on co and counter going ions at ITER [6].

References
[1] B. Breizman and S. Sharapov Plasma Phys. Control. Fusion 53 (2011) 054001
[2] M. Tardocchi, M. Nocente and G. Gorini Plasma Phys. Control. Fusion 55 (2013) 074014
[3] M. Nocente et al. Nucl. Fusion 52 (2012) 063009
[4] Y. Kazakov et al. Nature Physics 13 (2017) 973
[5] A. Lvovskiy et al. Plasma Phys. Control. Fusion 60 (2018) 124003
[6] M. Salewski, M. Nocente et al. Nucl. Fusion 58 (2018) 096019

Speaker: M. Nocente (EPS 2019)

184 I1.104 Extended magnetohydrodynamic hybrid simulations with kinetic thermal and fast ions for instabilities in toroidal plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I1.104.pdf

Magnetohydrodynamics (MHD) is a theoretical framework that explains well the macroscopic plasma behaviours. However, MHD is an unfinished framework for magnetically confined plasmas, because the MHD pressure equation assumes sufficiently high collision frequency which is not valid for the high-temperature plasmas. One typical example that needs an extension of MHD is energetic-particle driven instabilities. Kinetic-MHD hybrid simulations for energetic particles interacting with an MHD fluid are useful tools to understand and predict energetic particle driven MHD instabilities. We present a new hybrid simulation model where the gyrokinetic particle-in-cell simulation method is applied to both thermal and fast ions. It has been known that the Large Helical Device (LHD) plasmas are more stable for pressure driven MHD instabilities than MHD theory predicts [2]. We have applied the new simulation to the ballooning instabilities in LHD. Figure 1 demonstrates that the kinetic response of thermal ions to the MHD perturbations is significantly weaker than the adiabatic electron fluid response leading to the stabilization of the instability. The detailed particle dynamics in the nonaxisymmetric magnetic field that stabilizes the instability will be presented. In addition, the time evolutions of Alfvén eigenmodes (AEs) in tokamak plasmas and energetic particle driven geodesic acoustic modes (EGAMs) in LHD plasmas shown in Fig. 2 are simulated with kinetic thermal ions. It is demonstrated that fast-ion energy is transferred to thermal ions through the nonlinear interaction with the AEs and the EGAMs.

[1] Y. Todo and T. Sato, Phys. Plasmas 5 (1998) 1321.
[2] N. Nakajima et al., J. Plasma Fusion Res. 6 (2004) 45.

Speaker: Y. Todo (EPS 2019)

19:00 Welcome Party

Tuesday, 9 July

Plenary Session

Convener: S. Jacquemot (EPS2019)

185 I2.005 Hollow cathode plasma processes and applications

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.005.pdf

Hollow Cathodes are high-density plasma sources that are non-equilibrium from their principle. They are characterized by high activation and ionization degrees and can work in a broad range of parameters - pressures, powers and gas flows. They are scalable, versatile and cost effective. They enable both PVD (Physical Vapor Deposition) and PE-CVD (Plasma Enhanced Chemical Vapor Deposition) regimes and also both regimes in one hybrid mode. They can be used in various plasma-chemical processes.
Generation and performance of hollow cathodes are described both for reduced and atmospheric gas pressures. The evolution of Hollow Cathode Discharge and Hollow Cathode Arc is explained. For some metals, the discharge can even run only in target metal vapors, after closing the gas inlet.
Different applications require different arrangements of the hollow cathodes. The simple cylindrical hollow cathode can be used for local processing or for processing on inner surfaces and inside narrow tubes. Linear Arc Discharge arrangement and Magnet-in-Motion linear scalable hollow cathode enable large area processing. Combination with microwaves provides even more control of the discharge in a hybrid source. A new design with coupling of a magnetized hollow cathode with magnetron is presented. Examples of processes in PE-CVD, ionized PVD and hybrid regimes are given.
Principles and findings from performance of hollow cathodes at reduced pressures have been applied in atmospheric pressure hollow cathode based sources. Fused Hollow Cathode, Hybrid Hollow Electrode Activated Discharge utilizing teaming with the microwave antenna and Hollow Electrode Activated Discharge with aerodynamic stabilization are examples of these new concepts. They are employed in plasma surface engineering and in gas conversion. Similar designs are applied in liquids, for example for production of hydrogen and for production of high value chemicals from low value feeds.

Speakers: H. Baránková (EPS 2019), L. Bardos

186 I2.006 Magnetized laser plasmas for laboratory astrophysics

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.006.pdf

Coupling high-power lasers and high-strength magnetic fields helps gaining unique insight and understanding of a variety of phenomena of crucial importance for astrophysics. We have shown that such platform could be used to mimic the expansion of a young star isotropic disk wind threaded by a co-axial poloidal magnetic field [1, 2, 3]. The same system can also be used to study (i) the issue of accretion dynamics in young star [4], in particular to shed light on the deficiency of x-ray emissivity in these systems, or (ii) the issue particle energization in astrophysical plasmas [5]. These examples will be reviewed and discussed, as well as examples in investigating the fundamental issue of magnetic reconnection in plasmas. We will also discuss perspectives offered by the upcoming new generation of lasers that will offer unprecedented levels of power (up to 10 PW), which will allow to generate very dense bunches of particles at high energy. This could also have a positive impact on laboratory astrophysical studies, e.g. in the field of nucleosynthesis studies where extreme fluxes of neutrons are required in order to investigate double neutron capture, which is out of reach of existing, accelerator-based facilities, but which lasers might allow to tackle.

[1] D. P. Higginson, et al., "Enhancement of quasi-stationary shocks and heating via temporalstaging in a magnetized, laser-plasma jet", Phys. Rev. Lett. 119, 255002 (2017)
[2] D. P. Higginson, et al., "Detailed Characterization of Laser-Produced AstrophysicallyRelevant Jets Formed via a Poloidal Magnetic Nozzle", High Energy Dens. Physics 23, 48-59 (2017)
[3] B. Albertazzi et al., "Laboratory formation of a scaled protostellar jet by co-aligned poloidal magnetic field", Science 346, 325 (2014)
[4] G. Revet, et al., "Laboratory unravelling of matter accretion in young stars", Science Advances 3, no. 11, e1700982 (2017)
[5] D. P. Higginson, et al., "A Novel Platform to Study Magnetized High-Velocity Collisionless Shocks", High Energy Dens. Physics 17, 190-197 (2015)

Speaker: J. Fuchs (EPS 2019)

10:10 Coffee Break

BSAP-BPIF

Convener: L. Gremillet (CEA)

187 I2.J501 Investigation of collisional electron plasma waves and picosecond thermodynamics in a laser-produced plasma using Thomson scattering spectroscopy

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J501.pdf

The rapid, picosecond time-scale evolution of electron density and temperature in a laser-produced plasma was measured using collective Thomson scattering [1]. As is the case for many laser-plasma applications, an underdense (~10^19 cm^-3) H2 plasma was created by a 60-ps, 1053-nm laser pulse with an intensity of ~3 x 10^14 W/cm^2. Unprecedented picosecond time resolution, enabled by a pulse-front-tilt compensated spectrometer, revealed a transition in the plasma-wave dynamics from an initially cold, collisional state to a stable, collisionless state. The temperature heated from 3 eV to 16 eV over the first 18 ps. Over this time, the density increased from 8.4 x 10^18 cm^-3 to its plateau at 1.0 x 10^19 cm^-3. Once the plasma was fully ionized, the temperature rapidly increased to a plateau temperature of ~90 eV. The Thomson-scattering spectra were compared with theoretical calculations of the fluctuation spectrum using either a conventional Bhatnagar-Gross-Krook (BGK) collision operator or a full set of Landau collision terms--the BGK model overestimates the electron temperature by 50% in the most collisional conditions. This overestimation of collisions by the BGK model has implications that extend well beyond Thomson scattering as this is one of the most widely used collisional models in plasma physics. These picosecond electron temperature and density measurements can be applied to laser-plasma devices that require knowledge of the rapidly evolving plasma conditions. For example, laser-plasma amplifiers require frequency matching between an electromagnetic beat wave and the plasma frequency for efficient energy transfer from the pump laser to the seed, but if the plasma frequency is rapidly evolving, as it does in these experiments, the amplifier will be detuned and the efficiency will be poor. With measurements of the plasma evolution, the system could be properly tuned to recover efficient energy transfer.
This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the Office Fusion Energy Sciences under Contract Number DE-SC0016253, the University of Rochester, and the New York State Energy Research and Development Authority, and Development Authority, and the Department of Energy Fusion Energy Sciences user FWP100182.

Reference
[1] "Picosecond Thermodynamics in Underdense Plasmas Measured with Thomson Scattering," A. S. Davies, D. Haberberger, J. Katz, S. Bucht, J. P. Palastro, W. Rozmus, and D. H. Froula, Physical Review Letters (2019).

Speaker: A.S. Davies (EPS 2019)

188 I2.J502 Giant collimated gamma-ray flashes

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J502.pdf

Powerful gamma-ray emissions are ubiquitous in astrophysics, from active galactic nuclei [1] to pulsars [2] and neutron star mergers [3]. One of the key mechanisms leading to powerful gamma-ray emissions is thought to be the interaction of ultrarelativistic particle beams with a surrounding plasma environment, which was experimentally shown to lead to the formation of filaments [4] with the self-generation of ~ 10^4 gauss and long-lived magnetic fields [5]. Here we show that the filamentation of a high-density and ultrarelativistic electron beam in a high-density plasma background leads to the generation of 10^7-10^8 gauss magnetic fields with the emission of a very bright and collimated gamma-ray flash [6]. In addition to their intrinsic interest, these findings pave the way to new routes for reproducing astrophysical phenomena in the laboratory [7], and to novel investigations in strong-field QED and nuclear physics such as the interaction between real photons in vacuum [8].

References
[1] M. C. Begelman, R. D. Blandford, and M. J. Rees, Rev. Mod. Phys. 56, 255 (1984)
[2] P. A. Caraveo, Annu. Rev. Astron. Astrophys. 52, 211 (2014)
[3] B. P. Abbott, R. Abbott, T. D. Abbott et al., Astrophys. J. Lett. 848, L13 (2017)
[4] B. Allen, V. Yakimenko, M. Babzien et al., Phys. Rev. Lett. 109, 185007 (2012)
[5] J. Warwick, T. Dzelzainis, M. E. Dieckmann et al., Phys. Rev. Lett. 119, 185002 (2017)
[6] A. Benedetti, M. Tamburini, and C. H. Keitel, Nat. Photon. 12, 319 (2018)
[7] S. V. Bulanov, T. Zh. Esirkepov, M. Kando et al., Plasma Phys. Rep. 41, 1 (2015)
[8] A. Di Piazza, C. M¸ller, K. Z. Hatsagortsyan, and C. H. Keitel, Rev. Mod. Phys. 84, 1177 (2012)

Speaker: M. Tamburini (EPS 2019)

189 I2.J503 Towards a high efficiency amplifier based on Raman amplification

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J503.pdf

High power, short pulse lasers have become valuable tools for scientists exploring a wide range of phenomena and developing new technologies such as ultra-compact wakefield accelerators [1] and compact light sources [2] with applications ranging from particle physics to biology. To produce ultra-intense, short pulses, large-scale laser facilities rely on the chirped pulse amplification technique and require metre-scale optical components to restrict the laser intensity to below their damage thresholds. They are therefore currently extremely expensive and difficult to maintain. Twenty years ago a novel approach was suggested using plasma as a gain medium to superradiantly amplify a short seed pulse colliding with a counterpropagating pump [3]. This approach is based on the paradigm of three-wave interaction between the two electromagnetic waves and a plasma wave [4]. Since this seminal work, extensive theoretical and experimental studies have been conducted to develop plasma-based amplifiers where the energy exchange between the pump and seed is realised through Raman or Brillouin instability [4]. In this paper, we present an overview of the work that has been carried out by the Strathclyde University group on Raman amplification of short laser pulses [5]. We review the current challenges of increasing the energy transfer efficiency, which is currently low. In particular, we will discuss the use of the pump frequency chirp to control the amplification process.

References
[1] T. Tajima, J. Dawson, Phys. Rev. Lett. 43, 267 (1979)
[2] D.A. Jaroszynski, G. Vieux, AIP Conf. Proc. 647, 902 (2002)
[3] G. Shvets et al., Phys. Rev. Lett. 81, 4879 (1998)
[4] W.L. Kruer, The Physics of Laser Plasma Interactions (Addison-Wesley, Reading, MA, 1988)
[5] G. Vieux et al., New J. Phys. 13, 063042 (2011); X. Yang et al., Sci. Rep. 5, 13333 (2015); G. Vieux et al.,
Sci. Rep. 7, 2399 (2017)

Speaker: G. Vieux (EPS 2019)

190 I2.J504 Magnetic field generation dynamics and reconnection driven by relativistic intensity laser-plasma interactions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J504.pdf

The extremely energetic class of astrophysical phenomena - including high-energy pulsar winds, gamma ray bursts, and jets from galactic nuclei - have plasma conditions where the energy density of the magnetic fields exceeds the rest mass energy density (sigmacold = B^2/(µ0nemec^2)), the cold magnetization parameter). Laboratory studies of magnetic dynamics and reconnection provide an important platform for testing theories and characterizing different regimes. Here, we present experimental measurements, along with numerical modeling, of short-pulse, high-intensity laser-plasma interactions that produce extremely strong magnetic fields (>100T). Three-dimensional particle-in-cell simulations show the plasma density and magnetic field characteristics can satisfy sigma cold > 1. The generation and the dynamics of these magnetic fields under different target conditions was studied using proton radiography, and relativistic intensity laserdriven, magnetic reconnection experiments were performed. Evidence of magnetic reconnection was identified by the plasma's X-ray emission patterns, changes to the electron spectrum, and by measuring the reconnection timescales. [A. E. Raymond, et al., Physical Review E, 98, 043207 (2018)]

Supported by the Department of Energy / NNSA under Award Number DE-NA0003606 and by NSF under 1751462. The authors acknowledge the OSIRIS Consortium, consisting of UCLA and IST (Lisbon, Portugal) for the for providing access to the OSIRIS 2.0 and 4.0 framework. Work supported by NSF ACI-1339893.

Speaker: L. Willingale (EPS 2019)

LTPD

Convener: M. Mozetič (EPS2019)

191 I2.301 In-flight plasma modification of nanoparticles produced by means of gas aggregation sources

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.301.pdf

Tremendous progress that experiences the field of the nano-fabrication opens new entrancing opportunities in terms of the production of materials with advanced functionalities. In spite of undisputable successes of chemistry-based methods or strategies that utilize nanolithography, the use of these methods brings also certain disadvantages. These relate e.g. to the complexity of developed protocols, necessity to use potentially harmful solvents or precursors, low throughput or high costs, to mention at least some of them. Because of this, alternative strategies are urgently needed. As one of the promising candidate to act as challenger to above-mentioned techniques appeared procedures that utilize non-equilibrium plasmas. Among them increasing attention receive gas aggregation sources (GAS) of nanoparticles based on spontaneous volume condensation of supersaturated vapour generated by magnetron or products of plasma enhanced polymerization. Such sources were found to be very effective in the production of single material NPs comprising metallic, metal-oxide or plasma polymer ones with well-controlled size and structure. However, recent interest in the (multi)functional nanomaterials triggered off intensive research that explores the possible use of GAS systems for synthesis of such materials. In our previous works we have shown that nanocomposite or nanostructured coatings with different architectures may be fabricated when GAS systems are combined with other plasma deposition techniques (e.g. magnetron sputtering or PE-CVD). In this study we focus on a different strategy that is based on the inflight modification of nanoparticles that leave the GAS by an auxiliary plasma with aim to either modify their surface properties or to coat them with a thin film of other material before their reach the substrate. As it will be demonstrated on selected examples of metallic (Ti, Ag, Fe, Ni) or plasma polymer NPs this can be achieved by different configurations that employ either RF/DC/hollow magnetrons for coating of flying NPs or capacitively coupled RF plasma for treatment of NPs or their coating with a thin plasma polymer film. The dependence of the structure of produced NPs (determined by SEM, TEM, HRTEM, SAXS), their chemical composition (XPS, EDX), optical properties and wettability on the plasma process parameters will be discussed alongside with the possible applications of produced NPs for bio-sensing or bio-applications.

Speaker: O. Kylián (EPS 2019)

192 I2.302 Time dependent self-consistent electron energy distribution functions during nano-second repetitively discharges in reacting N2/H2 mixtures

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.302.pdf

Electron energy distribution functions (eedf), vibrational and electronic excited states are selfconsistently coupled for discussing the formation of ammonia under nano-second repetitively pulsed discharges. The Boltzmann equation for free electron is solved to determine the eedf, accounting for inelastic, superelastic collisions, affecting the heavy species kinetics. In particular superelastic collisions with electronically and vibrationally excited states of N2 and H2 molecules induce the strong non-equilibrium character of the eedf, reflecting on the rate coefficient of processes induced by electron collisions. This effect will be discussed to investigate the eedf of the mixture as a function of different applied reduced electric fields and of the inter-pulse delay time. The non-equilibrium character of the vibrational distributions of both N2 and H2 molecules and their role in affecting eedf will be discussed. Finally a comparison with existing numerical and experimental results will be presented.

Speaker: G. Colonna (EPS 2019)

193 O2.301 Ceramics' sheath probed using Laser Induced Fluorescence

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.301.pdf

The sheath standing in front of different ceramics -- used in Hall thrusters, where their nature is known to have an influence on the device efficiency [1] -- is studied thanks to the nonintrusive Laser Induced Fluorescence (LIF) diagnostic. The study aims to provide a better understanding of the sheath structure under the presence of hot/energetic electrons that are able to trigger secondary electron emission from the ceramic wall [2]. Performing LIF in front of surfaces implies the presence of an additional LIF signal due to the presence of the reflected laser beam. We present here an experimental artifact causing the reflected beam signal to be significantly higher than the incident beam one. Erroneous measurements interpretations may be carried because of this artifact. It is shown to be due to the LIF saturation effect on one hand and the diffuse reflection of the laser beam on the surface on the other hand [3]. The exposure of this experimental bias allowed the proper measurement of the (Argon) ion velocity distribution function (IVDF) in the sheath. Several ceramics were exposed to a low pressure multipolar plasma with a variety of discharge parameters (ne: 10^13-15 m^-3, Te: 2-5 eV, 10-15 % of 10-20 eV hot electrons, <5% of 50-120 eV energetic electrons) [4]. These experiments are expected to provide the first measurement of IVDF in sheaths in which the secondary electron emission is large enough for the space-charge limited (SCL) regime to appear.

[1] J-P Boeuf, Journal of Applied Physics 121, 011101 (2017)
[2] T. Tondu, M. Belhaj & V. Inguimbert, Journal of Applied Physics, 110, 093301 (2011)
[3] V. Pigeon, N. Claire, C. Armas & F. Doveil, Physics of Plasmas, 26, 023508, (2019)
[4] M. CarrËre, L. ChÈrigier, C. Arnas-Capeau, G. Bachet. & F. Doveil. Review of Scientific Instruments, 67, 4124-4129 (1996)

Speaker: V. Pigeon (EPS 2019)

194 O2.302 Generic Properties of Plasma Sheath over Emissive Planar/Grooved Walls

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.302.pdf

The plasma-wall interaction is a fundamental process determining the plasma parameters. The different types of sheathes over an planar/grooved emissive walls in electromagnetic fields of discharge plasmas are discussed in this paper. In kinetic simulations and in experiments, we found a plasma sheath rearrangement driven by a) an increase of the energy of electron beam bombarding the emissive wall, b) a nonuniformity of the surface due to erosion patterns or segments with the different secondary electron emission yields, or d) with a variation of magnetic field angle [1-3]. A new aspect of ion flux interaction with an emissive wall with Debye-scale erosion trenches in plasma at low gas pressure is discussed. A phenomena of ion current modulation along the grooved emissive surface with increasing the discharge voltage was studied in PIC MCC simulations for the experimental conditions [1,3]. Unexpectedly, after the transition between developed and collapsed sheaths over a front emissive surface, the ion flux directed inside erosion trenches was found considerably increasing.

1. Schweigert I V, et al 2015 Plasma Sources Sci. Technol. 24 025012
2. Schweigert I V, Keidar M, 2017 Plasma Sources Sci. Technol. 26 064001.
3. I. Schweigert et al 2018 Plasma Sources Sci. Technol. 27 045004
   The authors gratefully acknowledge FA9550-11-1-0160,. One of authors, IS, was partly supported by RSF 17-19-01375.

Speaker: I. Schweigert (EPS 2019)

195 O2.303 Influence of the gas-flow on the thermodynamic equilibrium of atmospheric-pressure microwave plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.303.pdf

Microwave plasmas sustained at atmospheric pressure are applied in many fields due to the flexibility and high chemical reactivity that result from non-equilibrium operation conditions. However, the performance of a plasma in a specific technological application is determined by the density of active species and their characteristic temperatures, which are interrelated by the thermodynamic equilibrium (TE) degree of the discharge. Though many studies have dealt with the impact of experimental conditions on TE, only few of them have focused on the impact of gas-flow [1]. In the present study, the influence of gas-flow in the axial distribution of plasma parameters along an atmospheric-pressure microwave argon capillary plasma sustained using a surfaguide [2] has been examined. Increasing gas-flow results in a reduction of gas and electron temperatures, as well as of electron density. Besides, important asymmetries in the axial distribution of some excited states appear (Figure 1). This can be explained by the dependence of these parameters on the dynamics of argon molecular ions, which is strongly affected by the decrease in gas temperature. Finally, increasing gas-flow affects TE degree too, leading more of the lower levels of argon out of partial Local Saha Equilibrium, although their population is still controlled by collisional processes.

[1] Martínez J, Castaños-Martínez E, González-Gago C, Rincón R, Calzada MD Muñoz J, Plasmas Sources Sci. Technol. 27 (2018) 077001
[2] Moisan M, Etemadi E and Rostaing J C 1998 French Patent No. 762748 European Patent No. EP.

Speaker: J. Muñoz Espadero (EPS 2019)

MCF

Convener: R. Coelho (Instituto Superior Tecnico)

196 I2.101 Assessment of alternative divertor configurations for a European DEMO

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.101.pdf

The European roadmap for fusion energy has identified plasma exhaust as a major challenge towards the realisation of magnetic confinement fusion. To mitigate the risk that the baseline scenario with a single null divertor (SND) and a high radiation fraction adopted for ITER will not extrapolate to a DEMO reactor, the EUROfusion consortium is assessing the feasibility and potential benefits of alternative divertor configurations.
A range of alternative configurations that rely only on conservative extrapolations of currently available technologies that could be readily adopted in the European DEMO design, are identified. They include the X divertor (XD), Super-X divertor (SXD), Snowflake divertor (SFD) and the double null divertor (DND). Basic engineering constraints on poloidal field (PF) coil current densities and forces, however, restrict XD and SFD characteristics to the outer divertor and limit the achievable poloidal and toroidal flux flaring to factors of ~1.5. All alternatives require additional conductors, which translates into higher capital costs, with the SXD requiring ~20% more toroidal field (TF) coil conductors and SXD and SFD ~50% more PF coil conductors. Structural analysis of the TF coil shape and remote maintenance requirements add further constraints that are used in a second step to refine the configurations.
Boundary models with varying degrees of complexity are used to predict the exhaust performance. Desired effects are a facilitated access to detachment, resilience of the detachment front to move along the divertor leg and an increase in divertor radiation without excessive core performance degradation. The extended 2-point model and achievable geometric variations indicate that SXD and SFD have the largest potential to decrease the SOL radiation required for the onset of detachment. A systematic study using the divertor transport code TECXY predicts similar trends, but with a more modest gain for the SFD. The predictions are further refined with the SOLPS and SOLEDGE2D-Eirene codes, which employ more sophisticated models for geometry and neutral particles. A SOLEDGE2D-Eirene scan, also including the DND, shows a stronger increase of the tolerable residual power (1-frad) for all alternatives ranging from +30% to +50%. It also confirms that a significant part of the improvement in the outer divertor of XD and SXD comes at the price of higher power loads directed to the respective inner divertors. Additional benefits of the SFD, not yet captured in the models, may be an ability to increase frad without adverse effects on the core performance and a potential SOL broadening in the low poloidal field region.
Next steps must address the controllability of each configurations. It should also include an assessment of the engineering challenges posed by placing PF coils inside the TF coils and a decrease of the admissible grazing angle of the field line at the target, which both promise further significant increases of the power exhaust potential of alternative configurations.

Speaker: H. Reimerdes (EPS 2019)

197 O2.101 Alternative divertor configurations - physics basis and plans for ASDEX Upgrade

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.101.pdf

Power exhaust is expected to become a problem in a future fusion reactor based on the Tokamak design in conventional single-null (SN) configuration. As a potential solution, alternative divertor geometries are currently discussed and investigated by many laboratories in the world [1]. In order to study a series of alternative configurations [2] in a machine with a high heating power (30 MW) compared to its size (R=1.65 m) and compare them to the conventional SN configuration the installation of a pair of in-vessel coils in the close proximity of the upper outer strike-point (SP) of ASDEX Upgrade is currently in preparation [3]. The upgrade offers unique possibilities to address, among others, the following outstanding scientific questions: Can the secondary SPs appearing in a snowflake (SF) configuration be activated, as it was partially observed in TCV [4]? Is the 'churning mode' postulated for the null-region of a SF [5] or another mechanism responsible for this enhanced cross-field transport and does it scale with beta-pol and/or machine size such that all SPs would be fully activated in a reactor? Can the position of the secondary X-point be controlled accurately enough to exploit the SOL splitting [6] observed in TCV [7,8] as a heat-flux mitigation effect? Does a SF configuration with a secondary X-point on the low-field side of the primary one (LFS SF-) offer a better radiation characteristics [6,9] than a SN and does this furthermore allow an easier access to detachment as predicted by recent SOLPS simulations [9]. Does the configuration affect the detachment threshold or only the degree of detachment after the roll-over as observed in TCV for the SF [10] and the X-divertor configurations [11]? Do engineering tolerances and/or 3D magnetic fields caused by the current-feeds of the new coils limit the exploitation of the large poloidal flux expansion of an X-divertor [3,12]? Where would we expect this limit in a reactor? This contribution will discuss the physics basis of these questions and present the status and the plans for the practical realization of the divertor upgrade as well as its diagnostics. In addition to that an overview over recent results of state-of-the-art SOLPS and EMC3-EIRENE modeling of alternative configurations will be given.

References:
[1] V. A. Soukhanovskii, PPCF 2017,
[2] T.Lunt, et al., NME 2017,
[3] A.Herrmann, et al., submitted to FED,
[4] T.Lunt, et al., PPCF 2014,
[5] D. Ryutov, et al., Phys.Scr. 2014,
[6] T.Lunt, et al., PPCF 2016,
[7] H.Reimerdes, et al., PPCF 2013,
[8] B.Labit, et al., NME,
[9] O.Pan, et al., PPCF 2018,
[10] H.Reimerdes, et al., NF 2017,
[11] Ch.Theiler, et al., NF 2017,
[12] T.Lunt, et al., accepted by NME

Speaker: T.A. Lunt (EPS 2019)

198 O2.102 The new Divertor Tokamak Test facility

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.102.pdf

Appropriate disposal of the non-neutronic energy and particle exhaust in a reactor is universally recognized as one of the high priority challenges for the exploitation of fusion as an energy source. The new Divertor Tokamak Test (DTT) facility, which will be built in Italy, is a tool to address that challenge in high-field, high performance tokamak with complete integration between core and edge plasma scenarios. DTT is superconducting tokamak with 6 T on-axis maximum toroidal magnetic field carrying plasma current up to 5.5 MA in pulses with length up to 100s. The D-shaped device is updown symmetric, with major radius R=2.11 m, minor radius a=0.64 m and average triangularity 0.3. The auxiliary heating power coupled to the plasma at maximum performance is 45 MW, shared between 170 GHz ECRH, 60-90 MHz ICRH and 400 MV negative ion beam injectors. This allows matching the PSEP/R values, where Psep is the power flowing through the last closed magnetic surface, with those of ITER and DEMO. DTT is in fact designed to reach PSEP/R =15 MW/m. The plasma facing material is tungsten, sprayed on the first wall and bulk in the divertor. The entire machine is up-down symmetric to allow the study of double null (DN) divertor configurations and will be maintainable through remote handling. The central solenoid, the toroidal and the poloidal field coils will all be superconducting (mostly Nb3Sn), with the possibility of adding in a second phase a hightemperature superconducting insert in the central solenoid to test this emerging technology in a fusion environment. Sets of copper internal coils will be used for vertical stabilization, divertor control and for ELM/RWM control. This presentation will discuss the state of the art of the project, illustrating its scientific background, the expected plasma scenarios - in particular as far as plasma exhaust is concerned - and the main technology choices so far. Emphasis will be given to highlight the effort to design an experimental tool, which will be a device not only for plasma exhaust studies, but also for the advancement of fusion science in the grand sense.

Speaker: P. Martin (EPS 2019)

199 O2.103 Comparison of three-dimensional plasma edge turbulence simulations in realistic double null tokamak geometry with experimental observations

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.103.pdf

In the present work, global, three-dimensional edge plasma turbulence simulations of a MAST L-mode attached plasma discharge are presented. Our study is based on the driftreduced Braginskii equations, solved with the STORM module of BOUT++ for realistic MAST parameters in disconnected lower double null configuration. The plasma profiles are evolved self-consistently, with no separation between equilibrium and fluctuations, on a grid of approximately 14 million points and a resolution at the outer mid-plane up to kperpRhos~1. The simulations reveal that plasma turbulence is characterized by fluctuations showing a strong ballooning character. Because of the strong magnetic shear near the X-points, fluctuations at the divertor targets are not correlated with the mid-plane near the separatrix. On the other hand, filaments are more homogenous along magnetic field lines in the far scrape-off layer (SOL), consistently with theoretical expectations (e.g., see [Krasheninnikov et al., J. Plasma Fusion Res. 6, 139 (2004)]). Moreover, ExB counter flows are observed in the divertor legs near the separatrix. As a result, filaments are generated locally in this region, enhancing the radial transport and widening the radial profiles both in the SOL and in private flux regions (PFRs). The numerical results are then validated against experimental measurements both qualitatively and quantitatively. Filaments have previously been observed to exhibit different properties in the SOL, in the PFRs and in the divertor legs [Harrison et al., Phys. Plasmas 22, 092508 (2015)]. This is recovered in our simulations. Striations on the divertor plates, as are seen with infrared imaging diagnostics, are also reproduced. Plasma profiles and statistical properties are validated against Langmuir probe measurements both at the outer mid-plane and at the divertor targets. Overall, the numerical results are in good agreement with experimental observations and theoretical expectations. This study gives a deep insight into the mechanisms that govern the SOL plasma dynamics in diverted configurations, providing a consistent picture of the diverse phenomena observed at the tokamak periphery.

Speaker: F. Riva (EPS 2019)

200 O2.104 Steady and oscillatory applied sheared flows in global gyrokinetic simulations

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.104.pdf

In order to get a better understanding of the linear and nonlinear plasma interaction of microinstabilities and associated turbulence with different specific modes, an antenna is implemented in the global gyrokinetic code ORB5. It consists in applying external chargeand current-density perturbations or, alternatively, external electrostatic and magnetic potentials, to the system. The contributions of the antenna are considered separately from the perturbed plasma fields and can thus be accounted for even in linear simulations where the perturbed field contributions to the particle orbits are neglected. In a first step, we use this antenna to excite zonal structures. As a proof of principle, we start by scanning the shearing rate of the applied ExB flow and measure its effect on the linear growth rate of electrostatic instabilities such as ion temperature gradient (ITG) instabilities and trapped electron modes (TEMs). Second, time-dependent antenna excitations are considered to address the effectiveness of the corresponding non-stationary ExB sheared flows in stabilizing such modes. Our results are consistent with previous analytical works [1]. Third, the nonlinear plasma response is included to study the effectiveness of the turbulence saturation by the oscillatory sheared flows. The antenna is also used to excite geodesic acoustic modes (GAMs) and study their coupling with microinstabilities. We then address the question of the origin of nonlinear zonal structures (avalanche-like features) observed to propagate at a frequency similar to the one of linear GAMs.

[1] T. S. Hahm et al., "Shearing rate of time-dependent E◊B flow", Physics of Plasmas, 6(3), 922-926, 1999

Speaker: N. Ohana (EPS 2019)

201 O2.105 Investigation of intermittent and continuous transport in the scrape-off layer of ASDEX Upgrade

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.105.pdf

In magnetic confinement fusion, transport processes in the plasma edge region determine the power load onto the first wall materials which has to be minimized on the way towards a fusion power plant. While a main fraction of the power is transported parallel to the magnetic field lines to the divertor, a significant part can directly reach the plasma facing components by turbulence driven transport perpendicular to the magnetic flux surfaces. The steady state part of the particle and power flux leads to a distinct power fall-off length in the divertor. Intermittent phenomena, however, lead to an increased radial transport by convection. These phenomena are caused by plasma instabilities like edge-localized modes (ELMs) or turbulence. To investigate these steady-state as well as fast transport processes, the thermal helium beam plasma edge diagnostic at ASDEX Upgrade (AUG) is used [1]. Providing unique simultaneous measurement of electron temperature and density over a wide radial range, this diagnostic resolves ELM and inter-ELM filaments with a lifetime on the order of 10 µs, velocities of up to several km/s and a typical structure size of 5-10 mm. This contribution addresses the radial position of the origin of filaments by comparing the radially resolved portion of the convective and diffusive part of density transport. For the formed filaments which propagate into the far scrape-off-layer, the radial propagation velocity as well as their temperature and density evolution is investigated. The detected perturbations inside the last closed flux surface are correlated with Doppler reflectometry measurements. The results are compared for different confinement regimes as well as plasma scenarios, comprising L and H-mode, type-I ELMs, small ELMs and inter-ELM filaments.

References
[1] M. Griener, E. Wolfrum, M. Cavedon, et al., Rev. Sci. Instrum. 89, 10D102 (2018).

Speaker: M. Griener (EPS 2019)

202 O2.106 Influence of edge plasma parameters on anomalous transport driven by current-convective turbulence in tokamak divertor plasma

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.106.pdf

Observations of divertor plasma turbulence in a series of experiments at the DIII-D tokamak has recently demonstrated the onset of parallel current and magnetic field fluctuations [1] with temporal parameters similar to those reported for the fluctuations of divertor plasma radiation intensity at the ASDEX Upgrade tokamak (AUG) [2], when it was operating in the fluctuating state of detachment. This regime is characterized by the strong asymmetry in detachment and, consequently, large difference in electron temperatures between the inner and outer divertor legs of the machine, which can possibly drive the onset of the current-convective instability [3] eventually leading to saturated turbulence with spatial and temporal properties similar to those experimentally observed in DIII-D and AUG [4-6].
In this contribution, we employ the physical model of the current-convective instability of Ref. [6] to analyze the influence of the divertor plasma parameters on the anomalous transport driven by saturated current-convective turbulence under the detachment conditions similar to the DIII-D tokamak. The spatial and temporal spectra of plasma fluctuations are shown and analyzed. In particular, the data on parallel current and magnetic field oscillations at the inner strike point are demonstrated and compared with the available experimental results [1]. Finally, the amplitudes, spatial and frequency compositions of turbulent oscillations of the plasma parameters is used to construct the anomalous transport coefficients in the form applicable for their use in global transport codes, such as SOLPS.

References
[1] J. Boedo, D. Rudakov, I. Bykov, et al., 60th APS DPP meeting, Bull. Am. Phys. Soc. (2018).
[2] S. Potzel, M. Wischmeier, M. Bernert et al., Nucl. Fusion 54, 013001 (2014).
[3] S. I. Krasheninnikov, and A.I. Smolyakov, Phys. Plasmas 23, 092505(2016).
[4] A. A. Stepanenko, and S. I. Krasheninnikov, Phys. Plasmas 25, 012305 (2018).
[5] A. A. Stepanenko, H. Q. Wang, Plasma Phys. Reports (accepted).
[6] A. Stepanenko, H. Wang, and S. Krasheninnikov, 60th APS DPP meeting, Bull. Am. Phys. Soc. (2018).

Speaker: A.A. Stepanenko (EPS 2019)

MCF

Convener: K. Crombé (Department of Applied Physics| Ghent University| Belgium)

203 I2.102 Wall conditioning in fusion devices with superconducting coils

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.102.pdf

This contribution reviews the currently applied wall conditioning methods in fusion devices with special emphasis on wall conditioning in the presence of a permanent magnetic field by applying RF discharges at the ion- and electron cyclotron range of frequencies (ICRF resp. ECRF). The review is built upon the results of tokamaks JET, TEXTOR, TCV, ASDEX Upgrade and JT60-U. Stellarators experience is based on W7-X, U2-M and LHD. The roles of traditional wall conditioning methods such as baking, glow discharge conditioning (GDC) and low-Z wall coatings on superconducting devices will also be discussed.
Wall conditioning is essential to increase the plasma performance in fusion devices by reducing the release of volatile plasma impurities from the first wall due to plasma-surface interactions, and to control the recycling of hydrogenic fuel fluxes [1]. In particular, ITER relies on conditioning to mitigate the tritium inventory build-up in the plasma-facing materials [2].
Current research efforts on RF conditioning aim at developing reliable RF plasma production methods for tokamaks as well as stellarators using ICRF and ECRH systems to produce a currentless plasma. RF conditioning plasmas, in reactive or noble gases, are characterized by a significant higher density than glow discharge plasmas. This enhances desorption of volatile species during conditioning, although requires pulsed plasma operation to reduce their re-ionisation. The location and size of the plasma-wetted area is determined by the shape of the confining magnetic field, allowing targeted interaction with limiters or divertor. For example, stellarator He-ECRH plasma, produced by localised power absorption at the EC resonance layers, was shown to effectively desaturate the divertor targets from hydrogen on W7-X.
ECRH plasma production in the tokamak vacuum magnetic field, with much reduced confinement, is hampered by a low single pass absorption. To increase the single pass absorption, high densities and temperatures at the resonance layer are required, and hence considerable launched power. Strong and volumetric collisional absorption at low density and temperature is characteristic for ICRF plasmas, relaxing the power requirements for these plasmas and simultaneously improving the discharge homogeneity. While not necessarily accessing the same areas, the amount of retained fuel in the plasma facing materials accessible to ICRF conditioning is larger than that of L-mode plasmas by a factor 2, and approaches that of GDC in isotopic exchange experiments on the JET-ILW.
RF wall conditioning discharges in future devices such as ITER and JT60-SA are studied with help of the codes TOMATOR, KIPT-RF and RFDINITY. A brief description of these simulations and the underlying physical principles will be presented.

[1] Winter J. Plasma Phys. Control. Fusion 38 (1996) 1503-1542.
[2] ITER Research plan, 17 Sept 2018, report no ITR-18-003

Speaker: T.M. Wauters (EPS 2019)

204 I2.103 Nitrogen transport inventory evolution and ammonia formation in N2-seeded discharges on ASDEX Upgrade and JET

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.103.pdf

To prevent damage to the divertor target plates, impurity seeding will be unavoidable in ITER. Among the tested impurities, nitrogen (N) is the most likely candidate impurity. Besides promoting the radiation in the plasma edge, nitrogen seeding also provides improved confinement in existing tokamaks. The drawback of using N is the related ammonia formation which could act as a mechanism of in-vessel tritium retention during the active phase of ITER operation. Ammonia formation was studied both in dedicated experiments with stable discharge conditions and as piggy back data analysis with significantly larger variation of discharge parameters. Formation of ammonia was observed through measuring its concentration in the neutral gas and the emission of the ND radical. Both diagnostics showed same global trends as well as a consistent spatial distribution which showed that the dominant contribution to ammonia formation comes from surface reactions on plasma-shaded surfaces surrounding the divertor. Amount of detected ammonia was proportional to the N density in the core, as detected with charge exchange spectroscopy, and this relation dominated over the impact of any other discharge parameter. The N density itself strongly was impacted by recycling, governed by the nitrogen wall inventory, which is related to the implementation of N into W and Be. As a consequence, variations of factor of 2 were detected in the N density in the core and edge at the same N2 seeding rates. In both datasets, the N was injected into the divertor area, which resulted in a very low seeding efficiency. The seeding efficiency was vastly improved with alternative injection locations (top and midplane), and the impact of the wall inventory was reduced, while keeping the same beneficial effects on the plasma. In discharges where N2 seeding was replaced with BN powder injections neither N2 nor ammonia was detected in the neutral gas, while the core N concentration was relatively high. However, the radiation pattern also diverged from the desired distribution around the X-point. Nevertheless, these results demonstrate that the N distribution in the plasma, and the resulting ammonia formation can be strongly affected with the choice of N source.

Speaker: A. Drenik (EPS 2019)

205 O2.107 Modelling of tungsten erosion transport and deposition in fusion devices

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.107.pdf

Tungsten (W) is a candidate for plasma-facing components in future fusion reactors like DEMO and already used in fusion experiments like JET-ILW and ITER, which is currently under construction. It is foreseen for wall areas of highest particle and power loads as it has high melting point and low physical sputter yield. However, already small amounts of W in the core plasma can lead to plasma cooling and radiation collapse. Thus, W erosion has to be minimised and for this understanding of the erosion and deposition mechanisms is needed. In [1] a dedicated pulse of JET-ILW has been successfully benchmarked with ERO modelling by comparing measured and modelled W emission in the outer divertor for inter- and intraELM phases. The focus of the present contribution is on ERO modelling studies of W erosion, transport and deposition under typical conditions present in the inner and outer divertor of JET-ILW. For this, the strike point plasma temperature and density for the interELM phases are assumed to be 7eV, 2.5E20m^-3 for the inner and 35eV, 6E19m^-3 for the outer divertor. For the ELM-phases the densities are increased and the background ions (deuterium and beryllium) are assumed to have impact energies in the keV range following the "FreeStreaming-Model". Under all conditions the deposition of eroded W is very high with surface-integrated values up to nearly 100%. The gross W erosion is largest during ELMs, whereas in particular the erosion in-between ELMs in the inner divertor is negligibly small. The W erosion in-between ELMs is dominated or exclusively due to the beryllium (Be) background ions, whereas during ELMs deuterium ions contribute significantly. The role of W self-sputtering and various Be plasma concentrations will be discussed. The deposition of Be from the background leads to W-Be surface mixing and thus a decrease of the W erosion with exposure time. However, the individual inter- and intra-ELM phases are too short to reach steady state surface concentrations within these phases. The results of a dynamic simulation with consecutive ELM- and inter-ELM phases will be presented.

[1] A. Kirschner et al., Nuclear Materials and Energy 18 (2019) 239

Speaker: A. Kirschner (EPS 2019)

206 O2.108 Effect of fuel isotope mass on q-profile formation in JET hybrid plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.108.pdf

The initial current ramp phase of JET hybrid plasmas is used to optimise the q-profile to allow access to high beta and avoid MHD instabilities. Mixed protium-deuterium experiments have shown that the q-profile evolution during this phase varies systematically with average main ion isotope mass (Meff), as seen in Fig.1, indicating the need for re-optimisation for future T and D-T experiments. <Te> increased with Meff, consistent with improved Ohmic confinement and/or reduced electron-ion coupling (a). But the 3.6 effect on plasma resistivity was compensated by an onset time of 1,1 MHD (s) increase in Zeff with Meff due to increased metallic impurity contamination, consistent with increased 3.4 sputtering by higher mass isotopes (b,c). Current diffusion modelling shows that the key factor for 3.2 the change in q-profile evolution was a reduction in Te peaking as Meff was increased, which was due to increased radiation. Reduced Te peaking can lead to magnetic shear reversal, 2/1 double tearing modes and disruptions, suggesting an increased likelihood of disruptions in T and D-T. To mitigate this risk Te peaking measurements are being included in the real-time control system to allow disruptions to be avoided by central heating, gas puffing or early pulse termination. These results and the experience being gained at JET will help to guide the safe transition to D and D-T in ITER.

(a) E. Delabie et al 2017 Proc 44th EPS Conference on Plasma Physics (Belfast, Northern Ireland, UK) P4.159
(b) D. Borodin et al 2018 Proc 27th IAEA Fusion Energy Conference (Ahmedabad, India) EX/P1-14
(c) S. Brezinsek at al 2018 Proc 27th IAEA Fusion Energy Conference (Ahmedabad, India) EX/9-4

Speaker: C.D. Challis (EPS 2019)

207 O2.109 Drift kinetic description of neoclassical tearing modes

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.109.pdf

Understanding the physics of the NTM onset and its suppression is a key problem in achieving controlled fusion. This requires better knowledge of the NTM threshold mechanism.
We solve the drift kinetic equation for the ion/electron response to the NTM magnetic perturbation, gi,e, assuming small magnetic island width, w<< 0, Vparallel is the parallel component of velocity. The particle distribution is then found to be attened across these drift islands rather than the magnetic island. This results in incomplete attening of the density/temperature pro le across the NTM island for w ~ rhotheta. As rho theta,e << rho theta,i, this effect is less signicant for electrons. To maintain plasma quasi-neutrality, an electrostatic potential is generated that slightly modifies the S island structure.
We identify a narrow collisional boundary layer in pitch angle around the trapped-passing boundary of width ~Sqrt(nu) , where nu is the collision frequency normalised to a characteristic drift frequency. In this region, collisions cannot be treated perturbatively and S no longer describes the streamlines. We provide a solution to the 2-D boundary layer problem, employing a momentum-conserving collision operator, allowing us to rigorously connect the trapped and passing regions. We show that the plasma response to the magnetic island is stabilising, providing a threshold island width for NTM instability of w<=wc = 2.67 rho theta,i [1,2] and 2.73 rho theta,i from full numerical and analytic solutions, respectively. This novel NTM threshold result appears to arise from the response of the electrons to the electrostatic potential required for quasi-neutrality.

References
[1] K. Imada et al., PRL 121, 175001 (2018)
[2] K. Imada et al., Nucl. Fusion 59 046016 (2019)

Speaker: A.V. Dudkovskaia (EPS 2019)

208 O2.110 Stationary ELM-free H-mode in ASDEX Upgrade

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.110.pdf

The H-mode is the preferable operation regime for a fusion reactor due to its superior confinement properties, but it comes with a major drawback: edge-localized modes (ELMs). These instabilities lead to unacceptably high heat loads on the divertor when extrapolated to large-scale machines [1]. The ELM-free phases traditionally observed in poorly heated H-modes are not a viable solution to this problem due to their transient nature and impurity accumulation. Therefore alternative regimes must be found or further studied to allow the successful operation of future reactors. This contribution reports on a stationary H-mode without ELMs recently achieved in the ASDEX Upgrade tokamak at moderate fueling by applying central electron cyclotron resonance heating with a power slightly above the L-H power threshold. This low-torque scenario has high Greenwald fraction, fGW ~ 0.8, and good energy confinement, with an enhancement factor H98y2~1, but no tungsten accumulation despite the absence of ELMs. It was naturally obtained in favorable B configuration without boronization for wall conditioning but it is sensitive to the fueling level and heating power. Additional experiments are planned to widen its parameter space and achieve higher performance. The ELM-free regime always features an edge electromagnetic quasi-coherent mode whose density fluctuations are measured by several diagnostics. Its magnetic signature is detected only by the pick-up coils closest to the plasma, probably because of the strong radial decay due to the high mode number as estimated with microwave reflectometry. The quasi-coherent mode seems to be responsible for enhanced transport losses as its appearance and disappearance are correlated with changes in edge and divertor parameters. This instability is likely a key player in the stationary ELM-free H-mode, which is a promising mode of operation for future reactors.

[1] Leonard, A. W. (2014). Edge-localized-modes in tokamaks. Physics of Plasmas, 21(9), 090501

Speaker: L. Gil (EPS 2019)

12:40 Lunch - Women in Plasma Physics Lunch

Poster P2

209 P2.1001 SPARC: Extending the high-field path to a net-energy tokamak

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1001.pdf

SPARC is designed to be a high-field (B0 = 12 T), compact (R0 = 1.65 m), D-T burning plasma tokamak with the goal of producing net energy gain (Q > 1) from magnetic fusion for the first time. Currently in the pre-conceptual design phase, SPARC will utilize new magnets based on rare-earth barium copper oxide (REBCO) high temperature superconductors (HTS), continuing the high-field path of the Alcator series of tokamaks. While previous high-field, net-energy tokamak designs (Ignitor, CIT, BPX, and FIRE) were considered technological dead-ends for power generation due to the power consumption in their copper magnets, HTS opens a new pathway to a high-field fusion power plant, as embodied in the conceptual ARC design [1, 2]. Using conservative plasma physics (H98 = 1), SPARC is projected to generate more than 50 MW of fusion power and achieve Q > 2.0, while being closer than ITER in dimensionless plasma parameters to current experiments. Additionally, SPARC is projected to achieve Q = 1.0 in L-mode with H89 = 1. Other aspects of the machine, such as the divertor and ICRF heating, will also be discussed in this presentation.

[1] B. Sorbom et al., Fus. Eng. Design 100, 378 (2015). [2] A.Q. Kuang et al., Fus. Eng. Design 137, 221 (2018).

This work is supported by Commonwealth Fusion Systems.

Speaker: A.J. Creely (EPS 2019)

210 P2.1002 Generalization of the Heuristic Drift Model for Finite Collisionality

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1002.pdf

Speaker: R. Goldston (EPS 2019)

211 P2.1003 RFX-mod2: a Reversal Field Pinch device with edge transport optimization

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1003.pdf

The edge of magnetically confined plasmas in toroidal configurations is characterized by the presence of various magnetic perturbations (MPs), appearing spontaneously as tearing modes in the Reversed Field Pinch (RFP) [1] or as peeling ballooning modes (ELM) in the tokamak. In the RFX-mod device during high-current discharges (R=2m, a=0.46m, IP>1MA) an almost monochromatic tearing mode (TM) spectrum spontaneously develops: this is the so-called quasisingle helicity (QSH) [2, 3], characterized by the presence of a single mode with helicity m/n, with (m=1, n=7) the poloidal and toroidal mode numbers respectively. However, the presence of secondary modes (m=1,n>7), with amplitudes one order of magnitude smaller than the dominant one, results in a local pattern of constructive interference (phase locking) and in a radial displacement of the plasma edge surface [4]. The intensity of the deformation can be comparable to that of the dominant mode, appearing as a sharp decrease ("hole") of the connection length to the wall at the locking angle, as shown by simulations with the ORBIT code [5,6]. An upgrade of RFX-mod device, RFX-mod2 [7], will be assembled in the near future. It will be characterized by a copper shell as continuous conductor nearest to the plasma and by a shellplasma proximity reduction from b/a=1.11 to b/a=1.04, likely improving feedback coils action. 3D MHD non-linear visco-resistive simulations show that secondary TM amplitude and the edge deformation due to phase locking will decrease by a factor 2 [8, 9]. Simulations with ORBIT show that in RFX-mod2 the average parallel connection length to the wall is expected to increase by a factor 8 with respect to RFX-mod, with no "hole" at the locking angle [6]. Having virtually cancelled the effect of TMs at r=a with a front end which behaves like an ideal wall, plasma wall interaction in RFX-mod2 could arise only due to the residual error fields at the gaps [8]: these upgrades are expected to lead to an optimized edge transport, with a well-formed SOL and to an improvement of the global plasma performance.
References [1] N. Vianello et al, Nuclear Fusion 53 (2013) 073025 [2] Escande D. et al, PRL 85 (2000) 1662 [3] Lorenzini R. et al, Nature Physics 5 (2009) 570 [4] P. Zanca and D. Terranova Plasma Phys. Control. Fusion 46 (2004) 1115 [5] R.B. White and M.S. Chance, Phys. Fluids 27 (1984) 2455 [6] P. Scarin et al, to be published in Nuclear Fusion (2019) [7] S. Peruzzo et al, Fusion Eng. Des. 136 (2018) 1605 [8] L. Marrelli et al, to be published on Nuclear Fusion (2019) and this conference [9] D. Bonfiglio et al, this conference

Speaker: M. Veranda (EPS 2019)

212 P2.1004 Towards the ITER NBI: impact of the plasma parameters on the performances of a large ITER-like beam.

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1004.pdf

The neutral beam injection (NBI) system for the ITER experiment will be based on the production and acceleration of negative H/D ions. The ion beam requirements combine high accelerated current density (230 A/m2 in H, 200 A/m2 in D) with low core divergence (<7 mrad) and high uniformity over the extraction surface (better than 90 %). The ELISE test facility has the same width and half the height of the ITER NBI source and 3 grids (ITER-like arrangements: 640 apertures grouped in 8 beamlets groups) with a maximum total high voltage of 60 keV. At ELISE, the simultaneous achievement of the ITER NBI requirements in terms of accelerated ion current density (at a stripping fraction of about 12%), electron-ion ratio lower than one at the operational filling pressure of 0.3 Pa in H have been successfully achieved [1]. In order to study the beam in terms of accelerated current and beam uniformity focusing on the vertical profile several beam diagnostics are installed along the beamline. The analysis on the surface of a diagnostic calorimeter provide a 2D map of the beam power density profiles (4×4 cm2 resolution) while beam emission spectroscopy gives divergence measurements along the vertical direction (5 cm spaced). The accelerated current shows different dependences on the source parameters and a clear inhomogeneity in terms of beamlet group intensity is observed. In this work, plasma parameters such as positive and negative ion densities will be studied at ITER-relevant source parameters in order to identify the main causes of the beam non-uniformity. This can give indications on how to actively improve and control the beam uniformity of the large beams for ITER NBI.

[1] HEINEMANN, B. et al. Achievements of the ELISE test facility in view of the ITER NBI. Fusion Engineering and Design, jan. 2019.

Speaker: I. Mario (EPS 2019)

213 P2.1005 A Compact Advanced Tokamak for a Steady State Fusion Pilot Plant

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1005.pdf

First of a kind physics-based simulations project a compact net electric fusion pilot plant with a nuclear testing mission is possible at modest scale based on the advanced tokamak concept, and identify the key parameters for its optimization. These utilize a new integrated 1.5D core-edge approach for whole device modeling to predict plasma performance, by self-consistently applying the latest transport, pedestal, equilibrium, stability and current drive physics models to converge fully non-inductive stationary solutions without any significant free parameters. This contrasts with previous "systems code" approaches, where parameters are simply set to desired values. This physics based approach has led to new insights and understanding of reactor optimization. In particular, results highlight the critical levering roles of density and plasma pressure or b (see figure), which increase fusion performance and self-driven `bootstrap currents', thereby reducing current drive demands to enable high pressure solutions at compact scale with net electricity generation.
Plasmas at 6-7T with ~4m major radius scale and 200MW net electricity are found with margins and trade-offs identified in achievable parameters. Auxiliary current drive is projected from neutral beam and ultra-high harmonic (helicon) fast wave, though other advanced current drive approaches presently being developed also have potential. The resulting low recirculating power in a double null configuration leads to a divertor heat flux challenge that is comparable to ITER, though reactor solutions may need to increase dissipation further. Neutron wall loadings also appear tolerable. Strong H-mode access (factor >2 margin over the L-H transition scaling) and ITER-like heat fluxes are maintained with ~20-60% core radiation.
The approach would benefit from high temperature superconductors, the higher fields of which increase performance margins, while their potential for demountability may facilitate a nuclear testing mission. However, solutions are possible with conventional superconductors. An advanced load sharing and reactive bucking approach in the machine centrepost region provides improved mechanical stress handling. The prospect of an affordable test device which could close the loop on net-electric production and conduct essential nuclear materials and breeding research is thus compelling, motivating research to prove the techniques projected here.

Speaker: R.J. Buttery (EPS 2019)

214 P2.1006 Equilibrium and stability calculations of MAST spherical torus plasmas in preparation for MAST-U

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1006.pdf

Disruption prediction and avoidance is necessary in future MAST-U spherical tokamak discharges to enable long-pulse plasma operation. Research examining the stability of plasmas in the MAST database utilizing new kinetic equilibrium reconstructions and comparisons to present models in the Disruption Event Characterization and Forecasting code (DECAF) [1] will illuminate relevant physics and enable subsequent analysis and control for MAST-U. A parametrized forecasting model for Nno-wall implemented in the DECAF code and tested for NSTX is compared to MAST using input from magnetics-only reconstructions. Initial ideal MHD stability analysis has also begun using the DCON code with unstable modes found above about N = 5 for the magnetics-only reconstructions. The DECAF model for Nno-wall was about 4.3 for similar plasma conditions. The continuing work is now examining improvements to the accuracy of global MHD stability analysis gained when using equilibrium reconstructions including kinetic plasma profiles and motional Stark effect data on MAST plasmas. It is also important for spherical tokamak plasmas to include currents in the device conducting structure, as they can comprise a significant component of the toroidal current during the discharge. An axisymmetric wall model of MAST created for EFIT analysis is also used in VALEN time-domain calculations using experimental currents in coils with and without plasma current for verification. The DECAF code consists of many separate physical event modules that provide warnings and declare occurrences of certain events leading to disruption and has been applied to the MAST database to examine density and vertical stability limits. Disruptivity diagrams indicate where disruptions occur in various parameter spaces, and examination of vertical displacement events show that they occur less often than in NSTX, but when they do occur it is in close time proximity to the disruption current quench. MAST operation was bound by the Greenwald density limit, and this limit was often reached in the current ramp-down which lowered the limit below the level of the experimental plasma density.
Supported by US DOE Grant DE-SC0018623. [1] J. W. Berkery et al., Physics of Plasmas 24 (2017) 056103

Speaker: J.W. Berkery (EPS 2019)

215 P2.1007 Design and engineering overview of the Alborz Tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1007.pdf

The Alborz tokamak project has been in the phase of construction at the Amirkabir University of Technology, Iran, since 2012. The completion of this new fusion experimental device fabrication accomplished recently and the start of its commissioning phase is scheduled for the near future. To this end, the initial system tests are now being in process to achieve the plasma with optimal design conditions. In this initial phase of the Alborz tokamak operation, the design purpose is to achieve a 20 kA plasma current with 20 ms duration. The 0.45 m major and 0.15 m minor radii of this tokamak leads to the allowed amount of 3 to the aspect ratio. In addition, the toroidal magnetic field at the axis is 0.85 T, which seems to be appropriate for a medium size tokamak. In this study, the main features of the Alborz Tokamak engineering design, including magnetic field systems, vacuum system and supporting structures have been addressed in detail and several key engineering progress and modifications of the current underway works have been elaborated.

Speaker: M. Ghasemi (EPS 2019)

216 P2.1008 Recent developments in the ITER Integrated Modelling Programme

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1008.pdf

The ITER Integrated Modelling & Analysis Suite (IMAS) is the software infrastructure developed using expertise from across the research facilities within the ITER Members to meet the needs of the ITER Integrated Modelling Programme. It builds around a standardised representation of data described by a Data Dictionary that is both machine independent and extensible. Machine independence is important for allowing tools and workflows developed in IMAS to be tested on existing devices, whilst extensibility allows the Data Dictionary to grow and evolve over time as more and more Use Cases are addressed. In addition to providing all the scientific tools for the scientific exploitation of ITER once operations start, IMAS also has a role to play during the construction phase by providing simulation data to support systems design, in particular for diagnostics, heating, fuelling and control systems. This aligns well with one of the primary simulation capabilities that IMAS needs to deliver, namely end-to-end simulations of ITER plasma scenarios capable of meeting the physics fidelity and runtime requirements of different Use Cases, including scenario design, PCS controller development and pulse validation. An IMAS database of ITER simulations has been created to help manage the exchange of physics data with ITER collaborators and Domestic Agencies. The database is being populated through a combination of translating existing data and running new simulations, with datasets representing all stages of the ITER Research Plan already available. In preparation for ITER operations, near-term plans include the development of experimental data processing and analysis pipelines. This activity will build upon the experience and best practices developed within the R&D facilities of the ITER Members. Whilst the detailed implementation of the processes for combining diagnostic contributions and validating the measurements is yet to begin, the need for a strictly managed, yet flexible, process is recognised, and infrastructure developments are conducted bearing this in mind.

Speaker: S.D. Pinches (EPS 2019)

217 P2.1009 Modification of SXB method for hydrogen isotopes in ITER main chamber

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1009.pdfAn analysis is carried out of the possibility of using the high-resolution spectroscopy (HRS)
data, specifically, the asymmetry of the spectral line shape of the radiation emitted in the
Balmer-alpha lines of hydrogen isotopes, to recover the flux of neutral hydrogen atoms and
molecules from the tokamak first wall to the SOL plasma in real time measurements. To this
end, a new method is proposed, which generalizes the well-known SXB method [1, 2], widely
used for recovery the impurity atoms/ions fluxes from wavelength-integrated spectral line
measurements, to the case of hydrogen. The proposed modification is motivated by the
impossibility of reliable interpretation of molecular spectra in the ITER main chamber
because of a strong background light from the divertor. The method makes it possible to
replace the equation corresponding to the DXB method for molecular spectra with another
equation using the relation between the asymmetry of the line shape of spectral intensity and
the atomic flux density. The method uses atomic and molecular flux density profiles,
simulated [3] with the modified Ballistic Model [4]. The modified SXB method is tested by
comparing the results with the data for deuterium neutral atom velocity distribution in the
SOL from the EIRENE code [5] stand-alone simulations [6] on the background plasma
modeled by the SOLPS code [7] with extended to the wall numerical mesh [8], for six
modelled types of the SOL plasma profiles in ITER (these data were used in synthetic H-
alpha diagnostics [9] based on solving a multiparametric inverse problem). The limitations
of the method are discussed, including the problem [9] of selecting the HRS signal from the
SOL under condition of a strong divertor stray light in ITER.
References
[1]. Behringer K. H., J. Nucl. Mater., 1987, 145­147, 145. [2]. Pospieszczyk A., et al., J. Phys. B: At. Mol. Opt. Phys., 2010, 43, 144017. [3]. Neverov V.S., private communications, 2018. [4]. Kadomtsev M.B., et al., Eur. Conf. Abstracts, 2012, vol. 36F, P4.093. [5]. Reiter D., et al., Fusion Sci. Technol., 47, 172 (2005). [6]. Lisgo S. W., et al., private communications, 2012. [7]. Kukushkin A.S., et al., Fusion Eng. Des. 86, 2865 (2011). [8]. Lisgo S. W., et al., J. Nucl. Mater., 415, 965 (2011). [9]. Kukushkin A.B., Neverov V.S., et al., Fusion Sci. Tech., 2016, 69, 628.

Speaker: R.I. Khusnutdinov (EPS 2019)

218 P2.1010 Spectral intensity of electron cyclotron radiation coming out of plasma in various regimes of ITER operation

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1010.pdf

Electron cyclotron radiation (ECR) in ITER (in contrast to all previous devices) is expected to play an important role in power loss balance due to high electron temperature and high magnetic field [1], [2]. This radiation is also a source of additional thermal and electromagnetic load for microwave and optical diagnostic [3]. ECR from the plasma dominates over the nominal stray radiation from electron cyclotron resonance heating (ECRH) and current drive (ECCD) microwave power sources in high performance discharges and therefore its implication for diagnostics must be investigated [3]. This is especially important for mm-wave diagnostics in ITER such as microwave reflectometers, and Collective Thomson scattering system, whose transmission lines allow, in principle, additional measurements of EC radiation spectra [4]. The transmission lines for HFS reflectometry are planned to use the same waveguides for X-mode observation in frequency band 12-90 GHz and O-mode observations in the band 18-140 GHz. Although the working frequency range is significantly lower than the operational frequency for ITER ECRH system (>170 GHz), the antennas and the waveguide can receive the entire emission spectrum at frequencies above 12 GHz. In this case, the absorption and heating in the primary and secondary vacuum windows and the residual power on the receiving mixers is determined both by the initial power of the EC radiation from the plasma and by the transmission line losses, which increase strongly with increasing frequency. Here we report on calculations, with the CYNEQ code [2], [5] of spectral intensity of the ECR coming out of plasma in various regimes of ITER operation in the view of its possible influence on in-vessel components and diagnostics.
References
[1] F. Albajar et al., Nucl. Fusion 45, 642-8 (2005) [2] A.B. Kukushkin, P.V. Minashin and A.R. Polevoi, Plasma Phys. Rep. 38, 211-20 (2012) [3] J.W. Oosterbeek et al., Fusion Engineering and Design 96-97, 553-6 (2015) [4] V.S. Udintsev et al., EPJ Web of Conferences 32, 03013 (2012) [5] A.B. Kukushkin, Proc. 14th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research
(Wuerzburg, Germany, 1992), IAEA, 2, 35-45 (1993)

Speaker: P.V. Minashin (EPS 2019)

219 P2.1011 High-energy neutron characterisation of scintillator and solid-state detectors for lost fast ions measurements in JT-60SA and ITER

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1011.pdf

Present day Fast Ion Loss Detectors (FILD) installed in tokamaks and stellarators are usually made of a scintillator coupled to a suitable optical system. For the conceptual design of an ITER-relevant FILD prototype for JT-60SA (using a scintillator as sensitive element) it was suggested that the neutron flux that will be produced by D-D reactions may be a cause of possible concern for detector operations. This will be even more relevant for high-power plasma discharges in ITER, where the neutron flux is expected to be roughly the same as the flux of ions. As a result, it may be possible that a very high neutron-induced background is present in FILD measurements, thus harming or even forbidding correct data interpretation. For this reason, neutron sensitivity of the selected scintillator for FILD application was thoroughly investigated, along with possible alternatives. In this poster we present the results of the characterization of the response of the TG-GREEN scintillator [1] to neutrons of both 14 MeV and 2.5 MeV energy. Tests were performed at the Frascati Neutron Generator [2], and accompanied by a GEANT4 [3] simulations apparatus for data interpretation. Further, Single-crystal Diamond Detectors (SDD) and Silicon Carbide Detectors (SiC) were also studied and identified as suitable alternatives for FILD application to the use of a scintillator coupled with a light detection system.

[1] M. Garcia-Munoz et al., JINST 6 P04022 (2011) [2] A. Pietropaolo et al., J. Phys.: Conf. Ser. 1021 012004 (2018) [3] S. Agostinelli et al., Nucl. Instr. Meth. A 506 (No. 3) 250 (2003)

Speaker: E. Perelli Cippo (EPS 2019)

220 P2.1012 Analysis of pumping conditions in DEMO-FNS

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1012.pdf

DEMO-FNS is a tokamak-based fusion neutron source project being developed in Russia [1]. Issues of energy removal from DEMO-FNS were considered in [2], [3] in the "closed box" [4] approximation where the external sources and sinks of the particles, such as gas puffing and pumping, are essentially neglected. In the present paper we consider particle balance in the edge plasma, in particular, for helium that is an intrinsic reaction product, taking into account the realistic pumping speed, gas puff and He production rate. We use the SOLPS4.3 code suite [5] for 2D modelling of the edge plasma transport in the realistic geometry of the double-null magnetic configuration. The plasma consists of the D (representing both D and T), He and Ne ions and atoms and D2 molecules. The results provide the data necessary for expanding parameterization of the separatrix plasma parameters [3] by inclusion of the He-related quantities, such as the He density at the separatrix and the He atom influx to the core. This provides the more comprehensive set of the boundary conditions for the core plasma modelling in the framework of the integrated model [3].
[1] B. V. Kuteev et al., "Status of DEMO-FNS development," Nucl. Fusion, vol. 57, no. 7, p. 076039 (8pp), 2017.
[2] A. S. Kukushkin, V. Y. Sergeev, and B. V. Kuteev, "Preliminary results of divertor modelling for DEMO-FNS reactor," J. Phys. Conf. Ser., vol. 907, no. 1, p. 012012 (5pp), 2017.
[3] A. Y. Dnestrovskiy, A. S. Kukushkin, B. V. Kuteev, and V. Y. Sergeev, "Integrated modelling of core and divertor plasmas for DEMO-FNS hybrid facility," Nucl. Fusion, vol. submitted, 2019.
[4] A. A. Pshenov, A. S. Kukushkin, and S. I. Krasheninnikov, "On detachment asymmetry and stability," Phys. Plasmas, vol. 24, no. 7, p. 072508 (10pp), 2017.
[5] A. S. Kukushkin, H. D. Pacher, V. Kotov, G. W. Pacher, and D. Reiter, "Finalizing the ITER divertor design: The key role of SOLPS modeling," Fusion Eng. Des., vol. 86, no. 12, pp. 2865­2873, 2011.

Speaker: A.S. Kukushkin (EPS 2019)

221 P2.1014 Overview of ST40 results and planned upgrades

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1014.pdf

Tokamak Energy Ltd. have recently completed the first programme of operations within the compact (R = 0.4 m) spherical tokamak ST40. During the first programme ST40 was operated without a central solenoid and start-up was achieved using the Merging/Compression technique. Plasmas with a 15 ms (flat top) duration were sustained with a plasma current of 220 kA (peak transient current of 400 kA) and with a toroidal field of 0.7 T at R = 0.4 m (highest TF field achieved: 1 T at R = 0.4 m). Magnetic reconstruction has been performed using both EFIT and a new real-time reconstruction algorithm which calculates the plasma current centroid (RIp, ZIp and Ip) and plasma shape. Ion doppler spectroscopy has been used to measure the ion temperature, which has exceeded 1.5keV. We have analysed the Merging/Compression startup and developed a dimensionally correct scalings for plasma current. We have also identified high frequency MHD activity with a strongly anti-ballooning nature and an n = 0 toroidal mode number.
In the next programme we will be installing a Diagnostic Neutral Beam (DNBI) and using charge exchange recombination spectroscopy to measure the ion temperature. The plasma current will be increased and sustained using a central solenoid. Later, Thomson Scattering will be installed to measure the electron temperature. In future programmes ST40 will be upgraded to its design parameters of 2 MA plasma current, 3 T toroidal field with up to 4 MW of heating from a combination of NBI and EC. Planned experiments on ST40 will look at how the energy confinement time scales with the toroidal field. How the integral power width, q, scales in spherical tokamaks. By varying the mix of NBI and EC heating we will explore how rotation affects the confinement time.

Speaker: P.F. Buxton (EPS 2019)

222 P2.1015 Recent Development of Wide-pedestal Quiescent H-mode on DIII-D

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1015.pdf

Wide-pedestal quiescent H-mode is characterized by a pedestal width exceeding the EPED-KBM limit and an Er profile that is shallower and broader than standard QH-mode or H-mode. This natural ELM-stable regime was first discovered when the NBI torque was ramped down from strong counter-Ip towards net-zero in high triangularity, balanced double null QH-mode plasmas in the DIII-D tokamak. Experimentally reducing the NBI torque in the standard QH-mode can effectively trigger the transitions into wide-pedestal QH-mode. Across the transition, the ExB shear profile exhibits unique bi-modal changes: decreases in
the edge (YN > 0.91) and increases inside of it. A local flattening is observed in the pedestal profiles (most pronounced in Te) where enhanced density fluctuations are also detected. It is posited that lower ExB shear in the pedestal steep-gradient region enables the destabilization of edge broadband MHD and turbulence, thereby reducing pedestal gradients below the KBM limit, while the higher ExB shear inside the pedestal top enhances core turbulence suppression to improve the overall confinement.
Significant parameter space expansion of the wide-pedestal QH-mode towards more ITER and reactor relevant conditions has been achieved in DIII-D. Recent experiments reveal this regime can operate at a large range of NBI torque (4.1Nm counter- to 1.9Nm co-current) completely covering the scaled ITER-equivalent applied torque, and a range of plasma rotation profiles from co- to ctr-Ip direction. Wide-pedestal QH-mode operation with net-zero NBI torque throughout the discharge [Burrell, APS 2018] and with dominant electron heating (the ratio of ECH: NBI power ~ 3:1) [Ernst IAEA 2018] have also been demonstrated. These results suggest compatibility of the wide-pedestal QH with low NBI torque and low plasma rotation expected in ITER and future reactors.
Wide-pedestal QH-mode has been obtained in not only double null plasma shape but
also in ITER-relevant shape (LSN, davg ~ 0.4). Plasma shape effects are investigated experimentally and numerically using ELITE. In the experiments using dRsep scan, it is found that the pedestal of the `wide-pedestal' QH decreases in height and width (still wider than that using EPED-KBM scaling) when the plasma shape moves away from DN (dRsep < -1cm) towards LSN but saturates after dRsep < -2.4cm. Peeling-Ballooning instability is not found to be the limiting factor in the simulation using ITER shape and q95=3. However, wide-pedestal QH-mode has not been obtained in USN. Experiments with torque ramp down in USN or with dRsep scan from DN towards USN encounter ELMs at low torque. ELITE calculations show the P-B stability boundary in USN and LSN are quite different even though the shape is almost identical (except one is flipped one upside-down). In the
USN configuration, the ion BxÑB drift is away from the x-pt and the upper divertor is more closed. The different SOL drift and fuelling could have affected the access to wide-pedestal QH regime. Simulations and new experiments are proposed to further investigate this.
This work was supported in part by the US Department of Energy under DE-FC02-04ER546981, DE-FG02-08ER549842, DE-FG02-94ER542353, DE-FG02-08ER549994.

Speaker: X. Chen (EPS 2019)

223 P2.1016 Effects of fuelling profile on pedestal density profile

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1016.pdf

Recent experiments performed in DIII-D provide strong evidence that the edge particle source has important effects on the density pedestal structure. These experiments were performed primarily in two divertor configurations, one a very open divertor (little baffling of neutrals) and one highly closed (good baffling of neutrals), to vary the ionization profile in the pedestal with other discharge parameters held constant. Consistent with previous studies [1], modeling of the particle source shows that the more closed divertor reduced the particle source inside the separatrix. Increase of divertor
closure caused a measured reduction of the density pedestal height at about the same separatrix density as compared to that obtained in a more open divertor, implying that the ratio of separatrix to pedestal density increased as divertor closure increased. Increased divertor closure was also found to increase the separation between the locations at which the electron density and temperature gradients have their maximum values

and provided ηe =Lne/LTe, parameters significantly above unity. The decrease of pedestal electron density obtained with more closure was accompanied by an increase of the pedestal electron temperature, resulting in pedestal electron pressures that were comparable between open and closed divertors. Controlled gas scans showed that the rate of pedestal density buildup at the L-H transition and after an ELM collapse increased markedly as the gas puff rate was
increased. Nevertheless, the achieved pedestal height increased weakly with gas puff rate due to earlier onset of ELMs with higher gas fuelling. Modeling of discharges in the open divertor as well as in a highly closed slot configuration, shows that the pressure profiles are consistent with limits
expected from MHD stability. The studies here show that the fueling profile, the ELM threshold and small scale transport in the steep gradient region interact together to control the pedestal electron density profile in ELMing H-mode discharges.

[1] S.L. Allen, J. Nucl. Mat. 290-293 (2001) 995 Work supported by US DOE under DE-FC02-04ER54698, DE-AC02-09CH11466 and DE-AC05-00OR22725.

Speaker: R.J. Groebner (EPS 2019)

224 P2.1017 Active divertor flux control by the supersonic molecular beam injectionwith magnetic perturbations induced by lower hybrid waves on EAST

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1017.pdf

A serious challenge for high-power long-pulse operations of the tokamak is how to prevent damage to the plasma-facing components by particles from the edge plasma. Recently, a potential actuator to control the divertor flux distribution by using the synergy of the supersonic molecular beam injection (SMBI) and magnetic perturbations induced by lower hybrid waves (LHWs) [1–3] has been observed on EAST experiments [4]. To reveal the physical mechanism behind, first simulations with good qualitative agreements to the experimental findings are per-formed by utilizing a fluid 3D edge plasma Monte-Carlo code (EMC3) [5] self-consistently coupled to a kinetic neutral particle transport code (EIRENE) [6, 7]. The redistribution of the divertor flux is more pronounced with an increase in either the SMBI injection rate or the LHW input power. The ions and electrons originating from the ionization of injected neutral particles in the plasma edge flow along the magnetic flux tube towards the divertor, thus directly increasing the divertor flux on the split strike lines in the footprint. Combining this with the multi-lobe structure of the edge magnetic topology, actively controlling the divertor flux can be realized by adjusting the SMBI position or the phase of the magnetic perturbations.

References
[1] Y. Lianget al.,Phys. Rev. Lett.110, 235002 (2013)
[2] M. Racket al.,Nucl. Fusion54, 064016 (2014)
[3] S. Xuet al.,Nucl. Fusion58, 106008 (2018)
[4] J. Liet al.,Nat. Phys.9, 817-821 (2013)
[5] Y. Fenget al.,J. Nucl. Mater.812, 266-269 (1999)
[6] EIRENE, http://www.eirene.de
[7] D. Reiteret al.,Fusion Sci. Technol.47, 172-186 (2005)

Speaker: S. Xu (EPS 2019)

225 P2.1018 The impact of symmetry breaking on pedestal stability of tokamak plasmas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1018.pdf

H-mode tokamak plasmas are typically characterised by quasi-periodic instabilities called edge localised modes (ELMs) driven by unstable peeling-ballooning modes [1]. For large scale fusion power plants, the predicted particle and heat fluxes are unacceptable, and an active ELM control method is required. One promising method relies on the application of external non-axisymmetric resonant magnetic fields (RMPs), where ELM mitigation or even complete suppression is observed. The symmetry breaking results in coupling of axisymmetric toroidal modes and significant modification of the plasma stability is observed above a critical value of the applied RMP field as well as poloidal
localisation of the peeling-ballooning mode at locations where the 3D normal displacement of the equilibrium crosses zero EN=0. We present a new computational framework that aims to understand the effect of RMPs on both plasma equilibria and stability. The ELITE [2] code is extended to find the linearised plasma response. This linear plasma
response is used with the peeling-ballooning eigenmodes of the axisymmetric system (also calculated by ELITE) to calculate the change in 3D stability. Previous work based on perturbation theory was performed to probe the effect of toroidal coupling [3]. In the limit where the external RMP field BN is small with respect to the axisymmetric field B0, BN/B010-4, perturbation theory is shown to be an accurate approximation. Therefore, a certain axisymmetric toroidal mode n couples only to the k=nN mode, where N is the applied mode number of the RMP field. For a monotonically increasing growth rate spectrum, the lower sideband has a destabilising contribution while the higher sideband has a stabilising contribution. A new analysis is based on a variational approach to examine the impact of non-axisymmetry on the ideal MHD plasma stability via minimisation of the individual poloidal harmonics of the axisymmetric toroidal basis functions for the triplet {n-N,n,n+N}.

References

1) P.B. Snyder et al., Physics of Plasmas 9, 2037 (2002)
3) C.C. Hegna, Physics of Plasmas 21, 072502 (2014)
2) H.R. Wilson et al., Physics of Plasmas 9, 1277 (2002)

Speaker: M. Anastopoulos (EPS 2019)

226 P2.1019 Effect of applied resonant magnetic perturbations on local plasma current density gradient and stability of m/n=2/1 magnetic island

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1019.pdf

The effect of externally applied resonant magnetic perturbations (RMPs) on the plasma current density gradient in the vicinity of resonant surfaces is investigated, based on two-fluid equations. In our paper we focus on m/n=4/2 or 6/3 RMPs. RMPs of moderate amplitude (~ 10-4 - 10-3 of the toroidal field) are found to be able to generate a significant change in the local m/n=0/0 component plasma current density gradient around the q=2 resonant surface, in addition to small 4/2 or 6/3 magnetic islands. The changes in the current density profile affect the stability of 2/1 magnetic islands. As an example we show that the growth of a 2/1 NTM, driven by both an unfavorable plasma current density profile and a bootstrap current perturbation, can be suppressed by a static RMP. Without applying RMPs, the NTM saturates at a width of 0.2a (a is the plasma minor radius). The 2/1 mode can be suppressed by static m/n=4/2 or 6/3 RMPs of moderate amplitude if the local electron fluid velocity at the resonant surface is sufficiently large. The influence of other plasma parameters, such as plasma resistivity/temperature, diamagnetic drift frequency and electron inertia, are also studied. We find in particular that higher plasma temperatures favour the stabilizing effect of external RMPs, suggesting a possible way to improve the 2/1 mode stability in ITER, considering that the 2/1 mode is one of the major causes for disruptions in tokamak discharges.

Speaker: Q. Yu (EPS 2019)

227 P2.1020 Ion orbit losses in a radially resolved model of the H-mode barrier

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1020.pdf

The radial electric field Er is thought to play a role in the suppression of turbulence in the edge transport barrier that causes H-mode confinement in tokamaks. A range of mechanisms have been proposed that may positively or negatively contribute to Er. Among the non-ambipolar particle transport channels that together determine the electric field, two processes are particularly localized near the last closed flux surface (LCFS) and may be dominant there: charge exchange friction of the plasma ions with incoming neutral atoms can reduce plasma rotation (i.e. weaken Er), whereas ion orbit losses can strengthen Er. The latter process is due to magnetically confined particles near the LCFS scattering into orbits that leave the plasma. In a single-null divertor configuration, the dominant channel is pitch-angle scattering into banana-type orbits that pass to the divertor-side of the x-point. This loss process generates a radial electric field because it is much stronger for ions than for electrons, due to the ions' larger banana orbit widths.
The proper calculation of this ion flux requires solving the Fokker-Planck equation for the ion distribution in (at least) the pitch angle and radial coordinate [1]. While pitch-angle scattering is essential for the loss process, further collisions on the loss orbit have the opposite effect of reducing the charge separation. In all, the process is very sensitive to the ions' velocity and radial position due to the strong gradient in loss orbit lengths and collisionalities.
In order to predict the H-mode barrier width, but also to model L-H transition dynamics, the total orbit loss flux across the LCFS, as given e.g. in [1] does not suffice. One needs a radially resolved ion flux, for which ad-hoc expressions have been given in e.g. [2, 3]. The present paper derives a different expression for the radially resolved flux from first principles. This flux is a function of the radial coordinate, the pitch angle scattering frequency, loss-orbit collisionality, and the radial electric field. It is demonstrated that all these dependencies are needed simultaneously if used in a model that determines the radial profile of Er across L-H bifurcations and bifurcations of the hysteresis PLH - PHL (the difference between the threshold heating powers for L-H and H-L transitions).[4]
References
[1] K.C. Shaing, Phys. Fluids B 4, 3310 (1992) [2] S. Toda et al., Plasma Phys. Contr. Fusion 39, 301 (1997) [3] T. Kobayashi et al., Nature Scient. Rep. 6, 30720 (2016), DOI: 10.1038/srep30720 [4] H.J. de Blank et al., Physica D 331, 13 (2016)

Speaker: H. de Blank (EPS 2019)

228 P2.1021 Analysis of Radial Electric Field and H-mode Transition based on Ion-Neutral Collisions

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1021.pdf

Underlying mechanisms of Bohm diffusion, E-field formation, and the suppression of turbulence have been remained unexplained for many years. The analysis of Gyro-Center Shift (GCS) is based on the ion-neutral collisions. GCS analysis provides a new perspective on how the electric fields can be generated and the particle distribution is influenced in the magnetized plasmas. GCS analysis explained not only magnetic fusion plasmas but also the phenomena in ionosphere [1]. In this presentation, definition of Reynolds number induced by ion-neutral friction and the characteristics of H-mode transitions in fusion devices including the limit cycle oscillations and the isotopes effect will be explained.
[1] Kwan Chul Lee, "Electric field formation in three different plasmas: A fusion reactor, arc discharge, and the ionosphere", Phys. Plasmas 24 112505, (2017)

Speaker: K. Lee (EPS 2019)

229 P2.1022 Evidence for toroidal regulation of edge fluctuations by nonaxisymmetric Er x B shear with applied 3D fields in the EAST tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1022.pdf

Edge coherent mode (ECM), previously identified as the dissipative trapped electron mode [1], is commonly observed in the H-mode pedestal with a relative high collisionality in the EAST tokamak. This mode is considered contributing significantly to suppression of crash of large ELMs benefitting from the remarkable particle and heat exhaust induced by the mode. Recently, when ELMs are suppressed by applying a slowly rotating resonant magnetic fields perturbations (RMPs) in the toroidal direction with a dominant n=1 component, both amplitude and spectral width of ECM are observed periodically with the rotation of RMP.
In this experiment, plasma stored energy and global density change less than 5% during application of 3D fields. Local measurements of radial electric field Er, plasma density and electron temperature in the pedestal are modulated by 3D fields. Pedestal moves outward with the increasing of local fluctuation intensity and bandwidth. Broadband ECM is presented and its fluctuation amplitude varies in phase by 100% or more. The enhanced fluctuation level is accompanied by a decreasing in pedestal pressure gradient by 8%. Meanwhile, poloidal velocity spins up in the ion-diamagnetic-drift direction slightly and induces a decrease in shearing rate by 27%. During the pedestal and ECM moving inward phase, ECM fluctuation amplitude decreases by 50% while the radial pedestal pressure increases by 6% and shearing rate increases by 30% in the same zone. The decrease in fluctuation amplitude is synchronous with a decrease of spectra width. The tilted ECM eddy is also observed by ECEI before ECM nearly disappear. These dynamical behaviors suggest that non-axisymmetric edge fluctuation is attributed to radial movement of electric potential in the plasma which is induced by RMP field.

[1] H.Q. Wang and G.S. Xu, et al, Phys. Rev. Lett. 112 185004 (2014)

Speaker: G. Hu (EPS 2019)

230 P2.1023 Symbolic Regression Analysis on the EUROfusion JET-ILW Pedestal Database

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1023.pdf

The EPED model [1] can predict the H-mode JET-ILW pedestal height and width within a relative error of about 20% when the pedestal is close to the Peeling-Ballooning (PB) boundary. However, when the pedestal is far from the PB boundary, our present understanding of the pedestal physics is still lacking [2,3]. Moreover, the extrapolation to future JET-ILW experimental scenarios and to different tokamaks is even more challenging. In addition, it should be desirable to use engineering parameters as inputs for future operative pedestal predictions. To face these issues a new multi-objective genetic programming (GP) [4,5] code has been implemented. This code is able to perform a multi-objective symbolic regression analysis [6] on the EUROfusion JET-ILW pedestal database [7] and to find new analytical regression models for the pedestal height and/or width testing different sets of input decision variables from the pedestal database. In order to avoid overfitting, the minimization of the model complexity is considered and all evolved models are tested on a validation set to measure their generalization capabilities. The GP code has been validated on simple test cases and preliminarily tested on the pedestal database deriving analytical expressions with EPED-like input quantities. The evolved models found so far, along with a final step of standard nonlinear parameter optimization, shows a good fit on the normalized pedestal pressure. To get more general results on the underlying pedestal physics, the work will test also new model selection criteria, new sets of input variables and new constraints on the model search space. The results of this work will be compared with those ones from the EPED model. The final goal of this work is to obtain regression models capable of explaining the pedestal database with, at the same time, high accuracy and low complexity, in order to get better insights on pedestal physics.
[1] P.B. Snyder, et al., Nuclear Fusion 51, 103016 (2011) [2] L. Frassinetti, et al., 27th IAEA Fusion Energy Conference (FEC 2018), 22­27 October 2018, Gandhinagar [3] S. Saarelma, et al., 60th Annual Meeting of the APS Division of Plasma Physics, Portland, Oregon, USA [4] E. Zitzler et al., Evolutionary Multi-Criterion Optimization, Proceedings of the First International Conference, EMO 2001, March 7-9 (2001), Zurich [5] J. R. Koza, Genetic Programming, MIT Press, Cambridge (1992) [6] A. Murari, et al., Nuclear Fusion 53, 043001 (2013) [7] L. Frassinetti, et al., 45th European Physical Society Conference on Plasma Physics, July 2nd-6th (2018), Prague

Speaker: F. Napoli (EPS 2019)

231 P2.1024 Predictive modelling of the Be main chamber erosion in the JET-ILW

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1024.pdf

JET is a unique tokamak equipped with the ITER-like wall (ILW) comprised of beryllium (Be) main chamber and tungsten (W) divertor. JET allows operation with tritium (T), thus studying the H/D/T isotope effect on the plasma-wall interaction (PWI). Be limiters meet the most of the direct plasma impact, however part of the liner and support structures made of nickel(Ni)-containing Inconel are exposed to the charge exchange (CX) ion flux. CX erosion is also dominates in the shadowed areas of the Be plasma-facing components (PFC). Be impurity typically causes the most of the W sputtering excluding intra-ELM: in the ohmic and the L-mode divertor plasmas and even in the H-mode inter-ELM. The radiation cooling issue due to the high-Z W (and Ni) impurities is critical for the plasma confinement and stability of the main scenarios foreseen for the upcoming JET DT campaign.
The 3D Monte-Carlo PWI and impurity transport ERO2.0 code [J.Romazanov et al., PSI-2018, invited, NME 18 (2019) 331­338] is an established tool, which was applied to erosion studies at JET with the extrapolation to ITER [D.Borodin et al., IAEA FEC-2018]. In the present work the previous simulations for the D plasma JET experiment are used as a starting point for the parameter studies aimed in the detailed study the variation range of the Be main chamber erosion with a focus on the a) isotope effect on physical sputtering (predictive); b) the role of the CX ion erosion, which is of particular importance in diverted magnetic configurations. In addition, the contribution of the chemical assisted physical sputtering (CAPS) is simulated using the refined reaction data and model in the ERO2.0.
In the previous studies [1] the passive Be spectroscopy in a single midplane sightline was used for the model and data validation. In the present work it is complemented with additional sightlines and comparison with the Z-effective measurements.
See the author list of "Overview of the JET preparation for Deuterium-Tritium Operation" by E.Joffrin et al. to be published in Nuclear Fusion Special issue: 27th Fusion Energy Conference (Ahmedabad, India, 2018)

Speaker: D.V. Borodin (EPS 2019)

232 P2.1025 Real-time wall conditioning through B powder injection in fusion devices

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1025.pdf

The performance and operation of magnetic confinement fusion devices strongly depend on the characteristics of PFCs, which represent the principal source of impurities and, through deuterium recycling, can contribute substantially to plasma fueling. A commonly-used method to reduce and control these effects is to pre-condition the walls with low-Z materials, e.g. boron (B). Although well-established, boronization entails handling hazardous gases (e.g. B2D6, B10D14), which require interruptions of experimental operation, with possible evacuation of facilities. Moreover, gas-based boronization procedures are inapplicable to long-pulse devices, where coatings will significantly erode during a single plasma discharge.
Experiments carried out in the DIII-D and ASDEX-Upgrade (AUG) tokamaks, explored the possibility of generating boron coatings in "real-time", by injection of B and B enriched powders during tokamak operation. The experiments were enabled by a new device designed to inject calibrated amounts of a wide range of impurity powders.
Boron injection into DIII-D H-mode plasmas (graphite plasma-facing components, PFCs) correlated with increase of wall pumping and impurity concentrations during the initial plasma current ramp2. Wall conditioning improvement similar to boronization was observed in AUG (tungsten PFCs) following injection of pure B and boron nitride (BN) powder into Hmode plasmas. The improvements included reduction of O and W influx from limiters. In both devices, the B injection appeared to be central to achieving low collisionality plasmas3.
The combined AUG-DIII-D dataset suggests that B powder injection could be used to supplement the standard boronization and extend its beneficial effects by regenerating the coatings during tokamak operation. Simulations with the UEDGE code, including powder transport and ablation through scrape-off layer via the DUSTT4 code, are used to reconstruct B fluxes to the wall. Preliminary results indicate that small particles ~ 1m will ablate in the far scrape-off layer, while large particles ~ 100m will penetrate near the separatrix. This leads to the prospect of an optimized real-time boronization using a range of particle sizes to thoroughly cover the PFCs.
1. Nagy, A. et al. . Rev. Sci. Instrum. 89, 10K121 (2018). 2. Bortolon, A. et al. in Bull. Am. Phys. Soc. 63 (2018). 3. A. Bortolon et al. Nucl. Mater. Energy (in review). 4. Smirnov, R. D. et al. J. Nucl. Mater. 415, S1067­S1072 (2011).

Speaker: A. Bortolon (EPS 2019)

233 P2.1026 Role of electric currents in the divertor target heat flux in ASDEX Upgrade analysed with Langmuir probes

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1026.pdf

In divertor tokamaks heat is flowing in a narrow channel of width q towards the divertor targets. Having a reliable extrapolation of q for ITER and DEMO is essential for the development of power exhaust scenarios, which led to the development of experimental multi machine scaling laws for q obtained from low edge density H-modes [1]. However, physics based models explaining the experimental results have only been partially successful. These models require assumptions for the parallel heat transport, which are not yet fully understood. Langmuir probes can help to disentangle the contributions from electrons and ions to the total heat flux, leading to a more complete picture of the parallel heat flux.
In this contribution the role of parallel electric currents in the Scrape-Off Layer (SOL) of the tokamak ASDEX Upgrade is investigated. These currents were measured in L and H-mode discharges by Langmuir probes located at the outer divertor target. It is shown that for low plasma densities the measured electric current can be in the order of the ion saturation current, while for high densities it becomes much smaller. By using an analytical SOL current model [2] the measured radial current profile can be largely explained by electric currents driven by the plasma potential difference created by the different electron temperatures between the outer and inner divertor targets. A comparison between the outer target heat flux calculated from the Langmuir probes with the one from thermography shows that the heat flux is underestimated considerably if the electric current to the target is neglected. Therefore, a significant part of the heat to the outer target is carried by the electrons in the current for such low density L and H-mode plasmas.
References
[1] Eich, T., et al., Nuclear Fusion 53, 9 (2013) [2] Staebler, G. M., Hinton, F. L., Nuclear Fusion 29, 10 (1989)

Speaker: D. Brida (EPS 2019)

234 P2.1027 Unraveling the coupling of divertor closure and impurity radiation in the first impurity seeding experiments in the new SAS divertor at DIII-D

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1027.pdf

First impurity seeding experiments with N and Ne injection in the new SAS (Small Angle Slot) divertor at DIII-D show the simultaneous achievement of divertor detachment, stable discharge behavior and unchanged (N) or even improved pedestal performance (Ne). N seeding in the SAS divertor leads to the simultaneous observation of detachment on all the boundary diagnostics including LPs, DTS, ASDEX Gauges, EUV spectrometer with a 20% increase in the pedestal density fluctuations. In matched N discharges with different strike point locations, the detachment onset requires different N levels, highlighting an important dependence of detachment on strike point location. Such dependence is also confirmed by the different N content reaching the core as indicated by both CER and SPREAD core measurements. SOLPS simulations investigating the role of impurity trapping in the divertor suggest that impurities may be more manageable when puffed into the SAS. The comparison of matched N and Ne cases indicates that N seeding does not change the pedestal profiles, while Ne leads to higher pedestal pressure gradients. ELITE simulations show that Ne injection is associated with improved ballooning branch stability due to increased diamagnetic ion frequency by impurity stabilization of ITG turbulence as indicated by DBS measurements. Evidence of reduced ion transport in the core are also supported by TRANSP analysis and linear GYRO simulations which indicate a reduction of the growth rate of the low-k instabilities at the radius where the ion transport drops significantly. These experiments might represent a possible path to improve pedestal ballooning stability with improved ion core transport.
Work supported under USDOE Cooperative Agreements DE-FC02-04ER54698 and DE-AC05-00OR22725.

Speaker: L. Casali (EPS 2019)

235 P2.1028 Insights into divertor profiles and fluctuations from two-dimensional probe measurements on the TCV tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1028.pdf

We will present first results from the fast-moving Reciprocating Divertor Probe Array (RDPA). This novel diagnostic provides two-dimensional (2D) Langmuir probe measurements across the TCV divertor plasma up to the X-point, enabling unprecedented insights into divertor profiles and fluctuations. The 2D region is covered in the poloidal plane by combining the fast vertical motion (up to 35cm into the plasma) and a radial array of 12 rooftop Mach probes (1cm radial resolution). The plunge duration is typically 0.35s, the maximum speed can be as high as 2.5m/s and the maximum acceleration reaches 80m/s^2 thanks to a linear electric motor. The diagnostic has been installed in 2018 and tested in the TCV December campaign (15 successful shots, ~10s spent in the plasma). The acquisition frequency for both voltage and current LP measurements was 200 kHz in the December 2018 campaign and will be increased to 2 MHz for the upcoming experiments in 2019. The voltage sweeping frequency has been increased up to 6 kHz in order to reduce the effect of probe arcing. These first experiments have predominantly been performed in L-Mode with a plasma current of IP=320kA and for different densities, accessing both attached and detached divertor conditions. The measurements reveal that in attached conditions, the electron temperature is approximately constant (~30eV) along the outer divertor leg. Near detachment, an abrupt parallel drop in electron temperature and pressure by ~50% is seen halfway along the outer divertor leg. This "thermal front" moves up towards the X-point after the onset of detachment. In both attached and detached conditions, the width of the ion saturation current profile increases along the divertor leg towards the target by a factor of ~2-3x. The role of fluctuations, both due to turbulence and sawtooth crashes, in determining the SOL broadening and the thermal front position will also be discussed.

Speaker: H. De Oliveira (EPS 2019)

236 P2.1029 Towards understanding the relative role of divertor geometry and magnetic topology on detachment

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1029.pdf

Plasma detachment needs to be achieved in ITER and future devices such as DEMO to dissipate most of the power in the Scrape-Off-Layer (SOL) and to reduce the particle flux reaching the divertor targets. To enhance our capability to improve current, and design future tokamaks, we must improve our understanding of the relative effect on detachment of physical (baffles, strike point angle) and magnetic geometry (conventional vs alternative topologies). For example, it is predicted by analytic calculations and modeling that the detachment threshold is reduced with increasing total flux expansion [1] [2] [3] (i.e. low Bt/high Rt at the target); how is that effect modified by varying the angle between the divertor leg and the target or the baffling? In this SOLPS-ITER modeling study of density-ramp discharges for TCV and MAST-U, the magnetic topologies are varied from a conventional divertor to the placement of the strike point at progressively larger Rt; divertor baffling and poloidal strike point angle are varied as well. From those scans we abstract out the sensitivity of the upstream density detachment threshold and window to variations of total flux expansion and neutral trapping. In the TCV equilibria that are considered in this study, total flux expansion is expected to lead to a ratio of detachment thresholds of low-Rt to large-Rt equilibria, Rthres, of 1.32. Instead, both recent TCV experiments [4] and modelling lead to a Rthres of 0.81. The SOLPS-ITER modelling demonstrates that the low value of Rthres is due to enhanced neutral trapping in the low-Rt configuration compared to that in the high-Rt configuration, an effect similar to that observed in DIII-D [3]. By making magnetic and physical divertor configuration changes in the modeling we much more closely equalize the neutral trapping as a function of Rt and we manage to get Rthres back to the predicted scaling. In MAST-U, the difference of neutral trapping between configurations is less important because of the divertor design providing strong baffling.

[1] B. Lipschultz, et al., Nucl. Fusion 56 (2016) 056007
[2] D. Moulton, et al., PPCF, 59 (2017) 065011
[3] T.W. Petrie, et al., Nucl. Fusion 53 (2013) 113024
[4] C. Theiler, et al., Nucl. Fusion 57 (2017) 072008

Speaker: A. Fil (EPS 2019)

237 P2.1030 Characterization of divertor heat fluxes in partially detached L-mode plasmas at COMPASS

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1030.pdf

Partial detachment is the required regime for the baseline burning plasma scenario in ITER and next ­step devices, as it allows to convert the majority of the energy carried by charged particles through the scrape-off-layer (SOL) into isotropic radiation and thus avoids a localized heat flux deposition in the divertor region.
Traditionally, the heat flux footprint in attached plasmas was analyzed using a fit to a special function - a convolution of an exponential decay and a Gaussian broadening. This approach reflects the simple model of transport in the SOL ­ the exponential decay of heat flux upstream and its broadening due to collisional processes and finite Larmor effects downstream. Since this function has 5 fitting parameters, it can be technically used to fit profiles in almost any conditions. However, should power dissipation become significant (as it is the case in detached plasmas), the two main parameters, q and S, lose their original meaning. In this work, we present two novel approaches to characterize such divertor heat flux profiles using experimental results from the COMPASS tokamak, where variable amounts of nitrogen seeding were applied into L-mode plasmas to achieve partial detachment [1].
The first approach we introduce is based on construction of a buffered heat flux qbuff, the heat flux which is removed from the footprint due to power dissipation. It was found that the radial profile of qbuff can be well characterized by an exponential decay and both fitting parameters depend linearly on the nitrogen content in the vessel. The success of this technique, however, relies on the availability of high-resolution divertor probe diagnostics, which may not be accessible on all machines. The second approach aims at characterizing the footprint by a new set of generic parameters: (i) peak heat flux qpeak, (ii) fraction of power delivered to the target fdiv and (iii) divertor footprint spreading factor Sf, which characterizes the spatial extend of the footprint. Possible application of both approaches on data from other machines is discussed.
[1] M. Komm et al., submitted to Nucl. Fusion (2019)

Speaker: M. Komm (EPS 2019)

238 P2.1031 Impact of tungsten charge state bundling on scrape-off layer transport simulations in JET L-mode plasmas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1031.pdf

he tungsten ion average charge states in EDGE2D-EIRENE simulations of the JET scrape-off layer are predicted to decrease by up to 40% when the 74 ion states are bundled into 6 fluid stages, compared to reference cases using the Monte Carlo code DIVIMP and a more elaborate bundling scheme in EDGE2D-EIRENE. The ionization state has a major impact on the W force balance in the SOL and thereby also on the accumulation of W in the core plasma.
W radiation cools down the core plasma such that W concentration much above 10^-5 causes intolerable loss of performance in a fusion reactor [1]. Comparison of W transport code predictions in computationally more accessible L-mode plasmas allows the identification of potential ways to improve prediction accuracy of the core W content using edge fluid codes. The studied simulations are L-mode plasmas [2] with deuterium as the main species
and beryllium and tungsten as intrinsic impurities. The main source of tungsten in the EDGE2D-EIRENE cases is sputtering due to beryllium ions at the HFS divertor and charge-exchange deuterium neutrals at the LFS divertor [3]. The simulations are validated against experiment using divertor spectroscopy of neutral and singly ionized tungsten emission lines.
EDGE2D-EIRENE simulations with tungsten ion stages for charges 1, 2-6, 7-12, 13-22, 23-73 and 74 predict the same tungsten charge profile as DIVIMP in the core region, but
the average charge states in the SOL tend to be approximately 30% lower in EDGE2D-EIRENE than in DIVIMP. This results in the core W concentration in DIVIMP exceeding EDGE2D-EIRENE predictions by around 50%. When the bundling scheme in EDGE2D-EIRENE is changed to include each individual charge up to 20+, all charge states residing in the SOL, the predicted charge states match those predicted with DIVIMP in all regions. Earlier assessments of the impurity bundling scheme in EDGE2D-EIRENE found only a weaker bundling effect of order 10% on W core leakage when injecting tungsten at the LFS mid-plane [4]. The usage of large amounts of ionization stages greatly increases computation time and lowers code stability. Therefore, the Monte Carlo approach or bundling schemes
prioritizing charge states 1-15 may be considered.
[1] T. Pütterich et al., Nucl. Fusion 50(2010)025012 [3] D. Harting et al., J. Nucl. Mater. 438(2013)S480-S483 [2] M. Groth et al., Nucl. Fusion 53(2013)093016 [4] J.D. Strachan et al., J. Nucl. Mater. 415(2011)S501-S504

Speaker: H. Kumpulainen (EPS 2019)

239 P2.1032 Effect of high neutral density on radiation measurements in Alcator C-Mod

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1032.pdf

Alcator C-Mod measurements of the radiated power density profiles using resistive bolometry in high density (up to 3.2E20 m-3) Ohmic L-mode plasmas show elevated signal levels, up to 0.9MW/m2, outside the separatrix. Such near scrape-off-layer observations are not present at lower densities of up to 1E20m-3, and it is thought that these measurements are due to an additional power flux onto the bolometer foils from neutral particles.
This work uses the kinetic neutral code KN1D, benchmarked against experimental measurements of Lya emissivity profiles, to validate a method for distinguishing photon flux and neutral flux contributions to edge bolometry measurements. We are able to estimate and remove the spurious neutral contribution to the measured brightness profiles, and therefore reconstruct emissivity profiles for high density shots which no longer show significant radiation outside the separatrix. This is in agreement with similar plasmas at lower densities.
Understanding and correcting for this effect is important for an extensive range of physics studies focussing on power exhaust from plasmas in high neutral density environments. Example include the successful interpretation of experimental data from detachment experiments on MAST-Upgrade, and more generally the ability to distinguish radiation and radial flux contributions which are important for understanding baffled, long-legged divertors at high power density.

This work is supported by US Department of Energy awards DE-AC05-00OR22725 and DESC0014264.

Speaker: J. Lovell (EPS 2019)

240 P2.1033 The key role of ExB drifts in W impurity transport and redeposition in the DIII-D divertor

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1033.pdf

Mixed-material DIVIMP-WallDYN modelling, now incorporating ExB drifts, is presented that simultaneously reproduces tungsten (W) erosion and deposition patterns observed during the DIII-D Metal Rings Campaign, in which toroidally symmetric W-coated tiles were installed in the carbon (C) DIII-D divertor. It is demonstrated that ExB drifts are required to reproduce the experimental observations, and that the spatial structure of modelled divertor poloidal ExB drifts correlates with boundaries of the observed deposition/erosion regions. With attached L-mode conditions and unfavourable ion grad-B drift direction, W and C coaccumulation is observed over a band ~5-8 cm outboard of the outer-strike-point (OSP) W source, but little W is observed closer to the OSP. In the mixed-material environment of DIIID, sputtering of W is suppressed in regions with strong target-directed drifts due to the formation of C codeposits. Time-dependent simulations with modified ExB impurity drifts (60% of the OEDGE-calculated drift velocity) quantitatively reproduce these features, including depth-resolved W/C ratios, within a factor of 2 over ~110 seconds of plasma exposure. These simulations suggest that ExB transport effects dominate over parallel force balance effects for high-Z impurities such as W in the divertor region. Including re-erosion of W changes the simulated redeposition by over an order of magnitude, leading to a better match with observed deposition patterns. The simulations also show that ExB drifts change the poloidal patterns of upstream W transport, but in a manner that remains qualitatively consistent with patterns measured on midplane SOL collector probes. This work represents the first self-consistent representation of global redeposition in a C divertor with W targets.
* Supported by US DOE via DE-FC02-04ER54698, DE-AC05-00OR22725, DE-SC0016318, DE-SC0019256, DE-FG02-07ER54917, DE-NA0003525, and the FES Postdoctoral Research Program.

Speaker: J.H. Nichols (EPS 2019)

241 P2.1034 SOLPS-ITER simulations of the GyM linear plasma device

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1034.pdf

It is well-known that to investigate plasma wall interaction in ITER-relevant conditions both experimental and theoretical efforts are needed. Concerning the former aspect, linear plasma devices are usually adopted, being able to generate ITER-relevant plasmas. On the numerical aspect, dedicated codes have been developed by the fusion community addressing the modelling of edge plasmas (e.g. SOLPS [1]) and plasma material interaction (e.g. ERO [2]). Edge plasma codes are widely used for the modelling of present-day tokamak devices, but are scarcely applied to linear machines, despite their great importance in fusion research. To bridge this gap, in this contribution, we show the first results concerning the application of the newest version of SOLPS, SOLPS-ITER [4], to the medium-flux linear plasma device GyM [3]. Since this is one of the first applications of this code version to linear configurations, necessary code adaptations were first identified and implemented. Both Argon and Deuterium simulations were performed, varying the radial transport coefficients, pumping and power delivered to the plasma by the microwave source. Simulated radial profiles of the main plasma parameters (electron density, temperature and plasma potential) were compared with those available experimentally and to those obtained using the 5.1 version of SOLPS. In the former case, a good qualitative and quantitative agreement was obtained, whereas deviation in quantitative values of the electron density was observed in the latter. Following these promising results, we aim to use simulated SOLPS background plasmas for material codes such as ERO2.0 to help to interpret experiments performed in GyM, concerning the exposures of complex/rough nanostructured materials like those presented in [5].
[1] R. Schneider et al, Contrib. Plasma Phys. 46, No. 1-2, 3 ­ 191 (2006) [2] A. Kirschner et al, Nucl. Fusion 40 (2000) 989. [3] G. Granucci et al., 36th EPS Conference on Plasma Physics, 2009 [4] D. Dellasega et al., Poster contribution presented at PSI-23 [5] S. Wiesen. et al., J. Nucl. Mater. 463 (2015) 480, 21st PSI, Kanazawa, Japan, 2014.

Speaker: M. Sala (EPS 2019)

242 P2.1035 The dynamics of filaments in attached and detached SOL conditions using 3D simulations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1035.pdf

Filaments are field aligned density and temperature perturbations, which provide a significant flux of particles and heat from the last closed flux surface to the far scrape-off layer (SOL). In order to design next generation tokamaks operating in high density regimes, it is beneficial to make robust predictions of wall fluxes, which requires understanding of these non-diffusive transport mechanisms in the presence of detached conditions.
We have carried out non-linear, three-dimensional simulations in a slab geometry, including neutral-plasma interactions, using the STORM [1, 2] module for BOUT++ [3], including selfconsistent collisional parameters and fluid neutrals, that are co-evolved with the filament. The filements are around the critical size , which is the perpendicular size for which filaments observe the highest radial velocity. The heat and particle influx is varied, generating self-consistent 1D parallel profiles without radial dependence. The high density simulation reproduce detached divertor conditions, featuring both a significant total pressure drop and target flux rollover.
Filaments were seeded on the backgrounds, and the resulting filament motion was studied. In attached conditions we found a strong target temperature dependence [2, 4] which is caused as the filament connects electrically with the target. In detached conditions the filament was found to be electrically insulated from the sheath, caused by a high resistivity in the cold area adjacent to divertor target.
A decreasing trend of the radial filament velocity with increasing density is observed, which is temporarily broken on the onset of divertor detachment, due to the filament becoming electrically insulated from the divertor target. This results in faster filaments, at least for filaments of critical size and larger. Further, the critical size increases with detachment, as sheath currents are suppressed. Detachment has been observed to coincide with shoulder formation [5], which could be explained by the increased radial velocity, and the associated decreased parallel transport caused by detachment.
[1] L. Easy, et al., Physics of Plasmas, vol. 21, no. 12, 2014. [2] D. Schwörer, et al., Nuclear Materials and Energy, vol. 12, pp. 825 ­ 830, 2017. [3] B. D. Dudson, et al., Journal of Plasma Physics, vol. 81, 1 2015. [4] D. Schwörer, et al., Plasma Physics and Controlled Fusion, vol. 61, p. 025008, Dec. 2018. [5] N. Vianello, et al.,, "SOL transport and filamentary dynamics in high density tokamak regimes." 27th FEC IAEA
India, 2018.

Speaker: D. Schwörer (EPS 2019)

243 P2.1036 SOL and divertor power decay lengths across all confinement regimes at ASDEX Upgrade

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1036.pdf

Understanding how the scrape-off layer (SOL) power decay length q scales with plasma quantities is essential for designing fusion reactors and developing a power exhaust solution. An inter-machine database [1] showed that, in inter-ELM H-mode, q scales approximately inversely with the poloidal magnetic field. Nevertheless, a unified cross-regime (L-mode, Imode and inter-ELM H-mode) and inter-machine q scaling is still missing. A first attempt in trying to find a cross-regime q dependence was done recently at Alcator C-mode [2]. It was found that q exhibits a dependence on the volume-averaged core plasma pressure. In this work a similar attempt is made with AUG data, although now q - inferred by infrared cameras is compared not only to plasma parameters characteristic of the confined region but also to near-SOL decay lengths measured by Thomson scattering.
Amongst all near-SOL decay lengths, q shows a close correlation across all confinement regimes with the near-SOL electron pressure decay length, pe and with the electron temperature decay length, Te. Furthermore, of particular interest is the correlation between q and plasma quantities characteristic of the confined region, as a power exhaust solution should still be accompanied by a large enough plasma confinement. It is observed that q exhibits a dependence on the pedestal top electron pressure and temperature across all confinement regimes. Also, it is found that the volume-averaged core plasma pressure captures the trend of q, albeit it overestimates by a factor two AUG H-mode q.
References
[1] T. Eich et al., Nucl. Fusion 53, 093031 (2013) [2] D. Brunner, B. LaBombard, A.Q. Kuang and J.L. Terry, Nucl. Fusion 58, 094002 (2018)

Speaker: D. Silvagni (EPS 2019)

244 P2.1037 ELM burn-through predictions for MAST-U Super-X plasmas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1037.pdf

During edge localised modes (ELMs) high heat fluxes are incident on divertor targets, which future fusion devices will not withstand [1]. A solution to reduce the heat fluxes could be the new Super-X divertor, which will be tested on the MAST-U tokamak. The divertor has an increased connection length, magnetic flux expansion and is designed to retain neutrals for divertor heat flux mitigation [2]. Predictions of the effect on ELMs in the new magnetic configuration are made using the nonlinear MHD code JOREK [3], which is being actively validated [4]. Using the simple JOREK diffusive neutrals model [5] good agreement, for a
MAST L-mode case, is seen in a comparison to SOLPS [6]. In the MAST-U Super-X configuration there is a rollover in the target density flux for increasing upstream density, indicating detachment, ELM burn-through has been simulated and the role of neutral divertor pressure is analysed. During the ELM, plasma ionises the neutrals front (fig. 1), the target temperature and heat flux increase and then significantly decrease after the ELM crash. The peak heat flux to the outer target due to the ELM is 0.8 MW/m2, which is low in comparison to conventional divertor heat fluxes measured in MAST type-I ELM experiments.

[1] R.A. Pitts et al., Journal of Nuclear Materials 438, S48-S56, (2013)
[2] I. Katramados et al. Fusion Eng. Des. 86 (2011) 1595­1598
[3] G.T.A. Huysmans and O. Czarny, Nucl.Fusion 47 (2007) 659­666
[4] S.J.P. Pamela et al., Nucl. Fusion 57
076006 (2017)
[5] A. Fil et al., Physics of Plasmas 22, 062509 (2015)
[6] E. Havlícková et al., Plasma Phys. Control. Fusion 57 (2015) 115001

Speaker: S.F. Smith (EPS 2019)

245 P2.1038 Investigating the influence of molecules on power/particle/momentum balance in the detached TCV divertor

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1038.pdf

The process of divertor detachment, whereby heat and particle fluxes to divertor surfaces are strongly mitigated, is required to reduce heat loading and erosion in a magnetic fusion reactor.
In previous research [1] we have provided a full interpretation of particle/power balance in the TCV (L-mode) divertor using spectroscopic techniques assuming atomic reactions alone, showing that the detachment sequence starts with power limitation of the ionisation source (~ 5 eV) limiting the ion target current. As the divertor becomes more strongly detached, momentum (< 5 eV) and eventually ion sinks (<1.5 eV) develop in the divertor volume. During this development, the molecular contribution to the D emission, obtained
spectroscopically [1], increases from 20% to 85% - in quantitative agreement with SOLPS modelling. We use this measurement, together with SOLPS simulations [2], to investigate the influence of molecules on power, particle and momentum balance during detachment. An increased concentration of H2+ and H- is required to explain the observed D emissivity, according to SOLPS/AMJUEL. This leads to significant radiative losses by up to 60 % of the hydrogenic excitation radiation in a region localised near the target and can also add to the effective ion sinks (MAR). SOLPS modelling for TCV also indicates that momentum loss through ion-molecule collisions can dominate over other momentum sinks at strongly detached states with low target temperatures (< 0.5 eV). Molecularly-enhanced D is not observed during N2 seeded detachment, likely due to higher
observed divertor temperatures during N2 seeded (compared to density ramped) detachment & lower molecular/ion densities ­ in qualitative agreement with MAST-U SOLPS simulations [3]. This also explains the lower volumetric recombination observed during N2 seeded detachment.
These observations are used to explore the validity of current treatments of molecules in SOLPS.

[1] K.Verhaegh, et al. Preprint https://doi.org/10.13140/RG.2.2.24292.48005/1
[2] A.Fil, et al. 2018, Contrib. Plasma Physics, vol. 58, issue 5-6
[3] O.Myatra, et al. PSI Conference 2018.

Speaker: K. Verhaegh (EPS 2019)

246 P2.1039 Impact of incorporating nonlocal thermal transport in 1D modelling of the ITER SOL

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1039.pdf

The divertor heat-flux problem remains a major challenge for both present and future high power tokamak fusion experiments and pilot power plant designs. Current divertor designs are informed by large-scale fluid simulation codes, e.g. SOLPS, UEDGE, EDGE2D, but none of these presently capture important kinetic effects in scenarios of steep parallel temperature gradients [1], where the thermal transport is not well described by local diffusive treatment but instead becomes `nonlocal' - depending on conditions in distant regions of the plasma. Such scenarios are becoming increasingly relevant for high-power devices, where large reductions in Scrape-Off-Layer (SOL) temperature are required to operate in fully/partially detached divertor conditions. Incorrectly calculating parallel thermal transport may have significant implications for divertor target heat-flux predictions and mitigation designs employed.

Various models have been proposed for capturing nonlocality in SOL heat-flux calculations [2]. In this work, we applied the nonlocal thermal transport model developed by Ji et al [3] and Omotani [4] to the BOUT++ 1D complex SOL model SD1D' [5] to produce theSD1D-nonlocal' code. The model is applied to 1D ITER conditions to investigate the relevance and potential impact of nonlocality for the ITER divertor, focusing particularly on predictions for plasma conditions and heat-flux at the divertor target plate. Results find the nonlocal model to be in broad agreement with the flux-limited Braginskii model (with a `flux-limiter factor' of 0.6) for standard steady-state ITER conditions, but the nonlocal model is itself able to self-consistently determine the level of flux limitation as density/collisionality regimes are varied, for which varying is required to reproduce. The ability to have self-calculated, temporally/spatially varying flux limitation has useful applications for extension into 2D SOL modelling.

[1] Batishchev, O.V. et al, Phys. Plasmas, 4, 1997, 1672. [2] Brodrick, J.P. et al, Phys. Plasmas, 24, 2017, 092309. [3] Ji, J. et al, Phys. Plasmas, 16, 2009, 022312. [4] Omotani, J. et al, Plasma Phys. Cont. Fusion, 55, 2013, 055009. [5] Dudson, B. et al, arXiv:1812.09402, submitted to Plasma Phys. Cont. Fusion, 2018.
Work supported by The Univ. of York and the UK EPSRC (under grant EP/LO1663X/1)

Speaker: M.R. Wigram (EPS 2019)

247 P2.1040 Non-axisymmetric heat flux patterns on tokamak divertor tiles

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1040.pdf

Non-axisymmetric heat flux patterns on a tokamak divertor can result for several reasons. Here we focus on the two most common causes. First, the plasma equilibrium itself can be nonaxisymmetric, either from applied or intrinsic 3D perturbation fields, and second, the plasma facing components (PFCs) may be toroidally asymmetric. For perturbed plasmas, a heat flux model based on guiding center ion drift in vacuum fields [A. Wingen et al., PoP 21, 012509 (2014)] is reintroduced. Divertor footprints, assuming an idealized axisymmetric wall, are simulated for multiple ion kinetic energies and combined based on their respective contribution to the ion's Maxwellian distribution. Recently, the model was extended to include E B drift effects. It is found that the E B flow reduces the edge stochastization and strike point splitting, as observed in MHD simulations. The modeled divertor heat flux patterns are compared to infrared camera measurements in DIII-D.
On NSTX-U it has been proposed to use a sawtooth-like profile in the toroidal direction for divertor tiles to shadow leading edges of neighboring tiles from incident heat flux. A new toolset was developed to model the effect of 3D shaped PFCs; a first result is shown in Figure 1. The tool uses a CAD model of the inner wall with all gaps, Figure 1: Simulated incident heat flux on NSTX-U and traces heat flux from an axisymmetric lower outer divertor for discharge 116313 at 851 ms. EFIT equilibrium to the wall, assuming an The white areas are holes in the wall's CAD model. Eich scaling [Eich et al., PRL 107, 215001 Swall is distance from HFS midplane, ccw along wall. (2011)] of the heat flux layer width. The figure shows the shaped tiles which shadow adjacent tiles for Swall > 1.8. The drift model will be added to the new toolset in the future. The tool will also be combined with a recently developed code that computes surface heat flux from measurements of sub-surface thermocouples, using machine learning. The work is supported by US DoE under DE-AC05-00OR22725, DE-AC02-09CH11466 and DE-FC02-04ER54698.

Speaker: A. Wingen (EPS 2019)

248 P2.1041 Role of filaments in setting the SOL width in tokamaks

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1041.pdf

Understanding the plasma transport at the boundary of magnetic confinement devices is needed to improve both confinement & power exhaust. Low to high confinement mode transition relates to the reduction of transport across flux surfaces near the separatrix, and transport in the scrape off layer (SOL) directly sets the width of heat load areas (𝜆𝑞). Transport across the plasma edge is often associated with the intermittent convection of plasma filaments, driven by interchange mechanisms. A few key questions still pending are to know if this filamentary transport can explain, at least qualitatively, the dependences of 𝜆𝑞 and confinement properties from current experiments, and if such models can provide predictions through scaling laws for future reactors (ITER and DEMO).
In this contribution, a generic model of 2D interchange turbulence is considered. Numerical simulations applied to simple SOL geometries feature exponentially decaying density profiles & intermittent convection of filaments as the main radial transport mechanism. Both filament velocities & SOL widths from the simulations are consistent with experimental measurements made in the SOL of Tore Supra circular plasmas. A predictive model of the turbulent flux associated with this filamentary transport is then exposed. To overcome the difficulty of modelling the filament intermittency, a new point of view is adopted: filaments are decomposed on poloidal wave numbers, where the flux is a simple convolution of density and potential spectra. A model of time average spectra is deduced from the conservation equations, following similar approximations made for isolated filaments. The model agrees with spectra from nonlinear simulations. The result is an analytical model of turbulent flux & fluctuation levels. Applied to SOL configurations, it translates into an analytical model for the SOL width. Quantitative agreement is found against a wide database from Tore Supra, regarding both SOL width & fluctuation levels. The sensitivity of the SOL width model with engineering parameters is very close to scaling laws built from international data bases for (1) startup limiter (2) L-mode diverted & (3) H-mode diverted conditions; although the model over predicts the absolute SOL width values in diverted configurations. Inclusion of specific geometrical features from diverted configurations is probably needed to generalize the model. A second important extension of the model is the inclusion of turbulence mitigation by sheared flows. Results from simulations with a background shear will be discussed. Last, a striking conclusion is drawn regarding global confinement. The analytical model of turbulent flux leads to a scaling of the energy confinement time close to the multi-machine trend. It suggests a certain genericity between core & edge transport, and confirms a close correlation between core confinement and SOL width as shown in experiment.
Keywords : edge tokamak plasmas, turbulent transport, scrape-off layer width, shear flows

Speaker: M. Peret (EPS 2019)

249 P2.1042 ELM electron temperature measurements on divertor compared to the pedestal temperature in the COMPASS tokamak.

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1042.pdf

Investigation of the ELM using divertor probes can provide heat loads and electron temperature with high temporal resolution [1, 2]. Recent evaluation of ELM electron temperature with JET divertor probes showed that the maxima of ELM electron temperature are almost one order of magnidute lower than the pedestal temperature [3]. However, JET probe results use conditionally averaged ELM I-V characteristics, which could underestimate the electron temperature maxima due to the filamentary structure of the ELMs [4]. We report on systematic measurements of the ELM electron temperature in the COMPASS divertor during a set of ELMy H-mode discharges aiming at a comparison between the ELM peak values and the corresponding pedestal temperature. The pedestal temperature in the last 30% of ELM cycle is routinely provided by a high-resolution Thomson scattering (HRTS) system using a conventional modified tangential (mtanh) fit. Newly, we have also obtained the electron temperature on top of the pedestal by means of the two-line fitting method (bilinear). The divertor electron temperature is monitored by a system of probes [1] with microsecond temporal and 3.5 mm spatial resolution. A downstream outboard profile of the peak values is obtained for each ELM. The resulting maxima of the profiles are compared to the pedestal temperature. It was found that the downstream ELM electron temperature maxima do not show any significant reduction with respect to the pedestal temperature. These results are discussed within the free-streaming model [5].
[1] J. Adamek et al., Nucl. Fusion 57 (2017) 116017
[2] L. Wang et al., Nucl. Fusion 53 (2013) 073028.
[3] C. Guillemaut et al., Phys. Scr. T167 (2016) 014005.
[4] J. Adamek et al., Nucl. Fusion 57 (2017) 022010.
[5] W. Fundamenski, R. A. Pitts et al., Plasma Phys. Control. Fusion 48 (2006) 109­156.

Speaker: J. Adamek (EPS 2019)

250 P2.1043 Investigating the role of hydrogen molecular effects on detachment using Magnum-PSI

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1043.pdf

In ITER and other next-generation fusion devices, divertor detachment will be crucial to limit the heat and particle fluxes to plasma-facing components to tolerable levels. This work investigates the importance of molecular effects on detachment. A type of molecular reaction of interest in this work is Molecule-Activated Recombination (MAR). MAR is a two-step process where a molecule collides with an ion and an electron, effectively resulting in recombination of the ion-electron pair and dissociation of the molecule, and could provide a recombination sink at relatively high electron temperatures of 1-3 eV where electron-ion recombination (EIR) has a negligible rate. MAR has been experimentally investigated mainly in linear devices with electron densities typically below.
The linear device Magnum-PSI can produce plasmas with electron temperatures of eV and densities, having significant overlap with the (semi-)detached ITER divertor region. This makes Magnum-PSI perfectly situated to study the effect that MAR will have on detachment in ITER. In Magnum-PSI, conditions of detachment with a high degree of plasma-neutral interactions near the target are mimicked by seeding hydrogen gas in the last of three differentially pumped vacuum chambers, raising the neutral background pressure from 0.4 Pa to up to 15 Pa in the final 80 cm in front of the target. Thomson Scattering is used to measure and in these different conditions of varying degrees of `detachment'. Optical emission spectroscopy (OES) of the Balmer enables the determination of radial profiles of excited in the plasma beam from excited state n=3 up to n10. The observed Balmer emissions are split into their EIR and MAR contributions to determine the relative importance of these
processes, similar to [1]. OES is also used to measure the Fulcher band, which provides information about the distribution of ro-vibrationally excited ,which can enhance the MAR rate by multiple orders of magnitude.
The experimental results are compared to numerical simulations of Magnum-PSI using the Eunomia-B2.5 code suite, a Monte Carlo neutral-fluid plasma model which contains a full set of molecular reactions and resolves the vibrationally excited states of.

[1] K. Verhaegh et al., Nuclear Materials and Energy 12 (2017) 1112­1117

Speaker: G. Akkermans (EPS 2019)

251 P2.1044 3D global impurity migration simulations with WallDYN and EMC3-EIRENE

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1044.pdf

To interpret impurity migration measurements in fusion experiments the evolution of the first wall surface composition and the resulting dynamics of impurity fluxes into the plasma have to be taken into account. The global impurity migration code WallDYN [1] calculates the surface compositions and impurity fluxes self consistently by combining models for implantation, erosion and reflection of impurities with a model for impurity transport through the plasma. As impurity transport model WallDYN uses the DIVIMP code [2] and thus is limited to toroidally symmetric geometries (WallDYN2D). While the plasma and SOL in tokamaks are essentially toroidally symmetric, the first wall contains 3D features like poloidal limiters. Thus impurity migration and resulting deposition patterns are not always fully captured [3]. Making accurate predictions of deposition patterns including 3D features of the first wall or modeling stellarator devices such as W7-X therefore requires taking the full 3D structure of both SOL and first wall into account. To that end WallDYN has been coupled to the 3D SOL and impurity transport code EMC3-EIRENE [4] (WallDYN3D). In [3] a 2D SOLPS plasma background for ASDEX Upgrade shot #32024 has already been used with DIVIMP for WallDYN2D. In this contribution a reproduction of that 2D SOLPS background has been calculated with EMC3-EIRENE as a 3D toroidally symmetric section of ASDEX Upgrade to be used in WallDYN3D. The migration results from WallDYN2D and WallDYN3D on these similar backgrounds and hence the results of the impurity transport models of DIVIMP and EMC3-EIRENE are compared. Furthermore, first 3D calculations of 15N migration results from and to the midplane manipulator in ASDEX Upgrade shot #32024 are presented.
References
[1] K. Schmid et al, Journal of Nuclear Materials, Volume 463, 2015, Pages 66-72
[2] P. Stangeby et al, Journal of Nuclear Materials, Volumes 196-198, 1992, Pages 258-263
[3] G. Meisl et al, Nuclear Materials and Energy, Volume 12, 2017, Pages 51-59
[4] K. Schmid, T. Lunt, Nuclear Materials and Energy, Volume 17, 2018, Pages 200-205

Speaker: L. Bock (EPS 2019)

252 P2.1045 First SOLPS simulations for COMPASS Upgrade tokamak

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1045.pdf

COMPASS Upgrade (COMPASS-U) is a medium-size, high-magnetic-field and high-density tokamak project with a flexible set of the poloidal field coils for generation of the single-null, double-null and snowflake divertor configurations. With its high plasma and neutral density, closed divertor and strong ITER-like target shaping, COMPASS-U is of particular interest for ITER in terms of similar divertor plasma and neutral parameters, as well as predicted power decay length and peak power loads to the divertor targets [1]. In this paper, we report on the first simulations of the COMPASS-U divertor plasma by the SOLPS4.3 code package [2]. The first COMPASS-U simulations were performed for pure D plasma with the fixed anomalous cross-field particle D= 0.3 m2s-1 and electron and ion heat e,i = 0.55 m2s-1 diffusivities, which are in the range of the coefficients used in the SOLPS-ITER Alcator C-Mod simulations [3]. The asymmetric double-null magnetic configuration is used with the magnetic equilibrium provided by the FIESTA [4] code for Ip=2 MA, Bt = 5T. The target and first wall are assumed to be metallic (W) with full recycling except for the pumping panels with the recycling coefficient of 0.99. The density and input power scans are carried out for the fixed radial transport coefficients and boundary conditions. The upstream and target profiles of the plasma parameters and the power and particle fluxes to the four targets are compared for different conditions. It is found that the upper divertor is cooler and less dense than the lower one. Comparison of the divertor target loads reveals the divertor asymmetry, high power fluxes to the lower divertor targets which are comparable with the predicted values for COMPASS-U and the relatively small power fluxes to the upper divertor targets. Simulations with different pumping slot position reveal a weak dependence on this parameter. Cases with the reduced cross-field transport inside the separatrix (reproducing the transport barrier) are also simulated and compared to the ones without it. Impurity seeded cases with neon as the radiating impurity are considered. The effect of Ne seeding resulting in a radiative fraction of the order of 30% on the plasma parameters and the fluxes in the divertor is presented and discussed.
[1] R. Panek, et al., Fusion Eng. Des. 123 (2017) 11­16;
[2] A.S. Kukushkin, H.D. Pacher, V. Kotov et al., Fusion Eng. Des. 86, 2865 (2011);
[3] W. Dekeyser et al. Plasma and Fusion Research 11, 1403103 (2016);
[4] G. Cunningham, Fusion Eng. Des. 88 (2013) 3238­3247.

Speaker: I. Borodkina (EPS 2019)

253 P2.1046 Towards applications of deep learning techniques to establish surrogate models for the power exhaust in tokamaks

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1046.pdf

One of the main challenges in the design of an economically viable fusion reactor are the highly localized thermal loads experienced by the plasma facing components, especially the targets in a divertor-based design, on which this work focuses. These thermal loads cause degradation of the target material and might severely damage the machine, resulting in longer downtime for maintenance. It is essential to predict these thermal loads for the design and operation of future fusion devices. Under attached conditions, simplified analytical models, such as the two-point model, are sufficient to determine the thermal load experienced by the divertor targets for given conditions of the upstream plasma. For scenarios with significant power dissipation there exist codes that take into account the complex physics of particle and heat transport in the plasma edge. However, since such codes are computationally very expensive and time consuming, modeling and predicting thermal loads under non-simplified operational conditions remains a challenging yet crucial task for current and future devices. In light of recent developments and successes in the field of machine learning techniques, datadriven modeling is an interesting option for the prediction of such heat loads. We present first steps towards predicting the power exhaust in tokamaks using deep learning methods (neural networks) and experimental data from the ASDEX Upgrade experiment. The work focuses on data selection and our initial approach of modeling the electron temperature in front of the divertor target given a set of accessible plasma parameters. In a first step we modeled a proxy for the electron temperature close to the target as a function of (indirect) operational parameters such as plasma current, toroidal magnetic field, heating power and radiated power. Although our first model yields subpar results the general approach seems to work.

Speaker: M. Brenzke (EPS 2019)

254 P2.1047 Arcing erosion effects and nanostructured "fuzz" growth on tungsten components under powerful plasma load in tokamak

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1047.pdf

Powerful plasma load on the plasma facing material in tokamaks during transients (disruption, ELMs, VDE etc.) produces several multiscale effects including surface erosion, redeposition of eroded materials, melting and melt motion over the surface, inhomogeneous solidification leading to specific surface clustering conditions and forming a corrugated roughen surface [1]. Conditions in plasma sheath over the roughen surface are favourable for arcs and sparks ignition affecting the material surface overheating. Such process is governed dominantly by universal mechanisms of surface growth and seems weakly dependent on the specific physical and chemical properties of the virgin materials [2,3]. This report summarizes recent experimental observations of tungsten materials exposed to extreme thermal plasma loads in the T-10 tokamak. Post-mortem analysis of tungsten has revealed unipolar arcs and sparking effects on tungsten targets exposed in the T-10 tokamak. These tungsten samples with corrugated surface were then used to irradiate with stationary plasma in the PLM plasma device [4] which is a divertor simulator facility. The growth of nanostructured "fuzz" was detected on the corrugated tungsten surface after the test during ~200 minutes with the PLM plasma of density ~ (2-5)·1012 cm-3 and electron temperature ~2-10 eV, such conditions are modelling the SOL plasma in a tokamak. Such "fuzz" surface can enhance the ignition of unipolar arcs and sparking on plasma-facing surface; arcing leads to an enhanced heat transfer from plasma to a surface. These arcs effects and "fuzz" growth on the corrugated surface should be analysed to evaluate the erosion of the tungsten divertor tiles in the ITER. The work was supported by the Grant RSF 17-19-01469, the ASNI on the PLM device was supported by Megagrant RF 14.Z50.31.0042.
[1] V.P. Budaev, Physics of Atomic Nuclei 79 (7), 1137-1162 (2016)
[2] V.P. Budaev, Physics Letters A 381, 43, 3706 (2017)
[3] V.P. Budaev, JETP Letters 105, 5, 307 (2017) [4] V.P. Budaev, et al , J. Phys.: Conf. Ser. 1094, 012017 (2018)

Speaker: V.P. Budaev (EPS 2019)

255 P2.1048 Reduction of intrinsic impurities by wall boronization in Wendelstein 7-X as observed by VUV spectroscopy

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1048.pdf

The recent operation phase OP1.2b of the superconducting stellarator Wendelstein 7-X (W7-X) was the first experimental campaign with a boronized wall in this machine. Wall conditioning by means of boronization is a standard technique to reduce the influx of intrinsic impurities, typically carbon and oxygen, from plasma facing components into the plasma. Three boronizations were performed during OP1.2b, each leading to a significant reduction of C and O radiation. While the beneficial effect of the boronization in terms of reduced impurity radiation losses is observed by a number of diagnostics, the High Efficiency XUV/VUV Overview Spectrometer (HEXOS) is the only system capable of simultaneously observing the line emission of a wide range of ionization states of the most relevant impurities. This broad spectral coverage, combined with an absolute intensity calibration of HEXOS and impurity transport characteristics derived from impurity injection experiments by means of laser blow-off, allows to estimate impurity concentrations using the 1D impurity transport code STRAHL with given profiles for plasma density and temperature. In this contribution, the effect of the three boronization efforts is assessed based on HEXOS measurements, and the reduction of the C and O concentrations is estimated by comparing calibrated HEXOS measurements with forward-modelling results from STRAHL. The results are further compared with the change of impurity radiation registered by the pulse height analysis system, as well as the reduction of total radiation as measured by the bolometer systems on W7-X.

Speaker: B. Buttenschön (EPS 2019)

256 P2.1049 Sensitivity analysis of collisional processes in a detached plasma in Magnum-PSI with B2.5-Eunomia

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1049.pdf

The realization of fusion energy requires breakthroughs in divertor control to withstand the tremendous heat flux from a burning plasma. One solution is to operate in the detached plasma state. Reaching and controlling this state require better understanding of the underlying mechanisms. By using linear plasma generators, the repetitive rate of discharges is very high, diagnostics are more flexible and with superconducting coils steady-state plasmas are achievable. With the addition of computational modelling, atomic processes can be investigated using data from experiments and then be transferred to more sophisticated tokamak models.
Magnum-PSI[1] can simulate the conditions of ITER divertor, characterized by Te 5 eV and high ion flux 1024 m-2 s-1. Many detached plasmas have been made by increasing the neutral background pressure or injecting impurities in the target vicinity. Energy and ion fluxes are measured to decrease as a function of increasing pressure [2, 3]. In this paper we present the analysis of experimental data with the B2.5-Eunomia[4] fluid-kinetic Monte Carlo code. The first step of the study is to align the model boundaries with experimental data. Quantities such as electron density and temperature profiles near the target are matched with one experimental setting to determine the radial transport parameters. Once these parameters are established, subsequent simulations are run with different neutral pressure settings from the experiment. The decrease of power and ion flux as a function of background neutral pressure are compared with experimental measurements. Having the model results matched the experiments, the simulations are rerun while atomic processes are selectively eliminated to identify power and ion loss channels that lead to the detached plasma state.
References
[1] G. de Temmerman, et al., Fusion Eng. Des. 88:6-8, 483 (2013)
[2] R. Perillo, et al. Nuclear Materials and Energy 19:87-93 (2019)
[3] K. Jesko, PhD thesis, TU/e and Aix-Marseille University (2018)
[4] R. C. Wieggers, et al., Contrib. Plasma Phys. 52, 440 (2012)

Speaker: R. Chandra (EPS 2019)

257 P2.1050 Global simulations of ion temperature gradient driven modes in Wendelstein 7-X with the gyrokinetic code XGC

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1050.pdf

In recent work, the total-f global gyrokinetic particle-in-cell code XGC has been extended to stellarator geometries. In this presentation, we show verification studies and initial results with the new stellarator version, XGC-S, for ion temperature gradient driven modes. XGC-S calculations are found to agree well with the gyrokinetic codes XGC1, GENE and ORB5 for a cyclone base case-like scenario in circular tokamak geometry. Growth rates calculated for linear ion temperature gradient-driven modes with XGC-S are found to agree with those calculated with the stellarator core global gyrokinetic code EUTERPE. Results of initial simulations in the Wendelstein 7-X geometry with equilibrium and gyrokinetic profiles derived from experimental measurements will be shown. Preliminary nonlinear results will also be presented.
On-going work extending the XGC-S physics model will be detailed. An interface for the resistive MHD code HINT3D, including island and stochastic field line physics, has been written for XGC-S. Orbit tracing tests in stellarator equilibria calculated by HINT3D will be presented, with preliminary results for electrostatic microinstabilities with HINT equilibria. Improved algorithms for electromagnetic gyrokinetic particle in cell simulation are being investigated and plans for incorporation in XGC will be detailed.
References
[1] M. D. J. Cole, R. Hager, T. Moritaka, S. Lazerson, R. Kleiber, S. Ku and C. S. Chang, Phys. Plasmas, accepted (2019)
[2] T. Moritaka, R. Hager, M. D. J. Cole, S. Lazerson, C. S. Chang, S. Ku and S. Ishiguro, Plasma, submitted

Speaker: M. Cole (EPS 2019)

258 P2.1051 Ion temperature profiles in NBI and ECRH heated W7-X plasmas

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1051.pdf

In a survey of ion temperature (Ti) profiles in ECRH dominated W7-X plasmas during the most recent W7-X campaign, it is found that no strong dependence of the central ion temperature on either electron temperature or plasma density exists. This indicates that the ion heating, which occurs through transfer of heat from electrons, has little influence on the ion temperature profile and suggests a critical ion temperature gradient which can not be exceeded under typical conditions. The addition of NBI heating to medium or high power ECRH discharges shows no significant rise of Ti despite significant direct ion heating, supporting the conclusion of a maximum Ti gradient. However, in some low ECRH power discharges, NBI heating induces a rapid Ti rise, transiently achieving a central Ti well above that typically seen at higher ECRH power and showing that the apparent limit on Ti gradient can be exceeded.
Ion temperature profiles are taken from the recently installed Charge Exchange Recombination Spectroscopy diagnostic which gives high resolution localised measurements over 3/4 of the full plasma diameter. The survey includes all discharges with significant NBI power as well as many ECRH discharges with short diagnostic NBI blips. The high resolution CXRS profile information is supported by a broader database of Ti information from X-ray Imaging Crystal Spectrometer (XICS)[1] measurements covering almost all discharges of the campaign as well as electron temperature and density profiles from the Thomson Scattering diagnostic[2].
References
[1] A. Langenberg, N.A. Pablant, Th. Wegner et al. Rev. Sci. Instrum. 89 10G101 (2018)
[2] E. Pasch et al. Rev. Sci. Instrum. 87 11E729 (2016)

Speaker: O.P. Ford (EPS 2019)

259 P2.1052 Fluid simulations of turbulence in stellarator geometries with BSTING

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1052.pdf

The topology of the Wendelstein 7-X edge and scrape-off-layer exhibits stochastic fields, island chains, highly varying connection lengths, and a non-uniform curvature drive for plasma turbulence. These challenges have previously inhibited successful development of a plasma fluid turbulence simulation framework. The BSTING project [1] has extended BOUT++ [2] to stellarator geometries, thereby providing the first nonlinear fluid simulation framework for stellarator geometries. Here we outline recent developments in the BSTING project, including a newly implemented curvilinear grid system suitable for stellarator edge magnetic topology, and present simulations of plasma filaments in stellarator geometries. Simulations of filaments in non-uniform drive scenarios [3], and the effects of strongly-varying connection length will also be presented. The application of these methods to Wendelstein 7-X edge scenarios will also be discussed.

[1] B. Shanahan, B. Dudson, and P. Hill, Plasma Physics and Controlled Fusion 61, 025007 (2018).
[2] B. D. Dudson, M. V. Umansky, X. Q. Xu, P. B. Snyder, and H. R. Wilson, Computer Physics
Communications 180, 1467 (2009).
[3] B. Shanahan, B. Dudson, and P. Hill, Journal of Physics: Conference Series 1125, 012018
(2018).

Speaker: B. Shanahan (EPS 2019)

260 P2.1053 Investigation of higher harmonics of electron cyclotron emission in the W7-X stellarator

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1053.pdf

The W7-X stellarator with its large aspect ratio has spectrally well separated electron cyclotron harmonics compared to tokamaks. Because of this geometrical advantage, it is easier to address the electron cyclotron harmonics (70,140,210...GHz) at a magnetic field of 2.5 T. In a standard electron cyclotron emission (ECE) diagnostic1, the optically thick second harmonic extraordinary mode (X2 mode) of ECE is used to determine the electron temperature profiles. For confinement reasons, W7-X plans to work at high plasma densities aiming at detached steady state operation. For such overdense plasmas with plasma density 1.2×1019 m-3, the optically thick X2 mode (120-160 GHz) of ECE is in cutoff and hence there is no direct access to electron temperature profiles from the standard ECE. For overdense plasmas, higher harmonics2 provide the only access to the ECE. And for such cases, the diagnostic capabilities of higher harmonics are explored as high density access to electron temperatures profiles. For this purpose, a Michelson interferometer3 with a time resolution of 22ms and spectral resolution of approximately 5GHz was used during operational phase OP1.2b of W7-X for broadband ECE (50-500 GHz) scan. The experimental results will be compared to the modeling of ECE at different plasma parameters applying radiation transport calculations (TRAVIS). Preliminarily results indicate that X3 mode of ECE above a certain density is optically thick and can be used to measure the electron temperature profiles.

1 M.Hirsch et al., this conference
2 N.Chaudhary et al., Proceedings of 20th workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating, May 14-17, 2018, Greifswald, Germany, EPJ Web of Conferences
3J.W. Oosterbeek et al., `Michelson Interferometer design in ECW heated plasmas and initial results', accepted for publication, Fusion Engineering and Design, 2019

Speaker: N. Chaudhary (EPS 2019)

261 P2.1054 ECE diagnostic measurements during first W7-X divertor campaign

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1054.pdf

The electron cyclotron emission (ECE) diagnostic system of W7-X is comprised of a 32 channel radiometer for detecting the 2nd harmonic emission1 in the frequency range from 126 to 162 GHz and a Michelson interferometer providing broadband spectra 2 that share the same line of sight. The EC emission was measured throughout the first W7-X divertor campaign. From that, calibrated electron temperature profiles were derived for a variety of magnetic configurations, heating- and density scenarios. Beyond blackbody conditions, the emission from hot core electrons is observed as well. Plasma dynamics has been studied also comprising the effects of pellet injection, ECRH induced heatwaves and ECCD driven fast temperature crashes as well as spontaneous propagating Te-perturbations, MHD phenomena and edge crashes reminiscent of ELMs.
Inference of the local electron temperature profile from the measured ECE radiation temperature spectra requires the iterative use of the radiation transport code TRAVIS and can be performed using forward modelling with the Bayesian analysis framework MINERVA. Steady state operation of W7-X employs detached scenarios as they have been developed in this campaign at operation densities beyond the 2nd harmonic X-mode cut-off, i.e. at ne > 1.2 1020 m-2 heated e.g. by the ECRH in O2 polarization. In view of these high densities, the diagnostic capability of the 3rd harmonic EC emission is being explored as an option to provide access to a continuous electron temperature measurement under conditions where the 2nd harmonic cannot be used.

1 M. Hirsch et al. Proc of the 20th Workshop on Electron Cyclotron Emission (ECE) and Electron Cyclotron Resonance Heating (ECRH), May 14-17 2018, EPJ Web of Conferences
2 N. Chaudhary et al., this conference

Speaker: M. Hirsch (EPS 2019)

262 P2.1055 Analysis of Balmer alpha spectra in W7-X using FIDASIM

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1055.pdf

Balmer-alpha spectroscopy allows important and versatile investigations of fusion plasmas. In particular active spectroscopy with lines of sight intersecting the paths of neutral beams has become an important diagnostic technique since it carries information on important plasma parameters such as the fast-ion density, the radial electric field, plasma rotation or the main-ion temperature.
However the complex shape of the spectra requires well developed models for its interpretation. Here we use for this purpose the Monte-Carlo based code FIDASIM [1], which is capable to predict the measured Balmer-alpha spectrum and was validated against axisymmetric cases from different tokamaks [2, 3]. The Monte-Carlo approach makes it possible to treat arbitrary 3D magnetic field geometry and full 5D fast-ion distribution thus to apply the forward modelling tool to stellarators as well.
For W7-X the capablities of FIDASIM have been extended to the 3D magnetic field from VMEC [5] and 5D fast-ion distribution function from ASCOT [4]. During the 2018 experimental campaign of W7-X neutral beam injection has been applied for the first time. First comparisons between FIDASIM results and spectroscopic measurements show good agreement between the measured beam emission and halo emission. Moreover, the observed attenuation of the beamemission is recovered, well. While good agreement is observed for the spectral shape of the fast-ion H-alpha emission, the absolute values do not match, possible reasons for this mismatch will be presented as well.
References
[1] W. Heidbrink et al., Communications in Computational Physics 10 716 (2011)
[2] B. Geiger et al., Plasma Physics and Controlled Fusion 53 065010 (2011)
[3] M. A. Van Zeeland et al., Plasma Physics and Controlled Fusion 52 045006 (2010)
[4] S. Äkäslompolo et al., Nuclear Fusion 58 082010 (2018) [5] S. P. Hirshman et al., The Physics of Fluids 26, 3553 (1983)

Speaker: P.Z. Poloskei (EPS 2019)

263 P2.1056 Acceleration of bayesian estimation of temperature and density profiles for W7-X

see full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1056.pdf

Plasma physics experiments often require a fast estimation of plasma parameters for machine control and safety. On the other hand, to do scientific inference a thorough post-processing analysis and uncertainty handling is carried out. The fast parameter estimation can benefit from a more rigorous handling of the uncertainty to have more reliable control of operating conditions. Concurrently, a faster version of the post-processing of inverse problems in parameter estimation can be crucial for rapid decision-making between or during plasma discharges. Besides this, it is not rare that two different plasma diagnostics in an experiment measure the same parameter but their analyses are often carried out separately. This particular scenario describes a great niche for an accelerated version of Bayesian analysis.
Bayesian analysis permits a quantitative estimation of parameters and their uncertainties and allows for a consistent joint data analysis of multiple diagnostics. This comes at the cost of slow processing times typically in the order of minutes or above and a high demand of processing power. The costs are mainly due to the exploration of the resulting non-linear multidimensional parameter distributions with sampling algorithms like Metropolis Hastings Markov Chain Monte Carlo. Faster alternatives like the Kalman filter or sub-optimal Bayesian on-line algorithms are ill-suited for the common time-independent non-linear problems in plasma physics.
This work shows how this analysis can be accelerated through FPGA hardware in order to provide reliable parameter estimations and uncertainties within a time frame useful for modern magnetic confinement devices. It does so by covering representative examples of inverse problems like the joint analysis of the W7-X Thomson scattering and the dispersion interferometer systems. The achieved and not yet optimized design can estimate in less than a second the temperature and density profiles with the data from these two diagnostics that share a near to coincident beam path. Thus, it shows the possibility of using a thorough parameter estimation approach to provide reliable the plasma parameters immediately after a discharge or for a possible operation control during longer discharges. With it, the described data analysis requirements for plasma physics experiments can be met without needing to resort to a speed vs. rigorosity trade-off.

Speaker: H. Trimino Mora (EPS 2019)

264 P2.1057 Validation of radial electric measurements derived from Doppler reflectometry at Wendelstein 7-X

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1057.pdf

In contrast to axi-symmetric devices, the particle fluxes in helical devices strongly depend on the radial electric field Er. This sets a constraint on the radial electric field for given plasma density and temperature profiles, and makes it a key quantity for the neoclassical transport. In recent years, Doppler reflectometry (DR) has been proven to be a versatile diagnostic to measure plasma flows with high temporal and spatial resolution [1]. However, the analysis and interpretation of the Doppler shifted spectrum of the scattered microwave electric field is often challenging. While the measured lab-frame velocity is dominated by the E × B-velocity, the phase velocity of plasma instabilities can contribute significantly to the frequency and spectral shape of the the Doppler peak. With a precise knowledge of the radial electric field such contributions can be investigated in detail to characterize the underlying instability and compare with gyrokinetic predictions. In order to validate the radial electric field derived from DR measurements in Wendelstein 7-X, flow estimates from charge-exchange recombination spectroscopy (CXRS) and X-ray imaging crystal spectroscopy (XICS) are considered. The comparison is performed for different magnetic configurations and the findings are compared with the radial electric field derived from the ambipolarity constraint of the neoclassical fluxes calculated with DKES.
References
[1] M. Hirsch it et al., Plasma Phys. and Control. Fusion 43 (2001) 1641.

Speaker: T. Windisch (EPS 2019)

265 P2.1058 Impact of impurity radiation locations on the plasma performance at W7-X stellarator

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1058.pdf

The optimized stellarator Wendelstein 7-X (W7-X) has recently conducted its first divertor operation. One of the main scientific objectives is to examine and optimize the island divertor as a potential concept for a future stellarator reactor. One promising approach is to keep the impurities released from the plasma-surface-interaction region in the scrape-off layer (SOL), which on the one hand prevents the impurity contamination of the core plasma as well as the deterioration of the plasma confinement, and on the other hand brings benefits to the plasma facing components from impurity radiation by heat load reduction, thus, avoiding material erosion. The search for optimized operating conditions, allowing for both, high-radiation and high plasma performance, is therefore of great concern to us. At W7-X, a two-camera bolometer system is used for measuring the plasma radiation. It consists of a horizontal and a vertical camera having lines of sight covering an entire triangular cross-section, including both the core- and the SOL-region. Information about 2D radiation intensity distribution, total radiated power loss Prad as well as power loss fraction from the SOL, frad_SOL= Prad_SOL/Prad, have been obtained from the line-integrated measurements of the channels. It has been observed that 1) at low-radiation levels, the radiation zone is located in the SOL, indicated by a high value of frad_SOL (>80%) outside the LCFS; 2) with increasing density, chord-brightness of SOL-channels weakens resulting in a reduction of Prad_SOL although the overall radiation level enhances. This is interpreted as an inward radial shift of the radiation zone; 3) for high-radiation regimes, the entire zone broadens in the radial direction and sometimes even penetrates into the confined plasma region indicated by a drop of frad_SOL. For the latter case a degradation of the plasma stored energy as well as the confinement time E are observed. This may explain the observations that E deviates from the ISS04-scaling at high density scenarios [1]. In this contribution, we will present systematic investigations concerning these issues. They are preconditions for understanding the underlying physics that will guide the future exploration of the optimum operational parameters for the island divertor concept involved in W7-X.
References:
[1] G. Fuchert et al, Preprint: 2018 IAEA Fusion Energy Conference, Ahmedabad EX/3-5

Speaker: D. Zhang (EPS 2019)

266 P2.1059 ECCD effects on the divertor power distributions on W7-X

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1059.pdf

Wendelstein 7-X (W7-X) is one of the world's most advanced stellarators. Electron cyclotron resonance heating (ECRH) [1] was the main heating system during the operation phase 1.2 (OP 1.2) in W7-X. Apart from heating, the remotely steerable launchers of the ECRH-system allow to drive current at different plasma radii during experiments.
The finite intrinsic toroidal plasma currents (on the order of 10 kA) composed of bootstrap and the accompanying time-varying shielding currents have been measured throughout the campaign with Rogowski coils [2, 3]. The evolution of these currents modifies the edge magnetic rotational transform, and, as a result, can change the magnetic topology of the three dimensional boundary. The effects of a freely evolving plasma current on the strike-line movement have been observed and analysed.
Electron cyclotron current drive (ECCD) [4] can be generated to control the local rotational transform of the magnetic flux surface inside the confined region, but also modify the rotational transform at the separatrix to shift the strike lines [5]. This paper focuses on the possibilities of ECCD for strike-line control. With co- and counter-ECCD, one can add current with the polarity of the bootstrap current or compensate the intrinsic bootstrap current. The power deposition on the divertor targets measured by an infra-red thermographic system for both cases (dedicated experiments in OP1.2) will be shown in this paper for a quantitative comparison.
References
[1] T. Stange et al. EPJ Web of Conferences, 157, 02008 (2017).
[2] M. Endler et al. Fusion Engineering and Design, 100, 468 (2015).
[3] K. Rahbarnia et al. Nuclear Fusion, 58 (9), 096010 (2018).
[4] M. Zanini et al. ECCD-driven temperature crashes at W7-X stellarator, in this conference (2019).
[5] J. Geiger et al. Plasma Physics and Controlled Fusion, 57 (1), 014004 (2015).

Speaker: Y. Gao (EPS 2019)

267 P2.1060 Impact of plasma pressure on the edge magnetic field of Wendelstein 7-X

see full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1060.pdf

The Wendelstein-7X (W7-X) experiment aims to demonstrate steady-state long-pulse discharges at high power and high performance. For heat- and particle-exhaust, W7-X makes use of an island divertor, which relies on a magnetic island chain between the divertor plates and the last closed flux surface. The strike-line shape on the divertor plates inherently depends on the shape and position of the magnetic islands. At high performance, the pressure-gradient driven plasma response can modify the magnetic islands, and therefore the heat-flux distribution onto the divertor plates. It is therefore essential to gain an understanding of the 3D plasma equilibrium to determine if - and how - changes in the edge magnetic topology need to be countered. In this work, the impact of plasma pressure on the edge magnetic field has been identified using a reciprocating magnetic probe on W7-X. A comparison between the measured field and finite-beta resistive MHD equilibria predicted using the HINT code will be reported.

Speaker: A. Knieps (EPS 2019)

268 P2.1061 Stable completely detached plasma operation in the first island divertor experimental campaign of Wendelstein 7-X

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1061.pdf

central aim of the superconducting stellarator Wendelstein 7-X (W7-X) is to demonstrate the suitability of the island divertor concept to meet the requirements of power and particle exhaust during continuous operation. Without boronisation, stable completely detached plasma operation (peak heat loads reduced by factors of 10 to 15) was successfully demonstrated with 3 MW ECRH heating power at line integrated densities of 3 1019m-2 for 3s, and little loss in diamagnetic energy (<10%). Low sub-divertor neutral particle pressures (~5 10-5 mbar) would have been sufficient, had the cryo-pumps been available, to pump all fuelled particles. However, high oxygen concentrations resulted in high Zeff values of 3.5-4 in stable discharges. Boronisation and the related oxygen gettering, in combination with a reduced carbon content, higher reliable heating power and O2-mode ECRH produced stable detached plasmas at densities of 1.1 1020 m-2 for up to 28 s with 5.5 MW ECRH and constant Zeff of ~1.5. Subdivertor neutral pressures of up to 8 10-4 mbar allowed efficient particle exhaust and will improve during the next campaign when the cryo-pumps will be available. First indications of increased divertor recycling conditions were observed and are expected to increase with the availability of higher reliable heating power in the next campaign (up to ~8 MW). The status of the detailed understanding of the detachment physics with and without boronisation, partly supported by first EMC3/EIRENE simulations, will be presented.

Speaker: R. Koenig (EPS 2019)

269 P2.1062 Carbon counter-streaming flow studies of attached and detached plasmas in the Wendelstein 7-X island divertor

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1062.pdf

The Scrape-Off Layer (SOL) of the Wendelstein 7-X (W7-X) stellarator is characterized by the presence of magnetic islands, which have been exploited for the island divertor configuration. The complex 3D magnetic topology of W7-X leads to a structure of SOL counterstreaming flows that is also 3D. This pattern, previously predicted, has been observed for the first time with a Coherence Imaging Spectroscopy (CIS) diagnostic during the last experimental campaign (OP1.2b). CIS is a camera-based interferometry diagnostic capable of measuring Doppler particle flow associated with a selected visible emission line from the plasma. The 2D measurement capability allows observation of the effects of the W7-X 3D edge geometry, supporting new physics investigations on SOL flows not possible with conventional 1D probes. Two CIS systems have been designed to monitor the same island divertor portion from nearly perpendicular directions for improved emission and flow interpretation. Thanks to a newly implemented calibration source, based on a continuous tunable laser, the intrinsic carbon impurity behavior has been investigated for different plasma conditions, e.g. density and heating power. The measured velocities vary in the range 0-35 km/s. Additionally, one of the most striking transition occurred during detachment: once this condition is achieved, the flow velocities decrease approximately by a factor 4. CIS detachment observations are compared with other diagnostics and dedicated EMC3-EIRENE simulations.

Speaker: V. Perseo (EPS 2019)

270 P2.1063 Mode observations and confinement characterization during configuration scans in Wendelstein 7-X

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1063.pdf

Wendelstein 7-X is a modular advanced stellarator, which successfully finished its second test divertor unit experimental campaign in October 2018. Besides establishing divertor operation, this campaign was devoted to the verification of the optimization principles of the machine in different magnetic configurations, created by the superconducting magnet system. In addition configuration scans were performed between several reference magnetic configurations with the aim to analyse confinement and performance changes by the gradual successive variation of the rotational transform.
This contribution focuses on the analysis of the intermediate configurations, performed between high iota' andstandard' reference magnetic configurations. The experimental programs of the scan were conducted with the same density and ECRH power in order to identify the relative changes between the configurations studied. A large set of diagnostics, including magnetic measurements and the ECE, accompanied these experiments. Observations include confinement changes and mode activities detected by various diagnostic systems. An overview of experimental results is presented as well as a study of the relation of the mode activity to the size of the internal magnetic islands.

Speaker: T. Andreeva (EPS 2019)

271 P2.1064 Validation of the BEAMS3D deposition model on Wendelstein 7-X

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1064.pdf

The BEAMS3D stellarator neutral beam injection (NBI) code [1] is validated against the experimental data of Wendelstein 7-X (W7-X). Experiments scanning density and magnetic configuration were performed in W7-X with the newly commissioned NBI system. Composed of two sources in a single beam box, this NBI system provided 3.6 MW of heating while fueling the plasma [2]. In order to properly benchmark the BEAMS3D code, equilibrium reconstructions of the plasma parameters were performed using the STELLOPT code [3]. These reconstructions included flux loops, segmented Rogowski coils, Thomson scattering, Electron Cyclotron Emission, and the X-Ray Imaging Crystal Spectrometer on W7-X. The reconstructed equilibria provide not only the three dimensional mapping via the VMEC equilibrium but also profiles of electron temperature, electron density, ion temperature, and radial electric field. Low, medium, and high density discharges are compared against measurements to verify the deposition model of the BEAMS3D code. In addition, configuration variation is explored via experiments in the high-iota and high mirror configurations. Simulation data is compared against shine through and beam deposition measurements.
References
[1] M. McMillan and S.A. Lazerson, Plas. Phys. Cont. Fusion 56 (2014)
[2] N. Rust et al., Fusion Eng. and Design 86 (2011) [3] S.A. Lazerson et al., Nucl.. Fusion 55 (2015)

Speaker: S.A. Lazerson (EPS 2019)

272 P2.1065 Dependence of the intrinsic toroidal current on heating power and density in the Wendelstein 7-X stellarator

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1065.pdf

The intrinsic, diffusion driven toroidal (bootstrap) current has been measured in the stellarator Wendelstein 7-X for several magnetic configurations at line integrated plasma densities between 2 and 16 × 1019 m-2 and heating powers between 0.5 and 6 MW. A Rogowski coil was employed to measure the net toroidal current in the plasma. This consists of the intrinsic bootstrap current and the counteracting, resistively dampened shielding current. The plasma parameters (with the exception of the shielding current) were kept constant over a time in the order of the decay time of the shielding current. The measured time trace of the net current was then fitted by a constant bootstrap current from which an exponentially decaying shielding current was subtracted. The main contribution to the experimental error is expected to be the unintentional current drive by the electron cyclotron resonance heating. It is expected to be in the order of 1 kA in most cases. The bootstrap currents obtained in this way varied between -7 and 5 kA for the high mirror and high iota configurations, which are optimized for small bootstrap current, and between -3 and 17 kA for the standard, intermediate (limiter) and low iota configurations. Currents generally decreased when the density was raised at constant heating power and generally increased when the heating power was raised at constant density.

Speaker: U. Neuner (EPS 2019)

273 P2.1066 MHD activity during the recent divertor campaign at the Wendelstein 7-X stellarator

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1066.pdf

During the past operational phase OP1.2b at Wendelstein 7-X (W7-X), wall conditioning via repeated boronization led to enhanced plasma performance. To further support safe W7-X operation, an additional plasma heating interlock system, based on the measured diamagnetic energy (Wdia), has been successfully operated during the whole campaign. For the first time at W7-X in addition to the electron cyclotron heating system a neutral beam injection system (NBI) was put into operation, which acted as a source of fast ions and provoked MHD activity under certain conditions. Based on measurements from a total of 125 Mirnov probes, the effect of the NBI on the underlying MHD mode structure in selected plasma scenarios is studied. Preliminary mode number analysis results are presented, complemented by Soft X-Ray, electron cyclotron emission and phase contrast imaging diagnostic measurements. The developed analysis techniques have been proven useful for ongoing investigations of sudden energy crashes, such as observed in transient high plasma energy phases (Wdia ~ 1.2 MJ) or in the presence of external electron cyclotron current drive, where they even led to a total collapse of the plasma. Observed decay times of the plasma energy and currents of the order of about 1-10 ms are up to 100 times faster compared to assumptions previously made in calculations concerning engineering layout and mechanical stresses on diagnostic components installed in the vacuum vessel. High induced currents and the resulting forces represent a potential threat to the structural integrity of these components and to a safe W7-X operation. It is essential to understand the mechanisms of the observed energy crashes and plasma collapses to develop strategies to stabilize high performance plasmas and to minimize the risk of machine damage in future operational phases.

Speaker: K. Rahbarnia (EPS 2019)

274 P2.1067 Parametric equilibrium reconstructions for Wendelstein 7-X with V3FIT

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1067.pdf

The reconstruction of the plasma equilibrium plays an important role in interpreting diagnostic signals and understanding the plasma performance for toroidal fusion experiments. Reconstructing the plasma parameters is an iterative process that involves solving the MHD equilibrium, computing synthetic diagnostic signals based on that equilibrium and comparing these signals to measured signals. The parameters that describe the equilibrium are adjusted between iterations to find a best-fit of the measured and synthetic signals. The shape of the plasma, the location of the plasma edge, and profile information regarding the plasma pressure, current, and individual plasma species (e.g. Te, Ne, Ti, Ni) are the output of the reconstruction. These profiles are then used to interpret diagnostic information and for further physics analysis.
The constraints for the reconstructions of plasmas at Wendelstein 7-X (W7-X) include magnetic diagnostics, Thomson Scattering, interferometry, electron cyclotron emission, soft x-ray arrays and x-ray imaging crystal spectroscopy. Constraints on the plasma last closed flux surface are discussed for the various experimental magnetic configurations of W7-X. Furthermore, the sensitivity of the equilibrium reconstruction to coil models (as-built',EM-loaded') is also presented. The MHD equilibrium solution is provided by VMEC, which assumes solution with nested, closed flux surfaces. A recently developed parameterization of the current density has been implemented which enables the reconstruction to more directly specify radially-localized regions of the current density, improving the range and flexibility of current density profiles that can be represented and reconstructed.
Equilibrium reconstructions of long-pulse discharges both with and without electron cyclotron current drive are shown. Future plans for the application of V3FIT reconstructions to W7-X plasmas are also discussed.

Speaker: J. Schmitt (EPS 2019)

275 P2.1068 Structure of island localized modes in Wendelstein 7-X

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1068.pdf

Low frequency edge fluctuations, localized near the last closed flux surface, which show discrete losses of stored energy with each event, are seen especially clearly in specific magnetic configurations in Wendelstein 7-X. While these are certainly ELM-likea, the questions of the cause of these fluctuations is still open, as is any linkage to an H-mode or profile changes (pedestals) with these events. Typically, 1-3% of the diamagnetic stored energy is lost per event, which when summed up over time accounts for ~20% of the overall plasma energy loss. The amplitude of the fluctuations increase with increasing ECRH input power. Bursts of energy and particles are picked up on the divertor. We see toroidal currents at the edge of the plasma (partial Rogowski response), with polarities dependent on magnetic island positions. The crashes, which we name "island localized modes" (ILM's) have a complex poloidal and temporal structure, and if not caused by breaking of islands themselves, are certainly modulated by energy flows to or through the magnetic islands. Using magnetic, visible light (filterscopes and imaging), infrared, microwave, soft x-ray, sodium beam, Thomson, Langmuir probes, and other diagnostics with sufficient time resolution, we will analyse and present further details of the events.

a G. A. Wurden, S. Ballinger, Bozhenkov, et al, "Quasi-continuous low frequency edge fluctuations in the W7-X stellarator", P5.1077, 45th EPS Conference on Plasma Physics, Prague, 2018.

Speaker: G.A. Wurden (EPS 2019)

276 P2.1069 Investigation of TESPEL cloud dynamics in Wendelstein 7-X stellarator

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1069.pdf

A Tracer-Encapsulated Solid Pellet (TESPEL) injection system was recently developed and installed on the Wendelstein 7-X (W7-X) stellarator. A tracer impurity (typically high-Z materials like iron or tungsten) for impurity transport investigations is embedded into a polystyrene polymer (C8H8)n sphere with a diameter of <1 mm. TESPEL is injected radially from the low-field side of the stellarator by a gas gun. Among other diagnostics, a fast framing camera looking from behind the TESPEL injection port was also installed in order to investigate the polystyrene ablation, cloud formation, expansion and drift processes. Wavelength selection by interference filters was used to separate certain ionic species (C I, C III and H I). The temporal resolution of the system is up to 500 kHz. The observation view allows to determine the vertical and poloidal movement of the TESPEL and to investigate the radiation distribution of the polystyrene cloud along and perpendicular to the magnetic field lines. The ablation rate of the polystyrene is similar to that of the cryogenic hydrogen pellet therefore it is not unexpected that similar features could be identified. It was observed that the TESPEL follows the designated radial trajectory, no vertical and poloidal deflection was seen. The pellet cloud distribution has a quasiperiodic fluctuation which is associated with the vertical detachment (drift) of the ionised cloud. First the pellet cloud expands parallel to the magnetic field for about 10 µs. Next, the ionised part of the cloud moves vertically (typically upward) detaching itself from the pellet. This takes about 10 µs. Finally, these processes are repeated. When the cloud is detached only a considerably reduced, and probably neutral, cloud remains around the pellet. At this time the shielding effect of the cloud is reduced thereby resulting in higher ablation and therefore more intense radiation. This contribution presents a detailed study of the cloud formation and drift based on the fast framing recordings of C I, C III and H I radiation distribution.

Speaker: G. Kocsis (EPS 2019)

277 P2.1070 Advanced RF heating schemes in preparation for ICRF heating and fast ion experiments in the W7-X stellarator

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1070.pdf

Fast ion confinement is crucial for the demonstration of the stellarator approach towards fusion energy. To study confinement of fast ions with today's stellarators advanced RF heating schemes can be used to generate fast ions. Secondly, advanced RF heating schemes are developed to improve ion heating performance. Advanced ICRH schemes (e.g. the 3-ion species scheme [1]) have the advantage of improved polarization, so the wave energy is nearly completely carried by the left hand polarized wave at resonance, thereby providing good power transfer to the ions. However, modelling of minority and 3-ion species heating in W7-X has shown that the fast ion tails are limited, and core heating is modest [3]. Additionally, the highly anisotropic distributions generated by the minority and 3-ion species schemes are not well confined. Furthermore, the high density plasma of W7-X creates difficulty heating thermal particles because of the high collisionality. An advantage of the so called RF-NBI synergetic scheme is that NBI born ions are weakly collisional at birth. Secondly, compared to other ICRH schemes the RF-NBI scheme heats more in the parallel direction, generating less trapped ions. Thirdly, a more isotropic velocity distribution is also desirable for fast ion studies since fusion born alphas are isotropic as well [2, 3]. The code SCENIC [4] is used to model ICRH scenarios in 3D. The code is comprised of a magnetic equilibrium code, a full wave code and a Fokker-Planck code. It is able to determine wave propagation and absorption in hot plasma with full FLR effects. Lastly, effects of finite orbit width effects and wave absorption on the distribution function are taken into account. This contribution will explore RF-NBI and other advanced heating schemes in W7-X relevant plasma scenarios prior to ICRF heating and fast ion experiments.
References
[1] Ye. O. Kazakov, D. Van Eester, R. Dumont and J. Ongena, Nucl. Fusion 55, 3 (2015)
[2] H. Patten et al., in preparation of Phys. Rev. Lett (2019) [3] H. Patten, "Development and optimisation of advanced auxiliary ion heating schemes for 3D fusion plasma
devices", EPFL, (2018)
[4] M. Jucker, "Self-consistent ICRH distribution functions and equilibria in magnetically confined plasmas",
EPFL, (2010)

Speaker: M. Machielsen (EPS 2019)

278 P2.1072 Simulation study of the influence on Zeff under different gas puffing location for CFETR phase II

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1072.pdf

In the future fusion reactor, power exhaust is one of the most critical issues due to the limit of the heat load onto divertor targets. Because the carbon are not suitable to be used as the first wall material, tungsten divertor is considered as the most appropriate candidate, which implies that impurity seeding is indispensable to mitigate heat load onto the divertor target via radiation. For CFETR phase II [1], whose fusion power is designed to be 1 GW, a large radiation fraction is required to dissipate the heat power entering the scrape-off layer. Therefore, considerable amount of impurities would be seeded into the tokamak. However, to avoid significant degradation of the main plasma, the impurity concentration should be kept at low level. In this work, the influence of the gas puffing location on the effective ion charge Zeff is studied using SOLPS5.0 code package. With the argon impurity and fixed radiation fraction ~ 85%, SOLPS simulations are performed for four different gas puffing schemes: (1) deuterium and impurity mixed gas injected from the outer leg (OL), (2) mixed gas injected from the inner leg (IL), (3) mixed gas injected from the top of main chamber (UP) and (4) deuterium injected from the top while impurity injected from the outer leg (UO). The simulated results are fitted to the Matthews' law [2] to give the relationship between the Zeff with the plasma density, which is considered to provide the boundary condition for further optimization of the performance of the core plasma [3]. For the four gas puffing schemes, it is found that the UO scheme has the best radiative efficiency. Furthermore, the puffing location of recycling impurities has a minor influence compared with the deuterium puffing location.

References
[1] Y.X. Wan et al, Nucl. Fusion 57 (2017) 102009.
[2] G. F. Matthews et al, J. Nucl. Mater. 241-243 (1997) 450-455.
[3] N. Shi et al, Nucl. Fusion 57 (2017) 126046

Speaker: M. Ye (EPS 2019)

279 P2.1073 Experimental observations of the avalanche-like electron heat transport events and their dynamical interaction with the shear flow structure

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1073.pdf

Non-diffusive avalanche-like transport events are observed in the L-mode and the weak ITB core plasmas in KSTAR when magnetohydrodynamic instabilities are absent. This observation implies that the avalanche-like event are a prevalent and universal process in the electron heat transport of tokamak plasmas. In addition, the electron temperature profile corrugation, which indicates the existence of the E×B shear flow layers, is clearly demonstrated. The measured width of the corrugation is around 45i. The avalanche activity is limited by this mesoscale shear flow structure, and the long range (macroscale) avalanche-like event occurs after the flow structure is destroyed.

Speaker: M.J. Choi (EPS 2019)

280 P2.1074 Hierarchical approach to first principle based reduced transport models

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1074.pdf

A framework to validate reduced particle and energy transport models based on the theoretical framework introduced in [1, 2] is proposed. The motivation of the present work is two-fold: (i) extending first-principle-based gyrokinetic simulations to long time scales is extremely demanding from a computational resource point of view; and (ii), the relevant physics processes can be illuminated and extracted from complex simulations by means of reduced models. In this context, the theoretical framework reviewed in Ref. [3] provides our starting point allowing to describe plasma dynamics with a level of simplification appropriate in regimes not correctly described by the quasi-linear approach. Consequently, in our work, particle and energy transport equations are formulated first, and then solved within three levels of increasing simplification based respectively on: the weak-amplitude expansion, i.e. |B|/B0 1; the assumption that the parallel mode structure is set by linear theory, i.e. NL L-1 ||-1; and, finally, the quasi-linear description. The systematic comparison of these levels of approximation against nonlinear gyrokinetic simulation results yield a verified reduced description retaining only the essential physics ingredients. Although completely general, this framework is particularly relevant for energetic particle (EP) transport and nonlinear dynamics in fusion plasmas. In particular, the hierarchy of verified reduced descriptions, discussed in this work, may be adopted for systematic analyses of the role of EPs as mediators of cross-scale couplings [3]. Accordingly, simplifying assumptions in their governing equations must be strictly and systematically validated in realistic scenarios. Experiments with a set of dimensionless parameters relevant for burning plasma studies such as the Divertor Tokamak Test facility (DTT) [4], are the ideal testbed for the further validation process.

References
[1] M. V. Falessi and F. Zonca. Physics of Plasmas, 25(3):032306, 2018.
[2] M. V. Falessi and F. Zonca. Submitted to Physics of plasmas, 2018.
[3] L. Chen and F. Zonca. Reviews of Modern Physics, 88(1):015008, 2016.
[4] R. Albanese, A. Pizzuto, et al. Fusion Engineering and Design, 122:274­284,
2017.

Speaker: M. Falessi (EPS 2019)

281 P2.1075 Advances in Understanding Plasma Rotation and Ion Thermal Transport Using Main-ion Measurements in DIII-D

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1075.pdf

Measurements of main-ion (D+) properties from the pedestal top to separatrix are challenging the commonly held assumption that the impurity toroidal rotation and temperature always provides a good proxy for the main-ion properties near the plasma edge. This has far-reaching consequences for SOL boundary conditions, pedestal stability, edge turbulence, momentum transport, and intrinsic rotation. Differences in the main-ion toroidal rotation include the absence of a commonly observed notch feature in the impurity toroidal rotation and the presence of a rapid co-current rotation near the separatrix which can reach values up to 100km/s for low collisionality QH-modes. This rotation is in agreement with ion orbit loss and global drift-kinetic calculations (XGC0) providing a clear demonstration of the importance of finite orbit width effects near the plasma edge and their possible role in intrinsic rotation generation.
The D+ temperature can be half the C6+ temperature at the separatrix in H-mode resolving the mystery of anomalously high and sometimes inverted ion temperature profiles inferred from impurities near the plasma edge. The difference in the ion temperatures is contrary to expectations given the rapid equilibration time between ion species and is thought to be due to a combination of non-local effects (presence of higher energy thermal tail ions from higher up the pedestal) and atomic physics processes near the plasma edge which act as an energy sink for D+ and a particle sink for C6+. In many cases using the main ion temperature profiles resolves issues with physically implausible negative ion heat fluxes which have long hindered energy transport studies in the pedestal region along with modifying the calculated drive for micro-instabilities which play a role in setting the pedestal structure.
Work supported by US DOE under DE-FC02-04ER54698 and DE-AC02-09CH11466.

Speaker: S. Haskey (EPS 2019)

282 P2.1076 Integrated core transport modelling of multiple isotope pellet cycle at JET

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1076.pdf

Due to the low gas puff fuelling efficiency in future reactors, pellets will be used to provide the necessary particle fuelling. Since the core isotope composition should be maintained and controlled at 50 : 50% D-T, it is important to understand and accurately model multiple-isotope particle transport, including during transient events such as pellets. Recent experiments at JET of Deuterium pellet fuelling in a pure Hydrogen plasma [1] has suggested a fast timescale for the Deuterium penetration in the core. This interpretation is in line with additional sets of multipleisotope experiments at JET, hinting that the ion particle transport coefficients in the ITG regime are significantly larger than those of electrons [2]. Such an interpretation is supported by recent analytical, nonlinear and quasilinear analysis [3], including the successful modelling of the multiple-isotope experiments [4].
This work directly models the mixed-isotope pellet fuelling experiment, through first-principlebased simulation of multiple pellet cycles. The quasilinear turbulent transport model QuaLiKiz [5], [6] and the pellet ablation model HPI2 are used within the JINTRAC integrated modelling suite [7]. The kinetic profiles and the Deuterium penetration timescale are successfully captured. The transport predictions of the quasilinear model in the presence of a negative density gradient are validated by comparison with linear GENE. This result has positive implications for the modelling of multi-isotope core fuelling and burn control.
References
[1] M. Valovic et al., To be Submitted to Nucl. Fusion.
[2] M. Maslov et al. 2018 Nucl. Fusion 58 076022.
[3] C. Bourdelle et al. 2018 Nucl. Fusion 58 076028.
[4] M. Marin et al., To be Submitted to Nucl. Fusion.
[5] C. Bourdelle et al. 2016 Plasma Phys. Control. Fusion 58 014036.
[6] J. Citrin, et al. 2017 Plasma Phys. Control. Fusion, 59(12):124005.
[7] M. Romanelli et al. 2014 Plasma and Fusion Research Volume 9, 3403023.

Speaker: M. Marin (EPS 2019)

283 P2.1077 Core transport studies in tokamaks plasmas via surrogate-based optimization techniques

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1077.pdf

Understanding transport and validating computer simulations in magnetically confined plasmas is critical for developing predictive models and designing scenarios for future burning plasmas, such as ITER and SPARC. However, the highly nonlinear nature of turbulence means that simulations of plasma behavior are very computationally expensive and very sensitive to small changes in input parameters. Optimization techniques combined with surrogate models are very promising to reduce computational cost of validation exercises, flux-matching frameworks and scenario optimization studies. The Validation via Iterative Training of Active Learning Surrogates (VITALS) framework [1] exploits surrogate strategies and a genetic-algorithm-based optimizer to test whether a combination of plasma parameters exists such that experimental transport measurements are reproduced by a transport model. For the first time, additional measurable quantities, such as incremental electron thermal diffusivity, temperature and density fluctuation levels, cross-phase angles, and particle diffusion and convection coefficients can be used simultaneously along with transport fluxes to study model validation. VITALS has been implemented to validate TGLF and QuaLiKiz turbulent transport models, and has been successfully used in the Alcator CMod and ASDEX Upgrade tokamaks to study the importance of multi-scale transport [2]. These results indicate that these machine learning algorithms are suitable and adaptable as a self-consistent, fast, and comprehensive validation methodology for plasma transport codes.

[1] P. Rodriguez-Fernandez et al 2018 Fusion Technol. 74:1-2, 65-76
[2] A.J. Creely et al (submitted to Plasma Phys. Controlled Fusion)
This work was supported by US DOE Awards DE-SC0014264, DE-FC02-99ER54512, DE-FC02-04ER54698, DE-SC0017381 and DE-FG02-91ER54109. P.R.F. was also supported by Fundación Bancaria "la Caixa" under Award LCF/BQ/AN14/10340041.

Speaker: P. Rodriguez-Fernandez (EPS 2019)

284 P2.1078 Nonlocal transport in toroidal plasma devices in the presence of magnetic perturbations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1078.pdf

Collisional particle transport in the presence of field perturbations originating from various MHD activity is examined theoretically on tokamaks (ITER, ASDEX Upgrade, NSTX and DIIID) and the reversed-field pinch RFX-mod [1]. For ITER and ASDEX Upgrade, modes typically leading to a disruption [2] are considered. On NSTX and DIII-D unstable Alfvén modes are investigated. Finally on RFX-mode the effect of saturated tearing modes is studied.
The existence of subdiffusive transport [3] for electrons is found to occur in some cases at very low mode amplitudes. Subdiffusion is also found for ions of high energy. In fact, orbit resonances can produce long time correlations and dynamical traps [4] for particle trajectories at perturbation amplitudes much too small for the orbits to be represented as uniformly chaotic. Besides this, in all devices orbits show a high degree of anisotropy, especially when comparing the angular (toroidal and poloidal) and radial directions. As a consequence, in the presence of field perturbations produced by MHD modes, the use of a traditional diffusive-convective scheme for transport, which is expressed by the Fick's law = -Dn + v n, leading to the well known transport scalings, is questionable. The existence and nature of subdiffusive transport is difficult to determine from first-principle theories, since it is found to depend on the nature of the mode spectrum and frequency, as well as on the mode amplitudes: this fact is mirrored in the different value of the Kubo number found in the devices analyzed in this paper. The connection between subdiffusive transport, Kubo and nonlocal models of transport [5] is also discussed.
References
[1] G. Spizzo et al, Nucl. Fusion 59, 016019 (2019) [
2] M. Maraschek et al, Plasma Phys. Controlled Fusion 60, 014047 (2018)
[3] R. Sanchez and D.E. Newman, Plasma Phys. Controlled Fusion 57, 123002 (2015)
[4] G.M. Zaslavsky, Hamiltonian Chaos and Fractional Dynamics (Oxford University Press) p. 187­199 (2005)
[5] D. del Castillo-Negrete, AIP Conf. Proc. 1013, 207 (2008)

Speaker: G. Spizzo (EPS 2019)

285 P2.1079 A new system of gyro-fluid equations with Onsager symmetry

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1079.pdf

Gyro-fluid equations are velocity space moments of the gyrokinetic equation. The damping due to kinetic resonances is included through a closure scheme chosen to match the collisionless density response functions. This damping allows for accurate linear eigenmodes to be computed, even in the collisionless limit, with a relatively low number of velocity space moments compared to gyrokinetic codes. The standard methods [1, 2] use the truncated moments to close the system of equations. An analysis of the gyro-fluid closure schemes will be presented that demonstrates a number of problems with the standard method. In particular, the Onsager symmetries [3] of the resulting quasilinear fluxes are not preserved. Onsager symmetry guarantees that the matrix of diffusivities is positive definite, an important property for a transport model. The constraints on the closure due to Onsager symmetry and other considerations are shown to be very restrictive. A new, simpler scheme for including the kinetic damping is found that preserves the Onsager symmetry and is scalable to higher velocity space moments without change of the damping model. Linear eigenmodes from the new system of equations are compared with gyrokinetic results, with and without collisions, including parallel and perpendicular electromagnetic fluctuations at high beta. The new system of gyro-fluid equations will be used to extend the TGLF quasilinear transport model [4] so that it can compute the energy and momentum fluxes due to parallel magnetic fluctuations, completing the transport matrix. The Onsager symmetries will enable faster transport solvers since the matrix of convection and diffusion coefficients will all be computed by a single call to the quasilinear transport model.
This work was supported by the U.S. Department of Energy under DE-FG02-95ER54309
and DE-FC02-04ER54698.
[1] G. W. Hammett and F. W. Perkins, Phys. Rev. Lett. 64 (1990) 3019.
[2] M. W. Beer and G. W. Hammett, Phys. Plasmas, 3 (1996) 4046.
[3] H. Sugama and W. Horton, Phys. Plasmas, 8 (1995) 2989.
[4] G. M. Staebler, J. E. Kinsey and R. E. Waltz, Phys. Plasmas 12 (2005) 102508.
Disclaimer-This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Speaker: G.M. Staebler (EPS 2019)

286 P2.1080 Study of heat transport in magnetic confinement devices using Transfer Entropy

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1080.pdf

Our recent studies [1-3] have shown that heat transport in magnetic confinement devices (the stellarators TJ-II and W7-X) is not a smooth and continuous (diffusive) process, but involves mini-transport barriers associated with low-order rational surfaces and rapid non-local radial `jumps'. This remarkable finding sheds a new light on the nature of anomalous transport and potentially provides insight into a long-standing conundrum of the physics of magnetically confined plasmas: power degradation or the enhancement of the radial transport coefficient as heating power is increased, a phenomenon encountered in all magnetic confinement devices, yet still not fully understood. In this work, we summarize our findings so far, and complement these by adding new, recent results obtained at the JET tokamak. The latter show that heat transport in tokamaks is also affected by the presence of the mentioned mini-transport barriers. These results are obtained using a relatively novel analysis technique (transfer entropy) that has been found to be extremely sensitive to the anomalous (non-local) transport component. We carefully verify the interpretation of the transfer entropy results by deducing effective diffusivities and comparing these to traditional results. We analyze transport as a function of different heating power levels and different magnetic geometry. The stellarator results are modelled qualitatively using a resistive MHD model, reproducing the salient features of the experimental observations. A main characteristic of this model is that it incorporates interactions between turbulence and the magnetic geometry, thus providing a route to understanding transport effects associated with loworder rational surfaces, such as those observed. Finally, the transfer entropy results are reinterpreted based on ideas from Continuous Time Random Walks, offering an interesting alternative view of heat transport, superseding the usual description in terms of diffusivities.
[1] B. van Milligen, J. Nicolau, L. García et al. Nucl. Fusion, 57(5):056028, 2017.
[2] B. van Milligen, B. Carreras, C. Hidalgo, et al. Phys. Plasmas, 25:062503, 2018.
[3] B. van Milligen, U. Hoefel, J. Nicolau, et al. Nucl. Fusion, 58(7):076002, 2018.

Speaker: B.P. van Milligen (EPS 2019)

287 P2.1081 Ion heat channel at the L-H transition in JET-ILW

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1081.pdf

During the last decades, the transition from low to high plasma confinement (L-H transition) has been analysed in several tokamaks showing that the L-H power threshold depends non-linearly on plasma density. A common finding shown both for AUG and C-mod experiments, with different mixes of heating systems, [F. Ryter et al. 2014 Nucl. Fusion 54 083003], [M. Schmidtmayr et al. 2018 Nucl. Fusion 58 056003] is that there is minimum in density for the L-H power threshold, with the power to the ion channel increasing monotonically with density. At JET, after the installation of the ITER-like wall (ILW), the L-H power threshold shows a minimum, or in some cases a flattening, in density, and the corresponding minimum density depends on the plasma shape [C. Maggi et al. 2014 Nucl. Fusion 54 023007], [J. Hillesheim et al., 2018, 27th IAEA Fusion Energy Conference, Ahmedabad, India]. The aim of the present work is to characterize the L-H transition in terms of power balance analysis (in particular regarding the ion heat channel) for a selection of JET-ILW discharges having the same toroidal field and plasma current but different plasma shape. We restricted the analysis to Neutral Beam Injection (NBI) only-heated discharges, with strong ion heating, divided in 2 datasets depending on the divertor configuration. The power crossing the separatrix at L-H transition has been calculated by integrated modelling with JETTO simulations using ASCOT code for NBI modelling. Due to the lack of core Ti measurements, predictive QuaLiKiz core transport simulations have been run, then validated against the available measurements, and finally used to estimate the thermal exchange power between electrons and ions. The resulting power balance indicates that, for the discharges analysed, the ion heating is dominated by direct NBI heating, and, at L-H transition, the total ion heat flux is not proportional to density. This was also the case for the subset of NBI-heated pulses in AUG.

Speaker: P. Vincenzi (EPS 2019)

288 P2.1082 Heavy impurity transport in tokamaks with plasma flows and saturated 3D perturbations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1082.pdf

Observations in JET hybrid scenarios show that early termination of the plasma can be caused by tungsten accumulation events, sometimes preceded by large living MHD perturbations [1]. Only recent investigations have been made into understanding the effects of 3D background rotation profiles and 3D MHD equilibria on the transport of heavy impurities. The VENUSLEVIS PIC code [2] has been used to follow heavy impurities in the presence of a 1/1 kink saturated 3D MHD equilibrium and strong toroidal rotation [3]. In the present work, a now selfconsistent treatment of the same problem is pursued. An implementation of the 3D centrifugal effects and 3D electrostatic potential correction on the VENUS-LEVIS code, based on the neoclassical 3D flow theory in [4] and the guiding center theory in [5], is presented. The code is used to follow heavy impurities on a 3D magnetic geommetry with 3D centrifugal effects, in order to understand how these 3D neoclassical effects will affect the overall neoclassical transport of heavy impurities. In particular, we focus our study on a saturated 1/1 internal kink mode as it has been seen in experiments that a correlation between this 3D magnetic structure and the inward flux of heavy impurities may exist. Simulations are performed to study this phenomena in both high (Pfirsch-Schlüter) and low (banana) collisionality regimes for the background ions in order to understand the impact of the saturated 1/1 internal kink mode on the peaking of tungsten distributions in JET hybrid scenarios exhibiting continuous 1/1 activity.
References
[1] L. Garzotti, C. Challis, R. Dumont, D. Frigione, J. Graves et al., "Scenario development for D-T operation at JET" (presented in IAEA 27th Fusion Energy Conference and to be published in Nuclear Fusion)
[2] D.Pfefferlé et al., Computer Physics Communications 185, 12 (2014)
[3] M. Raghunathan et al., Plasma Physics and Controlled Fusion 59, 124002 (2017)
[4] K.C. Shaing et al., The Physics of Fluids 55, 125001 (2015)
[5] A. J. Brizard, Phys. Plasmas 2, 459 (1995)
See the author list of "Overview of the JET preparation for Deuterium-Tritium Operation" by E. Joffrin et al. to be published in Nuclear Fusion Special issue: overview and summary reports from the 27th Fusion Energy Conference (Ahmedabad, India, 22-27 October 2018)

Speaker: E. Neto (EPS 2019)

289 P2.1083 Transport studies at ASDEX Upgrade: Cold pulses local or non-local? NBI particle source important or not? Pellet fuelling in or out?

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1083.pdf

Magnetic confinement plasmas are usually primarily driven by heat sources, with limited particle sources, particularly in the core. This is also the case of a fusion reactor, where the limited penetration of the neutral particles leads to the requirement of using fuelling pellets. Depending on plasma conditions, the particle source can impact the turbulence and the transport of particles and heat. Here three situations are analyzed with new experimental results from ASDEX Upgrade (AUG), linear and nonlinear simulations with the gyrokinetic code GKW, and integrated modelling with the transport code ASTRA, coupled to the transport model TGLF and the impurity transport code STRAHL. First, we identify the conditions under which the impact of the particle source produced by neutral beam injection on the density profile is significant. New AUG experimental results which match the conditions of a fusion reactor demonstrate the dominant role of convection with respect to source, and are consistent with both the gyrokinetic and the TGLF results. This clarifies possible differences between devices, such as AUG and JET [1], and increases the reliability of the density profile predictions for a reactor, a key element for the fusion performance. The second problem is related to the impact of a localized particle source as produced by fuelling pellets on the local shape of the density profile and the consequent turbulence and transport that can be destabilized by locally very steep profiles with both positive and negative gradients. A new microinstability with hollow density profiles is identified, and the associated turbulent particle transport is computed by means of non-linear gyrokinetic simulations and shown to be experimentally relevant and consistent with observations. However, the predicted inward diffusion decreases when collisionality is decreased to that of a reactor. Finally, the impact of a peripheral source of impurities, like those produced by laser ablation, on the plasma density profiles is analyzed from new experiments in AUG, which demonstrate the dominant role of the electron to ion heating fraction in determining the plasma response to cold pulses. At low density, the impurity penetration, modelled with STRAHL, is shown to modify the local turbulence causing a fast penetration of the particles, which explains the observation of a very fast flattening of the density profile. In trapped electron mode turbulence, this flattening causes a local reduction of the electron heat transport, leading to a fast increase of the central electron temperature, consistent with recent experimental and related modelling results in C-Mod [2]. Thereby, the complex and very fast density and temperature responses to a cold pulse can be fully explained by multi-channel interactions within a local model like TGLF.

[1] T. Tala et al, 27th IAEA Fusion Energy Conf., Gandhinagar, India, 2018.
[2] P. Rodriguez-Fernandez et al, Phys. Rev. Lett. 120, 075001 (2018).

Speaker: C. Angioni (EPS 2019)

290 P2.1084 1-dim Collisional Radiative impurity transport code with internal particle source for TESPEL injection experiments in RFX-mod2

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1084.pdf

Clear evidences that, due to a strong outward impurity convection, impurity core penetration is prevented have been found in the RFX-mod RFP device. A comparable convection of the main gas has not been observed [1] so that a favorable situation with peaked or flat density profiles and hollow impurity profiles is produced. Analysis of impurity transport relies on best reconstruction of impurity emission pattern with a 1-dim Collisional-Radiative code in which the radial impurity flux is schematized as a sum of a convective and a diffusive term [2,3]. The diffusion coefficient D and the velocity V, which are input to the simulation are varied until the experimental emission is reproduced. While the steady-state impurity profile is determined by the ratio V/D (peaking factor), the discrimination between D and V requires transient perturbative experiments. The experimental evidence of impurity outward convection in RFX-mod helical regimes occurring at high plasma current (I>1.2 MA) has been found in Li and C solid room temperature pellets experiments [4], Ne doped D2 cryogenic pellet injection, Ne gas puffing and Ni LBO experiments [5] (W LBO didn't show accumulation effects too). Similar D and V have been found for all the considered impurity species, without strong dependence on mass/charge. RFX-mod is now being upgraded to RFX-mod2, aiming at reducing secondary tearing mode amplitude which affects the duration of the improved confinement Single Helicity states [6]. In order to perform more detailed analysis of the impurity transport inside the outward convection barrier, the impurity source should be further inside the plasma. With this aim, Ni-tracer encapsulated solid pellet (Ni-TESPEL) experiments are foreseen in the new device [7]. The available 1-dimensional, time dependent Ni Collisional Radiative code, used to reconstruct experimental Ni emissions in RFX-mod [ 4] has been upgraded in preparation of such experiments in RFX-mod2 including the possibility of a Ni source (boundary condition) inside the plasma, placed in a time dependent position. The solid pellet injector already used in RFX-mod to inject C and Li solid pellets, will be adapted to inject TESPEL in RFX-mod2 (0.7/0.9 mm polystyrene ball with Ni powder inside, injection velocity up to 200 m/s can be reached). In this contribution, the solid pellet injector will be described, simulations of the pellet ablation [8] for different scenarios of RFX-mod2 plasma will be presented, Ni ion density, line and continuum emission profiles predicted by the code will be described and discussed.

[1] F.Auriemma et al Nucl. Fusion 55 (2015) 043010
[2] L.Carraro et al. Nucl. Fusion 36(1996) 1623
[3]M.Mattioli et al Plasma Phys. Control. Fusion 44 (2002)33 [4]T.Barbui et al. Plasma Phys. Control.Fusion 57 (2015) 025006 [5]S.Menmuir et al.PlasmaPhys.Control.Fusion 52 (2010) 095001
[6]L.Marrelli This conference
[7]N.Tamura "Versatility and Flexibility of the TracerEncapsulated Solid Pellet as a Diagnostic Tool in Magnetic Fusion Plasmas", 3rd ECPD, May 2019, Lisbon, Portugal
[8] K.V.Khlopenkov,S.Sudo Review of Scientific Instruments 69,9 (1998)3194

Speaker: L. Carraro (EPS 2019)

291 P2.1085 Linkage between LHCD and density fluctuation in edge region on EAST

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1085.pdf

Studies in EAST show that lower recycling and higher source frequency are preferred to improve LHCD (lower hybrid current drive) capability at high density due to the mitigation of parasitic effects of edge plasma, mainly ascribed to parametric instability (PI) and collisional absorption (CA) in edge region [1, 2]. A link between the degradation of current drive (CD) efficiency and the spectral broadening is found, showing that the spectral broadening has a negative and significant effect on CD efficiency. Recently, experimental effect of density fluctuation in edge region on LHCD, another candidate related to parasitic effect, has been observed for the first time in EAST. Results show that density fluctuation is affected by RMP application at density of 3.5x10^(19)m^(-3). The current drive capability indicated by the loop voltage improves with the decreasing density fluctuation. Meanwhile, the internal inductance enhances, indicating a peaked plasma current profile. Such degradation of LHCD at higher density fluctuation is mainly ascribed to the effect of density fluctuation in edge region on launching wave, which is firstly evidenced by the frequency spectrum measurement, leading to more power deposited in the edge region. Results are encouraging considering that the LHCD tool is essential for control of current profile in reactor grade plasmas. Also, the development of LH wave number measurement in the edge region for further mechanism understanding and the preliminary result obtained in EAST will be reported.

[1] B J Ding et al., Nucl. Fusion 53 (2013) 113027.
[2] B J Ding et al., Nucl. Fusion 58 (2018) 126015.

Speaker: B. Ding (EPS 2019)

292 P2.1086 ASCOT-AFSI simulations of fusion products for the main operating scenarios in JT-60SA

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1086.pdf

The JT-60SA is a large device with a plasma volume 50% larger than JET, and up to 34 MW of NBI heating power. High performance deuterium plasmas are expected to produce neutron rates in excess of 10^(17) n/s. A significant fraction of the fusion reactions will be produced by high-energy NBI ions from 24 MW positive (PNB) and 10 MW negative (NNB) neutral beam injectors with up to 500 keV energy. Additionally, tritons produced in the D-D reactions have a Larmor radius similar to that of fusion alphas, which are useful for improving the predictability of alpha particle behaviour in ITER and DEMO. High-fidelity simulations for both the fast ions as well as the fusion products are thus necessary. The fusion products are simulated with the calculation chain of BBNBI, ASCOT and AFSI codes. The beamlet-based NBI code BBNBI is used to calculate the fast ion source from the 85 keV PNB and 500 keV NNB injectors. The Monte Carlo orbit-following code ASCOT solves the slowing-down distribution function of the reactants, and the AFSI fusion source integrator is used to calculate the resulting fusion products for thermonuclear, beamthermal and beam-beam reactions. The D-D tritons can then be investigated with further ASCOT-AFSI simulations. In this contribution we present simulation results for fusion products in the planned main JT-60SA operating scenarios. Depending on the scenario, more than 75 % of the neutrons can originate from beam-thermal and beam-beam reactions, of which up to 80 % are produced by the 500 keV NNB ions. Furthermore, the neutron energy spectrum is significantly widened due to the high reactant energy. Estimates are also presented for the confinement of the tritons and the 14.1 MeV neutron rate due to the triton burn-up.

Speaker: T. Kurki-Suonio (EPS 2019)

293 P2.1087 Scattering of radio frequency waves by plasma turbulence

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1087.pdf

The scrape-off layer and the edge region in fusion plasmas are replete with turbulence induced incoherent fluctuations, and coherent fluctuations, such as blobs and filaments. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near the wall of a fusion device, encounter this turbulent region as they propagate towards the core. In order to optimize the heating of plasmas, or the generation of non-inductive plasma currents, it is necessary to properly assess the effect of this turbulence on RF waves. We have undertaken a set of theoretical and computational studies that model the propagation of RF waves through turbulent plasma. The theoretical models are mathematically tractable, and provide physical and intuitive insight into the effect of turbulence on RF waves. The computational studies provide support for these theoretical models. We use two complementary theoretical approaches ≠ geometrical optics and physical optics ≠ for magnetized plasmas with a tensor permittivity. The former, an approximation to the latter full-wave approach, is useful for incoherent fluctuations and leads to Snell's law and the Fresnel equations in plasmas. This is the basis for the Kirchhoff's approximation for scattering off density fluctuations [1]. The physical optics method is appropriate for studying scattering from coherent fluctuations [2, 3]. The two complementary analyses reveal important physical insights into the scattering processes. Besides refraction and reflection, the spatial uniformity of power flow into the plasma is affected by side-scattering, diffraction, shadowing, and interference. In addition, the incident RF wave power can couple to other plasma waves when interacting with density fluctuations. Within the framework of the COMSOL software, we have built a numerical code to study scattering of RF waves by fluctuations [4]. The code has been benchmarked against theoretical results, and is being used to study scattering from complex representations of fluctuations.

References
[1] P. Beckmann and A. Spizzichino, "The scattering of electromagnetic waves from rough surfaces," Artech House, Massachusetts (1987)
[2] A.K. Ram, K. Hizanidis, and Y. Kominis, Physics of Plasmas 20, 056110 (2013)
[3] A.K. Ram and K. Hizanidis, Physics of Plasmas 23, 022504 (2016).
[4] Z.C. Ioannidis et al., Physics of Plasmas 24, 102115 (2017).

Speaker: A. Ram (EPS 2019)

294 P2.1088 A 6-field fluid model for the study of turbulence-driven magnetic islands and impurity transport

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1088.pdf

Transport in a Tokamak is caused by several mechanisms. While at the plasma edge turbulent transport dominates, neoclassical transport is important in the core region especially for heavy impurities [1]. Furthermore, large-scale MHD instabilities like magnetic islands are known to influence the transport of heat, particles and impurites.It is insufficient to study these mechanisms independently, since the development of a magnetic island may be heavily influenced by small-scale turbulence as well as by neoclassical effects.
Therefore, we want to describe magnetic islands, turbulence and neoclassical physics in one model. We derive a new six fields model describing magnetic flux ψ , vorticity ω , ion and electron temperatures T_i, T_e, density n and parallel velocity u_(||) evolutions. This allows for the modelling of tearing modes as well as interchange and ITG turbulence. We model neoclassical physics by introducing an adequate closure relation on the pressure anisotropy, following [2]. We have implemented this model into AMON code [3]. This is a parallelised semi-spectral code that can evolve the fluid equations on large grids efficiently and which allows to study, both, large-scale MHD phenomena and small-scale turbulence self-consistently.
Our simulations focus on the situation where the tearing modes are linearly stable and a magnetic island grows due to nonlinear effects. First, we present the generation of a small magnetic island from turbulence [4-5] and the role of neoclassical physics in the process. We observe that while the initial growth rate of the magnetic island is imposed by the turbulence, its subsequent growth is strongly enhanced by neoclassical physics, leading to neoclassical tearing modes (NTMs). Second, we study the dependence of the saturation size of an NTM on the level of ITG turbulence present in our simulation. Finally, we discuss the potential impact of magnetic islands in interaction with turbulence on transport and the future extension of our model to describe the transport of heavy impurities.

[1] C. Angioni et al, Physics of Plasmas 22, 055902 (2015)
[2] P. Maget et al Nuclear Fusion, 56 (8), 086004. (2016)
[3] A. PoyÈ et al Physics of Plasmas 22, 030704 (2015)
[4] M. Muraglia et al, Phys. Rev. Lett., 107, 095003 (2011)
[5] O. Agullo et al, Phys. of Plasmas 24, 042308 (2017)

Speaker: J. Frank (EPS 2019)

295 P2.1089 Properties of density temperature and electric field structures in the turbulent regime of the simply magnetised toroidal plasma device THORELLO

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1089.pdf

Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as well as in basic plasma physics toroidal devices. In particular the understanding of turbulent transport mechanisms has a great interest for the improvement of the magnetic confinement. Here we report the results of an experimental investigation of plasma parameters fluctuations of a turbulent, low beta, low temperature plasma with a simply magnetised torus configuration. Experiments have been performed in the Thorello device, operating at the University of Milano-Bicocca [1]. There a low temperature, high density plasma can be produced in a steady configuration for long times in a hydrogen low pressure discharge. Plasma parameters have been studied by means of multiple pin electrostatic probes and fairly long time series of fluctuations have been obtained and correlated. At the edge of magnetic confinement devices, a large fraction of anomalous particles and energy transport is attributed to the propagation of density blobs [2]. These are isolated and intermittent structures, with density and temperature above the surrounding plasma, extending along field lines and propagating away from the bulk. In this contribution we discuss some properties of plasma structures that develops and propagates in the edge region. In particular we assess the role of transport flux events, defined by the simultaneous enhancement of plasma density and radial ExB velocity. Effects of such events on plasma transport (particle flux) has been analyzed for different scenarios [3].

[1] R.Barni, C.Riccardi, Plasma Phys. & Contr. Fusion 51 (2009) 085010.
[2] G.R. Tynan, A. Fujisawa, G. McKee, Plasma Phys. & Contr. Fusion 51 (2009) 113001.
[3] R. Barni, S. Caldirola, L. Fattorini, C. Riccardi, Physics of Plasmas 24 (2017) 032306.

Speaker: R. Barni (EPS 2019)

296 P2.1090 Effect of the isotope mass on the turbulent transport of ASDEX Upgrade and JET-ILW L-modes edge

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1090.pdf

Since the first comparisons between different hydrogen isotope plasmas in tokamaks it appeared that deuterium (D) plasmas have generally better performances than hydrogen (H) plasmas [1-4]. The energy and particle confinement times [1-3], the L-H power transition [4,5] and the H-mode pedestal [3,6], essential parameters for a reactor, have all been found to depend on the isotope mass. A general experimental observation is that the isotope mass has a strong impact at the plasma edge [3,6]. Past studies on the tokamak edge suggested a large variety of micro-instabilities and turbulence to explain the turbulent transport in this region [7-11]. However the effect of the isotope was not the focus in these studies. We use local gyro-kinetic simulations with the GENE code [12] to study the nature of the
turbulent transport at the edge of ASDEX Upgrade and JET-ILW plasmas (ρ_(tor) ~ 0.95) and the effect of the isotope mass on the micro-instabilities and turbulence in this region. For both devices pairs of D and H L-mode plasmas with matched density and temperatures have been analyzed. As reported in Ref. [3,13], higher input power and gas puff were needed in the H discharges to match the D profiles. For the JET discharges, EDGE2D/EIRENE simulations predicted diffusivity coefficients in H twice as in D in the edge region [3]. Our simulations indicate that the main micro-instability in the edge region of both machines is an electron
drift-wave-like mode destabilized by collisions (ν_(ei)/c_s), driven by R/L_(Te) (=R| \nablaT_e|/T_e) and connected to the kinetic electron dynamics, confirming what was found in past gyro-fluid simulations [8]. We find that the isotope mass has a strong impact on the micro-instability, effect enhanced by the high collisionality of the edge region. The effect of the ion mass appears already in linear electrostatic simulations and translates into a lower critical threshold in R/L_(Te) with lower isotope mass. Electromagnetic effects are found to play a strong role in non-linear simulations, with an enhancement of the level of the turbulence at low-k_y wavenumbers, similar to what was found in Ref. [7,8]. The external ExB shear is found to have a stabilizing effect on this type of turbulence, suggesting a possible role in the L-H transition. These results are valid for both JET-ILW and ASDEX Upgrade. Overall, our simulations are able to reproduce the experimental observations, in both the fluxes and their dependence on the isotope mass. These findings can help to predict the performance of future reactors such as ITER. A better understanding of the edge transport is an essential element for extrapolation to future reactors, affecting important aspects such as the L-H power threshold and the H-mode pedestal.

We are grateful to Alessandro DiSiena, Tobias Goerler, Alejandro Banon Navarro, Paul Crandall and Clarisse Bourdelle for precious discussions and suggestions. We acknowledge the CINECA award under the ISCRA initiative, for the availability of high performance computing resources and support. Part of the simulations presented in this work was performed at the COBRA HPC system at the Max Planck Computing and Data Facility (MPCDF), Germany. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

[1] M. Bessenrodt-Weberpals et al., Nucl. Fusion 33, 1205 (1993)
[2] S. D. Scott et al., Phys. Plasmas 2, 2299 (1995)
[3] C. F. Maggi et al., Plasma Phys. Control. Fusion 60, 014045 (2018)
[4] F. Ryter et al., Nucl. Fusion 49, 062003 (2009)
[5] E. Righi et al., Nucl. Fusion 39, 309 (1999)
[6] J.G. Cordey et al., Nucl. Fusion 39, 301 (1999)
[7] B. D. Scott, Plasma Phys. Control. Fusion 49, S25 (2007)
[8] B. D. Scott, Phys. Plasmas 12, 062314 (2005)
[9] C. Bourdelle et al., Plasma Phys. Control. Fusion 54, 115003 (2012)
[10] D. Told et al., Phys. Plasmas 15, 102306 (2008)
[11] D. R. Hatch et al., Nucl. Fusion 55, 063028 (2015)
[12] F. Jenko, et al., Phys. Plasmas 8, 4096 (2001)
[13] P. A. Schneider et al., Nucl Fusion 57, 066003 (2017)

Speaker: N. Bonanomi (EPS 2019)

297 P2.1091 Observations on edge GAM-turbulence interactions in ASDEX Upgrade

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1091.pdf

The interaction of Geodesic Acoustic Modes (GAMs) and Zonal Flows with small-scale turbulence is an important topic in magnetic confinement studies. Much progress has been made in recent years on the measurement, interpretation and numerical simulation of the GAM-turbulence interaction. Using microwave reflectometry diagnostics, we present here recent results from the ASDEX Upgrade tokamak on the temporal and spatial behaviour of coherent edge GAMs and their interaction with both the background incoherent flow fluctuations and the ambient density n_e turbulence. Experimentally, the L-mode GAM intensity displays a low frequency (few hundred Hz) intermittency or `breathing' modulation, of up to 50% of the p.t.p. flow amplitude, phase-shifted to a corresponding modulation of the GAM frequency, the RMS δn_e, and the incoherent flow perturbation levels. The GAM spectral peak width (indicative of the GAM lifetime) is narrow (Δf_(fwhm) few hundred Hz) but often displays splitting and/or a low frequency modulation, demonstrated by double (short and long) auto-correlation times. Envelope analysis reveals the high frequency (short wavelength) n_e fluctuations can also be modulated at the GAM frequency, indicating a non-linear energy (spectral) coupling to the GAM. This is also supported by auto and cross-bispectral analysis. From cross-phase analysis the GAM generally leads the turbulence, but the phase delay shifts and reverses in both time and space. The extent of these effects depend strongly on the plasma parameters and the radial location. Structurally, the GAM is zonal with radial widths of a few cms and inward radial propagation velocities of a few hundred ms^(-1). Radially, the GAM peak intensity coincides with maximal summed bicoherence (non-linear transfer) and with the maximal plasma pressure gradient. These experimental results are further supported by numerical simulations.

Speaker: G.D. Conway (EPS 2019)

298 P2.1092 Temperature ratio dependence on turbulence-driven impurity transport in Wendelstein 7-X

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1092.pdf

This contribution reports on the impurity confinement in Wendelstein 7-X which was studied with dedicated impurity injection by means of laser blow-off. Basically, the understanding of impurity transport is a demanding task for stellarators with the aim of steady state operation. Especially, the accumulation of impurities in confined plasmas can cause an early pulse termination due to a radiative collapse. Hence, the investigation of transport properties is inevitable and was done for different operation scenarios in the last operation phase of Wendelstein 7-X (W7X) to develop favorable operating scenarios that avoid these accumulations. From the analysis of the temporal evolution of the emission from several ionization stages of the injected impurity, it turns out, that for relevant plasma scenarios no impurity accumulation were found and the impurity transport time is mainly in the order of 100 ms. Additionally, the impurity transport tends to be turbulence-driven. These results are supported by core turbulence measurements and calculation from 1D transport code STRAHL involving the drift kinetic equation solver (DKES) for the neoclassical expectations. These calculations in sum enable for instance the comparison of the neoclassical and anomalous diffusion coefficient. As a result, the anomalous diffusion coefficient is two orders of magnitude larger compared to neoclassical expectation and supports the experimental finding of turbulence-driven impurity transport. Additionally, there are experimental indications for a temperature ratio dependent impurity confinement. The anomalous diffusion coefficient decreases meanwhile the impurity transport time increases with the temperature ratio T_i / T_e. This temperature ratio is the threshold for the ion-temperature gradient instabilities which seems to be the major turbulence mechanism in W7-X so far.

Speaker: T. Wegner (EPS 2019)

299 P2.1093 Properties of microtearing turbulence in the H-mode pedestal

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1093.pdf

Microtearing (MT) turbulence has been identified as a key player in the evolution of the Hmode pedestal due to its ability to produce electron thermal diffusivities very different from the ion heat and particle diffusivity channels [1]. However, important aspect of the physics of MT instability and turbulence under pedestal conditions are presently not well-understood.
Comparing between parameter points corresponding to JET-H-mode-like parameters as well as a core microtearing case [2], it is shown that much like ion-temperature-gradient-driven modes, the MT instability transitions from a toroidal branch to a slab-like branch. However, some of the central identifiers of MT are preserved across branches, such as mode parity and scaling with parameters such as the plasma pressure or the collision frequency.
Nonlinearly, zonal fields ≠ in addition to zonal flows and densities ≠ feature strongly in saturation, leading to significant variability in the electron heat flux. It is shown that the addition of external resonant magnetic perturbations acts differently on this turbulence type than it does on zonal-flow-regulated regimes [3].
Lastly, the impact of external ExB shearing as well as parallel flow shear on the MT turbulence is studied, and connections to pedestal evolution are established.

References
[1] D.R. Hatch et al., Nucl. Fusion 57, 036020 (2017)
[2] H. Doerk et al., Phys. Rev. Lett. 106, 155003 (2011)
[3] Z.R. Williams et al., Phys. Plasmas 24, 122309 (2017)

Speaker: M. Pueschel (EPS 2019)

300 P2.1094 Coexistence of magnetic island chains and resistive ballooning mode turbulence

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1094.pdf

Control of turbulent particle and heat transport is an important issue for magnetically confined fusion plasmas such as tokamaks and helical devices. Repetitive transport bursts due to the magnetohydrodynamic turbulence in the pedestal region, called the edge localized modes (ELMs), will be serious problems for future devices. Resonant magnetic perturbations (RMPs) by external current coils are used to generate magnetic island chains and mitigate or eliminate the ELMs[1]. It is not fully understood what kind of physical mechsnism exists in the background where RMPs affect ELMs. Similarly, it is not clear how plasma turbulence influences the formation of magnetic islands due to RMPs.
The goal of the present study is to self-consistently simulate the interaction between the resistive ballooning mode turbulence with magnetic island chains due to RMPs. We have been developing a simulation code, which solves a set of reduced two-fluid equations for threedimensional and multi-helicity perturbations in tokamaks with circular poloidal cross sections. In our previous work, repetitive and intermittent transport bursts driven by the resistive ballooning mode turbulence with external heating are simulated, and an effect of a RMP on turbulent heat transport is examined[2]. The transport bursts are found to be replaced by more moderate and continuous transport when the penetration of the RMP occurs. The change in the transport pattern is found to be associated with the effect of the RMP on nonlinear coupling of fluctuations. In the previous work, the effect of the ballooning mode turbulence on the stability of magnetic island chains is not examined. However, the stability of magnetic islands and the state of turbulence should be discussed simultaneously. We are planning to revisit this problem by recosidering values of transport coefficients and by sophisticating the flow model.

References
[1] T. E. Evans et al., Nucl. Fusion 48, 024002 (2008).
[2] S. Nishimura and M. Yagi, Plasma Fus. Res. 6, 2403119 (2011).

Speaker: S. Nishimura (EPS 2019)

301 P2.1095 Spatiotemporal evolution of turbulent plasma density fluctuations and of their kurtosis value during modulated ECRH at the L-2M stellarator

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1095.pdf

Non-local transport and non-Gaussian probability density functions (PDFs) of turbulent fluxes are fundamental physical issues for magnetic confinement fusion that were addressed well in set of works (e.g., review [1] and references therein). Deviation of PDFs from a Gaussian distribution most easily to monitor by calculating the kurtosis value and usually it is preferable to analyze not the original data set but its increments (first order differences) to deal with a stochastically independent data set.
Modulated electron cyclotron resonance heating (ECRH) is a useful tool to study changes in microturbulence characteristics. Such changes can be a result of a variety of nonstationary processes that accompany modulated ECRH. At the L2-M stellarator one form of modulated ECRH is a sequence of microwave (frequency f = 75 GHz for X2-mode ECRH) pulses. The pulse lengths and the lengths of pauses between the pulses can be regulated in a wide range. Heating power P_(ECRH) in the experiments [2, 3] on modulated ECRH was 0.2 MW and 0.4 MW, average electron density n_e was 1.8-2.1 x 10^(19) m^(-3), central electron temperature Te reached 1 keV (at P_(ECRH) = 0.4 MW). Density fluctuations from different plasma regions were measured by multiple collective scattering diagnostics.
In our previous work [3] four characteristic stages of evolution of energy losses during modulated ECRH were noted. The focus of the present work was to investigate thoroughly behavior of kurtosis value during the abovementioned stages. Following common features of density fluctuations measured by all collective scattering diagnostics were observed clearly: deviation of density fluctuations PDFs and PDFs of their increments from a Gaussian distribution has a bursty nature (100 - 200 μs is a typical length of a burst); the deviation of the fluctuations PDFs usually is more pronounced than the deviation of the increments PDFs.

The reported study was funded by RFBR according to the project 18-02-00621.

[1] T.S. Hahm and P.H. Diamond. Journal of the Korean Physical Society, 2018, v.73, pp. 747-792.
[2] G.M. Batanov, M.S. Berezhetskii, V.D. Borzosekov et al. 44th EPS Conference on Plasma Physics, 26 - 30 June 2017, Belfast, Northern Ireland, P2.154.
[3] G.M. Batanov, V.D. Borzosekov, S.E. Grebenshchikov et al. 45th EPS Conference on Plasma Physics, 2 - 6 July 2018, Prague, Czech Republic, P4.1099.

Speaker: G. Batanov (EPS 2019)

302 P2.1096 Numerical simulations of intermittent fluctuations in 2D scrape-off layer turbulence

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1096.pdf

Intermittent fluctuations in the scrape-off layer (SOL) are investigated by numerical simulations of two dimensional reduced fluid models describing the evolution of the electron density and electric drift vorticity in the two dimensional plane perpendicular to the magnetic field [1, 2, 3]. Long time series obtained by artificial Langmuir probes are compared to predictions of a stochastic model, describing the plasma fluctuations as a super-position of uncorrelated exponential pulses arriving according to a Poisson process. For all investigated fluid models the probability density functions for the particle density fluctuations change from a normal distribution near the last closed flux surface to an exponential tail in the far SOL. The waiting times and peak amplitudes of the bursts have both an exponential distribution. The average burst shapes are well described by a two-sided exponential pulse function. The effects of reducing the sampling frequency of the artificial Langmuir probes and adding Gaussian noise are shown to result in a frequency power spectral density with a Lorentzian shape. The fluctuation statistics obtained from the numerical simulations are in excellent agreement with experimental measurements [4, 5, 6] . These findings are discussed in the light of prevailing theories for a stochastic model for intermittent scrape-off layer plasma fluctuations and recent experimental measurements.

References
[1] Sarazin, Y., et al. "Theoretical understanding of turbulent transport in the SOL." Journal of nuclear materials 313 (2003): 796-803.
[2] Garcia, O. E., et al. "Turbulence and intermittent transport at the boundary of magnetized plasmas." Physics of plasmas 12.6 (2005): 062309.
[3] Bisai, Nirmal, et al. "Edge and scrape-off layer tokamak plasma turbulence simulation using two-field fluid model." Physics of plasmas 12.7 (2005): 072520.
[4] Theodorsen, Audun, 4t al. "Scrape-off layer turbulence in TCV: Evidence in support of stochastic modelling." Plasma Physics and Controlled Fusion 58.4 (2016): 044006.
[5] Kube, Ralph, et al. "Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer." Plasma Physics and Controlled Fusion 60.6 (2018): 065002.
[6] Garcia, O. E., et al. "SOL width and intermittent fluctuations in KSTAR." Nuclear Materials and Energy 12 (2017): 36-43.

Speaker: G. Decristoforo (EPS 2019)

303 P2.1097 Correction of turbulent flow moments measured by Langmuir probes in the vicinity of the L-H transition in COMPASS

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1097.pdf

The analysis of turbulent flows in the edge region of tokamak plasmas requires the measurement of time-averaged turbulent stresses and fluxes such as the Reynolds stress (RS), which has been identified in recent models and experiments [1] as a likely driver of poloidal zonal flows expected to play a key role in the L-H transition. However, the common method of using floating potential fluctuations measured by Langmuir probes (LP) V^(LP)(fl) suffers from being contaminated by electron temperature fluctuations T_e[2, 3]. For the interpretation of such experiments it is worth-while to seek a correction of V^(LP)(fl) statistics by the exploitation of additional knowledge of T_e statistics offered by e.g. the combination of LP with ball-pen probes (BPP) [4].
A proof-of-principle correction scheme for the RS measured by LP was found for experimental data measured in the COMPASS tokamak with the modified Reynolds stress probe head [5]. The correction scheme is based on the decomposition of RS into statistical moments such as variance and poloidal and radial covariances of V^(LP)_(fl) measured by LP with statistical moments of T_e from BPP measurements. The correction scheme was further compared with the relationships between the associated statistical moments in comparable turbulent HESEL [6] simulations.
The correction scheme was further tested for the time-evolving phenomena of Limit Cycle Oscillations (LCO) observed in the vicinity of the L-H transition in the COMPASS tokamak [5]. The LCO typically have a frequency of 3-5 kHz. Their frequency is observed to scale inversely with the plasma density as well as with other global parameters.

References
[1] G. R. Tynan, I. Cziegler, P. H. Diamond, et al., Plasma Physics and Controlled Fusion 58, 044003 (2016)
[2] B Nold, et al., New J. Phys. 14 063022, (2012)
[3] O. Grover, J. Adamek, J. Seidl, et al., Review of Scientific Instruments 88, 063501 (2017)
[4] J. Adamek, H. W. M¸ller, C. Silva, et al., Review of Scientific Instruments 87, 043510 (2016)
[5] O. Grover, J. Seidl, J. Adamek, et al., Nuclear Fusion 58, 112010 (2018)
[6] A.H.Nielsen, G.S.Xu, J.Madsen, et al., Physics Letters A 379, 3097-3101 (2015)

Speaker: O. Grover (EPS 2019)

304 P2.1098 Modelling of turbulent fluctuations measured in the TCV tokamak with gyrokinetic simulations and a synthetic phase contrast imaging diagnostic

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1098.pdf

Proper comparison of simulated turbulent fluctuations with experimental observations is necessary for code validation, and for establishing a link between experimental fluctuation measurements and the underlying physics. In this contribution we report on the progress of modelling localised measurements of turbulent electron density fluctuations, obtained with the tangential phase contrast imaging (TPCI) diagnostic installed on the TCV tokamak. The modelling is done in two steps. First, nonlinear flux-tube gyrokinetic simulations are performed with the Eulerian (grid-based) GENE code, taking into account realistic TCV geometry and profiles. A synthetic diagnostic that has been developed in MATLAB is then applied to the simulated density fluctuations to model the experimental measurement procedure, allowing detailed comparison between simulation and experiment. Using these tools, we extended a previous computational analysis of the role of plasma triangularity in improved confinement in TCV. In previous such studies, the focus was on comparing heat flux levels between simulation and experiments. Large discrepancies were found, which were attributed to the large experimental error bars on the input profile gradients, to the simplification of not including electron scales in the simulations, to possible global effects, or to a combination of all three. With the synthetic diagnostic a more in depth comparison is performed, investigating the importance of such effects also in the observed wavenumber and frequency spectrum. After motivating and verifying the described procedure for modelling density fluctuations at TCV, we make initial predictions on the role of electron scale turbulence on transport levels in highly shaped plasmas. This is performed in preparation of first electron scale measurements that are envisioned to be performed with TPCI, as a result of an upgrade currently underway.

Speaker: A. Iantchenko (EPS 2019)

305 P2.1099 Upstream and downstream properties of turbulent transport at tokamak COMPASS

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1099.pdf

Turbulent transport in the Scrape-Off Layer (SOL) is an important issue in contemporary tokamak physics due to its role in deteriorating plasma confinement and enhancing the plasmawall interaction. This work compares turbulence properties on two poloidal locations, the outer midplane (upstream) and the divertor target (downstream), and interprets their similarities and differences in terms of parallel transport of turbulent structures. The experimental data was measured at tokamak COMPASS, Prague, using Langmuir and ball-pen probes mounted on a reciprocating manipulator or embedded into a divertor tile. The analysis input are mainly measurements of the ion saturated current I_(sat), supplemented by measurements of the electron temperature T_e with high temporal resolution (several µs) using the ball-pen/Langmuir probe technique [1]. To compare the upstream and downstream fluctuations of these quantities, several techniques are employed. Probability distribution functions (PDF) of the fluctuations are drawn, together with the skewness and kurtosis profiles, and their dependence on the plasma collisionality is investigated. To estimate the blob coherence along the field line, correlation of upstream and target fluctuations is attempted; however, uncertainties in the magnetic equililibrium reconstruction prove to be a major challenge in this task. The importance of T_e fluctuations on the I_(sat) ∝ n_e \sqrt(T_e) PDF is investigated, and it is found to be quite large, distorting the exponential tail of ne fluctuations into a more general shape.

References
[1] J. Adamek et al, Review of Scientific Instruments 87, 043510 (2016)

Speaker: K. Jirakova (EPS 2019)

306 P2.1100 Deuterium retention in liquid Sn samples exposed to D2 plasmas of GyM

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1100.pdf

Divertor plates of tokamaks are known to be subjected to extremely high heat loads. Melting, cracking and other damages of Plasma Facing Components (PFCs) may occur [1]. Experiments in tokamaks after severe melting of tungsten (W) tiles in the divertor demonstrated that such damage events could compromise the reliable machine operation. Liquid Metals (LMs) present many potential advantages when compared to solid tungsten PFCs. Both laboratory experiments replacing tokamak environment and tokamak experiments themselves [2] have already shown that LMs can be a viable solution as PFCs. Tin (Sn) is one of the most promising candidates [3] to be used as a liquid metal PFC due to its low evaporation rate and melting point. In order to qualify Sn as a PFC, a fundamental aspect that needs to be carefully investigated is how much deuterium is retained in liquid Sn under fusion conditions. While some tests devoted to evaluate the heat load handling capability of liquid Sn systems were done [4], data on deuterium retention of Sn when exposed to a D_2 plasma are still very few [5]. In this contribution, we present a systematic investigation of deuterium retention in liquid Sn (at a temperature of 600 K) exposed to the D2 plasma of the linear machine GyM [6], as a function of plasma fluence. The typical deuterium ion fluxes of GyM are 10^(19)-10^(20) m^(-2)s^(-1) at an electron temperature of 5-10 eV. Free liquid Sn targets were exposed (horizontal exposure) for plasma fluence in the range of 1-4 x10^(24) m^(-2). Ex-situ analysis by Nuclear Reaction Analysis (NRA) on Sn after exposure has proved that the amount of atomic deuterium retained is very low, in the range of 0.1-0.2 at %, a retention value lower than that reported for W [7]. Furthermore, the study carried out as a function of fluence shows that deuterium retention does not increase for the investigated experimental parameters.

[1] J.W. Coenen et al., Presentation at the 20th PSI Conference, Aachen, Germany (2012)
[2] F. L. TabarÈs et al., Plasma Phys. Control. Fusion 58 (2016) 014014
[3] A. Cremona et al., Nuclear Materials and Energy 17 (2018) 253-258
[4] T.W. Morgan, et al., Plasma Phys. Control. Fusion 60, 014025 (2018)
[5] J.P.S. Loureiro et al., Nuclear Materials and Energy 12 (2017) 709
[6] D. Ricci et al., Proc. of the 39th EPS Conference, Stockholm, Sweden, ECA, vol. 36F (2012)
[7] T. Tanabe 2014 Phys. Scr. 2014 014044

Speaker: M. Pedroni (EPS 2019)

307 P2.1101 Homogenization and PCE method: Application in tokamak plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1101.pdf

Homogenization methods for dielectric mixtures have existed for over two decades, but their limitations regarding the wavelength of incoming beam did not allow them to be used extensively in tokamak plasmas. We present a new method which does not have the same limitations, with application to a dielectric plasma mixture with embedded filamentary structures of different density than the background plasma. Polynomial chaos expansion (PCE) method determines, in a computationally efficient way, the evolution of uncertainty in a dynamical system due to the probabilistic uncertainty in the system parameters. By use of the PCE method we calculate the statistical properties of the output (reflection-transmission) of a slab-scattering system for uncertain parameters regarding tokamak plasma and blobs and in conjunction with the homogenization method to approximate the plasma-blob dielectric mixture.

References
A. Sihvola: Homogenization of a dielectric mixture with anisotropic spheres in anisotropic background , Lund University, 1996
T.G. Mackay, A. Lakhtakia : Modern Analytical Electromagnetic Homogenization , Morgan & Claypool Publishers, 2015
D. Xiu, G. E. Karniadakis : The Wiener-Askey polynomial chaos for stochastic differential equations , SIAM journal of scientific computing, 2002

(*) This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053 (except author A.K.R.). The views and opinions expressed herein do not necessarily reflect those of the European Commission. A.K.R. is supported by the US Department of Energy grant nos. DE-FG02-91ER-54109 and DE-FC0201ER54648.

Speaker: F. Bairaktaris (EPS 2019)

308 P2.1102 Control of sheared flow stabilized Z-pinch plasma properties with electrode geometry

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1102.pdf

The FuZE device produces a 0.3 cm radius by 50 cm long Z-pinch between the end of the inner electrode of a coaxial plasma gun and an end wall 50 cm away. The plasma column is stabilized for thousands of instability growth time by an embedded radially-sheared axial plasma flow, a method proposed in Shumlak and Hartman Phys. Rev. Lett. 1995 and demonstrated experimentally in other sheared flow-stabilized Z-pinch devices, ZaP and ZaPHD. The mechanisms that affect sheared flow are investigated. Sheared flow is generated upstream of the pinch in the coaxial accelerator and can be influenced by the downstream boundary conditions, composed of the anode end wall. Different nose cone geometries are tested and their effects on flow and pinch properties are analyzed. MACH2 MHD simulations show that abrupt transitions from the coaxial accelerator to the Z-pinch create less favorable sheared flow profiles while gradual transitions promote adiabatic compression and favorable shear. Different end wall geometries are also tested. The transparency is increased by changing the center hole design to a spoked design. It is found that the end wall influence on the upstream Z-pinch is minimal. The plasma is frozen in the magnetic field, preventing the increased end wall transparency from allowing plasma to escape the assembly region, which acts as a flux conserver. However, plasma can be transiently allowed to exhaust with increased ram pressure. The ram pressure can be increased by changing the input energy, controlled by the bank voltage, and changing the injected density, controlled by the gas valves. At low density and low energy, it is found that the upstream properties are minimally affected by the end wall geometries as stagnated, frozen in flux plasma create a virtual end wall. Increasing the plasma velocity and density can lead to a short-lived exhaust and a delay in the formation of the virtual end wall.

Speaker: E. L Claveau (EPS 2019)

309 P2.1103 Contribution of the Hall effect to radial electric field and spontaneous/intrinsic rotation in tokamak core plasmas

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1103.pdf

The Hall effect, defined as the separation of electric charges of opposite sign when they move in a magnetic field, is suggested to contribute substantially to the observed negative radial electric field E_r in the core plasma in tokamaks and, respectively, to the spontaneous/intrinsic rotation of plasma. A detailed study of the Hall effect in plasmas began with the study in [1] -- within the framework of two-fluid magnetohydrodynamics (2FMHD) -- of the effect of the frozenness of magnetic field mainly in the electron component of plasma. This effect is important for stationary plasma flows [2], and it plays a dominant role in plasma open switches, Z-pinches, plasma foci, and is widely studied in the literature [3]. In the 2F-MHD, the tokamak poloidal magnetic field compresses only the plasma electrons (the pinch by toroidal electric current), and this separation of electric charges produces E_r which, in turn, generates "spontaneous" plasma rotation in the crossed ExB fields. A simple way to evaluate the Hall effect contribution to the E_r value, using the independently measured space distributions of magnetic field, electron pressure and plasma rotation velocity, is suggested. Application of this procedure to experimental data from the TM-4 [4] and T-10 [5] tokamaks yields high negative values of Er in the core plasma (~ few hundreds of V/cm) which are in qualitative agreement with the measured values (~ 100 V/cm). The data from other tokamaks are considered as well. The results suggest that the contribution of other mechanisms (e.g., neoclassical kinetics) to E_r (and spontaneous/intrinsic plasma rotation) in tokamaks should be treated with account of a strong hydrodynamic effect of the Ampère force, described in the framework of the 2F-MHD.

References
[1]. A.I. Morozov and A.P. Shubin 1964 Sov. Phys. JETP 19, 484.
[2]. A.I. Morozov and L.S. Solov'ev, in Reviews of Plasma Physics, Ed. by M.A. Leontovich (Atomizdat,
Moscow, 1974; Consultants Bureau, New York, 1980), Vol. 8. [3]. A.S. Kingsep, K.V. Chukbar, and V.V. Yan'kov, in Reviews of Plasma Physics, Ed. by B.B.
Kadomtsev (…nergoizdat, Moscow, 1987; Consultants Bureau, New York, 1990), Vol. 16.
[4]. V.I. Bugarya, et al. 1985 Nucl. Fusion 25 1707.
[5]. A.V. Melnikov, et al. 2013 Nucl. Fusion 53 093019.

Speaker: M.G. Levashova (EPS 2019)

310 P2.1104 Pulse shape dependence of vapor shielding efficiency during transient loads

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1104.pdf

Erosion of wall materials during transient events is a large concern for ITER and future fusion devices with high external heat power. The extensive heat loads cause melting, vaporization, and ablation of wall materials. It is known that the vapor shielding can be an inherent protection mechanism for the wall erosion during the extensive heat loads. The generated vapor from surface strongly interacts with the incoming plasma loads and dissipates the plasma energy to elsewhere. The phenomenon has been studied by fluid-based models, but kinetic behaviors of the multi-component plasma during the transient event accompanied with the wall erosion was not analyzed. The authors develop a particle-in-cell (PIC) simulation code [1, 2], called PIXY, and applies it to simulation of the vapor shielding at fusion devices. During the vapor shielding, the number of surface-ejected particles is a strong function of the surface temperature and significantly spreads over a very wide range. Thus, in order to treat the sufficient numbers of numerical super-particles, a weighted particle model is applied. Using the weighted particle code, previous study [2] investigated wall erosion under a rectangular pulse shape with a fixed time duration. However, in the transient heat loads, it is known that the erosion is strongly dependent on the pulse shape [3]. Thus, pulse shape dependence of wall erosion including vapor shielding is studied using the weighted particle code. Three triangle pulse shapes with a fixed energy flux, peak heat flux, and pulse duration are examined. The results are compared with rectangle pulse shapes with the same energy flux but a different peak heat flux and time duration. Erosion amounts and vapor shielding efficiency are evaluated and compared between these pulse shapes.
[1] K. Ibano, S. Togo, T.L. Lang, Y. Ogawa, H.T. Lee, Y. Ueda, and T. Takizuka, Contrib. Plasma Phys. 56 (2016) 705
[2] K. Ibano Y. Kikuchi, A. Tanaka, S. Togo, Y. Ueda, and T. Takizuka, Nuclear Fusion, in press.
[3] J.H. Yu, G. De Temmerman, R.P. Doerner, R.A. Pitts and M.A. van den Berg, Nuclear Fusion, Nucl. Fusion 55 (2015) 093027

Speaker: K. Ibano (EPS 2019)

311 P2.1105 Introduction of kinetic effects to 1-D SOL/divertor plasma fluid simulation by collaborating with a particle model

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1105.pdf

Development of SOL/divertor simulation codes is important to understand physics of edge plasma which determines huge heat fluxes to plasma-facing components, i.e., the bottleneck of fusion device designs. Fluid modeling is mainly used for SOL/divertor plasma simulations. However, there are a number of discrepancies between simulated and experimental results [1]. One of the causes is the kinetic effect, which is not fully considered in the present fluid modeling. Thus, kinetic codes, e.g., PARASOL [2], XGC1 [3] etc., have been developed for the edge plasma studies.
Within less computational cost compared with general PIC method, we have been introducing the kinetic effects into a 2-D fluid simulation by an add-on particle model. In this particle model at first, plasma parameters obtained from a fluid simulation, such as SONIC [4], are converted into initial velocity distributions of individual weighted-particles for electrons and ions. Next, particle trajectories and collisions are calculated for a short timescale without solving self-consistent electric field. Finally we obtain plasma parameters such as heat flux and viscosity, in which kinetic effects are correctly included.
In the present study, we developed a hybrid method for the fluid and particle models in a 1-D scale to establish the fundament of this hybrid concept. We started with a 1-D fluid simulation ranging from stagnation point to a divertor plate. As mentioned above, a timeslice of the fluid-simulation result is converted into a particle-simulation initial condition, and short-timescale particle simulation is carried out.
In order to verify the add-on particle model, we examine the influence of kinetic effects on the SOL/divertor plasma for a wide range of collisionality. We extend the preliminary addon model to the hybrid model where the particle-simulation result is now feedbacked to the fluid simulation.
[1] A.V. Chankin et al., J. Nucl. Mater. 390-391 (2009) 319
[2] T. Takizuka, Plasma Phys. Control. Fusion 59 (2017) 034008
[3] C.S. Chang et al., Phys. Plasmas 15 (2008) 062510
[4] H. Kawashima et al., Plasma Phys. Control. Fusion 49 (2007) 77

Speaker: M. Obiki (EPS 2019)

312 P2.2001 Determination of 100 TW femtosecond laser contrast from measurements of specular reflectivity from solid target

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2001.pdf

Temporal contrast is a crucial parameter for high-power short-pulse laser facilities. At insufficient contrast, amplified spontaneous emission (ASE) prepulse - which is inherent to lasers based on chirped-pulse amplification scheme - can create plasma on surface of a solid target before arrival of the main pulse. This preplasma reduces coupling of the main laser pulse energy to dense target layers. Contrast influences laser-driven ion acceleration [1], Kα radiation source properties [2], higher order harmonics generation [3]. Precise determination of contrast is a challenging task. It requires measurements with dynamic range higher than 10^10 in time interval of ~10 ns with resolution of the order of the main pulse duration. A simple method for estimation of ASE prepulse energy was proposed in [4]. It is based on measuring brightness of specularly reflected from a solid target laser radiation on a scattering screen. Using this method, we investigated ASE contrast of 100 TW femtosecond laser facility before and after insertion of RG-850 saturable absorber into amplification chain. ASE intensity was also measured over delay times from -400 ps to 0 ps by a 3rd order crosscorrelator. Analysis of the images from scattering screen has shown that, in addition to ASE prepulse, contrast is affected by change of laser light absorption mechanisms at intensities 10^16...10^17 W/cm^2. This factor limits applicability of the method [4].
References
1. D.Neely et al., Appl. Phys. Lett. 89, 21502 (2006).
2. S. Fourmaux, J.C. Kieffer, Appl. Phys. B 122:162 (2016).
3. I.J. Kim et al., Journal of Opt. Soc. Of Korea 13, 15 (2009). 4. A.S. Pirozhkov et al., Appl. Phys. Lett. 94, 241102 (2009).

Speaker: K.V. Safronov (EPS 2019)

313 P2.2002 Thermal effects in a triplet and beam interaction in a plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2002.pdf

A lot of interesting results come from the triplet concept, where three waves with wavenumber and frequency match conditions interact with themselves, exchanging energy. For example, if the coupling factor is small in a way the frequency of the envelope of each wave is slower than the slowest frequency of the carriers, the dynamics is regular [1-3]. However, the dynamics of the triplet may be dramatically affected if a charged particle beam is introduced in the system. This case was previously studied for a cold beam [4]. The present work extends the results to a warm beam, considering a water bag initial distribution for the velocities. The focus is on the beginning of the system dynamics. Some features of the beam as the center of the distribution as well as the distribution width are of interest and their role is discussed.

References
[1] S. G. Thornhill, and D.ter Haar, Phys. Reports, 43, 43 (1978)
[2] P. M. Drysdale, and P. A. Robinson, Phys. Plasmas, 9, 4896 (2002)
[3] P. Iorra, S. Marini, E. Peter, R. Pakter, and F. B. Rizzato, Physica A, 436, 686 (2015)
[4] E. Peter, S. Marini, R. Pakter, and F. B. Rizzato, Phy. Plasmas 24, 102124 (2017)

Speaker: E.A. Peter (EPS 2019)

314 P2.2003 Collective absorption of laser radiation in plasma at sub-relativistic intensities

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2003.pdf

Processes of laser energy absorption and electron heating in a hot plasma in the range of irradiances s Iλ^2 = 10^15 – 10^16 W µm^2/cm^2 are of prime importance for the shock ignition scheme of inertial confinement fusion. We studied these processes with large scale kinetic simulations [1, 2] and identified particular zones of plasma where laser absorption takes place and hot electrons are produced. Strong laser reflection due to the process of stimulated Brillouin scattering (SBS) and significant collisionless absorption related to the process of stimulated Raman scattering (SRS) near and below the quarter critical density have been observed and analyzed. They are induced by strong laser beam self-focusing and modulational instabilities. These processes are complemented with the parametric decay instability and resonant excitation of plasma waves near the critical density. All these processes result in excitation of high amplitude electron plasma waves and electron acceleration. The spectrum of scattered radiation is significantly modified by the secondary parametric decay instability, which provides information on the spatial localization of nonlinear absorption and hot electron characteristics.
The considered domain of laser and plasma parameters has been studied in a series of experimental campaigns carried out on the PALS facility in Prague [3] at the first and third harmonics of the iodine laser. A comparison with experimental results will be discussed.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. This work was supported by the projects HiFI (CZ.02.1.01/0.0/0.0/15_003/0000449), CAAS (CZ.02.1.01/0.0/0.0/16_019/0000778), ADONIS (CZ.02.1.01/0.0/0.0/16_019/0000789) and ELITAS (CZ.02.1.01/0.0/0.0/16_013/0001793) from the European Regional Development Fund.
References
[1] Y.J. Gu et al., HPLSE submitted (2019).
[2] V.T. Tikhonchuk et al., MRE submitted (2019).
[3] D. Batani et al., Nuclear Fusion 59, 032012 (2019).

Speaker: V.T. Tikhonchuk (EPS 2019)

315 P2.2005 Novel criteria for efficient Raman or Brillouin amplification of laser beams in plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2005.pdf

Twenty years have passed since the seminal paper on Raman amplification in plasma by Malkin, Shvets and Fisch [1]. While Raman amplification has been explored very successfully in theory and simulations [2], no significant Raman amplification of a laser pulse beyond 0.1 TW or 6% efficiency has been achieved [3], and there exists only one tentative report of Brillouin amplification beyond 1 TW [4]. In this paper, we investigate one aspect of Raman amplification that has been consistently overlooked until now: the parameters and quality of the initial seed pulse. We have developed new criteria for the initial seed pulse in Raman and Brillouin amplification, and show through analytic theory and numerical simulations, that the energy gain and efficiency of the amplification will be significant if and only if these criteria are met. We will analyze the plasma-based Raman amplification experiments carried out to date, and show that the input seed pulses in these experiments all fall short of our criteria, which is the likely explanation for the poor efficiency obtained in them. Finally, we apply our findings to the results of the most promising Raman and Brillouin amplification experiments available [3, 4] to test how well those conform to our model.

References
[1] V.M. Malkin, G. Shvets and N.J. Fisch, Phys. Rev. Lett. 82, 4448 (1999).
[2] R. M. G. M. Trines et al., Nature Physics 7, 87 (2011).
[3] J. Ren et al., Nature Physics 3, 732 (2007).
[4] J.-R. Marquès et al., arXiv:1812.09229 (2018).

Speaker: R. Trines (EPS 2019)

316 P2.2006 Evaluation of bubble detectors for characterising laser-driven neutrons

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2006.pdf

Laser-driven neutron sources have recently attracted significant attention due to their potential uses in science, industry, healthcare, and security. In laser-matter interaction experiments, neutrons can be efficiently produced by nuclear reactions involving the laser-driven light ions [1]. Characterisation of these sources is important for their further development, as well as to investigate the properties of their parent ions. Neutrons from a laser driven source are typically characterised using diagnostics such as bubble detectors, nuclear activation and ToF detectors [2,3]. The fast (MeV) neutrons produced by the source are scattered by every object in the target area, bouncing around for a long time until they are sufficiently slowed down. Characterisation of the neutron source therefore poses a significant challenge, especially for the time-integrated dosimeters. The performance of bubble detector dosimeters was therefore studied in a recent experiment at the Vulcan petawatt laser of the CLF, STFC, UK, by deploying the dosimeter simultaneously with bubble detector spectrometers and ToF scintillator detectors. The results from a large number of shots were compared to evaluate the performance of the dosimeters; the experimental and simulation results to this end will be presented.

[1] S. Kar et al, 2016, Beamed neutron emission driven by laser accelerated light ions, New Journal of Physics
[2] D. Jung et al, 2013, Characterization of a novel, short pulse laser-driven neutron source, Physics of Plasmas
[3] S. R. Mirfayzi et al, 2015, Calibration of time of flight detectors using laser-driven neutron source, Review of Scientific Instruments

Speaker: B. Greenwood (EPS 2019)

317 P2.2007 All-optical staged acceleration of proton beams using helical coils

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2007.pdf

All-optical approaches to ion acceleration are attracting a significant research effort internationally. Energetic ion beams can be readily generated by high intensity lasers via the target normal sheath acceleration (TNSA) process [1]. While the ion energies of such beams remain constrained by available laser intensities and limitations related to target fabrication, methods of post-accelerating the TNSA ions have lately gained significant interest. In 2016, a concept channelling the extremely high electromagnetic pulse emanating from a laser irradiated target along a miniature helical coil was demonstrated capable of post-accelerating TNSA ions from the same initial laser interaction [2]. Furthermore, synchronous propagation of the electromagnetic pulse and the protons within the helical coil reduces beam divergence during acceleration providing a collimated, narrow energy band of protons suitable for applications. Recent experiments have demonstrated pencil beams up to 50 MeV by deploying helical coil targets at petawatt-class lasers [3]. In a proof-of-principle experiment, we are currently investigating the possibility of staging helical coil modules at the Vulcan Laser of the Central Laser Facility located in the United Kingdom. The experiment employs a dual beam laser configuration and a two-stage target geometry, where each beam interacts with a separate helix target. This arrangement allows the second helix's effect on the proton beam, produced by the first helix, to be studied through varying the time delay between the two laser beams. Results from this experiment will be presented with supporting particle tracing simulations.

[1] M. Borghesi, 2014, Laser-driven ion acceleration: State of the art and emerging mechanisms, Nuclear Instruments and Methods in Physics Research A
[2] S. Kar et al, 2016, Guided post-acceleration of laser-driven ions by a miniature modular structure, Nature Communications
[3] H. Hamad, S. Kar et al, to be submitted 2019, Quasi-monoenergetic pencil beam up to 50 MeV employing laser-driven helical coil

Speaker: S. Ferguson (EPS 2019)

318 P2.2008 Density enhancement of microprojectiles and plasma streams produced at laser acceleration experiments

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2008.pdf

Investigations using the so-called Cavity Pressure Acceleration (CPA) method were carried out on the Prague Asterix Laser System (PALS). The main goal of this research was to test and analyze a possibility of increasing density of plasma objects accelerated by laser light in channel cavity targets. The microprojectiles/plasma streams leaving the open channel rapidly lose density expanding in the hemisphere. In the case of a covered channel, the expansion is much slower. A thin foil covering the target causes local compression of the bursting plasma. A significant part of the energy of expanding plasma is transferred to the thin covering foil (with a solid density) which means higher density and higher energy density of the accelerated plasma object. Experimental measurements were made for cavity targets with 12 micron and 6 micron polystyrene foils. The foils covering the target channel were 1 or 2 micron thick. Iodine laser ( lambda= 1.315 micron) energy was several hundred (up to 600) joules. In addition, numerical calculations were also performed, using a hydrodynamic code that takes into account significant physical processes influencing the acceleration process in order to check and compare experimental results. The main conclusion is that the proposed method allows an evident increase of density of the accelerated plasma objects (up to one-two orders) without significant drop in velocity.

Speaker: S. Borodziuk (EPS 2019)

319 P2.2009 Self-modulated laser wakefield acceleration driven by CO2 laser in hydrogen plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2009.pdf

Developments in CO_2 laser technology at BNL Accelerator Test Facility (ATF) has opened the possibility of exploring CO_2 laser driven wakes, a regime capable of producing large accelerating structures, enabling better probing of wakes and precise external injection. 3D numerical simulations motivated by laser wakefield accelerator experiment AE71 being conducted at the BNL ATF are presented. Parallel relativistic Particle-in-Cell code SPACE has been used in these studies. SPACE implements novel atomic physics algorithms to resolve ionization, recombination and other atomic physics transformations on the grid and transfer them to particles [1, 2, 3]. Simulations investigate the interaction of a powerful CO_2 laser with hydrogen jets and the characteristics of induced wakes in the self-modulated regime at previously inaccessible densities (∼10^17 – 10^18cm-3). Simulations show that the front portion of the long (∼ ps) CO_2 laser undergoes self-modulation instability and the rear portion self-channels when the ionization model with mobile ions is used. Growth rate of self-modulation instability has been characterized for several gas number densities. Effects of variation in laser energy and focus position on the intensity of Stokes and anti-Stokes waves have been studied and compared with experimental results. Simulations show that the highest intensity sideband signals are observed when the laser is focused close to the beginning of the jet. Multi-mode laser beams have been utilized to mimic the experimental laser imperfections and comparisons with perfectly Gaussian beams have been presented. In addition, self-injection and trapping of electrons into the self-modulated wakes has been observed and analyzed. Simulations have shown accelerated electron bunches with total charge on pC-scale having multi-MeV peak energies.
References
[1] K. Yu, R. Samulyak, K. Yonehara, and B. Freemire, Physical Review Accelerators and Beams 20, 32002 (2017).
[2] P. Kumar, K. Yu, and R. Samulyak, Journal of Physics: Conference Series 1067, 42008 (2018).
[3] P. Kumar, K. Yu, R. Zgadzaj, R. Samulyak, L. Amorim, M. Downer, V. Litvinenko, N. Vafaei-Najafabadi,
and J. Welch, Physics of Plasmas, submitted (2019).

Speaker: P. Kumar (EPS 2019)

320 P2.2010 Shaping laser-wakefield beams through magnetic controlled particle injection

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2010.pdf

Plasma based acceleration (PBA) is seen as a promising candidate for future accelerators. While magnetic fields are commonly used in conventional accelerators, our previous work [1] has shown that magnetic fields can be used for controlling injection in PBA scenarios. On this paper we extend this work by using the recent 3D extension of the ponderomotive guiding center (PGC) solver [2] in OSIRIS [3] to examine the contribution of different shaped magnetic profiles on the injected electron beams in laser-wakefield acceleration (LWFA) scenarios through parametric studies. In particular, we analyze scenarios involving magnetic quadrupoles, that can only be accurately modelled through three-dimensional simulations. The use of the PGC algorithm allows for speedups on the order of ∼ (λ_p/ λ_0)^2 when compared to a full PIC algorithm, allowing for a much wider parametric scan. We will present the effects on the injected charge, final beam energy and emittance. We will also discuss the possibility of multi-beam injection and experimental realization of these scenarios.
References
[1] J. Vieira et al., Phys. Rev. Lett., vol. 106(22), 225001­4 (2011)
[2] A. Helm et al., to be submitted J. Comput. Phys.
[3] R.A. Fonseca et al., Lect. Notes Comp. Sci., 2331, 343 (2002)

Speaker: A. Helm (EPS 2019)

321 P2.2011 Uphill acceleration in a spatially modulated electrostatic field particle accelerator

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2011.pdf

Spatially modulated electrostatic fields can be designed to efficiently accelerate particles by exploring the relations between the amplitude, the phase velocity, the shape of the potential and the initial velocity of the particle. The acceleration process occurs when the value of the velocity excursions of the particle surpass the phase velocity of the carrier, as a resonant mechanism. The ponderomotive approximation based on the Lagrangian average is usually applied in this kind of system. The mean dynamics of the particle is well described by this approximation far from resonance. However, the approximation fails to predict some interesting features of the model near resonance, such as the uphill acceleration phenomenon. A canonical perturbation theory is more accurate in these conditions and may be applied in different systems. We compare the results from the Lagrangian average and from a canonical perturbation theory, focusing in regions where these two approaches differ from each other.

References
[1] Alamnsa, I. ; Burton, D. A. ; Cairns, R. A. ; Marini, S. ; Peter, E. ; Rizzato, F. B. ; Russman, F. B. . Uphill acceleration in a spatially modulated electrostatic field particle accelerator. Physics of Plasmas, v. 25, p. 113107, 2018.
[2] D. Bauer, P. Mulser and W.-H. Steeb, Phys. Rev. Lett. 75, 4622 (1995).

Speaker: F.B. Russman (EPS 2019)

322 P2.2012 Analytical and numerical approaches of bubble wakefield acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2012.pdf

The particle accelerators are the most promising and useful devices for mankind. Plasma based accelerators are fascinating as there is no problem of electrical breakdown and these can generate large accelerating fields [1 ­ 2]. Laser wakefield acceleration is one of the techniques that employs plasma and high intensity laser pulses. Here plasma electrons are expelled by the short intense laser pulse and an electron wave is excited in the plasma which acquires high electric field. This field is used for the particle acceleration. When the laser intensity exceeds some limit, plasma electrons can be expelled by the ponderomotive force of the laser pulse in such a manner that the electrons free region can be created, which is called ions cavity and the situation corresponds to bubble regime [3]. On the other hand, the electrons in plasma wakefield acceleration are expelled by space charge force, creating a blow out or ions cavity in underdense plasma.
In the present work, we focused on the laser generated bubble in underdense plasma. For this, we used different Gauge conditions and obtained wakefield potential for controlling the bubble shape for electrons acceleration with the help of d'Alembert differential equations in electromagnetic field. We also carried out analytical calculations for finding the different shapes of the bubble, enabling us to realize longitudinal and ellipsoid bubbles instead of spherical bubble regime on which people have generally worked on. In addition, we considered the presence of residual electrons in the bubble regime and found that the shape of the bubble can be controlled by the bubble velocity. We also found electric and magnetic fields for different gauge conditions. We use a numerical method to find the trajectory of trapped background plasma electrons in bubble regime [4].

References
1 H.K. Malik, J. Appl. Phys. 104 (2008) 053308.
2 T. Tajima and J.M. Dawson, Phys. Rev. Lett. 43 (1979) 267.
3 X.F. Li, Q. Yu, Y.J. Gur, S. Huang, Q. Kong and S. Kawata, Phys. Plasmas 22 (2015) 0831112.
4 D. Lu, X. Y. Zhao, B. S. Xie, M. Ali Bake, H. B. Sang, & H. C. Wu, Phys. Plasmas 20 (2013) 063104.

Speaker: S. Kumar (EPS 2019)

323 P2.2013 Plasma bubble evolution related electron beam parameter estimation in laser wakefield acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2013.pdf

Laser-wakefield acceleration offers a compact electron acceleration scheme for generating a multi-GeV electron beam, utilizing the high longitudinal electric field gradient induced by high intensity, ultrashort laser pulse. The bubble regime of the laser wakefield acceleration is one of the most recent and promising mechanism for generating quasimonoenergetic electron beams^1,2. In this work, we propose simulation based studies for plasma bubble evolution and corresponding electron beam quality parameters. The major focus of this work is to find out the dependency of the electron beam energy and quality on the shape of the bubble. The evolution of bubble with time, and correlation of bubble length (longitudinal and transverse radius) with the intensity of laser pulse has been revealed in this study. The results show that the bubble longitudinal length grows until the dephasing length but with different rate because of various determining factors (laser pulse focusing, beam loading, residual electrons, bubble velocity etc.). It has also been confirmed that the shape of the bubble cannot be predicted using fixed shape models as spherical or elliptical. Moreover, the simulation based findings predict that as the bubble traverses in plasmas, it evolves from spherical shape to the highly elliptical shape. And, as it approaches the dephasing length the eccentricity decreases further. A comparison of the electron beam parameters for different laser intensity has also been provided for future accelerator development.
1 S. Kalmykov, S. A. Yi, V. Khudik, and G. Shvets, Phys. Rev. Lett. 103, 135004 (2009).
2 B. S. Xie, H. C. Wu, H. Wang, N. Y. Yang, and M. Y. Yu, Phys. Plasmas 14 (2007) 073103.

Speaker: M. Yadav (EPS 2019)

324 P2.2014 Ponderomotive and resonant effects in the acceleration of particles by electromagnetic modes

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2014.pdf

In the present analysis we study the dynamics of charged particles under the action of slowly modulated electromagnetic carrier waves. With the use of a high-frequency laser mode along with a modulated static magnetic wiggler, we show that the ensuing total field effectively acts as a slowly modulated high-frequency beat-wave field typical of inverse free-electron laser schemes. This effective resulting field is capable of accelerating particles in much the same way as space-charge wake fields do in plasma accelerators, with the advantage of being more stable than plasma related methods. Acceleration occurs as particles transition from ponderomotive to resonant regimes, so we develop the ponderomotive formalism needed to examine this problem. The ponderomotive formalism includes terms that, although not discussed in the usual applications of the approximation, are nevertheless of crucial importance in the vicinity of resonant capture. The role of these terms is also briefly discussed in the context of generic laser-plasma interactions.
References
[1] I. Almansa, F.B. Russman, S. Marini, E. Peter, G.I. de Oliveira, R. A. Cairns, F.B. Rizzato. Ponderomotive and resonant effects in the acceleration of particles by electromagnetic modes. Physics of Plasmas, Accepted for Publication, 2019.
[2] S. Marini, E. A. Peter, G. I. de Oliveira, and F. B. Rizzato, Phys. Plasmas 24, 093113 (2017)

Speaker: I.D. Almansa (EPS 2019)

325 P2.2015 Radiation reaction in the acceleration of particles by slowly modulated high-frequency large amplitude electrostatic waves

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2015.pdf

In the present analysis we incorporate radiation effects to the study of the relativistic dynamics of charged particles submitted to the action of slowly modulated, high-frequency electrostatic waves with large amplitudes. Previous analyses ignoring radiation reaction indicate that this setting may be very efficient in terms of particle acceleration [1, 2]. As lower velocity particles are injected in low field end of the modulated pulse, uphill ponderomotive forces pull particles to higher velocities until they are trapped by the high-frequency carrier with subsequent extreme resonant acceleration.
The first acceleration stage provided by the ponderomotive effects is relatively smooth, but we have observed that the trapping and subsequent intense resonant acceleration is significantly affected by radiation reaction effects. Under circumstances where trapped particles extract energy from the slowly modulated wave in an adiabatic fashion, radiation reaction becomes critical in determining how long the process lasts until particles are ejected from the wave troughs.
We make use of the well known formalism of Landau and Lifschitz [3] to estimate radiative losses. Results reveal good agreement with modern accounts on the subject [4]. The equivalent process driven by lasers shall be briefly discussed as well.
References
[1] S. Marini, E. Peter, G. I. Oliveira, and F. B. Rizzato, Physics of Plasmas 24, 093113 (2017).
[2] I. Almansa, D. A. Burton, R. A. Cairns, S. Marini, E. Peter, F.B. Rizzato, and F. Russman, Physics of Plasmas
25, 113107 (2018).
[3] L. Landau and E. Lifchitz Théorie du Champ, Mir, Moscow (1966). [4] M. Tamburini, Radiation Reaction Effects in Super Intense Laser-Plasma Interaction, Ph. D Thesis, University of Pisa (2011).

Speaker: F.B. Rizzato (EPS 2019)

326 P2.2016 High-energy photon generation in ultrarelativistic laser-plasma interactions

See the full abstract here.
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2016.pdf

Forthcoming multi-petawatt laser systems (e.g., CoReLS, Apollon, ELI, CAEP-PW) will soon make it possible to achieve laser intensities in excess of 10^22-10^23 Wcm^2. Laser-matter interactions under such extreme conditions will give rise to copious synchrotron or Bremsstrahlung emission of γ-ray photons, which may subsequently convert into electron-positron pairs, through the Breit-Wheeler or Bethe-Heitler processes [1]. These phenomena may strongly alter the mechanisms that are known to rule the laser-plasma interaction at lower laser intensities.
A self-consistent modeling of the future experiments requires the widely used particle-incell (PIC) codes to include the aforementioned high-energy processes. Such is the case for the code CALDER developed at CEA/DAM, which now describes all relevant radiation and pair production processes [2, 3]. Using this simulation tool, we present a number of recent results on high-energy radiation by 10^22 Wcm^-2 laser pulses, likely available during the first years of operation of the aforementioned facilities.
First, we review the properties of synchrotron emission in laser-driven plasmas of varying density, complementing previous work on this topic [5]. We then address the potential of nanowire-array targets for enhancing synchrotron emission. We examine the dependencies of the photon spectra on the target parameters, and compare the performance of nanowire targets with that of uniform plasmas. Finally, we study the competition between Bremsstrahlung and synchrotron emission in copper foils.
References
[1] A. Di Piazza, C. Müller, K. Z. Hatsagortsyan, and C. H. Keitel, Rev. Mod. Phys. 84, (2012)
[2] M. Lobet et al., Phys. Rev. Lett. 115, 215003 (2015); Phys. Rev. Accel. Beams 20, 043401 (2017)
[3] B. Martinez, M. Lobet, E. d'Humières, and L. Gremillet, High-Energy Radiation and Pair Production by
Coulomb Processes in Particle-In-Cell Simulations , to be submitted (2019)
[4] B. Martinez, E. d'Humières, and L. Gremillet, Plasma Phys. Control. Fusion 60, 074009 (2018) [5] C. P. Ridgers et al., Phys. Rev. Lett. 108, 165006 (2012); C. S. Brady, C. P. Ridgers, T. D. Arber, and A. R. and Bell, Phys. Plasmas 21, 033108 (2014)

Speaker: L. Gremillet (EPS 2019)

327 P2.2017 Radiation emission from twisted plasma acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2017.pdf

The recent experimental and theoretical progresses have shown that plasma accelerators are very promising because they may provide a new generation of more compact particle accelerators and light sources for various technological and scientific applications. Plasma accelerators often use intense laser beams or particle beam drivers to excite relativistic plasma wakefields, which can trap and accelerated particles to high energies. As a result of the rich wakefield structure in the plasma, these particles also execute transverse betatron oscillations that lead to intrinsically ultra-fast bursts of X-ray radiation as they accelerate. Here, using theory, and three-dimensional particle-in-cell simulations using Osiris [1] and the new Radiation Diagnostic for Osiris (RaDiO) [2] together with jRad [3], we investigate betatron radiation emission when the plasma wave has orbital angular momentum [4]. These high amplitude twisted plasma waves can be driven by intense light spring lasers that contain a helical intensity profile [5]. Radiation emission depends on the trajectories followed by the accelerated particles. To compute these trajectories, we first derived the trapping conditions in a twisted plasma wave. By investigating the constants of the motion, we find that trapped particles execute radial betatron oscillations in conjunction with helical trajectories around the wakefield, which can be the dominant one motion in typical conditions. We show that these trajectories can efficiently produce X-ray beams, which contain a strong circular polarization level. In addition to the spin angular momentum, we also compute the optical chirality of the ensuing radiation and its orbital angular momentum contents distribution.

References
[1] R.A. Fonseca et al., Plasma Phys. Control. Fusion, 55 124011 (2013).
[2] M. Pardal et al, to be submitted (2019).
[3] J. Martins et al, Proc. SPIE 7359 73590V (2009).
[4] G. Pariente, F. Quéré, Optics Lett. 40, 2037-2040 (2015). [5] J. Vieira, J.T. Mendonça, Phys. Rev. Lett. 112 215001 (2014).

Speaker: J. Vieira (EPS 2019)

328 P2.2018 RaDiO-Radiation Diagnostic for Osiris: an efficient radiation processing tool for particle-in-cell simulations

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2018.pdf

Radiation processes in plasmas are extremely relevant for a number of fields, ranging from astrophysics [1] to small scale microscopy [2]. These processes are usually associated with the motion of a large number of electrons, under the action of intense electric and magnetic self-consistent fields and require numerical descriptions in order to be explored. Particle-In-Cell (PIC) codes like OSIRIS [3] are able to accurately describe the motion of the individual particles but they cannot be employed to capture radiation emission at wavelengths much smaller than the grid size because of the large computational requirements. To circumvent this issue, here, we present RaDiO [4], which is fully integrated into Osiris and is capable of capturing the spatiotemporal properties of the radiation emitted by tens of millions of charged particles. RaDiO has built-in spatial and temporal coherence and uses a sophisticated radiation deposition algorithm that allows for radiation to be deposited in a grid with much higher resolution than the PIC simulation grid. This tool recovers the theoretical spectra for well-known scenarios of radiation emission, and has been thoroughly tested and benchmarked for typical trajectories associated with undulator radiation in the undulator and wiggler regimes, as shown in Figure 1. In this work, we use RaDiO to explore the properties of radiation emission in unexplored scenarios such as new regimes of High Harmonic Generation (HHG). We show that our algorithm strongly reduces the computational requirements associated with HHG simulations in three-dimensions, allowing to describe HHG to very high harmonic orders in 3D.

References
[1] F. Tamburini, et al., Nature Physics 7, 195-197 (2011)
[2] S. Hell et al., Optics Letters 11, 780-782, (1994)
[3] R. Fonseca et al., LNCS 2331, (2002)
[4] M. Pardal et al., to be submitted (2019)

Speaker: M. Pardal (EPS 2019)

329 P2.2019 Laser pulse propagation in a collisional plasma in weakly-relativistic regime

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2019.pdf

We investigate the propagation of laser pulse in plasmas to estimate the pulse compression based on collisional absorption under weak-relativistic ponderomotive nonlinearity. The physical mechanism behind it is analyzed theoretically. Absorption of laser energy in plasma has been a curial issue, which has been, attracting continued interest ever since the invention of lasers. In the range of laser intensity around 10^15 W/cm^2, the laser absorption can be dominated by inverse bremsstrahlung or collisional absorption during the laser≠solid interaction, where the laser pulse compression is very important in determining the particle energy during acceleration. We have analyzed the longitudinal pulse compression in 1D geometry, assuming a uniform transverse distribution of the irradiance profile. An equation for the dimensionless pulse compression parameter has been derived and the effects of absorption on laser pulse compression have been studied. The laser pulse compression is reduced due to the collisional absorption in plasmas. Fast pulse dispersion is also observed due to pulse absorption, which is obviously associated with the strong energy attenuation in plasmas in this regime. A picosecond pump pulse compression is reduced to about 25% due to the collisional absorption. For large absorption coefficient, the nonlinearity associated with the laser absorption in plasmas is affected severely and the pulse compression is reduced. The present work is motivated by the need to gain understanding of laser pulse propagation in a collisional plasma and its implications on particle acceleration by high-intensity laser irradiation of targets. The results, in particular the compression of the laser pulse, have taken a further step towards a broad application of laser-plasma interaction in a large variety of fields such as accelerator physics and electromagnetic radiation generation.

References:
[1] M. Singh and D. N. Gupta, Phys. Plasmas, 23, p 053119, (2016)
[2] M. S. Sodha, A. K. Ghatak and V. K. Tripathi, Prog. Opt., 13, p 168, (1976)

Speaker: M. Singh (EPS 2019)

330 P2.2020 Efficient electromagnetic emission from plasma with continuously injected counterstreaming electron beams

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2020.pdf
Plasma with an electron beam is considered as a source of powerful electromagnetic (EM) emission in various space and laboratory environments. It is well known that in presence of two counterstreaming beams radiation efficiency significantly grows in contrast to the single beam case. This is explained by the fact that the most intense counterpropagating beam-driven Lang- muir waves in such a system can directly participate in three-wave interactions with EM waves. In the case of a single beam, such emission becomes possible only due to some intermediate nonlinear processes producing backward propagating Langmuir waves.
We have shown [1] that it is possible to find the regime in which the most unstable beam- driven modes with the growth-rate (k , k) lies inside in the region of three-wave interaction: -------------------------
This has been achieved through a new algorithm, which allow to calculate the dielectric tensor in the framework of the relativistic kinetic theory that allows one to consider arbitrary axially symmetric beam and plasma distribution functions in arbitrary magnetic field.
Predictions of the linear theory has been verified by electromagnetic particle-in-cell simulations in the model of infinite plasma[1]. But in this widely used model, beams have a finite amount of energy and only a discrete spectrum of EM waves is possible. In the real problem of continuous injection of a fresh electron beam through a plasma boundary, the nonlinear stage of beam-plasma interaction differs substantially. In particular, in the regime found in [1], beam currents are not compensated by plasma electrons and beams are significantly compressed near the collision point.
In this work we investigate the possibility to find appropriate beam-plasma regimes for EM emission through three-wave process, which will holds for a realistic model[?] with open boundary conditions and continuously injected electron beams.
This work is supported by the RFBR grant 18-32-00107.

References
[1] Timofeev, I. V. & Annenkov, V. V. Phys. Plasmas 21, 083109 (2014).

Speaker: E.P. Volchok (EPS 2019)

331 P2.2021 Cylindrical fast electron beam in a plasma density gradient

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2021.pdf

A theoretical study of a uniform fast electron beam propagating in a plasma density gradient targets (low density core-high density cladding) is presented. The self-generated magnetic field is calculated using a rigid beam model in cylindrical geometry. It is found that the spontaneous magnetic field peaks at the interface and evanesces exponentially into the outer target over a characteristic skin depth. This method is used for reducing the transverse angular distribution of a fast electron beam (control of the divergence of fast electron beams). The numerical simulations showed that a low density core-high density cladding structure target in Cartesian geometry can also generate a mega gauss interface magnetic field, which collimates fast electrons [1-3].

[1] C. T. Zhou et al., Phys. Plasmas 17, 083103 (2010)
[2] S. Z. Wu, C. T. Zhou, and S. P. Zhu, Phys. Plasmas 17, 063103(2010).
[3] H. Cai, S. Zhu, M. Chen, S. Wu, X. T. He, and K. Mima, Phys. Rev. E 83, 036408 (2011).

Speaker: M. Niroozad (EPS 2019)

332 P2.2022 Ignition requirement for HBRPA C6+ beam driven fast ignition

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2022.pdf
In fast ignition, an ultra-intense pico-second laser is irradiated to heat a pre-compressed fusion fuel up to the ignition temperature. When the laser-accelerated electron beam is used for core heating, the large beam divergence, the broad energy spectrum and the difficulty in generating fast electrons having suitable energy to the core heating inhibit the efficient core heating. One of the alternative core heating schemes is use of ion beam generated by the hole boring radiation pressure acceleration (HBRPA). The 1D theoretical and numerical predictions [1,2] showed that it is possible to accelerate ions to the energy suitable for the core heating with the small energy spread and the small angular divergence. However, the 2D PIC simulations [2,3] showed the broader energy spectrum, the larger angular divergence and the lower conversion than those obtained in the 1D predictions. In addition, there are no ignition requirement evaluations based on the integrated simulation including the ion acceleration, the core heating and the fusion burning. In the present study, we have evaluated the ignition requirement for HBRA-Carbonbeam-driven fast ignition by the integrated simulations where the ion beam properties were evaluated with 2D PIC simulations using picls2d [4] and the following core heating and fusion burn processes were simulated by a 2D hybrid code FIBMET [5]. In the conference, we will show the detailed dynamics of ion and also electron accelerations, core heating and fusion ignition, and the heating laser condition required for fusion ignition.

References
[1] A. Macchi et al, Phys. Rev. Lett. 94, 165003 (2005).
[2] N. Naumova et al., Phys. Rev. Lett. 102, 025002 (2009). [3] O. Klimo, et al., Phys. Rev. ST Accel. Beams 11, 031301 (2008).
[4] Y. Sentoku and A. Kemp, Comput. Phys. 227, 6846 (2008).
[5] T. Johzaki, et al., Proc. of IFSA 2003, ANS, 474 (2004).

Speaker: T. Johzaki (EPS 2019)

333 P2.2023 Resonantly accelerated electrons from a tightly focused laser beam

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2023.pdf
One of the most promising techniques to enhance focused laser intensities is to tightly focus the beam using an ellipsoidal plasma mirror. It has been successfully employed to obtain subµm spot size [1] resulting in an order of magnitude increase in focused intensity in comparison with a typical spot size of about 4 µm obtained with f/3 off axis parabolic mirror. The tightly focused laser beam has some important properties, which modify the laser target interaction
process. First of all, it is associated with a large curvature of the wavefront of the laser beam out of focus, which has an influence on the propagation angle of accelerated particles. Secondly, the field is not purely transverse but it also includes non-negligible longitudinal field components. In particular the longitudinal electric field is very important as its amplitude is ' 0.14λ0/w0 of the transverse field at the periphery of the focal spot, where λ0 is the laser wavelength and w0 the Gaussian beam waist.
The electron acceleration process under tight focusing is studied using PIC simulations with the code EPOCH [2]. The electrons are first pulled from the target surface by the longitudinal component of the laser electric field. In the next phase, the electrons are accelerated by the transverse laser electric field component. Depending on their distance from the target surface, they are accelerated either towards the centre of the focal spot (electrons close to the target surface) or in the opposite direction as the transverse component of the laser electric field has a different phase in these two regions. Finally, the vxB Lorentz force accelerates these electrons into the target or into the vacuum away from the target and they propagate further ballistically. As the longitudinal field has an opposite phase on both sides of the focal spot, the bunches originating from this process are phase shifted by half a laser period and they propagate in different directions because of the wavefront curvature. This opens the possibility to diagnose the absorption process with coherent transition radiation (CTR) at the rear side of the target, where the bunches arrive at a rate given by the laser frequency (0) in contrast with the simple vxB heating process where the rate is given by 20.
This work is supported by Czech Science Foundation project 18-09560S and European Regional Development Fund Project "CAAS" (No. CZ.02.1.01/0.0/0.0/16_019/0000778).

References
[1] M. Nakatsutsumi, A. Kon, S. Buffechoux et al., Opt. Lett. 35, 2314-2316 (2010)
[2] T. D. Arber, K. Bennett, C. S. Brady et al., Plasma Phys. Control. Fusion 57, 1-26 (2015)

Speaker: O. Klimo (EPS 2019)

334 P2.2024 Effects of laser focusing on plasma channeling by ultrahigh intense laser in fast ignition

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2024.pdf

A target is imploded by long-pulse implosion lasers and its compressed core is heated by fast electrons, which are generated by a short-pulse ultrahigh-intense laser, in the fast ignition scheme. As the location where fast electrons are generated is far from the core due to ablation plasmas, few of them can hit the core. Therefore, a cone-guided target, which can shorten such distance, is used in FIREX experiments at ILE, Osaka University. On the other hand, it is reported that the ultrahigh-intense laser can penetrate into long-overdense plasma region due to relativistic transparency and self-focusing in many laser plasma experiments [1]. This so-called `super-penetration' approach can open the possibility of direct irradiation fast ignition, which has significant advantages from the viewpoint of the reactor engineering.
The plasma channeling is one of key issues for the super-penetration approach, but it is well-known that the laser hosing instability, which disturbs stable laser propagation, occurs under such conditions. Thus characteristics of the laser propagation and plasma channeling in long plastic (CH) coronal plasmas and effects of laser focusing on plasma channeling are investigated by 2D PIC simulations. When the heating laser is tightly focused by small F-number optical system, the waist size becomes small and the peak laser intensity increases, resulting in formation of a sharp plasma channel. The magnetic field pressure is high enough to sustain the channel and stabilize the hosing instability. So efficient propagation of the ultrahigh-intense laser can be expected, and the direct irradiation scheme should be still investigated as the alternative way to cone-guided scheme in fast ignition.
This work is partially supported by JSPS KAKENHI Grant number JP15H05751, and is performed with the support and under the auspices of the NIFS Collaboration Research program (NIFS17KUGK110).

References
[1] H. Habara, et al., Plasma Phys. Contr. Fusion, 57, 064005 (2015).

Speaker: H. Sakagami (EPS 2019)

335 P2.2025 Enhanced electron heating in picosecond relativistic laser-plasma interaction

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2025.pdf

High power lasers with relativistic intensities above 1018 W/cm2 and pulse lengths exceeding picosecond (ps) have been developed in recent years. In over-ps laser-plasma interactions, energy slope of high-energy electrons tends to be higher than the scaling laws used in the sub-ps regime. One of the key mechanisms of such a superthermal electron generation is stochastic heating in a laser-irradiated thin foil, where fast electrons recirculate around and suffer multiple kicks from the laser field during the pulse duration [1]. The blowout of hot plasma towards the laser, which takes place under the ps laser heating [2], also enhances the multiple interactions of fast electrons with laser light. Understanding characteristics of the energy distribution resulted from the new accelerations arise in ps relativistic regime is essential for various applications for intense lasers, such as laser ion acceleration and the fast ignition.
Two-dimensional PICLS simulations had been carried out to study the ps relativistic laserplasma interaction, especially, an effect of laser focal spot size on the electron energy distribution. We find that the steady distribution is formed after ps laser-plasma interaction inside the spot area. The electrons in the case with small focal spot (2 um) are kicked only one time by the laser light, i.e. the hot electron average energy is given by the ponderomotive scaling. While in the case with large focal spot (50 um) the electrons interact with the laser light multiple time during the interaction. That makes the laser-plasma interaction stochastic and number of hot electrons are significantly increased. The details will be in the presentation.
Figure 1: Stationary electron distributions produced by laser light with different focal spots, 2, 5, and 50 µm, with the same intensity of 2 ×1018 W/cm2. The laser is continuously irradiated on a 5 µm solid deuteron target with 40nc. The
distribution is normalized with the input energy.

References
[1] N. Iwata et al, Phys. Plasmas 24, 073111 (2017).
[2] N. Iwata et al., Nat. Commun. 9, 623 (2018).

Speaker: Y. Sentoku (EPS 2019)

336 P2.2026 Effect of Schott term in Lorentz-Abraham-Dirac equation

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2026.pdf

Laser focused intensity has been increasing since its invention, and is going to reach 1024 W/cm2 and beyond. These intense fields open the new regime of laser-matter interactions. One of the effect playing an important role in laser-matter interaction in this regime is a radiation reaction effect which is a back reaction of the radiation emission from an accelerating electron onto the motion of the electron itself. Numerical investigations on the laser-plasma interactions including radiation reaction effect showed that high energy photons are emitted from laser-generated plasma, resulting in a possibility of generating an intense and collimated laser-driven -ray source. In order to correctly describe the motion of electrons under these strong electromagnetic fields, the radiation reaction effect should be taken into account in the equation of motion. One of the candidate for the equation of motion of the radiating electron is the LorentzAbraham-Dirac (LAD) equation [1], which is a Lorentz covariant expression including the self-force derived by Lorentz, and relativistically generalized by Abraham. The LAD equation, however, leads to unphysical solutions such as a run-away solution, or a solution with pre-acceleration. In this work, we pay attention to the Schott term in the LAD equation, which is the third time derivative with respect to the proper time, and plays an important role in the behavior of the solution. We investigate the effect of the Schott term on the behavior of the solution, and its role in the energy dissipation and exchange with fields.
[1] P.M.Dirac, Proc. R. Soc. A 167, 148 (1938).

Speaker: T. Nakamura (EPS 2019)

337 P2.2027 The open-source PIC code SMILEI: Physics modules & HPC capabilities

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2027.pdf

SMILEI [1] is an open-source, collaborative Particle-In-Cell (PIC) code co-developed by plasma physicists and high-performance computing (HPC) specialists. This poster presents the current status of the project with a special focus on (i) the physics modules available and (ii) the HPC developments and its performance on the latest super-computer architectures.
Used by laser-plasma physicists and astrophysicists, the code benefits from a wide range of physics modules: arbitrary-angle tighly-focused laser injection, binary collisions, field and collisional ionization, QED processes in strong electromagnetic fields (inverse Compton scattering, Breit-Wheeler pair production), etc. Running in 1D, 2D and 3D cartesian geometries, the code also benefits from a quasi-cylindrical geometry with the electromagnetic fields decomposed on azimuthal modes, as well as from an envelope model for the propagation of laser pulses, e.g. for laser-wakefield acceleration.
On the HPC side, strong efforts have been made in terms of hybrid MPI-OpenMP parallelization including dynamic load balancing, and more recently on the development and implementation of an adaptive SIMD (vectorization) strategy [2].

[1] Derouillat et al., SMILEI: A collaborative, open-source, multi-purpose particle-in-cell code for plasma simulation, Comp. Phys. Comm. 222, 351 (2018); www.maisondelasimulation.fr/smilei.
[2] Beck et al., Adaptive SIMD optimizations in particle-in-cell codes with fine-grain particle sorting, https://arxiv.org/abs/1810.03949.

Speaker: M. Grech (EPS 2019)

338 P2.2028 Laser-plasma instabilities in the shock ignition regime at the Vulcan TAW facility

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2028.pdf

In the Shock Ignition (SI) approach to Inertial Confinement Fusion (ICF), an intense laser spike is used to launch a high pressure converging shock in the spherical capsule at the end of the compression phase. In this way the compression and the ignition phases are separated and can be optimized independently. The shock driving laser pulse propagates at high intensity (~1E16 W/cm2) in a long scale-length plasma and is therefore prone to parametric instabilities, mainly Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS) and Two Plasmon Decay (TPD) that may affect laser-plasma interaction (LPI), possibly yielding hot electrons (HE) which impact on the shock pressure and heat the fuel capsule. While LPI was extensively investigated at lower intensities for both direct and indirect drive ICF, it is poorly known at the SI conditions. It is therefore crucial to carry out dedicated experimental investigations. We carried out an experiment at the Vulcan TAW laser facility using high energy long pulse beams for the production of a hot and long scale-length plasma and a separate high intensity beam for mimicking the SI laser spike. The effect of interaction conditions on LPI was investigated by varying the interaction beam intensity, the delay between drivers and interaction beam and the chirp and bandwidth of the interaction beam. X-ray spectroscopy of K-shell emission from He-like and H-like chlorine dopant of the target is used to infer plasma temperature which is then compared with hydrodynamic DUED simulations, while calorimetry of backscattered light reveals a significant SBS/laser and SRS reflectivity, where SRS strongly depends on the steepness of plasma density profile. Time-resolved spectroscopy of backscattered light shows that SRS is driven at surprisingly low plasma densities (0.03-0.12 nc), suggesting a significant suppression of Landau damping of SRS driven electron plasma waves. Modification of laser bandwidth from a narrow band to a chirped 2 nm broad band also yields a dramatic variation of SRS spectral evolution and a shift of the coupling region. Finally, Cu K and Bremsstrahlung continuum spectra give information on the generation of hot electrons. An overview of the experimental results will be given in the poster presentation.

Speaker: G. Cristoforetti (EPS 2019)

339 P2.2029 High charge electron acceleration from solid target

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2029.pdf

Collimated electron beams produced by intense laser pulses focused onto solid-density plasmas are studied intensively for many applications. Experiments and simulations have shown that the electron beams are emitted at an angle between laser specular and the target normal direction. In particular, an electron jet emitted along the target surface has been observed using large angles of incidence during laser irradiation of solid targets. However, the target surface electron energy spectrum shows a 100% energy spread in most cases, save for a few experiments [1] with low beam charge and large beam divergence angle (> 200).
We systematically studied the relationship between the guiding of target surface electrons and fs laser parameters. When a nanosecond prepulse was added without picosecond ASE, the electron beam became concentrated and intense. We obtained a 0.8-MeV peaked electron beam with a charge of 100 pC in a single shot and a divergence angle as small as 30 [2].
High-quality monoenergetic target surface accelerated electron beams with small normalized emittance (0.03 mm mrad) and large charge per shot have been observed from a 3 TW lasersolid interactions. The 2D PIC simulation reveals that a bubble-like structure as an accelerating cavity appears in the near critical density plasma region. A bunch of electrons is pinched transversely and accelerated longitudinally by the wake field in the bubble [3].
Besides these results obtained by using small size fs lasers, we also performed TSA experiment using sub-ps high power lasers such as PHELIX in GSI and TITAN in LLNL. Ten MeV monoenergetic and highly collimated (< 20) electron beam with 8nC was observed on PHELIX. The Maximum beam charge of 100 nC are obtained on TITIAN [4]. The Direct Laser Acceleration might be the acceleration mechanism in ps-laser/solid interaction. The good pointing stability and reproducibility of such a ultra-high charge electron beam makes it possible an ideal beam for fast ignition on ICF and drive the warm/hot dense matter.
[1] T. E. Cowan et al, NIMA 455, 130 (2000); L. M. Chen et al., Phys. Rev. Lett.100, 045004 (2008); A. G. Mordovanakis, Phys. Rev. Lett.103, 235001 (2009)
[2] J. Y. Mao et al, PRE 85, R025401(2012); W. M. Wang et al, HEDP 9, 578(2013)
[3] J. Y. Mao et al, Appl. Phys. Lett. 106, 131105(2015)
[4] Y. Ma et al, PNAS 115, 6980(2018); J. Y. Mao et al, Opt. Lett. 43, 3909(2018)

Speaker: L.M. Chen (EPS 2019)

340 P2.2030 Optimization of gamma-ray source driven by picosecond laser using gold foams

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.2030.pdf

Experiments and numerical simulation show that -ray radiation can be effectively enhanced with gold foam through a new mechanism. As shown in Fig.1and Fig.2, the intensity laser can enter into the high density reign which is close to the foam's bubble cavity region due to the "hole boring "effect. The reflux cold electrons mainly move along the bubble wall due to the sheath electric field (E) in the bubble. Thus a strong positive current is formed at the bubble wall, producing a 100 trillion Gauss magnetic field (B). Then a magnetic barrier is formed, which plays the role of energy selection: high-energy electrons can pass through the foam while the low energy electrons will be kicked back into the laser field to gain energy again, until electrons have enough energy to overcome the "magnetic barrier". Therefore, foam can significantly change the relativistic electrons spectrum, increasing the proportion of high-energy electrons, and enhancing the efficiency of -ray production.

Fig.1 2D PIC numerical simulation results about relativistic electrons in foam target;

Fig.2 Experimental results of -ray spectrum and spatial distribution between planar target and foam target;

Speaker: J. Xiong (EPS 2019)

341 P2.3001 Forced nonlinear vertical oscillations of a single dust particle trapped in a standing striation

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3001.pdf

The nonlinear features of the oscillatory motion of a single dust particle trapped in a standing striation are investigated. The method of the discharge current modulation [1, 2] is used to excite the nonlinear oscillations with the large amplitude of the order of 1.5 mm. The multi-resonance curves are obtained under the different shapes of modulating signal. are investigated depending on value of the modulation depth. In this paper the parametric instabilities, which were previously observed under the conditions of rf discharge in [3, 4, 5], are investigated in dc plasma. The detailed measurements of the amplitude-frequency characteristic near resonances at the fundamental and doubled frequencies make it possible to detect the vibrational hysteresis. The theory of the anharmonic oscillator provides a good quantitative description of the experimental data. The values of the thresholds of excitation of parametric instabilities, the anharmonic coefficients and the critical values of the oscillation amplitude for the hysteresis are calculated. The potential well, in which the microparticle oscillates, is calculated using the values of anharmonic coefficients. The vertical electric field in the vicinity of the dust particle equilibrium position is reconstructed.
Acknowledgements Work was supported by RFBF grant No. 18-32-00685.

References
[1] Yu.Golubovskii, V.Karasev and A. Kartasheva, Plasma Sources Science and Technology 26, 11 (2017)
[2] Yu.Golubovskii, V.Karasev and A. Kartasheva, Plasma Sources Science and Technology 27, 6 (2018)
[3] H. Schollmeyer, A. Melzer, A.Homann, and A.Piel, Physics of Plasmas 27, 7 (1999)
[4] C. Zafiu, A. Melzer, and A.Piel, Physical Review E 63, 6 (2001)
[5] A. Ivlev, R. Sütterlin, V.Steinberg, M.Zuzic and G. Morfill, Physical Review Letters 85, 19 (2000).

Speaker: A. Kartasheva (EPS 2019)

342 P2.3002 Forces applied on a spherical metal nanoparticle in a magnetized plasma

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3002.pdf

The study of nanoparticle (NP) dynamics is done in a DC unbalanced magnetron discharge using argon plasma at 30 Pa. The plasma is produced between two electrodes: a 7.62 cm diameter tungsten cathode negatively biased and a stainless steel grounded anode 10 cm apart. The discharge current was fixed at 0.3 A and 0.5A.
NPs are produced from cathode sputtering. They grow near the cathode and acquire a negative charge proportional to their size. They are transported in the plasma under the action of the following forces: two ion drag forces, one due to the collection of ions on a NP where the ions transfer their momentum to the NP and the second one due to the Coulomb scattering of the plasma ions on the NP where the ions deflect in the local electric field in the sheath surrounding the NP, electric force due to the plasma electric field, thermophoretic force due to a temperature gradient in the neutral gas, neutral drag force due to the resistance experienced by a nanoparticle moving through the gas, and the gravity.
The determination of the plasma parameters is necessary to calculate the applied forces. For this, the 2D magnetic field mapping of the magnetron system was established using a Hall probe. The 2D mappings of the plasma potential, the electron density and temperature were achieved using a cylindrical Langmuir probe. The 2D mapping of the balance of the forces applied to an isolated NP was then deduced as well as the trapping positions. The latter were discussed according to the magnetic field and electric field configurations. These results on the NP transport will be verified with laser extinction.

Speaker: A. Chami (EPS 2019)

343 P2.3003 Functionalized porous silicon structures for promising plasma energy systems

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3003.pdf

Currently, the developments in the field of alternative energy are becoming increasingly important due to the need to solve a vast number of problems associated with the creation of compact, reliable, autonomous power sources for spacecraft and other applications, where the conversion of solar energy into electrical energy is of particular interest. Traditionally, this process is implemented according to one of two fundamental principles: "quantum" approach, presented in photovoltaic cells, and "thermal" mechanism, requiring the presence of concentrated radiation to generate electricity using various heat engines (i.e. thermionic energy converters or TECs). In practice, devices that combine both paradigms lose their effectiveness due to the rapid destruction of photovoltaic cells, caused by a significant increase in operating temperatures required to maintain the thermionic emission current density at a reasonably high level.
Concentrators based on the effect of photon-enhanced thermionic emission (PETE) make it possible to realize photovoltaic and thermionic phenomena in a single physical process. The possibility of synthesizing systems based on PETE with semiconductor (GaN) electrodes was demonstrated in [1], however, the number of incident photons, exceeding the band gap of GaN (Eg = 3.3 eV), is less than 1% of their total thus the combined energy conversion efficiency decreases dramatically. In this study new materials based on porous silicon (PS) for the subsequent synthesis of PETE electrodes are proposed, since the value of Eg for PS varies in a wide range from 1 to 3 eV due to the quantum confinement effect, as well as mechanisms for surface functionalization [2, 3].

References
[1] Schwede J W, Bargatin I, Riley D C, Hardin B E, Rosenthal S J 2010 Photon-enhanced thermionic emission for solar concentrator systems Nature Mater. 9 762.
[2] Smerdov R S, Spivak Yu M, Levitsky V S, Moshnikov V A 2018 The characterisation of nanostructured porous silicon/silver layers via Raman spectroscopy Journal of Physics: Conference Series 1038 012064.
[3] Smerdov R S, Mustafaev A S, Spivak Yu M, Moshnikov V A 2018 Porous silicon and graphene-based nanostructures for novel solar energy systems Journal of Physics: Conference Series 1135 (1) 012038.

Speaker: A. Mustafaev (EPS 2019)

344 P2.3004 Helix jet - a novel glow plasma jet for surface treatment and PECVD at atmospheric pressure

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3004.pdf

We present the helix jet - a stable plasma source with a large homogeneous plasma volume at atmospheric pressure. Challenging applications of material science in high-tech technology implement sources combining homogeneity and stability of vacuum based techniques with a multidimensional flexibility and instrumental modularity of atmospheric pressure plasma sources. In particular, scalable sources generating non-contracted glow discharges are a subject of great interest. The typical glow discharges are designed in planar geometry [1]. However, steep gradients of light emission and other plasma parameters occur perpendicularly to the surface or, in a cylindrical geometry, radially to the plasma channel. Based on the investigation of the self-organized behaviour of a filamentary plasma jet [2], we derived a double helix electrode configuration. The helix jet represents a capacitively coupled radiofrequency plasma source operating at 27.13 MHz. The argon gas flows through a pipe with a diameter of 9 mm at flow rates between 1 and 0.1 slm. The glow discharge has been ignited homogeneously in the whole volume at the surprising length of approximately 10 cm at powers between 40 and 100 W. The radial homogeneity of the discharge has been certified by a high-speed camera with an exposure time of 3 ns. The stability of the glow mode has been tested during an operation for eight hours. Additionally, a computer simulation of the electrostatic potential has been performed. The results show that the electric field exhibits a homogeneous channel with low field magnitude along the axis of the jet which favours the formation of a glow like plasma throughout the full length of the plasma tube discharge. Hence, the helix jet is a suitable plasma source for homogeneous treatment of small 3D objects like powders, seeds or for an upscaled thin film deposition, e.g. PECVD of silicon dioxide films for anticorrosive protection of surfaces. Here, we show the deposition rates and morphological structure of SiOx nanostructures by means of SEM and microgravimetry. Octamethylcyclotetrasiloxane was used as precursor for the PECVD of the coatings. The resulting films are extremely smooth and laterally homogeneous.

[1] F. Massines et al., https://doi.org/10.1063/1.367051
[2] J. Schäfer et al., https://doi.org/10.1088/1361-6587/aa8f14

Speaker: J. Schäfer (EPS 2019)

345 P2.3005 High-pressure gases breakdown in strong longitudinal magnetic fields

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3005.pdf

Here we present the results of experimental studies on the effect of an external longitudinal magnetic field in a high pressure discharge. Fig. 1 shows typical experimental time dependences of the voltage (upper), current density (middle) and calculated conductivity (lower) in the channel (argon, H=1.6·107 A/m, P=3 atm.). We’ve found that a longitudinal magnetic field leads to: (i) an increase in current density, conductivity, specific energy input, and plasma temperature, (ii) a decrease of formation times in all stages, transverse integral radiation, channel expansion rate, and (iii) shifts the maximum spectral radiation density in the ultraviolet region with the generation of new spectral lines. Explaining our results we can conclude that because of the expansion rate of the spark channel is greater than the diffusion rate of
the magnetic field lines, the expanding spark channel shifts the magnetic field lines, reducing them in the center and increasing at the electrodes (cathode and anode), and therefore the system acquires the properties of a magnetic mirror trap [1], and it leads to the significant increase in the channel temperature. This approach can be used to create a source of intense X-ray and ultraviolet radiation and other applications.
[1] O.A. Omarov, et al. 2019 High Temperature 57

Speaker: A.A. Aliverdiev (EPS 2019)

346 P2.3006 Influence of charged particles on a strong shock wave of a neutral component in a weakly ionized gas

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3006.pdf

The interaction of neutral and charged gas components is in a high interest of modern physics. This attention is caused mostly by the aerospace applications as well as for exploring the nonlinear wave processes in the near-Earth space (ionosphere). In this work, the interaction of strong shock waves (supersonic bodies) with low-ionized plasma is discussed.
The basic principles of nonlinear ion-acoustic waves formation in a weakly ionized nonisothermal gas (Te Ti Tn) subjected to a strong stationary shock wave of the neutral component is studied on the base of computer-aided calculations and analytical methods. The ionacoustic approximation is employed to describe the plasma component of charged gas. Within a such approach the ion-acoustic waves arise via the collisions of charges with the neutral particles.
Recently, the ion-acoustic wave formation in a weakly ionized non-isothermal gas was considered in [1, 2], where the charged particles influence on neutral one was not taken into account. In this work, this problem was was solved numerically with the use of scientific packages Comsol and Matlab.
Found in such analysis patterns reveal the additional mechanism for the reduction of the strong shock wave intensity of the neutral component without heating energy release in the region ahead of the front. The reciprocal action of the charged components on the neutral particles lead to significant modification of the structure and reduction of the intensity of the shock wave.
It is found that the low-ionized plasma (the nonperturbed state) effects strongly on the neutral component and reduces the shock wave intensity. The same physical picture was observed in the experiment [3].

References
[1] V.A. Pavlov. Ya.V. Tryaskin, Journal of Applied Mechanics and Technical Physics, 56, 3 (2015)
[2] V.A. Pavlov. J.V. Triaskin, 45th EPS Conference on Plasma Physics, 42A, (2018)
[3] G. Mishin. 15th Applied Aerodynamics Conference, American Institute of Aeronautics and Astronautics 1, 1 (1997)

Speaker: J.V. Triaskin (EPS 2019)

347 P2.3007 Influence of radiation transport on discharge characteristics of an atmospheric pressure plasma jet in argon

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3007.pdf

Non-thermal atmospheric pressure plasma jets have been subject to numerous scientific studies during the last decades [1]. An extremely wide application field of such devices demands deep understanding of the plasma processes. One of those, which influences the formation of various spatiotemporal structures in the gas discharge plasma, is the transport of resonance atoms caused by radiation trapping [2]. The correct treatment of the radiation transport, along with diffusion and convection, is important point in plasma modelling. The majority of multi-scale complicated models use local Holstein or Biberman approximation to describe radiation transport, which does not take into consideration the spatial redistribution of excited atoms.

Efficiency of the matrix method [2] of correct account of the radiation trapping effect, demonstrated on the certain examples [3] embodies the basic motivation of the current study. In the work [5], adapted 1D method was successfully applied to a plasma jet model described in [6] and characterized by complex geometry and chemistry.

The main goal of the current work was to develop a new technique for treating 2D axisymmetrical geometries. The developed method allows discretization of the radiation transport integral operator, calculating corresponding matrix and setting up a system of linear equations with particular excitation source. The implementation of the developed method of radiation transport treatment in plasma jet modelling and results of the calculations, taking into account both complex geometry of the device and large set of plasma-chemical reactions, will be discussed.

References:
[1] Winter, J. et al. Plasma Sources Sci. Technol. 24, 64001 (2015)
[2] Golubovskii, Y. et al. Plasma Sources Sci. Technol. 22, 023001 (2013)
[3] Golubovskii, Y. and Maiorov, V. Plasma Sources Sci. Technol. 24, 25027, (2015)
[4] Golubovskii, Y., et al. J. Phys. D: Appl. Phys. 49, 475202, (2016)
[5] Valin, S et al Proceedings of the 22th GD, September 2-7, 2018, Novi Sad, Serbia. [6] Sigeneger, F. & Loffhagen, D. Plasma Sources Sci. and Technol., 25 (3), 035020, (2016)

Speaker: S. Valin (EPS 2019)

348 P2.3008 Inhomogeneity of structural and dynamic properties of dusty plasma structures

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3008.pdf

Dusty plasma is a system of charged micron-sized particles immersed in a plasma. This system is strongly non-ideal due to high charges of particles and strong interaction between them. Thus, observation of ordered structures in a dusty plasma is possible. Such ordered structures are called dusty plasma crystals.

The configuration of dusty plasma crystals is often well described by the model of particles interacting through the Yukawa potential inside of a parabolic trap [1]. As was shown by Henning et al. [2], such crystals are fundamentally nonuniform: mean inter-particle separation is higher at the periphery of the structure than in its center.

In this work, we extend analysis to dynamics properties (root mean square displacement, Lindemann parameter, diffusion coefficient in a liquid state) and coupling parameter of confined Yukawa system. We develop an analytic model demonstrating that the listed dynamic properties are also nonuniform and grow with radial distance from the center of the trap while the coupling parameter decreases. In order to verify this effect, we conduct molecular dynamics simulations on two-dimensional and three-dimensional systems. Results of MD simulations show a good agreement with the analytic model. Influence of charge fluctuations on the dynamics properties and coupling parameter is also discussed.

From the nonuniformity of confined Yukawa structures, it is shown that the process of melting in them is fundamentally heterogeneous and starts from the periphery of the structure.

1. Baumgartner, H., Block, D., & Bonitz, M. (2009). Structure and phase transitions of Yukawa balls. Contributions to Plasma Physics, 49(4-5), 281-302.
2. Henning, C., Baumgartner, H., Piel, A., Ludwig, P., Golubnichiy, V., Bonitz, M., & Block, D. (2006). Ground state of a confined Yukawa plasma. Physical Review E, 74(5), 056403.

Speaker: V.S. Nikolaev (EPS 2019)

349 P2.3009 Investigating the effect of different carrier gases on plasma-assisted multi-walled carbon nanotube growth

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3009.pdf

A theoretical model is created consolidating the charging rate of the carbon nanotube (CNT), the energy of all the species present in plasma, and the growth rate of the multi-walled carbon nanotube (MWCNT) owing to the surface and bulk diffusions and accumulation of particles on the catalyst nanoparticle surface. Using acetylene as the hydrocarbon source, we have compared the influence of distinctive carrier gases on the structure of CNT. The conclusion drawn from the results obtained were that while argon favors growth rate of nanotubes, ammonia contributes to diminishing its growth rate whereas nitrogen hinders both the growth rate and radius of nanotube1-3. The work can be thought useful to serve to a better understanding of the growth of MWCNT in the plasma environment and to study their field emission applications.

1. V. Kayastha, Y. K. Yap, S. Dimovski, and Y. Gogotsi, Appl. Phys. Lett. 85, 3265 (2004).
2. W. Mi, J. Y. Lin, Q. Mao, Y. Li, and B. Zhang, J. Nat. Gas Chem. 14, 151 (2005).
3. S. M. Toussi, A. Fakhru'l-Razi, A. L. Chuah, and A. R. Suraya, Sains Malays. 40, 197 (2011).

Speaker: U. Sharma (EPS 2019)

350 P2.3010 Investigation of radiation spectrum from pulse discharge in atmospheric pressure argon

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3010.pdf

An experimental and theoretical study of the formation of radiation spectra of cathode plasma in a pulsed discharge in argon at atmospheric pressure has been performed. To study the effect of small impurities of the material of the cathode material on the kinetics of ions and electrons in the discharge, the methods of numerical simulation using the particle and Monte Carlo methods were used.
In the experiment, it was found that with the formation of a cathode spot, the spectrum of cathode plasma is characterized by intense lines of the Al II cathode material 396.1 nm, 394.4 nm, 280.1 nm, 281.6 nm with high excitation potentials and an intense continuum in the range 260-360 nm. Aluminum ion lines are recorded simultaneously with the onset of a sharp current increase and reach a maximum value in 20-30 ns. It is shown that after 30 ns from the beginning of a sharp increase in the current, the Stark half-width of the argon line at 480.6 nm is 0.5�0.6 nm, and the line at 422.8 nm is 0.5 nm. These half-widths correspond to an electron density of ~ 1019 cm-3, and after 20 ns the concentration decreases to a value of 21018 cm-3.
It has been established that with increasing magnetic field strength, the maximum of the radiation energy is shifted to the short-wave region of the spectrum: at H = 0 max = 420 nm, at H = 140 kOe - 400 nm, and at H = 200 kOe - 380 nm. Thus, in a magnetic field, the intensity of continuous radiation increases, and the brightness of ion lines in the ultraviolet region also increases: Ar II -- 280.6 nm, Ar IV -- 280.9 nm, and Al material lines of Al electrodes are: 280.1 nm, 281.6 nm. Starting from the moment t = 500 ns, the brightness of the Al I aluminum lines increases: 302.9 nm, 308.2 nm; Al II - 281.6 nm, 280.1 nm . Since t = 700 ns, the luminescence of aluminum lines 281.6 nm strongly increases in the longitudinal magnetic field: 280.1 nm; 309.27 nm and 308.216 nm.
Estimates were made of the temperature of the channel plasma at various magnetic field strengths determined from the relative intensity of three pairs of argon ion lines (448.2 nm and 454, 5 nm; 480.6 nm and 476.4 nm; 484.7 nm and 476.4 nm). It is shown that the plasma temperature decreases within 300 ns by 10-15%, i.e. at the stage of rapid expansion of the channel, the temperature of the plasma channel practically does not change. In the absence of a magnetic field, the temperature drops rapidly (t = 1.5 s, T26000 K); in a magnetic field, the rate of temperature change decreases (t = 1.5 s, T28000 K).
The Monte Carlo method was used to calculate the kinetic characteristics of the drift of ions and electrons in argon in the presence of aluminum vapor at an electric field strength of E/N = 1-100 Td, taking into account inelastic collisions. The effect of metal vapor concentration on the drift velocity, average energy, diffusion coefficients, and mobility of ions and electrons is analyzed.
This work was supported by the grant of the Russian Foundation for Basic Research No. 19-08-00611a.

Speaker: S.A. Mayorov (EPS 2019)

351 P2.3011 Ion-acoustic waves in collisional dusty plasma: effects of grain charge fluctuations

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3011.pdf

Dust grains acquire electric charges (eg) due to absorption of electrons (e) and ions (i) from the surrounding plasma, i.e. each grain is charged by the plasma currents Ich ( = e, i) to its surface. The electric field fluctuations influence the charging currents and, thus, give rise to the grain charge fluctuations. Such self-consistent influence gives the additional contribution to the dielectric permittivity of dusty plasma (k, ), which determines the dispersion and damping of waves. The obtained expression for dielectric permittivity has the form [1] .---------------------------

where ch = ceh + cih is the charging frequency (ch = - Ich/ eg), Ig = ngIch/e n is the frequency of plasma particles collisions with grains, n is the number density. We used the dielectric susceptibility of collisional plasma (k, ) obtained from the Bhatnagar-Gross-Krook kinetic equation. For the ion charging current Icih, we used the interpolation formula proposed in [2]. The influence of dust charging and charge fluctuations on dispersion and damping of ion-acoustic waves is illustrated in Fig. 1.

Figure 1: Eigenfrequencies k (a) and damping rates |k| (b) of ion-acoustic waves in nonisothermal (Te/Ti = 100) argon plasma as results of numerical solution of the dispersion equation (k, k + ik) = 0 for in = 0.02pi, a = 0.15D and P = egng/eeni = 0, 0.2, 0.5, 0.8. The insert shows the ratio k/|k|.

References
[1] A.I. Momot, A.G. Zagorodny, and O.V. Momot Phys. Plamas 25, 073706 (2018)
[2] S.A. Khrapak and G.E. Morfill, Phys. Plasmas 15, 114503 (2008)

Speaker: A. Momot (EPS 2019)

352 P2.3012 Kinetics effects in a plasma crystal induced by an electron beam

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3012.pdf
The kinetic effects on the dust particles observed in a plasma crystal locally irradiated by a narrow pulsed electron beam with energy 12 and 13 keV and peak current 4 mA are presented [1]. We observe in the top layer of the plasma crystal the formation of a stable dust flow along the irradiation direction in the first hundred milliseconds of the interaction. The spatial velocity profile of the dust flow can be well fitted with the sum of two Gaussian curves, one representing the velocity spread of the core stream due to the dust being pushed by the electron beam and the second being a measure of the kinetic energy deposited into the flow edge. The dust flow eventually becomes perturbed later in time, with the dust particles having chaotic trajectories as they are still drifting in the beam direction. The speed of the dust flow is mapped in a horizontal plane using the particle image velocimetry technique (PIV) [2]. A strong transversal heating of the dust particles takes place at the impact of the beam with the plasma crystal. At 13 keV the heating wave propagates rapidly sideways from the impact zone with a speed between 66 ± 2 mm/s and 81 ± 5 mm/s. It appears that in a transversal direction the kinetic energy decays exponentially with distance, with a decaying rate given by L-1, where L= 6.3-7.1 mm. The rich complexity of kinetics effects observed in the experiment presented here recommends the ensemble electron beam-plasma crystal as a suitable system for studying strongly coupled charged flows at convenient spatiotemporal scales.
[1] C.M. Ticos, D. Ticos and J.D. Williams (unpublished). [2] J.D. Williams, J. Plasma Phys. 82, 615820302 (2016).

Speaker: C.M. Ticos (EPS 2019)

353 P2.3013 Large-scale ferromagnetic enhanced ICP in Ar/Cl2 mixture

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3013.pdf
Ferromagnetic enhanced inductively coupled plasma sources (FMICP) are considered to be a
promising solution to produce large volumes of dense (~1012 cm-3) uniform plasma for largearea
(450 mm) plasma processing systems, due to a high power transfer efficiency, reduced
driving frequency (<0.4 MHz), the absence of capacitive coupling and a low plasma potential
[1]. Although the properties of large-scale FMICP sources are well investigated for the case
of inert gases [1–4], the impact of halogens addition on the FMICP characteristics is still
unknown. To investigate the plasma parameters of a large-scale FMICP in Cl2/Ar mixture, an
experimental setup has been developed. The scheme of the setup is similar to that of
[2], except of the ferrite antennas construction (which are optimized for higher voltage
operation), gas discharge chamber size and the construction of U-shaped gas discharge tubes
(which are adapted for high heat loads). New experimental data have been obtained on the
dependence of FMICP electric field strength vs. gas pressure (10–100 mTorr), discharge
current (5–20 A) and Cl2 content. The impact of Cl2 addition on the electrical characteristics
of large-scale FMICP was analyzed and compared with the properties of RF and DC
discharges in Ar/Cl2 mixture.
References
[1] Godyak V 2013 Journal of Physics D: Applied Physics 46 283001
[2] Kyeonghyo Lee, Youngkwang Lee, Sungwon Jo et al. 2008 Plasma Sources Sci. Technol. 17 015014 [3] Jin-Young Bang, Jin-Yong Kim and Chin-Wook Chung 2011 Physics of Plasmas 18 073507
[4] Hyun Jun Kim, Hye-Ju Hwang, Dong Hwan Kim et al. 2015 Journal of Applied Physics 117 153302 The work is supported by the Russian Science Foundation, Grant No. 18–19–00205.

Speaker: M. Isupov (EPS 2019)

354 P2.3014 Laser diagnostics of helium low temperature plasmas using Stark broadening

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3014.pdf
Atoms and ions in plasmas are suffered by collision with another particle, local electric field by electron and ion, plasma radiation, and so on. These interactions cause spectral line broadening of plasma radiation such as natural broadening, Doppler broadening, van der Waals broadening, resonance broadening, and Stark broadening [1]. Among these spectral line broadening, Stark broadening is widely used to determine the electron density of the astrophysical plasmas and the atmospheric pressure plasmas because Stark broadening is larger than Doppler broadening in those field [2,3]. In low temperature plasmas, Stark broadening is quite smaller than Doppler broadening so that Doppler broadening has to be removed to measure Stark broadening. In this research, we have constructed ICP plasma source to investigate Stark broadening in helium low temperature plasmas and we have composed of saturated absorption spectroscopy configuration using high resolution laser diode system of which linewidth was less than 1 MHz. Doppler-free absorption spectrum for 21S-41P transition of helium plasmas was measured when pressure was 20mTorr and RF power of 800 W was applied to the plasma source. As well saturation parameter was determined using the saturated absorption spectrum and laser power broadening was determined. Stark broadening was measured using the saturated absorption spectrum and the electron density of helium low temperature plasmas was determined. The determined electron temperature was compared with those by the electric probe and the collision-radiative model.

Reference
[1] M.A.Gigosos, J. Phys. D: Appl. Phys. 47, 343001 (2014). [2] M.A.Gigosos, S.Djurovi, I. Savi, D.González-Herrero, Z. Mijatovi, and R. Kobilarov, A&A 561, A135 (2014). [3] A. Y. Nikiforov, C. Leys, M. A. Gonzalez, and J. L. Walsh, Plasma Sources Sci. Technol. 24, 034001 (2015).

Speaker: W. Lee (EPS 2019)

355 P2.3015 laser-driven synthesis of nanoparticles for therapeutic applications

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3015.pdf
Gold nanoparticles (GNP) have a wide range of applications in medicine, such as a radiosensitiser in radiotherapy[1], GNP coated single walled carbon nanotubes (SWCNT), to be used as a photothermal agent[2], targeted drug delivery systems, and other forms of cancer treatment and diagnostics[3]. Research into GNP production focuses on quality factors; such as size distribution, shape and purity, versus the cost of production. Mainstream synthesis of GNP, such as wet chemistry, has its main challenges due to impurities in the process. Laser ablation in liquids (LAL) offers an alternative method of a cheaper and quicker production of ultra-pure NP solutions and the reduced material heating with ultra-fast lasers allow NPs with narrower size distribution, and better controllability in shape and size compared to other methods[4][5]. In a preliminary experiment, a 99.95% purity gold disc of 4mm diameter, 0.1mm thick, submerged in a few mm of DI water. A 337fs pulsed laser of wavelength 1040 nm was focussed onto the surface of the gold producing a fluence of 6J/cm2, ablating individual sites over 2.6mm x 2.6mm square on the gold. Two samples were prepared using exposure times of 1s and 0.5s for each site, producing solutions of a dark red and a light red/pink colour, respectively. Characterisation via UV-Vis Spectroscopy gave diameters of 40nm in the 1s exposure sample and to 15nm in the 0.5s sample, with the difference most likely due to material heating with the longer exposure time. In another experiment, the craters produced in water and in air with varying laser power (20-100%) investigated via SEM can relate the laser intensities between water and air, with the heated affected area of the craters ranging from 40-90µm. The craters produced in air were larger than in water, indicating a reduction in intensity possibly due to water affecting the focus. For future experiments, The NP size dependency on laser fluence, crater investigations and retrospective imaging of the ablation process.

[1] Jain (et al), Oncology Biology Physics, Vol. 79, Pgs: 531­539, Year: 2011. [2] Meng (et al), Applied Materials Interfaces, Vol. 6, no.7, Year: 2014. [3] Ling (et al), Nanotoday, Vol. 9, no. 4, Year: 2014. [4] Kabashin (et al), Journal of Applied Physics, Vol. 94, Pgs: 7941-7943, Year: 2003. [5] Gamaly (et al), Physics Reports, Vol. 508, Pgs: 91-243, Year: 2011

Speaker: C. Rafferty (EPS 2019)

356 P2.3016 Lower hybrid waves excitation by a relativistic electron beam in a magnetized dusty plasma: kinetic theory

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3016.pdf
In the present paper, we study the kinetic theory of instability of electrostatic lower hybrid waves1 (LHWs) in a dusty plasma containing potassium positive ions (K+). A relativistic electron beam (REB) propagating through the plasma containing dust grains, positive potassium ions, and electrons, drives the LHWs to instability through Cerenkov interaction. Analytical expressions and numerical calculations using Vlasov equations2 have been carried out for the frequency and the growth rate of LHWs for the existing experimental parameters. It is found that the growth rate of the instability increases with increase in the relative density of the dust grains. In addition to this, the growth rate of the LHW decreases with the increase in the frequency. Our theoretical results are in complaince with some of the experimental results.
1. Ved Prakash, Vijayshri, Suresh C. Sharma, and Ruby Gupta, Physics of Plasmas 20, 053701 (2013). 2. C. S. Liu and V. K. Tripathi, Physics Reports, 130, 143 (1986).

Speaker: A. Dahiya (EPS 2019)

357 P2.3017 Lower-hybrid wave processes during the interaction of the Earth's magnetotail with dusty plasma near the lunar surface

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3017.pdf
The lower-hybrid wave processes that take place under the interaction of the Earth's magnetosphere with dusty plasma near the lunar surface are considered. Lower-hybrid waves are excited in the regions of the transient magnetic and/or boundary magnetospheric layers due to the development of linear hydrodynamic instability. The instability is caused by the relative motion of the magnetospheric electrons and ions with respect to charged dust grains. The dynamics of the development of lower-hybrid turbulence is investigated. Lower-hybrid turbulence is described in terms of strong turbulence theory. The energy density of oscillations, the effective collision frequencies, and the electric fields arising in the system are determined for lower-hybrid turbulence. The obtained effective collision frequencies should be taken into consideration when deriving hydrodynamic equations for dusty plasmas with allowance for turbulent plasma heating. This work was supported by the Russian Science Foundation (project no. 17-12-01458).

Speaker: T.I. Morozova (EPS 2019)

358 P2.3018 Model to self-consistently describe the RF coupling in low pressure high power hydrogen ICPs

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3018.pdf
In ion sources for neutral beam heating systems used in fusion, low temperature hydrogen plasmas are sustained by inductive RF coupling in compact cylindrical discharges of several dm3. The sources are typically operated at low pressures up to 0.3 Pa and powers of 100 kW yielding power densities of 10 MW/m3 to reach plasma densities up to 1019 m-3. The high RF power is close to a technological limit, since high RF voltages promote unwanted arcing between different RF components. It is well known that only the fraction = Pplasma/PRF is absorbed by the plasma, whereas the rest is lost in the RF circuit and other structures surrounding the RF coil. To avoid arcing and thus increase the reliability of the system, optimization of is required by decreasing PRF while holding Pplasma constant. In order to do so, the complex interplay of plasma parameter (profiles) and electrical quantities such as has to be known.
depends not only on PRF, but also on geometries of the source and RF coil, gas type (H2 or D2), pressure, RF frequency and on the strength of magnetostatic stray fields which are present in the source. Since it is too expensive and time consuming to systematically investigate the impact of all of these parameters on experimentally, a predictive model of the source is needed, that calculates the coupling between the plasma and the RF fields self-consistently.
Therefore, a 1D fluid model has been set up, where the particle and momentum balances for the positive ions H+, H+2 , H+3 and for the electrons are solved. The RF heating is modeled by the electron energy balance coupled to Maxwell's equations that describe the RF fields. The low pressure regime requires that the electron heating is collisionless rather than collisional. To describe this adequately with a fluid approach, kinetic effects have to be incorporated [1]. The model is experimentally validated at the flexible and well diagnosed small scale laboratory experiment CHARLIE [2] and at the high power RF-driven ion source test bed for negative ions BATMAN Upgrade [3]. Since the dissociation degree is known to be an important parameter in hydrogen and deuterium, the model is then used to study its impact on in both cases.
References
[1] M Turner, J. Phys. D: Appl. Phys.42 194008 (2009) [2] D Rauner et al., RF power transfer efficiency of low pressure ICPs in light molecular gases (this conference) [3] B Heinemann et al., AIP Conference Proceedings 1655, 060003 (2015)

Speaker: D. Zielke (EPS 2019)

359 P2.3019 Electrode design for X-ray lithography fast shutter speed

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3019.pdf
Advantages of X-ray which is emitted by dense plasma focus (DPF) are high-speed shutter and high energy. It can be used as a tool for researching on the property and structure of an object with high speed movement such as turbine blade. This is the target research for Thailand Plasma 1 (TPF-1). The X-ray yield strongly depends on a pinch current (Ipinch), that is - 4. In this work, Lee code is used to calculate the parameters of plasma focus in order to optimize the TPF-1 electrodes; anode radius (a), cathode radius (b) and electrodes length (z) for Argon or Neon as a working gas. The optimized electrode radii are a = 1.88 cm and b = 2.25 cm. The optimized electrode length depends on the filling gas, 5.2 cm and 3.5 cm for Neon and Argon, respectively. The important parameters of plasma focus consisting of pinch current, pinch temperature and pinch duration are calculated. Their values are 99.5 kA, 3.2 x 105 K and 30.8 ns for Neon gas and 99.5 kA, 1.9 x 105 K and 42.0 ns for Argon gas, respectively.

Speaker: A. Tamman (EPS 2019)

360 P2.3020 Controlled CVD growth of MoTe2 and their use for photodection

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3020.pdf
Monolayer 2D materials, including graphene and transition metal dichalcogenides (TMDs) are promising materials for applications in optoelectronics. In our laboratory, we have developed a series of strategies to synthesis high-quality graphene and TMDs layers, as well as their heterostructure, with tuneable properties using chemical vapor deposition (CVD). For example, we demonstrate a salt-induced CVD strategy to synthesize mono- and few-layer 1T' and 2H phase MoTe2, exploiting rich electronic properties of this materials. In addition, we have utilized lithography method to fabricate heterostructures that allow the enhance of plasmon-induced charge transfer and eventually demonstrate great performance when used for near-infrared (NIR) light detection. This study provides a new materials synthesis method aiming for the fabrication of for highly efficient and broadband NIR photodetector.

Speaker: Z. Luo (EPS 2019)

361 P2.3021 Diffusion coefficients of nickel hydride molecule in hydrogen

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3021.pdf

We present experimental investigations of the transport properties of NiH radical in molecular hydrogen gas. We use NiH to model the behaviour of the first row transition metal monohydrides (e.g. CrH, FeH,TiH) that are established markers for cool stellar atmospheres - i.e. M, L, T-type stars. The data presented here will contribute to various models needed to simulate processes in the stellar atmospheres and to calculate stellar opacities.
The hydride molecules are produced in a discharge source with coaxial geometry. It consists of a glass tube inside which are placed eight ring-shaped cathodes, made of thin sheet of Nickel metal, and an anode assembly which resides concentrically within the cathode rings. Operating the source in pulsed mode allows for a peak value of the discharge current of about 1 A to be achieved. The working pressure of the H2 falls in the range 50 - 600 mTorr. The diffusion coefficient of NiH in hydrogen is determined by measuring the decay of the absorption in the time interval between 1 - 6 ms after the discharge has been extinguished. The experimental data are fit to a non-linear model [1] from which we extract information about the diffusion coefficients of NiH in H2 and the coefficient of reflection from the source walls.
This work was supported by the National Science Fund of Bulgaria through project No. DN 18/12 2017 and by the Bulgarian National Science Program 2018 "Young Scientists and Postdoctoral Researchers".

References
[1] I. M. Rusinov, G. W. Paeva and A. B. Blagoev, J. Phys. D 30, 878-1884 (1997)

Speaker: G. Dobrev (EPS 2019)

362 P2.3022 Study of polymerization process in a capacitively coupled discharge operating in aniline argon mixture

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.3022.pdf

Plasma enhanced chemical vapour deposition (PECVD) is a technique that originates from the conventional chemical vapour deposition (CVD). PECVD is a technique that allows in particular the deposition of ultra-thin and pinhole free polymer films on a great class of substrates. The main role of cold plasmas in this kind of processes is to dissociate the monomer at lower temperatures compared to classical CVD, without completely destroying it. The species formed in this way are subsequently used for the deposition of thin films or under some circumstance for the production of nanoparticles [1]. This contribution will deal with the study of polymerization process in capacitively coupled discharge operating in aniline argon mixture. In this context, the contribution will mainly focus on the role of positive ions and different kind of radicals on the properties of plasma polymerized thin films. For this purpose, different kinds of electrode designs will be used to separate the influence of different species.

[1] C.Pattyn; E.Kovacevic; S.Hussain; A Dias; T.Lecas; J.Berndt; Applied Physics Letters, 2018, 112, 013102

Acknowledgements: The authors want to acknowledge the support obtained by PEGASUS (Plasma Enabled and Graphene Allowed Synthesis of Unique Nanostructures) project, funded by the European Union Horizon research and innovation program under grant agreement No. 766894. The authors would also like to acknowledge support obtained by French National Research Agency via project ANR PlasBioSens and to thank Helmholtz Zentrum Berlin for the allocation of synchrotron radiation beam time at BESSY II. Experiments at BESSY have been also supported with H2020 Calypso Plus project, grant Nr. 18207084-ST and 18207393-ST.

Speaker: D. Sciacqua (EPS 2019)

363 P2.4001 Formation and stability of vortex structures in the flute mode turbulence

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4001.pdf
Flute oscillations are vortical motions which are highly elongated along the magnetic field. Their characteristic dimensions are much larger than the Larmor radius, and their frequency much smaller than the cyclotron frequency, of the ions. In contrast to the electrostatic drift wave, the flute mode belongs to the reactive system, i.e. the flute mode is linearly unstable even in the absence of any dissipation and is easily excited in a non-uniform plasma if there is an unfavorable ratio of the gradients of the plasma density and the magnetic field. Moreover, for these modes the assumption of adiabatic electrons is not valid and therefore the linear and nonlinear analysis involves the studies of density fluctuations. The oscillations are assumed quasineutral. In this paper we investigate the stationary states which are established under the influence of the nonlinear effects associated with the flute instability. The nonlinearity, which is increased in importance by this instability, give rise to the reduction the characteristic dimension of the initial perturbations, so that the size of a vortex may fall below the critical value which is the threshold for the instability. It can thus be expected that the evolution of the flute instability will terminate in a set of such vortices. The particular interest in these studies is to formulate the conditions for the formation and existence of the infinitely long rows of vortices or vortex streets with finite vorticity associated with flute modes. To perform the analysis, we use the two-field nonlinear model equations for the flute oscillations. The Hamiltonian structurer of these equations has been then identified and used to find the complete set of integral invariants. We focus the discussion on two-dimensional (2-D) vortex flows that are described by the 2-D stationary propagating solutions to the equations for flute modes. These solutions are localized in the direction of the plasma inhomogeneity, periodic in the direction of the translation symmetry and correspond, physically, to so-called "vortex streets" known in fluid dynamics. The knowledge of a full set of integral invariants provides a general characteristic of these stationary solutions and give s tools to investigate their stability. In these studies, we refer to Lyapunov's direct method. First, we form the Lyapunov functional for the stability analysis and then, by varying this functional, we find that the considered 2-D vortex flows are stable to long wave length perturbations.

Speaker: V. Pavlenko (EPS 2019)

364 P2.4002 Challenges in controlling perpendicular electric fields for crossed-field rotation

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4002.pdf
The question of how to impose an electric field perpendicular to the magnetic field in a highdensity magnetized plasma is central to a variety of applications with high societal impact. In recent years, it has been shown for instance that "crossed-field" rotating configurations could offer unique opportunities both for developing plasma mass separation techniques [1], as envisioned for nuclear spent fuel reprocessing [2], nuclear waste cleanup [3] and rare earth elements recycling [4], and to design alternative magnetic confinement fusion concepts [5].
Whether it is using biased electrodes or waves, the ability to sustain an electric field perpendicular to the magnetic field in a plasma depends on perpendicular conductivity. Yet, while it is well recognized that many different driving mechanisms (e. g collisions with neutral, instabilities and turbulence, magnetic fluctuations, ion viscosity) can contribute to , a comprehensive picture for perpendicular conductivity is still missing. Importantly, it has recently been shown that the combined effects of inertia and collisions in a fully-ionized rotating plasma lead to a new, non-linear, contribution to perpendicular conductivity [6]. Progress towards the development of plasma processes harnessing crossed-field rotation hence calls for theoretical and experimental investigation of perpendicular conductivity.
In this talk, we review what can be inferred about perpendicular electric field control from past experimental studies, and compare these results to our incomplete theoretical picture for perpendicular conductivity. These findings are then used to provide clues as to what the important next steps are.
References
[1] S. J. Zweben, R. Gueroult and N. J. Fisch, Phys. Plasmas, 25, 090901 (2018) [2] (a) A. V. Timofeev, Sov. Phys. Usp. 57, 990 (2014) (b) R. Gueroult and N. J. Fisch, Plasma Sources Sci.
Technol. 23, 035002 (2014) (c) V. B. Yuferov et al., Prob. Atom. Sci. Tech. 23, 223 (2017) [3] R. Gueroult, D. T. Hobbs and N. J. Fisch, J. Hazard. Mater. 297, 153 (2015) [4] R. Gueroult, J.-M. Rax and N. J. Fisch, J. Clean. Prod. 181, 1060 (2018) [5] J.-M. Rax, R. Gueroult and N. J. Fisch, Phys. Plasmas, 24, 032504 (2017) [6] J.-M. Rax, E. J. Kolmes, I. E. Ochs, N. J. Fisch and R. Gueroult, Phys. Plasmas, 26, 012303 (2019)

Speaker: R. Gueroult (EPS 2019)

365 P2.4003 Selective excitation of Kelvin-Helmholtz modes with rotating electric fields

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4003.pdf
The dynamics of a two-dimensional (2D) inviscid and incompressible fluid can be conveniently studied using a strongly-magnetized pure electron plasma confined in a PenningMalmberg trap, thanks to a mathematical analogy where the fluid velocity is equivalent to the plasma E × B velocity, and fluid vorticity and stream function correspond to plasma density and electrostatic potential, respectively [1]. Experimental investigations have shed light on dynamical features of the fluid flow ranging from the insurgence and decay of diocotron (KelvinHelmholtz) waves to the development of coherent structures and turbulence in conditions of free evolution and more recently also under the effect of an external forcing [2, 3, 4].
Typically, diocotron modes are excited applying multipolar static or oscillating electric fields on an azimuthally-sectored trap electrode, limiting the maximum mode wavenumber to Ns/2, with Ns the number of sectors. We have previously reported on a scheme that removes this limit on the accessible wavenumber, based on the application of suitable multipolar rotating electric fields with a drive frequency closely matching the frequency of the desired mode [5]. These earlier proof-of-principle measurements were affected by experimental limitations related to the plasma generation process [6]. We present now a systematic analysis of the phenomenon based on both theoretical and particle-in-cell simulation studies as well as on improved experiments exploiting an upgraded protocol for the preparation of the initial plasma configuration. We evaluate the mode growth rates, the broadening of resonances, and the presence of unwanted modes depending both on plasma properties like the initial density profile and on the drive amplitude and duration.
References
[1] C. F. Driscoll and K. S. Fine, Phys. Fluids B 2, 1359 (1990) [2] N. C. Hurst, J. R. Danielson, D. H. E. Dubin and C. M. Surko, Phys. Rev. Lett. 117, 235001 (2016) [3] M. Romé, S. Chen and G. Maero, Plasma Phys. Control. Fusion 59, 014036 (2017) [4] S. Chen, G. Maero and M. Romé, J. Plasma Phys. 83, 705830303 (2017) [5] M. Romé, G. Maero, N. Panzeri and R. Pozzoli, 45th EPS Conference on Plasma Physics, ECA 42A, P1.4003
(2018) [6] G. Maero, S. Chen, R. Pozzoli and M. Romé, J. Plasma Phys. 81, 495810503 (2015)

Speaker: M. Romé (EPS 2019)

366 P2.4004 Ion instability and off-axis equilibrium in a RF-sustained nonneutral plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4004.pdf
Penning-Malmberg traps are known and extensively used as unique tools for long-term charged particles storage, precise manipulation and measurement of trapped samples, creation of highquality bunched beams [1]. This array of opportunities results from decades of theoretical and experimental studies of the dynamical and equilibrium properties of nonneutral, magnetized plasmas as well as from an ever-increasing stretching of the concept, structure and operation of electro-magnetostatic traps themselves [2, 3]. In these terms, we have previously reported on experimental studies concerning the in-trap production of electron plasmas by background ionization due to a low-power radio-frequency (RF) excitation [4], an alternative way to the generation of electron samples to be used in studies of collective systems with interesting fluid analogues (e.g., fluid vortices and two-dimensional turbulence) [5, 6, 7].
Our previous measurement have led to the observation of stable states where a coherent vortex rotates around the longitudinal axis of the trap. This rotational motion (first diocotron mode) is resilient to typical perturbations and instability mechanisms (e.g., resistive-wall or ion-induced mode growth), which makes the control and manipulation of plasma properties unusually hard. In some cases the mode exhibits an amplitude modulation, accompanied by the periodic variation of the total number of electrons at the same modulation frequency [8, 9]. With a series of tailored experiments, we demonstrate how we can manipulate the vortex trajectory and simultaneously acquire key features (plasma charge, density profile, diocotron mode amplitude and frequency, temperature) finally leading us to a model of the off-axis equilibrium and stability.
References
[1] J. R. Danielson, D. H. E. Dubin, R. G. Greaves and C. M. Surko, Rev. Mod. Phys. 87, 247 (2015) [2] M. R. Natisin, J. R. Danielson and C. M. Surko, Phys. Plasmas 22, 033501 (2015) [3] A. P. Povilus et al., Phys. Rev. Lett. 117, 175001 (2016) [4] G. Maero, S. Chen, R. Pozzoli and M. Romé, J. Plasma Phys. 81, 495810503 (2015) [5] C. F. Driscoll and K. S. Fine, Phys. Fluids B 2 1359 (1990) [6] S. Chen, G. Maero and M. Romé, J. Plasma Phys. 83, 705830303 (2017) [7] N. C. Hurst, J. R. Danielson, D. H. E. Dubin and C. M. Surko, J. Fluid Mech. 848, 256 (2018) [8] B. Paroli, G. Maero, R. Pozzoli and M. Romé, Phys. Plasmas 21, 122102 (2014) [9] G. Maero, Il Nuovo Cimento C 40, 90 (2017)

Speaker: G. Maero (EPS 2019)

367 P2.4005 Supersolitary waves in electron-ion plasma?

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4005.pdf
The newly developed concept of supersolitary wave (supersoliton) describes a novel type of nonlinear localized structure. Its signature features are a very large amplitude in the electrostatic potential (pulse) and a characteristic wiggly structure in the associated electric field. Firstly, supersolitons were suggested in the context of four-species plasmas [1]. Further studies showed that they can exist even in three-species plasmas [2]. It has been argued that such a structure cannot occur in two-species (electron-ion) plasmas [3] based on fluid theory.
Our numerical investigation presented here, based on the kinetic approach using a VlasovPoisson simulation algorithm, provides evidence that supersolitary waves may indeed exit in two-species plasmas. Fig. 1 presents two different snapshots from our simulation results, at = 0 and at = 70 periods. Although our results suggest that these solutions remain stable during propagation, the observed structures fail to survive head-on collisions.

Figure 1: Two time snapshots are shown of the electron and ion distribution function(s) (first and second
row), the charge density (3rd row), the electric field (4th row) and the electrostatic potential (last row).
References
[1] A. E. Dubinov and D. Y. Kolotkov., IEEE Transactions on Plasma Science 40, 1429-1433 (2012) [2] F. Verheest, M. A. Hellberg, and I. Kourakis, Physics of Plasmas 20, 012302 (2013) [3] F. Verheest, G. S. Lakhina, and M. A. Hellberg, Physics of Plasmas 21, 062303 (2014)

Speaker: S. Hosseini Jenab (EPS 2019)

368 P2.4006 Analysis of sheath formation and charged species density in collisional electronegative warm plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4006.pdf
Plasma is a multi-component gas, composed of ions, electrons and neutrals. Therefore, collisions between different plasma species must be entertained. Moreover, energy and momentum are redistributed by their presence in the plasma. The presence of negative ions in the system has a huge impact on the characteristics of various quantities like sheath thickness, density and potential profile. Also, their presence plays a crucial role in semiconductor industries, microelectronics industries, plasma cleaning, plasma etching, plasma propulsion and plasma nitriding [1–3]. In this paper, we accomplished a mathematical model to examine the behaviour of charged species present in electronegative plasma under the effect of their finite temperature and collisions with neutral atoms. It is found that collisional parameter as well as temperature have an intense effect on the plasma species profile. These result in the modification of sheath structure and hence, the sheath thickness. In this proposed mathematical model, both the ions, i.e. positive ions and negative ions, are described by fluid equations considering their drift term with collisional and pressure gradient terms. Here, we considered the CF4 electronegative plasma [4], primarily composed of CF3+ and F- ions where former ions are produced by the ionization and later ions by the attachment of electrons with neutral CF4. Rate of detachment of electrons from F- ions, which results in reduction of negative ions, is also taken into consideration. Therefore, ionization, attachment and detachment frequencies are also included in proposed model to execute real behaviour of charge species. CF4 plasma is adopted because of its increasing applications in etching and film deposition processes.
References
O. Singh, H. K. Malik, R. P. Dahiya, and P. Kumar, Ceram. Int. 42, 18019 (2016). C. P. Fenili, F. S. de Souza, G. Marin, S. M. H. Probst, C. Binder, and A. N. Klein, Diam. Relat. Mater.
80, 153 (2017).
A. Aanesland, D. Rafalskyi, J. Bredin, P. Grondein, N. Oudini, P. Chabert, D. Levko, L. Garrigues, and G. Hagelaar, IEEE Trans. Plasma Sci 43, 321 (2015). O. V Proshina, T. V Rakhimova, A. T. Rakhimov, and D. G. Voloshin, Plasma Sources Sci. Technol. 19, 65013 (2010).

Speaker: R. Dhawan (EPS 2019)

369 P2.4007 Alterations in anode sheath behavior in a leaky DC discharge system

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4007.pdf
This paper reports the behavior of anode sheath in a planar dc discharge system brought about by changing the plasma boundary. Asymmetric parallel electrodes (anode dia. = 38 mm, cathode dia. = 76 mm, separation = 35 mm) were placed in a glass tube and covered by mica discs at the two ends of the glass tube. The whole assembly was placed in a stainless steel chamber. Both cathode and chamber were grounded. A small annular aperture in the mica disc was made on the anode side through which plasma can leak into the outer stainless steel chamber (partially exposed). Although no Negative Differential Resistance (NDR) region was observed in the current ­ voltage (Id -Vd) characteristics of the discharge in fully open or fully closed cases [1], an NDR (sudden increase in Id along with sudden drop in Vd) region is observed in partially exposed cases due to the plasma leaking into the stainless steel chamber. Typically, the NDR is triggered at a threshold value of Id which depends on the gas pressure (argon). Plasma parameters were estimated from Langmuir probe (LP) characteristics. Another interesting feature observed is that as Id and Vd increase monotonically from their initial values, a minute but sharp kink (a sudden, small increase (drop) in Id (Vd)) can be seen in the discharge characteristics. After the kink there is small reduction in the slope of the Vd versus Id characteristic that is indicative of an increase in the conductance of the circuit. It is believed that this behavior is due to the onset of additional paths for the plasma current due to leakage of plasma into the conducting chamber (extended cathode) outside, via the orifice in the mica cover. Overall, the steepness of the slope of the Vd versus Id characteristic indicates an ion sheath at the anode, even though there is a slight decrease in this slope after the kink. This is also borne out by the difference between the anode and the plasma potentials (through LP measurements). As Id is increased further, a second threshold is reached where the Id - Vd characteristics exhibit a pronounced NDR with voltage drops and current jumps of order 90 V and 7 mA respectively (at 1200 mTorr). It will be shown that after the NDR an electron sheath is formed at the anode and that the flipping from an ion to electron sheath is an outcome of the large current required to be supplied by the anode.

Reference:
[1] P. K. Barnwal, R. Narayanan, S. Kar, A Ganguli and R. D. Tarey, 6th PSSI Plasma Scholar Colloquium (PSC-2018), SMIT, Sikkim, India (2018).

Speaker: P.K. Barnwal (EPS 2019)

370 P2.4008 Characterization of a TE10-TM01 mode converter for microwave plasma interaction experiments.

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4008.pdf
An experimental system SYMPLE (System for Microwave Plasma Experiments) is developed to investigate interaction of high power microwave (HPM) with an over-dense plasma ( plasma > microwave) to address the physics of various linear and non-linear mechanisms related to wave absorption in plasma1. A washer-gun based pulsed (100 µs duration) plasma system1 has been developed for this purpose, having plasma density ne ~ 1x1018 m-3 and electron temperature ~ 10 eV. The HPM source is an S-band pulsed magnetron (3 GHz, 3.1 MW, 5 µs flat-top, TE10 mode), satisfying the condition ½ 0E2 /nekTe ~1 where E is the wave field, 0 is the free space permittivity, k is the Boltzmann constant and Te is electron temperature. The coupling between the HPM and Plasma is achieved with the help of WR 284 based coupling components. In order to have the wave launched to the experimental volume with E directed parallel to n(plasma density gradient), a TE10-TM01 mode converter is incorporated in the coupling scheme2. Prior to taking up experiments involving wave interaction with plasma, a low power (~ 20 dBm, 3 GHz) characterization of the TM01 mode output has been carried out first in free space, free of boundary effects, followed by experiments in the vacuum chamber which is a bounded media. The diagnostics used consist of a double ridge horn antenna, a D dot sensor and an isotropic electric field probe. The observed power and field distribution confirms effective TE10-TM01 mode conversion. A detailed account of the experiments and results will be presented in this paper.
References: 1 Anitha V. P., Priyavandana J. Rathod, Jayesh Raval, Renu Bahl and Y. C. Saxena, Rev. Sci. Instrum. 90, 013502(2019). 2 Anitha V. P., Priyavandana J. Rathod, Raj Singh and D V Giri, IEEE Transaction on Plasma Science, vol. 44,
2226(2016).

Speaker: P.J. Rathod (EPS 2019)

371 P2.4009 Electron Temperature Control in a Double Plasma Device by Selective Charging of Multi Grid Assembly

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4009.pdf
A double plasma device comprising of two isolated SS304 chambers namely, source and target plasma chambers is used to develop understanding on mechanism involved in realizing a control on electron temperature in the target region. Electron temperature is controlled locally as well as radially by charging a single grid and by charging radially, different regions of a multiple grid assembly. Unmagnetized plasma is produced in the grounded source chamber at a fill Argon pressure of 3 x 10-4 mbar by applying a bias voltage of -70V with respect to a multi filamentary plasma source. The target chamber receives primarily the diffused plasma from the source chamber. The role of floating and biased grids, grid transparency and Debye screening are investigated in the two chambers for the control on plasma parameters. Observations with floating grid demonstrate significant reduction of ~ 50% and 70% in electron temperature and plasma density respectively in the target region. For two different grid bias ranges, plasma cooling and heating is observed in the target region. Plasma cooling is seen for a grid bias between - 25 to 0 V and plasma heating for 0 to +15V for grid( mesh size =0.8mm) without really disturbing the source plasma. More prominent heating is observed for larger mesh sized grids. We have successfully established a correlation between mesh size and control on plasma parameters and have shown that control is more prominent when the ratio of source to target density is maximum. The EEDF analysis depicts suppression and enhancement of energetic electrons for the cooling and heating grid bias domains. We expanded this concept for realizing a radial control of electron temperature by charging differently a cassette of radially separated, isolated concentric multiple grids for the two bias ranges. Using this concept, a radial control on electron temperature with gradient scale length of 10cm is achieved. Detailed results on developed understanding on the
mechanism involved will be presented in the conference. References:
[1] R. J. Taylor, K. R. MacKenzie, and H. Ikezi, Review of Scientific Instruments 43, 1675 (1972); [2] Kohgi Kato, Satoru Iizuka, and Noriyoshi Sato, Applied Physics Letters 65, 816 (1994). [3] K. H. Bai, J. I. Hong, S. J. You, and H. Y. Chang, Phys. Plasmas 8, 4246 (2001).

Speaker: P. Alex (EPS 2019)

372 P2.4010 Hamiltonian Formulation of the Non-perturbative Guiding Centre Equation

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4010.pdf
Guiding Centre theory refers to the problem of finding an exact description for the motion of a charged particle in a given magnetic field. Recently, a new, exact, approach to guiding centre theory has been proposed [1], [2]. In this new approach the guiding centre is defined geometrically as the reference frame in which a particle moves in a closed orbit. Then exact equations are derived, for the motion of the particle in this reference frame, and for the motion of the origin of the reference frame in the laboratory frame. In this work we propose a hamiltonian formulation of these equations, even in the relativistic regime.
References
[1] C. Di Troia, Phys. Plasmas 22, 042103 (2015) [2] C. Di Troia, Journal of Modern Physics 09, No.04 (2018)

Speaker: L. Valvo (EPS 2019)

373 P2.4011 BO: A Unified Tool for Plasma Waves and Instabilities Analysis

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4011.pdf

A unified numerically solvable framework for dispersion relations with an arbitrary number of species drifting at arbitrary directions and with Krook collision is derived for linear uniform/homogenous kinetic plasma, which greatly extended the standard one [say, T. Stix, {\em Waves in Plasmas}, AIP Press, 1992]. The purpose of this work is to provide a kinetic plasma dispersion relation tool not only the physical model but also the numerical approach be as general/powerful as possible. As a very general application example, we give the final dispersion relations which assume further the equilibrium distribution function be bi-Maxwellian and including parallel drift, two directions of perpendicular drift (i.e., drift across magnetic field), ring beam and loss-cone. Both the electromagnetic and electrostatic versions are provided, with also the Darwin (a.k.a., magnetoinductive or magnetostatic) version. The species can be treated either magnetized or unmagnetized. Later, the equations are transformed to the matrix form be solvable by using the powerful matrix algorithm [H. S. Xie and Y. Xiao, Plasma Science and Technology, 18, 2, 97, 2016], which is the first approach can give all the important solutions of a linear kinetic plasma system without requiring initial guess for root finding and thus can be extremely useful to the community. To the best of our knowledge, the present model is the most comprehensive one in literature for the distribution function constructed bases on Maxwellian, which thus can be applied widely for study waves and instabilities in space, astrophysics, fusion and laser plasma. We limit the present work to non-relativistic case.

Speaker: Huasheng Xie (EPS 2019)

374 P2.4012 Experimental investigation of the ordinary wave anomalous absorption in the plasma filament

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4012.pdf
A number of effects, such as anomalous backscattering and anomalously ion acceleration, observed in experiments on electron-cyclotron resonant heating (ECRH) in magnetic fusion toroidal devices [1-2] are not explained within the conventional linear theory. The theoretical model proposed in [3] explains the anomalous backscattering as a result of the two upperhybrid (UH) plasmon parametric decay (TUHPD) instability possessing very low threshold due to trapping of excited plasmons in the vicinity of the density maximum. Model experiments [4] have shown that the anomalous absorption in a plasma filament related to the TUHPD instability can reach 80%. A similar situation, which can occur in the case of ordinary pump wave polarization, is under investigation in the present paper. A plasma filament is created by RF power (~ 100 W, frequency ~ 27 MHz) in a quartz tube (inner diameter 2.2 cm) filled with argon at a pressure of about 1-2 Pa and placed in magnetic field of up to 45 mT. The maximal average plasma density in the filament is slightly exceeding 2×1010 cm-3 and electron temperature is about 1 eV. The tube with plasma passes through a waveguide with a cross section of 7.2×3.4 cm2 perpendicular to the wide wall. Microwave pulses (power up to 200 W) at a frequency of 2.35 GHz significantly exceeding the ECR and UH frequencies are incident along the waveguide onto the plasma in ordinary polarization. At the pump power exceeding a threshold of about 30 W the strong (30-35%) anomalous absorption of the incident power in a plasma filament is observed leading to decrease of the transmitted and reflected microwave power and to the growth of plasma luminosity. Dependence of the effect on the magnetic field, plasma density and microwave power as well as the microwave plasma emission is investigated. The observed effect is explained by decay of the pump wave into two electron plasma waves possessing frequencies smaller than electron cyclotron one.
Financial support of the of the RFBR grant 18-52-00010 and BRFBR grant F18R-040 is acknowledged.
[1] S.K. Nielsen, M. Salewski, et al., Plasma Phys. Control. Fusion 55, 115003 (2013) [2] S. Coda for the TCV Team, Nucl. Fusion 55, 104004 (2015). [3] E.Z. Gusakov and A.Yu. Popov, Physics of Plasmas 23, 082503 (2016) [4]A.B. Altuhov et al., Europhysics Letters, 2019, to be published.

Speaker: L. Simonchik (EPS 2019)

375 P2.4013 Automodel solutions for nonlocal transport by Lévy walks in plasmas

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4013.pdf
The phenomena of nonlocal (superdiffusive) transport are closely related to long-free-path carriers, called «Lévy flights» by B. Mandelbrot (see [1] and references therein). The processes of non-local transport with account of the finite velocity of carriers (i.e. of the retardation effect) are called «Lévy walks» [2, 3], including the scattering of carriers with account of their trapping (e.g., absorption and re-emission) («Lévy walk + rests», see Fig. 1 in [3]). It was shown for the Green function of non-stationary superdiffusive transport by Lévy flights that a wide class of perturbation transfer phenomena in a homogeneous medium has an approximate automodel (self-similar) solution [4, 5]. A generalization of this approach to the case of finite velocity of carriers is given in [6].
Here it is shown that the method of obtaining an approximate automodel solution for non-stationary transport by Lévy flights and «Lévy walks» has a wide range of applicability in laboratory and space plasma physics. Necessity to take into account the finite velocity of carriers means that the phenomenon belongs to the «Lévy walks». The phenomenon of nonlocality (superdiffusion) for the transport of electromagnetic (EM) waves in plasmas can be realized in the coexistence mode of (i) local (diffusive, Brownian) trapping of a carrier by strong fluctuations of scatterer's density and (ii) distant flights of a carrier between events of local trapping. Such a transport mode can be realized in (a) the propagation of diagnostic EM waves in a magnetized turbulent laboratory plasma; (b) nonlocal transport of heat and particles in such a plasma; (c) scattering of radio waves from pulsed sources (flares) in the interstellar medium. The paper presents approximate automodel solutions for some examples from the indicated class of non-local transport phenomena. References
[1]. Shlesinger M, Zaslavsky G M and Frisch U (ed) 1995 Lévy Flights and Related Topics in Physics (New York: Springer).
[2]. Shlesinger M F, Klafter J, and Wong J 1982 J. Stat. Phys. 27, 499. [3]. Zaburdaev V, Denisov S and Klafter J 2015 Lévy walks Rev. Mod. Phys. 87, 483. [4]. Kukushkin A B and Sdvizhenskii P A 2016 J. Phys. A: Math. Theor. 49 255002. [5]. Kukushkin A B, Neverov V S, Sdvizhenskii P A and Voloshinov V V 2018 Atoms 6(3) 43. [6]. Kukushkin A B, Kulichenko A A 2018 Preprint https://arxiv.org/abs/1812.08871.

Speaker: A.A. Kulichenko (EPS 2019)

376 P2.4014 Cross-field chaotic transport of electrons by E X B electron drift instability in Hall thruster

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4014.pdf
In Hall thruster geometry, the electric and magnetic field configuration creates a huge difference in drift velocity between electrons and ions, which generates electron cyclotron drift instability or E × B electron drift instability[1]. Unstable modes generated from this instability have an important role in cross-field anomalous transport of electrons. One special interest for the industrial development of Hall thruster is characterizing the anomalous cross-field electron transport observed after the channel exit. Since the ionization efficiency is more than 90%, the neutral atom density in that domain is so low that the electron collisions cannot explain the high electron flux observed experimentally. Here we are focusing on collision-less chaotic transport of electrons by the E × B drift instability generated unstable modes.
The dynamics of electrons are studied numerically in a slowly time varying (w c) potential profile in presence of a constant axial electrostatic field E and a radial magnetic field B, using Boris numerical integration scheme. The time varying potential is associated with the unstable modes generated by E × B drift instability which follow a dispersion relation [1] and their frequencies w are very small compared to the gyration frequency c. In presence of those unstable electrostatic modes, the electron trajectories become chaotic, whereas without the wave they are regular with a constant drift motion along E × B direction. We consider a Cartesian coordinate system with x along B direction, y along E × B direction and z along E direction. Their y- and z-components of velocity vy and vz, respectively, oscillate with the gyration frequency. vy oscillates around the drift velocity vD. Since the background electrostatic wave, in the x - y plane, has very slow phase velocity (w/k vD), the electrons strongly interact with the background electrostatic wave when their vy becomes very small, vy w/k. Depending upon the interaction time they exhibit different dynamical behaviours. During the interaction, their x-component of velocity (vx) suddenly changes to higher/lower velocity which depends on the potential of the wave at the particle location, and if the bounce frequency is larger than the gyration frequency be c, sometimes the electrons are trapped within the potential deep and again with increase of vy they become untrapped. Due to this strong interaction, their motion becomes chaotic. We characterize this three dimensional chaotic motion and associated transport in the perpendicular direction.

[1] T. Lafleur, S. D. Baalrud and P. Chabert, Phys. Plasmas 23, 053503 (2016)

Speaker: D. Mandal (EPS 2019)

377 P2.4015 Energy parameters of Cs-Ba triode in the unstable discharge mode

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4015.pdf
Low-temperature plasma finds a wide practical application in devices used in the current control circuits of space and ground-based nuclear power plants: modulators, thermionic converters, current and voltage stabilizers and etc. One of the most important requirements for devices of such appointment is the ability of troubleproof work under conditions of high temperature and considerable radiation load [1].
The paper presents the results of studies of the electrokinetic parameters of Cs-Ba vapor triode modulators. The possibility of effective current modulation due to the development of nonlinear plasma structures formed during the excitation of the BursianPierce instability is discovered. Potential distribution with a virtual cathode is formed, which leads to a current breakage. The current changes almost instantly, since the process of the formation of a virtual cathode proceeds over a time of the order of the electron mean free time through the gap, what is important for the successful practical use of triode modulators.
The achieved high transition process rates had a positive effect on the efficiency and frequency characteristics of the device. A high electric strength has been realized, which makes possible to keep the triode in the locked state after a current breakage for a long time. In the considered operating regimes the role of the grid is reduced to maintaining the locked state, ensuring high electrical strength and reigniting the discharge. High energy parameters of triode modulators were achieved:
- at an interelectrode gap of 4 mm and Ps 10­2 torr, the values of current density were up to 100 A/cm2, the voltage losses in the open state were in the range of 0.8­2.5 V;
- stably modulated power of 1.8 kW/cm2 with an efficiency of more than 95%; - modulator operating modes were found in which, with an increase in the density of the modulated current, energy consumption in the grid circuit falls. With an anode voltage of 50 V, a stable modulation was obtained at frequencies of 1-10 kHz with a specific electric power of 5 kW/cm2 and an efficiency of more than 95%. References
[1] Mustafaev, A.S. Low-voltage beam discharge in light inert gases to solve problems of voltage stabilization / A.S. Mustafaev, A.Y. Grabovskiy - High Temperature. - 2017. - Vol. 55, 1. - pp. 20-26.

Speaker: A. Mustafaev (EPS 2019)

378 P2.4016 Apparatus for investigating non-linear microwave interactions in magnetised plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.4016.pdf
In many plasma applications, electromagnetic (EM) waves are key to providing energy. Plasmas can demonstrate complex dynamics when exposed to multiple EM signals. Raman coupling (by Langmuir oscillation) or Brillouin scattering (through ion-acoustic waves) are important in laser plasma interactions: Microwave beams can be formed at normalised intensities comparable to those used some laser plasma interactions, and can interact in tenuous, cool and accessible plasmas potentially enhancing insight into the plasma dynamics. Magnetic confinement fusion physics may directly benefit from multifrequency microwave interaction in plasma to access, for example, cyclotron and hybrid resonances in dense plasma, either for heating or current drive.
Building on earlier research investigating geophysical cyclotron wave emissions [1,2], a new "linear plasma" experiment is under construction to test multifrequency microwave interactions in magnetised plasma. The magnetic field will reach up to 0.05T, and the plasma will be created by a helicon wave launched from an RF antenna. This will produce a large, dense, cool plasma with potential for a high ionisation fraction. Fixed frequency, and wideband sources and amplifiers will provide microwave beams for the multi-signal interaction experiments. The paper will present progress on this system.
The authors gratefully acknowledge support from the EPSRC, MBDA UK Ltd and TMD Technologies Ltd.
[1] Ronald K., Speirs D.C., McConville S.L., Phelps A.D.R., Robertson C.W., Whyte C.G., He W., Gillespie K.M., Cross A.W., Bingham R., 2008, Phys. Plasmas, 15, art.056503
[2] Speirs D.C., Bingham R., Cairns R.A., Vorgul I., Kellett B.J., Phelps A.D.R., Ronald K., 2014, Phys. Rev. Lett., 113, art 155002

Speaker: R. Bingham (EPS 2019)

16:00 Coffee Break

BPIF

Convener: L. Willingale (University of Michigan)

379 I2.201 Correlated emission of electrons and XUV harmonics via relativistic surface plasmons

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.201.pdf

Experiments of laser-solid interaction at ultra-high contrast have recently demonstrated the possibility of exciting resonant propagating surface plasmons at relativistic intensities (> 10^18 W/cm^2) on solid grating targets [1]. Not only this encourages the development of a suitable theoretical description of plasmonic phenomena in such a non-linear regime, but it also allows exploring the properties of the radiation sources raised by SP excitation.
In particular, the SP field accelerates dense bunches of collimated electrons up to few MeV of energies along the surface of the laser-irradiated target [2]. This process is correlated in the same direction with a bright emission of high order harmonics of the laser frequency [3]. Experimentally, we have investigated some of the parameters of the laser-grating interaction that optimize both emissions (shape and material of the grating, formation of a controlled preplasma at its surface). 2D PIC simulations not only reproduce the experimental results but also highlight a spatio-temporal correlation between accelerated electrons and harmonics that gives insight on the generation mechanism of the XUV beam. Future work is now centred both on the optimization of the radiation sources in view of possible applications, and on the adaptability of new concepts and plasmonic configurations from the linear to the relativistic regime. In this context, a scheme for exciting few-cycles SPs with rotating wavefront laser pulses has been demonstrated numerically [4].

References
[1] A. Macchi, Physics of Plasmas 25, 031906 (2018).
[2] L. Fedeli et al., Physical Review Letters 116, 015001 (2016). G. Cantono et al., Physics of Plasmas 25,
031907 (2018).
[3] G. Cantono et al., Physical Review Letters 120, 264803 (2018).
[4] F. Pisani et al., ACS Photonics 5 (3), 1068-1073 (2018).

Speaker: G. Cantono (EPS 2019)

380 I2.202 Hard X-ray sources using a picosecond laser driven plasma accelerator

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.202.pdf

X-ray photon beams in the keV to MeV energy range are essential to study high energy density (HED) matter and to improve the understanding of inertial confinement fusion and astrophysical systems. HED experiments produce highly transient matter under extreme states of temperatures and pressures and it is essential to develop light sources that are: in the hard x-ray energy range (0.01-1 MeV), directional, high-yield, low-divergence, and short-duration (ps and sub-ps). In this work we show that by using a laser plasma accelerator (LPA) driven by a kJ-ps class laser it is possible to generate a broadband (0.01-1 MeV) hard x-ray source that satisfies the previous requirements. A series of experiments were conducted on the Titan laser at Lawrence Livermore National Laboratory where a >10 nC electron beam in the 10-400 MeV energy range was generated through LPA. The electrons generate x-rays via their betatron motion (few-30 keV) [1,2] and hard x-rays rays through inverse Compton scattering [3] (10-300 keV) and/or Bremsstrahlung [4] (up to 100 MeV). Due to its unique characteristics this source can be an important tool on large-scale international laser facilities opening up the prospect for many applications.

[1] N. Lemos, et al, Plasma Phys. Control. Fusion 58, 034018 (2016)
[2] F. Albert, N. Lemos et al, Phys. Rev. Lett. 118, 134801 (2017)
[3] N. Lemos, F. Albert et al, submitted to Phys. Rev. Lett.
[4] N. Lemos, F. Albert et al, Plasma Phys. Control. Fusion 60, 054008 (2018)

Speaker: N. Lemos (EPS 2019)

381 O2.201 Efficient generation of atto-pulses and positrons at the interaction of ultra-intense laser radiation with the shaped targets

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.201.pdf

Recently we have proposed an efficient scheme of generation of short dense electron bunches and atto-pulses during the interaction at large angles of incidence of a laser pulse with a limited foil target [1]. Later [2], the generation of high-intensity atto-pulses has been investigated also in a hollow cone-like target. We found the source and direction of the coherent radiation that ensures the existence of atto-pulses. Since the laser pulse reflected from plasma inherently contains low-order harmonics, a second reflection from a fresh plasma surface leads to the increase of spectral intensity. In [3], we have made an extensive study of multiple reflections of a short pulse between two solid density plasma walls at oblique incidence, with the help of PIC simulations. It is shown that even in the weakly relativistic regime the intensity of high harmonics can be amplified by three orders of magnitude with help of this method. Increasing the photon energy from the x-ray to gammaray regime makes probing of extremely small space-time domains accessible. In [4] we proposed the mechanism for generating attosecond gamma photon and positron bunches with small divergence using laser intensities below 10^23W/cm^2 which will become reachable at the ELI. In contrast with previous works, in our scheme a single laser pulse is sufficient instead of two counterpropagating pulses. Numerical simulations are used to formulate the conditions for confined radiation and to characterize the generated photon and positron bunches. The threshold intensity for the generation of a significant number of positrons is shown to be in the order 10^22 Wcm^-2, when optimal target properties, as presented in [5], are considered. With the help of a modified particle-in-cell code, the detailed angular-energy distribution of positrons is presented, which is in good agreement with our analytical model.

References
1. A. Andreev, K. Platonov Optics and Spectroscopy 114, 788( 2013)
2. Z. Lecz, A. Andreev, Phys Rev E 93, 013207 (2016)
3. Z. Lech, A. Andreev Journal of the Optical Society of America B 35, A51 (2018)
4. Z. Lech, A. Andreev Phys. Rev. E 99, 013202 (2019)
5. Z. Lech, A. Andreev Plasma Physics and Controlled Fusion (2019)

Speaker: A. Andreev (EPS 2019)

382 O2.202 Powerful electromagnetic emission from a plasma with counterstreaming different-size electron beams

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.202.pdf

It was found recently [1] that counterpropagating plasma wakefields driven by a pair of femtosecond laser pulses with different transverse structures can produce powerful and narrowband EM emission near double plasma frequency. Such a nonlinear process can proceed in a homogeneous plasma, does not require the creation of superstrong magnetic fields, and is not sensitive to the effect of plasma screening. Therefore, using this scheme, it is possible not only to significantly increase the power and energy of THz pulses (up to 1 GW and 10 mJ) but also to provide a small width of the frequency spectrum (1%).
In order to excite colliding plasma waves more efficiently and increase the duration of the intense THz generation, we propose [2] to use kiloampere relativistic electron beams of picosecond and nanosecond duration instead of femtosecond laser drivers. Such beams can reach the high level of power (tens of GW) and are able to continuously pump plasma waves at ionic times via the two-stream instability. Our PIC simulations for the collision of low-density beams with different transverse sizes show that the produced radiation is characterized by a narrow line-width (~1%), and its power enables reaching several percent of the total beam power. It is also found that the same radiation mechanism can work with the close efficiency in a system of dense electron beams with initial equal sizes. In such a system, different beam density shapes and different amplitude profiles of excited waves are automatically produced by the filamentation instability. This new emission mechanism cannot only produce gigawatt-class narrow-band THz radiation by multi-gigawatt electron beams typical for linear induction accelerators, but also play the role in a natural beam and plasma environments such as type II and type IV solar radio-bursts in which emission regions may contain counterstreaming electron populations.
This work is supported by the RFBR grant 18-32-00107.

References
[1] Timofeev, I. V., Annenkov, V. V., & Volchok, E. P. (2017). Physics of Plasmas, 24(10), 103106.
[2] Annenkov, V. V., Berendeev, E. A., Timofeev, I. V., & Volchok, E. P. (2018). Physics of Plasmas, 25(11), 113110.

Speaker: V. Annenkov (EPS 2019)

383 O2.203 High resolution imaging of transition radiation emitted from resonantly accelerated electrons from relativistic laser matter interaction

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.203.pdf

At focused intensities above 10^18 W/cm^2, a laser pulse accelerates bunches of electrons into a solid target by the v x B component of the Lorentz force. These bunches are separated by half the laser period and hence emit visible light by coherent transition radiation (CTR) at twice the laser frequency (20) as they escape the rear surface of the target. CTR was measured in a previous experiment using short pulse lasers focused to relativistic intensities of the order of 6 x 10^19 W/cm^2[1]. The results indicated that about 1% of laser energy is converted into the kinetic energy of these resonantly accelerated electrons and that the resonantly accelerated electrons are highly collimated as they traverse the solid target.
Recent experiments at the PEARL laser facility at Nizhny Novgorod (10 - 20 J, 60 fs, I > 10^20 W/cm^2) extended previous results to higher intensities. CTR emission at 20 was measured from the rear side of Al foils of thickness ranging from 10 - 100 µm using an f /2 off-axis parabola imaging mirror which provided a spatial resolution of about 2 µm. The results from the CTR diagnostic indicate that the resonantly accelerated electrons are highly collimated and have a mean energy of about 30 MeV. In situ measurement of K-shell spectra from Al ions revealed that the plasma at the focus is extremely dense and hot (ni 10^22/cm^3, Te 400 eV).
Understanding the generation and transport of these collimated bunches of high energy electrons is important for laser driven ion acceleration schemes. Additionally, these collimated electrons can be harnessed to develop hard X-ray sources from table top lasers.
Our work is supported by Czech Science Foundation project 18-09560S.

References
[1] J. J. Santos, A. Debayle, Ph. Nicolaï et al, Phys Plasmas 14, 103107 (2007)

Speaker: D. Kumar (EPS 2019)

BSAP

Convener: S. Servidio (University of Calabria! Italy)

384 I2.J801 Energetic Particle Scattering in Solar Flares

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J801.pdf

Efficient particle acceleration is produced in association with solar flares. These particles play a major role in the active Sun because they contain a large amount of the magnetic energy released during flares. Energetic electrons and ions interact with the solar atmosphere and produce high-energy X-rays and -rays. Energetic particles can also escape to the corona and interplanetary medium, produce radio emissions (electrons) and may eventually reach the Earth's orbit. It is currently admitted that solar flares are powered by magnetic energy previously stored in the coronal magnetic field and that magnetic energy release is likely to occur on coronal currents sheets along regions of strong gradient of magnetic connectivity. In this talk, I will review our current understanding of particle acceleration and transport in solar flares and comment on the role of scattering in these processes. I will also present recent results on the transport of energetic electrons in the solar corona obtained from X-ray and radio (gyro-synchrotron) imaging spectroscopy and will show how these observations support electron diffusive transport in the corona. Radio emissions from escaping electron beams (known as type III bursts) result from the interaction of the beams with the background plasma resulting in the excitation of Langmuir waves and subsequent production of electromagnetic radiation. Recent results on the simulations of these emissions and on the relation between escaping electrons that generate radio emissions in the corona and in the interplanetary medium and electrons confined to the lower atmosphere of the Sun that produce HXRs will be discussed. I will finally describe how these studies can be continued in the future using measurements from the new solar and heliospheric missions.

Speaker: N. Vilmer (EPS 2019)

385 I2.J802 Thermal non-equilibrium in solar coronal loops: from coronal rain to long-period intensity pulsations

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J802.pdf

The complex interaction of the magnetic field with matter is the key to some of the most puzzling observed phenomena at multiple scales across the universe, from tokamak plasma confinement experiments in the laboratory to the filamentary structure of the interstellar medium. King among these is the phenomenon of coronal heating. The solar corona is the outer layer of the Sun's atmosphere and, like most stars in the universe, it is permeated by closed magnetic structures called coronal loops filled with plasma at multi-million-degree temperatures, hundreds of times hotter than the underlying photosphere, the Sun's surface. Detecting heating mechanisms in action has proved very difficult, particularly because of the lack of resolution in hot lines of current instrumentation and also because the coronal magnetic field is largely unknown.
However, the corona also conceals a cooling problem. Indeed, recent observations indicate that, even more mysteriously, like snowflakes in the oven, the corona hosts large amounts of cool material termed coronal rain, hundreds of times colder and denser, that constitute the seed of the famous prominences. Numerical simulations have shown that this cold material does not stem from the inefficiency of coronal heating mechanisms, but because of the specific spatiotemporal properties of these. As such, a large fraction of coronal loops is suspected to be in a state of thermal non-equilibrium, characterised by heating and cooling cycles whose telltale observational signatures are long-period intensity pulsations in hot lines and periodic coronal rain in cool lines, now ubiquitously observed. In this talk, I will present this yet largely unexplored strong connection between the observed properties of cool material and the coronal heating mechanisms, which constitutes a new, rapidly growing field of solar physics.

Speaker: P. Antolin (EPS 2019)

386 I2.J803 3D anisotropy of turbulence in the solar wind

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J803.pdf

The solar wind is a supersonic turbulent flow that spreads out radially form the Sun. Several spacecrafts explored different regions of the Heliosphere and provide us in-situ data of plasma and electromagnetic fluctuations from daily to sub-second scales. The solar wind can be though as a wind tunnel in which spacecrafts serve as probes, making it a unique astrophysical laboratory for turbulence studies. However, measurements are basically limited to one direction in space and the spherical expansion of the flow introduces important modifications in the energetic and in the symmetry properties of turbulent fluctuations. I will first give a brief overview of observations at scales larger than the proton scales to highlight the most important features of solar wind turbulence and the limitations of measurements, as compared to an idealized wind-tunnel experiment. I will then present results from numerical simulations of magnetohydrodynamic (MHD) turbulence that account for the solar wind expansion and can be used to complement observations and can help interpreting some of the aspects of solar wind turbulence, in particular its anisotropy.

Speaker: A. Verdini (EPS 2019)

387 O2.J801 A Laboratory Model for the Parker Spiral and Solar Wind

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.J801.pdf

In 1958, Eugene Parker first predicted the existence of the supersonic solar wind [1], which was subsequently verified by early spacecraft missions [2]. He also theorized how this solar wind interacts with the dynamo-generated magnetic field of the Sun - carrying the magnetic field lines away from the star, while their footpoints are frozen into the corona and twisted into an Archimedean spiral by stellar rotation. This magnetic topology is now known as the Parker spiral and is the largest magnetic structure in the heliosphere. The transition between magnetic field corotating with a star and the field advected by the wind is thought to occur near the so-called Alfvén surface - where inertial forces in the wind can stretch and bend the magnetic field. According to the governing equations of magnetohydrodynamics, this transition in a magnetic field like the Sun's is singular in nature and likely highly dynamic. However, this region has yet to be observed in-situ by spacecraft or in the laboratory, but is presently the primary focus of the Parker Solar Probe mission [3, 4]. Here we show, in a synergistic approach to studying solar wind dynamics, that the large scale magnetic topology of the Parker spiral can also be created and studied in the laboratory. By generating a rotating magnetosphere with Alfvénic flows, magnetic field lines are advected into an Archimedean spiral, giving rise to a dynamic high- current sheet that undergoes magnetic reconnection and plasmoid ejection. These plasmoids are born near the Alfvén surface, at the tip of the helmet streamer cusp, and carry blobs of plasma outwards at super-Alfvénic speeds, mimicking the dynamics of unstable coronal helmet streamers, which fuel much of the slow solar wind [5].

*The author would like to acknowledge DOE, NSF, and NASA for their support throughout this investigation.

References
[1] E.N. Parker, Dynamics of the Interplanetary Gas and Magnetic Fields, The Astrophysical Journal 128, 664 (1958)
[2] M. Neugebauer and C.W. Snyder, Solar Plasma Experiment, Science 138, 1095-7 (1962)
[3] N.J. Fox et al., The Solar Probe Plus Mission: Humanity's First Visit to Our Star, Space Science Reviews 7-48
[4] A. Szabo et al., Flying into the Sun, Nature Astronomy, 2, 829 (2018)
[5] G. Einaudi, P. Boncinelli, R.B. Dahlburg, J. Karpen, Formation of the slow solar wind in a coronal streamer,
Journal of Geophysical Research: Space Physics 104, 521-534 (1999)

Speaker: C. Forest (EPS 2019)

388 O2.J802 Determination of plasma physical properties across collisionless shocks driven by solar eruptions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.J802.pdf

Over the last decades the availability of continuous observations of the solar atmosphere (the corona) from space allowed to study in great details solar eruptions, namely Coronal Mass Ejections (CMEs; see review by Webb & Howard 2012). For major CMEs it was shown (Vourlidas et al. 2003; Ontiveros & Vourlidas 2009) that coronagraphic observations acquired in Visible Light (VL) band contain faint arch-shaped intensity increases surrounding the eruption front (Figure 1), that have been identified as compression fronts due to CME-driven interplanetary shock waves. This talk will review recent results on the physics of CME-driven shocks as obtained with the analysis of VL and UV coronagraphic images, EUV full disk images, combined with radio dynamic spectra and MHD numerical simulations.
Combination of these data allowed us to infer unique information on the plasma across the shock surface, such as the density compression ratio (Bemporad & Mancuso 2010), but also the Alfvénic Mach numbers and the magnetic field compressions all along the shock fronts (Bemporad et al. 2016; Susino, Bemporad & Mancuso 2015; Frassati et al. 2019); the reliability of these results has been also tested with numerical MHD simulations (Bacchini et al. 2015).

Bacchini, F., Susino, R., Bemporad, A., Lapenta, G., The Astrophysical Journal, Vol. 809, Issue 1, id. 58, 2015.
Bemporad, A., & Mancuso, S., The Astrophysical Journal, Vol. 739, Issue 2, id. L64, 2011.
Bemporad, A., & Mancuso, S., The Astrophysical Journal, Vol. 720, Issue 1, 2010.
Bemporad, A., Susino, R., Frassati, F., Fineschi, S., Frontiers in Astron. & Space Sciences, Vol. 3, id.17, 2016.
Frassati, F., Susino, R., Mancuso, S., Bemporad, A., The Astrophysical Journal, Vol. 871, Issue 2, id. 212, 2019.
Ontiveros, V., & Vourlidas, A., The Astrophysical Journal, Vol. 693, Issue 1, 2009.
Susino, R., Bemporad, A., & Mancuso, S., The Astrophysical Journal, Vol. 812, Issue 2, id. 119, 2015.
Vourlidas, A., Wu, S. T., Wang, A. H., et al., The Astrophysical Journal, Vol. 598, Issue 2, 2003. Webb, D. F., & Howard, T. A., Living Reviews in Solar Physics, Vol. 9, Issue 1, article id. 3, 2012.

Speaker: A. Bemporad (EPS 2019)

LTDP-MCF

Convener: J Benedikt (Asociaci__n EURATOM-CIEMAT)

389 I2.J701 Tailored Voltage Waveforms as a new RF excitation technique for unique plasma processing

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J701.pdf

Since the pioneering work of the Bochum team on exciting plasmas with non-sinusoidal "Tailored" Voltage Waveforms and generating an Electrical Asymmetry Effect [1], the complexity and power of this technique has come into clearer focus. By decoupling the ion bombardment energy from the ion and radical flux at the surface, one can gain great insight into links between process parameters and outcomes. Going further, such asymmetric excitation allows us to gain access to internal constants (such as ion transport coefficients and reaction cross-sections) that are often hidden when exciting plasma symmetrically, allowing one to generate more accurate numerical models [2]. A specific subset of these waveforms, resembling sawtooths, has recently attracted particular attention ([3][4]), due to what has been dubbed the "slope asymmetry" effect, wherein they create an asymmetric ionization profile in the plasma that depends strongly on the electronegative character of the plasma ([5],[6]), as shown in figure 2 (from [5]). The location of the ionization peak is very sensitive to the electron heating mode (and thus linked to the electronegativity of the plasma). Such waveforms can therefore be used to determine the dominant heating mode under varying plasma conditions [7,8]. Finally, combining such unusual excitation with certain gas chemistries allows one to perform completely new processes, such as selective deposition, wherein a given plasma process occurs on one electrode but not the other.

[1] J Schulze, E Schungel and U Czarnetzki, J. Phys. D: Appl. Phys. 42 (2009) 092005
[2] J-M. Orlac'h et al, Plasma Sources Sci. Tech. https://doi.org/10.1088/1361-6595/ab067d.
[3] B Bruneau et al, Plasma Sources Sci. Technol. 24 (2015) 015021.
[4] B. Bruneau et al Phys. Rev. Lett. 114 (2015) 125002.
[5] B Bruneau et al, Plasma Sources Sci. Technol. 25 (2015) 01LT02.
[6] B. Bruneau et al, J. Appl. Phys 119, 163301 (2016).
[7] G Fischer et al, Plasma Sources Sci. Technol. 27 (2018) 074003.
[8] J. Wang and E.V. Johnson, Plasma Sources Sci. Technol. 26 (2017) 01LT01.

Speaker: E.V. Johnson (EPS 2019)

390 I2.J702 Low pressure plasma deposition of nanotextured metal and metal oxide thin films for catalytic applications

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J702.pdf

Nanotextured metal and metal oxide thin films are of interest for an increasing number of catalytic applications ranging from fuel cells to photoelectrochemical water splitting, from photochemical wastewater treatment to biodiesel production. The need for enhanced performance and versatility has correspondingly stimulated the development of thin film materials combining suitable chemistry and morphology. In this talk, we will present some examples of catalytic layers developed in our laboratory. In the context of fuel cells, a single-step process combining Plasma Enhanced- Chemical Vapour Deposition (PE-CVD) of hydrocarbons or fluorocarbons and RF sputtering of platinum, is used to obtain nanocomposite polymer/metal films with controlled dispersion of catalyst nanoparticles. The versatility, as well as, the limitation of such process in terms of catalyst performance will be discussed. Our recent work focuses on the sputter deposition of nanotextured iron oxide thin films as catalysts for photoelectrochemical water splitting. A complete chemical, structural, morphological, optical and photoelectrochemical characterization will be presented. Finally, we will also explore the use of such metal oxide films as catalyst for photochemical wastewater treatment and for biodiesel production.

Speaker: A. Milella (EPS 2019)

391 I2.J703 Influence of molecules on outer layers of JET plasma - spectroscopic study

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J703.pdf

In the fusion plasma reactors most of the plasma is contained in the hot core. Nevertheless, there is a cold outer layer of plasma in the vicinity of the walls, which is crucial to the survival of the plasma vessel and therefore the reactor itself. This layer is cold enough to have a significant molecular component, and its understanding must include the study of creation and destruction of different molecules. Chemical erosion by hydride creation is an important component of the wall erosion, hydrogen fuelling and nitrogen seeding introduce large amount of molecules, which dissociate and are recreated by interaction with the vessel walls. Stable molecules created in this layer may help the tritium fuel to escape the plasma vessel and contaminate the pumps or even escape entirely. Last but not least, the plasma edge has a strong impact on the overall plasma thermal confinement (and thus, on fusion power) which is not yet understood, though the codes can reproduce correctly the core plasma state if a proper plasma edge condition is put in. There is a significant probability that correctly described molecular dynamics will help to understand this dependence.
Determination of the density and internal state of molecules present in the plasma is most often being done by optical emission spectroscopy, because of its simplicity of use. We present the results of the molecular spectroscopy analysis of spectra of the dominant hydrogen (and its isotopes) containing molecules present in outer layers of the plasma. We show the molecular dynamics of hydrogen, influence of seeding on chemical erosion of the walls deducted from hydrides molecular radiation, and its connection with the changes in local ELM dynamics. We also compare the experimental results with the current results of plasma modelling, providing information about the validity of the modelling codes and improving our understanding of the physical processes within this important plasma region.

Speaker: E. Pawelec (EPS 2019)

392 I2.J704 An insight on the beryllium dust sources in JET ITER-like wall based on numerical simulations

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.J704.pdf

Tokamak experiments approaching thermonuclear conditions, like ITER, must face seriously the safety issues related to the release of debris in dust or droplet form from the vessel first wall. In case of loss-of-vacuum accidents, there is a safety hazard due to remobilisation of inhalable toxic or radioactive dust accumulated during operation. For this and other reasons, the investigation of the sources and the collection of dust in JET with the ITER-like wall (ILW), supported by a systematic modelling of dust transport, is a crucial task for ITER. In JET-ILW, experimental observations have provided evidence that molten particle ejection from the beryllium (Be) upper dump plates (UDPs) during unmitigated vertical displacement events (VDEs) is the main source of dust and debris. This work presents a first realistic assessment of the migration and redistribution of particulate of metallic Be and composites in the JET vessel, mobilized during a typical unmitigated VDE from the UDPs. The investigation is based on real observations and is carried out by means of the numerical code DUSTTRACK, which provides full information on the dynamic and thermodynamic history of the debris. The general objectives, basic assumptions and physical model of DUSTTRACK are discussed with an eye also to those of the other dust transport codes developed in the fusion community. With the aim of connecting the dust post-mortem data with the dust source, both qualitative and semi-quantitative statistical descriptions are provided to establish the dependence of the dust deposition (state, location, size, impact speed) on the initial conditions. The focus is here given to the comparison between the output of DUSTTRACK and the experimental data from the UDPs weighting and photographic survey and from the dust collection techniques. The numerical results show consistency with observations. In particular, most of the simulated droplets impinge on the surface of near-by tiles as shown by the camera images of the upper part of JET vessel. Moreover, in agreement with the very low density of particulate found into the dust collection systems placed just above the inner and outer divertor, DUSTTRACK predicts that a small percentage of the simulated particles can reach the collectors position. In outlook, numerical calculation with DUSTTRACK can help choosing the positioning of dust collection systems. Furthermore, confidence is gained that predictive modelling can give support to scenario development for the next deuterium-tritium JET operation.

Speaker: A. Uccello (EPS 2019)

MCF

Convener: E. Wolfrum (Max Planck Inst. f. Plasmaphysik)

393 I2.104 Simultaneous estimation of transport and power deposition profiles and its consequences for transport

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.104.pdf

In perturbative experiments, the power deposition profile is a crucial ingredient in the analysis of the (turbulent) transport [1, 2]. Typically, the deposition profile is calculated with a forward model and used for the computation of the transport [3, 4, 5]. We will show that allowing for uncertainties in the deposition profiles has significant impact on the estimated transport. In fact, such uncertainties can result in paradoxical results, such as apparent non-local transport and significant errors on the estimated transport coefficients such as diffusion and convective velocity [6, 7].
Therefore, it is important to not only assess the sources in the forward direction (ray-tracing) but also in the backward direction by extracting the (effective) deposition profiles directly from the measurements. We present recent results to show that this is possible in case of perturbative experiments and leads to non-paradoxical results. This will allow the next step in perturbative transport analysis in which we no longer need to know the deposition profile to assess the transport and gives a different view on nonlocal transport. This talk will show some state-of-the-art analysis techniques for perturbative analysis allowing for the simultaneous estimation of effective deposition profiles and transport coefficients which in principle is applicable to various transport channels.

References
[1] N.J. Lopes Cardozo, Plasma Phys. Control. Fusion, 37, 799, 1995.
[2] M. van Berkel, T. Kobayashi et al., Nucl. Fusion, 57, 126036, 2017.
[3] F. Ryter, R. Dux et al., Plasma Phys. Control. Fusion 52, 124043, 2010.
[4] M. van Berkel, A. de Cock, et al., Phys. Plasmas 25, 082510, 2018
[5] S. Inagaki, T. Tokuzawa et al., Nucl. Fusion, 53, 113006, 2013.
[6] M. van Berkel, G. Vandersteen et al., Nucl. Fusion 58, 106042, 2018.
[7] M. van Berkel, T. Kobayashi, et al., Nucl. Fusion, 58, 096036, 2018.

Speaker: M. van Berkel (EPS 2019)

394 I2.105 Validation of low-Z impurity transport theory using charge exchange recombination spectroscopy at ASDEX Upgrade

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.105.pdf

Impurities are unavoidable in fusion plasmas and potentially highly problematic as they result in fuel dilution and radiative energy losses. Accurate predictions of fusion plasma performance, therefore, require a validated theoretical description of impurity transport, which in turn requires high accuracy measurements of the impurity populations in present day devices. Recent work at ASDEX Upgrade (AUG) demonstrated the importance of an oftenneglected contribution to the CX emission, the n=2 neutral beam halo, for accurately determining the gradient of low-Z impurity density profiles [2]. This is a critical ingredient for theory validation, as the measured and predicted normalized impurity density gradients are the most commonly and easily compared quantities for theory validation. Previous work at AUG made this comparison for a database of helium and boron density profiles [3] and demonstrated strong discrepancies between experiment and theory as well as clear differences between the impurity species. Motivated by this work, this database has been expanded to include also neon measurements and dedicated experiments were performed to separately identify the diffusive and convective components of the boron particle flux [4]. The transport coefficients from these experiments have been compared to both linear and flux-matched nonlinear simulations using the gyro-kinetic code GKW and demonstrate quantitative agreement in the diffusion coefficient for most cases, together with a systematic under prediction of the observed outward convection. To resolve the discrepancy between the measured and predicted convective velocities a variety of effects have been tested, including the impact of the neoclassical distribution function on the turbulent impurity flux [5] and the inclusion of fast ions in the gyro-kinetic simulations. Lastly, the convection, diffusion and normalized gradients calculated by GKW are compared to those from GENE and against the results from an integrated modeling approach using ASTRA coupled to NEO and QualLiKiz. In this contribution an overview of these works will be given with the aim of determining how best to develop reliable predictive capability of the impurity density behavior in future devices.

[1] A. Kappatou, et al. Plasma Phys. Control. Fusion 60 (2018) 055006
[2] R. M. McDermott, et. al. Plasma Phys. Control. Fusion 60 (2018) 095007
[3] A. Kappatou, et. al., Submitted to Nuclear Fusion, 2019
[4] C. Bruhn, et. al. Plasma Phys. Control. Fusion 60 (2018) 085011
[5] P. Manas, et. al. Plasma Phys. Control. Fusion 59 (2017) 035002

Speaker: R. McDermott (EPS 2019)

395 I2.106 Isotope effects on transport and turbulence in LHD

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I2.106.pdf

In LHD, hydrogen and deuterium isotope experiments were extensively carried out from the 2017 experimental campaign. In ECRH plasma, positive isotope effects in global energy confinement time taoE ECH proportional to A^(0.22±0.01) ne bar ^(0.60±0.01) Pabs^(-0.51±0.01) and negative isotope effects in global particle confinement time taoP ECH proportional to A^(-0.33±0.02) ne bar^(0.52±0.02) Pabs^(-0.69±0.02) were found [1]. Figure 1 shows comparison of profiles for almost identical ne bar and Pabs in H and D plasma. As shown in Fig.1 (a), ne profiles are clearly different. In D plasma, ne profile is clearly hollow, while it is flat in H plasma. Since neutral penetration of H and D are almost identical, the difference of ne profile is due to the difference of transport. Te is clearly higher in D plasma at reff/a99<1.0, while ECH power deposition profiles are almost identical. In H plasma, logarithmic gradient (LTe^-1) of Te is constant at reff/a99=0.2~0.9. In D plasma, however, LTe^-1 varies depending upon the location. Stronger stiffness is found in H plasma. Figure 1 (d) shows comparison of ion scale (ki~0.2) turbulence level measured by two-dimensional phase contrast imaging [2]. The edge turbulence levels at reff/a99>0.9 are almost identical both in H and D plasma, while, core turbulence level at reff/a99<0.9 in H plasma is clearly higher than turbulence levels in D plasma. Trapped electron mode (TEM) and ion temperature gradient mode (ITG) are possible candidates for measured turbulence. Both TEM and ITG can be stabilized in the positive density gradient of hollowed profile [3]. Suppressed turbulence level in the positive gradient region qualitatively agrees with gyrokinetic linear prediction.

[1] K. Tanaka et al, submitted to Nucl. Fusion,
[2] K. Tanaka et al, Rev. Sci. Instrum. 79, (2008), 10E702 3,
[3] M. Nakata et al, Plasma Phys. Control. Fusion in press

Speaker: K. Tanaka (EPS 2019)

396 O2.111 H-mode power threshold studies at ASDEX Upgrade in mixed ion species plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.111.pdf

Understanding the dependence of the H-mode power threshold, PLH, on the main ion composition is critical for the pre-nuclear operational phase of ITER, which will be perfomed in H and He plasmas. For pure H plasmas it is well known that PLH(H) = 2PLH(D), while in the case of pure He plasmas the results vary between PLH(He) = PLH(D) and PLH(He) = 1.8PLH(D) [1, 2]. Moreover, PLH studies in mixed ion species plasmas at JET show a non-linear increase of PLH with increasing H/(H+D) ratio and a reduction of PLH in H by about 40 % when increasing the He concentration, cHe, to 0.05 [3].
Recently, experiments were conducted at AUG studying the impact of He seeding on PLH in H plasmas and the behaviour of PLH in mixed H-D plasmas. A reduction of PLH(H) by He seeding is not observed, with cHe ranging from about 0.01 to 0.2. The non-linear dependence of PLH on the H/(H+D) ratio has been confirmed, but unlike the JET results the AUG experiments show a step-like change of PLH(D) ~ 1 MW to PLH(H) ~ 2.5 MW at an H/(H+D) ratio between 0.5 and 0.8.
All the discharges in this study are in the high density branch, slightly above or at the density minimum of AUG. This allows us to determine PLH in both electron cyclotron and neutral beam heated plasmas, where it is seen that PLH(H) is by 30 % higher in the neutral beam heated cases. The overall behaviour of PLH as described above does not change with different heating schemes.
The evolution of kinetic ion and electron profiles before the L-H transition will be shown, as well as charge exchange measurements of the radial electric field at the plasma edge. Dedicated TRANSP power balance and torque calculations will be performed and compared to the experimental results.

References
[1] P. Gohil et al., Nucl. Fusion, 51 103020 (2011)
[2] F. Ryter et al., Nucl. Fsuion, 49 062003 (2009)
[3] J. C. Hillesheim et al., 27th IAEA Fusion Energy Conf., 2018

Speaker: U. Plank (EPS 2019)

397 O2.112 Impact of SOL-like boundary layer on edge turbulence in global flux-driven gyrokinetic simulations

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O2.112.pdf

Turbulent transport and its impact on ITER performance is investigated with the global flux-driven gyrokinetic code GYSELA. In that framework, a heat source, balanced by turbulent cross-field transport, determines the temperature profile. It is expected that the heat sink at the boundary and turbulence in the edge may interplay with the core conditions. Consistently with such a global property, an immersed outer boundary with axisymmetric limiter and toroidally and poloidally symmetric first wall geometry has been implemented in the code. These regions are penalized towards a cold temperature and act as a heat sink. The Scrape-Off Layer is identified in the ensemble of magnetic field lines intercepting the poloidally asymmetric limiter. There, the flux surface averaged potential is modified to take into account the sheath effect in the case of adiabatic electrons, affordable in terms of numerical cost. The geometry of the immersed boundary can be varied through the definition of several masks. Also the limiter can be biased with respect to the wall.
A staged verification of the physics and first global results are reported here. First, the parallel propagation of heat in the SOL has been investigated. A cold front propagation is recovered matching the analytical modelling [Caschera, JPCS, 2018]. Second, a reversal of the radial electric field is recovered at the interface between the SOL and core plasma. Third, the drift velocity governed by the magnetic field inhomogeneity drives plasma polarization which is enhanced by the limiter. Indeed, the latter intercepts the parallel currents, and a strong shear region of the poloidal velocity develops close to the separatrix. High amplitude zonal flows and large scale ExB convection yield poloidally inhomogeneous shearing. The strong electric field modifies the density pattern which, together with the enhanced shear, yields opposite effects: on the one hand the shear layer and large radial density gradient tend to stabilize ITG turbulence, and, on the other hand the shear layer can become Kelvin-Helmholtz unstable favoring the spreading of turbulence both inward towards the core and outwards in the SOL. Qualitative agreement has been observed with the edge turbulence fluid code TOKAM3X and will be further investigated.

Speaker: E. Caschera (EPS 2019)

EPS Town meeting on EUROfusion strategy and preparations for Horizon Europe

Introduction - AmbrogioFasoli
EU R&D Energy policy and the role of fusion research - Elena Righi-Steele
Overview of the revised EU roadmap - Tony Donné
Preparations for ITER operation - Xavier Litaudon
DEMO and perspective R&D developments - Richard Kembleton
Public debate - AmbrogioFasoli

Convener: A. Fasoli (SPC)

Wednesday, 10 July

Plenary Session

Convener: K. McCarthy

398 I3.007 AWAKE: physics of self-modulation of a relativistic proton bunch in a plasma and electron acceleration results

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.007.pdf

Relativistic proton bunches available today carry large amounts of energy (tens to hundreds of kilojoules) and can thus, in principle, drive wakefields in long plasmas, possibly leading to the acceleration of electrons to very high energies (TeVs). Since these bunches are long (6 to 12 cm), the self-modulation process is necessary to drive large amplitude wakefields (GV/m) [1]. Experimental results obtained in the AWAKE [2] experiment highlight many of the physics aspects of the self-modulation process. They include: first observation of the self-modulation of a relativistic particle bunch in a plasma [3]; growth of the process both along the bunch and along the plasma [4]; excitation of large amplitude wakefields; transition from a self-modulation instability process to a seeded-self-modulation process with two seeding mechanisms; observation of the non-axi-symmetric hosing instability. In addition, observation of electrons exiting the plasma with up to 2 GeV energy after external injection at 19 MeV [5] demonstrates that acceleration of particles is possible in these wakefields. We will introduce plasma wakefields and the particular case of those driven by the self-modulation process. We will describe the AWAKE experimental setup and present the main physics and acceleration experimental results. We will briefly outline plans for the next experiments, as well as possible applications for the acceleration scheme.

References
[1] N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010)
[2] P. Muggli, AWAKE Collaboration, Plasma Physics and Controlled Fusion, 60(1) 014046 (2017)
[3] AWAKE Collaboration, Phys. Rev. Lett. 122, 054802 (2019)
[4] M. Turner, AWAKE Collaboration, Phys. Rev. Lett. 122, 054801 (2019)
[5] AWAKE Collaboration, Nature 561, 363 (2018)

Speaker: P. Muggli (EPS 2019)

399 I3.008 Wendelstein 7-X: Towards high-density long-pulse operation

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.008.pdf

Stellarators have intrinsic advantages with respect to a fusion reactor operating in steady-state. They, however, need optimization to bridge the gap to tokamak plasma performance. The superconducting stellarator Wendelstein 7-X (W7-X) is optimized for neoclassical transport and improved plasma stability. The set of 50 non-planar and 20 planar magnetic field coils generate a magnetic field of 2.5T on axis with low shear and a range of rotational transform between 5/6 and 5/4. The third operation campaign of W7-X was finished in 2018. The primary focus of the campaign was the development of high-density plasma scenarios, which are compatible with divertor operation and have the potential for long-pulse steady-state plasma discharges, and the demonstration of the optimization criteria. This paper summarizes the key experimental findings of the campaign. Improved wall conditioning via boronization was applied to W7-X for the first time. The resulting strong reduction of plasma impurities, particularly oxygen, reduces core impurity radiation considerably and allowed plasma densities exceeding 1x10^20 m^-3 with ECRH heating powers up to 6MW in O2 mode polarization. At those high densities divertor detachment is observed with a neutral compression, which is sufficient for active neutral gas pumping envisaged for the next operation campaign. The predicted impurity accumulation in the plasma core is not observed and suggests that turbulent transport plays a significant role in the radial regulation of heat and particle transport. This scenario could be stabilized to a discharge length of 30s, corresponding to 150MJ of heating energy. At reduced heating power, an even longer discharge length of 100s with 200MJ injected heating energy was demonstrated. Improved confinement is observed when the plasma density is centrally peaked by pellet fuelling. High ion temperatures Ti=Te=3keV are achieved in this case. This phase is correlated with the suppression of turbulent fluxes. Gyrokinetic simulations suggest that this suppression is due to a stabilization of ion temperature gradient modes by the core density gradients, while trapped electron modes remain widely stable. This is a particular feature of the magnetic field optimization and stands in general contrast to the tokamak situation. Neutral beam injection heating with a maximum heating power of 3.5MW was operated at W7-X for the first time. It was demonstrated that the plasma can be sustained with neutral beam injection heating only and the highest plasma densities of 2x10^20 m^-3 were achieved in this scenario.

Speaker: O. Grulke (EPS 2019)

10:10 Coffee Break

BPIF

Convener: S. Atzeni (Università di Roma "La Sapienza" and CNISM)

400 I3.201 Review of hydrodynamic instability experiments in ICF implosions on National Ignition Facility

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.201.pdf

In Inertial Confinement Fusion (ICF), an indirectly driven implosion begins with an acceleration phase when the hohlraum x-rays ablate the shell surface and the capsule starts to converge. At this stage, outer-shell non-uniformities grow due to the acceleration-phase Richtmyer-Meshkov (RM) and Rayleigh≠Taylor (RT) instabilities. As the shell accelerates, these front-surface perturbations feed through the shell, seeding perturbations on the ablatorice and ice-gas interfaces. During the deceleration phase, the inner surface of the shell is subject to RT instability.
Several new platforms have been developed to experimentally measure hydrodynamic instabilities in all phases of implosions on NIF. At the ablation front, instability growth of preimposed modulations was measured with face-on x-ray radiography platform in the linear regime using the Hydrodynamic Growth Radiography (HGR). In addition, modulation growth of 3-D "native roughness" modulations was measured in conditions similar to those in layered DT implosions.
A new experimental platform was developed to measure instability growth at the ablator-ice interface. 2-D modulations were laser-imposed at the inner surface of the plastic capsule for implosions with DT layers to probe stability of the ablator-ice interface using xray radiography with this new Layered Hydrodynamic Growth Radiography (LHGR) platform.
In the deceleration phase of implosions, an innovative method was developed to use the self-emission from the hot spot to "self-backlight" the shell in-flight. Capsules used argon dopant in the gas to enhance x-ray emission at the beginning of the deceleration phase that serves as a "backlighter" to image growing shell modulations. In addition, atomic mix between plastic shell and a gas was studied at peak compression using plastic "Symcap" shells filled with tritium gas and imbedding localized CD diagnostic layer in various locations in the ablator. Experimental results from all these campaigns will be reviewed.

This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

Speaker: V. Smalyuk (EPS 2019)

401 I3.202 Experimental investigation of the collective Brillouin and Raman scattering of multiple laser beams in ICF experiments

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.202.pdf

The direct and indirect drive schemes to ICF make use of a large number of laser beams arranged in a symmetric angular distribution. The preferential decay geometry of the three waves resonant couplings, mainly responsible for backscattered light in single beam experiments, may then be deeply modified in the region of crossing beams where collective laser plasma instabilities could develop [1].Such instabilities can occur for laser beams having a common symmetry axis along which they drive a common daughter wave. The collective coupling results in an increase of the growth gain with the increase of the number of interacting beams. These collective instabilities also produce energy losses in new backward directions. Two categories of experiments have been performed on the Omega facility to study these collective instabilities in the regimes relevant of the direct and indirect drive schemes to ICF.
The first class of experiments [2] was performed in a planar open geometry relevant of megajoule direct drive. They have evidenced the large amplification of stimulated Raman scattering (SRS) electromagnetic waves almost transverse to the density gradient as theoretically predicted 40 years ago [3]. This was achieved in long scale-length hightemperature plasmas in which two beams couple to the same scattered electromagnetic wave further demonstrating for the first time this multiple-beams collective SRS interaction. The collective nature of the coupling and the amplification at large angles from the density gradient increase the global SRS losses and produce light scattered in novel directions out of the planes of incidence of the beams.
The second class of experiments [4] was performed in an indirect drive configuration in rugby ball shaped Hohlraum irradiated by 40 beams. Large (>30%) Brillouin sidescattering was evidenced to originate from the collective Brillouin amplification of a shared ion acoustic wave driven along the Hohlraum axis by a cone of 10 beams. We further demonstrate and interpret the efficient control of such large Brillouin scattering losses by the temporal incoherence optically imposed on the interacting beams and by the electronic density in the crossing beams domain.

[1] D.F.DuBois et al., Phys. Fluids B4, 241 (1992).
[2] S. Depierreux, et al., Phys. Rev. Lett. 117, 235002 (2016).
[3] C. S. Liu, M. N. Rosenbluth, and R. B. White, Phys. Fluids 17, 1211 (1974).
[4] C. Neuville, et al., Phys. Rev. Lett. 116, 235002 (2016).

Speaker: S. Depierreux (EPS 2019)

402 O3.201 Experiments and simulations up to ignition scales on the laser direct drive shock ignition approach to laser fusion

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.201.pdf

Shock ignition is a promising route for laser fusion ignition; in principle high fusion energygain can be achieved with modest driver energies and hence capital investment.

This talk will detail both simulations and ongoing collaborative experiments on the Omega, and NIF laser facilities. These are being performed both to improve our understanding of the physics of shock ignition and in an effort to develop improved modelling capabilities in the intensity-regime required for shock ignition. Discussions will include new concepts which may enable shock-ignition to be achieved on today's laser facilities without the need for extensive modifications.

Speaker: K. Glize (EPS 2019)

403 O3.202 Octahedral spherical hohlraum for Rev. 6 NIF Beryllium capsule

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.202.pdf

We design an octahedral spherical hohlraum with 6 laser entrance holes (LEHs) for the Rev. 6 Be ignition capsule [A. N. Simakov et al., Phys. Plasmas 21, 022701 (2014)]. With an Au spherical hohlraum of 4400 $\mu$m in radius and six LEHs of 1200 $\mu$m in radius, a laser pulse of 2.15 MJ energy and 630 TW power is required to deliver the radiation drive for the Rev. 6 Be ignition capsule. Both our 1D and 2D simulations show that the expansion of Be capsule is slightly slower than that of the CH capsule under the same radiation drive in the spherical hohlraum, in spite of the higher ablation rate of Be. The reason is that the CH capsule has a higher opacity which causes a hotter ablated plasma and then a faster expansion of the CH ablated plasmas. The large volume of spherical hohlraum, together with the incident angle of 55$^\circ$ in its laser arrangement, leaves enough room for the laser transportation, thus avoiding the laser being absorbed by the Be capsule plasma and consequently the high risk of laser plasma instabilities (LPI). That means the higher mass ablation rate of Be does not affect the hohlraum energetics and symmetries inside the spherical hohlraum. With the high radiation drive symmetry and low risk of LPI of the octahedral spherical hohlraum, the superior ablation properties of Be capsule can be fully exploited and will have a higher opportunity to achieve ignition.

Speaker: G. Ren (EPS 2019)

404 O3.203 High-efficiency rugby-shaped hohlraum designs for driving large gas-filled capsules on the NIF

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.203.pdf

In indirect-drive inertial confinement fusion (ICF) a high-Z enclosure (or "hohlraum") surrounds a low-Z capsule containing DT fuel inside a low-Z spherical shell. Laser beams irradiate the interior of the hohlraum through a pair of laser entrance holes, in turn creating an x-ray radiation "bath" that compresses the fuel to ignition conditions. The coupling of laser light to the capsule is typically ~10%, resulting in ~200 kJ absorbed energy for the ~2 MJscale laser at the National Ignition Facility (NIF). A 7 mm-wide rugby-shaped Au hohlraum design is found that can accommodate ~50% larger (DT) gas-filled capsules for up to 500 kJ capsule absorbed energy and ~30% coupling efficiency. This new integrated design is made possible by using a high-density gas fill (6-8 mg/cc) that limits the fuel convergence ratio (C) to <14. The low C greatly limits the degrading effects of hohlraum drive asymmetry and hydro-dynamic instability from surface roughness and target-fielding fixtures, e.g., capsule tent supports and the DT fuel-delivery fill tube. Integrated hohlraum simulations in 2-D show good implosion symmetry with peak radiation temperatures reaching 295 eV at <1.8 MJ of laser energy and 440 TW peak power while delivering nearly 100 kJ of energy (compared with ~60 KJ in DT-layered implosions). The hohlraum design is made possible by employing a shaped two-shock laser power history for compressed energy delivery and desired margin to late-time hohlraum filling (and loss of symmetry control). Confidence in this design is supported by a recently reported campaign on the NIF using a reverse-ramp pulse shape to drive a similar rugby-shaped hohlraum and a ~ 3.5 mm-scale Al shell filled with 7 mg/cc DT gas [1]. The high fuel-adiabat (alpha ~6-7) character of the 2-shock design is tolerated due to the higher performance margin from the large-capsule design. This platform can be extended to include varying thicknesses of DT solid-fuel layering for increased yield (> 1 MJ), while benefitting from the favorably low C (<20). Further inroads into understanding ignition thresholds and the transition from volume-dominated (-PdV) ignition to higher-C hot-spot ignition could result from initially leveraging an optimized low-C gas-fill design.

[1] Y. Ping, V. Smalyuk, P. Amendt et al., Nature Phys. (https://doi.org/10.1038/s41567-018-0331-5).
Work performed under the auspices of U.S. Department of Energy by LLNL under Contract DE-
AC52-07NA27344 and supported by LDRD-17-ERD-119

Speaker: P.A. Amendt (EPS 2019)

405 O3.204 Design and analysis of a 3D ICF implosion campaign on the Omega laser with the TROLL code

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.204.pdf

For the last couple of years, large efforts have been invested at CEA/DAM to develop the 3D radiationhydrodynamics code TROLL. Indeed, 2D radhydro codes are the main tool to design and analyze HED and ICF experiments. Yet, many of the first are intrinsically 3D, for example: few laser beams in directdrive or study objects on the equatorial plane of a hohlraum in indirect drive. For the second, the axisymmetry is assumed due to the number of beams per irradiation ring. Yet, numerous studies pinpointed the importance of 3D effects, in particular for the expansion of the outer plasma bubbles, which affects the propagation of the inner cone beams. Finally, in the framework of the progressive commissioning of LMJ up to its final 44 quads configuration, ICF experiments might be conducted with suboptimal azimuthal laser irradiation. While the TROLL code has already been challenged by numerous 3D hohlraum experiments, questions remained about its capability to simulate indirect drive implosions with a poor azimuthal irradiation symmetry. In order to tackle this, an experiment has been performed in 2018 at the Omega laser facility (LLE, U. of Rochester), during which a rugby hohlraum was driven either by 18 beams at full power (asymmetric irradiation) or 30 beams at 3/5 power (symmetric irradiation), such as to keep the cavity energetics constant. Three types of targets were used to asses the effects of the asymmetry : reemits for early time, foamballs for intermediate time and D2 filled capsules for late / integrated time measurements. We will present the design, results, and interpretation of this experiment, validating now TROLL for 3D implosion calculations, and paving the way for the design of more ambitious ICF experiments on the LMJ.

Speaker: R. Riquier (EPS 2019)

406 O3.205 Modeling of laser-plasma interaction in the shock ignition regime with LPSE: Comparison with particle in-cell simulations and experiments

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.205.pdf

The shock ignition (SI) approach to inertial confinement fusion promises ignition at a lower laser energy than conventional hotspot schemes. The target is initially driven at a low-implosion velocity, which reduces hydrodynamic instabilities, and then ignited by a high-intensity spikethat launches a strong shock into the hot spot. The high-intensity spike, however, can trigger laser-plasma instabilities (LPIs) that generate hot electrons, which migth pose a serious preheat threat to the capsule (preheating) or rather contribute to increase the shock pressure, depending on their energy. Here, we present LPSE simulations studying LPIs for parameters relevant to SI.By employing time-enveloping and a fluid plasma response, LPSE models scales intermediate to hydrodynamics and kinetics and has a lower numerical noise than particle-in-cell (PIC) codes,making it particularly suited for studying LPI processes in the plasma corona. Comparison of LPSE simulations, including stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) for parameters relevant to OMEGA EP experiments are performed: in particular, prediction on SRS and SBS time-averaged reflectivities and Raman spectrum obtained in LPSE simulations show a good agreement with PIC results[1].

This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester,and the New York State Energy Research and Development Authority, and by EUROfusion Enabling Research Project: AWP17-ENR-IFE- CEA-01 ’Preparation and Realization of EuropeanShock Ignition Experiments’ and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressedherein do not necessarily reflect those of the European Commission.

References
[1] O. Klimo and V.T. Tikhonchuk, Plasma Phys. Control. Fusion 56 055010 (2014)

Speaker: A. Ruocco (EPS 2019)

BSAP

Convener: J. Egedal (Physics Department!UW-Madison1150 University Avenue!53706! Wisconsin! USA)

407 I3.401 Cherenkov radiation from the quantum vacuum

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.401.pdf

A charged particle moving through a medium emits Cherenkov radiation when its velocity exceeds the phase velocity of light in that medium. Since light in vacuum is usually assumed to move at the universal speed c, causality appears to preclude vacuum Cherenkov radiation (VCR). Under the influence of a strong electromagnetic field, however, quantum fluctuations can become polarised, imbuing the vacuum with an effective permittivity tensor and reducing the speed of light. It follows that sufficiently energetic particles can emit Cherenkov radiation even when travelling in vacuum [1]. The required field strengths and particle energies suggest it is unlikely that VCR will be observable in near-future laboratory experiments. However, for high energy cosmic rays traversing the magnetic fields around a pulsar, VCR can be comparable to, and even substantially exceed, other known forms of radiation.

References
[1] A.J. Macleod, A. Noble and D.A. Jaroszynski, arXiv:1810.05027 (2018).

Speaker: A. Noble (EPS 2019)

408 I3.402 Phase-space cascade in turbulent plasmas: observations simulations and theory

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.402.pdf

Plasma turbulence has been investigated using unprecedented high-resolution ion velocity distribution measurements by the Magnetospheric Multiscale mission (MMS) in the Earth's magnetosheath. This novel observation of a highly structured particle distribution suggests a cascadelike process in velocity space [1], as shown in figure 1. Complex velocity space structure is investigated using a three-dimensional Hermite transform, revealing, for the first time in observational data, a power-law distribution of moments. In analogy to hydrodynamics, a Kolmogorov approach leads directly to a range of predictions for this phase-space transport. The scaling theory is found to be in agreement with observations and new simulations. The combined use of state-of-the-art MMS data sets, novel implementation of a Hermite transform method, scaling theory of the velocity cascade and kinetic simulations opens new pathways to the understanding of plasma turbulence and the crucial velocity space features that lead to dissipation in plasmas [1, 2, 3, 4].
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 776262 (AIDA, www.aida-space.eu)

References
[1] S. Servidio, A. Chasapis, W. H. Matthaeus, D.Perrone, F. Valentini, T. N. Parashar, P. Veltri, D. Gershman, C. T. Russell, B. Giles, S. A. Fuselier, T. D. Phan and J. Burch, Physical Review Letters 119, 205101 (2017)
[2] A. A. Schekochihin, J. T. Parker, E. G. Highcock, P. J. Dellar, W. Dorland and G. W. Hammett, J. Plasma Phys. 82, 905820212 (2016)
[3] S. S. Cerri, M. W. Kunz and F. Califano, Astrophys. J. Lett. 856, L13 (2018)
[4] O. Pezzi, S. Servidio, D. Perrone, F. Valentini, L. Sorriso-Valvo, A. Greco, W. H. Matthaeus and P. Veltri, Velocity-Space Cascade in Magnetized Plasmas: Numerical Simulations, Physics of Plasmas 25, 060704 (2018)

Speaker: S. Servidio (EPS 2019)

409 I3.403 Observation of nonlocal electron transport in Warm Dense Matter

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.403.pdf

We present the first measurement of nonlocal electron transport on Warm Dense Matter (WDM) [1]. The experiment was carried out at the OMEGA laser facility, where we used 15 beams drove a fast compression wave in low-density CH foam generating WDM conditions. We combined multiple independent diagnostics including spatially and spectrally X-ray Thomson Scattering (XRTS), velocity interferometry (VISAR) and streaked optical pyrometry (SOP) to provide a robust measurement of the thermodynamic conditions in the sample. XRTS observed elevated temperatures within the compression wave reaching to 17 - 35 eV, while the SOP and and VISAR both detected abnormally high shock velocities with a significant decay profile. The SOP diagnostic also registered early emission indicating presence of preheat of the cold material ahead of the compression wave. The experimental results were first compared with Cassio simulations, but consistency with the measurement was not found. These simulations in conjunction with FLYCHK calculations confirm that x-ray flux deposited in the CH was negligible.
In order to study the contribution of the nonlocal electron transport, we used the Plasma Euler and Transport Equations Hydro code (PETE), which is a Lagrangian fluid model that includes nonlocal transport hydrodynamic model (NTH) [2]. These simulations provided excellent agreement with the experiment and additional insight into the physics within this experiment. We find that it is the nonlocal electrons originating from the compressed plasma close to the shock front that are allowed to transport further ahead leading to a spatial structure of the shock wave and formation of the preheat region. These findings enable bench-marking of electron conduction models in conditions relevant to inertial confinement fusion, such as those employed in the modelling of experiments performed at the National Ignition Facility or Laser Megajoule, as well as laboratory astrophysics including convection phenomena in white dwarfs or supernova explosions.

References
[1] K. Falk et al., Phys. Rev. Lett. 120, 025002 (2018).
[2] M. Holec, J. Nikl, and S. Weber, Phys. Plasmas 25, 032704 (2018).

Speaker: K. Falk (EPS 2019)

410 O3.401 Positron confinement exceeding 1s in a magnetic dipole trap

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.401.pdf

Magnetic dipole fields have exellent confinement properties for charged particle ensembles with an arbitrary degree of neutrality. One idea to create a magnetized low-energy electron-positron pair plasma pursued by the APEX/PAX collaboration relies on the initial formation of a non-neutral plasma in the confining magnetic field and hence the dipole geometry is a promising candidate to study such a system. While electron injection and confinement have been readily achieved in a magnetic dipole trap the positron counterpart is more challenging due to the limited positron flux provided even by world class positron sources such as NEPOMUC (Neutron-Induced Positron Source Munich).
In this contribution we present results from recent positron confinement experiments conducted with a supported magnetic dipole trap at the NEPOMUC facility. After suppressing parallel losses onto the magnet surface by applying a positive electrostatic bias to the magnet we have observed positron confinement in a magnetic dipole field in excess of 1 s. Supported by single-particle simulations we identify transport due to scattering off of neutrals as the dominant mechanism limiting confinement. The importance of the results for the electron-positron pair plasma experiment will be discussed.

Speaker: J. Horn-Stanja (EPS 2019)

411 O3.402 Nonlinear wave-particle interaction in helix traveling-wave tubes using N-body simulations in time domain

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.402.pdf

Nonlinear synchronisation is a key process in wave-particle interaction [1], responsible for Landau damping as well as for the amplification in devices like traveling wave tubes and gyrotrons [2]. We investigate it using the finite-N approach from a self-consistent hamiltonian formalism [3]. This description is combined with a recent field decomposition [4] that allows drastic degree-of-freedom reduction while preserving conservation laws (from symplectic properties) for periodic waveguides. Those advantages enable fast time domain simulations compared to alternative particle-in-cell codes.
The model is assessed, with success, against a well-established frequency model in the linear regime [5], against nonlinear simulations [3] and against measurement from industrial TWTs [6]. Currently, our simulations handle non-sinusoidal fields (like multi-carriers). A specific formulation of this model is in preparation for helical waveguides.
Finally, we outline the occurence of the Abraham-Minkowski dilemma for waveguide amplifiers and plasmas [7]. This dilemma (well-known in dielectrics) highlights two different formulas for the momentum of light. For the wave-particle interaction, the dilemma resolution involves a non-negligible flowing momentum from Maxwell's electromagnetic stress.

References
[1] F. Doveil, Y. Elskens and D. F. G. Minenna, Wave-particle interaction studied in a traveling wave tube, 20th International Congress on Plasma Physics (ICPP 2018), Vancouver, invited (2018).
[2] A. S. Gilmour, Klystrons, Traveling Wave Tubes, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons (Artech House, Boston, 2011).
[3] D. F. G. Minenna, Y. Elskens, F. André and F. Doveil, EPL, 122, 44002 (2018).
[4] F. André, P. Bernardi, N. M. Ryskin, F. Doveil and Y. Elskens, EPL, 103, 28004 (2013).
[5] D. F. G. Minenna, A. G. Terentyuk, Y. Elskens, F. André and N. M. Ryskin, Phys. Scr., in press, doi:
10.1088/1402-4896/ab060e.
[6] D. F. G. Minenna, et al., DIMOHA : Traveling-wave tube simulations including band edge and multitone
operations, 20th International Vacuum Electronics Conference (IVEC 2019), Busan, accepted (2019).
[7] D. F. G. Minenna, Y. Elskens, F. Doveil and F. André, Universality of the Abraham-Minkowski dilemma for
photon momenta beyond dielectric materials, arXiv: 1902.06431.

Speaker: D.F. Minenna (EPS 2019)

412 O3.403 Long-term nonlinear dynamics of electron-ion Weibel instability in laser plasmas and stellar winds

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.403.pdf

In laser plasmas, as well as in solar and stellar winds, ions and electrons can have comparable energies and strongly anisotropic velocity distributions. Under those conditions both fractions of a collisionless plasma can make a significant contribution to the development of the Weibeltype instability and the subsequent formation of self-consistent current structures and magnetic fields, i.e. the evolution of the spectral properties of quasi-magnetostatic turbulence.
In the report we consider, for the first time to our knowledge, the nonlinear stage of the Weibel instability in a two-component plasma with strong temperature anisotropy and equal initial energies of electrons and ions [1] on the basis of numerical simulation with the 2D3V PIC-code DARWIN [2]. The Maxwellian distributions of particles by each velocity projection were initially set, but with different temperatures along and across the z axis of the Cartesian coordinates, with the longitudinal temperature being the greater, so that the development of the instability led to the formation of current filaments along this axis.
The simulations, carried out in the plane orthogonal to the z axis, made possible to investigate the long-term evolution of a quasi-stationary magnetic field and current filaments created first by the electrons and then jointly by the electron and ion fractions. In the process of saturation and non-linear power-law decay, the small-scale magnetic fields, created by the electron currents of the Weibel instability, induce an electric field that generate ion currents, which determine the long-term slow evolution of large-scale magnetic field perturbations. Over time the electrons become isotropic and a significant part of them becomes magnetized. It "freezes" the evolution of magnetic fields, eliminating or significantly delaying the ion Weibel instability, which could otherwise develop due to remaining for a long time anisotropy of ion temperatures.
We discuss the possibility of implementing this scenario in laser plasma, solar and stellar winds and estimate the expected parameters of the resulting self-consistent current filaments and their evolution rates. The influence of the large-scale (external) magnetic field on the rate of formation and spectral characteristics of the magnetostatic turbulence is also discussed.

References
[1] L. V. Borodachev et al., Radiophys. Quantum El., 59 (12), 991 (2017)
[2] L. V. Borodachev and D. O. Kolomiets, J. Plasma Phys., 77 (2), 277 (2011)

Speaker: V.V. Kocharovsky (EPS 2019)

LTPD

Convener: C. Riccardi (Dipartimento di Fisica! University of Milano-Bicocca)

413 I3.301 Tuning a microwave plasma for the synthesis of few-layers graphene sheets from ethanol decomposition

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.301.pdf

The study of ethanol decomposition process to synthesize few-layers graphene together with hydrogen using an argon microwave plasma sustained by a Torche à Injection Axiale sur Guide d'Ondes opened to the atmosphere is presented. In this work, plasma kinetics and by-products formation are deeply studied to identify the key plasma parameters leading to graphene production. Optical Emission Spectroscopy was utilized to measure plasma gas temperature and to identify plasmas species produced by the decomposition of ethanol molecules. Simultaneously, gaseous products at the plasma exit were identified by Mass Spectrometry. Carbon powder was analyzed by High-Resolution Transmission Electron Microscopy (HRTEM), Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Thermogravimetric analysis (TGA) and it was identified as few-layers graphene. Graphene synthesis took place only for certain argon and ethanol flows, which had an impact too on the influence of the air surrounding the discharge. In addition, plasma gas temperature value was also found to have a remarkable influence on ethanol decomposition chemistry; giving place to two different ethanol decomposition routes: (i) at higher temperatures (>4500 K) graphene flakes, H2 and CO were produced whereas, (ii) for lower gas temperatures (<4500 K) graphene was not synthetized and H2, H2O, CO and CO2 gases were produced (Figure 1). These results show that the complete ethanol decomposition by means of an atmospheric-pressure microwave plasma sustained with high gas temperatures can be tuned to result in the production of few-layers graphene and hydrogen through a clean and simple process.

Speaker: R. Rincón (EPS 2019)

414 I3.302 Creating green nanostructures and nanomaterials for advanced energy nanodevices

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.302.pdf

Securing safe and cheap energy and using it effectively is a serious problem for modern society. As a solution to this, he is performing research on innovative green nanodevices. We are developing power generating devices, storage devices, low-power-consumption devices, multifunction Nano-devices and nano-energy systems that use these devices. To manufacture these nanodevices, it is necessary to be able to do so precisely without damaging the nanostructures and to derive the intrinsic characteristics of the nanomaterials and nanostructures. For the first time, such devices are made possible through the mastery of our unique intelligent nano-processes such as a super-low-damage neutral beam processes, pulsed plasma processes, and ultimate processing utilizing biotechnology.
In this paper, we focuse on bio-template and neutral beam etching fusion top-down process to realize nanoscale structures. The optical, electrical, spintronics and phononic characteristics have been already demonstrated in nanoscale structures. Our fabricated nanostructure can precisely control the transport of electron, hole, spin and phonon by diameter, hight, gap and interlayer materials of nanostructure respectively. Now, based on these results, we are trying to develop QN solar cells, QN thermo-electric conversion elements, QN Laser/LED, QN spin devices and so on.

Speaker: S. Samukawa (EPS 2019)

415 O3.301 The role of thermal effects in constriction of positive column in inert gases

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.301.pdf

Constriction, which is the fundamental phenomenon of gas discharge physics, has been attracting the attention of scientists for more than a century. However, scientists still discuss [1], what is the main mechanism, which leads to a constriction. Among all mechanisms one can name the inhomogeneous heating of a neutral gas, which causes a decrease of the reduced electric field and a compression of the ionization sources. Inhomogeneous heating also leads to a decrease of the dissociation degree of molecular ions and to an increasing loss of charged particles in the radial direction due to the dissociative recombination, which either results in the plasma compression. Constriction may be also caused by an abrupt non-linear dependence of the ionization rate on the electron density. Depending on the discharge conditions (discharge current, pressure, gas type) one or another mechanism may dominate.
Current work presents the experimental study of the influence of the inhomogeneous gas heating on the formation of constricted positive column in neon and argon at intermediate pressures (pR=50-500 Torr cm). Discharge current, exceeding the critical value, was modulated by rectangular pulses of short duration to avoid the inhomogeneous gas heating. Temperature field of neutral atoms was determined using interferometry method basing on the Michelson interferometer. Fig. 1 gives an example of the interference pattern in the stationary constricted neon and ascending argon discharges during the heating of the neutral gas.
The heat equation, solved along with the Navier-Stokes equation, allowed describing the buoyancy effect in a constricted discharge in argon, which had not been previously done. It is shown that under described discharge conditions, in spite of the absence of inhomogeneous gas heating, discharge switches to the constricted regime in neon and argon. It can be concluded that at presented discharge conditions a nonlinear dependence of the ionization rate on the electron density is the basic mechanism of constriction.

References
[1] Ridenti M. A., de Amorim J., Dal Pino A., Guerra V. and Petrov G. M., Phys. Rev. E, Vol. 97, p. 13201 (2018)

Speaker: A. Siasko (EPS 2019)

416 O3.302 Influence of molecular admixtures on filamentation in microwave plasma torch

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.302.pdf

Microwave (MW) discharges are one of the most flexible plasma devices operating under wide range of experimental conditions which makes them suitable for many practical applications. However, at atmospheric pressures, the plasmas tend to contract, forming the spatially inhomogeneous and possibly temporally unstable plasma filaments. In contrast, most applications require homogeneous, stable and repeatable operating conditions. Detailed study of filament formation and sustaining is therefore of utmost importance for both basic and applied plasma science.
We investigated a filamentary regime in MW plasma torch, which used atmospheric pressure argon flowing through central electrode [1]. Main experimental parameters were the input MW power, flowrate of argon and amount (0-10%) of admixture (oxygen, hydrogen, nitrogen). With an outlook to a graphene synthesis more complex molecular admixture (ethanol) was used, too.
Fast imaging and optical emission spectroscopy were used as diagnostics.
The process of contraction and filamentation was strongly influenced by the molecular admixture. Observed reduction of filament length can be easily explained by the loss of energy to vibrational and rotational excitations of the molecular admixture. The causes of changes in radial intensity profile are more complex as they involve e.g. thermal conductivity of various gases [2]. Nitrogen admixture generally produced more diffuse filaments than other admixtures. Spatial profile of the local gas temperature was calculated from the emission spectra, too.

This work was supported by The Czech Science Foundation (GA CR) under project 18-08520S and in part by the project LO1411 (NPU I) funded by Ministry of Education, Youth and Sports of Czech Republic.

References
[1] L. Zajickova et al., Plasma Phys. Control. Fusion, 47, (2005). [2] M. Moisan et al., Springer Science, (2012).

Speaker: M. Snirer (EPS 2019)

417 O3.303 Experimental observation of large 2D plasma crystals

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.303.pdf

Two-dimensional (2D) complex plasma crystals are popular model systems where various generic as well as plasma-specific phenomena can be studied in real time at the level of individual particles. System-size dependence of the plasma crystal properties is an important issue which is not fully understood due to the limited size (and particle number) of the crystals obtained so far. To achieve larger plasma crystals, a new experimental setup was built at the DLR Institute of Materials Physics in Space [1]. It is based on a relatively large (90 cm in diameter) vacuum chamber where a capacitively coupled radio-frequency (rf) discharge is used to suspend a 2D cloud of micrometer-size polymer particles. The discharge is created between the lower rf electrode and the grounded chamber walls, the particles levitate in the plasma (pre)sheath above the electrode.
The main parameters of the 2D plasma crystal obtained in an experiment with argon pressure of 0.4 Pa and discharge power of 150 W are shown in the Table. The particles were arranged in a triangular lattice with hexagonal symmetry. The pair correlation function for particles g(r) has a sharp first peak and fully split second peak. This plasma crystal is much larger and contains more particles than the crystals produced in previous experiments using the GEC rf reference cell. In preliminary tests, plasma crystals with a diameter of up to 50 cm were achieved.
Further tests showed that stable 2D plasma crystals can be suspended in argon plasma at the pressure as low as 0.1 Pa. In these experimental conditions, the Epstein neutral gas damping rate is a small fraction (around 0.5%) of the complex plasma's Einstein frequency. Therefore, virtually undamped dynamics can be studied in detail in this system.

1. V. Nosenko, J. K. Meyer, S. K. Zhdanov, and H. M. Thomas, AIP Advances 8, 125303 (2018).

Speaker: V. Nosenko (EPS 2019)

418 O3.304 Plasma assisted synthesis of carbon nanowalls

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/O3.304.pdf

Plasmas can be used for the fabrication of novel materials. The interest in novel, often carbonaceous materials with large effective surfaces, high conductivity, stability, is growing due to the downsizing of electrical devices and the demand for low-cost new materials. In particular this work will focus on the analysis of a low temperature plasma (RF –discharge)used for the production of carbon nanowalls (CNWs).
The resulting nanowalls (CNWs) demonstrate interesting characteristics, and have a potential for variety of applications. In our case, we tested electrochemical devices,transistors and biosensors. This work with CNWs is a part of the research on carbon based microelectronic parts of biosensors.
Besides the material analysis of nanowalls (graphene 2D structures) the plasma parameters were analysed and connected with the material analysis in order to understand and control better the plasma processes itself. For example, the self-bias voltageiscorrelated with OES and XPS and NEXAFS analysis of CNW produced in ethylene or acetylene/hydrogen gas mixtures.

Acknowledgements: The authors want to acknowledge the support of the PEGASUS (Plasma Enabled and Graphene Allowed Synthesis of Unique Nanostructures) project, funded by the European Union’s Horizon research and innovation program under grant agreement No. 766894. The authors would also like to acknowledge supportobtained by French National Research Agency via project ANR PlasBioSensandANRPlasmaBondand to thank Helmholtz Zentrum Berlin for the allocation of synchrotron radiation beamtime at BESSY II. Experiments at BESSY have been also supported with H2020 Calypso Plus project, grant Nr. 18207084-ST and 182¬07393-ST. F. Traeger acknowledges the funding in the framework of the Erasmus+ Programme of the EU commission.

Speaker: A. Jagodar

419 O3.305 Real-time control of the CIII emission front using MANTIS

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/O3.305.pdf

One of the major challenges in realizing a commercially viable fusion reactor is the handling of the power and particle exhaust into the divertor of most used magnetic configurations today. A proposed approach isoperation in the so-called detached regime. An actuator, often local neutral gas puffing, increases the powerloss mechanisms, leading to a significant particle and heat flux reduction at the divertor target. However,such a detached regime has its internal dynamics and is sensitive to external perturbations that can be controlled through active monitoring and control of the gas puff actuator in real-time.Unfortunately, in detached conditions, many of the existing plasma diagnostics have a low signal-to-noise ratio or are not real-time capable.We sensed the radiation front location in real-time in TCV with imaging spectrometer MANTIS. In detached TCV L-mode plasmas, the radiation front is well approximated by the C-III emission front. The poloidal location of this front can be estimatedin real-time by newly developed image processing software acting upon direct camera images.The present set-up featuresa temporal resolution of 5ms and a -hardware limited-latency of 1 ms.A gas introduction valve with Deuterium gas was used as actuator. Theinput-output dynamics of the detached plasmas identified using a multi-sine system identification approach in two L-mode discharges. This yields the transfer function from the gas valve actuation to the measured front location,which was used to synthesise a conservative controller off-line. Subsequent closed loop experiments were carried out in which good tracking of the radiation position reference was achieved without additional tuning of the feedback controller. We will present MANTIS and the real-time emission front identification algorithm. We then will introduce the concept of system identification and the specific multi-sine identification procedure applied to the gas injection actuator. We show how the controller was derived and the resulting performance in TCV plasma detachment experiments.

Speaker: T. Ravensbergen

MCF

Convener: H.-S. Bosch (EPS2019)

420 I3.101 First-time realization of a stably detached efficient-particle-exhaust divertor regime in the island divertor at Wendelstein 7-X

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.101.pdf

The island divertor concept is an innovative and promising idea to handle heat and particle exhaust in stellarators. At the recently started stellarator Wendelstein 7-X, this divertor concept plays a central role in the device mission to demonstrate reactor relevant plasma confinement for steady-state time scales of up to 30 minutes in the high-performance campaign phase, OP2, starting in 2021. During the recently concluded first campaign with the island divertor, a large step in the experimental qualification of this divertor concept has been made. In discharges heated with Electron Cylotron Resonance Heating of 5-6 MW, central densities in the range of 0.8-1.2 10^20 m^-3 have been reached in combination with full divertor heat flux detachment and significant neutral gas compression for the first time. The divertor heat loads drop by an order of magnitude from >5 MW m^-2 to below 0.5 MW m^-2 with increasing density, and the compression of neutrals in the divertor reaches at least 30 with neutral pressure in the subdivertor volume of >8.0 10^-4 mbar. This is likely compatible with the steady-state particle exhaust requirements for high-performance steady-state operation in OP2. These discharges were held stably detached for up to 30 seconds, which is equivalent to several hundred energy confinement times and beyond the time scales for current relaxation. Electron temperatures above 2 keV in the plasma edge and 5keV in the plasma center were maintained. No impurity accumulation was seen at constant Zeff~1.5 and the stored energy stayed constant at around 600kJ. This contribution will explain the island divertor concept in W7-X, provide an overview of this recently discovered divertor regime, and describe the status of the physics understanding of these results including modeling of these regimes with the EMC3-EIRENE code.

Acknowledgement: This work was funded by the U.S. Department of Energy under grant DE-SC00014210 and DE-SC00013911 and has been carried out within the framework of the EUROfusion Consortium with funding from the Euratom research and training program 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: O. Schmitz (EPS 2019)

421 I3.102 Understanding ion and impurity flows in the Wendelstein 7-X stellarator

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I3.102.pdf

Two of the highest priorities in stellarator research are to verify the effects of orbit driftoptimization on the energy core confinement and to learn to prevent the accumulation of impurities in high-density plasmas. The basic framework for understanding energy and particle transport in these devices is neoclassical theory and plasma flows is one of its most fundamental predictions, upon which further transport modeling relies.
In this talk we will present an integral interpretation of flow measurements, in terms of the neoclassical ambipolar radial electric field and the Pfirsch-Schl¸ter and net parallel velocities, to test our understanding of plasma flows in high-density, low-collisionality (i.e. optimization relevant) plasmas. Furthermore, the deviation of impurity flow fields from an incompressible spatial variation has been linked to significant inhomogeneities of impurity density on flux surfaces (see e.g. [1] and references), which, in turn, give rise to a damped low-frequency oscillation in the radiation traces after sudden profile changes such as those caused by pellet injections [1]. The observation of a similar oscillation in W7-X plasmas [2] has sparked the question whether such impurity density variations can also be observed in W7-X and whether or not they are important in determining the radial impurity fluxes. In the talk, fluid and kinetic modeling of the density variation and radial fluxes will be presented and confronted with the observed X-ray oscillations as well as with the stationary radial fluxes calculated with the three-charge-states technique [3] to provide an up-to-date status of our understanding of these questions.

[1] J A Alonso, J L Velasco, I Calvo et al. 2016 Plasmas Phys. Control. Fus. 58 074009.
[2] C. Brandt, H. Thomsen, T. Andreeva et al. 2018 EPS Plasma Phys. Conference, P4.1056.
[3] A. Langenberg, N. Pablant, O. Marchuk et al. 2017 Nucl. Fusion 57 086013.

Speaker: J.A. Alonso (EPS 2019)

422 O3.101 Role of the radial electric field in Wendelstein 7-X

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.101.pdf

The role of the radial electric field in high performance ion-root plasmas on Wendelstein 7-X (W7-X) is examined and compared with neoclassical predictions. In stellarator plasmas the neoclassical radial electric field (Er) is not intrinsically ambipolar, and is instead strongly tied to the plasma profiles. The properties of the Er profile strongly influence neoclassical transport of heat, particle and impurities.
Measurements of the core radial electric field (Er) have confirmed that ion-root conditions (negative Er in the plasma core) have been achieved in W7-X with highdensity plasmas, central ERCH heating and temperature equilibration (Te~Ti). This is an important achievement as these are precisely the plasmas conditions for which W7-X has been optimized. These measured Er profiles agree well with the neoclassical ambipolar Er predicted by the code SFINCS. This good agreement provides confidence in the validity of neoclassical calculations in high-density ionroot conditions, and enables initial studies on the role of neoclassical transport in the optimized high-density regime of W7-X. In addition, these results provide validation that turbulent particle fluxes are intrinsically ambipolar.
Experimental radial electric field profiles are inferred from the perpendicular
velocity (u perp), as measured by the XICS diagnostic, and available with a high time resolution of up to 10ms. These diagnostic measurements provide the detailed profile evolution of the radial electric field in response to changes to the plasma density and heating power. Profile measurements of electron temperature (Te), ion temperature (Ti) and electron density (ne) along with approximations for the average value of Zeff have been used as inputs to the SFINCS code to calculate the ambipolar Er profile along with neoclassical ion and electron heat flux profiles (Qi, Qe). Finally the total experimental energy input to the electrons and ions, from ECRH heating and collisional heat transfer, has been compared to the neoclassical heat fluxes to provide a first estimate for the fraction of transport that can be attributed to neoclassical processes in reactor relevant high-density ion-root conditions.

Speaker: N.A. Pablant (EPS 2019)

423 O3.102 Study of impurity transport in deuterium and hydrogen plasmas in the edge stochastic magnetic field layer of Large Helical Device

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.102.pdf

The ergodic layer located at the plasma edge of Large Helical Device (LHD) consists of stochastic magnetic fields with three-dimensional structure intrinsically formed by helical coils. Reduction of impurity penetration into confinement region due to existence of the ergodic layer, so called "impurity screening", has been studied in LHD. Intensities of carbon line emissions have been monitored for multiple charge states with the different ionization potential, Ei. CIII (Ei = 48 eV, lambda = 977.03 Å) and CIV (Ei = 65 eV, lambda = 1548.02 Å) are measured using a 20 cm normal incidence vacuum ultraviolet (VUV) spectrometer while CV (Ei = 392 eV, lambda = 40.27 Å) and CVI (Ei = 490 eV, lambda = 33.73 Å) are measured using a grazing incidence extreme ultraviolet (EUV) spectrometer. A line intensity ratio of (CV + CVI) / (CIII + CIV) can be regarded as an indicator of the impurity screening effect. It has been observed that the ratio decreases with the electron density due to an increase of carbon lines emitted from outer region of the ergodic layer (CIII, CIV) as well as a decrease of those from inner region (CV, CVI), indicating enhancement of the impurity screening in high density regime [1]. Recently, we found that the impurity screening is more obvious in the deuterium (D) plasmas compared to the hydrogen (H) plasmas. The carbon flow in the ergodic layer was also measured by Doppler profile measurement of CIV line with space-resolved VUV spectroscopy [2]. The direction of the observed flow in both D and H plasmas was same as the friction force in the parallel momentum balance calculated with the impurity transport simulation based on a three-dimensional simulation code, EMC3-EIRENE, indicating enhancement of the impurity screening by the friction force. The impurity flow velocity in the D plasma was, however, smaller than that in the H plasma, which is considered due to the mass dependence of the thermal velocity of the bulk ions. Impurity transport analysis in terms of the screening effects are presented.

[1] M. B. Chowdhuri, S. Morita, M. Kobayashi et al., Phys. Plasmas 16 (2009) 062502.
[2] T. Oishi, S. Morita, S. Y. Dai et al., Nucl. Fusion 58 (2018) 016040.

Speaker: T. Oishi (EPS 2019)

424 O3.103 Energetic-particle-driven MHD instabilities and their control by ECH/ECCD in helical plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.103.pdf

Energetic alpha particles generated by D-T fusion reaction and beam ions for plasma heating interact resonantly with shear Alfvén waves through damping process when their velocity is comparable with Alfvén velocity, resulting in excitation of energetic particle (EP)-driven MHD instabilities. Several types of EP-driven MHD instabilities including toroidicity-induced AEs (TAEs), helicity-induced AEs (HAEs), global AEs (GAEs), energetic particle modes (EPMs) have been observed in NBI-heated plasmas of stellarators/heliotrons, Heliotron J, TJ-II and LHD. We have successfully demonstrated that electron cyclotron heating (ECH) and current drive (ECCD) are effective to mitigate and suppress the EP-driven MHD instabilities in the three devices [1-4]. The experimental and theoretical results suggest that the mode excitation in the shear Alfvén continua and the continuum damping related to magnetic shear have a key role on mode suppression. Some GAEs and EPMs have been stabilized in both co- and counter-ECCD in the low shear Heliotron J device, indicating that the magnetic shear is an important factor regardless of its sign. They are also suppressed by both on- and off-axis ECH in a magnetic field condition in TJ-II, while they are stabilized or destabilized in Heliotron J and LHD, depending on ECH power and deposition location. Discussed are the change in energetic ion profile by ECH through the change in bulk plasma, and/or the collisional damping due to trapped electrons in terms of AE stability.

[1] K. Nagaoka, et al., Nucl. Fusion, 53 (2013) 072004.
[2] K. Nagasaki, et al., Nucl. Fusion 53 (2013) 113041
[3] S. Yamamoto, et al., Nucl. Fusion 57 (2017) 126065
[4] S. Yamamoto, et al., 27th IAEA FEC, 2018, Gandhinagar, EX/1-3Ra

Speaker: K. Nagasaki (EPS 2019)

425 O3.104 Energy confinement in the pellet-enforced high-density regime at ASDEX Upgrade

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.104.pdf

Operation in a future fusion reactor will aim to establish a high plasma core density n0 in order to harvest a maximum output power. Hence, for example the near term EU-DEMO1 concept foresees operation at n0 values at or even beyond 1.2 the Greenwald density nGw. Like for most envisaged reactor scenarios this approach assumes as well a confinement that can be achieved as predicted by the H98(y,2) scaling. This scaling predicts that the energy confinement time E increases with the line averaged electron density as 0.41. However, the data set employed for deriving this scaling contains very little input from the high density regime. This is due to the fact that a significant loss of confinement sets in when gas puff fuelling is applied, encountering the H-mode density limit at about 0.8 - 0.85 x nGw. Reliable access to the high density regime while sustaining good confinement is typically allocated to the injection of fuelling pellets, mm sized bodies formed of solid hydrogen. Accordingly, fuelling experiments proved H-mode operation at trans-Greenwald density, the achievable confinement however never showed the favourable ~ 0.41 correlation. In order to provide a better understanding of the confinement behaviour in this pellet generated high-density regime, a data base was created covering a wide range of experiments performed at the all-metal-wall tokamak ASDEX Upgrade. They include plasma scenarios run with and without ELM mitigation, with and without impurity seeding, the ITER base line configurations but also straightforward technical discharges for actuator tests. In total, the data base contains 598 time slices from 47 different discharges; ranging from 0.5 - 1.85 x nGw. As expected, data above 0.8 x nGw shows a rather poor correlation with the H98(y,2) predictions, which are significantly overestimating observed values. Much better agreement is found with the more sophisticated scaling H06 which predicts a roll-over to ~ 0 when approaching high densities. Efforts taken for performance enhancement by e.g. shaping or seeding result in a clear positive impact below 0.8 x nGw; however these improvements are quickly fading away with increasing until beyond 1.2 x nGw no visible improvements remain. In the pellet-enforced high-density regime, the achievable plasma confinement becomes virtually insensitive to measures usually found effective for low and moderate densities. Major excursions from this behaviour are only observed for cases when deterioration is caused by adversities like e.g. excessive edge fuelling, core impurity accumulation or strong mode activity.

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: P.T. Lang (EPS 2019)

426 O3.105 Plasma performance in high-density and high-confinement regimes in Wendelstein 7-X

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O3.105.pdf

High-density operation is an attractive target for a fusion reactor, as it raises the fusion power output. Stellarators are especially suitable for such a regime, because they are not restricted by the disruptive density limit and because their energy confinement is roughly proportional to the square root of the density. The collisional coupling between ions and electrons is also improved, which is important for the dominant electron heating either by fusion alpha-particles or by ECRH. In addition, divertor detachment can be realized at sufficiently high densities, and, thus, the integrated operation with high power output and tolerable exhaust seems possible. In the last divertor campaign, OP1.2b, the operational space of the large optimized stellarator Wendelstein 7-X was expanded to relevant high densities. We present experimental results and transport analysis of three typical scenarios in the density range 0.8 x 10^20 - 2 x 10^20 m^-3 with closely equilibrated electron and ion temperatures: ECRH heated plasmas with edge gas fuelling, predominantly NBI heated plasmas and discharges with central pellet fuelling. Gas fuelled discharges with ECRH heating are characterized by flat density profiles, ion temperatures limited to values below about 2 keV and the energy confinement time close to the ISS04 scaling. NBI heated plasmas exhibit a pronounced density peaking and a particle barrier at the half radius, where the density peaking can be controlled by addition of a low fraction of ECRH heating. In pellet fuelled discharges, transient phases with improved energy confinement, ion temperatures as high as 3.5 keV and strong temperature gradients are observed. These phases demonstrate the highest stored plasma energy and the highest ion temperatures observed in W7-X so far. The significant improvement in the plasma performance seems to be related to strongly peaked density profiles. Also, in the last two scenarios a consistent reduction of broadband density fluctuations is found. Power balance is used to quantify energy losses in the neoclassical and turbulent channels, and to understand the influence of profile shaping on the transport and on the achievable plasma parameters.

Speaker: S. Bozhenkov (EPS 2019)

13:00 Lunch

Excursions

Thursday, 11 July

Plenary Session

Convener: A. Arefiev (UC San Diego)

427 I4.010 Plasma turbulence in the interstellar medium

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.010.pdf

The interstellar medium is a multi-phase, magnetized, and highly turbulent medium. In this talk, I will address both theoretical and observational aspects of interstellar turbulence. In the first, theoretical part of the talk, I will discuss the sources of turbulence, the properties of the turbulent cascade, the dissipation mechanisms, and the role played by turbulence in the interstellar medium. In the second, observational part of the talk, I will review the main diagnostics of interstellar turbulence, with emphasis on radio wave propagation effects.

Speaker: K. Ferriere (EPS 2019)

428 I4.011 Beyond a classical description of plasma physics. What does QED bring and change?

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.011.pdf

Plasma physics generally involves well-known physics of electromagnetism, special relativity and statistical mechanics. Various descriptions of the plasma state (kinetic, fluid, MHD) have been developed and each of them have a specific scope that depends on time/length scales, chemical composition, density, and temperature. Whereas these descriptions are well established, we could wonder when quantum electrodynamics (QED) comes into play. The answer lies in the threshold of QED cross sections which become non negligible for certain critical lengths, energies and fields. The presence of ultra-strong electromagnetic field and relativistic temperatures modifies the underlying basic physics to such a great extent that relying on classical plasma physics is often not justified.
The zoo of QED processes implies emission of hard photons, photon-lepton collisions, nonconstant number of particles (creation and annihilation), stochastic particle orbits, which have stimulated the community for constructing a QED-based plasma physics. While the state of development of QED-based plasma physics theory is still far from being as mature as that of the classical plasma theory, progress in this area has been achieved in the past few decades. These advances have implications in many astrophysical and laboratory scenarios (associated to new PetaWatt class lasers), that share common underlying microphysics and collective plasma effects associated with intense fields.
This new physics is highly nonlinear and multi scale, and require a combination of theory and large scale numerical simulations. The main challenges in this area with be presented and the recent progresses triggered by large scale simulations of compact objects and of multi dimensional laser/beam-plasma interactions in the presence of fields close to the critical Schwinger field will be discussed, emphasising the interplay between collective plasma dynamics and QED processes.

Speaker: T. Grismayer (EPS 2019)

10:10 Coffee Break

BPIF

Convener: L. Volpe (MIB)

429 I4.201 Theoretical modelling of picoseconds petawatt laser-plasma interactions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.201.pdf

With the development of kJ, petawatt (PW) class lasers, laser pulses with relativistic intensities (>= 10^18 W/cm^2) and over-picosecond (ps) pulse durations are becoming available. In such a ps relativistic regime, the energy transfer enters in a new regime as indicated by the recent multi-ps PW laser experiments, e.g., superthermal electron acceleration beyond the conventional ponderomotive scaling, and the consequent boosting of ion acceleration beyond the isothermal plasma expansion theory [1,2]. Laser-plasma interactions (LPI) with such a ps relativistic regime belong to the mesoscale between kinetic and fluid regimes, where energetic acceleration of kinetic electrons by the laser field takes place with the dynamic change of plasma structure in the ion fluid time scale. In this mesoscale regime, numerical simulation is challenging due to the extremely-high computational cost for the kinetic model.
Here, we present theoretical modeling of particle acceleration and plasma heating in the relativistic ps LPI. Relativistic laser lights push the overdense plasma surface by the giga-bar level light pressure, i.e., the hole boring (HB) process, which makes a steep laser-plasma interface and is essential for particle acceleration/heating. During over-ps laser irradiation, the pressure balance between plasma and laser light is established, and the HB stops eventually, owing to the formation of a steady ion flow at the HB front in the ps time scale [3]. After the HB stops, the hot plasma starts to blowout back towards the laser. This transition from the HB stage to the blowout stage enhances energetic electron acceleration and also bulk plasma heating. Moreover, in the case of thin foil plasmas, a Fermi-type stochastic acceleration of electrons takes place in the expanding plasma, which results a superthermal tail in electron energy spectrum. Such enhanced electron accelerations in the ps LPI result a boosted TNSA ion acceleration [1,4]. For high contrast lasers, the heat in the pre-plasma region can be transferred diffusively into the solid density region with the heat velocity of O(µm/ps), which enables a volumetric over-keV heating of dense plasmas with rich radiations [5]. These understandings are of fundamental importance not only for the ps PW lasers but also for LPI for the pedestal component of femtosecond ultrahigh intensity lasers.

[1] A. Yogo et al., Sci. Rep. 7, 42451 (2017).
[2] D. Mariscal et al., 60th APS-DPP, Portland, USA, Nov. 2018.
[3] N. Iwata et al., Nat. Commun. 9, 623 (2018).
[4] N. Iwata, et al., Phys. Plasmas 7, 073111 (2017).
[5] Y. Sentoku, IFSA2017, Saint Malo, France Sep. 2017; N. Higashi et al., 60th APS-DPP, Portland, USA, Nov. 2018.

Speaker: N. Iwata (EPS 2019)

430 I4.202 Volumetric Ion Acceleration

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.202.pdf

Mass-Limited Targets (MLT) represent an interesting option for many applications, based on laser-plasma interactions. Various theoretical studies investigated MLT's extensively. Experimental verification of these schemes is extremely demanding, due to the technological challenges on targetry and requirements on the laser system. In this talk, we present a target system for MLT. By the use of a Paul Trap we levitate targets of spherical geometries and position these targets with submicron precision. This target system can handle a range of target masses from 0.5 femtogram to 5 nanogram, corresponding to plastic spheres with radii ranging from 500 nm to 50 µm. In this talk we present experimental evidence on volumetric ion acceleration of plastic spheres with 1 µm diameter. Target pre-expansion was measured via an inline holography. It was found that the target density drops to near critical values. These microscopically small near critical plasmas enable the volumetric acceleration of protons beams with mono-energetic features. 3D-particle in cell simulations reproduced the experimental results. The simulations helped to gain insight into the acceleration mechanism from these small under-critical plasmas. Routes for future optimizations are shown.

Speaker: P. Hilz (EPS 2019)

431 O4.201 Plasma-based dynamic volume holographic elements for high-intensity lasers

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.201.pdf

The manipulation of intense laser fields by solid-state devices is severely limited due to nonlinearities and damage threshold issues as the fluence of high-intensity laser pulses is more than five orders of magnitudes larger than what conventional materials can sustain. In recent years, novel concepts how structured plasmas can be used as damage-less optics, e.g. in the form of mirrors [1], wave-plates and polarizers [2,3], emerged. Plasma holograms created by the overlap of two lasers at the surface of a flat foil where demonstrated to be able to induce optical angular momentum to high-intensity pulses [4]. We demonstrate that it is possible to create volumetric plasma holograms that allow to store complex phase information of optical fields. Our concept allows to create holographic optical elements using moderate intensity laser pulses which are subsequently read out by highintensity pulses. These holograms can e.g. act as focussing elements that at the same time can compensate phase-errors in the read-out pulse via pre-compensation. In order to demonstrate the high phase-sensitivity of the volume hologram, we show in simulations that it is possible to store and retrieve complex phase information such as that of Laguerre-Gaussian (LG) laser pulses. LG laser pulses are of strong current interest in the context of particle acceleration concepts, their production with intensities far above the relativistic threshold, however, remains challenging. Plasma volume holograms offer a potential way to produce such pulses at ultra-relativistic intensities.

[1] S. Monchocé, S. Kahaly, A. Leblanc, L. Videau, P. Combis, F. Réau, D. Garzella, P. D'Oliveira, P. Martin, and F. Quéré, Phys. Rev. Lett. 112, 145008 (2014)
[2] D. Turnbull, P. Michel, T. Chapman, E. Tubman, B. B. Pollock, C. Y. Chen, C. Goyon, J. S. Ross, L. Divol, N. Woolsey, and J. D. Moody, Phys. Rev. Lett. 116, 205001 (2016)
[3] G. Lehmann and K. H. Spatschek, Phys. Rev. E 97, 063201 (2018)
[4] A. Leblanc, A. Denoeud, L. Chopineau, G. Mennerat, P. Martin, and F., Quéré, Nature Phys. 13, 440 (2017)

Speaker: G. Lehmann (EPS 2019)

432 O4.202 mpact of ultrafast laser generated Weibel magnetic fields on propagation dynamics of relativistic electron bunches

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.202.pdf

During laser-solid target interactions, the onset of Weibel instability can generate super-strong magnetic field structures (up to several tens of MG) on the surface and within the bulk of the solid targets. Such magnetic fields can be used to understand several physical events in astrophysics such as blast wave shocks in gamma ray bursts, supernovae remnants, energetic inflows and outflows in white dwarfs and Active Galactic Nuclei. Further the instability is equally important for laser driven inertial confinement fusion (ICF) process and gamma-ray generation experiments. Here we report on the probing of Weibel magnetic fields at femtosecond time scale during the interaction between ultrashort (30 fs) highly relativistic (intensity I0 > 10^18 W/cm^2) laser pulses and solid targets, using electron bunches from laser wakefield accelerators. We will present experimental and simulation results showing integrated B-field of few kT⋅𝜇m generated at the surface and in the bulk of the solid target within a depth of a few of microns. The results show that Weibel instability at femtosecond time scale can be explored with a convenient and simple method based on laser wakefield acceleration.

Speaker: G. Raj (EPS 2019)

433 O4.203 Influence of near wavelength sized focal spots on laser driven ion acceleration

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.203.pdf

A study of the influence of laser focal spot size on the acceleration of protons at intensities up to 5 x 10^21 Wcm^-2 is presented. Through the use of ellipsoidal, F/1 focusing plasma mirrors, focal spot sizes (~ 1.5 µm) on the order of the laser wavelength (1.054 µm) are achieved [1, 2]. Results are compared with measurements made using the same laser, but instead employing a conventional planar plasma mirror, producing focal spots of approximately 4 µm full width at half maximum, from an F/3 off-axis parabola.
The effect of using wavelength scale focal spots on maximum proton energy is initially explored for micron thick targets, where the acceleration is dominated by target normal sheath acceleration. Furthermore, the spatial and spectral properties of the accelerated proton population are investigated, with a significant enhancement in the laser-to-proton energy conversion efficiency observed for tight focus. We also present measurements using ultra-thin foil targets, in a regime where the acceleration of high energy protons is driven by a hybrid mechanism involving significant radiation pressure and transparency effects [3]. In this case, we observe a reduction in the maximum achieveable proton energies for tight focus, with the proton energy exhibiting plateau-like behaviour as intensity is increased beyond ~10^21 Wcm^-2.

References
[1] R. Wilson, M. King, R. J. Gray, D. C. Carroll, R. J. Dance, C. Armstrong, S. J. Hawkes, R. J. Clarke, D. J. Robertson, D. Neely and P. McKenna, Phys. Plasmas 23, 033106 (2016)
[2] R. Wilson, M. King, R. J. Gray, D. C. Carroll, R. J. Dance, N. M. H. Butler, C. Armstrong, S. J. Hawkes, R. J. Clarke, D. J. Robertson, C. Bourgenot, D. Neely and P. McKenna, Quantum Beam Sci. 2018, 2(1), 1
[3] A. Higginson, R. J. Gray, M. King, R. J. Dance, S. D. R. Williamson, N. M. H. Butler, R. Wilson, R. Capdessus, C. Armstrong, J. S. Green, S. J. Hawkes, P. Martin, W. Q. Wei, S. R. Mirfayzi, X. H. Yuan, S. Kar, M. Borghesi, R. J. Clarke, D. Neely and P. McKenna, Nature Communications 9, 724 (2018)

Speaker: T. Frazer (EPS 2019)

434 O4.204 Achieving extreme light intensities using optically-structured plasma mirrors

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.204.pdf

Achieving a light source delivering intensities up to the Schwinger limit of 10^29W/cm^2 would allow exploring novel regimes of strong-field Quantum ElectroDynamics (QED) where vacuum would be ripped apart. A promising candidate to build such a light source would be to find a realistic implementation of the Curved Relativistic Mirror (CRM) concept which consists in: (i) inducing a Doppler upshift and temporal compression of a counter-propagating incident laser (ii) focusing the upshifted radiation down to a focal spot size much smaller than the one possible with the incident laser. Since its emergence in 2003 [1], many implementations of the CRM concept were proposed. However, none has led to a detailed and feasible experimental proposal, mainly because they make use of idealized experimental conditions that are either not realistic or beyond present experimental know-how. In this context, we propose a novel and realistic all-optical scheme [2] to implement the CRM concept using so-called relativistic 'Plasma Mirrors' (PM) formed when an ultraintense laser with high-contrast is focused on an initially-flat solid target. In this scheme, the PM surface is optically curved, either by radiation pressure or using secondary pre-pulse beams. As we demonstrate, this enables a considerably higher control of the PM shape than the one obtained with all other schemes proposed so far relying on the use of pre-shaped solid targets, which are beyond present State-Of-The-Art of manufacturing techniques. Besides and as opposed to previous implementations, our new scheme is validated using cutting-edge 3D PIC simulations at an unprecedented scale using the pseudo-spectral 3D PIC code WARP+PICSAR. These simulations show that intensities between 10^25W/cm^2 and up to 10^28W/cm^2 can be achieved with a 3PW laser. The very high robustness of this scheme to potential laser/plasma defects and its feasibility are demonstrated by inputting the measured spatio-temporal profile (amplitude and phase) of the BELLA PW laser in PIC simulations. To account for the QED effects occurring at such intensities, novel QED modules have been added in the code and will be discussed here. These modules will be essential to find clear signatures of the intensities achieved in experiments. As our scheme is achievable with current experimental know-how on a multi-PW laser, it should soon become a game-changer in high field Science.

[1] S. V. Bulanov et al, PRL, 91, 085001 [2] H. Vincenti, PRL, in review, ArXiv: 1812.05357

Speaker: L. Fedeli (EPS 2019)

435 O4.205 Identification of coupling mechanisms between ultraintense laser light and dense plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.205.pdf

The interaction of intense laser beams with plasmas created on solid targets involves a rich non-linear physics. Because such dense plasmas are reflective for laser light, the coupling with the incident beam occurs within a thin layer at the interface between plasma and vacuum. One of the main paradigms used to understand this coupling, known as Brunel mechanism, is expected to be valid only for very steep plasma surfaces.
Despite innumerable studies, its validity range remains uncertain, and the physics involved for smoother plasma-vacuum interfaces is unclear, especially for ultrahigh laser intensities. We report the first comprehensive experimental and numerical study of the laser-plasma coupling mechanisms as a function of the plasma interface steepness, in the relativistic interaction regime. Our results reveal a clear transition from the temporally-periodic Brunel mechanism to a chaotic dynamic associated to stochastic heating. By revealing the key signatures of these two distinct regimes on experimental observables, we provide an important landmark for the interpretation of future experiments.

Speaker: G. Blaclard (EPS 2019)

BSAP: C. Fendt

Convener: C. Fendt (EPS2019)

436 I4.401 Alfvénic fluctuations in the solar wind: nonlinearities and kinetic effects

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.401.pdf

Large amplitude, turbulent Alfvénic fluctuations have been commonly observed in the solar wind since the first in-situ measurements. An important but still unexplained property of such nonlinear fluctuations seen typically in the fastest streams is that, despite the large excursion of the magnetic field fluctuations, the magnitude of the total magnetic field remains nearly constant, a condition that corresponds to spherical polarization. How is this Alfvénic turbulent state achieved in the solar wind remains a fundamental open question of Heliophysics, and in all of Astrophysics.
Although nonlinear Alfvénic fluctuations have been studied for several decades, most of previous work has considered a plasma in thermodynamic equilibrium. The solar wind however displays many non-thermal features, such as pressure anisotropies and drifting populations of protons and heavy ions. After reviewing the fundamental properties of Alfvénic fluctuations in the solar wind, we investigate how non-thermal effects (in particular pressure anisotropy), the presence of different ion populations and nonlinearities affect their stability and nonlinear evolution in different plasma-beta regimes.

Speaker: A. Tenerani (EPS 2019)

437 I4.402 High-realism gyrokinetic simulations for solar wind turbulence

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.402.pdf

One of the most eminent unsolved problems in space plasma physics is the nature of turbulent energy dissipation at small spatial scales, which is thought to explain the heating of the heliospheric plasma that has been consistently observed through space craft measurements[1].
Three-dimensional kinetic simulations (reduced or fully kinetic) are increasingly used to study the properties of turbulence and instabilities that occur in such plasmas[2, 3, 4, 5]. Owing to the large computational expense of such simulations, these are commonly carried out with just a single particular means of turbulence generation, hindering a comparison of the results obtained from different simulations and physics models. Furthermore, no systematic studies have been performed of how the kinetic turbulence properties (and hence the resultant heating) depend on the manner of energy injection.
Here, we address both gaps by means of gyrokinetic turbulence simulations using the GENE code[6]. In particular, we apply the code to parameters comparable to the near-Earth solar wind, and examine the effects of moving from a isotropic, balanced energy injection scheme to a more realistic imbalanced or aligned injection scheme that mimics conditions as they may be found in the solar wind.

References
[1] R. Bruno, V. Carbone, Living Rev. Sol. Phys. 10: 2 (2013)
[2] M. Wan et al., Phys. Rev. Lett. 114, 175002 (2015)
[3] D. Told et al., Phys. Rev. Lett. 115, 025003 (2015)
[4] S.S. Cerri et al., Astrophys. J. Lett. 846 L18 (2017)
[5] D. Groselj et al., Phys. Rev. Lett. 120, 105101 (2018)
[6] F. Jenko et al., Phys. Plasmas 7, 1904 (2000)

Speaker: D. Told (EPS 2019)

LTPD

Convener: E. Kovacevic (PG)

438 I4.301 A diffusion approach to vibrational kinetics of molecules in plasma

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.301.pdf

Modelling of vibrational kinetics of molecules in a plasma environment is a very important and interdisciplinary topic linking plasma physics to chemical physics and has applications to clean energy issues, materials science and space exploration. In particular, CO2 is presently under widespread investigation in the perspective of carbon neutral fuels and oxygen production on Mars. Most of present literature on the subject is based on the Stateto-State approach (STS) which is convenient but time consuming and hinders somewhat the insight. The authors have developed a new approach which is based on reconsidering the powerful and mathematically appealing diffusion approaches developed mostly in the 70s. In these lasts, a function F is introduced, F being a doubly derivable extension of the vibrational distribution to a continuum of internal energy. This function F is assumed to be the solution of a Fokker-Planck equation. The new method proposed is based on numerical and semi-analytical approaches and allows us to remove some approximations limiting the original approach and reproduces closely present STS calculations. Furthermore, the possibility to apply the language and techniques of transport and diffusion processes to vibrational kinetics provides a complementary view, somewhat faster codes and new insight into molecular physics and process optimization.

Speaker: S. Longo (EPS 2019)

439 O4.301 Theoretical backgrounds of the apokamp-type atmospheric plasma jet in the electro-negative gas medium

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.301.pdf

In 2016 the group of experimentalists led by Eduard Sosnin in the Institute of High Current Electronics has been discovered a new phenomenon in gas discharge physics: an extended plasma jet developing perpendicular to the bending point of the arc discharge channel between two electrodes (E.A. Sosnin et al., JETP Lett., 103, 2016). This phenomenon occurs if the discharge ignites between two electrodes, one - is under the high pulse-periodic potential, and the other has floating potential, i.e. connected via a capacitor to a ground. The discharge has been entitled as "apokamp" from Greek απó -“off” and καμπη -“bend”). As it was found, a single needle or a conical jet of 6-7 cm length being attached to the bending point of the current channel represents an apokamp. This unusual new type of gas discharge is observed at high (atmospheric) and medium pressures in gas mixtures containing a small portion of an electronegative gas, e.g. oxygen or chlorine. In inert gases, this phenomenon does not exists. It should be noted that depending on the parameters of voltage pulses, the apokamp can be also represented by several plasma jets developing perpendicular to the current channel from the points of its bending (E.A. Sosnin et al., EPJ D, 71, 2017).
We use the deterministic model ("two-moment model") of a multicomponent discharge plasma to describe a self-sustained periodic discharge in pure oxygen both in the inter-electrode gap and in the surrounding space above the electrodes. To simplify the consideration a 2D-model is used instead of 3D, so the discharge between two plane electrodes with similar to experimental physical conditions has been considered. The high-voltage potential is connected to the pulse voltage source through the 10 kOhm ballast load. The floating potential electrode is connected to the ground through the 10 pF capacitance. The model also includes grounded electrode far beyond the discharge electrodes system. We consider simplified plasma-chemical reactions and species sets for oxygen. Namely, the reduced formulation includes only electrons, neutral molecules O2, positive O2+ and negative O2- single charged ions. The reactions number are restricted to four: electron impact ionization, impact dissociation, electron attachment and ion-ion recombination.

Speaker: V. Kozhevnikov (EPS 2019)

440 O4.302 Theory of transport coefficients in Yukawa fluids (complex plasma)

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.302.pdf

The purpose of this paper is to present simple and accurate practical expressions to estimate the viscosity and self-diffusion coefficients of three-dimensional Yukawa fluids in a wide parameter regime. The expression for the viscosity coefficient is based on a freezing temperature's scaling discussed recently by Costigliola et al. [1] in the context of dense simple fluids (LennardJones system, argon, methane, and liquid sodium). It is demonstrated that this scaling applies well to Yukawa systems, which allows estimation of the shear viscosity in a very extended range of temperatures, from the melting point to 100 times the melting temperature [2]. One of the recent approaches to the self-diffusion coefficient in strongly coupled Yukawa fluids [3] is briefly discussed. However, more attention is focused on the Stokes-Einstein (SE) relation. When self-diffusion of atoms in simple pure fluids is considered, the SE relation takes the form

D eta(Delta/T) = Alpha

where D is the self-diffusion coefficient, eta is the viscosity coefficient, Delta= n^(-1/3) is the mean interparticle distance, n is the particle density, T is the temperature (in energy units), and alpha is the SE coefficient. Theory predicts that the coefficient can be related to the properties of collective excitations [4], and expressed in terms of the longitudinal-to-transverse sound velocity ratio [5]. As a consequence alpha ~ 0.13 for soft long-range repulsive interactions, including Yukawa fluids as a representative example. Using existing numerical data it is documented that SE relation with 0.13 works extremely well for strongly coupled Yukawa fluids, providing a useful tool to estimate one of the transport coefficients when the other is known. Some aspects of the temperature dependence of the shear viscosity and diffusion coefficients on approaching the fluid-solid phase transition are discussed. The results are mainly intended for the field of complex (dusty) plasmas. However, relations to other related systems are pointed out, in particular, to the transport coefficients of liquid metals at the melting temperature.

References
[1] L. Costigliola et al., J. Chem. Phys. 148, 081101 (2018).
[2] S. Khrapak, AIP Adv. 8, 105226 (2018).
[3] S. Khrapak, B. Klumov, L. Couedel, J. Phys. Commun. 2, 045013 (2018).
[4] R. Zwanzig, J. Chem. Phys. 79, 4507 (1983).
[5] S. Khrapak, J. Chem. Phys. (2019, submitted).

Speaker: S.A. Khrapak (EPS 2019)

MCF

Convener: C. Maggi (CCFE)

441 I4.101 Dynamics of the edge transport during edge localized mode cycles

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.101.pdf

Recent advances in the diagnostic capabilities at ASDEX Upgrade (AUG) allow us to measure the edge profiles on a sub-ms timescale and with a spatial resolution of less than 5 mm. This makes it ideal to study the profile recovery during fast transient events. Here, we present the dynamic behaviour of the energy, particle and momentum transport during edge localized mode cycles at the plasma edge of AUG by combining a comprehensive set of pedestal measurements with interpretive and predictive modelling. The dynamics of the ion and electron kinetic profiles were measured in deuterium and helium plasmas with unprecedented time resolution down to 100 s. At the ELM onset, the separatrix Ti increases, leading to a reduced gradient in the pedestal [1]. Shortly after the initial separatrix increase, the whole profile drops and then the pedestal starts to build up again. The pre-ELM profile is fully recovered 3-4 ms after the ELM crash. Comparing the ion to the electron temperature profile revealed that the ion temperature gradient reaches its pre-ELM value after the ELM crash on a faster timescale than the electron temperature gradient. The ion temperature and electron density gradient recover to their pre-ELM values on similar timescales, while the electron temperature gradient recovers only 7-8 ms after the ELM onset. The saturation of DeltaTi and Delta ne is correlated with the onset of medium-frequency fluctuations (f~50 kHz) [2], while high-frequency fluctuations (f~200 kHz) appear when Delta Te recovers [3], indicating a different clamping mechanism for the ion and electron energy and particle transport. The edge toroidal rotation recovers on a similar timescale as Delta Ti. This was observed in both deuterium and helium plasmas, the latter enabling measurements of the main ion species. Compared to the impurity toroidal rotation, which exhibits a local minimum at the plasma edge during the inter-ELM phase, the edge main ion toroidal rotation has a much less pronounced dip and is rather flat. During the ELM the main ion toroidal rotation in the pedestal drops by about 5-10 km/s. This is in contrast to the behaviour of the impurity toroidal rotation, which shows a flattening of the toroidal dip feature. Integrated modelling of the various transport channels allows us to shed light on the dynamic behaviour of the transport coefficients during the ELM cycle. The analyses reveal that the ion heat transport is at the neoclassical level before the ELM crash in the region where the edge ion temperature gradient is maximal. Further inwards, the ion heat transport is about a factor of 4-5 above the neoclassical level. Two possible mechanisms for the additional energy transport in the electron channel (electron temperature gradient modes and neutral ionization) that could cause the delay in the DeltaTe recovery, were studied. The energy loss due to ionization of neutrals was found to be insignificant, while ETGs cannot be excluded. The dominant effect comes from the depletion of energy caused by the ELM. The local sources and sinks for the electron channel in the steep gradient region are much smaller compared to the energy flux arriving from the pedestal top, indicating that the core plasma may dictate the local dynamics of the Delta Te recovery during the ELM cycle.

[1] M. Cavedon et al, PPCF 59 105007 (2017)
[2] F. Mink et al, NF 58 026011 (2018)
[3] F. M. Laggner et al, PPCF 58 065005 (2016)

Speaker: E. Viezzer (EPS 2019)

442 I4.102 Gyrokinetic Comparison of JET-ILW and JET-C Pedestal Transport

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.102.pdf

An ITER-like wall (ILW), composed of a tungsten divertor and beryllium chamber, was installed on JET in order to study material erosion and tritium retention in preparation for ITER. The ILW has successfully demonstrated long-term tritium retention but has had an unexpected impact on confinement via its effect on the H-mode pedestal. Since commencement of JET-ILW operation, the JET pedestal is limited to lower pedestal top temperatures than were accessible during earlier JET-carbon (C) operation. This talk focuses on the changes in turbulent transport that arose due to the transition from JET-C to JET-ILW. Understanding these transport dynamics may be key to maximizing confinement in the upcoming JET deuterium-tritium campaign as well as ITER. We will present a comparison of the gyrokinetic instabilities and resulting transport produced in two representative pedestals-one from JET-C and another from recent JET-ILW operation. A comparison of the profiles and heating power reveals a stark qualitative difference between the discharges: JET-ILW requires twice the heating power to sustain roughly half the temperature gradient of JET-C. This points to heat transport as a central component of the dynamics limiting the JETILW pedestal and reinforces the following emerging JET-ILW pedestal transport paradigm, which is the focus of this talk. ILW conditions modify the density pedestal in ways that decrease the pedestal density gradient. This is attributable to some combination of direct metal wall effects and the need for increased fueling to mitigate tungsten contamination. The modification to the density profile increases eta (the ratio of the normalized temperature gradient to that of the density gradient), thereby producing more robust ion temperature gradient (ITG) and electron temperature gradient (ETG) driven instabilities. Collectively, these effects limit the pedestal temperature and demand more heating power to achieve good pedestal performance. Impurity seeding has been observed to mitigate the JET-ILW pedestal limitations. We will present analysis of impurity seeded discharges and discuss mechanisms by which seeding can result in improved pedestal structure.

Speaker: D. Hatch (EPS 2019)

443 O4.101 Formation of a staircase pedestal with suppressed Edge-Localized-Modes (ELMs) in the DIII-D tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.101.pdf

We observe the formation of a high-pressure staircase pedestal (~16-20 kPa) in high beta p plasmas (beta p>1.5) in the DIII-D tokamak when large amplitude ELMs are suppressed using resonant magnetic perturbations (RMP). The pedestal cyclically transitions from a one-step structure to a wider two-step staircase structure, with a period of ~40-60 ms. In the wide pedestal phase a strong flattening of the electron density and temperature develops in mid-pedestal, producing the staircase pedestal structure[1]. Also, localized bursting fluctuations are seen in the this flat region (rho~0.95). Fluctuations at the pedestal top (rho~0.8) are periodically enhanced by RMP[1], and drive the narrowing of the pedestal width. Gyrokinetic analysis using the newly developed CGYRO[3] code and experimental fluctuation measurements (BES diagnostic) reveal that the feedback effect of reduced ExB shear in mid-pedestal on the enhancement of transport by trapped electron modes results in transport bifurcation which eventually leads to local flattening of profiles and staircase pedestal formation[3]. By enhancing the confinement and drastically reducing the peak of heat flux to diverter, formation of the staircase pedestal opens a path for optimizing the steady-state operation in ITER and future reactors.

Work supported by US DOE under DE-FC02-04ER54698 and DE-AC02-09CH11466.
[1] R. Nazikian, et al., Nuclear Fusion 58 (2018)
[2] J. Candy, et. al., J. Comp. Phys. 324 (2016)
[3] A. Ashourvan, et al., submitted to PRL

Speaker: A. Ashourvan (EPS 2019)

444 O4.102 Isotope dependence of the pedestal in JET-ILW type I ELMy H-modes

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.102.pdf

A strong, favourable isotope dependence of the energy confinement (tao E,th ~ A^0.4) has been found in Hydrogen (H) and Deuterium (D) JET-ILW type I ELMy H-modes, originating at the pedestal [1]. Also, the plasma density is systematically lower in H than in D plasmas [1]. This contribution examines the isotopic dependence of the pedestal on linear MHD stability, ELM losses and pedestal structure in low delta type I ELMy H-modes in H and D. The direct isotope effect on pedestal stability is taken into account by including the diamagnetic frequency in the stability criterion with the ideal MHD HELENA/ELITE codes [2, 3, 4] and is found to be small. Interpretative EDGE2D-EIRENE simulations [5, 6] using the so-called 'corner-corner' divertor configuration and simultaneous upstream (ne, Te from Thomson-scattering (TS)) and outer divertor target profile (heat flux deposition from IR camera) constraints indicate higher separatrix temperature (Te,sep) and lower separatrix density in H than in D for a pair of discharges at similar stored energy (which required higher input power in H than in D). As Te,sep is used to position the profiles with respect to the separatrix, higher Te,sep in H translates into significant destabilisation of Peeling-Ballooning modes compared to D, which is consistent with type I ELMs being triggered at lower pedestal pressure in H. The ELM energy losses, evaluated from EFIT stored energies and TS kinetic profiles are found to be dominated by density loss both in H and D. At low ELM frequency (fELM), ELM particle losses (evaluated from interferometry) increase with fELM, in correlation with decreasing pedestal top density (ne,PED). Thus, the observed higher fELM in H than in D at same input power possibly contributes to the lower ne,PED in H. However, ELM particle losses saturate at higher fELM, both in H and in D, implying that other mechanisms may also play a role in the lower ne,PED in H. The pedestal density width is found to be narrower, or at most similar, in H than in D, in contradiction with the neutral penetration model (NPM) [7]. This challenges the validity of the NPM in the analysed pedestals and implying that fuelling inside the separatrix is not the only responsible physics mechanism for the difference between ne,PED in H and D. The EDGE2D-EIRENE simulations indicate that higher edge heat and particle transport in H than in D could be the main reason for the different pedestals.

[1] C.F. Maggi et al., PPCF 60, 014045 (2018)
[2] G.T.A. Huysmans et al., Comp. Phys. Proc. Int. Conf. 371 (1991)
[3] H.R. Wilson et al., PoP 9, 1277 (2002)
[4] P.B. Snyder et al., PoP 9, 2037 (2002)
[5] D. Reiter, JNM 196-198, 80 (1992)
[6] R. Simonini et al., CPP 34, 368 (1994)
[7] R.J. Groebner et al., PoP 9, 2134 (2002)

Speaker: L. Horvath (EPS 2019)

445 O4.103 Pedestal modes interactions triggering bursts and leading to the onset of edge localized modes on DIII-D

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.103.pdf

We report on recent investigations in DIII-D of three-wave interactions between pedestal modes during quasi-stationary inter-ELM phases leading up to the type I ELM onset. Prior to eruptive events such as ELMs, these pedestal modes, also called quasi-coherent fluctuations, are observed in the edge of fusion devices[1]. Analysis of these dominant modes, with density and magnetic signatures, identifies them as a key player in the triggering mechanism of a certain class of ELMs. This class of ELMs appears to be triggered far away from the peeling ballooning limit, similar to observations in JET-ILW [2]. We demonstrate that one of these modes is amplified by the two others through three-wave interactions. This result is obtained using bicoherence analysis of magnetic signals to show that coherent wave coupling leads to the amplification of a third mode of frequency that is the sum of the first two modes. The intensity of the third mode increases during the second half of the ELM cycle and is radially shifted relative to the other two modes towards the last-closed flux surface as the ELM event approaches[ 3]. This shifting is observed with spatially localized measurements of density fluctuations at the same frequencies as observed in the magnetics. In addition, there are regimes where the pedestal modes' nonlinear interaction results in burst activities prior to ELMs[4,5]. The talk will describe analyses of the two regimes and argue that pedestal modes interaction via three-wave coupling, associated with radial distortions pushing out of the pedestal, is a possible mechanism for the triggering of low frequency type I ELMs relevant for future fusion devices.

[1] Perez et al., PPCF, 46, 61 (2004); Diallo et al Phys. Rev. Lett. 112, 115001 (2014); Laggner et al. PPCF, 58, 065005, (2016);
[2] C. Maggi et al. Nucl. Fusion 57 (2017) 116012
[3] Diallo et al., Phys. Rev. Lett. 121, 235001 (2018)
[4] C. Bowman et al., Nuclear Fusion, 58(1):016021, 2018.
[5] P. Hennequin et al., In 44th EPS Conf. on Plasma Physics, number PI.167, 2017.

Speaker: A. Diallo (EPS 2019)

446 O4.104 The ballooning structure of small edge localized modes on AUG and TCV

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.104.pdf

In future fusion devices the collisionality Nue proportional to ne/Te^2 at the pedestal top will be very low, i.e. nue,pedtop ∼0.06 [1], due to the expected high temperature. On the other hand at the very edge it should be high, nu*e,sep ∼12, because a high separatrix density is necessary for efficient power exhaust. These conditions cannot be reached simultaneously in nowadays machines. ASDEX Upgrade [2] and TCV [3] discharges with high separatrix collisionality, comparable to ITER, exhibit small Edge Localized Modes (ELMs) if the plasmas are highly shaped, i.e. high triangularity and close to double null at high elongation. Stability calculations have shown that these small ELMs are close to the ballooning stability boundary and ballooning modes are therefore promising candidates [4]. This is underlined by experimental observations showing that they are located close to the separatrix, driven by the pressure gradient and stabilized by magnetic shear.
The former is demonstrated by locally changing the pressure gradients via local gas fuelling in contrast to pellet fuelling. The dependence on the magnetic shear is experimentally validated by small changes in the z position, which modifies the shear close to the separatrix and thus, properties of small ELMs. Infinite n-ballooning calculations performed with the HELENA code are shown to give more evidence for the instability of these plasmas in a narrow region close to the separatrix. It is demonstrated how these small ELMs modify the shape of the pedestal close to the separatrix in such a way that it is stable against large type-I ELMs. Using data from Doppler reflectometry as well as the thermal He beam diagnostics this contribution will also show that the filamentary structure changes significantly in the small ELM phases. The modification of the pedestal profile due to the enhanced transport can therefore be of great importance for the power exhaust in future ITER discharges.

References
[1] A Loarte et al. 2003 Plasma Phys. Control. Fusion 45 1549
[2] G.F. Harrer et al. 2018 Nuclear Fusion 58 112001
[3] B. Labit et al. 2018 IAEA Fusion Energy Conference
[4] S. Saarelma et al 2013 Nuclear Fusion 53 123012

Speaker: G.F. Harrer (EPS 2019)

BPIF-BSAP

Convener: M. Grech

447 I4.J501 High-quality gamma-rays driven by petawatt laser pulse in near-critical density plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.J501.pdf

The nonlinear synchrotron radiation of direct laser-accelerated electrons in nearcritical density (NCD) plasmas recently has been proposed as a very efficient scheme to produce multi-MeV gamma-rays [1]. In this presentation, we demonstrate that by employing a plasma density channel, the divergence angle and transverse size of the gamma-rays can be much reduced [2]. In addition, we propose a highly efficient gamma photon emitter obtained by irradiating a not-so-intense laser pulse on a miniature plasma device consisting of a plasma lens and a plasma mirror [3]. In this novel scheme, brilliant gamma-rays with very high conversion efficiency (higher than 1%) and spectral intensity (higher than 10^9 photons/0.1%BW/s) can be achieved by employing currently available lasers with intensity of 10^21 W/cm^2. The practical effects of different nanostructures in the plasma lens and the oblique laser incidence are also discussed in this scheme [4]. At last, a novel scheme by exploiting an intense Laguerre Gaussian laser pulse interacting with under-dense plasmas is also proposed to produce helical gamma-rays with very small divergence angle (less than 5Deg) and ultra-high brilliance (~10^24 photons/s/mm^2/mrad2/0.1%BW) at a laser intensity of 10^22 W/cm^2 [5]. Such high-quality gamma-rays generated in these schemes would find applications in wideranging areas.

References
[1] D. J. Stark et al., Phys. Rev. Letts. 116, 185003 (2016).
[2] T. W. Huang et al., Appl. Phys. Letts. 110, 021102 (2017).
[3] T. W. Huang et al., New J. Phys. 21, 013008 (2019).
[4] T. W. Huang et al., Plasma Phys. Control. Fusion 60, 115006 (2018).
[5] L. B. Ju, T. W. Huang et al., submitted (2019).

Speaker: T. Huang (EPS 2019)

448 O4.J501 Plasma grating: Giant standing ion acoustic waves

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.J501.pdf

We study formation of large amplitude standing ion acoustic waves (SIAW) by nonlinear phase-locking (autoresonance) with a weak, chirped frequency standing ponderomotive drive. These waves comprise a nonlinear two-phase solution each phase locked to one of the two traveling waves comprising the drive. The autoresonance in the system is guaranteed provided the driving amplitude exceeds a threshold. The phenomenon is analysed via Whitham's averaged variational principle applied to a nonlinear warm fluid model. The local ion and electron densities in the autoresonant SIAW may significantly exceed the initial unperturbed plasma density and are only limited by the kinetic wave-breaking. Work supported by the NSF-BSF grant #1803874 (BSF #6079), and performed under the auspices of the U.S. DOE by LLNL under Contract No. DE-AC52-07NA27344, with support from the LLNL-LDRD Program under Project tracking #18-ERD-046.

Speaker: L. Friedland (EPS 2019)

449 O4.J502 Magnetic reconnection in a semi-collisional regime

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.J502.pdf

Magnetic reconnection is a phenomenon which is of great interest to many researchers because of both its application to astrophysical situations and potential effects within hohlraum geometries. Laser-solid interactions allow a reconnection region to be generated in between laser spots, as previously investigated by several different laser experiments [1, 2, 3]. However, experimental verification of the mechanisms within the interaction region has remained elusive. This experiment produces a semi-collisional environment in which the importance of anisotropic pressure effects in mediating the reconnection process is demonstrated.
The Orion laser facility was used to perform a two, long-pulse beam experiment, with probing of the reconnection region using both protons and an optical probe. Field strengths can be extracted from results and with the support of modelling and analytical techniques the evolution and redistribution of the fields can be observed. Novel targets were used to allow for easier probing in multiple directions, allowing for a more detailed 3D projection to be built up of the interaction. Simulations were performed using IMPACTA [4, 5] and shown to support the experiment, demonstrating anisotropic pressure effects dominating the reconnection region field dynamics. Other diagnostics such as gated X-ray spectrometers and imagers were also fielded on the experiment, yielding temperature measurements of plasma conditions within the regions of interest.

References
[1] P. Nilson et al., Phys. Rev. Let. 97, 255001 (2006)
[2] M. J. Rosenberg et al., Phys. Rev. Let. 114, 205004 (2015)
[3] C. K. Li et al., Phys. Rev. Let. 2007, 055001 (2007)
[4] A. G. R. Thomas et al., New Journal of Physics 11, 033001 (2009)
[5] R. Kingham and A. Bell, Journal of Comp. Phys. 194, 1 (2004)

Speaker: E.R. Tubman (EPS 2019)

450 O4.J503 One order of magnitude enhancement of laser intensity with a single re-entrant micro-cone target in the petawatt regime

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.J503.pdf

Re-entrant cone was so far mainly used in the high energy density physics research especially in the laser fusion and has been proven to have an effective control on the fast electrons mainly for the fast ignition research [1]. Sentoku has shown that the re-entrant cone can increase the laser intensity up to 20 times from the level of 4 x 10^18 Wcm^-2 [2].
We show an improvement of Sentoku's results by using a plastic re-entrant micro-cone to increase the intensity of the light 12 times considering the initial intensity value from a higher intensity value of 8 x 10^20 Wcm^-2. Our work is a step forward in the global effort to push the laser intensity beyond 10^23 Wcm^-2 [3].
Laser beam intensity increase in the pettawatt regime has been enhanced by using an optical setup based on a single re-entrant micro-cone target. The model is described by two dimensional Particle-In-Cell simulations of the interaction of ultra-high intensity laser pulses with the microcone in predefined conditions. This approach is completed by a detailed study of the spatiotemporal electromagnetic field distribution at the laser matter interaction point which has been performed considering the incidence angle of the laser pulse on the micro-cone alpha = 0.1Deg, as can be seen in Figure 1. This technique aims to provide effective solutions to obtain high laser fields relevant for experiments proposed at multi-petawatt scale laser facilities such as Extreme Light Infrastructure (ELI).

This work has been financed by the national project PN III 5/5.1/ELI-RO No. 16-ELI/2017 ("SIMULATE"), under the financial support of Institute for Atomic Physics-IFA.

References
[1] W. Theobald et al., Phys. Plasmas 18, 056305 (2011)
[2] Y. Sentoku, K. Mima, H. Ruhl, Y. Toyama, R. Kodama and T. E. Cowan, Phys. Plasmas 11, 3083 (2004)
[3] G. Mourou and T. Tajima, EPJ ST 223, 979 (2014)

Speaker: O. Budriga (EPS 2019)

BSAP-MCF

Convener: C. Fendt (EPS2019)

451 I4.J601 Modeling drift-wave turbulence as quantumlike plasma

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.J601.pdf

Inhomogeneous drift-wave turbulence with zonal flows (ZFs) can be modeled as effective quantum plasma where the ZF velocity serves as a collective field [1, 2]. This effective plasma can be described, quite intuitively, by a Wigner-Moyal kinetic equation (WMKE), which was originally introduced as phase-space description of quantum mechanics [3]. We report the first explicit application of the Wigner-Moyal formalism to analytic and numerical modeling of ZF physics [4, 5] within the generalized Hasegawa-Mima model. The corresponding WMKE is more delicate and rich in physics than that for optical turbulence, to which a similar approach was applied in the past. The WMKE is also an improvement to the traditional wave kinetic equation for DW turbulence in that it contains "full-wave" effects, i.e., those associated with the finite ratio of the ZF scales to the drift-wave wavelengths. The full-wave effects are found to be essential and can qualitatively alter the formation and stability of ZFs [4, 5, 6]. The quantumlike approach elucidates the nonlinear saturation and oscillatory dynamics of collisionless ZFs [7] and also the physics of propagating coherent structures [8], which can be viewed as drifton condensates (Fig. 1). A systematic procedure for extending the quantumlike Wigner–Moyal formulations tomore general turbulent systems is also proposed.

References
[1] D. E. Ruiz, J. B. Parker, E. L. Shi, and I. Y. Dodin, Phys. Plasmas 23, 122304 (2016).
[2] D. E. Ruiz, M. E. Glinsky, and I. Y. Dodin, J. Plasma Phys. 85, 905850101 (2019).
[3] J. E. Moyal, Math. Proc. Cambridge Philos. Soc. 45, 99 (1949).
[4] H. Zhu, Y. Zhou, D. E. Ruiz, and I. Y. Dodin, Phys. Rev. E 97, 053210 (2018).
[5] H. Zhu, Y. Zhou, and I. Y. Dodin, Phys. Plasmas 25, 072121 (2018).
[6] H. Zhu, Y. Zhou, and I. Y. Dodin, Phys. Plasmas 25, 082121 (2018).
[7] H. Zhu, Y. Zhou, and I. Y. Dodin, arXiv:1902.04970
[8] Y. Zhou, H. Zhu, and I. Y. Dodin, arXiv:1902.06870.

Speaker: I. Dodin (EPS 2019)

452 I4.J602 Time intermittency in non-diffusive fast ion transport in turbulent toroidal plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.J602.pdf

Fast ions denote a part of the ion population of a plasma that exhibits speeds far above the thermal average. They appear in astrophysical plasmas, e.g. as Solar Energetic Particles (SEPs)[1]. In fusion plasmas, fast ions originate from fusion reactions or neutral beam injection and their confinement is crucial to the performance of any reactor [2]. Understanding their interaction with turbulence and transport properties is of high relevance across all these domains.
Fast ion turbulent transport is therefore a key research objective on the TORoidal Plasma EXperiment at the Swiss Plasma Center [3]. With a low-temperature (ca. 1 eV) in helical open magnetic field-lines, TORPEX plasmas feature a dominant interchange mode giving rise to electrostatic plasma turbulence and the intermittent propagation of coherent filament structures, termed 'blobs' [3] . The cross-field spreading of a toroidally injected Li-6 fast ion beam has been identified as generally non-diffusive through comparisons with predictions from the Global Braginskii Solver (GBS) code [4]. Fast ions of higher energies (70 eV) exhibit sub-diffusion, while lower energies (30 eV) result in superdiffusion, which transitions to quasi-diffusion at longer propagation times [3, 4]. During initial studies, superdiffusive transport appeared time intermittent, as local fast ion time-series showed significant skewness [5], but did not in subdiffusion.
We report the findings of an extensive 3D set of fast ion time-series, demonstrating the prevalence of time intermittency across all observed non-diffusive transport regimes [6]. We introduce an analytical model [7] for the prediction of skewness of the time-series based on the motion of a concentrated instantaneous fast ion beam within its time-average. While possibly of direct interest in similar systems, these efforts illustrate the general importance of concrete physical models when relating time intermittency and non-diffusive transport.

References
[1] G. Zimbardo et al. , J. Plasma Phys. 81, 06 (2015).
[2] M. Albergante et al. , Plasma Phys. Contr. F. 53, 05 (2011).
[3] I. Furno et al. , J Plasma Phys, 81, 03 (2015).
[4] A. Bovet et al. , Phys. Rev. E 91, 041101(R) (2015).
[5] A. Bovet et al. , Phys. Rev. Lett. 113, 225001 (2014).
[6] F. Manke et al. , (submitted to Phys. Rev. E).
[7] M. Baquero-Ruiz et al. , Phys. Rev. E 98, 032111 (2018).

Speaker: F. Manke (EPS 2019)

12:40 Lunch

Poster P4

453 P4.1001 Development of an Ultrahigh-bandwidth Phase Contrast Imaging system for detection of electron scale turbulence and Gigahertz Radio-Frequency waves

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1001.pdf

This work presents initial results of the development of a Phase Contrast Imaging (PCI) diagnostic operating with a probe wavelength of 1.55 µm. While worldwide PCI systems use a 10.6 µm probe laser to relax technical constraints on the interferometric measurement, this reduced wavelength would permit new capabilities by significantly extending the range of measurable wave-numbers and frequencies owing to, respectively, reduced scattered angles and detectors at much larger bandwidth that are available at this laser wavelength. Namely, while maintaining medium wave-number detection capability (k >= 1 cm-1), fluctuations at wave-numbers exceeding k >= 80 cm-1 would also be accessible at frequencies up to 1 GHz, thus covering density perturbations induced by electron-scale fluctuations and Radio-Frequency waves.
Various optical set-ups using variable number of lenses were designed and are being tested on an optical bench-top. A number of phase plates with various groove dimensions suitable for this probing wavelength were manufactured using a masked coating technique; acceptable specifications were achieved using industry-standard techniques. This prototype system uses only off the shelf components to maximize ease of construction in future experiments; more specifically, a 100 mW fiber optics laser is collimated, expanded, focused on the phase plate and subsequently imaged on an array of detectors. Calibrating sound waves of 4 mm wavelength were propagated through the expanded beam and detected in the mV range without the need for pre-amplifiers. Future work will focus on quantifying the signal to noise ratio of the system at various scattered wavelengths, as well as evaluating the impact of mechanical vibrations on the detected signal.
Work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award DE-SC0018095.

Speaker: A. Marinoni (EPS 2019)

454 P4.1002 Development of nuclear radiation based tomography methods for runaway electrons in fusion plasmas: first results and prospects

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1002.pdf

Phase-space tomography is an established technique for inferring physical properties (namely temperature, density and drift velocity) of thermal species in fusion plasmas. Consistent efforts have already been made to extend those techniques to fast ions generated by fusion reactions or auxiliary heating in order to reconstruct their 2D velocity-space distribution [1]. The benefits of reconstructing fast particles distributions is two-fold: from the experimental point of view it permits a more detailed description of plasma species dynamics (e.g. the interaction between fast ions and MHD modes) and also a direct comparison of simulated and experimentally reconstructed distribution. There is an interest in developing new analysis routines to perform a phase-space tomography of Runaway Electrons (REs), benefiting from the experience with fast ions. At present 1D energy distribution reconstruction of runaway electrons at ASDEX Upgrade has been achieved using inversion techniques [2]. In this work we present a new deconvolution tool for reconstructing the RE distribution starting from Gamma-Ray Spectroscopy (GRS) data. Different methods were tested on both synthetic and experimental data for comparison purposes. The algorithms performances when analysing RE spectra were established and multiple transfer matrices, containing information on the sensitivity of the diagnostics to different RE energies, were calculated (e.g. using MCNP or GENESIS codes). Differences in the reconstructions produced using those matrices were studied and robust figures of merit to describe the evolution of the RE beam during a plasma discharge were identified.

[1] M. Salewski et al., Nucl. Fusion 53 (2013) 063019 [2] M. Nocente et al., Rev. Sci. Instrum. 89, 10I124 (2018)

Speaker: E. Panontin (EPS 2019)

455 P4.1003 Simulations of Segmented Rail Probes for COMPASS Upgrade

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1003.pdf

Tokamak COMPASS Upgrade will be a high-field high-density fusion experiment aimed also at investigation of advanced divertor scenarios. One of proposed diagnostic systems is based on time-proven technique of Langmuir probe measurements. However, to operate these probes in the harsh environment of such machine, specific precautions must be taken.
The first is the elimination of the protruding electrode, which would be easily sputtered or melted away by high particle and heat flux. Probes adapted in such fashion are commonly known as flush mounted probes. However, this is not sufficient, since the inclination angle of the magnetic field lines will be very low and the sheath expansion would significantly affect the collected current. This can be counteracted by extending the probe along the field line, forming a stripe, or a rail. Probes of such design were a part of diagnostic setup at Alcator C-mod [1].
In this contribution, a study aimed at exploration of operational range of a newly constructed probe array will be presented. The probe in question will be simulated by a particle-in-cell model SPICE2 [2], which enables us to observe not only stationary heat or particle fluxes deposited on the probe, but also to artificially obtain the I­V curve measured by the probe.
It has been found out that the sheath expansion affects especially the leading edge part of the probe, where the extra collected current is focused ­ majority of the current is being collected near the leading edge, covering the extent of only a few Larmor radii. While it can cause overheating of the edge and possible melting, which can be mitigated by shaping of the leading edge, the flux focus can also be used as an advantage. Dividing the probe into several segments can improve the quality of the measured data as the analysis of artificial current-voltage curve indicates, especially with respect to ion saturation current and electron temperature measurements.
References
[1] A. Q. Kuang et al., Nuclear Materials and Energy 12, 1231­1235 (2017) [2] M. Komm et al., Nuclear Fusion 57, 126047 (2017)

Speaker: A. Podolnik (EPS 2019)

456 P4.1004 System of high-speed video and infrared cameras for joint control of the lithium limiters behavior on tokamak T-11M. First results

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1004.pdf

Lithium is the most promising liquid metal, considered as potential for plasma-facing elements. It was experimentally shown, that the use of lithium in tokamaks increases plasma confinement time, decreases the amount of impurities in the plasma, and decreases hydrogen recycling on the plasma facing components. Experiments on the tokamak T-11M are devoted to the development of a closed-loop lithium circulation system. Within the framework of this program, it is necessary to investigate the thermal loads goes to the plasma facing components of vacuum chamber, in particular, the longitudinal limiters - collectors of lithium. The T-11M tokamak is equipped with two high-speed cameras Baumer HXG20C operating in the visible range. It allows to record processes on two limiters or to take pictures of one limiter from two angles during the tokamak pulse. There are various light filters used in experiments: LiI (671 nm.), LiII (549 nm) and H (656 nm). Also, the T-11M diagnostics is equipped with two infrared camera Infratec VarioCam HD Head 680 and Infratec VarioCam HD Head 880, operating in the wavelength range of 7.5 - 14 microns. The launch of all cameras is synchronized. The observation of two longitudinal collectors in tokamak T-11M is carried out simultaneously in the visible and IR wavelength ranges. Cameras operating in the infrared range are used for recording the temperature distribution on the surface of lithium collectors. This allow to determine the distribution of heat load on the collectors surfaces. The work carried out at NRNU MEPhI to determine the temperature dependence of the lithium and CPS with lithium emissivity (grayness coefficient) made it possible to increase the accuracy of the data obtained from IR cameras. Currently, on the T-11M tokamak experiments are being carried out to determine the thermal loads on the surface of lithium limiters during the discharge process, depending on their temperature and position relative to the plasma.

Speaker: A.S. Prishvitcyn (EPS 2019)

457 P4.1005 Application of Laplacian Eigen Functions for the tomographic reconstruction of tokamak

See the full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1005.pdf

The estimation of 2D plasma emission profile via tomographic reconstruction inherits the ill-posed inversion characteristic and is constrained by the limited number of plasma observations sights/directions. Such complex estimation is carried out by special mathematical treatments like the series expansion method. These methods hold some drawbacks especially while dealing with signals harboring significant noise. In the case of the Fourier-Bessel function (FBF)[1,2], the emission profile is decomposed in orthogonal basis patterns and exhibits robust 2D emission profile with the noisy signals, while ignoring high-frequency components. However, FBF works well for the circular cross-section but it has problems in applying to noncircular cross-section or 3D shaped case. A new approach based on Laplacian Eigen Functions (LEF) [3,4], very often employed in image data processing, is discussed here for the tomographic reconstruction of the fusion plasma. Under LEF procedure the Eigen-functions of the Laplacian are computed over the 2D or 3D emission areas and the line integrated data is then expanded into these Eigen-functions. As a first step, the formulation of the tangential viewing tomographic reconstruction on the 2D emission profile is conducted and it is used to find the magnetic axis and the X-point from the visible camera image of the tokamak.

[1] Wang L and Granetz R S 1991 Rev. Sci. Instrum. 62 842­3 [2] Wang L and Granetz R S 1991 Rev. Sci. Instrum. 62 1115­6 [3] Saito N 2005 IEEE/SP 13th Workshop on Statistical Signal Processing, 2005 (IEEE) pp 425­30 [4] Saito N 2008 Appl. Comput. Harmon. Anal. 25 68­97 [5] van Wieringen W N 2018 arXiv:1509.09169

Speaker: S. Purohit (EPS 2019)

458 P4.1006 Algorithm of calculating the passive signal of tokamak edge plasma for CXRS diagnostics

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1006.pdf

Predictive modeling of passive signal of tokamak edge plasma charge-exchange recombination spectroscopy (CXRS) diagnostics remains a problem because of the necessity to combine solutions of theoretical problems, which need sophisticated numerical modeling. This includes: (i) modeling of the SOL(+divertor) plasma with account of impurities to be diagnosed with the Edge-CXRS diagnostics (such data are accumulated and being extended; for ITER see, e.g., the SOLPS (B2-EIRENE) [1] and OSM+EIRENE+DIVIMP [2] simulations); (ii) cross-sections of charge exchange reactions, which produce highly-excited atomic states of H-like impurity ions from collisions of impurity nuclei with hydrogen isotopes neutral atoms (including their low-lying excited states) of background plasma; (iii) the rates of the above-mentioned reactions for essentially non-Maxwellian velocity distributions function (VDF) of hydrogen isotopes neutral atoms (the VDF data may be generated, e.g., by stand-alone EIRENE code [3] simulations using the background SOL plasma data); (iv) the photon emission coefficients (PEC) data for interested impurity visible-light spectral lines in the case "iii" which is beyond the available data in ADAS and similar sources (these data may be generated, e.g., with the code [4], similarly to evaluation of active CXRS signal in [5]). Here we describe the algorithm of modeling the passive signal of edge-CXRS diagnostics in tokamaks, which uses the data (i)-(iv). Some preliminary results for passive signal of the ITER Edge CXRS diagnostics are presented.

References
[1]. Kukushkin A.S., et al., Fusion Eng. Des. 86, 2865 (2011). [2]. Lisgo S. W. et al., J. Nucl. Mater., 415, 965 (2011). [3]. Reiter D., et al. Fusion Sci. Technol., 47, 172 (2005). [4]. M.B. Kadomtsev, M.G. Levashova, V.S. Lisitsa, JETP 106 (2008) 635-649. [5]. Tugarinov S.N. et al. 36th EPS Conf. Plasma Phys. Sofia, 2009 ECA Vol. 33E, P-5.214 (2009)

Speaker: P.A. Sdvizhenskii (EPS 2019)

459 P4.1007 Study of the eddy current effect on the magnetic diagnostic on J-TEXT

See ful abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1007.pdf

The accuracy of measuring Magnetohydrodynamic (MHD) instabilities by inductive loops (formed as Mirnov probes and saddle loops on J-TEXT) is significant affected by the eddy current, which determined by the placement of the inductive loops and the material of the conductors nearby. In various frequency range, e.g. high frequency for Mirnov probes and quasi-static frequency for locked mode detectors, different compensation methods should be applied.
Mirnov probe measured high frequency magnetic perturbations, induced by eddy currents in the conductors near Mirnov probes, might exist significant phase shift and amplitude decay with respect to that from MHD instabilities. Investigation of the eddy current on the high frequency response of the Mirnov probe is based on a test platform, which is capable of generating uniform AC magnetic field within the frequency range of 1-300 kHz. The eddy current is related to the frequency of the magnetic perturbations, materials of the conductors, thickness of the conductors and distance of the conductors and the probes. Improving the electromagnetic environment around the probes and compensating for experimental measurements through test results both are methods to improve the high frequency measurement capability of the Mirnov probe. While for locked mode detector measured quasi-static radial magnetic field, feature of the related eddy currents is variations of low frequency MHD instabilities and equilibrium field. An analytical model based on lumped eddy current circuits can be established to analyze the mutual inductance between the detectors and equilibrium field, as a result to compensate the eddy current. The array of locked mode detector outside the vacuum has been installed already and an array of locked mode detector inside the vacuum is installed recently on J-TEXT. The impact of eddy current on them will be compared through the coming experiment, which might bring further study of the eddy current on locked mode detectors.

Speaker: C. Shen (EPS 2019)

460 P4.1008 Development of 3D Geant4 tokamak model for particle interaction

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1008.pdf

A 3D model of transport and interaction of particles with tokamak components using Geant4 toolkit is presented. Main goal was to analyse impact of population of relativistic electrons on vacuum vessel and other critical components. These so-called runaway electrons (RE) behave like in a particle accelerator and can cause damage by depositing large amounts of energy in short duration. The model was tested using 3D design of COMPASS tokamak, it is capable of simulating trajectories, generation of secondary particles and energy deposition. By providing initial estimates of RE beam, it can be used for better understanding of diagnostic systems and their response, as well as using the results for heat transfer and damage of components.

Speaker: P. Svihra (EPS 2019)

461 P4.1009 Simulation of Doppler backscattering off filaments in the Globus M spherical tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1009.pdf

Filamentary-like plasma perturbations are routinely observed in many tokamaks. They are the result of non-linear development of some peripheral MHD instabilities in the region of the maximum plasma pressure gradient [1]. As soon as filaments can play a key role in the anomalous transport of particles and energy at plasma periphery studies of filaments are actively continuing in various tokamak experiments for better understanding of filament physics and extrapolating of filament parameters to the tokamaks of ITER scale [2]. Recently, authors proposed to use the Doppler backscattering (DBS) method for filaments investigation [3]. The results of backscattering from filaments can be easily interpreted within the framework of the Born approximation. However, the description of the experimental data under the transition from linear to non-linear backscattering is a rather complicated task that could be solved with the help of full-wave simulations. Two-dimensional full wave simulations were done with finite-difference time-domain codes IPF-FD3D [4] and REFMULF [5] in slab geometry. The goal was to calculate the DBS responses depending on various filament amplitudes (0.1%, 1%, 5%, 10%, 50% and 100% of density at cut off). This dependency was also calculated for various filament positions in relation to the cut off, filament shapes and motion directions. The detailed comparison of the simulation result and experimental data obtained at the tokamak Globus-M was performed and has shown in particular the amplitude at which transition to the non-linear regime occurs. The work is supported by RSCF grant 18-72-10028 and Ioffe Institute.
[1] Spolaore M et al 2017 Nucl. Mater. Energy 12 844 [2] Snyder P B et al 2009 Nucl. Fusion 49 085035 [3] Bulanin V V et al 2011 Tech. Phys. Lett. 37 340 [4] Lechte C et al Proc of the 8th International reflectometry workshop, 2007, Saint-Petersburg, Russia, 67-73 [5] da Silva F et al Proc of the 13th International reflectometry workshop, 2017, NFRI, KOREA

Speaker: N. Teplova (EPS 2019)

462 P4.1010 The direct detection of runaway electrons using the semiconductor strip detector

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1010.pdf

The runaway electrons have serious detrimental effects on the vacuum components of tokamaks. They emerge during plasma disruptions and the energy of accelerated electrons can reach the order of tens of MeV. Recent advances in semiconductor detectors allowed their widespread application in high-temperature plasma diagnostics. They have fast response and offer a good spatial and temporal resolution. For these reasons a silicon strip semiconductor detector (PH32) was installed on tokamak GOLEM (R = 0.4 m, a = 0.085 m, Btor < 0.5 T, Ipl < 8 kA). The detector (fig. 1a) was placed in the vacuum chamber near the plasma edge, mounted on a radial manipulator, therefore it was possible to observe RE directly. Data from 32 strips of a detector was acquired digitally in hit-count mode. An analog output from one strip was connected to an oscilloscope. Measurements were compared with already existing diagnostics, especially with an output from HXR scintillators . The analog output from detector provides comparable results to scintillator measurements (fig. 1b), during vacuum discharge no signal was produced. In addition, data from multiple discharges shows great dependency on detector position in respect to the radial orientation of the detector to plasma and direction of plasma current.

Speaker: M. Tunkl (EPS 2019)

463 P4.1012 Spectroscopic diagnostics for deriving electron temperature and density from an Argon plasma in GyM

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1012.pdf

A non-intrusive diagnostic based on Optical Emission Spectroscopy (OES) is under study in GyM for measurements of electron temperature (Te) and density (ne) to complement Langmuir probes. This technique provides values of Te and ne averaged along the line-of-sight through the analysis of spectral line pairs, as emitted by the plasma, which depend on Te and ne and the comparison with the reconstructed emission calculated within the ADAS (Atomic Data and Analysis Structure) project. The multiplets at 487.6 nm and 489.9 nm arising from Ar+ for the ne and the lines at 751.6 nm and 738.6 nm from Ar0 for the Te have been used. Further line pairs have been also investigated and the results compared to local values obtained using Langmuir probes in the range Te ~ 1-10 eV, ne ~ 10^10 - 2 10^11 cm-3 on the machine axis at different longitudinal positions. Since accurate estimates of Te and ne depend critically on atomic data and modelling used for the theoretical calculations, a great effort has been devoted to revise the available atomic coefficients and to apply them to the experimental data. In this framework GyM is used as facility to test atomic data in a specific range of Te and ne to identify the critical issues to be improved for accurate estimate of the plasma parameters. The OES method, here applied to GyM, has the potential to be extended to other plasmas where Ar impurities can be added as tracers or injected to cool radiatively the SOL or divertor plasma.

Speaker: A. Cremona (EPS 2019)

464 P4.1013 Poloidal impurity asymmetry studies using the upgraded high field side edge CXRS diagnostic at ASDEX Upgrade

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1013.pdf

A detailed characterization of flows, density and temperature profiles is necessary to shed light on transport in magnetically confined fusion devices. The most common technique to measure these profiles is Charge Exchange Recombination Spectroscopy (CXRS). The CXRS systems are usually located at the low field side but several studies [1, 2, 3] have shown that impurity density and flows are poloidally asymmetric in the pedestal region. At ASDEX Upgrade, the inboard-outboard impurity density asymmetry can reach a factor of 3, while the temperature and the electrostatic potential are found to be flux functions [4]. However, at Alcator C-Mod, inboard-outboard variations were also found in plasma potential or ion temperature, indicating that both might not be constant on flux surfaces [5]. The maximum observed inboard-outboard impurity density asymmetry on Alcator C-Mod reached a value of 10. These differences may be related to different methods of aligning the profiles [5]. The high field side CXRS system at the plasma edge of ASDEX Upgrade has been upgraded with a new gas valve and a new poloidal optical head in order to understand these differences. The fast opening and closing of the new piezoelectric valve allow for a better characterization of the background emission. Dedicated calibrations for different gases have been performed in order to determine the flowrate accurately. Moreover, the number of lines of sight has been increased to improve the radial resolution. First studies of poloidal asymmetries using the measurements of the new diagnostic will be presented.

[1] K.D Marr et al. Plasma Physics and Controlled Fusion, 52:055010, 2010. [2] T. Pütterich et al. Nuclear Fusion, 52:083013, 2012. [3] R.M. Churchill et al. Nuclear Fusion, 53:122002, 2013. [4] E. Viezzer et al. Nuclear Fusion, 55:123002, 2015. [5] C. Theiler et al. Nuclear Fusion, 54:083017, 2014.

Speaker: D. Cruz Zabala (EPS 2019)

465 P4.1014 Comparison of new He II atomic data with JET line ratio measurements and their application to EDGE2D-EIRENE simulations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1014.pdf

Helium is widely used in laboratory fusion experiments both as a fuel, for example in the first phase of ITER, as a minority gas for some RF heating schemes and will occur as ash from the thermonuclear reactions. In order to make reliable predictions for future devices and analyse discharges produced in ITER's non-nuclear phase, particularly the modelling of edge and divertor plasmas, it is essential that its atomic physics is documented and confirmed by comparison with experiment. To this end, hydrogenic He II (He+) line intensity ratios measured during JET He density limit pulses with both single line-of-sight and scanning spectrometers are being compared with a newly created He II atomic physics database, which enables theoretical line intensity ratios to be determined through modelling of the populations of energy levels fed by all significant collisional and radiative channels [1,2]. A model in which a flow of fully stripped He ions populating the continuum is being tested to explain the VUV Lyman series line intensity ratios. He II atomic data is connected to the EDGE2D transport code through the ADAS database. Although agreement between ADAS and the new data has been found for the modelled power radiated by He II, significant differences are found when describing the electron power loss or gain used in the simulations. At the lowest temperatures (<1 eV) a gain in the electron power is expected, largely due to the mismatch in collisional excitation (a power loss, but vanishingly small) and de-excitation (a larger power gain) of the n = 1-2 transition, where n is the principal quantum number. The difference in the power gain between the two databases can be more than on order of magnitude, the ADAS data effectively preventing the simulations from reaching the lowest temperatures. The radiated power increases with decreasing temperature and so the question arises as to whether this could explain the previously observed discrepancy in the measured and simulated radiated powers [3,4]. Lawson et al. [5] demonstrated that the simulated temperatures were particularly sensitive to this term. EDGE2D-EIRENE simulations are being run to compare the effect of using the different atomic databases.

[1] Lawson et al., 2019, J. Phys. B, 52, 045001

[2] Lawson et al., 2019, To be submitted to J.Phys. B

[3] Groth et al., 2013, Nuc. Fus., 53, 093016 [5] Lawson et al., 2018, Proc. 45th EPS Conf., Prague

[4] Canik et al., 2017, Phys. of Plas., 24, 056116

*See the author list of E. Joffrin et al., to be published in Nucl. Fusion Special Issue, overview and summary reports from the 27th Fusion Energy Conference (Ahmedabad, India, Oct. 2018)

Speaker: K.D. Lawson (EPS 2019)

466 P4.1015 Quantifying physical parameters in an outer divertor region using the Balmer line spectroscopy

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1015.pdf

Mitigating head load on the divertor target is considered as one of the critical challenges to achieve a commercial fusion reactor. Fortunately, both density and temperature at the divertor target can be reduced significantly through a process called "detachment", leading to tolerable heat flux. However, our current understanding of the detachment process is mostly based on empirical laws and qualitative descriptions, and the extrapolation of the current detachment behavior to future reactors is not reliable.
The Balmer line spectroscopy is a non-intrusive diagnostic technique to characterize physical parameters in the cold divertor region. While this technique has successfully provided useful information at various devices[1, 2], the interpretation of the measurements is not straightforward due to line-integration effects. Modeling using the SOLPS code shows that spatial variations of the physical parameters need to be taken into account in the outer closed-divertor at ASDEX Upgrade(AUG). In the private flux where the density is high, both excitation and recombination emissions can possibly contribute to the total light intensity. On the other hand, in the scrapeoff-layer where the density is low, the recombination emission is typically negligible compared to the excitation emission. In order to interpret the Balmer line spectroscopy at AUG correctly, a "two-volume emission model" is developed. In this model, the emission along a line of sight is assumed to originate from two volumes to accommodate the spatial variations of the physical parameters. A Bayesian frame work is employed to determine the optimum values for the physical parameters based on the forward model. The two-volume emission model is applied to synthetic data and L-mode discharges with a density ramp. It is shown that this model robustly estimates important physical parameters, including the particle source and sink, in the outer divertor region.
References
[1] B.A. Lomanowski el al., Nucl. Fusion 55 123028 (2015) [2] K. Verhaegh et al., Nucl. Mater. Energy 12, 1112 (2017)

Speaker: T. Nishizawa (EPS 2019)

467 P4.1016 Plasma Edge Turbulence Characterization Using Gas Puff Imaging on the TCV Tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1016.pdf

Understanding turbulence and anomalous transport in tokamaks remains an important open issue in plasma physics for fusion devices. A prominent feature of turbulence in the Scrape Off Layer (SOL) region are blobs, coherent filamentary plasma structures that drift across the magnetic field lines at high velocities (~km/s) and interact with the vessel wall. Besides providing cross-field transport of particles and energy, blobs are a concern for future fusion reactors since they pose a potential threat to plasma-facing components. The mechanisms dominating blob propagation in the SOL, and thus the level of plasma-wall interaction, are sensitive to a number of conditions and parameters such as plasma collisionality and magnetic configuration, and are not yet fully understood. The Tokamak à Configuration Variable (TCV) at EPFL, with its unique flexibility in plasma shaping, is a powerful tool to disentangle the different mechanisms at play. In 2018, to study blob dynamics with adequate temporal and spatial resolution, we built and commissioned a Gas Puff Imaging (GPI) diagnostic at TCV. The GPI is situated at the outer midplane, where it collects emission from a neutral gas cloud (helium or deuterium) tangentially to the local magnetic field. We acquire data from a field of view of 50x42 mm, covered by a 12x10 optical fiber array with a spot size of about 4mm on the image plane. The light is acquired with an avalanche photo-diode array at 2MHz, such that we can resolve structures with the diameter of the order of a cm with velocities of the order of km/s. In December 2018, we collected first data in attached and detached L-mode plasmas, and we were able to detect blobs being formed near the LCFS and drifting through the SOL. We will present the first analysis of the data, in which we will describe size and velocity distribution of the blobs, and compare them to previous, more indirect measurements deduced from reciprocating Langmuir probes. We will further analyze the differences in transport in attached and detached plasma conditions and the connection between divertor and upstream turbulence.

a: See the author list of S. Coda et al, 2017 Nucl. Fusion 57 102011

Speaker: N. Offeddu (EPS 2019)

468 P4.1017 Quantitative analysis of high n Balmer lines using multispectral imaging in detached divertor plasmas at TCV

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1017.pdf

Plasma detachment is required to reduce the particle and heat loads in the divertor of fusion experiments. Atomic and molecular processes play a crucial role in this. To study the
interplay between these processes, a novel, real-time capable, visible multispectral imaging system (MANTIS [1]) was installed on the TCV tokamak. The images are analysed using a novel, high n Balmer line ratio method [2] to apportion the hydrogenic line emission between excitation and recombination processes. Particular emphasis is placed upon estimating the measurement uncertainties and the accuracy of the following tomographic inversions to obtain 2D maps of line emission. The emission ratios together with the experimental uncertainties are used to infer profiles of hydrogenic radiation, ionisation and recombination rates, charge exchange to ionisation ratios, and a characteristic
Balmer temperature for excitation and recombination. The advantages and limitations of the quantitative multispectral imaging are evaluated and compared with the line integrated
spectroscopic measurements acquired by the TCV's Divertor Spectroscopy System [2]. The possibility of using a real-time analysis to obtain approximated profiles for the ionisation front tracking is presented. Execution time and projected accuracy are evaluated in context of MANTIS's camera systems. With sufficiently fast and accurate algorithm, the ionization front position could be used together with the existing CIII (465nm) emission front estimation currently employed in detachment control efforts [3].

[1] W.A.J. Vijvers et al. JINST 12, C12058, 2017
[2] K. Verhaegh et al. to be published. DOI: 10.13140/RG.2.2.24292.48005/1.
[3] T. Ravensbergen et al. Real-time detection of the radiation front during divertor detachment using multi-spectral imaging, to be submitted.

Speaker: A. Perek (EPS 2019)

469 P4.1019 Bayesian equilibrium reconstruction using JET's microwave diagnostics

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1019.pdf

For the JET tokamak, standard equilibrium reconstructions find solutions of the Grad-Shafranov equation given diverse constraints on plasma pressure and/or magnetic field [1]. The most basic reconstruction neglects plasma pressure entirely and constraints the magnetic field via measurements of pick-up coils located around the plasma. A more advanced reconstruction exploits polarimetry and motional-stark-effect diagnostics which provide information about the magnetic field inside the plasma. These conventional approaches provide different results, estimating to some extent the systematic uncertainties of the reconstruction. An alternative approach uses Bayes' theorem to estimate the equilibrium quantities [2] by a joint posterior probability. This allows to obtain a joint solution of the Grad-Shafranov equation consistent with the underlying physics model and with uncertain data measured by magnetic and motional-stark-effect diagnostics.
The work presented infers probabilistically the axisymmetric equilibrium of an Ohmic JET plasma, relying on data measured with broadband ECE diagnostics and an extra-ordinary mode reflectometer [3]. Besides probing the plasma centrally, the data of both diagnostics constrain the local electron pressure and the magnetic field.

References
[1] M. Gelfusa et al., "Influence of plasma diagnostics and constraints on the quality of equilibrium reconstructions on Joint European Torus", Rev. Sci. Instrum., 84, 103508 (2013).
[2] J. Svensson, A. Werner, and JET EFDA contributors, "Current tomography for axisymmetric plasmas", Plasma Phys. Control. Fusion, 50, 085002 (2008).
[3] S. Schmuck, J. Svensson, L. Figini, D. Micheletti, "Bayesian Inference Using JET's Microwave Diagnostic System", Submitted to IFP and JET pinboards, (2019).

Speaker: S. Schmuck (EPS 2019)

470 P4.1020 The study of L-mode filament dynamics using synthetic and experimental BES diagnostics

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1020.pdf

Fluctuation beam emission spectroscopy (BES) is an active plasma diagnostic used for density measurements which has sufficient spatial and temporal resolution for the study of turbulent density fluctuations and associated flows. A high energy neutral beam consisting of hydrogen isotopes or light alkali metal atoms is shot into the plasma. Through various collisional processes with plasma particles, the beam atoms get excited and the photons originated from their spontaneous emitted is collected by an observation system. RENATE is a fluctuation BES modelling code [1], featuring 3D beam and 3D observation geometry modelling capabilities as well as accounting for the underlying magnetic geometry, thereby incorporating all relevant spatial artefacts of the diagnostic [2]. Time-dependent density and temperature fluctuations are taken as input, provided by 2D fluid model, HESEL, used to study interchange dynamics in the SOL. Flux tube expansion of turbulent structures within the beam geometry allows for 3D modelling of the synthetic diagnostic signal [3]. In the present contribution, the statistical properties of synthetic BES signals are discussed and compared to corresponding experimental measurements of L-mode plasmas. Filament frequencies, amplitudes, sizes and velocities are acquired for both synthetic and experimental signals alike. Our work focuses on the reproducibility of experimental observations with the RENATE-HESEL synthetic diagnostic, by coupling the HESEL results to the RENATE BES modelling code. The HESEL code was run in a Kepler workflow, developed within the EUROfusion Integrated Modelling framework. A workflow for passing HESEL fluctuation data via integrated data structures to the RENATE BES code will be discussed. Our work was carried out using BES diagnostics on the ASDEX-Upgrade tokamak, where the magnetic field dependence on filament dynamics was discussed in a previous work [4]. Measurements and modelling of SOL turbulence were also carried out for on the EAST tokamak data, a density dependence on SOL dynamics, as well as poloidal sizes and velocities of filaments are discussed.
[1] D. Guszejnov et al. RSI 83, 113501 (2012). [2] O. Asztalos et al. EPS P4.107 (2017). [3] A.H. Nielsen et al. Submitted NF (2019). [4] G. Birkenmeier et al. PPCF 56, 075019 (2014).

Speaker: O. Asztalos (EPS 2019)

471 P4.1021 Analysis of density profiles inside magnetic islands with Alkali Beam Emission Spectroscopy at Wendelstein 7-X

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1021.pdf

The Alkali Beam Emission Spectroscopy (A-BES) system is a fast time-resolution diagnostic injecting a 60 keV Sodium atomic beam through the mid-plane of the W7-X stellarator [1]. It is capable of density reconstruction with a time resolution of 50 µs and for the analysis of turbulent processes. The diagnostic was operated during the OP1.2 campaign at W7-X.
For the standard iota configuration the sodium beam crosses the O point of a magnetic island. The high sensitivity of the diagnostic in the island region suffices for an analysis of the transport processes in this region, which is the aim of the poster presentation. The reconstructed density profiles indicate a density-peak near the O-point of the island for a number of shots. An analysis for the dependence of the prominence of this peak on plasma parameters has been performed. Moreover, the temporal and spatial correlation function of the A-BES light profiles of outward propagating filaments indicates that their radial transport across the island is not straightforward: the time delay between the correlated fluctuations of the inner and outer sections of the island is less than between the inner section and the island O point. Therefore, in order to characterize the parallel transport, the Poincaré map of the magnetic field lines and the distribution of the connection lengths inside the island has been compared with the observed density profiles.
References
[1] Anda, G., Dunai, D., Lampert, M., Krizsanóczi, T., et al., Review of Scientific Instruments, 89(1), 013503 (2018).

Speaker: M. Vecsei (EPS 2019)

472 P4.1022 Drift waves in a plasma column: POD analysis of high speed imaging

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1022.pdf

Low frequency waves turbulence developing in magnetized plasma columns are well known to trigger important radial transport, a major issue for fusion devices [1]. We present here analysis from very fast imaging of low frequency waves in a magnetically confined plasma column, as well as concomitant measures of radial transport.
Our experimental set-up consists in a cylindrical chamber containing an Argon plasma column of 10 cm diameter of ionization rate 20% and at low pressure ( 1 mTorr) generated via an electromagnetic induction source of power 1 kW. The plasma is confined by a magnetic field ranging from 0.01 T to 0.15 T [2].
A very fast camera records images of spontaneous radiated light fluctuations in a plane transverse to the plasma column axis, at a 200 kfps rate, showing the presence of azimuthally rotating waves at frequencies of order the kHz. These images are analysed using a Proper Orthogonal Decomposition technique [3] which is compared to 2D axisymmetric Fourier transform analysis. The POD results exhibit m-modes closely following the eim spatial form of the modes extracted by 2D Fourier transform. The non-linear interactions between these modes is then investigated while increasing the magnetic field (a well known control parameter for drift waves turbulence [4]). Finally the radial transport is measured using an advanced triple probe (following the 5-tips probe design of [5]), and compared to the images analysis of drift waves development.
Références
[1] W. Horton, Rev. Mod. Phys. 71, 735 (1999) [2] N. Plihon et al., Journal of Plasma Physics 81, 345810102 (2015) [3] G. Berkooz et al., Annu. Rev. Fluid Mech. 25, 539-75 (1993) [4] S. C. Thakur et al., Plasma Sources Sci. Technol. 23, 044006 (2014) [5] C. Theiler et al., Review of scientific instruments 82, 013504 (2011)

Speaker: S. Vincent (EPS 2019)

473 P4.1023 Observation of electron temperature fluctuation on the J-TEXT tokamak via correlation ECE

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1023.pdf

Turbulence is important for the transport in tokamak. An eight-channel correlation electron cyclotron emission (CECE) system has been developed based on the Joint-Texas Experimental (J-TEXT) tokamak to measure the electron temperature fluctuation. With the CECE diagnostic, the relation between electron temperature fluctuation and plasma parameters has been observed on J-TEXT. The influence of magnetic islands on the electron temperature fluctuation has also been studied on J-TEXT with the resonant magnetic perturbation (RMP) system. These results will be showed on this report.

Speaker: Z. Yang (EPS 2019)

474 P4.1024 Investigation of the Kelvin-Helmholtz instability in EAST

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1024.pdf

The Kelvin­Helmholtz (K-H) instability has been observed by Doppler Backscattering system(DBS) in EAST H-mode operation. The frequency range of the K-H instability is
about 40-90 kHz, and is distinct in the Er fluctuation. Although it can be hardly observed in density and magnetic field fluctuation, the coherences between them and the Er fluctuation are quite strong, and the cross-phase between the density fluctuation and Er fluctuation is between Pi/2 and Pi . The evolution of Er and Er shear during the appearance of K-H instability have been revealed, and it shows that the edge Er shear is important to arouse the K-H
instability. The electric density and stored energy decrease significantly and the ELMy H-mode becomes an ELM-free H-mode operation when the K-H instability is aroused. The
GAM can sometimes be observed accompanying with the K-H instability, and the nonlinear interaction between them has been observed through the bi-coherence analysis.

Speaker: C. Zhou (EPS 2019)

475 P4.1025 First results of the Globus-M2 fast ion studies

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1025.pdf

Globus-M2 [1] is a new generation one-Tesla compact spherical tokamak with two 1 MW neutral beam injectors and 0.5 MW ion cyclotron resonance heating system. Additionally Globus-M2 is equipped with a set of new diagnostics, suitable for fast ion studies, including scanning two-neutral particle analyzer system, neutron detectors and spectrometer.
Fast ion study was one of the main research topics on the previous Globus-M tokamak [2]. Former experiments with plasma current Ip = 200 kA and toroidal magnetic field BT = 0.4 T demonstrated high level of energetic particle losses. Increase of Ip and BT up to 250 kA and 0.5 T respectively led to fast ion confinement improvement [3]. In this presentation the impact of the further Ip and BT rise is discussed. Besides the new diagnostics, mentioned above, a set of new modeling techniques, based on different approaches, is used. Benchmark of these techniques and comparison of their results with the experimental data is described. Neoclassical and MHD-induced losses, neutron generation and fast ion distribution in the Globus-M2 discharges are investigated. Predictions for the full-scale Globus-M2 experiments with the BT = 1 T, Ip = 500 kA and 5 MW/m3 heating power density are presented. References
[1] Gusev V.K. et al. 2013 Nucl. Fusion 53 093013. [2] Bakharev N.N. et al. 2015 Nucl. Fusion 55 043023. [3] Bakharev N.N. et al. 2018 Nucl. Fusion 58 126029.

Speaker: N. Bakharev (EPS 2019)

476 P4.1026 Comprehensive benchmark studies of ASCOT and TRANSP-NUBEAM fast particle simulations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1026.pdf

The ASCOT [1] and TRANSP-NUBEAM [2] Monte-Carlo codes are the most commonly used tools for analysing fast particle and fusion product distributions in JET plasmas. Differences have been observed in the physics included in the codes and the resulting predictions, including differences between experimental and modelled neutron production rates. A thorough benchmarking exercise between these two codes has been undertaken in view of the upcoming DT campaign at JET. The results from ASCOT (incorporated in JINTRAC [3]) are compared with TRANSP results with input settings chosen as to match the physics models as much as possible and using identical kinetic input profiles. Two discharge were chosen for detailed comparisons: a highperformance baseline discharge and a high-performance hybrid discharge, both with total input power exceeding 30MW. The main differences between the two discharges were a higher density and lower fast particle fraction in the baseline discharge. To match the boundary conditions and minimise non-model related causes for differences in the results, several settings were modified from their default values, mainly in ASCOT-JINTRAC. These include the beam divergence, ionisation cross section, plasma rotation, the magnetic equilibrium, the Coulomb logarithm and sources of neutrals. A large number of output quantities were compared for NBI heating, including fast particle density and energy, power depositions and neutron production. The most significant differences between ASCOT and TRANSP were observed in the electron heat deposition (15-20%) and the neutron production rate (around 10%) when the plasma rotation has been taken into account in the simulation. Important differences in profile shapes can also arise from differences in the equilibrium, unless the same equilibrium is enforced in both codes. [1] E. Hirvijoki et al. 2014 Comput. Phys. Commun. 185 1310-1321 [2] A. Pankin et al. 2004 Comput. Phys. Commun. 159 157-184 [3] M. Romanelli et al. 2014 Plasma Fusion Res. 9 3403023

Speaker: P. Sirén (EPS 2019)

477 P4.1027 Impact of ICRF and NBI heating on the fast ion distribution function during the plasma termination phase

Seee full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1027.pdf

Reliable and quantitative modelling of the behaviour of fast ions is an essential step in the ITER scenario development because of their important contribution to the plasma energy balance. The fast ion distribution strongly depends on various factors, in particular, on plasma MHD activity and on sources of plasma heating such as neutral beams and RF waves [1, 2]. In our research, we focus on the final stage of a plasma discharge, where the plasma current is ramping down along with a strong reduction in the input power. The main difficulty of modelling and successful experimental performance of this termination phase of a plasma discharge lies in the fast and simultaneous changes of many plasma parameters. Integrated modelling supported by further experimental tests on existing devices will help to inform ITER on robust termination schemes.
Nowadays, tools for integrated modelling are on high demand and under active development. The tokamak transport code TRANSP [3] is used in this work for predictive simulations of equilibrium evolution and transport during the termination phase. The NUBEAM module [4], a Monte Carlo code integrated to TRANSP, provides information on the time-dependent deposition and slowing down of fast ions resulting from neutral beam injection. The interaction between fast ions and RF waves is taken into account through the RF "kick" operator [5]. The effect of low-n MHD instabilities on fast ion transport is then introduced through a reduced model [6]. In the presented research, we will discuss the impact of heating scenarios on the fast ion distribution and how it affects the evolution of other plasma parameters in the plasma termination phase. Correlations between the plasma stability limits, the HL transition, particle and power balances will be considered.

References 1. A. Fasoli, et al, 2007 Nucl. Fusion 47 pp S264­S284. 2. V. G. Kiptily et al, 2009 Nucl. Fusion 49 065030. 3. R. J. Hawryluk, 1980 Physics of Plasmas Close to Thermonuclear Conditions 1 pp. 19-46. 4. A. Pankin, D. McCune, R. Andre et al., 2004 Computer Physics Communications 159 pp. 157-184. 5. J.-M. Kwon et al, 2007 Bulletin of the American Physical Society, 49th meeting of the Division of Plasma Physics, Orlando (FL). 6. M. Podestà, et al, 2014 Plasma Phys. Control. Fusion 56 055003.

Speaker: A.A. Teplukhina (EPS 2019)

478 P4.1028 Instabilities and fast ion confinement on the TCV tokamak

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1028.pdf

A newly installed 1 MW 25 keV NBI (2016) combined with the ECH-ECCD system allow the TCV machine [1] to join the on-going worldwide (DIII-D, AUG, TJ-II, etc.) research for studying wave ­ fast ion interaction phenomena of interest for burning plasmas, an important point for ITER and DEMO. Alfvén modes were observed on the TCV [2,3] during the 2017/18 EUROfusion MST1 campaign, in the presence of simultaneous off-axis sub-Alfvenic NBI (vA/3<vbeam<vA) and off-axis ECRH. No beam-driven instabilities were observed without ECH. The properties of EM fluctuations (AEs and GAMs) are studied using the Mirnov signals and soft-X emission. The impact of EM fluctuation on the plasma performance and on fast ions has been identified by comparing the neutron rates, total plasma energy (DML), fast ion D- (FIDA) spectra and CX NPA signals with integrated modelling. ASTRA and TRANSP codes are used for transport modelling of plasma heating, fast ion CX losses and current drive. TRANSP/NUBEAM and FIDASIM codes have been implemented at TCV to calculate synthetic FIDA and NPA measurements. A high edge neutral density ­ consistent with CX losses of the order of 25% ­ is required to explain the experimental results [2,3], but a FIDA and NPA signal deficit remains in the case of NBH & ECRH, possibly suggesting additional to neo-classical anomalous fast ion losses [3]. The paper presents the recent status of the data analysis and the strategy for continuation of experimental work, in particular with installation of new diagnostics, availability of new numerical tools and installation of the second high energy (50-60 keV) neutral beam [1].

1. S.Coda, et al., 27th IAEA Fusion Energy Conference (FEC 2018), Gandhinagar, India, OV/5-2 2. B.Geiger, et al., Plasma Phys. Control. Fusion 59 (2017) 115002 3. B.Geiger, et al., 27th IAEA Fusion Energy Conference (FEC 2018), Gandhinagar, India, EX/P8-24 * See the author list H. Meyer et al 2017 Nucl. Fusion 57 102014

Speaker: A.N. Karpushov (EPS 2019)

479 P4.1029 High-order time-stepping algorithm for tracking fast ions in fusion reactors

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1029.pdf

Fast ions play an important role in the heating of Tokamak plasmas, e.g. by NBI (Neutral Beam Injection) and other sources. Numerical particle trackers are employed to simulate huge numbers (often of the order of millions) of trajectories of fast ions in Tokamaks. Such simulations can require high numerical accuracy and thus take a long time, even on modern high performance clusters.
We will present the high order algorithm GMRES-Boris-SDC [1] for solving the Lorentz equations, based on Boris-SDC [2], a combination of the widely used classical Boris method [3] for the Lorentz equations and Spectral Deferred Corrections (SDC), plus a GMRES-based convergence accelerator [4]. Integrating the GMRES-based convergence accelerator leads to faster convergence and a substantial improvement in the long-term energy error compared to original Boris-SDC.
The GMRES-Boris-SDC algorithm has been implemented into the GPU-accelerated LOCUST simulation suite [5]. LOCUST leverages the high performance of modern Nvidia GPU hardware, employs realistic equilibrium including fields outside the separatrix and has the ability to perform very high statistics simulations in a comparatively short time. The performance of the GMRES-SDC algorithm will be compared against the "classical" Boris integrator for several fusion related benchmarks, using magnetic fields similar to those in the DIII-D and JET experimental reactors.
1. K. Tretiak, D. Ruprecht, An arbitrary order time-stepping algorithm for tracking particles in inhomogeneous magnetic fields, (2018) [Online]. Available: https://arxiv.org/abs/1812.08117
2. M. Winkel, R. Speck, D. Ruprecht, A high-order Boris integrator, J. Comput. Phys., 295 (2015) 456-474 3. J. Boris, Relativistic plasma simulation-optimization of a hybrid code, in: Proc. of the Fourth Conference on
Numerical Simulation of Plasmas, Naval Research Laboratory, Washington, DC, (1970) 3-67 4. J. Huang, J. Jia, M. Minion, Accelerating the convergence of spectral deferred correction methods,
J. Comput. Phys., 214 (2006) 633-656 5. R. Akers et al., High fidelity simulations of fast ion power flux driven by 3D field perturbations on ITER,
(2016) [Online]. Available: https://nucleus.iaea.org/sites/fusionportal/Shared%20Documents/ FEC%202016/fec2016-preprints/preprint0489.pdf

Speaker: K. Tretiak (EPS 2019)

480 P4.1031 Interaction of energetic particles from neutral beam injection with Alfvén Eigenmodes in JT-60SA

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1031.pdf

The JT-60SA device offers unique conditions before ITER for the study of the interaction of energetic particles with plasma waves. With similar dimensions to JET e.g. major radius but with a slightly more elongated plasma volume, JT-60SA is a high power device where an additional heating power (including 10MW of 500keV Neutral Beam Injection) up to 41MW and the potential for high non-inductive plasma current operation pave the path for numerous physics challenges on MHD stability. The work presented here addresses the MHD stability of shear Alfvén Eigenmodes (AE) in a variant of one of the working scenarios of JT60-SA, namely the high power full inductive single null at high density (Scenario 3). The plasma scenario has a plasma current of 5.48MA, toroidal magnetic field of 2.05T, 9.89/10.9x1019m-3 ion/electron densities on axis, ~5.94keV of ion/electron temperatures on axis and very low shear q~1 safety factor in the core. A comprehensive assessment of all shear AE with frequencies up to 2.7 normalised to on axis Alfvén frequency and with toroidal mode number up to n=25 was performed. The plasma scenario stems from CRONOS [1] simulations and the energetic particle distributions were calculated with the ASCOT code [2]. The drive/damping contributions from the NBI energetic ions were calculated with the CASTOR-K code [3-5]. The simulations were performed using either the full set of NBI sources foreseen for this scenario and only the lower energy (85keV) sources (no counter current positive beams are used). It is found that co-passing orbits from the highly energetic (500keV) N-NBI beams alone can effectively drive modes located dominantly at the plasma core region. With only the low energy units or away from the deep plasma core, the beam contribution is found to be stabilizing.
[1] J.F. Artaud et al 2010 Nucl. Fusion 50 043001; [2] E. Hirvijoki, O. Asunta, T. Koskela, T. Kurki-Suonio, J. Miettunen, S. Sipilä, A. Snicker and S. Äkäslompolo, Comput. Phys. Commun. 185 1310­21 (2014); [3] D. Borba and W. Kerner, J. Comput. Phys. 153, 101 (1999) ;[4] F. Nabais, D. Borba, R. Coelho, A. Figueiredo, J. Ferreira, N. Loureiro, P. Rodrigues, Plasma Science and Technology 17, 89 (2015) [5] P. Rodrigues, A. Figueiredo, J. Ferreira, R. Coelho, F. Nabais, D. Borba, N.F. Loureiro, H.J.C. Oliver and S.E. Sharapov, Nucl. Fusion 55, 083003 (2015)
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: R. Coelho (EPS 2019)

481 P4.1032 Dependence of reconstructed equilibria on input data sets using EFIT on COMPASS and comparison with experimental observations

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1032.pdf

The dependence of equilibrium properties obtained by the EFIT Grad-Shafranov equation solver on constraining input data was studied. Following sets of constraining data were supplied to EFIT: (i) minimal input (16 internal partial Rogowski coils), (ii) optimized minimal input (16 internal partial Rogowski coils with adjusted geometry), (iii) optimized minimal input with flux loops and divertor Mirnov coils (16 internal partial Rogowski coils, 4 flux loops, 8 tangential divertor Mirnov coils, 8 normal divertor Mirnov coils). Reconstructions using the abovementioned sets of input data were performed using first- and second-order polynomial flux functions representation (p = P2(), f f = P2()). Resulting reconstructed observables were compared to experimental measurements obtained in selected discharges in COMPASS tokamak. Outer-midplane separatrix position was compared to the separatrix position obtained by reciprocating probe and divertor strike point positions were compared to the maximum of heat flux measured by divertor array of Langmuir and ball-pen probes. Separatrix position in H-mode discharges was compared to the pedestal positions obtained by Thomson scattering. Observed dependencies were summarized, showing systematically better agreement between EFIT and diagnostics for various versions of input constraints.

Speaker: O. Kovanda (EPS 2019)

482 P4.1033 Towards the integrated analysis of tokamak plasma equilibria: PLEQUE

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1033.pdf

The equilibrium solution of the Grad­Shafranov equation in the form of the 2D function of psi and of the F() = R Btor function and the pressure p() profile offers fundamental information about the tokamak plasma state. The combination of these functions provides complex information about the plasma such as the topology, plasma currents, and the magnetic field. Plasma equilibrium is used for both data analysis and as one of the inputs of computer simulations. Known plasma equilibrium plays a key role in a design of new machines like COMPASS-U in Prague. As a consequence, equilibrium analysis tools are part of the most of simulation codes and they are included among the equipment of many tokamak plasma scientists. Nevertheless, a unified and universal package for simple and fast manipulation of equilibria is still missing. In this contribution, we present a new open-source python package PLEQUE (PLasma EQUilibrium Enjoyment) [1] which aims to solve this issue. We focus on four aspects of the package. Firstly, we introduce methods used for the input analysis which allow obtaining self-consistent information (e.g. x-point, magnetic axis, strike-points, or plasma boundary). Secondly, we demonstrate its possibility to be integrated with other codes via the IMAS (ITER Integrated Modelling & Analysis Suite) format or standard equilibrium g-eqdsk format. The ability to read some real tokamak machine equilibria is demonstrated as well. Thirdly, we show the simple high-level interface to obtain the requested data as simply and easily as possible. The interface allows an elegant ability to work with various tokamak coordinate system and to map profiles of various quantities of psi to the plasma equilibrium. Finally, applications such as field line tracing will be demonstrated and used for magnetic field reconstruction in the presence of resonant magnetic perturbations.
[1] https://github.com/kripnerl/pleque

Speaker: L. Kripner (EPS 2019)

483 P4.1034 Impact of massive material injection on runaway electron generation

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1034.pdf

In current carrying fusion devices, the sudden loss of thermal energy, referred to as disruptions, poses a serious threat to the plasma vessel, as relativistic runaway electrons (REs) generated in the process may cause intense localised damage to plasma facing components. In future high-Ip devices such as ITER, the risk of replacing a large fraction of the pre-disruptive current by REs is significantly greater than in present-day devices due to exponentiation of a postdisruption seed. As countermeasure, massive material injection is foreseen in ITER. However in dedicated experiments in present-day devices such as ASDEX Upgrade (AUG), clear correlations between the amount injected material, the plasma response and the runaway behaviour are challenging to observe [1,2].
In this work, their interactions are studied by transport modelling of particles and heat in a realistic magnetic tokamak geometry with the 1.5D transport code ASTRA [3] coupled to the impurity radiation code STRAHL [4], a toolkit previously used for modelling the prethermal quench of AUG MGI experiments [5]. Impurity ionisation states are evolved individually by STRAHL following atomic data based rate equations, thus allowing the simulation of non-equilibrium phenomena. Considering additional impurity electrons and radiation, the background plasma is evolved by ASTRA. The generation of REs is described by fluid equations for small-angle momentum-space diffusion (Dreicer mechanism) [6] and for large-angle knock-on collisions (avalanche mechanism) [7], corrected by the impact of partially ionised impurities on the critical electric field required for runaway generation [8]. Comparison of this toolkit with the disruption code GO [9] shows accurate implementation of these equations in ASTRA. Within this framework, the impact of varying amounts Ninj, type and radial distribution of injected material on RE generation in AUG plasmas is investigated and compared to experimental observations.

References
[1] G. Pautasso et al., 45th EPS Conference on Plasma Physics, 02.-06.07.2018, Prague, Czech Republic, P4.1058
[2] G. Pautasso et al., Plasma Phys. Control. Fusion 59, 014046 (2017)
[3] E. Fable et al., Plasma Phys. Control. Fusion 55, 124028 (2013)
[4] R. Dux et al., Nucl. Fusion 39, 1509 (1999)
[5] E. Fable et al., Nucl. Fusion 56, 026012 (2016)
[6] J.W. Connor et al., Nucl. Fusion 15, 415 (1975)
[7] M.N. Rosenbluth et al., Nucl. Fusion 37, 1355 (1997)
[8] L. Hesslow et al., Plasma Phys. Control. Fusion 60, 074010 (2018)
[9] G. Papp et al., Nucl. Fusion 53, 123017 (2013)

Speaker: O. Linder (EPS 2019)

484 P4.1035 Beta-induced Alfvén eigenmodes destabilized by resonant magnetic perturbations in J-TEXT Tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1035.pdf

Beta-induced Alfvén Eigenmodes (BAEs) destabilized by resonant magnetic perturbations (RMPs) are investigated in J-TEXT tokamak. Two kinds of BAEs are observed with RMPs of finite amplitude. One is considered as m-BAE, due to the strong correlation with magnetic island, frequency characteristic, mode number and driving mechanism. Specifically: 1. The exciting threshold is studied. After RMPs penetration, m-BAE could be excited when the width of the magnetic island exceeds a threshold (about 2.6 cm) and lower than an upper limit (about 4.2 cm). A similar result is also found in the experiments that a pair of m-BAE is excited along with TM. 2. In the exciting condition range, the amplitude of m-BAE decrease with enlarging magnetic island. 3. The m-BAE forms a standing wave structure. The nodes of m-BAE are located around O point and X point of the magnetic island while the BAE perturbs between the O point and X point. 4. The frequency of detected m-BAE locates in the BAE gap calculated by NOVA-K code. Another mode is identified as the magnetic island-induced AE (labeled as MIAE-like mode in this work), consistent with the prediction of theory (Biancalani A. et al 2010 Phys. Rev. Lett. 105 095002). The frequency of MIAE-like mode is approximately proportional to the square of magnetic island width. In addition, the pressure gradients may have a driving effect on MIAE-like mode. In addition, m-BAE becomes weaker and MIAE-like mode becomes stronger with growing magnetic island, so we assume that energy exchanging would take place between the magnetic island and m-BAE. The free-energy source of pressure gradients may have a driving effect on MIAE-like mode.

Speaker: L. Liu (EPS 2019)

485 P4.1036 Impurity transport and its modification by MHD in tokamak plasmas with application to Tungsten in the WEST tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1036.pdf

The concern about impurity migration in tokamak plasmas arises because of its considerable impact on core radiation, leading to performance degradation and potentially to confinement loss. Highly charged particles are particularly deleterious as not only their radiative emission is large but also their radial flux, since it is to first approximation proportional to their charge. This flux has a strong collisional contribution described by neoclassical theory [1], as well as a turbulent contribution. We address here the issue of the 'natural' impurity transport and poloidal distribution, i.e. without toroidal momentum source nor ion temperature anisotropy, by comparing analytical theory with numerical simulations with the XTOR code [2] where neoclassical physics [3] and impurity evolution [4] are implemented. The asymmetry pattern can be determined analytically and depends on both the equilibrium gradients and the collisional friction between the impurity and the main ion species. The neoclassical impurity flux and poloidal asymmetry are investigated in non linear simulations for a light impurity (162C) and a heavy one (17844W). We find that the radial impurity flux is strongly damped by the poloidal asymmetry, the drive being inward or outward, with a good agreement between theory and simulations. The application to a typical WEST plasma shows for example that the inward Tungsten flux (for a flat impurity profile) is reduced by more than a factor two at mid-radius compared with predictions without poloidal asymmetry, although their level remains below 5%.
The modification of impurity transport by a magnetic island is expected to be large, and some experimental observations confirm this, because the temperature screening effect that is driving outward flux is largely lost [5]. Numerical simulations for a (2, 1) island in WEST confirm this mechanism, with an inward flux that is increased, in qualitative agreement with the theoretical result where temperature screening is becoming less effective.
References [1] C. Angioni et al., Plasma Physics and Controlled Fusion 56, 124001 (2014). [2] H. Lütjens et al., Journal of Computational Physics 229, 8130 (2010). [3] P. Maget et al., Nuclear Fusion 56, 086004 (2016). [4] J.-H. Ahn et al., Plasma Physics and Controlled Fusion 58, 125009 (2016). [5] T. Hender et al., Nuclear Fusion 56, 066002 (2016).

Speaker: P. Maget (EPS 2019)

486 P4.1037 Core magnetic fluctuation and current profile dynamics during improved H mode plasma discharge with flat central q profile on EAST

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1037.pdf

Improved H mode operation has been achieved on EAST with high using NBI and LHW. Better confinement was obtained with flat central safty factor q profile in the core area, and the minimum q is slight above unity contributing to sawteeth free plasma. Core magnetic fluctuation and current profile dynamics are provided by the 11 chords polarimeter-interferometer measurement. Current profile evloution shows that anomalous current transport exists during transition to improved H mode phase. The characteristics of internal MHD modes evolution are analyzed spatially and temporally. It is infered that nonlinear coupling among different MHD modes may play a important role for sustained flat q profile operation by correlation analysis. Results from other internal diagnostic systems, such as ECE and SXR, also show consistent phenomena.

Speaker: W. Mao (EPS 2019)

487 P4.1038 MHD dynamics and error fields in the RFX-mod2 Reversed field Pinch

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1038.pdf

RFX-mod is a Reversed Field Pinch device that allowed performing experiments in regimes with a plasma current up to 2 MA. Due to its low value of the safety factor (q<<1) and the central peaking of current density, the RFP is characterized by the presence of MHD modes that, in RFX-mod, are controlled by a combination of a passive boundary and an active control system. While at low current several MHD modes of comparable amplitudes are simultaneously present (Multiple Helicity), in high plasma current regimes, a single resonant m=1 (dominat) MHD mode frequently increases its amplitude while the others (secondary) decrease (Quasi Single Helicity). In order to improve the control of secondary modes, a modification of the layout of the RFX-mod device is in progress consisting in the removal of the Inconel vacuum vessel and a modification of the stainless steel supporting structure to be made vacuum tight. In the upgraded device, dubbed RFX-mod2, the shell-plasma distance decreases from b/a=1.11 to b/a=1.04 and copper, instead of Inconel, is the conducting structure nearest to the plasma.
RFXLocking simulations [1] have shown that in RFX-mod2 secondary Tearing Modes amplitude and the edge bulging due to their phase locking will decrease; moreover the plasma current threshold for Tearing Modes wall locking will also significantly increase, from the measured RFX-mod 80-120kA to values from 2 to 5 times higher [2].
On the other hand, due to the shorter distance from the shell, the plasma will be more sensitive to magnetic field errors at its boundary, produced by the shell eddy currents near the poloidal cut for the penetration of the electric and magnetic fields and the holes for diagnostic access. A finite element code (CAFE BEM) that computes the induced currents in thin conducting structures with complex 3D geometry, has been used to determine error fields in RFX-mod2 during the plasma start-up phase. No significant variation of wall locking threshold has been found [3].
For plasma currents below the wall-locking threshold, TM will rotate at frequencies in the kHz range, as observed, e.g., in the MST RFP device [4] and in the very low current RFX-mod discharges [5]. The error fields induced by MHD modes in this frequency range are best modelled by a volume integral formulation of induced eddy currents [ 6 ]. A simplified vacuum approach is adopted where each harmonic is represented by a toroidal surface current density J(theta,phi ) = GradPhi(theta,phi ) × n, where the scalar stream function is given by (theta,phi,t) = sin(mtheta+nphi+t*omega), where m and n are the poloidal and toroidal numbers respectively. Effects of shell proximity and error fields on edge plasma properties in this frequency regime will be discussed. Moreover, error fields generated by fast MHD dynamics (such as sawteeth crashes or back transitions from Single Helicity to Multiple Helicity states) may cause wall locking if their amplitude is sufficiently high [4]: the impact of error fields for RFX-mod2 will be evaluated by means of RFXLocking simulation.
[1] Zanca, P., et al, Plasma Phys. Control. Fusion 51 (2009) 015006 [2] Marrelli, L. IAEA 2018 [3] Marrelli, L., et al., Fus. Eng. Des., In press (2019) https://doi.org/10.1016/j.fusengdes.2019.01.054 [4] Almagri, A.F. et al., Phys. Fluids B 4 (1992) 4080 [5] Innocente, P., et al., Nucl. Fusion 54 (2014) 122001 [6] Bettini P., et al., IEEE Trans. Mag. 53 (2017) 7204904

Speaker: L. Marrelli (EPS 2019)

488 P4.1039 Global structure of stationary zonal flow in rotating tokamak plasmas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1039.pdf

Zonal flows (ZF) are low-frequency, predominantly electrostatic plasma oscillations ( is the poloidal wave-number, is the toroidal wave-number) widely
observed in modern toroidal magnetic plasma confinement systems, such as tokamaks and stellarators [1]. It is believed that ZFs are able to regulate the level of anomalous transport in plasma through nonlinear interaction with small-scale drift-wave turbulence. Earlier, in the framework of ideal MHD, the local dispersion relation demonstrating coupling of ZF and geodesic acoustic mode (GAM) in rotating plasma was obtained [2,3]. Under the assumptions of the adiabatic equation of state and the equilibrium with constant on magnetic surfaces ( is the plasma pressure, is the mass density, is an arbitrary function of the magnetic surface) the continuous spectrum of ZFs and GAMs in the presence of toroidal plasma rotation is described by Eq. (1) [2,3] reported at http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1039.pdf.
The high-frequency branch of the oscillations described by Eq. (1) corresponds to GAM, and the low-frequency branch corresponds to the so-called stationary ZF. In this paper we consider the possibility of the existence of global mode of stationary ZF in tokamak with toroidal plasma rotation. The eigenfrequencies and the structure of corresponding eigenfunctions are calculated. It is shown that for typical profiles of tokamak plasma parameters global ZFs are localized at the periphery of plasma column. The stability of modes, their frequencies and increments are mainly determined by the type of plasma equilibrium, i.e. by the parameter .

[1] Fujisawa A., Nucl. Fusion 49 (2009) 013001 [2] Lakhin V.P., Sorokina E.A., Ilgisonis V.I., Konovaltseva L.V., Plasma Physics Reports 41 (2015) 975 [3] Havekort J.W., de Blank H.J., Koren B., J. Comp. Phys. 231 (2012) 981

Speaker: N. Marusov (EPS 2019)

489 P4.1040 Comparison of plasma current asymmetry with vessel currents asymmetry on COMPASS during disruptions.

See full abstratc here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1040.pdf

Determination of vessel currents magnitudes and distribution plays crucial role in understanding of mechanical loads on the machine [1]. Asymmetrical disruptions are of particular concern because they possibly cause severe asymmetric electromagnetic loads [2, 3]. For the first time plasma current asymmetries are compared with vessel currents asymmetries on COMPASS. These might help to understand whether localization of vessel currents and therefore mechanical stresses are caused by plasma current asymmetry. Both toroidal and poloidal components of the vessel current are considered. Experimental measurements of poloidal currents in the vacuum vessel during thermal and current quenches are compared with recent analytical predictions [4]. The COMPASS tokamak has unique magnetic diagnostics including full internal and full external Rogowski coils (having same poloidal position), three sets of Mirnov coils (each coil capable of measuring radial, toroidal and poloidal components of magnetic field), internal and external partial Rogowski coils (having the same toroidal position) [5, 6]. Plasma current has been measured in 5 toroidal locations, its asymmetry magnitude and phase have been determined. Asymmetry comparison with local poloidal and toroidal vessel currents (including their poloidal distribution) from Halo region and any other sources has been analysed.
[1] C. Bachmann et al., Fusion Engineering and Design, 86, 2011 [2] S.N. Gerasimov et al., Nuclear Fusion, 55, 2015 [3] R. Roccella et al., Nuclear Fusion, 56, 2016 [4] V.D. Pustovitov, Fusion Engineering and Design, 117, 2017 [5] P.J. Knight et al., Nuclear Fusion, 40, 2000 [6] Panek et al, Czech. J. Phys. 56, 2006

Speaker: E. Matveeva (EPS 2019)

490 P4.1041 Global MHD stability of plasma in Galatea traps

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1041.pdf

Magnetic plasma confinement systems with conductors embedded into plasma is an important class of magnetic traps with high beta, known as Galateas [1], alternative to the mainstream toroidal system designs. As summarized in [2], Galateas are widely diversified and it provides additional reason to consider them, unlike low-beta traps, as promising systems for many plasma technologies and for advanced fuel reactors while the technical difficulties arising from the magnetic suspension of the embedded conductors ("myxines") and their operation in reactor conditions can be overcome with present-day technologies.
The studies of geometric and other parameters of axisymmetric plasma configurations maintained in an equilibrium by the magnetic field of both plasma current and toroidal currents in the myxines at zero toroidal field is based on the solution of the GradShafranov equation (for recent results see [3,4]). A variety of equilibria with complicated magnetic field surface topology can be realized in Galateas. The use of the unstructured grid ideal MHD stability code MHD_NX [5] makes possible plasma stability studies in Galatea traps [6]. Apart from the localized convective mode stability criteria (like RosenbluthLongmire-Kadomtsev [2]), global mode stability calculations in multiply connected plasma domain can be performed taking into account a gap between the plasma and the vacuum vessel (external modes). For equilibrium configurations in the Galatea magnetic trap "Trimix" [7], the dependence of the growth rates of ideal MHD modes with different toroidal wave numbers on the pressure magnitude is investigated.
Acknowledgement This research is supported by the Russian Science Foundation (Grant No. 16-11-10278).
[1] A.I. Morozov. Fizika Plasmy 18 (1992) 305. [2] A.I. Morozov, V.V. Savelyev. Uspekhi Fiz. Nauk. 168 (1998) 1153. [3] K.V. Brushlinskii, A. S. Goldich. Differ. Equ. 52 (2016) 845. [4] A.N. Kozlov at al. Preprint Keldysh Institute of Applied Mathematics. 182 (2018). [5] S.Yu. Medvedev et al. Plasma Phys. Rep. 45 (2019) 108. [6] S.Yu. Medvedev et al. Preprint Keldysh Institute of Applied Mathematics. 253 (2018). [7] A.I. Morozov et al. Plasma Phys. Rep. 32 (2006) 171.

Speaker: S. Medvedev (EPS 2019)

491 P4.1042 Magnetic reconnection driven by plasmoid instability in coaxial helicity injection current drive on HIST

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1042.pdf

The Spherical Torus (ST) is a promising candidate for an advanced fusion reactor due to the compactness. Elimination of the central solenoid coil to allow an approach to lower aspect ratio configurations requires for the non-inductive plasma start-up. The transient coaxial helicity injection (T-CHI) is a leading candidate for its method. One of the most important issues in T-CHI is whether it can establish closed flux surfaces due to the magnetic reconnection in the high Lundquist number S regime. Understanding the flux closure during the start-up process is the primary purpose of the T-CHI experiment on the Helicity Injected Spherical Torus (HIST: R=0.30 m, a=0.24 m, A=1.25) [1]. Also, the CHI provides a good platform for pursuing MHD relaxation and magnetic reconnection physics. Magnetic reconnection is an essential element in understanding of self-organization phenomena such as sawtooth oscillations and Taylor relaxation in fusion plasmas and also eruptive mass ejection of solar flares in astrophysical plasmas. To prove the flux closure issue in the CHI start-up, we have investigated the fast magnetic reconnection driven by multiple plasmoids [2].
In the CHI experiment on HIST, we have found that two or three small-size plasmoids are generated in elongated toroidal current sheet with the full width ~0.05 m, a long length L=0.6-1 m and a high density ne= 0.3-2x1020 m-3. The frequency of the regular oscillation of the reconnected magnetic field observed in the H discharge is analyzed to be 175 kHz, which well correlated with that of electron density. The magnetic oscillation originated from the reconnection point propagates outwardly in the radial location by the Alfven speed of 30 km/s. The frequency depends on the gas species (H, D and He) and the external toroidal (guide) field strength. In the He discharge, the oscillation is much slower than that in the H2 discharge, leading to the formation of the doublet-type closed flux surfaces. These findings could verify that the plasmoid reconnection in the elongated current layer in the presence of the strong toroidal field allows the fast flux closure in the T-CHI.

References [1] M. Nagata, et al., Phys. Plasmas 10, 2932 (2003). [2] F. Ebrahimi and R. Raman, Phys. Rev. Lett. 114, 205003 (2015).

Speaker: M. Nagata (EPS 2019)

492 P4.1043 Coupled resonant layer responses to rotating 3D fields in the presence of static error fields

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1043.pdf

Single and compound helicity tearing mode (TM) responses to a rotating 3D resonant magnetic perturbation (RMP), in the presence of a static error field (EF), have been observed in the partially penetrated regime [1] of the TM unlocking bifurcation process [2] in DIII-D experiments. This regime has been proposed as a stable window over the 3D frequency dependence on simulations with the non-linear resistive reduced MHD code AEOLUS-IT [3,4]. The single helicity structure is formed when the external 3D field rotates with a frequency slightly higher than a critical value, avoiding full-penetration but reaching to a rational surface where the static EF has already formed a magnetic island. The unique standing wave response characteristic of this regime was observed experimentally in high beta, H-mode, DIII-D discharges when the magnitude of the EF was comparable to the rotating 3D field, in qualitative agreement with AEOLUS-IT simulations [1,4]. A similar structure was reported also in ohmic plasmas in J-TEXT [5]. The single helicity perturbation seems resilient to perturbations due to small ELMs.. When sufficiently perturbed, however, the response spreads over neighboring rational surfaces through the poloidal coupling inherent to shaped tokamak plasmas. This results in the formation of a compound (double) helicity state. This helicity deterioration will be compared with new simulations including double resonant surfaces at q=2 and 3.
This work was supported in part by the US Department of Energy under DE-AC02-09CH11466, DE-FC02-04ER54698, DE-AC0506OR23100 and DE-FG02-04ER54761. Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. [1] Okabayashi, M., et al., 2018 IAEA Fusion Energy Conf., EX/P6-25, [2] Fitzpatrick, R., Nucl. Fusion 33 1049 (1993), [3] Inoue, S., al., Plasma. Phy. Control. Fusion 60 025003 (2018), [4] Inoue,S., et all, 2018 IAEA Fusion Energy Conf. TH/P5-24, [5] Wang H, et al 2018 Nucl. Fusion in press

Speaker: M. Okabayashi (EPS 2019)

493 P4.1044 Rotating halo current during disruption phase of vertical displacement event in KSTAR

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1044.pdf

Disruption in the TOKAMAK device is generally known as one of the most harmful events. The thermal and current quench and the consequent heat load and magnetic force on the facing components are destructive. These are relatively well conceivable because it is a consequence of the eruption of two kinds of the energies, thermal and magnetic field energies, stored in the device. During the disruption, abrupt change of the magnetic energy associated with the plasma current induces the eddy and halo current on the facing component and structures. The induced current cooperation with the externally applied magnetic field results in magnetic forces on the structure. In addition to the direct magnetic forces by the eddy and the halo current, there is a relatively unknown harm source. During the disruption followed by the vertical displacement event (VDE), several devices reported the toroidally rotating halo current. Even if the magnetic force caused by the halo current itself is not strong enough, the resonant coupling of the rotating and the structural vibration frequency might be destructive. Recently it has emerged as one of an important issue for the ITER safe operation. Even though the projection to ITER is urgent, there is no relevant explanation of the rotation frequency and the direction so far. Through the data analysis of the KSTAR disruption event from 2015 to 2018 campaign, we found ample examples of rotating halo current. With the statistical analysis of the data, we propose a new physics model which elucidating the rotation frequency and the direction of the halo current. The model is assuming that the tokamak plasma can be regarded as a rigid body with the momentum and then the external torque exerted on the plasma results in a precession motion of the plasma. We explain the rotating halo or any other induced current on the structure is a consequence of the precession motion. The KSTAR experiment is analyzed based on this model and compared with the diagnosed data.

Speaker: B. Park (EPS 2019)

494 P4.1045 Modelling of shattered pellet ablation: a discussion

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1045.pdf

The massive injection of material into a tokamak is a technique considered for disruption mitigation. Presently, several shattered pellet injectors (SPIs) [1] are foreseen for the ITER disruption mitigation system. According to reference [2], the assimilation of 14 kPam3 of deuterium fully prevents the conversion of magnetic energy into runway electrons during the induced current quench of a 15 MA ITER plasma. This amount of gas corresponds to a volume averaged density increase of the order of 41021 m-3, which should take place in a time interval of the order of 10 ms. In addition, the density increase has to occur in the plasma centre where the plasma current peaks and the toroidal electric field is maximum. It is presently not know, whether this is physically and technically doable. The Neutral Gas Shielding (NGS) model has been implemented in JOREK and used to simulate the interaction of shattered pellets with JET-like plasmas [3]. The simulations were done with injected amounts of deuterium of the order of 1022 molecules, which correspond to a density rise of the order of 1020 m-3. These quantities are one order of magnitude smaller than the one needed for RE suppression in a full current ITER mitigated disruption. This conference contribution reports on calculations of deuterium pellet ablation and density increase carried out with the HPI2 code [4] for different ITER- and DEMO-relevant [5] plasma and pellet (shattered and not) parameters. The comparison between the NGS model and the HPI2 results and the limitations of the two models are also discussed. The ultimate purpose of this exploratory work is to understand whether RE suppression by massive material injection is possible in a future fusion reactor.
[1] L. Baylor et al., 27th IAEA Fusion Energy Conference FIP/P1-1 (Gandhinagar, 2018) [2] J.R. Martin-Solis et al., Nuclear Fusion (2017) 57 066025 [3] D. Hu et al., Nuclear Fusion (2018) 58 12605 [4] F. Koechl et al., "Modelling of pellet particle ablation and deposition: the hydrogen pellet injection code HPI2", Report EFDA-JET-PR(12)57 [5] M. Siccinio et al., to be published in Nuclear Fusion (2019)

Speaker: G. Pautasso (EPS 2019)

495 P4.1046 Data on runaway electrons in JET

See full abstract herer
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1046.pdf

In tokamak-reactor, such as ITER, the generation of runaway electrons (RE) is unacceptable. Disruption Mitigation System (DMS) designed in ITER should be a reliable tool for suppression of RE and mitigate other detrimental consequences of disruptions. Elaboration of the RE database and its comprehensive analysis should stimulate further advances in understanding of the physics of RE and their interaction with plasma and neutral gases (fuel and injected impurities) for development of ITER DMS. From the beginning of JET operations there were several attempts to review the data on RE generation events (for example, [1]). However, these attempts are still waiting a compiling into joint database.
This report presents the first summary analysis of the most extended data on RE generation in JET disruptions. This data includes more than 1800 RE generation events in disruptions before and after divertor installation, with metal and carbon limiters (JET-C) and with ITER-like Wall (JET-ILW), in spontaneous disruptions and those triggered by slow gas puff and Massive Gas Injections (MGI). This analysis confirms some previous results from JET-C and JET-ILW on the current conversion < 0.6-0.7 for both cases. Present work revealed a generation of RE plateaux in several high current spontaneous disruptions in JET-C with maximal values of the disrupted currents < 6.25 MA extending upper currents boundary of the data. In JET-ILW the RE data was collected in MGI experiments with currents 2MA. Unlike to previous studies carried out on the basis of limited number of RE generation events, this report shows that RE plateaux were detected in JET-C at very low q(a) < 2.5, with current plateaux sometimes achieving 3 MA and with up to 2 MA of the RE fraction. In contrary to our previous conclusions, a systematic analysis of the data on RE in JET-C and JET-ILW revealed an absence of the "so-called" threshold on magnetic field values. Analysis of current quench (CQ) stages allowed distinguishing several groups of disruptions: with constant CQ rate during the first milliseconds (3-8) in the beginning of decay, which corresponds to exponential decay of the resistive plasma current; the disruptions with substantially varied CQ rates; and, a third group includes disruptions with RE but without measurable CQ stage, i.e. when generation was detected immediately after the thermal quench. All data on CQ and RE plateaux dynamics was used in study of the functional dependencies of photo-neutron and HXR emissions vs. RE currents allowing assessment of densities and energies of RE fractions. Measurements of HXR, gammas and photo-neutrons with time-resolved HXR monitors, neutron rate fission chamber monitors, NaI(Tl), BGO and LaBr spectrometers together with JET neutron/gamma profile monitor (2 cameras, vertical and horizontal, with 9 and 10 lines of sight) allowed evaluation RE energy (up to 30 MeV in JET-C and 10-15 in JET-ILW) and observe spatial evolution of RE beam [2].
[1] 1990 Preprint JET-R(90)07, Harris G.R. Comparison of the current decay during carbon-bounded and beryllium-bounded disruptions in JET. [2] 1988 Nuclear Fusion O.N. Jarvis et al "Photo-neutron production accompanying plasma disruptions in JET"

Speaker: V.V. Plyusnin (EPS 2019)

496 P4.1047 Analytic equilibrium of elongated plasmas bounded by a magnetic separatrix and the problem of resistive axisymmetric X-point modes

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1047.pdf

Theoretical and experimental considerations [1] suggest that axisymmetric perturbations that are resonant at the X-point(s) of a magnetic divertor separatrix may play a role for the understanding of ELMs and their active control via "vertical kicks" [2] in tokamaks.
We present the first step in the development of an analytic model for resistive axisymmetric X-point (RAXP) modes, i.e., finding an adequate, but at the same time relatively simple analytic MHD equilibrium for a plasma column with noncircular cross section bounded by a magnetic separatrix. An early example is Gajewski's equilibrium solution [3], which however has the shortcoming that infinite external currents placed at an infinite distance from the Xpoints produce the elliptical elongation of the plasma column.
Therefore, we have extended Gajewski's equilibrium to the case where external currents are located at a finite distance from the boundary of the plasma current density and the latter is distributed uniformly over a domain bounded by a nearly elliptical magnetic flux surface.
This analytic equilibrium is expected to be unstable to ideal MHD vertical displacements of the plasma column. Just like in the case of a tokamak plasma with elongated cross section, we can also expect that modulating in time the external currents can stabilize the vertical instability. In the ideal MHD case, this would mimic the passive feedback stabilization scenario of real tokamak plasmas, where time-dependent image currents are induced on the metallic wall of the toroidal vacuum chamber.
Of more interest will be to study the case of a resistive plasma extending to the magnetic separatrix. In this situation, a vertical displacement would be resonant at the magnetic Xpoints, giving rise to current sheets centred at the X-points. In the equivalent tokamak scenario, this type of perturbation is what we refer to as RAXP mode. A preliminary, conceptual analysis of RAXP modes is discussed in this article.
[1] F. Porcelli 1996 JET Report IR(96)09; J. Lingertat et al 1997 J. Nucl. Mat. 241, 402; E. R. Solano et al 2008 Nucl. Fusion 48, 065005. [2] E. de la Luna et al 2016 Nucl. Fusion 56, 026001. [3] R. Gajewski 1972 Phys. Fluids 15, 70.

Speaker: F. Porcelli (EPS 2019)

497 P4.1048 Dispersion relations for resistive wall modes in tokamaks

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1048.pdf

It is well known that the ideal MHD cannot describe the resistive wall mode (RWM) dynamics in the DIII-D tokamak [1, 2]. This is true, in particular, with respect to the rotational stabilization [1] that makes plasma stable essentially above the no-wall stability limit predicted by the ideal MHD. The uncertainty in the underlying physics illustrated by detailed analysis [2] of a wide spectrum of competing models still remains unresolved.
Ultimately, the main challenge to theory is to find the energy sink that could be effective without exponential growth of the magnetic perturbation. Facing a necessity of expanding the search beyond the limits of conventional MHD, it is natural to move consistently so that the well established results would be strictly reproduced as proper asymptotes. This requires an approach with new elements introduced as extensions of the MHD, both physically and mathematically. The latter means the use of the MHD equations as a kernel of the model and the energy principle algorithm [3] as the guide in derivations.
Such a strategy has been outlined in [4, 5]. We use it here with a focus on the dispersion relations for RWMs in tokamaks. A general approach discussed here is constructed to provide a universal backbone for possible extensions of interest. If the resistive wall is incorporated as proposed in [6], the resulting dispersion relations for slow modes will be in the form first introduced in [6], but with additional terms representing the non-MHD mechanisms [4]. The representation of the magnetic perturbation in vacuum in the method of [6] is the approximation which has never been analyzed for consistency. This will be discussed here, the limitations of the plasma-wall coupling model of [6] will be exposed and better solutions proposed.

[1] E.J. Strait, J. Bialek, N. Bogatu, M. Chance, M.S. Chu, et al., Nucl. Fusion 43, 430 (2003). [2] M.S. Chu and M. Okabayashi, Plasma Phys. Control. Fusion 52, 123001 (2010). [3] I.B. Bernstein, E.A. Frieman, M.D. Kruskal and R.M. Kulsrud, Proc. R. Soc. Lond. A 244,
17 (1958). [4] V.D. Pustovitov, J. Plasma Phys. 81, 905810609 (2015). [5] V.D. Pustovitov, Phys. Plasmas 24, 112513 (2017). [6] S.W. Haney and J.P. Freidberg, Phys. Fluids B 1, 1637 (1989).

Speaker: V.D. Pustovitov (EPS 2019)

498 P4.1049 Analysis of the initial phase of current quenches in the DIII-D tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1049.pdf

In this study, we analyzed current quenches in 3 types of DIII-D disruptions (low-q, error field and shell pellet injection) to investigate the determination mechanism responsible for the initial phase of current quench in DIII-D tokamak. Disruptions are one of the most critical issues for realization of DEMO reactor. During the current quench (CQ), the plasma current (Ip) decays rapidly because of the sudden in increase in plasma resistance following the thermal quench. The rapid
current decay generates potentially damaging eddy
currents and electromagnetic force in conducting materials around plasma. To reduce these effects, Massive Gas Injection (MGI) and Shattered Pellet Injection (SPI) are candidate methods to mitigate the effects of thermal quench and CQ in ITER [1]. In this study, we focused on the initial phase of the CQ (between 100% to 80% of maximum Ip in CQ) to determine the mechanism governing the CQ decay time. In a previous study of JT-60U, it was found that there was also fast current decay during the initial phase of CQ in a high electron temperature Te disruption discharges (Te at the plasma center: over 100eV) and Ip decay varied with the change in plasma inductance Lp during the CQ, especially internal plasma inductance Li [2]. In this study, we analyzed CQ in 3 types of DIII-D disruptions to confirm the impact of the time evolution of the Li on the decay time of the CQ. To evaluate the Li during the initial phase of the CQ, we used the CCS method. Fig.1 shows the relationship between time derivative of Li and CQ time during the initial phase of the CQ. It is found that dLi/dt is increased with decrease of CQ time as same to JT-60U results. To investigate the mechanism of increase of Li, we are simulating the CQ waveform by using DINA [3]. We will show results of DINA analysis in presentation. This material is based upon work supported by the US Department of Energy under Award Number(s) DE-FC02-04ER54698.

[1]T.C. Hender, et. al., Nucl. Fusion 47 S128-202 (2007). [2] Y. Shibata, et. al., Plasma Phys. Cont. Fusion56 045008 (2014). [3] R. Khayrutdinov and V. Lukash, J. Comput. Phys. 109 193(1993).

Speaker: Y. Shibata (EPS 2019)

499 P4.1050 Comparison of tokamak plasma midplane with divertor conditions

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1050.pdf

In tokamaks, the scrape-off layer between the midplane and the divertor is experimentally not well diagnosed. Specifically, there is scarce experimental comparison of the ion temperature fluctuation and little information about the parallel velocity of the plasma. To gain a better understanding of the behaviour of the plasma as it streams down from the outboard midplane towards the divertor, a Langmuir-Mach probe is currently mounted on the x-point manipulator at ASDEX Upgrade (AUG) [1]. The probe scans the x-point region from the low field side to the high field side. For standard AUG equilibrium, the probe is operated below the x-point. Thus, making measurements through the private flux region (PFR) possible, allowing the investigation of the filamentary transport towards the divertor and understanding the spreading factor as related to diffusion.
This contribution presents experimental results in the x-point region and their correlation to the midplane will be discussed. During the 2019 campaign of AUG, the New Probe Head (NPH)[2], in which an electron emissive probe, two Langmuir probes, two magnetic pick-up coils and two retarding field analyzers (RFA) are integrated, will be mounted. With the RFA, it might be possible to verify the local evolution of the ion temperature and the correlation of fluctuations at the midplane and the x-point. The experimental results will be compared with the simulation code HESEL (Hot Edge SOL Electrostatic). It is a 2D energy conserving, four field model based on Braginskii equations, which solves for the electron density ne, generalized vorticity , electron and ion pressure pe,i. In HESEL, the parallel dynamics is parametrized, making it possible to map the profiles and the fluctuations at the outboard midplane down to the divertor region. The measurements in the x-point and divertor region may then add to validate the parallel parametrization.
References
[1] H. Meyer et al. Nuclear Fusion 57, 102014, (2017) [2] B.S. Schneider et al. PPCF-102229, in press, (2019)

Speaker: R.D. Nem (EPS 2019)

500 P4.1051 Nonlinear MHD simulation of plasma termination events in stellarators

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1051.pdf

Nonlinear dynamics of plasma termination events in stellarators are studied using a 3D nonlinear MHD simulation code. In this study, two types of plasma termination events, which are MHD instabilities driven by the pressure gradient and plasma current, are studied, respectively. In the Large Helical Device (LHD) experiment, many MHD instabilities are observed. In particular, if the peaked pressure profile was sustained by the pellet injection, a collapse event, so-called the core density collapse (CDC), was happen. In nonlinear MHD simulations, it is expected the CDC is driven by the resistive ballooning mode [1]. Recently, a new imaging diagnostics of the two-dimensional soft-X ray arrays is installed in the LHD. Using the new diagnostics, perturbations localized at the outward of the torus. That is a characteristic of the ballooning mode. So, it seems the ballooning mode is observed in the LHD experiments. However, to interpret the experimental observation, we need to know what kind mode patterns should be observed. On the other hand, in Wendelstein 7-X (W7-X) experiment, collapse events simultaneously happened in the plasma core, if the strongly localized plasma current is driven in the plasma core. That expects a MHD event driven by the plasma current. But, we did not identify what kind mode makes the collapse event in such a case. In this study, we study 3D MHD equilibria with reconstructed pressure profile using a 3D MHD equilibrium code, which does not assume nested flux surfaces [2]. And then, we will study nonlinear MHD simulations based on the 3D MHD equilibrium with the magnetic island [3]. In this study, we note nonlinear saturation to compare with the experimental observation.

1. N. Mizuguchi, et al., Nucl. Fusion 49 (2009) 095023 2. Y. Suzuki, et al., Nucl. Fusion. 46 (2006) L19 3. Y. Todo, et al., Plasma Fusion Res. 5 (2010) S2062

Speaker: Y. Suzuki (EPS 2019)

501 P4.1052 SPH simulation of cylindrical and toroidal MHD systems

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1052.pdf

Smooth Particle Hydrodynamics (SPH) [1] is a Lagrangian numerical method to solve the equations of hydrodynamics. It has been used by the Astrophysical community to model MHD phenomena quite successfully and it has been recently extended to include laboratory plasmas in cylindrical geometries [2]. Its Lagrangian nature allows us to discretise the MHD equations without the need of an underlying mesh and its derivation endows the resulting equations with simultaneous conservation of mass, momentum and energy. In SPH all the MHD fields are defined over a discrete set of moving particles and smooth fields are constructed through an interpolation technique. Temporal integration of the SPH equations does not require large matrix inversions which gives SPH the potential to be efficiently parallelised into many processors. Also, the ability of the method to construct its evolution equations in Cartesian coordinates allows it to tackle complex geometries like ITER and the Wendelstein-7X, with relative simplicity.
In this contribution we aim at extending the applicability of the SPH method by creating initial conditions for toroidal geometries restricted to circular cross-sections and aspect ratios a/R > 2 and around its curved boundaries. Finally, we test our Smooth field constructed with SPH. results by initialising our system to Solo'vev equilibrium solution of the Grad-Safranov equation and addressing stability questions and conclude by sketching the way towards a general toroidal geometries and realistic fusion scenarios.

References
[1] J.D.Price, "Smoothed particle hydrodynamics and magnetohydrodynamics", Journal of Computational Physics, 231, 759-794, (2012)
[2] Vela Vela L et. al., "Magneto-hydrodynamical nonlinear simulations of magnetically confined plasmas using smooth particle hydrodynamics (SPH)", PoP, 26, 1, 012511 (2019)

Speaker: L. Vela (EPS 2019)

502 P4.1053 Energy balance during disruptions

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1053.pdf

One of the major threats for the integrity of future fusion devices are disruptions [1], i.e. events during which the plasma energy content is lost on a very fast time scale and can be released under various forms to the structures circumventing the plasma. Consequently, significant heat
loads, particle loads, electromagnetic loads may arise on the surrounding structures, which may cause non negligible damage. It is hence fundamental to study and quantify the energy exchange between the plasma and the structures, which is the focus of the present paper. Being a fusion plasma an intrinsically multiphysics system, particular care must be taken when deriving an overall energy balance. Supposing that the one-fluid MHD equations describe the system [2], the following equations must be considered:
Poynting theorem. This is a direct consequence of Maxwell's equations only and can be interpreted in terms of electromagnetic power balance, involving toroidal and poloidal magnetic energy , Wmag,pol + Wmag,tor , and the flux Phi of Poynting vector.
Kinetic energy balance. This is derived from the momentum balance equation and states that kinetic energy varies due to work done both by pressure force and by Lorentz force.
Internal energy balance. From thermodynamics, we know that plasma internal energy may vary due to deformation work, heat flux (bremmstrahlung, radiation losses, external heating, etc.) and Joule losses. None of these equations can be considered alone, since each is coupled to the others by one or more terms. Adding up all these relations, we obtain the energy balance over a fixed volume (see equation at http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1053.pdf)
This relation will be used first of all for deriving some theoretical consequences on the required closure conditions (e.g. adiabatic equation), also considering that some differences arise in the proposed approach as compared to available results [2]. Secondly, it will give hints about the
possibility of "conversion" among the various forms of energy during disruptions, supporting the interpretation of results of detailed simulations [3] of present day and future devices.

[1] T. Hender et al, Nucl. Fusion 47 (2007) S128 [2] K. Miyamoto, Plasma Physics and Controlled Fusion, Springer (2005) [3] F. Villone et al., Plasma Phys. Control. Fusion 55 (2013) 09500

Speaker: V. Scalera (EPS 2019)

503 P4.1054 Singular global components and frequency shift of the continuum GAMs in shaped tokamak plasmas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1054.pdf

Geodesic acoustic modes (GAMs) of a global character are frequently observed in tokamak plasmas. While many aspects of GAMs require a kinetic treatment, the MHD model offers a suitable framework for analytically studying various global aspects of these modes, including higher-order effects of plasma shaping, plasma flows, and the magnetic perturbations connected with the GAM [1]. In this contribution, we extend the MHD analysis in [1] in order to study two additional aspects of the GAM. We first show that, as a part of the continuous MHD spectrum, the GAM eigenfunctions include components that exist outside the GAM surfaces and have singularities of type (P - P0)^-1 or ln|P - P0|, where P is a flux function that labels the magnetic surfaces, and P = P0 defines the singular (or GAM) surface [2]. Hence, in addition to the m = 0 and m = 1 delta function components of the plasma flow and of the density and pressure perturbations existing at the GAM surface, the GAM continua also include = 0 and = 1 singular components varying as (P - P0)-1 near P = P0, and extending from the plasma centre to the edge. This gives these Fourier components of each GAM in the continuum a global character. We also calculate the effects of a finite aspect ratio and a non-circular plasma cross section on the GAM frequency, and recover the dependence on inverse aspect ratio and Shafranov shift of the GAM frequency previously derived within gyrokinetic theory by Gao [3]. While the dominating shaping effect on the GAM frequency comes from plasma elongation, we show here that there is a higher-order triangularity effect that can also be significant. The calculated triangularity effect predicts a nearly linearly increasing GAM frequency with increasing triangularity, a phenomenon observed also in the TCV tokamak.
[1] Wahlberg C and Graves J P 2016 Plasma Phys. Control. Fusion 58 075014 [2] Pao Y P 1975 Nucl. Fusion 15 631 [3] Gao Z 2010 Physics of Plasmas 17 092503

Speaker: C. Wahlberg (EPS 2019)

504 P4.1055 Fast observations of post-disruption runaway electron beams at the COMPASS tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1055.pdf

Energetic electrons, which are foreseen to be produced during disruptions in ITER, represent a potentially dangerous threat for plasma facing components [1]. Therefore, behaviour of runaway electron (RE) beams has been studied at the COMPASS tokamak in the frame of dedicated experiments focused on their generation and subsequent mitigation [2], mainly using massive gas injection. In this contribution, we introduce fast observations of the generated RE beams done by different types of high-speed cameras, AXUV detectors as a proxy of fast bolometers, ECE and hard X-ray and photo-neutron detectors [3]. Time dependence and spatial localization of RE have been investigated with respect to several aspects: formation of the beam, with a special attention to observed filamentary and quiet phases of the beam existence; interaction of the beam with the background plasma as well as with the tokamak control system; beam extinction by slow decay or by sudden termination. Tomographic inversions have been applied to data measured by the mentioned diagnostics and have proven to be a valuable source of information about beam properties. A mutual relation between the electron energy and the parameters listed above has been investigated [4].

References
[1] T.C. Hender et al., 2007 Nucl. Fusion 47 S128. [2] J. Mlynar et al., 2019 Plas. Phys. Contr. Fusion 61 014010. [3] V. Weinzettl et al., 2017 JINST 12 C12015. [4] M. Vlainic et al., Atoms 2019, 7, 12.

Speaker: V. Weinzettl (EPS 2019)

505 P4.1056 Poloidal currents in COMPASS vacuum vessel during symmetrical disruptions: measurements using diamagnetic loop and comparison with CarMa0NL modelling

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1056.pdf

For the first time diamagnetic measurements were used to calculate poloidal current in the tokamak vacuum vessel during thermal and current quenches as was recently proposed in [1]. The experimental results are compared with analytical predictions [2] and numerical modelling with CarMa0NL code [3] considering the wall resistivity and geometry. The COMPASS tokamak has a unique set of diagnostics for measuring of poloidal distribution of poloidal current in the vessel, specifically, 3x24 sensors for the toroidal magnetic field (toroidal Mirnov coils) in three different toroidal locations [4, 5]. This feature allowed to distinguish between different poloidal harmonics of the poloidal current and to perform comparison with the diamagnetic measurements.

[1] Pustovitov V D 2019 Fusion Eng. Des. 138 53-58 [2] Pustovitov V D 2017 Fusion Eng. Des. 117 1-7 [3] Villone F et al 2013 Plasma Phys. Control. Fusion 55 095008 [4] Panek R et al 2006 Czech. J. Phys. 56 B125 [5] Knight P J et al 2000 Nucl. Fusion 40 325

Speaker: V. Yanovskiy (EPS 2019)

506 P4.1057 Observation of poloidally asymmetric transport during sawtooth crash on J-TEXT tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1057.pdf

Combining with the data of the three-wave Polaris-interferometer system (Polaris), the Soft Xray array system (SXR) and the electron cyclotron emission system (ECE), it is observed that the radial transport in the region between reversed radius and mixing radius is asymmetrical, which is related to the phase of the precursor oscillation when sawtooth crash happened. The precursor oscillation is thought to be a 1/1 mode whose structure consists a hot-bubble and a cold-crescent.[1],[2] And both the electron temperature and density in hot-bubble are higher than in cold-crescent. During the sawtooth crash, the particle would be transported to the region closed to the cold-crescent side and between reversed radius and mixing radius. After about 80s, the region between reversed radius and mixing radius would be symmetrical. More details about the poloidally asymmetric transport during the period of sawtooth crash will be reported in the meeting.

References [1] S. Von Goeler et.al 1974 Phys. Rev. Lett. 33 1201. [2] B. B. Kadomtsev 1975 Sov. J. Plamsa Phys. 1 5

Speaker: Y. Zhou (EPS 2019)

507 P4.1058 Analysis of rotating mhd perturbations to identify disruptive phases in TCV tokamak

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1058.pdf

MagnetoHydrodynamic instabilities appear in several cases as the main cause of a disruption, since they can strongly reduce the plasma confinement and lead to a mode locking. Mode locking signals are routinely used as a disruption alarm to trigger mitigating actions. However, in order to reduce the number of disruptions and then to minimize the stress on the plasma facing components, earlier disruption alarms can be used to trigger avoidance actions and lead the discharge to a "soft" landing. The presence of rotating MHD instability is already a clue of unhealthy plasma conditions (e.g., large NTM Islands, or impurity accumulation, et cetera), which can justify the early and safe termination of a discharge. However, such an approach would lead to terminate also discharges that could be recovered, motivating the application of advanced RT processing, like SVD, to MHD signals in order to provide additional information and, then, to disentangle such ambiguity. Magnetic pick-up coils signals from TCV experiments are applied to a Singular Value Decomposition (SVD) code. SVD is a processing already implemented in the TCV real time control system [1] to provide a trigger for NTM control. In the present work, simple post-processing are applied to SVD results to provide up to 24 variables, which give a complete description of the MHD fluctuations state. The code has run over a set of 196 safe discharges and 82 disruptions, performed at TCV in 2015-2017 campaigns. Data are analysed with the aim of assessing the minimum number of variables required for a disruption precursor and of assessing the potentiality of such a processing to evaluate the probability of a disruption. The number of SVD variables required to describe the MHD state is defined by means of a preliminary Principal Component Analysis. Then, different sets with a varying number of SVD variables are input to a Generative Topographic Mapping [2] to compare the results in homogeneous 2D maps.
References: [1] C.Galperti et al., 2017 IEEE Trans. on Nucl. Science 64, no. 6, 1446 [2] A.Pau et al., 2018 45th EPS, July 2nd-6th, Prague
See the author list of H. Meyer et al 2017 Nucl. Fusion 57 102014 * See the author list of S. Coda et al 2017 Nucl. Fusion 57 102011

Speaker: E. Alessi (EPS 2019)

508 P4.1059 Modelling of neoclassical toroidal viscosity from internal MHD modes in ASDEX-Upgrade

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1059.pdf

Corrugations of tokamak magnetic flux surfaces in the location of a kink mode and/or around the islands created by a tearing mode introduce in combination with toroidal magnetic field inhomogeneity 3D modulations of magnetic field strength within the perturbed flux surfaces and, respectively, give rise to non-ambipolar neoclassical transport [1]. This transport polarizes the plasma changing its rotation, i.e. effectively causing the neoclassical toroidal viscous (NTV) torque onto it. Generally, NTV torque is a strong function of toroidal plasma rotation frequency with respect to the reference frame where perturbations are (quasi) static. Due to the summary toroidal momentum conservation of plasma and electromagnetic field, any torque onto the plasma from the internal modes, which do not interact with plasma exterior, comes from electromagnetic momentum change of the modes. Since this momentum is very small, the condition of zero torque determines mode eigenfrequency. In this work, the typical situation of coupled (3,2) tearing and (2,2) kink modes in ASDEX Upgrade (AUG) is modelled with help of the code NEO-2 [2, 3] for realistic equilibrium field and plasma parameters with perturbation field described in terms of radial flux surface displacement fitted to experimental observations. For mode amplitudes typical for AUG, values of NTV torque are of the order of a few Nm what is comparable with typical NBI torque values. Mainly, NTV torque is due to non-ambipolar transport of ions interacting with the perturbation field in the collisionless regime of bounce resonances, what is similar to Ref. [3]. Besides the effects of this transport on mode and plasma rotation, its implications for the impurity transport and other mechanisms of momentum transfer between plasma and perturbation field are also discussed.
References
[1] K.C. Shaing, Phys. Rev. Letters 87, 245003 (2001) [2] S.V. Kasilov, W. Kernbichler, A.F. Martitsch, et al, Phys. Plasmas 21, 092506 (2014) [3] A.F. Martitsch, S.V. Kasilov, W. Kernbichler, et al, Plasma Phys. Contr. Fusion 58, 074007 (2016)

Speaker: W. Kernbichler (EPS 2019)

509 P4.1060 The variation of the radial and poloidal coherency after middle-amplitude sawteeth crashes in T-10 regimes with central ECRH

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1060.pdf

Small scale turbulence widely treated as one of the causes of abnormal transport genesis. The variation of the turbulence amplitude at T-10 is correlated with the variations of the particle flow mainly [1]. The enhanced heat transport with quick reduction along the time was observed during "ballistic" stage and typical enhanced heat pulse propagation during diffusive stage of the pulse propagation induced by sawteeth crush [2, 3]. The scope of this report is the study of the correlation of heat flux perturbation with the variation of poloidal and radial coherences of small scale density perturbations.. The middle-level sawtooth oscillations without nonlocal "ballistic" phase have been analyzed in series of shorts with 250kA/2.45T, n_lineav (0) = 2.3, P_ECRH=0.8 MW. ECE diagnostics is used for electron temperature observations while the electron density measured by 15-channel interferometer. Density fluctuations are measured by heterodyne correlation reflectometry at the low field side. The probing frequency was changed from shot to shot to vary the radial position of reflection point. Special sawtooth selection procedure was used to achieve averaging over 20-25 "good" sawteeth in each shot and decrease noise levels that is crucial for reflectometry signals analysis. Reflectometry data demonstrate the fluctuation amplitude level growth after internal crash accompanied by radial and poloidal fluctuations coherency increase. The maximum value of the turbulence amplitude locates near the peak value of the growth of Te after crash. The spacetime evolution of the turbulence amplitude, radial and poloidal coherence are sophisticated and all variations propagate outwards. The correlation of the heat flux perturbation and the variation of radial and poloidal coherency is under analysis now.

[1] V.A. Vershkov, D.A. Shelukhin, G.F. Subbotin, Yu.N. Dnestrovskij et al, Density fluctuations as an intrinsic mechanism of pressure profile formation, Nucl. Fusion 55 (2015) [2] N.J. Lopes Cardozo and A.C.C. Sips Plasma Phys. Control. Fusion 33 1337(1991) [3] Neudatchin S.V., Cordey J.G. and Muir D.J. 1993 20th EPS Conf. (Lisboa, 1993) vol.I (EPS), p 83

Speaker: G.F. Subbotin (EPS 2019)

510 P4.1061 Time evolution of electron temperature profiles in RFX-mod helical states

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1061.pdf

RFX-mod (R = 2 m, a = 0.459 m) is the largest Reversed Field Pinch experiment which allowed characterizing the RFP plasmas up to currents of 2MA. Improved plasma performances are obtained when, in the resonant part of the m=1 spectrum, one dominant Tearing Mode is much higher than the other secondary ones (Quasi Single Helicity states), and the plasma core magnetic topology becomes helically shaped [Puiatti M.E. et al. 2015 Nucl. Fusion 55 104012]. Helical states and the amplitude of the dominant mode are not stationary: they increase with plasma current but are eventually interrupted by back transitions to Multiple Helicity states (all tearing modes have similar amplitudes). Moreover, even during helical states, minor magnetic reconnection events occurs, characterized by a sudden, though limited, increase of secondary modes. The dynamics of secondary modes still play an important role in helical states. The time evolution of the electron temperature profile during helical states is investigated by means of a Double Filter, multi-chord SXR diagnostic [Franz P. et al. 2013 Nucl. Fusion 53 053011]. High temperature structures are observed to occur more frequently in the first phase of the QSH (rising phase when the dominant mode is emerging from the set of m=1 modes) while in the stationary phase (when the amplitude of the dominant mode reaches a constant value) they are more intermittent. The role of secondary modes, and in particular the innermost ones n=8 and n=9, is investigated and compared with magnetic topology reconstructions performed with the ORBIT code [White R.B. and Chance M.S. 1984 Phys. Fluids 27 2455]

Speaker: P. Piovesan (EPS 2019)

511 P4.1062 Preliminary experimental scaling of the helical mirror confinement effectiveness

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1062.pdf

Advanced plasma confinement in open magnetic mirrors features high relative pressure ( Beta about 60%), mean energy of hot ions of 12 keV and the electron temperature up to 0.9 keV in quasistationary regime [1]. In modern concepts simple mirror ratio of ~15­20 and improved longitudinal confinement are proposed [2, 3]. Existing method of multiple-mirror suppression of the axial flux combined with gas-dynamic central cell [4] can provide effective mirror ratio of the order of 100, which gives feasible fusion gain appropriate at least for neutron source. New idea of the helical mirror confinement was suggested in [5]. This concept considers a flow of a rotating plasma through a linear magnetic system with helical corrugation that looks like a straightened stellarator. Periodical variations of helicoidal magnetic field moving upstream in plasma's frame of reference transfer momentum to trapped particles and lead to plasma pumping towards the central trap. The helical mirror traps should have two important improvements over the classical multiple-mirrors: the exponential (instead of the quadratic) law of the confinement improvement with the system length and the radial pinch of ions that can counteract the diffusive broadening of the plasma stream. Concept exploration device «SMOLA» with a helical mirror system was put in operation in the end of 2017 in BINP [6, 7]. Plasma flux suppression by the helical sections was demonstrated in the first experimental campaign [8]. This work presents the preliminary experimental results on the dependences of the suppression effectiveness on guide magnetic field, mean corrugation ratio, plasma density and rotation velocity.

[1] P. A Bagryansky, et al., Phys. Rev. Lett. 114, 205001 (2015). [2] A. V. Anikeev, et al., Materials. 8, (No. 12), 8452 (2015), DOI: 10.3390/ma8125471. [3] A. D. Beklemishev, et al., Fusion Sci. Technol. 63 (No. 1T), 46 (2013). [4] V.V. Postupaev, et al., Nuclear Fusion, 57, 036012 (2017). [5] A. D. Beklemishev, Fusion Sci. Technol. 63 (No. 1T), 355 (2013). [6] V.V. Postupaev, Fusion Eng. Design. 106, 29-33 (2016). [7] A. V. Sudnikov, Fusion Engineering and Design. 122, 85 (2017), DOI: 10.1016/j.fusengdes.2017.09.005 [8] A. V. Sudnikov, Plasma and Fusion Research, 14, 2402023 (2019), DOI: 10.1585/pfr.14.2402023

Speaker: A.V. Sudnikov (EPS 2019)

512 P4.1063 Start plasma production in GOL-NB multiple-mirror trap

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1063.pdf

The GOL-NB project is a physics demonstration experiment on multiple-mirror plasma confinement that is currently under development in the Budker Institute of Nuclear Physics [1]. The final configuration of the device will include a 2.5-m-long central gasdynamic trap with two attached multiple-mirror sections of 3 m each, and two end magnetic flux expanders that house a start plasma creation system, plasma receiver endplates and a system of biased electrodes for plasma stabilization. Plasma will be heated by two 0.75 MW, 25 keV neutral beams. GOL-NB will be a scaled-down physical model of a future fusion-grade open trap [2]. Currently, the start configuration of GOL-NB is assembled [3]. It includes both expander tanks, an arc source of start cold plasma, a multiple-mirror solenoid with 34 coils of 4 m length, and a short temporary section for the on-site commissioning of NBIs. Experiments demonstrated that the plasma stream with ~1020 m-3 density was successfully generated, compressed in the increasing magnetic field and transported through the full length of the solenoid. These processes imitate the initial filling of the central trap of GOL-NB with the start cold plasma. Parameters and properties of plasma in this first experimental campaign are discussed.

[1] V.V. Postupaev, et al., Nuclear Fusion, 57, 036012 (2017). [2] P.A. Bagryansky, A.D. Beklemishev, V.V Postupaev, J. Fusion Energy, 38, 162 (2019). [3] V.V. Postupaev, et al., Proc. EPS-2018 (Prague, 2018), paper P1.1035.

Speaker: V.I. Batkin (EPS 2019)

513 P4.1064 Studies of two plasmon decay and wave trapping at the 2nd harmonic upper hybrid layer in magnetically confined fusion plasmas using particle-in-cell simulations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1064.pdf

Microwave gyrotron beams play an important role in magnetically confined fusion plasmas due, in particular, to the electron cyclotron (EC) frequency typically being in that range. EC resonance heating (ECRH) is a popular method of heating the plasma to thermonuclear temperatures, especially for non-inductively driven reactors such as stellarators. Several heating schemes involving microwaves have been devised; placing the 2nd harmonic EC resonance (ECR) inside an optically thick region of the plasma allows for X-mode heating while bypassing the R cutoff.
Propagating through a plasma, the X-mode beam may decay through parametric decay processes and near the 2nd harmonic upper hybrid (UH) layer, two plasmon decay (TPD) may excite two daughter UH waves at around half the frequency. In a non-monotonic density profile, the UH daughter waves can find themselves trapped between two UH layers, allowing for waves to build up in what may be thought of as optical cavities in the plasma. This way, the trapped waves may eventually exceed parametric decay instability (PDI) amplitude thresholds, thereby exciting other waves. The energy contained in the trapped waves has been estimated to be around 18% [1] of the ECRH energy meant for absorption at the 2nd harmonic ECR. This significant portion might be trapped in the edge region and could be considered lost altogether.
The particle-in-cell (PIC) code EPOCH [2] is used to simulate X-mode gyrotron beams passing a density bump with a 2nd harmonic UH layer found on both sides of the it. Density and magnetic field are loosely based on experimental parameters during shots where observed strong scattering is expected to be related to wave trapping. TPD and further PDIs are investigated in terms of timescales and implicated modes in frequency and wavenumber.
References
[1] E Z Gusakov et al, Physics of Plasmas 23, 082503 (2016) [2] T D Arber et al, Plasma Phys. Control. Fusion 57, 113001 (2015)

Speaker: M.G. Senstius (EPS 2019)

514 P4.1065 The concept of the compact ultra-low aspect ratio tokamak CULART

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1065.pdf

Compact device with an Ultra-Low Aspect Ratio Tokamak plasma (CULART) is proposed. The major objective of CULART is twofold. First, to explore very high beta (VHB) limits (~ 1) via passive stabilization under relatively low toroidal field (TF). Secondly, as a proof-of-concept, to use these VHB plasmas as a target for applying the adiabatic compression (AC) technique aiming for 1MW of D-T fusion power with relatively high Q factor. The design must incorporate present day technology without necessarily using superconducting coils and with the advantage of using ohmic heating regimes exclusively.
Using the AC technique, CULART sets a pathway to study the potential for a high efficiency, ultra-compact, repeatedly-pulsed neutron source based on the spherical tokamak (ST) concept. CULART will serve as a benchmark for appropriate scaling towards a fusion reactor and related material studies, alongside broad areas of physical science beyond fusion energy.
The main characteristics of CULART plasmas prior to the use of the AC technique are: plasma major radius Ro = 0.51m, plasma minor radius a = 0.47m, aspect ratio of A = 1.1, plasma vertical elongation k = 2 (at A = 1.1), triangularity = 0.8, TF of BT(Ro) = 0.1T, plasma current of Ip = 0.5MA, central density of ne(0) = 1×1019m-3, central electron and ion temperatures of Te(0) = 300 and Ti(0) = 500eV, respectively, and discharge duration of = 100ms. These parameters should lead to toroidal beta limits around unity (100%), as scaled from an identical regime in the Pegasus experiments [1].
The vessel is a stainless-steel sphere that is insulated from the naturally diverted plasma by thin (~ 2cm) semi-circular tungsten limiters. No internal poloidal field coils or solenoid are envisioned. With the plasma conforming relatively closely to the vessel walls, wall stabilization is possible. Plasma protection and minor neutron shielding can be achieved using thin (~ 2-3mm) tungsten plates covering the copper central stack. All these features together make the whole design simple, compact, and cheap. The major source of initial heating is provided by Ip created primarily via the Local Helicity Injection (LHI) technique, as has been demonstrated by the Pegasus device in several regimes [1,2].
After a very high beta configuration is attained (that potentially is already operating in Hmode as all the scaling laws and ST experiments indicate), the AC technique is applied (a and R-compression) via raising BT(Ro) (< 1T) and the vertical equilibrium field. A simulation was performed using standard compression scaling laws [3] applied to a CULART VHB plasma target leading to the following parameters: Ro = 0.16m, a = 0.10m, A = 1.6, k = 1.6, = 0.2, BT(Ro) = 2.4T, Ip = 1.6MA, Te(0) = 4.6keV, Ti(0) = 8.0keV, and ne(0) = 1×1021m-3. These values produce 1MW of D-T fusion power with a neutron flux of 3.6×1017n/s.
Preliminary equilibrium and stability simulations prior to and after the use of the AC technique, basic engineering issues, and engineering constrains will be also presented.
[1] D J Schlossberg et al., Phys. Rev. Letters, 119, 035001 (2017). [2] J.M. Perry et al., Nucl. Fusion 58 096002 (2018). [3] H. P. Furth and S. Yoshikawa, Phys. of Fluids, 13, 2593 (1970).

Speaker: C. Ribeiro (EPS 2019)

515 P4.1066 Studies of RWM feedback control in EXTRAP T2R

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1066.pdf

The RWM instability, relevant for the advanced tokamak operation scenario, grows on the time scale of magnetic field diffusion through the conducting structures surrounding the plasma. Substantial progress has been made in the understanding and stabilization of the RWM [1]. In this work, models of resistive wall mode (RWM) instability are studied and validated in dedicated plasma experiments. The aim is to contribute to the development of high-performance, model-based active magnetic feedback algorithms for RWM control. Statespace, model based feedback control algorithms have potential advantages compared to conventional controllers such as proportional-integral-derivate (PID) control [2]. However, in order to benefit from these advantages, it is a necessary prerequisite to have a realistic model of the RWM instability including both plasma and the conducting structures. There are in principle two main methods to obtain such a model; 1) through first-principles physics, leading to "white box" models of the controlled plant, and 2) through empirical modeling experiments, often referred to as "system identification" leading to "black box" models [3]. In this work, first principles RWM instability models are experimentally validated in the EXTRAP T2 reversed-field pinch (RFP) device [4]. Due to the low toroidal magnetic field of the RFP equilibrium, current-driven RWMs are robustly unstable at all values of beta. The easy access to the RWM instability makes the RFP configuration suitable for studies of RWM control. The unstable RWM spectrum of the RFP consists of a wide range of modes. For a high aspect ratio, circular cross-section RFP device, the circular cylinder MHD model is approximately valid, and the RWMs are in this model Fourier modes with poloidal mode number m= 1 and a range of toroidal mode number n. The unstable range depends on the aspect ratio of the device. For EXTRAP T2R with aspect ratio R/a = 1.24 m/ 0.183 m = 6.8, the unstable spectrum consists of toroidal mode numbers in the range from around n=-11 to n=+6 for a typical equilibrium. The sign of the mode number indicates here the handedness of the mode helicity. Since the mode spectrum consists of modes with variation of spatial structure in the toroidal direction, different modes can easily by separated experimentally using toroidal array of sensors. The aim of the present work is to validate the model spectrum over a wide range of n-modes, also including stable modes at higher n values.

[1] Chu M.S and Okabayashi M., Plasma Phys. Control. Fusion 52 (2010) 123001. [2] Clement M., et al, Nucl. Fusion 58 (2018) 046017. [3] Olofsson K.E.J., et al, Plasma Phys. Control. Fusion 53 (2011) 084003. [4] Brunsell P R, Plasma Phys. Control Fusion 43 (2001) 1457-1470.

Speaker: E. Saad (EPS 2019)

516 P4.1067 Physics of the collisionless microtearing mode

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1067.pdf

Microtearing modes are fine-scale instabilities in magnetised plasma with a sheared magnetic field, typically driven by an electron temperature gradient [1, 2]. They are characterised by large toroidal and poloidal mode numbers, and localised in the vicinity of rational flux surfaces in tokamak plasmas [3, 4]. The key role of the energy dependence of the collisions suggests that they are stable in collisionless plasma, which was widely reported in early theories [1, 2, 3].
However, recent numerical simulations in toroidal geometry have found that microtearing modes can be unstable at low collision frequency [4, 5] of relevance to next step tokamaks such as ITER. This indicates extra physics may be required in theories for microtearing modes. Using the gyrokinetic code GS2 [6, 7] to explore the behaviour of microtearing modes as the geometry evolves from toroidal to slab, we have found unstable microtearing modes even in the collisionless slab limit. This collisionless mode seems to be a different branch with a different mode frequency to the collisional mode. We have carefully re-derived the instability eigenmode equations in slab geometry and checked the assumptions typically employed for the classic microtearing mode to explore which hold or fail for the collisionless mode. Having studied both adiabatic and kinetic ions, the energy dependency in the collision operator and the finite Larmor radius effects, we are gradually starting to shed some light on the possible physics mechanism for driving the collisionless microtearing instability in slab geometry.
References
[1] N. T. Gladd, et al., Electron temperature gradient driven microtearing mode, Phys. Fluids 23, 1182 (1980). [2] J. F. Drake, et al., Kinetic theory of tearing instabilities, Phys. Fluids 20, 1341 (1977) [3] J. W. Connor, et al., Micro-tearing stability in tokamaks, Plasma Phys. Control. Fusion 32, 799 (1990). [4] D. Dickinson, et al., Microtearing modes at the top of the pedestal, Plasma Phys. Control. Fusion 55, 074006
(2013). [5] D. J. Applegate, et al., Micro-tearing modes in the mega ampere spherical tokamak, Plasma Phys. Control.
Fusion 49, 1113 (2007) [6] M. Kotschenreuther, et al., Comparison of initial value and eigenvalue codes for kinetic toroidal plasma instabilities, Comput. Phys. Commun. 88, 128 (1995) [7] W. Dorland, et al., Electron Temperature Gradient Turbulence, Phys. Rev. Lett. 85, 5579 (2000)

Speaker: C. Geng (EPS 2019)

517 P4.1068 Three-dimensional features in burning plasmas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1068.pdf

A next major step in the research toward magnetic fusion energy production is to carry out experimental campaigns exploring regimes with relevant amount of fusion power. So far, the theoretical knowledge of the path toward a fusion burning plasma has been acquired mainly by performing numerical studies in 0 or 1-1.5 dimensions. Due to the marked anisotropy of magnetically confined plasmas, however, three-dimensional effects might play a role. In particular, the drastic change in magnetic topology associated with reconnecting modes on selected rational magnetic surfaces [1] may decrease the thermal electron conductivity parallel to the magnetic field lines, with a consequent impact on the electron heating due to fusion products. We describe this new scenario, and present analytical and numerical calculations aimed at verifying the impact of reconnection on fusion heating.
References
[1] B. Coppi, et al., Nucl. Fusion 55, 053011 (2015)

Speaker: R. Gatto (EPS 2019)

518 P4.1069 Axial electron conductivity in open magnetic trap

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1069.pdf

The presented work is part of the fundamental research on the implementation of a controlled thermonuclear reaction in open-type magnetic traps. The interest in such systems is defined by the development of powerful neutron sources, which are necessary, in particular, to control hybrid fusion-fission reactors, and, with further development, the creation of purely fusion reactors for energy production. The main parameter from the applications point of view is the energy efficiency of the system, which rapidly increases with increasing of electron temperature. One of the factors limiting the electron temperature is the high thermal conductivity of the plasma along the magnetic field lines, which is determined by a number of complex kinetic processes in the expanders -- regions of the expanding magnetic flux behind the magnetic plugs. The main goal of the work is to study this loss channel in detail and determine conditions under which these losses could be suppressed to levels acceptable for thermonuclear applications of mirror magnetic traps. All the experiments were performed on GDT [1] device in Budker Institute of Nuclear Physics. In previous work [2] experimental results describing the electric potential in the Debye layer near the surface of the plasma absorber and the average electron energy along the longitudinal coordinate were presented. The present work is devoted to measuring of energy carried out from the trap by one ion-electron pair along the length of the expander using a set of probes namely pyroelectric bolometer and ion flux probe. This dependence on the residual gas density in the expander tank has also been investigated. These data will make it possible to complete the theoretical model currently being developed [3], which describes the kinetics of processes in the expander of mirror trap.

1. A. Ivanov and V. Prikhodko, Plasma Phys. Controlled Fusion 55, 063001 (2013). 2. E. Soldatkina, et al. Physics of Plasmas 24, 022505 (2017). 3. D. Skovorodin, Physics of Plasmas 26, 012503 (2019).

Speaker: E.I. Soldatkina (EPS 2019)

519 P4.1070 Interpretation of suprathermal emission at deuteron cyclotron harmonics from deuterium NBI plasmas in KSTAR

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1070.pdf

Intense suprathermal radiation, with spectral peaks at multiple harmonics of the deuteron cyclotron frequency, is detected from the outer midplane edge of KSTAR deuterium plasmas that are heated by tangential neutral beam injection (NBI) of 100keV deuterons. We identify how this deuterium ion cyclotron emission (ICE) is generated, and distinguish this signal from the ICE driven by fusion-born protons in KSTAR deuterium plasmas (B. Chapman et al., Nucl. Fusion 57, 124004 (2017) and 58, 096027 (2018)). We first combine particle orbit studies in approximate KSTAR magnetic field geometry with an analytical treatment of the magnetoacoustic cyclotron instability (MCI), to identify the sub-population of freshly ionised NBI deuterons that can excite deuterium ICE by the MCI. These deuterons are then represented as an energetic minority, together with the majority thermal deuteron population and electrons, in kinetic particle-in-cell (PIC) computational studies where all particle gyro-orbits are fully resolved. The PIC approach solves the Maxwell-Lorentz equations for many millions of interacting particles, with the self-consistently evolving electric and magnetic fields. It enables us to study the collective relaxation of the NBI deuterons through the linear phase of the MCI and deep into its saturated regime. The Fourier transform of the excited fields displays strong spectral peaks at multiple successive deuteron cyclotron harmonics, mapping well to the observed KSTAR deuterium ICE spectra. The time-evolution of the energy densities of the particle populations and field components in the PIC computations further supports our identification of the driving sub-population of NBI deuterons, whose relaxation through the MCI generates the observed deuterium ICE signal. We conclude that the physical origin of this signal in KSTAR is broadly the same as the NBI-driven ICE seen in TFTR tokamak and LHD stellarator plasmas. Its spatially localised character suggests that planned ion beam-plasma experiments in simpler magnetic geometries could also generate ICE of this kind.
This work was carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The work received support from the RCUK Energy Programme grant no. EP/P012450/1, NRF Korea grant no. 2014M1A7A1A03029881 and (SCC) US AFOSR grant FA9550-17-1-0054. The views and opinions expressed herein do not necessarily reflect those of the European Commission. ROD and GSY acknowledge the hospitality of Kyushu University and the National Institute for Fusion Science, Japan.

Speaker: R. Dendy (EPS 2019)

520 P4.1071 Preliminary design of electron cyclotron resonance heating for the COMPASS Upgrade tokamak

See ful abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1071.pdf

COMPASS-Upgrade (COMPASS-U) is a compact-sized, high magnetic field (up to 5 T) and high density ( 1020) tokamak under developement at IPP Prague. COMPASS-U will address the key challenges related to the plasma exhaust physics and it will contribute to provide scalings towards ITER and DEMO.
Heating of plasma in COMPASS-U will be provided by an NBI and ECRH system. Power of 4 MW is planned for both the heating systems. The injection of 140 GHz waves is considered for the fundamental harmonic heating of O-mode [1] from the low-field side. The main purposes of the ECRH heating are to prevent the heavy impurity accumulation [2] (tungsten, nickel etc.), assist the plasma breakdown and suppress instabilities e.g. neoclassical tearing modes (NTMs) [3].
Preliminary evaluations of EC wave propagation and absorption, obtained from simulations with the beam-tracing code TORBEAM [4], will be shown. The key parameters of considered technical solution will be described including the specification of high voltage power supplies and gyrotrons and the design of matching optical units, transmission lines, windows, and mirrors.
References
[1] M. Bornatici, et al., Nucl. Fus. 23(9) 1153-1257 (1983) [2] R. Dux, et al., Journal of Nuclear Materials 313 1150-1155 (2003) [3] M. Maraschek, et al., Nucl. Fus. 52 074007 (2012) [4] E. Poli, et al., Comp. Phys. Comm. 225 36-46 (2018)

Speaker: M. Farnik (EPS 2019)

521 P4.1072 A real case of complex network controllability: the NIO1 ion beam source

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1072.pdf

A negative ion beam source is a key component of a neutral beam injector such as that under development for ITER. Its efficient and reliable operation depends on a network of processes affecting generation, extraction and acceleration of the negative ions. Such processes interact with each other in a complex fashion. Controllability of complex networks [1] can offer interesting new tools to both identify the most crucial processes in the negative ion beam source NIO1 [2] [3] and to verify its controllability. In this contribution a model based on this theory has been developed and tested. NIO1 processes have been mapped into a network of 40 nodes and 292 links to highlight the most important processes (the driver nodes). Predictions obtained with the model have then been compared with the observed behaviour of NIO1. The test has been performed by numerically perturbing the model with input signals that mimic the ones used in NIO1 experimental campaigns. Experimental data and outputs from the model have then been compared. Preliminary results show a good agreement between model predictions and experimental behaviour of the source so that a subset of processes which in principle allow the system to be driven towards any state has been identified. As an outcome of the analysis the most crucial processes have been identified and discussed in terms of emerging diagnostic and modelling necessities required to improve the understanding of the physics behind them.
References
[1] Y.-Y. Liu, J.-J. Slotine and A.-L. Barabasi, "Controllability of complex networks," Nature, vol. 473, 2011. [2] M. Cavenago et al., "Design of a versatile multiaperture negative ion source," Review of Scientific
Instruments, no. 81, 2010. [3] M. Cavenago et al., "First experiments with the negative ion source NIO1," Review of Scientific Instruments,
no. 87, 2016.

Speaker: N. Ferron (EPS 2019)

522 P4.1073 Optimal exploitation of the electron cyclotron heating and current drive system in ITER for reduced magnetic field operations

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1073.pdf

In the current ITER research plan, the path toward the full-performance DT plasma is based on a staged approach. The power available from the external Heating and Current Drive (H&CD) systems will be limited during the first phases of operation, the Electron Cyclotron (EC) system being the only one available for the first plasma [1]. The EC H&CD system, operating at 170 GHz, has been designed for optimal performances in the reference B0 = 5.3 T scenarios, with the injected O­mode wave interacting with the plasma at the first harmonic resonance. However, the first plasma will be obtained at B0 = 2.65 T, half of the nominal magnetic field strength, and one-third-field operations are foreseen during the first Pre-Fusion Power Operation (PFPO) phase in order to reduce the L-H transition power threshold and demonstrate H-mode in an early phase [2, 3]. This strategy means that the EC system will operate under potentially non-optimal conditions for an extended period. X-mode injection in half-field scenarios allows good H&CD efficiency at the second harmonic, but third harmonic absorption on the low field side may affect the CD performance of the EC Equatorial Launcher (EL). At one-third-field EC absorption can be incomplete at low temperature, due to the lower efficiency of higher order harmonics, while on the other hand the simultaneous presence of 3rd and 4th harmonic resonances in the plasma can deteriorate CD localization and efficiency. The work presented here aims at providing an overview of the EC H&CD performances expected at half- and one-third-field, with a particular focus on critical issues such as beam shine-through due to partial absorption, delocalized absorption over multiple harmonics causing loss of CD efficiency, and imperfect mode coupling because of polarization mismatch. The results are presented for a wide range of plasma parameters, and different beam injection geometries, in order to assess the best strategy to make optimal use of the EC system in the most demanding situations.
[1] M. Henderson et al, Phys. Plasmas 22, 021808 (2015) [2] Y. R. Martin et al, Journal of Physics: Conference Series 123 (2008) 012033 [3] M. Schneider et al, Nuclear Fusion, submitted (2018)

Speaker: L. Figini (EPS 2019)

523 P4.1074 Kinetic full-wave analysis of electromagnetic waves in tokamak plasmas using an integral-form of dielectric tensor

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1074.pdf

Full-wave analysis including kinetic effects of plasmas has been extensively employed in studying wave heating and current drive in tokamak plasmas. Most of previous kinetic analyses of wave propagation and absorption in an inhomogeneous plasma are based the wave number.
The dielectric tensor in a hot plasma has been usually expressed as a function of wave number. In the full-wave numerical analysis using the finite element method (FEM) or the finite difference method (FDM), however, the wave number is not available a priori. In order to describe the response of plasma without wave number, it is appropriate to use an integral form of the dielectric tensor derived by integrating along an unperturbed particle orbit. Maxwell's equation with the integral form of dielectric tensor (see formula at http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1074.pdf)
can be numerically solved as a boundary-value problem by FEM. Numerical analysis with FEM may have higher performance with parallel processing owing to sparse coefficient matrix. Though the integration is localized in an element in usual FEM for differential equations, coupling between different elements occurs in FEM for integro-differential equations. In a magnetized plasma, the guiding center motion along an inhomogeneous magnetic field and the cyclotron motion perpendicular to the magnetic field can be separately taken into account in deriving the dielectric tensor as an integral operator. 1D full-wave analysis using the integral form of dielectric tensor was applied to ion cyclotron (IC) heating in the presence of energetic ions and the O-X-B mode conversion of electron cyclotron (EC) waves. In this presentation, 2D full-wave analysis with the integral form of dielectric tensor is provided. The first application is the analysis of 2D mode structure of the O-X-B mode conversion on the horizontal plane of tokamak. The tunneling of the wave over the evanescent layer between O-mode and X-mode
cutoffs is described without any assumptions, and the results are compared with the convention ray tracing analysis with some adjustments. The second application is the analysis of 2D mode structure on the poloidal plane of tokamak. The inhomogeneity of the magnetic field along the field line is taken into account, and the magnetic mirror motion of charge particles is taken into account. Examples of the O-X-B mode conversion of EC waves, Landau damping of lower-hybrid (LH) waves, and IC higher harmonic heating will be demonstrated.

Speaker: A. Fukuyama (EPS 2019)

524 P4.1075 Recent progress of the development of an experimental arc-driven negative hydrogen ion source

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1075.pdf

An experimental negative hydrogen ion source has been developed for the preparation of a negative-ion-based neutral beam injector for HL-2M. This ion source is driven by filament-arc discharge with multi-cusp magnetic field and external filter filed. The plasma chamber has a rectangular cross section with inner dimensions of 240 mm in width, 266 mm in length and 560 mm in height. The four-grid accelerator has 168 apertures and the extraction area is 130 ×412 mm2. Two Cs ovens were installed onto the ion source to enhance the production of negative hydrogen ions by seeding Cs. In the preliminary experiment, the negative hydrogen ion beam reached 470 mA at extraction voltage of 3 kV. Improvements on the arc efficiency, Cs oven and accelerator are still in progress.

Speaker: S. Geng (EPS 2019)

525 P4.1076 Possibility of anomalous emission at half-integer pump wave frequency harmonics in the X2 ECRH experiments

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1076.pdf

A while ago it was revealed theoretically [1,2] that in presence of a non-monotonic plasma density profile, originating due to the magnetic island or the density pump-out effect at onaxis electron cyclotron resonance heating (ECRH), the low-power-threshold absolute twoupper-hybrid (UH)-plasmon parametric decay instability (TPDI) of a pump microwave can occur in the hundred-kilowatt X2 ECRH experiments. Its excitation leads to the generation of both UH waves localized in the vicinity of the local maximum of a plasma density profile and of the non-trapped UH waves. Depending on the dominating saturation mechanism (the cascade of secondary decays or the pump depletion) from 10% up to more than 60 % of the pump power can be transferred to the daughter UH waves as a result of TPDI. This instability manifests itself in anomalous backscattering effect [3] leading to emission of radiation at frequency down-shifted by several GHz in respect to the pump wave. According to the theory [1] reproducing the frequency spectrum and intensity of the backscattering signal, this emission is generated due to nonlinear coupling of parametrically excited UH plasmons.
In the present paper we consider a possibility of anomalous emission in X2 ECRH experiments of electromagnetic waves possessing a larger frequency shift, namely, of the pump frequency half-integer harmonics. As a substantial fraction of the pump power can nonlinearly be deposited into the different daughter waves, trapped in the vicinity of the local maximum of non-monotonic density profile and non-trapped ones, one could expect the strong emission of electromagnetic waves at half the pump wave frequency in the high-magnetic field-side direction. This is due to the linear mode-conversion of the non-trapped UH waves into the extraordinary waves propagating inwards at the UH resonance. The corresponding radiation temperature is estimated in the paper. It is also shown that the nonlinear coupling of the daughter UH waves with the pump could lead to the measurable level of the plasma emission at the 3/2 harmonic of the pump, in the way similar to that occurring in the laser driven inertial fusion experiments [4].
[1] E.Z. Gusakov and A.Yu. Popov, Physics of Plasmas 23, 082503 (2016) [2] E.Z. Gusakov, A.Yu. Popov, A.N. Saveliev Physics of Plasmas 25, 062106 (2018) [3] E. Westerhof, S. Nielsen, J.W. Oosterbeek et al., Phys. Rev. Lett. 103, 125001 (2009) [4] E.Z. Gusakov, Sov. Tech. Phys. Lett. 3, 504 (1977)

Speaker: E.Z. Gusakov (EPS 2019)

526 P4.1077 ICRF heating with poloidally phased antennas

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1077.pdf

The ITER ICRF system is designed such that there is a 90 degree phase shift in the currents between the upper and lower rows of antenna straps. The consequences of this design has previously been studied from the point of view of the coupling, but not with respect to plasma heating. In this work the effects of poloidal phasing on the core plasma heating, as well as the coupling, is studied for the ITER, JET and WEST tokamaks. The work is carried out with the new ICRF wave solver FEMIC. We show that poloidal phasing cause destructive interference near the equatorial plane between the waves launched from the upper and lower antennas, which may modify the central heating and the coupled power. A difference has been identified between the coupled ICRF power for 90 and -90 degree phase difference between the two antennas halves. We show that this difference is due to the plasma gyrotropy and that it depends sensitively on the pedestal parameters.

Speaker: T. Jonsson (EPS 2019)

527 P4.1078 The depolarizing effect of plasma density fluctuations on microwave beams

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1078.pdf

Microwaves play an indispensable role in plasma experiments for heating and diagnostic purposes. This is especially true for fusion experiments on the path towards a burning plasma in which only little space is available for any type of internal hardware installations. Electromagnetic waves in the microwave frequency range offer the advantage of requiring comparatively little space inside the machine [1].
Microwaves injected into the plasma or being emitted by it have to traverse the plasma edge, a region where significant plasma density fluctuations with fluctuation levels of several 10 % are known to occur [2]. If those fluctuations are located at very low plasma density values, an energy transfer between the two modes of the microwave, the O- and X-mode, can occur. This mode scattering can be a problem for high-power microwave injection as the unwanted mode would likely not be absorbed at the intended spatial location but could instead deposit its power elsewhere and might even constitute a threat for wall components. Here we present full-wave simulations [3, 4] to illustrate and estimate the importance of this effect. We will discuss its relevance for the next generation tokamak ITER, currently under construction. The full-wave simulations will also be used to compare with previously performed calculations using a wavekinetic equation solver which accounts for the effect of density fluctuations in the limit of the Born approximation [5].
References
[1] H.-J. Hartfuss et al., Fusion Plasma Diagnostics with mm-Waves (Weinheim: Wiley, 2014) [2] S.J. Zweben et al., Plasma Phys. Control. Fusion 49, S1 (2007) [3] A. Köhn et al., Plasma Phys. Control. Fusion 50, 085018 (2008) [4] P. Aleynikov et al., EPJ Web of Conf. 149, 03007 (2017) [5] A. Snicker et al., Plasma Phys. Control. Fusion 60 014020 (2018)

Speaker: A. Köhn (EPS 2019)

528 P4.1079 First applications of the ICRF modelling code PION in the ITER integrated modelling and analysis suit

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1079.pdf

Ion Cyclotron Resonance Frequency (ICRF) heating is one of the three auxiliary heating methods foreseen for ITER. The ICRF scenarios in ITER have been recently reassessed with emphasis on the heating and current drive performance and H-mode access capabilities [1,2] based on simple one-dimensional wave damping calculations. Detailed studies using self-consistent transport simulations taking into account the various plasma heating sources due to ICRF waves in ITER are still lacking. For such studies, the ITER Integrated modelling and Analysis Suite (IMAS) [3] provides a natural platform. In this work, we report on the integration and the first applications of the ICRF modeling code PION [4] in IMAS. PION computes the ICRF power absorption and the distribution functions of the resonant ions in a self-consistent way. It has been extensively compared against experimental results for a large variety of ICRF schemes on JET, AUG, DIII-D and Tore Supra. It is based on simplified models, which makes it relatively fast and, thereby, suitable for use in an integrated modelling framework such as IMAS. In our first PION simulations in IMAS we have studied the ICRF schemes foreseen in the early non-active phase of ITER operation at magnetic fields of 1.8, 2.65 and 5.3T in H and 4He plasmas. References [1] M. Schneider et al. Proc. 44th EPS conf on Plasma Physics, ECA 41F, P5.153 (2017). [2] M. Schneider et al., EPJ Web. Conf. 157, 03046 (2017). [3] S. D. Pinches et al., Proc. 27th IAEA Fusion Energy Conf., TH/P6-7 (2018). [4] L.-G. Eriksson, T. Hellsten and U. Willén, Nucl. Fusion 33, 1037 (1993).

Speaker: I.L. Arbina (EPS 2019)

529 P4.1080 Comparative lower hybrid ion heating experiments in hydrogen and deuterium high density plasma at FT-2 tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1080.pdf

Investigations of lower hybrid heating (LHH) of plasma ion component very wide and active in 70th and 80th did not result in development of a reliable heating scheme. Excitation of parametric decay instabilities accompanied by ion acceleration observed at different tokamaks at densities exceeding a certain threshold value in majority of experiments did not lead to a substantial ion heating. Only few experiments had reported observation of ion temperature growth [1], therefor the main application of the LH frequency range RF power in tokamaks since that time was related to LH current drive, which is only effective at low plasma densities.
In the present paper we make an attempt to revisit the area of ion LHH in dense plasma. The experiment is performed at FT-2 tokamak (a=0.08 m, R=0.55 m, 19kA < Ipl <34 kA, 2T < BT < 2.5 T, q95~3-6) involved in studies of the interaction of LH waves (f = 920MHz, PRF 200kW) with plasma since early 80th. The exact magnetic field value BT =2.2 T in the experiment was chosen to satisfy the condition for the RF frequency f2=fcefcd, under which the LH resonance could appear in the deuterium plasma only at the highest achievable density values close to the Greenwald limit <ne res> ~ 1020m-3 [2]. This way the linear interaction of the LH power with ion component should concentrated in deuterium in the central plasma region, unlike hydrogen where it should be situated in the gradient zone at <ne LHres> ~ 3.5 1019m-3. Another important feature of the experiment is the effect of prolonged linear increase of the energy confinement time E(<ne>) with density recently discovered in deuterium ohmic heating regime. The so-called LOC mode persists up to <ne> ~ 1020m-3 and makes a transition at high density to the improved confinement mode [3]. For hydrogen plasma, on the contrary, there is a saturation of the dependence E(<ne>) already at <ne> ~ 5 1019m-3 (SOC mode).
As a result of the noted experimental features at the launched RF power PRF 75kW, <ne> 1.2 1020m-3 and Te 700eV for the first time the effective long lasting central LH heating of ions from Ti(0) = 250eV to 400 eV was observed in the dense deuterium plasma, in contrast to the hydrogen plasma of similar parameters where the heating effect was negligible.
1. V.N. Budnikov, M.A. Irzak Plasma Phys. Contr. Fus. 38, A135 (1996). 2. S.I. Lashkul, A.B. Altukhov, A.D. Gurchenko et al. Nucl. Fusion 55 (2015) 073019 (7pp) 3. D. Kouprienko, A. Altukhov, L. Esipov et al et al., 45th EPS Conf. on Pl. Ph, P4.1097 (2018)

Speaker: S.I. Lashkul (EPS 2019)

530 P4.1082 3D finite element modelling of ICRH in JET

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1082.pdf

We have assessed the possibility of using the finite element method to solve the electromagnetic wave equation in a fusion plasma in 3D for ICRH applications. In particular, we have studied on-axis hydrogen heating and second harmonic deuterium heating. The purpose of this code is to develop a 3D model with more realistic antenna and wall geometry. A projection of the 3D wave field onto a poloidal plane is compared to the 2D wave field produced by the FEMIC code for validation. The comparison was made with good results. The coupling resistance of the 3D model is compared to the coupling resistance of a 1D analytic model, with some discrepancies, since the model of the coupling resistance does not properly take the current induced into the reactor wall into account. The agreement of the coupled power however, is good. Future work includes taking the wall currents into account when computing the coupling resistance, and integrating the 3D analysis with FEMIC.

Speaker: B. Ljungberg (EPS 2019)

531 P4.1083 Mapping of power deposition zone of electron Bernstein waves externally excited via mode conversion in tokamak plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1083.pdf

In tokamak plasmas, electron Bernstein (EB) waves mode-converted from X waves at the upper hybrid resonance (UHR) layer propagate toward the higher field side and are cyclotron-damped away at Doppler shifted frequency before arriving at the electron cyclotron resonance (ECR) layer. Resulted power deposition profile depends on local density, temperature and field profiles and is usually analysed using the ray tracing technique for EB wave propagation and absorption in inhomogeneous magnetized plasmas [1].
In the case of axisymmetric low beta tokamak plasmas, possible power deposition zone can be mapped and also associated current drive efficiency [2] can be estimated directly from the information on wave frequency and plasma profiles including the density, temperature and field profiles, without ray racing calculations. Mapping results in the case of a moderately over dense plasma analytically generated using Solov'ev profiles [3] to solve the Grad-Shafranov equation are shown to well predict the ray tracing results for both XB and OXB schemes of mode conversion. In the cases of highly over dense, low q and low aspect ratio plasmas ω/Ωce is rather close to 2 at the UHR layer and the second harmonic cyclotron damping can take place along the ray trajectory just after OXB mode conversion, depending on the parameters. Mapping is shown to work in this case as well. The mapping technique is based on distinctive characteristics of EB wave propagation and absorption, and, therefore, is useful to guide the ray racing calculations and to understand the ray tracing results.
[1] T. Maekawa, S. Tanaka, Y. Terumichi and Y. Hamada, J. Phys. Soc. Jpn. 48 (1980) 2247. [2] Y.R. Lin-Liu, V.S. Chan and R. Prator, Phys. Plasmas 10 (2003) 4064. [3] A.J. Selfon and J.P. Freidberg, Phys. Plasmas 17 (2010) 032502.

Speaker: T. Maekawa (EPS 2019)

532 P4.1084 Progress in the experiment on the neutral beam injection on the spherical tokamak Globus-M2

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1084.pdf

The first plasma on the new spherical tokamak Globus-M2 [1] was obtained in the spring of 2018. During the test experimental campaign, the routine Globus-M shot with moderate density, current of 0.2 MA and magnetic field of 0.5 T [2] was reproduced. The main discharge parameters were monitored using routine diagnostics, such as magnetic probes and loops, microwave interferometer, etc. Since the vacuum vessel in the new tokamak remained the same, the existing injector was docked simultaneously with the tokamak assembly. During testing of the injector, a beam of 26 keV 0.7 MW deuterium atoms was applied. After testing campaign, the experiment was suspended to complete work on upgrading the tokamak power supplies, setting up the diagnostics and heating and non-inductive current drive systems. In the course of these works a second injector with atomic energy up to 50 keV and power up to 1 MW was docked to the tokamak. Like the first one, the second beam is coinjected into the plasma tangentially in the middle plane of the torus. The impact parameter (0.3 m) was chosen on the basis of minimizing direct losses and ensuring the possibility of beam transportation through turns of a toroidal magnetic field coil. The injection pulse overlaps in time the entire plasma discharge, due to the injector power supply system, fed from the AC mains. The paper presents the results of the first experiments on plasma heating using neutral beam injection in discharges with an increased magnetic field and plasma current. The results of the study of the ion component using the NPA and CXRS diagnostics are reported.
References: [1] V.B. Minaev, V.K. Gusev, Y.V. Sakharov, et al., Nucl. Fusion 57 (2017) #066047. [2] V.B. Minaev, V.K. Gusev, Y.V. Sakharov, et al., Proc. 45th EPS Conf. on plasma physics (Prague, 2018) P4-
1065.

Speaker: V.B. Minaev (EPS 2019)

533 P4.1085 Modelling of merging-compression formation of high temperature Tokamak plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1085.pdf

The merging-compression formation method is used in spherical tokamaks (STs) to produce high temperature plasmas without using flux from a central solenoid. Plasma rings are formed around two in-vessel poloidal field coils (MC-coils) and merged via magnetic reconnection into one plasma ring. The ring is then radially compressed to form the ST configuration. This method is used to form plasma in a small tokamak ST40 (design parameters: R/a=0.4/0.25m, B_t=3T, I_pl=2MA pulse duration 1-2 sec, P_aux up to 4MW) and Ipl ~ 400kA and T_i = 1-2keV have been recently achieved without use of auxiliary heating or central solenoid /1/. The modelling of merging-compression in ST40 has following aims: (1) To determine the deposition profile D(r) of the ions accelerated to Alfven speed during magnetic reconnection by means of the fast particle code NFREYA. (2) To calculate the ion temperature after the reconnection heating and compression. (3) To estimate the electron ohmic heating power, Ampere's law is applied to the current sheet formed at the X-point of the reconnecting rings. The TSC describes the plasma behaviour using D(r) for ions and ohmic heating for electrons. The following results have been obtained: (1) Assuming flux conservation in TSC simulations, the ramp-down of the current in MCcoils from I_MC~600kA to zero produces plasma current of ~1 MA. After acceleration of ions to the Alfven speed in the electric field produced by the reconnection, the corresponding Alfven energy of fast ions is ~10 keV. In ST40, lower values of the plasma current of 400 kA have been obtained using swing of current in MC coils ~ 450kA. The overestimation of the induced plasma current in simulations is due to the presence of losses of the poloidal flux in passive structures of the tokamak, not accounted for in TSC simulations. (2) Since the reconnected ions are released in the vicinity of the X - point and run in codirection /2/ with a small spread (~10 degrees) in pitch angle, the deposition profile is peaked at the plasma boundary and was found to have a width of ~5 cm. (3) Assuming in TSC a reconnection heating power of 20 MW with the deposition D(r), a temperature of Ti~1 keV was obtained in a rough agreement with the ST40 findings /1/. (4) Using Spitzer resistivity (which underestimates the heating), the central electron heating power is around 0.5MW. With the central deposition, T_e~600 eV was obtained in simulations.
/1/ www.tokamakenergy.co.uk /2/ K G McClements et al, Plasma Phys. Control. Fusion 60 (2018) 025013

Speaker: A. Nicolai (EPS 2019)

534 P4.1086 Simulation of lower hybrid current drive in the presence of inductive electric field in the FT-2 tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1086.pdf

The development of non-inductive current drive methods is a central problem on the way of a fusion reactor development within the tokamak concept. The low-hybrid (LH) method of current maintenance can potentially be used in solving this problem, since it has one of the highest efficiencies of current drive [1]. This method is proposed as a possible technique for current generation at the middle and periphery radii of plasma core for the current profile broadening in ITER, which will operate with a mixture of heavy hydrogen isotopes [2]. Recently the isotope effect on the LHCD efficiency dependence on main parameters of hydrogen and deuterium plasmas have been studied at the FT-2 tokamak [3]. To interpret the experimental results indicating the high LHCD efficiency complex simulations of the propagation and absorption of LH waves in the FT-2 plasma were performed. The Grill3D code [4] was used to calculate the parallel refractive index spectrum of the lower hybrid wave launched into the plasma by two-waveguide antennae. The magnitude and direction of the current generated by the lower hybrid wave were computed using the Fast Ray Tracing Code (FRTC) [5], the calculated LH wave spectrum, and the measured profiles of the plasma parameters. The magnetic equilibrium of the plasma column was provided by the ASTRA code [6] with using of the measured radial profiles of the plasma parameters. However simulations performed in [3] did not take into account the effect of the residual inductive electric field on the electron distribution function, generation of super-thermal electrons and hence on the LHCD efficiency. In the present work a new one-dimensional approach to the lower hybrid current drive modelling in the presence of the inductive electric field suggested recently in [8] is applied to calculate LHCD for hydrogen and deuterium plasmas at FT-2 experiments. The simulation results are compared to the experimental data.
[1] N.J. Fisch, Mod. Phys. Rew. 59 1987 [2] P. Bonoli, Phys. Plasmas 21, 2014 [3] S.I. Lashkul et al Nucl. Fusion 55 (2015) 073019 [4] M. A. Irzak and O. N. Shcherbinin, Nucl. Fusion 35, 1341 (1995) [5] A.D. Piliya, A.N. Saveliev, JET Joint Undertaking, Abingdon, Oxfordshire, OX14 3EA, 1998 [6] G.V.Pereverzev and P.N. Yushmanov, Automated System for TRansport Analysis IPP-Report IPP 5/98, (2002) [7] A.N. Saveliev, EPJ Web of Conferences 157, 03045 (2017)

Speaker: G. Troshin (EPS 2019)

535 P4.1087 Effective electron Bernstein wave heating by polarization adjustment of incident microwave for non-inductive formation of spherical tokamak in LATE

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1087.pdf

Non-inductive formation of spherical tokamak (ST) by electron cyclotron heating and current drive (ECH/ECCD) using electron Bernstein (EB) wave is an important issue for realization of a compact and economical reactor without a central solenoid. In order to use EB waves for ECH/ECCD, EB waves have to be coupled from EC waves via mode-conversion (MC) process in the plasma. Improving MC rate to EB waves results in effective heating because EB wave may be strongly absorbed even in low temperature plasma. The MC rate can be improved by adjusting the polarization and the parallel refractive index of the incident EC wave for the density gradient near the upper hybrid resonance (UHR) layer as shown by the linear MC rate theory with cold plasma resonance absorption model in a slab geometry [1].
In the LATE device, overdense ST plasmas are non-inductively formed by oblique injection of the microwaves at 2.45 GHz from low field side on the midplane when the fundamental ECR layer is located in the plasma core and the 2nd ECR layer is outside the UHR layer [2]. To study the polarization effects on plasma production, the polarization of incident microwave is converted from the linearly-polarized one originally generated by magnetrons to three types of elliptically-polarized ones (from O-mode like one to X-mode like one) by the circular waveguide polarizers [3]. The radial density profile on the midplane is reconstructed by Abel inversion from line-integrated density data measured by 4 ch 70 GHz microwave interferometers, and the UHR location and the density gradient are obtained.
When the density gradient near the UHR layer is low, the density and the soft X-ray intensity near the core of the plasma formed with O-mode like polarization are the highest among three types of polarizations. When the density gradient is high, those of the plasma formed with Xmode like polarization are the highest. In both cases, the MC rate calculated with the measured values are also the highest, which means that the plasma heating near the plasma core is brought about by improvement of the MC rate and increase of power deposition via EBW absorption.
References
[1] H. Igami, H. Tanaka and T. Maekawa, Plasma Phys. Control. Fusion 48 573 (2006) [2] M. Uchida, et al., Fusion Energy Conf. 2012, IAEA-CN-197/EX/P6-18. [3] Y. Noguchi, et al., Plasma Phys. Control. Fusion 55 125005 (2013)

Speaker: Y. Nozawa (EPS 2019)

536 P4.1088 New neutral beam injector for Globus-M2 spherical tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1088.pdf

The choice of available auxiliary heating and current drive schemes is limited in spherical tokamaks (STs) due to tight aspect ratio, low toroidal magnetic field, and high plasma density approaching the Greenwald limit. The most successful heating and current drive method used to date in STs is Neutral Beam Injection (NBI).
Toroidal magnetic field and plasma current will more than double in Globus-M2 ST [1], which could cause a significant increase in plasma density. Therefore, in order to ensure the optimal depth of atomic beam penetration into plasma before beam ionization, it is necessary to increase the energy of injected atoms. In order to enhance the power and duration of auxiliary plasma heating, NBI upgrade program for Globus-M2 stipulates the installation of a new neutral beam (NB) injector in addition to existent heating injector [2]. The main characteristics of new NB injector are as follows:
- maximum atomic beam power ­ 1MW;
- maximum accelerating voltage ­ 50kV;
- maximum ion beam current ­ 40A;
- maximum beam pulse duration ­ 1sec;
- beam divergence ­ 1.2˚;
- focal length ­ 3.5±0.5m.
The paper (1) details NB injector structure, process of atomic beam formation, and the choice of optimal experiment layout, (2) discusses experimental results on discharge characteristics of high frequency plasma source, as well as its emissivity, (3) describes the dependence of beam divergence on its current and acceleration voltage, emission spectrum of the atomic beam, and power distribution across the NB, and (4) demonstrates that NB injector is capable of changing the NB power incrementally and modulating the injection power. With the installation of the new injector, Globus-M2 has greatly extended the range of accessible plasma parameters that are highly relevant to tokamak fundamental physics and machine operation studies and will strongly contribute to fusion neutron source projects. References: [1]. Minaev V.B., Gusev V.K., Sakharov N.V., et al., Nuclear Fusion, 57 (2017) 066047 [2]. Gusev V.K., Dech A.V., Esipov L.A., et al., Technical Physics, 52 (2007) No. 9, 1127-1143

Speaker: P.B. Shchegolev (EPS 2019)

537 P4.1089 An analysis of the ECRF stray radiation in JT-60SA

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1089.pdf

The JT-60SA large superconducting tokamak being built under the Broader Approach agreement jointly by Europe and Japan [1] will start operation in 2020. It is designed to address many areas of fusion science in preparation of the burning plasma era of ITER and DEMO, in particular the ones related with the control of high β steady state plasmas and the confinement of high energy particles. A key tool in the machine will be the 7 MW, 9 gyrotrons ECRF system which, as for the 34 MW NBI system, will be available in the Integrated Research Phase. Up to 1.5 MW of ECRF power will be available during the Integrated Commissioning without beam steering capabilities, while the system will be upgraded to 3 MW power with wide steering capabilities [2] in the Initial Research Phase. The ECRF system will support several applications since the plasma commissioning phase namely assisted start-up, EC wall conditioning, bulk heating and later on current drive and magneto-hydrodynamic instabilities control. In order to allow the needed flexibility the ECRF system will operate at three different frequencies, 82 GHz, 110 GHz and 138 GHz. An analysis of the residual non-absorbed ECRF power fraction expected in the various applications and plasma scenarios is presented in this contribution, studying its dependence on the steering angle and on the plasma main parameters such temperature and density. Both transient conditions, such plasma start-up, and flat-top scenarios are taken into consideration. Moreover, the expected stray power density distribution in the vessel and particularly around the potentially critical areas such diagnostics windows or pumping ducts is evaluated.

[1] JT-60SA Research Unit, JT-60SA Research Plan, Version 4.0, September 2018, http://www.jt60sa.org/pdfs/JT-60SA_Res_Plan.pdf
[2] T. Kobayashi et al., Fusion Eng. and Des, 96-97, Pages 503 (2015)

Speaker: C. Sozzi (EPS 2019)

538 P4.1090 ICRF modelling with Non-Maxwellian distributions in JET

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1090.pdf

Ion Cyclotron Range of Frequency (ICRF) Heating is an important heating source on the Joint European Torus (JET). For the D-T campaign, various scenarios of ICRF heating are considered including second harmonic Tritium resonance and the three species hybrid resonance method [Y. Kazakov et al, Nature Physics 973 13 (2017)]. The ICRF full wave modelling codes TORIC and AORSA have both been coupled to the Fokker-Planck solver, CQL3D, and are used routinely to model wave propagation and absorption and the generated fast ion distributions in C-Mod experiments with validation through experimental comparisons with synthetic diagnostics [J. Wright et al, Plasma Physics and Controlled Fusion, 025007 56 (2014).] We will show parametric dependence of ion tail temperatures and neutron fusion rates on species concentration for various scenarios as well as comparisons between the finite Larmor radius TORIC code and the all orders Larmor radius AORSA code.

** See author list of "Overview of the JET preparation for Deuterium-Tritium Operation" by E. Joffrin et al to be published in Nuclear Fusion Special issue: Overview and summary reports from the 27th Fusion Energy Conference (Ahmedabad, India, 22-27 October 2018.)

Speaker: J.C. Wright (EPS 2019)

539 P4.1091 New position control tools for runaway experiments at JET

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1091.pdf

Runaway beam confinement and dissipation remain one of the main concern for ITER operation and a clear solution has not been found yet. ITER will be provided with a Shattered Pellet Injection (SPI) system as the primary disruption mitigation technique given the promising results provided by DIII-D [3]. To further study such technique an SPI system has been recently installed at JET and to provide reliable results an improved runaway beam position control system [2, 1] is proposed. In this work we propose to use a dynamic observer to estimate in realtime the vertical speed of the runaway beam. This dynamic observer should replace the standard static estimator used at JET by the vertical stabilization system, once the runaway beam is detected. In particular, the instantaneous input/output matrix of the new observer, whose inputs are the magnetic measurements, is equal to the standard observer, meanwhile the dynamic and state-to-output matrices are optimized in order to fit the vertical position reconstructed using EFIT. The new observer has the same high frequency behavior of the standard one plus the capability of detecting the RE beam slow vertical drift. An innovative tool to improve the beam position control is also described. This method uses a graph data structure to store an adaptive probabilistic route-map that links different states of the plasma and that can be obtained either using experimental data or via a simulators. Such structure is then used to estimate an optimal control policy via reinforcement learning techniques.

References
[1] L. Boncagni et al., A first approach to runaway electron control in FTU, FED 88 (6-8), 1109-1112
[2] D. Carnevale et al., Runaway electron beam control, PPCF 61 (1), 014036 (2018)
[3] N. Commaux et al., First demonstration of rapid shutdown using neon shattered pellet injection for thermal quench mitigation on DIII-D, Nucl. Fusion 56 046007 (2016)
[4] C. Reux et al, Runaway electron beam generation and mitigation during disruptions at JET-ILW, Nucl. Fusion 55 129501 (2015)
[5] B. Esposito et al., Runaway electron generation and control, PPCF 59 (1), (2017)

Speaker: L. Calacci (EPS 2019)

540 P4.1092 Recent progress and plans of inboard-limited ITB experiments on KSTAR

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1092.pdf

It has been exploring the inboard-limited ITB (Internal Transport Barrier) as an alternative advanced operation scenario for KSTAR since 2016. The experiment of ITB formation in L-mode plasma with a marginal NBI majority heating successfully demonstrated that the ITB is an alternative candidate to achieve a high performance regime in KSTAR. Here, the approach with the inboard limited configuration to avoid the H-mode transition prior to the formation of the ITB was effective at a given L-H transition characteristics and heating resources in KSTAR. In 2018 campaign, we have tried to extend its operation window by controlling the plasma shape and position. The key control parameters of the experiment were the triangularity and vertical position of the plasma. The shape control attempted to divert the plasma to a vertically shifted Upper Single Null (USN), with a marginal touch of the inboard limiter, so that the plasma can remain in L-mode at the boundary. Here, the NBI off-axis heating provides current density profile modification and it flattens the q-profile. This was intended in the lifted USN configuration. In this work, we present recent progress and plans of inboard-limited ITB experiments on KSTAR.

Speaker: J. Chung (EPS 2019)

541 P4.1093 Some Issues in Realizing the RF Current Condensation Effect

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1093.pdf

Since the suggestion that magnetic islands produced by tokamak tearing modes might be stabilized by non-inductive currents [1], a great number of experimental, theoretical, and computational efforts have been exerted. The stabilization effect relies upon rf waves driving current preferentially at the island center. The most studied rf current drive methods for producing these currents for stabilizing the tearing mode, particularly the neoclassical tearing mode, are lower hybrid current drive (LHCD) [2] and electron cyclotron current drive (ECCD) [3]. Both can be localized to stabilize the neoclassical tearing mode, although the localization of the current produced through ECCD might be more easily localized. Both exploit the fact that a high current drive efficiency is obtained when the rf waves are damped in plasma by superthermal electrons. In both cases it is thought that the neoclassical tearing modes must be stabilized before they grow too large, because the current required to stabilize large islands would be correspondingly greater and therefore more expensive. The requirement to stabilize islands while they are small makes more severe the requirement for precise localization.
However, power dissipated within the islands tends to lead to a temperature peaking at the island center, which induces more dissipation at the center. This positive feedback leads to a current condensation effect, where the current tends to condense on the island center, exactly where it is most effective at stabilizing the neoclassical tearing mode [4]. This effect makes it possible both to stabilize larger islands and to do so with less precise localization. Since this condensation effect relies on the sensitivity of the power deposition to the electron temperature, the condensation will tend to be most pronounced when the current is carried by the fastest electrons, which is also where the current drive efficiency is highest. Here we explore what are the issues in reaching this regime of both high rf current drive efficiency and effective rf current condensation, both for lower hybrid current drive and for electron cyclotron current drive.
References
[1] A. H. Reiman, Suppression of magnetic islands by rf-driven currents, Physics of Fluids 26, 1338 (1983).
[2] N. J. Fisch, Confining a tokamak plasma with rf-driven currents, Phys. Rev. Lett. 41, 873 (1978).
[3] N. J. Fisch and A. H. Boozer, Creating an asymmetric plasma resistivity with waves, Phys. Rev. Lett. 45, 720 (1980).
[4] A. H. Reiman and N. J. Fisch, Suppression of tearing modes by radio frequency current condensation, Phys. Rev. Lett. 121, 225001 (2018).

Speaker: N.J. Fisch (EPS 2019)

542 P4.1094 Physics aspects of the COMPASS Upgrade tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1094.pdf

Recently, the construction of the COMPASS-U tokamak, a medium-size (R = 0.894 m; a = 0.27 m), high-magnetic-field (5 T) device, has started in the Institute of Plasma Physics of the Czech Academy of Sciences in Prague, Czech Republic. COMPASS-U will be capable to operate with plasma current up to 2 MA and, therefore, also at high plasma densities (~1020 m-3). The device is designed to generate and test various DEMO relevant magnetic configurations, such as conventional single null, double null, and snow-flake; it will be also capable to operate with hot walls (up to 500°C). The plasma will be heated using 4 MW Neutral Beam Injection (NBI) heating system with future extension by at least 4 MW Electron Cyclotron Resonant Heating (ECRH). COMPASS-U aims at addressing the knowledge gaps associated with the plasma operation at the high magnetic field and related areas of the plasma and energy exhaust. The device will focus on the open physics questions such as the demonstration of detached operation at ITER/DEMO relevant heat fluxes, studies of enhanced confinement modes (QH-, I- and EDA-modes), and integrated core-edge scenarios. The design of the divertor will allow to test both the conventional materials as well as liquid metal technologies under high heat fluxes. Conventional materials will be used during the first stage of operation. In the later phase, a conventional upper divertor will be installed and liquid metal materials will be used in the bottom divertor. In this contribution, the focus of the COMPASS-U tokamak and its physics goals will be presented. The reference operational scenarios and relevant key plasma parameters will be shown.

Speaker: M. Hron (EPS 2019)

543 P4.1095 Estimation of controllability region of unstable vertical plasma position and plasma separatrix multivariable reachability area of a spherical tokamak

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1095.pdf

The paper deals with plasma controllability and reachability regions in the spherical tokamak Globus-M (Ioffe Inst.). Plasma magnetic control system [1] of Globus-M consists of 2 loops for plasma vertical Z and horizon R position control with thyristor current invertors [2], and 6 inner cascades for control of currents I_CS&PF (Fig.1) with thyristor multiphase rectifiers [1]. All these loops contain PID-controllers and two of them for plasma position control were adjusted by Quantitative Feedback Theory approach based on the Nichols chart analysis of an open loop linear model [3]. The linear plant model [1] has one unstable real pole because of plasma elongation in vertical direction, and the voltage on horizon field coil (HFC) is restricted. Therefore, the controllability region of vertical plasma displacement is restricted as well [4]. For plasma linear model of 40 order [1] this region was estimated by application of the maximum voltage of proper sign on the HFC to return Z back (Fig.2) [5] for Z(0). The value of this region namely  0.15 m coincided with numerical calculation of the same region by the linear model. Upper and lower reachability region estimations of the plasma separatrix shape were obtained at the plasma diverter phase (Fig.3) for the multivariable and multicascade control system in Fig.1. There are no shapes beyond the upper estimation because of the given limits and there are any shapes inside the lower estimation. Values of these estimations are about 10^-3÷10^-2 m. They were obtained using matrix relations between inputs and outputs of the system in Fig.1 in steady-state regime at restrictions. For calculation of upper estimation the maximum allowable inputs with needed signs were applied and for calculation of lower estimation the maximum possible displacement of each shape projection P1-P6 available with all restrictions was reached.
[1] Mitrishkin Y.V., Prokhorov A.A., Korenev P.S., Patrov M.I. Fusion Eng. Design, v. 138, 2019, pp. 138-150.
[2] Kuznetsov E.A., Mitrishkin Y.V., Kartsev N.M. Fusion Engineering and Design, 2019.
[3] Garcia-Sanz M. Robust Control Engineering. Practical QFT solutions. Taylor & Francis Group, 2017.
[4] Mitrishkin Y.V. Plasma Devices and Operations, v.4, no 2, 1995, pp. 111-140.
[5] Humphreys D.A., et al. Nuclear Fusion, 2009; vol. 49.

Speaker: Y.V. Mitrishkin (EPS 2019)

544 P4.1096 Actuator Management via Real-time Optimization for Integrated Control in Tokamaks

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1096.pdf

In ITER, only a limited number of actuators is available to carry out a great variety of control tasks, some of which may be closely coupled. Safe operation while attaining high plasma performance will require an integrated Plasma Control System (PCS) that has the capability of simultaneously regulating as many aspects of the plasma dynamics as possible. Moreover, such integrated PCS must include supervisory and actuator management systems. The goal of such systems is to determine and assign in real time the authority of each control task over the available actuation mechanisms depending on the plasma state. In this work, an integrated controller with actuator management capabilities is proposed for simultaneous control of the central safety factor, q_0, the edge safety factor, q_edge, the total stored energy, W , the bulk toroidal rotation, Ωφ , and/or line-average electron density,n ̄_e. Figure 1 shows a simplified schematic of a possible PCS architecture in which the integrated controller proposed in this work could be embedded. The integrated controller is based on zero-dimensional, controllevel models of the plasma dynamics, and is synthesized using nonlinear, robust Lyapunov techniques to ensure high performance despite nonlinear, unknown plasma dynamics. The actuator management algorithm employs the time-varying, plasma-state-dependent control priorities to decide which actuators are utilized for each control task. The actuator management problem is solved as a real-time optimization problem, providing substantial flexibility to include changing control objectives in the form of time-varying constraints. Also, this scheme allows for performing the two main kinds of actuator sharing envisioned for ITER: Simultaneous Multiple Mission (SMM) sharing and Repurposing (RP) sharing [1]. The proposed control algorithm is tested in onedimensional simulations using the Control Oriented Transport SIMulator (COTSIM) code.

References
[1] D. Humphreys et al, Novel aspects of plasma control in ITER, Phys. Plasmas 22, 021806 (2015)

Speaker: A. Pajares (EPS 2019)

545 P4.1097 Integrated study of solenoid free tokamak startup on the URANIA experiment

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1097.pdf

Developing attractive means of initiating current without using magnetic induction from a central solenoid is a critical scientific and technical challenge facing the spherical tokamak (ST). The PEGASUS program has focused on developing the physics basis and predictive models for non-solenoidal tokamak startup using local helicity injection (LHI). LHI utilizes compact, edge-localized current sources (A_inj ≤ 8 cm², I_inj ≤ 8 kA, Vinj ≤ 1.5 kV) for plasma startup and sustainment, and can initiate more than 200 kA of plasma current in a low-field (B_T ~ 0.15 T), near-unity aspect ratio (A) ST. Typical LHI plasmas have n_e ≤ 3x10^19 m^-3 and T_e ≤ 150 eV, values comparable to Ohmic L-mode discharges at these B_T values in PEGASUS. I_p increases linearly with increased helicity input. Choice of injector location allows a tradeoff between poloidal induction and helicity injection (HI) dominated current drive. In both cases, significant anomalous ion heating is seen, and has been found to scale as expected from twofluid reconnection theory. Internal magnetic measurements show three main features are present in LHI: a ~20­40 kHz peak from n = 1 line-tied kink motion of the injector current streams; an intermediate region near 0.6 MHz with higher fluctuation power; and broadband turbulence for f < 3 MHz. In HI dominated LHI plasmas, a novel regime is found at low B_T ≤ 0.075 T where the n = 1 activity is suppressed, power at frequencies f > 0.1 MHz increases, and current drive efficiency is improved. This suggests that high-frequency, short wavelength activity could play a critical role in the current drive process. A major upgrade is underway to convert the PEGASUS facility into a solenoid-free ST with a four-fold increase of B_T to 0.6 T. The upgraded experiment (URANIA) will have a new mission: to examine and compare several leading non-solenoidal tokamak startup candidates in a single experiment. Initial techniques under consideration are: LHI; sustained and transient coaxial helicity injection; electron Bernstein wave electron heating and current drive; and poloidal field induction. The overarching goal is to establish routine non-inductive plasma startup that can project to MAclass startup on NSTX-U and beyond.
*This work is supported by U.S. Department of Energy grants DE-FG02-96ER54375 and DE-SC0019008.

Speaker: J.A. Reusch (EPS 2019)

546 P4.1098 Magnetic configuration and plasma breakdown in the spherical tokamak Globus-M2

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1098.pdf

This paper describes characteristics of plasma inductive start-up in the spherical tokamak Globus-M2. The Globus-M2 [1] is the result of Globus-M upgrade, based on the replacement of toroidal and poloidal magnetic coils in order to increase the toroidal magnetic field and the plasma current by 2-2.5 times up to B_T = 0.8-1 T and I_P = 0.4-0.5 MA. The vacuum vessel remained the same. The plasma inductive breakdown is performed by means of the central solenoid with total stored magnetic flux of 0.4 Wb at the current swing ±70 kA. At the moment of plasma breakdown the solenoid stray magnetic field within the breakdown region is about 0.04 T. This stray field is compensated by a set of external poloidal field (PF) coils. The magnetic configuration in the breakdown stage is determined by processing signals of 21 flux loops installed on the vacuum vessel surface. Also the input signals for the magnetic reconstruction are currents in PF coils, current in the central solenoid and induced toroidal currents in the vacuum vessel, determined from flux loop data. The paper presents distributions of the poloidal magnetic flux and the module of the poloidal magnetic field inside the vessel in the plasma breakdown stage. The range of hydrogen pressures and electric field at which steady breakdown occurs is determined.

References: [1] V.B. Minaev, V.K. Gusev, Y.V. Sakharov et al, Nucl. Fusion 57, 066047 (2017).

Speaker: N.V. Sakharov (EPS 2019)

547 P4.1099 Vacuum estimation of error field correction on ASDEX Upgrade

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1099.pdf

A study of the vacuum magnetic field produced by the Poloidal Field (PF) coil system of ASDEX Upgrade is presented. In the model both coils and their power­supply feedthroughs are considered. The latter contribute to the error fields (EFs) that have already been observed and reported in [1, 2]. The effect on the B field due to PF coils, assumed to be perfectly axisymmetric, is addressed by analytical formulas, while a 1-D model is applied to feedthroughs [3]. The model is applied to a reference shot (#35352) for the computation of the normal component of B (i.e. B_n) projected on the q = 2 rational surface. The resulting EF pattern is located near the feedthroughs region, with a maximum value close to 0.25 mT. ASDEX Upgrade is equipped with a set of 16 in­vessel saddle coils [4], that can be used to minimize the effect of EFs on plasma discharges. A preliminary correction strategy of the non-axisymmetric field generated by feedthroughs is based on a Virtual Shell Approach, that is made up by 8 upper and 8 lower saddle loops built on the q = 2 surface. The matrix M_16×16 of the mutual inductances between active coils and virtual shell is computed numerically, such that I = M−1φ , where φ is the vector of the fluxes linked by the virtual shell loops and I stores the unknown currents needed for compensating those fluxes. A more detailed analysis is foreseen to include further possible sources of Efs (e.g. passive conductive structures, ferromagnetic tiles, tilting of PF coils). Moreover, MARS-F [5] can be used for calculations of plasma response to a prescribed m, n harmonic of the EF distribution, and a new correction strategy may be applied for reducing the resulting EF pattern.
[1] M. Maraschek, et al., Proc. 40th European Physical Society Conf. on Plasma Physics, P4.127 (Espoo, 2013) [2] V. Igochine, et.al., 2017 Nucl. Fusion 57, 116027 [3] J.D. Hanson, and S.P. Hirshman, Physics of Plasmas 9, 4410 (2002) [4] W. Suttrop, et al., Fusion Engineering and Design 84, 2 (2009) [5] Liu, Y.Q., et al., Physics of Plasmas 7, 3681 (2000) See the author list: H. Meyer, et al., 2017 Nucl. Fusion 57, 102014

Speaker: D. Voltolina (EPS 2019)

548 P4.1100 Investigation of the impact of ETGs on electron heat transport in TCV plasmas with NBI and ECH injection

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1100.pdf

Electron Temperature Gradient (ETG) micro-turbulence modes have been recently shown to impact the electron heat transport in tokamaks in conditions when ion-scale turbulence is close to marginality and electron heating is significant [1]. Given the relevance of these mechanisms for ITER scenarios, a new study has been carried out on the TCV tokamak at the Swiss Plasma Center (Lausanne, CH), which is equipped with both ECH and NBI heating, allowing to investigate the relevance of ETG transport. An experimental characterisation of the electron threshold at mid-radius was carried out in TCV by comparing two experimental cases (EUROfusion WP MST1 TCV, 2017) with on- vs off-axis ECH power, with/without NBI heating. Each discharge features different time intervals, corresponding to NBI only, mixed NBI/ECH, ECH only phases. ECH was injected both steady and modulated, in order to gain additional information from perturbative analysis. The experimental analysis of the two discharges shows a moderate stiffness for the ECH only phases. Linear flux-tube gyrokinetic simulations have been performed with the GENE code [2], showing the possible importance of ETGs in the electron heat transport for the mixed NBI/ECH case. The numerical ETG thresholds have been found in good agreement with the theoretical dependence on Z_effTe/Ti. The results of non-linear ion-scale gyro-kinetic simulations seem to indicate that, while in the ECH only case the experimental fluxes are well matched by the simulations, in the mixed NBI/ECH case the ion-scale flux is not able to explain the experimental one, invoking the possible contribution of ETGs. The simulations have been run considering a three species (gyrokinetic) electron-deuteron-carbon (main impurity) plasma. Fast ions (gyrokinetic) have been included in the cases with NBI. References
[1] N. Bonanomi et al. 2017, 44th EPS Conf. on Plasma Physics
[2] F. Jenko et al. 2000 Phys. Plasmas 7

Speaker: A. Mariani (EPS 2019)

549 P4.1101 Simulation study of a net toroidal torque generation by suprathermal electrons of ECH in non-axisymmetric tokamak plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1101.pdf

Spontaneous toroidal flows have been observed during ECH without direct momentum input in tokamak and helical plasmas[1-3]. We have studied the j × B toroidal torque due to radial diffusion of suprathermal electrons during ECH in LHD applying GNET code[4]. It is found that the j × B torque related to the suprathermal electrons plays an important role in the toroidal flow generation in the LHD plasma[5]. On the other hand, in axisymmetric tokamaks, it is well known that this j × B torque and the collisional torque by the precession motion of suprathermal electron would cancel each other, and no net toroidal torque is generated. However, in the real tokamaks, there exists finite non-axisymmetric magnetic field; such as the toroidal field ripple, magnetic resonance perturbation, RMP, etc., and these nonaxisymmetric magnetic fields would generate the net toroidal torque.
In this study, we investigate the j × B and the collisional torques due to suprathermal electrons by ECH in the non-axisymmetric tokamaks (finite toroidal field ripples and RMP). To evaluate the toroidal torques, we apply the GNET code, which can solve the 5D drift kinetic equation for suprathermal electrons[4]. We assume a simple tokamak A=6.7 (LHD size) and add a toroidal field ripple as B = B_axisym + B_0,18 cos(18 ϕ ) and the RMP (m, n = ±3) as B = B_axisym + B_m,±3 cos(mθ ± 3ϕ). We have found that the JxB torque is larger than that of collisional torque due to the radial motion of ripple trapped electrons, and have obtain significant net toroidal torques by ECH. The peak value of torques gradually increases as the nonaxisymmetric component increases. A simple model of the radial flux of suprathermal electrons has been derived and has shown relatively good agreements with the simulation results.

[1] M. Yoshida, et al., Phys. Rev. Lett. 103, 065003 (2009)
[2] J. S. deGrassie, et al., Phys. Plasmas 14, 056115 (2007)
[3] S. T. A. Kumar, et al., Plasma Phys. Control. Fusion 60 054012 (2018)
[4] S. Murakami, et al., Nuclear Fusion 40, 693 (2000)
[5] Y. Yamamoto, et al., Int. Stellarator-Heliotron Workshop, Kyoto P1-43 (2017)

Speaker: S. Murakami (EPS 2019)

550 P4.1102 Isotope effect on energy confinement time and thermal transport in NBI-heated plasmas on LHD

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1102.pdf

Energy confinement time and thermal transport has been investigated in NBI heated hydrogen (H), deuterium (D) and mixture (H&D) plasmas in a large-scale stellarator-heliotron LHD. Regression analysis of thermal energy confinement time has indicated no significant dependence on the isotope mass (A) in the expression of operational parameters such as τ^(scl)(E,th) ∝A^(-0.01+-0.02) B^(0.85+-0.02) n_e^(0.78+-0.01) P_abs^(-0.87+-0.01), where B, n_e and P_abs are magnetic field, line-averaged density and absorbed heating power, respectively. An isotope effect on energy confinement time seems degenerate like an MHD model. This expression can be rephrased into the expression of non-dimensional parameters such as τ^(scl)(E,th)Ω_i ∝ A^(1.01)ρ^(-3.03)υ^(0.19)β^(-0.28) where ρ, υ and β are normalized gyro radius, normalized
collisionality and normalized pressure, respectively. This expression suggests co-existence of gyro-Bohm nature (τ_(E,th) Ω_i ∝ ρ^(-3) ) and clear but un-known mass dependence, or this could be consequence of violation of gyro-Bohm nature. H and D plasmas with the same non-dimensional parameters such as ρ, υ* and β have been compared in order to assess these two contrasting conjectures. These plasmas which are non-dimensionally similar but have different mass have been obtained by adjusting magnetic field, density and heating power to realize density ratio of nD/nH=2 and temperature ratio of T_D/T_H=sqrt(2) at B_D/B_H=2^(3/4). Gyro-Bohm model as well as neoclassical transport predicts the same thermal diffusivity normalized by Ω_i for these pairs of non-dimensionally similar plasmas. However, significant improvement of thermal diffusivity has been identified in deuterium plasmas compared with hydrogen plasmas in particular electron loss channel. Since it should be noted that electron heating is predominant for these plasmas, typically P_e/P_i~4, this local thermal transport characteristics is consistent with a conjecture from energy confinement time τ_(E,th) Ω_i ∝ A . Effects of heating channel in other words T_e/T_i ratio and isotope mixture as well as configurational effect due to enhanced neo-classical helical ripple transport are also discussed.

Speaker: H. Yamada (EPS 2019)

551 P4.1103 Benchmarking the TGLF turbulent transport code for a Q=10 burning spherical tokamak plasma using GS2

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.1103.pdf

Spherical Tokamaks (STs) could provide a route towards a compact fusion reactor due to advantageous properties such as high plasma beta. A GW-scale ST plasma is explored where Q=10 and R=2.5m. In this design 110 MW of NBI is needed to provide 9 MA of non-inductive current, where the remaining 12 MA is pressure driven. To penetrate into the core a 1 MeV on-axis beam is needed, leading to low momentum injection into the plasma. An estimate of the resulting flow suggests a Mach velocity of M~O(0.01) compared to the ion sound speed. A key question is whether this is sufficient to stabilise turbulence. A burning ST would operate in an unexplored regime and high fidelity modelling is required to assess confinement in such a device. Codes such as TGLF and GS2 have been used to model the turbulent transport. Predictive heat transport calculations have been performed with JINTRAC using the TGLF transport model. Figure 1 illustrates that the predictions are highly sensitive to flow. In the M=0 case confinement insufficient to achieve the target profiles for Q=10. The confinement dramatically improves with M and the target profiles are reached at M=0.03. This would suggest that the low flow generated by the NBI may suppress the turbulence sufficiently to recover the confinement necessary for Q=10. TGLF must be verified and tuned for high beta ST plasmas with subsonic flows, as they are different to the conventional regimes for which TGLF was developed. TGLF linear micro-instability calculations have been compared to GS2 for STs and conventional tokamaks, which reveal differences in growth rates at lower aspect ratio. Priorities are to understand these differences and to assess whether TGLF's prediction of sensitivity to flow is physical. Comparing against MAST shots will help validate TGLF in the ST regime.

Speaker: B. Patel (EPS 2019)

552 P4.2001 Large-scale implosions using HDC ablators for the Frustraum driven at 2 omega

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2001.pdf

A diamond-shaped hohlraum ("Frustraum") proposed by Amendt et al. may provide adequate radiation symmetry for large capsules (1500 µm radius) while requiring < 1.8 MJ of laser energy using 3ω light and is capable of providing peak radiation temperature in the 290 ­ 300 eV range. The capsule size can be increased to 1900 µm or larger if 2ω light is used at 2.8 MJ of driver energy and 600 TW of power. The implosion physics and designs for these large capsules are presented here and compared to nominal scale (1100 µm radius) HDC implosions. The fuel adiabat for the large-scale capsules ranges from 2.5 to 6 multiples of the Fermi degenerate limit. Large scale has high 1D margin or Generalized Lawson Criterion e.g., the α = 4 design gives a 2D yield of 20 MJ while the nominal-scale α= 4 design has a 2D yield of only about 0.5 MJ. Lower hard x-ray fraction (14%) from the Frustraum with DU wall results in a neutral Atwood number on the fuel-ablator interface at peak velocity. This reduces mix and gives a high clean fuel fraction of 95%. Large-scale capsules are also robust to fuel pre-heat, hotspot contamination, and tent and fill -tube perturbations. The improved robustness allows the use of liquid-DT foam as a viable fielding option for a 2 ω driver. The disadvantage of large-scale is that the ablation-front growth factor increases with capsule size. Therefore, it is advantageous to use a lower-Z ablator, e.g., boron, to reduce the growth factor. The modeling method used for the large-scale designs is the same for recent large Al capsules in a rugby-shaped hohlraum, which gives close agreement with the data.

This work is supported by LLNL LDRD-17-ERD-119.
1. Amendt et al., APS-DPP 2018 and Amendt et al., to be submitted to Phys. Plasmas 2019.
2. Ping, Smalyuk, Amendt et al., Nature Phys. (https://doi.org/10.1038/s41567-018-0331-5)

Speaker: D. Ho (EPS 2019)

553 P4.2002 Matching laser frequency to electron energy for a Thomson source

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2002.pdf

A Thomson source generates high energy radiation by colliding a laser pulse with an electron beam. This process can be described fully by classical electrodynamics [1]. The bandwidth of the emitted radiation depends, amongst others, by the energy spread of the electrons. When the energy spread is correlated a chirp can be introduced on the laser pulse such that the frequency of the laser is matched to the energy of an electron. Two different geometries have been investigated: an energy spread along propagation and in the transverse direction. For both geometries the bandwidth of the emitted radiation can be reduced to that of the case of a monochromatic electron beam.

References
[1] A. I. Nikishov and V. I. Ritus, Sov. Phys. JETP, 19, 529-541 (1964)

Speaker: M. Ruijter (EPS 2019)

554 P4.2003 High Coupling Efficiency of Foam Spherical Hohlraum Driven by 0.53 micrometre Laser Light

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2003.pdf

The majority of solid state laser facilities built for laser fusion research irradiate targets with third harmonic light (0.35 μm) up-converted from the fundamental Nd wavelength at 1.05 μm. The motivation for this choice of wavelength is improved laser-plasma coupling. Significant disadvantages to this choice of wavelength are the reduced damage threshold of optical components and the efficiency of energy conversion to third harmonic light. Both of these issues are significantly improved if second harmonic (0.53 μm) radiation is used but theory and experiments have shown lower optical to x-ray energy conversion efficiency and increased levels of laser-plasma instabilities resulting in reduced laser-target coupling. We propose to use the 0.53 μm laser for future ignition facilities with a configuration designed for the octahedral spherical hohlraums, and to use a foam wall to increase the coupling efficiency from laser to capsule. The 2-dimensional radiation hydrodynamic code LARED-Integration is employed to simulate and compare the coupling efficiency between the Au foam and the solid Au spherical hohlraums driven by, respectively, the 0.53 μm and the 0.35 μm laser. The simulations show that the reduced optical depth of the foam wall leads to an increased laser-light conversion into thermal x-rays and about $10\%$ higher radiation flux on the capsule than that achieved with 0.35 μm laser irradiating a solid density wall commonly used in laser indirect drive fusion research. A new concept, effective laser to x-ray conversion efficiency, is defined. For laser fusion, this new concept is more accurate in describing the coupling efficiency from laser to capsule than the traditional definition of laser to x-ray conversion efficiency, because most part of the generated x-rays is stored inside the wall instead of transferring into hohlraum cavity to irradiate capsule.

Speaker: Y. Chen (EPS 2019)

555 P4.2004 Measurement of the hot-spot self-emission images and asymmetry tuning by varying beam cone fraction

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2004.pdf

A high degree of spherically symmetric implosion is required for inertial confinement fusion ignition. The self-emission image of hot-spot can be used to describe the integrated compression symmetry. A KB microscopy and an x-ray framing camera (XFC) have been developed for the self-emission image measurement in Laser Fusion Research Center (LFRC). The detailed introduction of these two systems will be given in this talk.
The self-emission images have been measured in the symmetry tuning experiments. The KB microscopy measured the time-integrated image, while the time-resolved images were measured by XFC. Discrepancies of shape distortion have been observed in the images from these two systems. A model based on the 1D radiation-hydrodynamic simulation has been developed to understand the discrepancy.
The experiment has shown the ability of symmetry tuning by varying the cone fraction (CF, the ratio of total inner cone beam energy over total beam energy). Also, we observed the effect of plasma bubbles caused by the laser beams on the driving symmetry.
Keywords: Inertial confinement fusion; symmetry tuning; KB microscopy, x-ray framing camera

Speaker: Z. Chen (EPS 2019)

556 P4.2005 Investigation of spontaneous magnetic fields electron and ion emissions in laser-produced plasma in experiments at PALS

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2005.pdf

Multi-frame femtosecond polaro-interferometry in combination with measurements of electron and ion emission open great opportunities for detailed studies of laser plasma properties in a wide range of applications from the inertial confinement fusion (ICF) to laboratory astrophysics. We present the 3-frame-complex-interferometry investigation of spontaneous magnetic fields (SMF) produced at planar massive and double-layer Cu targets (massive Cu coated by different thickness layers of plastic) irradiated by the 1st harmonic frequency of the PALS iodine laser with intensity above 10^16 W/cm^2. Along with the SMF parameters, the parameters of electron emission were measured by using the 2D Cu K_alpha x-ray imaging and the multi-channel magnetic electron spectrometer. Moreover, the return target current associated to hot electrons escaping the plasma was measured with the use of a current probe, and the angular distribution of ion emission was measured using a grid system of ion collectors. Obtained information allows defining the current density distributions associated with the flow of electrons in ablative plasma, the energy deposited in SMF, the fast electron energy and their spectrum The combined analysis helps to advance in verification of possible absorption mechanisms of laser radiation, which are assumed responsible for energy transport with participation of fast electrons, an important issue in the SI concept of the ICF. 2D numerical simulations with the ATLANT-HE code and an analytical model that include fast electron generation and transport have been used to support the interpretation of experimental data.

Speaker: J. Dostal

557 P4.2006 Experiments and simulations of laser-irradiated additive-manufactured foams

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2006.pdf

In indirect drive inertial confinement fusion (ICF), a high-Z enclosure (or "hohlraum") surrounds a low-Z capsule containing DT fuel. Laser beams irradiate the interior of the hohlraum, creating an x-ray radiation bath that compresses the fuel to ignition conditions. Motion of the irradiated hohlraum wall induces dynamic drive symmetry swings leading to a degradation of the implosion performance. Lining the inside of the hohlraum wall with a low density foam material has been proposed as a method to help control the wall motion thus minimizing the radiation symmetry swings. The interaction of laser radiation with foams of various porosity sizes and densities has been the subject of several numerical and experimental studies [1]. In all cases, modelling low-Z foams (as a uniform gas of the same average density) using standard rad-hydro codes have shown considerably disagreement with experimental observations. We have shown that this deficiency can be largely overcome by taking advantage of modern computer architectures (many processors) coupled to a simple statistical representation of the foams [2]. Recently, developments in additive manufacturing (AM) have allowed for the fabrication of structured foams, thus eliminating the statistical nature inherent in the chemical fabrication process. This technique also allows for composition and density variations that may be beneficial in reducing possible laser backscatter losses. To understand the behaviour of these foams, experiments were carried out at the Jupiter Laser Facility. Foam samples were heated with a single 0.5 micron (green light) laser at 3x10^14 W/cm^2 intensity (conditions similar to ICF implosions). Several materials and structures were tested and the laser-foam interaction was quantified by measuring several aspects of interest to lined-hohlraums dynamics. We use the rad-hydro code HYDRA configured to assess our ability to simulate these foams and to improve our constitutive material models. Here we present comparisons between data and simulations and lay out possible ICF implosion experiments using these foams.

Speaker: J.L. Milovich (EPS 2019)

558 P4.2007 Development of the space-resolving flux detection technique for the localized radiation flux measurement in inertial confinement fusion

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2007.pdf

Space-resolving flux detection (SRFD) is a novel tool for the radiation field diagnostic within the hohlraum in indirect inertial confinement fusion, as it is useful to decouple the radiation fluxes from different positions experimentally[1-4]. The typical spatial coverage of the SRFD system is about 200 um, which is smaller than the size of the laser entrance hole (LEH), and the time resolution is about 150 ps, while uncertainty of the measured radiation flux is less than 15%. The radiation fluxes from the laser spot and re-emitted area within a vaccum cylindrical hohlraum are obtained, and good consistence is found between the experimental data and the numerical simulation with two-dimensional (2D) LARED simulation[1]. Then the radiation flux from the capsule within a gas-filled cylindrical hohlraum is obtained, and it is found to be consistent with the hydrodynamical simulation results. Moreover, this technique is also applied for the radiation flux measurement within octahedral spherical hohlraum, and radiation flux from the laser spot and re-emitted area are obtained, and it proves to be a necessary tool for the radiation field diagnostic in novel hohlraums with more than two LEHs.

[1] K. Ren, S. Liu, L. Hou, et al., Optics Express 23, A1072 (2015).
[2] Kuan Ren, Shenye Liu, Xufei Xie, et. al, Plasma Phys. Control. Fusion 59, 085006 (2017).
[3] X. Xie, K. Ren, H.Du, et al., Journal of Instrumentation 12, P08021 (2017).
[4] Xufei Xie, Huabing Du, Jinwen Chen, et.al, Rev. Sci. Instrum. 89, 063502 (2018)

Speaker: X. Xie (EPS 2019)

559 P4.2009 Interactions of crossing laser pulses in plasma with applications to auxiliary heating

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2009.pdf

It has been suggested that crossing two electron beams within the fusion plasma may increase the energy transfer to the fuel, improving heating of the fuel and possibly pushing the hot-spot over threshold for ignition. The interaction and its dispersion relation were first derived in a theoretical study by Ratan et al. [1]. This interaction is collisionless and so is expected to perform better than collisional stopping for relativistic electron beams. For this reason it shows promise as an auxiliary heating process for conventional hotspot implosions, especially in variants which trade heating for improved implosion stability such as the wetted-foam implosions described by Olson et al. [2].
In this work I present a simulation study of effects observed at a Vulcan laser experiment in which crossing filaments of a channelling laser pulse produced turbulent magnetic field structures observed using proton radiography. This turbulence fits expectations of the cascade of energy from crossing electron beams through Langmuir waves into breaking ion-acoustic waves and the simulations provide insight into the mechanism by which this turbulence is formed.
References
1. Ratan, N. et al. Dense plasma heating by crossing relativistic electron beams. Phys. Rev. E
95, 013211 (1 Jan. 2017).
2. Olson, R. E. et al. First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility. Phys. Rev. Lett. 117, 245001 (24 Dec. 2016).

Speaker: B.T. Spiers (EPS 2019)

560 P4.2010 On the role of non-equilibrium relativistic hot electron populations in Target Normal Sheath Acceleration

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2010.pdf

Laser-driven ion acceleration is a long-standing topic of great appeal in the field of laserplasma interaction, both because of the rich physics at play and the foreseen applications [1]. Various laser-ion acceleration mechanisms have been identified in the literature. Among them, Target Normal Sheath Acceleration (TNSA) has emerged as the most robust and reliable one, being active in a wide range of experimental conditions, including advanced target configurations [2]. Considerable theoretical effort has been put into understanding the role played by several key parameters in TNSA experiments, as for the case of static models that feature a self-consistent electrostatic potential, which have been proven to be a simple, yet effective approximate tool to describe the physics of TNSA [3,4]. In this work, we overcome a number of severe limitations affecting such approach, by proposing a fully relativistic, self-consistent model that includes non-thermal features in the theoretical description of TNSA. By means of an analytical investigation we show how the presence of non-equilibrium features in the relativistic electron population affect the ion acceleration process. In addition, complementary 3D PIC simulations demonstrate that nonthermal processes are particularly relevant, especially in the case of advanced target configurations involving a nanostructured, near-critical plasma layer. Therefore, besides its fundamental interest, the model hereby proposed can serve as a predictive tool to design future experiments investigating enhanced TNSA scenarios.

[1] A. Macchi et al., Reviews of Modern Physics 85.2 (2013): 751.
[2] M. Passoni et al., Phys. Rev. Acc. Beams 19, 061301 (2016)
[3] M. Passoni and M. Lontano, Physical review letters 101.11 (2008): 115001.
[4] D. Bennaceur-Doumaz et al,. Jour. App. Physics 117, 043303 (2015).

Speaker: A. Maffini (EPS 2019)

561 P4.2011 A helicon plasma source for wakefield accelerators

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2011.pdf

The need for higher energies in particle colliders led to the development of several types of particle accelerators, like plasma-based accelerators as a promising concept. The achievable electric fields in a plasma in the order of GV/m [1] exceed by orders of magnitude the conventional electric field generation by RF cavities and scales with the plasma density E(n). Circular accelerators are able to provide high energetic protons which serve as drive to induce plasma wakefields in a linear proton driven wakefield accelerator [2]. A current experiment as design study is the AWAKE project [3] at CERN. To realize a plasma wakefield accelerator, homogeneous, high density plasma columns of n_e ≥ 7 · 10^20m-3 are needed with a sufficiently long discharge duration [4]. The plasma cell must be modular and scalable to the needed target length of up to several 100 m. Such a plasma can be maintained, in principle, by a helicon discharge. The temporal evolution of radial plasma parameter profiles, in particular for neutral and charged plasma species measured by laser-induced fluorescence and corresponding plasma densities measured by a laser interferometer are investigated at the argon plasma cell PROMETHEUS-A. By combining both techniques with a reaction rate model and line-ratio measurements the electron temperature is calculated and compared to the principle of helicon wave heating. Neutral depletion in the center of the discharge and the influence on plasma density evolution is analyzed by calculating the ground state for argon neutrals and ions. It is shown that the maximum plasma density of n_e = 6 ± 1 · 10^20 m-3 is centrally peaked with a maximum electron temperature of 1.4 eV. The plasma density peaking time and width are determined to be 270 µs and 50 µs, respectively. This shows that the requirements for a plasma wakefield accelerator cell can be established. The duration of the peak plasma density is sufficient for a relativistic particle to pass a 1 km long plasma cell. Time-resolved LIF profile measurements show a hollow profile with highest densities at the edges. The ionization mean-free paths indicate increased ionization of neutral argon while dissipating inwards. This results in a depletion of neutrals in the center of the discharge.
References
[1] P. Muggli and M. J. Hogan, Comptes Rendus Physique, 10 : 116 (2009)
[2] A. Caldwell et al., Nucl. Instr. and Methods in Physics Res. Sec. A (2016)
[3] E. Gschwendtner et al., Nucl. Instr. and Methods in Physics Res. Sec. A, 829 (C) : 76-82 (2016)
[4] R. Assmann et al., Physics and Controlled Fusion , 56 (8) : 084013 (2014)

Speaker: N. Fahrenkamp (EPS 2019)

562 P4.2012 Long-term evolution of electron-beam-driven plasma wakefields in radially bounded plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2012.pdf

In plasma wakefield accelerators, intense laser or particle beams drive strong Langmuir waves with the energy density as high as the rest energy of plasma electrons. A large fraction of this energy remains in the plasma after passage of the accelerated beam and causes rapid expansion of the plasma column boundary. Under conditions of FACET experiment [1] with lithium plasma of density 10^17cm^-3, the expansion velocity exceeds 10^6 m/s for over 1 ns. The energy initially stored in coherent electron oscillations first transforms into incoherent motion of plasma electrons with multi-keV velocities and, later, into radial motion of plasma ions. The resulting stream of fast ions escapes the initial plasma channel, penetrates the surrounding neutral gas and creates some "seed" plasma there through impact ionization. Once new ions appear at a given location, more electrons come there and further ionize the gas causing near-exponential growth of the plasma density. The energy needed for gas ionization is small compared to the initial wave energy, so the plasma boundary expands with nearly constant velocity corresponding to the velocity of the fast ion front, with the plasma amount growing proportionally. Numerical simulations that include the described effects show quantitative agreement with results of pstime-resolved optical shadowgraphy that measured evolving plasma density profile at FACET.
References
[1] M. J. Hogan, et al., New Journal of Physics 12, 055030 (2010)

Speaker: K. Lotov (EPS 2019)

563 P4.2013 Divergence and direction control of laser-driven energetic proton beam using a disk-solenoid target

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2013.pdf

A scheme for controlling the divergence and direction of energetic proton beam driven by intense laser pulse is proposed. Simulations show that a precisely directed and collimated proton bunch can be produced by a sub-picosecond laser pulse interacting with a target consisting of a thin solid-density disk foil with a solenoid coil attached to its back at the desired angle. It is found that two partially overlapping sheath fields are induced. As a result, the accelerated protons are directed parallel to the axis of the solenoid, and their spread angle is also reduced by the overlapping sheath fields. The proton properties can thus be controlled by manipulating the solenoid parameters. Such highly directional and collimated energetic protons are useful in the high-energydensity as well as medical sciences.

Speaker: K. Jiang (EPS 2019)

564 P4.2014 Excitation of plasma wakefields by proton drive beam

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2014.pdf

A discussion have been made to demonstrate travelling wave solution for nonlinear relativistic electron plasma wave excited by an intense proton beam. The structures of the excited wake wave electric field and the perturbed plasma electron fluid density are obtained by considering a rectangular proton beam source. This theoretical investigation is primarily aimed to benchmark the proposed AWAKE (Advanced Wake Field Acceleration) experimental programme on proton beam driven plasma wake field accelerator (PDPWFA) at CERN. Alongside an alternative method is adopted to find the stationary wave solution for the wake wave excited by single proton beam as well as equi-spaced train of small proton bunches with the inclusion of the non-relativistic plasma ion dynamics.

Speaker: M. Karmakar (EPS 2019)

565 P4.2015 Proton-boron-11 fusion revisited

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2015.pdf

We revisit the proton-boron-11 (p-B11) nuclear fusion for igniting and sustaining an idealized fusion reactor. The large radiation loss due to electron bremsstrahlung introduces a formidable challenge against harvesting net power in thermalized p-B11 plasmas. However, the recent measurement of the p-B11 cross section provides a new hope. We show that ignition and scientific breakeven can be achieved with the new data. We also discuss the conditions and parameters required for a p-B11 fusion reactor.

Speaker: Y. Li (EPS 2019)

566 P4.2016 Surface plasmon excitation and electron acceleration by a high-intensity laser pulse with wavefront rotation

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2016.pdf

Recently, Pisani et al. [1] have shown the possibility of generating nearly single-cycle (less than 4 fs) propagating surface plasmons at the micro-structured surface of a grating target by a laser pulse with wavefront rotation. Since the surface plasmon can be excited when the grating is irradiated at a specific angle, using wavefront rotation the resonance condition holds for only a fraction of the laser duration, resulting in a few-cycle surface plasmon. Extending this concept to the relativistic regime of interaction [2] is of interest for the development of surface plasmonenhanced ultrashort sources of high-energy electrons and XUV harmonic photons [3]. Using the open-source Particle-In-Cell (PIC) code SMILEI [4], we performed fully self-consistent kinetic simulations of the interaction of relativistically intense laser pulses with wavefront rotation, aiming at characterizing and optimizing the generation of extremely ultrashort high-field surface plasmons and the related acceleration of electron bunches.
References
[1] F. Pisani, L. Fedeli, and A. Macchi, ACS Photonics 5, 1068 (2018).
[2] M. Raynaud et al., Plasma Phys. Contr. F. 60, 014021 (2018), A. Macchi, Phys. Plasmas 25, 031906 (2018).
[3] L. Fedeli et al., Phys. Rev. Lett. 116, 015001 (2016); G. Cantono et al, Phys. Rev. Lett. 120, 264803 (2018).
[4] J. Derouillat et al., Comput. Phys. Commun. 222, 351 (2018)

Speaker: S. Marini (EPS 2019)

567 P4.2017 Impact of the laser pulse parameters on the angular-spectral distributions of protons accelerated from its tight focus

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2017.pdf

Today one of the important issues of the laser technologies is the development of the highpower laser facilities. In despite of the rapid growth of powers, which magnitudes have already broken through the PW values, the problem of achieving the extraordinary intensities and their measurement stays topical. For the considered characteristics of the beams, such as possible peak intensity and tightness of the focal spot, traditional methods of the laser diagnostics in the focal area are out of the applicability range. New methods should take into account the fact that any target will be ionized by such ultraintensity laser field, at the same time phenomena underlying the new technique should depend only on the laser parameters, i.e. they need to be free from plasma effects. The process of the particle (protons or electrons) acceleration can act as such alternative approach. To satisfy the requirement of smallness of the plasma effects, the rarefied gases or ultrathin nanofoils should be used as sources of the charged particles. This report is devoted to the laser diagnostics via proton acceleration. The laser intensities in the range from 10^21 to 10^23 Wcm^-2 do not achieve the relativistic values for protons. It means that the amplitude of the particle oscillations is negligible as compared with characteristic scales of the laser beams. This assumption allows us using approximation of ponderomotive force, which is proportional to the gradient of the laser intensity. Performed calculations show the dependence of the angular-spectral characteristics of protons on the laser parameters, such as peak intensity, spatial distribution, focal spot size and pulse duration, so that the proton acceleration could be used for their diagnostics. However since proton drift is insignificant during the interaction time, temporal form of laser pulse does not affect particle final characteristics (for the same-energy pulses).
This work was supported by RFBR (Grants No. 18-32-00406_mol_a, 18-02-00452_a) and Foundation for the Advancement of Theoretical Physics "BASIS" (No. 18-1-5-102-1).

Speaker: O. Vais (EPS 2019)

568 P4.2018 Physics of the laser-plasma interface in the relativistic regime of interaction

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2018.pdf

The interaction between relativistically intense lasers and near-critical plasmas is a rich field of study, both for basic and applied science, e.g. providing the possibility for producing singularly intense and short XUV bursts of radiation. There are several models describing the highly complex and nonlinear dynamics at the surface of interaction between the laser and the plasma. The relativistic electron spring (RES) model [1] constitutes an example of such, which accurately describes the position and radiation from the electron sheath formed at the vacuumplasma interface. However, the model assumes that the sheath has zero thickness, limiting the possibilities to describe the peak intensity and duration of XUV-bursts, which appear as a singularity of the theory, e.g. depending on the γ-factors for electrons in the sheath. Here, we show that the RES model can be extended to include a description of the γ- distribution of electrons, which is proportional to the thickness of the sheath, or equivalently to its total energy. Guided by analytical estimates and simulations, it is indicated that the layer thickness ∆x ∼ a_0^a, with α ∼0.5, which implies that the similarity normalized quantities γ_max/a^2_0, where max is the maximum γ-factor, as well as W/a^2_0, where W is the energy in the sheath, go to zero for high a_0, showing that a description of properties of the layer relevant for applications (such as the generation of high harmonics) goes beyond S-parameter similarity.
References
[1] A. Gonoskov, A. V. Korzhimanov, A. V. Kim, M. Marklund, A. M. Sergeev, Ultrarelativistic nanoplasmonics as a route towards extreme-intensity attosecond pulses, Phys. Rev. E 84, 046403 (2011).
[2] B. Svedung Wettervik, M. Marklund, A. Gonoskov, Physics of the laser-plasma interface in the relativistic regime of interaction, arXiv:1901.04175 [physics.plasm-ph], 2019.

Speaker: B.F. Svedung Wettervik (EPS 2019)

569 P4.2019 Target curvature influence on particle beam characteristics resulting from laser ion acceleration with microstructured enhanced targets at ultra-high intensity

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2019.pdf

With the latest advances in laser science, the need to produce superior quality ion and electron beams has been a hot research field in the past decade. The hot electron density and temperature in the rear vacuum depend on the target geometrical and composition properties such as target curvature, pulse focusing structures and microdots for enhanced proton acceleration [1-10]. This paper studies the effects of different target density profiles on the spatial distribution of the accelerated particles, the maximum energies achieved, and the characteristics of the photon distribution using the same laser pulse parameters. The study expands the work done in the past [11] describing a curved foil target which presents a proton-rich microdot on its backside, and the effects of the variation of the target curvature while using a cone structure for laser focusing. This work has been done in order to determine which is the optimal target curvature at which the accelerated particle bunch is best collimated while still achieving optimal particle energy. For this purpose, we have investigated the proton energy and angular distributions by means of two-dimensional (2D) particle-in-cell (PIC) simulations of the interaction of ultra-short laser pulses with several microstructured target geometries using the PICLS code [12].

References:
1. J. H. Bin et al., Phys. Plasmas 16, 043109 (2009).
2. D. Dahiya et al., Laser and Particle Beams 33, 143 (2015). 3. A. A. Andreev and K. Yu. Platonov, Contrib. Plasma Phys. 53, 173 (2013).
4. Y. Sentoku et al., Physics of Plasmas 11, 3083 (2004).
5. N. Renard-Le Galloudec and E. d'Humieres, Laser Part. Beams 28, 513 (2010).
6. D. Margarone et al., Phys. Rev. Lett. 109, 234801 (2012). 7. H. Schwoerer et al., Nature 439, 445 (2006).
8. B. Qiao et al., Phys. Rev. E 87, 013108 (2013).
9. C. McGuffey et al., in Conf. on Lasers and Electro-Optics (Optical Soc.of America 2013), pp. TuD4_1.
10. M. Zakova et al., in SPIE Optics+Optoelectronics, (SPIE 2015), pp. 95151F.
11. D. Tatomirescu et al., AIP Conf. Proc. 1796, 020013 (2017); D. Tatomirescu et al., AIP Conf. Proc. 1916, 030002 (2017).
12. Y. Sentoku and A. Kemp, J. Comp. Phys. 227, 6846 (2008).

Speaker: D.E. Tatomirescu (EPS 2019)

570 P4.2020 Identifying quantum radiation reaction by using colliding ultra-intense lasers in gases

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2020.pdf

In the past year, huge progresses have been made to detect radiation reaction effect in the collision of an ultraintense laser and a high-energy electron beam.
However, there still remain large uncertainties on the quantum effect of radiation reaction.
Here, we propose a scheme for identifying the quantum radiation reaction effect on relativistic electron motion in strong electromagnetic fields, where two ultraintense lasers are used to collide with each other in a tenuous gas.
Different from the previous method by laser-beam collisions, in which the radiation reaction effect is evidenced by the energy loss in the electron energy spectrum, here the transition between the classical and quantum radiation reaction regimes is distinguished from the angular distribution of the total electron radiations. With no need of additional relativistic electron beams, the
scheme is more robust and easily achievable in experiments. Both theory and 2D particle-in-cell simulations show that the classical radiation dominates in the transverse direction perpendicular to laser axis, forming a dipole-like pattern, while that in the quantum regime dominates at four diagonal directions, constituting a butterfly-like structure.

References
[1] J.M. Cole, et al. Phys. Rev. X 8, 011020 (2018)
[2] K. Poder, et al. Phys. Rev. X 8, 031004 (2018)
[3] X.B. Li, B. Qiao, et al. Phys. Rev. A 98, 052119 (2018)

Speaker: X. Li (EPS 2019)

571 P4.2022 Generating bright gamma-ray pulses via ultra-intense laser colliding with a flying plasma layer

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2022.pdf

With the forthcoming laser intensities (I≥10^23 W/cm^2), synchrotron radiation in a laser-plasma interaction has attracted particular interest because it can lead to an extremely bright source of γ-rays. Here, a scheme to generate a bright γ-ray pulse with high efficiency is proposed and numerically demonstrated. Using a circularly polarized (CP) laser pulse impinged on a thin foil, a relativistic flying plasma layer is formed. With another counterpropagating CP pulse colliding with the flying layer, it is found that the electrons are efficiently accelerated in the longitudinal direction by the space-charge field. The energetic electrons interact with the counterpropagating CP pulse, producing ultra-brilliant (~10^24photons/s/mm^2/mrad^2/0.1%BW) highly dense (~270nc) femtosecond (~5 fs) γ-ray pulses. At a moderate laser intensity of 4x10^22 W/cm^2, the fraction of laser energy transferred into the γ-ray pulse is as high as 10%, which is comparable to that previously predicted for an order of magnitude higher in laser intensity. The enhanced γ-photon emission might pave the way for its potential applications in the near future.

Speaker: Z. Zhang (EPS 2019)

572 P4.2023 Researches on laser driven neutron source and applications in Japan

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2023.pdf

Laser driven neutron sources and their applications have been explored in the projects of the A-STEP program of the JST, since 2016 at ILE, Osaka University and GPI, Hamamatsu. In this paper, the status and prospects of the projects are overviewed.
In the neutron source research, the pitcher-catcher schemes with the LFEX laser at ILE and repetition rate short pulse laser at HPK and GPI were studied. In the LFEX experiments, we carried out the efficient laser ion acceleration experiments, where the 0.5-1 kJ, multi picosecond pulse irradiated CD thin foils for accelerating deuterons which are injected into the Be catcher. The total neutron yield reaches more than 10^11 n/sr/shot (namely, 10^8 n/shot/sr/J) which is the world record of this type neutron source. Those neutrons were used to demonstrate the fast neutron imaging of infrastructure. The higher ion and neutron yield are realized by forming a pre-plasma in the TNSA in the preliminary experiments. The yield of proton beam of the energy higher than 10 MeV reaches 10^14 /shot. The neutron yield will increase to higher than 10^9 n/J according to the simulation. The photo neutron produced by interaction of laser multi MeV gamma rays with high Z target is also investigated to develop a collimated short pulse neutron source.
The neutron is partially moderated by a compact moderator, therefore the pulse duration of the moderated neutron beam is much shorter than the accelerator driven neutron source. Therefore, X-ray image and neutron image can be taken by temporally resolved imaging. The actual example of the image will be discussed in the conference.
The neutron imaging technologies such as the nuclear resonance imaging, the compact moderator design for pulse laser neutron source and so on are also investigated. We will also present that the fast neutron imaging was demonstrated by using the RNSA neutron beam of RIKEN to achieve higher S/N with the fast imaging technique.

Speaker: K. Mima (EPS 2019)

573 P4.2024 Light-shining-through-wall searches for axion-like particles using laser-driven plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2024.pdf

Not all key questions in fundamental physics can be readily investigated using conventional high-energy particle collider technology. In particular, alternative methods are required to search for novel low mass particles with very weak coupling to ordinary matter. It is anticipated that the next generation of high-intensity laser facilities will offer vital new methods for investigating axion-like particles, or ALPs, which are natural by-products of string theory. ALPs are relatives of the QCD axion, which remains the most popular explanation for the lack of CP violation in the strong interaction. Furthermore, ALPs and QCD axions remain popular candidates for dark matter, and confirmation of their existence would be an outstanding milestone in fundamental physics.

Thus far, most of the work devoted to high-intensity laser-based searches for ALPs have focussed on the interplay between laser pulses in the vacuum. However, our approach exploits laser-plasma interactions; in particular, we suggest that combining the laser-wakefield accelerator paradigm with state-of-the-art magnet technology provides an interesting alternative to conventional searches for ALPs. We will introduce our new approach to "light-shining-through-wall" searches for ALPs [1], and discuss recent developments.

[1] David A Burton and Adam Noble 2018 New J. Phys. 20 033022.

Speaker: D.A. Burton (EPS 2019)

574 P4.2025 Powerful X-ray plasma radiation as a result of high-energy plasma flows collision

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2025.pdf

Experimental results related to soft X-ray (SXR) radiation generated during a head-on collision of two low-temperature plasma flows immersed in a longitudinal magnetic field are presented. The plasma flows with velocities of (2-4)x10^7 cm/s and energy contents of 70-100 kJ were produced in these experiments by a pair of counter-facing electrodynamic coaxial plasma accelerators with pulsed gas injection. Nitrogen and neon, as well as their mixtures with deuterium, were used as plasma-forming gases.
Diagnostic equipment is described, and the results obtained under different operating conditions are discussed. Measurements provided by a set of photodiodes covered by different filters showed that SXR (photon energies from 0.4 to 1 keV) pulses with the duration of 10-15 μs and total energy of 2-10 kJ were generated in collisions of two plasma flows. Also, Xray spectroscopy was used to study the high-temperature plasma produced during a collision of these plasma flows. Observed intensities of spectral lines were compared with results of detailed kinetic calculations performed in a steady-state approximation. In the experiments with plasma flows containing nitrogen ions, the electron temperature in a central part of the plasma column was found to be 120-130 eV, whereas in the experiments with neon plasma flows it was at the level of 160-170 eV. At the same time, the temporal evolution of the plasma electron temperature in this cross-section of the plasma volume was determined with help of the absorber foils method based on the X-ray continuum plasma emission registration by the detectors covered by different filters. The plasma electron temperature was at the level of 170-200 eV both in the nitrogen plasma and in the neon plasma.
Also, some preliminary experimental and numerical results concerning plasma flow interaction with a gas jet are reported.
This work was supported by the Russian Foundation for Basic Research (Project No. 18-29-21013).

Speaker: D. Toporkov (EPS 2019)

575 P4.2026 Towards separated Doppler harmonics through the lighthouse effect

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2026.pdf

When an ultra-intense, femtosecond laser irradiates a solid target, an over dense plasma is generated at the target surface, acting as a non linear reflective media for the incident laser (known as a plasma mirror) that reflects the incident fields and emits a train of attosecond pulses of X-UV radiation . For ultra-high laser intensities (I >= 10^19W.cm^-2 for λ = 0.8µm), the laser field induces a relativistic motion of the plasma surface, leading to a strong and periodic Doppler shift of the laser field, each optical laser cycle. This periodic modulation in the form of an attosecond pulse train is associated to a high-harmonic spectrum in the frequency domain. To generate isolated attosecond pulses instead of trains of such pulses, which are more convenient for time-resolved experiments, an approach has recently been proposed in [1], known as the attosecond lighthouse effect. This technique consists in introducing a controlled spatio temporal coupling (STC) on the incident laser field. This STC leads to a wave front rotation at focus. Hence, attosecond beams are emitted in different directions and a single pulse can be spatially filtered in the far field. This approach has been successfully applied to harmonics in gases and solid targets in non-relativistic regime (through Coherent Wake Emission process) using a fewcycle lasers(~5 fs). Nevertheless, it has never been successfully applied to Doppler harmonics as those are usually generated with many cyle laser beams (typically ∼25 fs) which leads to a drop of pulse separation. Moreover, separating attosecond pulses in the relativistic regime supposes very short gradient lengths, which leads to a significant drop in harmonics generation efficiency. In this study, we propose an optimized scheme to separate Doppler attosecond pulses based attosecond lighthouse effect with realistic experimental setup. For this purpose we have conducted an extensive numerical and theoretical study in order to assess optimal parameters for pulse separation in the relativistic regime. Our study shows that pulse separation efficiency can be improved by introducing a spatial shift between the target and the laser focus, in order to reduce harmonics divergence. This study also shows that maximizing wave front velocity is not necessarily optimal for pulse separation. A numerical model that predicts optimal separation parameters has been developed and confronted to first principle Particle In Cell simulations.
References
[1] H. Vincenti, F. Quere. Phys. Rev. Lett. 108, 113904 (2012).

Speaker: H. Kallala (EPS 2019)

576 P4.2027 Progress of the light-ion laser acceleration beamline at the ILIL-PW

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.2027.pdf

A Laser driven Light Ions Acceleration Beamline (L3IA) has been established recently based on the high intensity femtosecond laser system recently upgraded and now routinely operating at >100 TW peak power at the ILIL-PW laser facility at INO. The original concept of the beamline relies on the Target Normal Sheath acceleration mechanism to generate light ions with MeV energy to use for material science and radiobiology applications. In the poster we will describe the most recent experimental results obtained using thin foil targets where accelerated ions were characterized using a wide range of detection techniques, optimized for the severe conditions typical of a laser-plasma acceleration environment. Data show ion energy up to 7 MeV, with significant shot-byshot fluctuations as typical of the TNSA mechanism. The origin of these fluctuations is being investigated including possible role of target imperfections, laser-beam energy, pulse duration and pointing stability. Further enhancement of the ion energy is being pursued via further increase of the laser intensity in the focal region, to be obtained by correction of the residual laser beam phase front distortions to increase the Strehl ratio, currently approaching 70%, and by further increasing the pulse energy, as planned in the next phase of the laser upgrade. At the same time, advanced targets are also being explored with special attention to nanostructured targets, including nano-pillars and porous materials that are used for their role of modifying the laser-target interaction regime, affecting the generation of fast electrons, namely their phase space distribution. This is mainly investigated via characterization the properties of the fast electron and the high energy ions escaping from the target. Preliminary results show that a key role is played in these measurements by the level of interstitial plasma filling gaps and cavities in the target, before the ultrashort laser pulse hits the target. This can be controlled by changing the temporal contrast of the laser pulse. Our approach to these studies will also be described in the poster.

Speaker: L.A. Gizzi

577 P4.3001 Molecular dynamics study of structural phase transition in a dusty plasma bilayer

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3001.pdf

The crystalline bilayers formation in dusty plasma medium depicted by the Yukawa interaction amidst dust grains has been investigated using molecular dynamics simulations [1]. Charged dust grains are made to levitate in two distinct layers forming bilayer structures in the presence of a combined gravitational and external electric field force (representing the sheath field in experiments). The structural properties of these bilayer systems have been investigated in detail identifying them with the help of pair correlation functions and Voronoi diagrams. It has been shown that each of these crystalline layers undergo a structural phase transition from hexagonal (often also referred to as triangular) to square lattice configurations when the three-dimensional effects arising from the interaction amidst particles in different layers become important. By calculating the ensemble averaged angle between lattice vectors, it is shown that these structural transitions are completely re-entrant type.
1. Srimanta Maity and Amita Das, Physics of Plasmas 26, 023703 (2019).

Speaker: S. Maity (EPS 2019)

578 P4.3002 Numerical simulation of Penning gas discharge in 2D/3D setting

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3002.pdf

This work presents a numerical simulation of the Penning discharge in 2D/3D formulation. The simulation is based on the electrostatic Particle-In-Cell (PIC) method using structured rectangular grids and implemented in the VSim [1] software package. To simulate the kinetic processes in a gas-discharge plasma, the Monte-Carlo collision method was used. The calculations were carried out for several sets of chemical kinetics reactions, and their comparison is given. Various characteristics of the Penning discharge in 2D and 3D formulation were calculated, such as anodic/cathodic currents, the distribution of charged particles in space and energies, etc. Dependences of the discharge current on the applied external magnetic field obtained experimentally and numerically are in reasonable agreement. The experiment [2] show that there exists Imax and corresponding Bmax after which further increase in B leads to decrease in I. Our calculations showed that a similar behavior of the discharge current is observed in the simulation. Such a behavior of the discharge current from the magnetic field is due to the disturbance of the axial symmetry of the field ϕ and the redistribution of electrons.
References
[1] C. Nieter, J.R. Cary, VORPAL: a versatile plasma simulation code, Journal of Computational Physics 196, 2004
[2] A.V. Sy, Advanced Penning-type source development and passive beam focusing techniques for an associated particle imaging neutron generator with enhanced spatial resolution, Berkley: University of California, 2013

Speaker: A. Rokhmanenkov (EPS 2019)

579 P4.3003 On confinement and plasma acceleration from a small ECR plasma source

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3003.pdf

The use of the Electron Cyclotron Resonance (ECR) for electron heating for Magnetic Nozzle (MN) thrusters have recently received increased interest, as they have been shown (Cannat et al, Phys. Plasmas, 22, 053503 (2015)) to provide improved thrust efficiency up to 16% at only 30 W input power. Such performance make such thrusters viable for use on small, e.g. Cubesat, spacecraft. An ECR plasma source similar to that described by Jarrige et al., 35th Int. Electrical Prop. Conf., Atlanta, USA, Oct. 8-12, 2017, IEPC-2017-382, was recently installed in a 30 cm diameter and 60 cm long cylindrical chamber at UiT. This source is grounded, as opposed to the previously described one, which is shielded from ground. The source consists of a cylindrical sleeve antenna of diameter 2.6 cm, and was operated at 10 - 20 W, at mass flow rates from 0.2 - 0.8 mg/s, which result in pressures ranging from 0.08 - 0.3 Pa. High-resolution radial profiles of plasma parameters were obtained by means of Langmuir, ion energy analyzer and Mach probes, at two different axial positions 20 cm and 50 cm from the source, i.e. in the far plume of the source. The configurations were i) a monotonous expanding magnetic field, ii) a bottle-shaped magnetic field, and iii) a nearly homogeneous magnetic field with straight lines. Here, we will focus on results with the monotonous expanding magnetic field. Results in terms radial profiles of density n_e, electron temperature T_e, plasma potential V_p, and ion energy with respect to the background plasma potential is reported and compared to available models and previous experimental results. While the plasma stream from the source has come to a complete halt at 50 cm from the source, the speed of the ions at 20 cm equals the ion sound speed of about 4.4 km/s.

Speaker: A. Fredriksen (EPS 2019)

580 P4.3004 One dimensional kinetic model of an inverted sheath in a bounded plasma system

See full abstract here: :
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3004.pdf

A one-dimensional kinetic model of an inverted sheath [1] is presented. The model is based on a bounded plasma system model, introduced by Schwager and Birdsall [2]. A onedimensional bounded plasma system is considered. The system is bounded by two very large planar electrodes perpendicular to the x axis. The left hand electrode is called collector and the right hand electrode is called the source. The source is at zero potential, which is taken as the reference. The collector is electrically floating with respect to the source. The source injects electrons (plasma electrons) and singly charged positive ions into the system, both with half-Maxwellian velocity distributions and different temperatures. Collector absorbs all the particles that reach it, but it also emits electrons (emitted electrons) also with halfMaxwellian velocity distribution and their own temperature. It is assumed that potential decreases monotonically from the collector to the source. Based on this assumption and the assumption that the energy of the particles is conserved cutoff Maxwellian distribution functions of all 3 particle species are `'derived''. Zero moments of the distribution functions give particle densities and first moments give fluxes. Based on this the Poisson equation and the floating condition of the collector is written. At a certain position the plasma is neutral and at this point the potential has inflection point. Two first integrals of the Poisson equation give 2 equations that give electric fields at the collector and at the source. The floating condition, the neutrality condition at the inflection point and 2 electric field conditions give 4 basic equations of the model from which the floating potential, the inflection point potential and electric fields at the source and at the collector can be found, if the other parameters are selected. It is then shown that stable inverted sheath [1] potential profiles are possible in such a bounded plasma system, provided that injections of positive ions and emitted electrons are both sufficiently large.

References
[1] M. D. Campanell, A. V. Khrabrov and I. D. Kaganovich, Phys. Rev. Letters, 108, 255001 (2012).
[2] L. A. Schwager and C. K. Birdsall, Phys. Fluids B, 2, 1057, (1990).

Speaker: T. Gyergyek (EPS 2019)

581 P4.3005 Oxygen production by CO2 dissociation using a pulsed plasma discharge for Mars missions

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3005.pdf

Any future space missions involving people on board must solve the problem of oxygen required for life support. In the case of Mars oxygen is not present in the rarefied atmosphere. We suggest a possible approach to solve the oxygen problem for Mars missions by the use of a high power coaxial plasma gun to split the dioxide carbon molecule in the fundamental components [1]. The Martian atmosphere is made up mainly of CO_2 (95.9%), Ar (1.9%), and N_2 (1.9%). Carbon dioxide can be split into oxygen for life necessities and CO that can be used as propellant for space travel. To dissociate CO_2 we use a coaxial plasma gun using two electrodes made of tungsten. The coaxial plasma gun is powered by a capacitor charged up at 1 to 2 kV. The ejected plasma has a peak electron temperature of 5~15 eV and a peak electron density of ~10^21 m^(-3). Spectroscopic analysis of several oxygen emission lines (e.g. 615 nm and 777 nm) in the discharge at a pressure in the range 1-5 torr show a clear dissociation of CO_2, which depends of the amount of power injected into the discharge.

[1] C.M. Ticos, A. Scurtu, D. Ticos, New J. Phys. 19, 063006/1-11 (2017).

Speaker: A. Scurtu (EPS 2019)

582 P4.3006 PIC/Monte Carlo Simulation of Dielectric Barrier Discharge in Argon Plasma at atmospheric pressure

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3006.pdf

Interest in dielectric barrier discharges (DBD) for plasma actuators has seen an important growth in the last years. A barrier discharge occurs when an alternating high voltage is applied to conductive electrodes, at least one of them covered with a dielectric layer, allowing only the passage of the displacement current. One-dimensional models for the dielectric barrier discharge dynamics are based on the numerical solution of the electron and ion continuity and momentum transfer equations coupled to Poisson equation. Particle-In-Cell (PIC) simulations take into account the detailed kinetic behavior of charged particles, which is not achievable in fluid simulations [1]. The present work deals with the study of plasma behavior in a parallel-plate dielectric barrier discharge (DBD) by a one-dimensional particle-in-cell/Monte Carlo collision model in argon, at atmospheric pressure. The top dielectric plate is bounded by a planar metal electrode and the bottom dielectric boundary is connected to the grounded electrode. In the model, electron-neutral collisions, both elastic and inelastic, have been considered. In particular, superelastic collisions and electron impact ionization have been accounted for [2]. In the Poisson solver, the surface charge accumulation on all dielectrics are included by selfconsistently accounting for the deposited surface charges, as well as the dielectric coefficients. Moreover, perfect dielectrics have been considered with null conductivity and no charge leaking. The kinetic model has been coupled self-consistently with a proper electric circuit model. Results show the effect of superelastic collisions on the discharge and, in particular, on the electron energy distribution function which is typically calculated by considering inelastic collisions only with ground state neutrals.

References
[1] E. Boella, G. Coppa, A. D'Angola, B. Peiretti Paradisi, Computer Physics Communications 224, 136 (2018)
[2] G. Colonna, G. D'Ammando, L.D. Pietanza, Plasma Sources Science and Technology 25, 054001 (2018)

Speaker: A. D'Angola (EPS 2019)

583 P4.3007 Picosecond laser-induced ablation techniques for depth-resolved quantitative analysis of plasma-facing components

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3007.pdf

Monitoring the fuel content in plasma-facing components is essential to get a detailed understanding of the plasma-wall interaction. Laser-induced material analysis is frequently used in fusion devices [1, 2], but there is a lack of diagnostics which can provide depth resolved and quantitative information when no reference sample can be manufactured. We present a post mortem analysis using laser-induced breakdown spectroscopy (LIBS) combined with quantitative residual gas analysis (RGA) after picosecond laser ablation for this challenge.
Using a laser spot diameter of 700 µm on the sample and an intensity of ~150 GW/cm^2, typical material ablation rates are ~100 nm per laser pulse for graphite and ~30 nm per pulse for tungsten. With short pulse durations of the laser ( τ= 35 ps) and a wavelength of λ= 355 nm, the ablation rates are in the same order of magnitude as heat and optical penetration depth of the laser. Thus, sequential ablation steps offer a depth-resolved analysis of the material composition using picosecond laser-induced breakdown spectroscopy (ps-LIBS). Volatile components are detected by a calibrated quadrupole mass spectrometer, providing quantitative concentrations without the need for reference samples. The simultaneously operated techniques are applied for post mortem analysis of plasma-wall interaction processes like erosion, deposition and fuel retention of Wendelstein 7-X graphite tiles [3]. In this work we focus on the application for retention measurements of deuterium in tungsten as preparation of a potential in situ application in fusion devices. Particle densities as low as 1x10^20 deuterium atoms per cm^3 could be quantified.

References
[1] V. Philipps, A. Malaquias, A. Hakola, et al., Nuclear Fusion 53, 93002 (2013).
[2] C. Li, CL. Feng, H.Y. Oderji, et al., Frontiers of Physics 11, 114214 (2016).
[3] J. Oelmann, C. Li, S. Brezinsek, et al., Nuclear Materials and Energy 18, 153-158 (2019)

Speaker: J. Oelmann (EPS 2019)

584 P4.3008 Current-Voltage analysis in SDBD plasma discharge

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3008.pdf

The aim of this project is to study the current-voltage properties in a Surface Dielectric Barrier Discharge (SDBD) plasma. Our plasma device is made by a 3 mm thickness dielectric barrier in Teflon and two 12 cm long conductive electrodes applied on the opposite side with 2 cm overlapping. One of the electrode is feed to the high voltage (HV) and is buried, while the other is conneted to the ground. We apply a radiofrequency (RF) power between 20-40 W. The multiplicative factor from the RF generator to HV transformer goes from a minimum of 450 to a maximum of 650 depending on the applied voltage.
We used an homemade Rogowski coil to collect the current associated to the plasma. Our probe is such that the displacement current is not detectable so the current is due to only the plasma contribution. We collected the temporal series of the plasma current by varying the RF generator voltage in the range between 7 to 14 V with 1 V step. We defined the region of HV phase in which current spike are concentrated. Subsequently we studied the statistical properties of the current spike, such as maximum intensity, time duration, charge collection and HV phase position.
This work is preparatory for the study of the VOC abatement to find a link between plasma current properties and the noxious molecules depletion.

References
[1] I.Biganzoli, R.Barni, and C.Riccardi, Review of Scientific Instruments, 84, 1 (2013), 10.1063/1.4773233
[2] I.Biganzoli, Ph.D. Thesis, Characterization of Atmospheric Pressure Plasmas for Aerodynamic Applications

Speaker: C. Piferi (EPS 2019)

585 P4.3009 Precursor phenomena ahead of a re-entry vehicle into Earth atmosphere

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3009.pdf

Thermochemical and radiative transfer processes in a shock layer should be clarified to develop a future space vehicle because of their affecting the aerodynamic forces and heating rates. Although the two-temperature model has been utilized widely for a long time, the accuracy of the reaction rate coefficients might be not enough due to its being deduced from the limited experimental data which is different from those of an actual vehicle flight. In this study the chemical reaction process in the shock layer is investigated by observing not time-frozen but temporal radiation profiles in a re-entry flight condition and comparing with the calculated ones with the two-temperature model. We predict that these profiles will not coincide and the reason for the discrepancy would come from the precursor phenomena, which is photochemical and excitation reactions ahead of the shock wave and re-absorption of radiation emitted from a shock layer.
The shock tube facility is shown in Fig.1, which can generate the normal shock speed of 6.0 km/s under the pure N_2 gas pressures of 50 and 100 Pa. Time-resolved emission spectroscopy is applied to measure the temporal profile of radiation emitted from the shock layer through the test section. Radiations of N_2 (2+) (1, 0) band head, N2+ (1-) (0, 0) band head and N 3p 4S0 - 3s 4P triplet are targeted in the study. The calculated flow with the two-temperature model is one-dimensional, and the species considered here are N2, N, N2+, N+ and e-. Therefore, a thermal nonequilibrium is considered.
The experimental and numerical results are shown in Fig.2. The precursor radiation of N_2^+ ahead of the shock front indicates photoionization reaction occurs far from the shock front. The fast decline of the measured radiation intensity means the precursor phenomena has a great influence on chemical reactions

Speaker: H. Kawazoe (EPS 2019)

586 P4.3010 Propagation of atmospheric pressure argon plasma jet impinging on targets with different conductivity

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3010.pdf

Atmospheric pressure plasma jets (APPJs) today serve as a tool for treating various surfaces from metals to polymers and biological tissues sensitive to temperature [1]. Adhesion, hydrophilic and bacteriostatic properties of the surface can be changed under plasma treatment. The latest studies showed that not only the plasma affected the object, but also the object could influence the plasma. It was shown in [2] that the target conductivity influenced on the production of reactive species in the plasma. This work was conducted to study the jet propagation, its current and intensity in dependence of the target. An electrophysical installation consisted of a DBD plasma jet source [3] with a solid-state power pulse supply system [4], targets with different conductivity: copper with σ= 6x10^7 S/m, medical conductive gel Uniagel with σ = 1 S/m and plexiglass with σ = 10^-13 S/m, and a diagnostic unit that allowed measuring the jet current and the jet intensity while propagating in the air. Rectangular unipolar pulses with an amplitude of 4-6 kV at 3 kHz frequency from the source were applied to the electrodes. The APPJ was formed in the air when pumping the tube with argon with a rate of 4 litres per minute. The plasma jet impinged on the target, located at a distance of 1.5 cm from the tube outlet. As a result, it was found that the presence of the target changed the parameters of the plasma jet. The conductivity of the target affects both the jet current amplitude and the jet intensity. This work was partially supported by the RFBR, grant N 19-08-00069a.

References
1. Winter, J., Brandenburg, R., & Weltmann, K. D. (2015). Atmospheric pressure plasma jets: an overview of devices and new directions. Plasma Sources Science and Technology, 24(6), 064001.
2. Koné, A., Sainct, F. P., Muja, C., Caillier, B., & Guillot, P. (2017). Investigation of the Interaction between a Helium Plasma Jet and Conductive (Metal)/Non-Conductive (Dielectric) Targets. Plasma Medicine, 7(4).
3. Moshkunov, S. I., Podguyko, N. A., & Shershunova, E. A. (2018, November). Compact high voltage pulse generator for DBD plasma jets. In Journal of Physics: Conference Series (Vol. 1115, No. 2, p. 022032). IOP Publishing.TCL
4. Moshkunov, S. I., Khomich, V. Y., & Shershunova, E. A. (2019). A high-voltage switching supply for cold plasma jets. Technical Physics Letters, 45(2), 93-95.

Speaker: E.A. Shershunova (EPS 2019)

587 P4.3011 RF power transfer efficiency of low pressure ICPs in light molecular gases

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3011.pdf

Inductively coupled plasmas (ICPs) are a widespread and versatile radio frequency (RF) driven plasma generation technique. Thus, significant efforts have been made to optimize them according to the individual requirements at hand. The analysis of the RF power transfer efficiency - or analogously of the plasma equivalent resistance - has been of particular interest. Both quantities describe the power absorption by the plasma, since not all of the delivered RF power is necessarily coupled to the plasma itself. Even if an ideal match between the generator and the load is achieved, substantial transmission losses can occur, originating e.g. from ohmic heating of the coil and the RF network. Most of the fundamental investigations of the RF power transfer in low pressure ICPs and its dependence on pressure, power or excitation frequency have been conducted in noble gas discharges, whereas light molecular gases such as hydrogen or deuterium are scarcely treated. However, the multitude of additional processes in molecular discharges such as ro-vibrational excitation or dissociation can have a distinct impact on the plasma parameters which determine the power transfer. Thus, the transferability of results obtained in noble gases to molecular discharges is not necessarily provided without limitation.
Accordingly, experimental investigations of the RF power transfer efficiency of low pressure H_2/D_2 ICPs in a broad parameter range are presented and compared to corresponding results obtained in noble gases. The studies are conducted at a cylindrical setup in the pressure range between 0.3 and 10 Pa and for different excitation frequencies between 1 and 4 MHz at RF powers up to 1 kW. By applying a subtractive method which quantifies the transmission losses within the plasma coil and the RF network, the RF power transfer efficiency is determined. The key plasma parameters of the discharges are measured via optical emission spectroscopy and a double probe, which allows to discuss the obtained power transfer efficiency against the background of electron heating and the influence of atoms in molecular discharges.

Acknowledgement
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: D. Rauner (EPS 2019)

588 P4.3012 Role of Oxygen in nanoparticle structure and composition under various sputtering discharges

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3012.pdf

The properties of nanoparticles (NPs) depend on their shape, size, chemical composition, inner structure (atom arrangement) as well as their adhesion forces, the later determining the final state of collected aggregates. It is shown here that there are differences of structure and chemical composition of NPs which are produced from tungsten cathode sputtering in magnetron discharge and conventional sputtering discharge (without magnetic field). These differences mainly due to the presence of oxygen are discussed according to the presence or not of an oxide layer at the cathode surface, the residual oxygen in the device and the device venting.
An usual method to remove a cathode oxide layer is the sputtering at low pressure and high input power. After this operation, NPs which are grown from tungsten sputtering in magnetron discharges are of core-shell type when they are analyzed after several days of air exposition. The core is mainly a mono-crystal in the metastable beta-tungsten phase and the shell is made of tungsten oxide. The origin of the metastable phase is attributed to the presence of residual oxygen in the device. Since this phase transforms into the stable alpha-tungsten phase by annealing [1], a standard model on the thermal balance of nanoparticles was used to find the temperature that they can reach under the considered experimental conditions. It is shown that this temperature is significantly higher than the gas one but not high enough to transform the metastable beta-phase during the plasma process.
Similar experiments were performed in sputtering glow discharges. In such a case, to remove the tungsten oxide of the cathode is particularly tricky at low pressure (no plasma breakdown). Hence, the effect of sputtering the oxide layer at a pressure where the nucleation appears is to produce NPs in tungsten oxide (W03) with no control of the oxygen content in the device.

[1] T. Karabacak, P-I. Wang, G-C Wang, T-M Lu, Thin Sol. Films 493, 293 (2005)

Speaker: C. Arnas (EPS 2019)

589 P4.3013 Rotational and vibrational temperatures of the OH A2Sigma state for several different plasma sources

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3013.pdf

The resonant transition A^2Σ → X^2Π of the hydroxyl molecule OH is studied in detail in the wavelength range 280-330 nm. Emission from an atmospheric glow discharge, an RF micro jet plasma, a microwave torch as well as a plasmoid are considered. The parent molecule to the OH molecule is water vapor for each of the plasma sources. Water, in turn, is either the main gaseous constituent, an intentional admixture to the discharge gas or an impurity to the discharge. For comparison the spectrum of a low pressure ICP discharge in a gas mixture of 85 % H_2 and 15 % O_2 is studied. Analysis of the spectra is performed by using the LIFBASE Spectroscopy Tool [1].
The determined population temperatures strongly depend on the specific discharge under observation: virtually thermal equilibrium between vibrational and rotational populations could be observed, as well as two-temperature rotational populations, and spectra which are strongly affected by quenching processes. The relevance of these aspects for spectra fitting is discussed. Where possible, comparison of the obtained temperatures to rotational and vibrational temperatures of the hydrogen [2, 3] or nitrogen molecule [2] in view of the gas temperature is performed [4].

Acknowledgement: The authors thank J. Golda and J. Benedikt from Christian-Albrechts-Universität zu Kiel, M. Fiebrandt and P. Awakowicz from Ruhr-Universität Bochum, and E. Carbone from MaxPlanck-Institut für Plasmaphysik in Garching for providing OH emission spectra from their respective discharges.

References
[1] J. Luque and D. R. Crosley, SRI International, 1999.
[2] S. Briefi, D. Rauner and U. Fantz, J. Quant. Spectrosc. Radiat. Transf. 187, 135 (2017).
[3] U. Fantz and B. Heger, Plasma Phys. Control. Fusion 40, 2023 (1998).
[4] P. J. Bruggeman, N. Sadeghi, D. C. Schram and V. Linss, Plasma Sources Sci. Technol. 23, 023001 (2014).

Speaker: R. Friedl (EPS 2019)

590 P4.3014 Schlieren imaging and flow simulation results of an axial injection torch

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3014.pdf

METU Plasma Research Laboratory microwave plasma torch is a high power (up to 2kW) microwave source operating at 2.45 GHz via a surfaguide waveguide. Argon gas is fed from one end, the plasma column generated inside a 20 mm diameter quartz tube comes out as a high-speed continuous jet from the other end. Due to its geometry, this type of microwave torches is referred to as TIA "Torche a Injection Axiale" in the literature [1]. In general, TIAs can be used for numerous plasma applications including surface treatments of materials, nanopowder synthesis and for the production of carbon nanotubes. Some of these applications may require a certain understanding of the plasma flow and target interactions. In our studies, we mainly focus on the flow analysis of the plasma jet coming out of the torch nozzle. The plasma is surrounded by colder, ambient nonionized gas. It is observed that the interaction of these multiphase fluids in a narrow tubing leads to large eddies, which are separated into smaller ones, developing turbulent flows. Based on the gas flow rates Reynolds number can be evaluated. Using a "Z- type" Schlieren imaging technique, we confirm that turbulence takes place at various microwave power settings. The plasma plume length and width are also measured at various microwave power settings. Thermal effects are investigated via numerical simulations using COMSOL Multiphysic CFD Module [2]. These simulations provide a better understanding about the flow dynamics observed in the captured images. This work is supported by METU Research Grants YOP-105-2018-2840.

[1] E A H Timmermans et al 2000 Plasma Sources Sci. Technol 9 625.
[2] COMSOL Multiphysic v. 5.4. www.comsol.com. COMSOL AB, Stockholm, Sweden.

Speaker: I. Uzun-Kaymak (EPS 2019)

591 P4.3015 Self-consistent Electron Energy Distribution Functions in Reacting CO2 discharge and post-discharge conditions

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3015.pdf

Large attention is nowadays devoted to the understanding of the activation of CO_2 by cold plasmas in different conditions (MW, DBD, nano-pulsed discharges). Theoretical efforts are being developed to better understand the electrical conditions necessary for maximizing the CO_2 dissociation process [1-2]. In particular, Bogaerts et al. [1] concentrated their efforts on the vibrational plasma kinetics, while Pietanza et al. [2] devoted particular attention to the development of the electron energy distribution function (eedf) in pure CO_2 and CO plasmas. In this contribution, we present new results for MW CO_2 reacting mixture, emphasizing the role of CO_2 and CO species in affecting the eedf through their non-equilibrium vibrational distributions, as well as their concentration of electronic states. Vibrational and electronic states play an important role in superposing structures in eedf especially in the post-discharge regime due to the action of superelastic collisions. A sample of results is reported in the following figure for discharge (a) and post-discharge (b) conditions characterized by the following values: P=20 torr, Tg=300 K, power density W=80 W/cm^3, discharge time td=50 ms, post-discharge time tpd=800 ms). The role of excited states in affecting eedf is well evident in the postdischarge regime where the plateau created by the CO_2 metastable at 10.5 eV and a multitude of peaks mainly due to the electronic states of CO clearly appear, these structures being hidden under discharge conditions by the applied field.

1. T. Kozac, A. Bogaerts, A. Berthelot PSST 23 (2014) 045004; A. Bogaerts J. Phys. Chem. C 121 (2017) 8236
2. L.D. Pietanza, G. Colonna, G. D'Ammando, A. Laricchiuta, M. Capitelli Phys. Plasmas 23 (2016) 013515; M. Capitelli, G. Colonna, L.D. Pietanza PSST 26 (2017) 055009; L.D. Pietanza, G. Colonna, M. Capitelli PSST 27 (2018) 095004

Speaker: A. Laricchiuta (EPS 2019)

592 P4.3016 Self-consistent simulation of hydrogen-methane plasmas for growth of carbon materials

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3016.pdf

MW assisted hydrogen methane plasmas have been extensively used for growth of CVD diamond and graphene. In this article, we discuss the results of self-consistent simulation of hydrogen-methane plasmas in a microwave resonating cavity over wide range of operating conditions (25-200mbar) and different concentrations of methane. Details of the self-consistent model is provided elsewhere [1]. The results indicate that the pressure, power and concentration of methanne in the H_2 -CH_4 methane affect the characteristics of the coupling between MW and plasma. Figure 1 shows the atomic hydrogen concentration and microwave power density atn a pressure of 110 mbar and power 1250 W. It is seen that the addition of methane increases the temperature of the reactor. As a result the the dissociation of hygrogen increases with addition of methane. Addition of small amounts of methane can change the characteristics of the MW-plasma interaction and is a function of pressure and precursor gases. More results with regard to different operating conditions will be presented. These results are important in the context of growth of carbon based materials.

References
[1] S. Prasanna et al. Plasma Sources Science and Technology 26.9 (2017)

Speaker: K. Hassouni (EPS 2019)

593 P4.3017 SNSS discharge propagation velocity dependence on gas pressure and microwave power

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3017.pdf

It is essential to know discharge propagation velocity dependences on various operational parameters as for understanding of discharge development physics as for applications. This applies as well for self-non-self-sustained (SNSS) discharges [1] in subthreshold microwave fields. For microwaves at wavelength λ = 2 cm it was found [2] that two modes of supersonic discharge propagation exist: step-like propagation with λ/4 steps at air pressures below 200 Torr and step-like propagation with 2 mm step at pressures above 200 Torr. Another result was the decrease of the discharge axial propagation velocity from 2x10^5 cm/s to 1x10^5 cm/s at increase of air pressure from 200 Torr to 750 Torr. These experiments were carried out at microwave power density 20 kW/cm^2. Yet still there are no systematic measurements of the SNSS discharge propagation velocity in subthreshold microwave fields of millimeter wavelengths.
In this work we present results of the first measurements of SNSS discharge propagation velocity at varying of microwave power (wavelength λ= 4 mm) in the range of 90 kW...360 kW (3.8...15 kW/cm^2 power densities respectively) and varying air pressure 200...600 Torr. Velocity measurements [3] were done using phase shifts measurements of microwave radiation reflected from the head of the discharge. It was found that the discharge propagation velocity exceeds 3x10^4 cm/s at air pressure 200 Torr and microwave power above 100 kW, at air pressure 400 Torr and microwave power above 230 kW, at air pressure 600 Torr and microwave power above 280 kW. The comparison of supersonic propagation velocities at air pressures 200 Torr, 400 Torr, and 600 Torr shows that the propagation velocity decreases as the pressure increases but with a bit slower rate. The obtained results indicate necessity to update physical model of the SNSS discharge.
This study was funded by the Russian Science Foundation project 17-12-01352.

[1] K.V. Artem'ev, G.M. Batanov, N.K. Berezhetskaya et al. Journal of Physics: Conf. Series, 2017, V.907, 012022.
[2] G.M. Batanov, S. I. Gritsinin, I.A. Kossyi et al. Plasma Physics and Plasma Electronics, ed. by L.M. Kovrizhnykh, Nova Science Publishers, Commack (1985), p. 241.
[3]. K.V. Artem'ev, G.M. Batanov, N.K. Berezhetskaya et al. JETP Letters, 2018, V.107, I.4, pp. 219-222.

Speaker: V. Borzosekov (EPS 2019)

594 P4.3018 Spectral investigations on concentric double hollow grid cathode discharges

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3018.pdf

Spectral investigations were carried out on a cathode system, consisting of two concentric spherical hollow grids with aligned orifices to diagnose Complex Space Charge Structures (CSCS) bordered by an electric double layer. CSCS in form of a single or multiple quasi-spherical luminous plasma bodies are called fireballs, plasma bubbles or anode dots, appearing frequently in plasmas attached to electrode surfaces due to electric field perturbations [1-3]. Inverted fireballs are structures which require a special electrode configuration, appearing inside a closed gridded, usually spherical cathode mesh. An electron beam forms through the orifices once the elementary processes assure the necessary electric charge equilibrium [1,2]. Experimental investigations have been carried out to understand the reactions that play a role in the phenomenology. Data obtained from optical emission spectroscopy were used to estimate the axial profiles of electron and ion excitation temperature and density, respectively. The increasing peaks of particle temperatures and densities, respectively, near the orifices are due to local constrictions of the plasma, as well as to an acceleration of the electrons in a potential gradient, which is reported here, and in previous research [2], in the double grid [1] as well as in the single grid configurations [4]. Besides research on basic phenomena present in the formation of such multiple CSCS, the importance of a multiple concentric cathode discharge configuration is revealed for deposition applications.

References [1] R. Schrittwieser et al., Phys. Scr. 92 (2017) 044001.
[2] C.T. Teodorescu-Soare et al., Int. J. Mass Spectrometry 436 (2019) 83.
[3] S. Gurlui et al., Rom. J. Phys. 54(7-8) (2009) 705.
[4] C.T. Teodorescu-Soare et al., Physica Scripta 91 (2016) 034002.

Speaker: C.T. Teodorescu-Soare (EPS 2019)

595 P4.3019 A small sized electron beam source utilizing hollow cathode plasma for an electron supply source

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3019.pdf

Hollow cathode discharge is able to generate a high density plasma inside the hollow cathode cavity [1]. To develop a small sized electron beam source with a high current and high durability, the hollow cathode discharge is applied to an electron source for the high current electron beam in this research. The schematic diagram of the electrode parts of a newly designed electron beam source is shown in Fig.1. The maximum diameter of this device is φ 36 mm. The diameter and length of the hollow cathode cavity are φ 10 and 40 mm respectively. The distance between the hollow cathode and the anode is 5 mm, and the distance between the anode and the extraction electrode is 12 mm. The diameter of electrode holes for the electron beam is φ 6 mm. A gas is injected into the hollow cathode side after the interior of the vacuum vessel is evacuated by using a vacuum pump. The used gas is air in this experiment. First, to generate hollow cathode plasma, a high voltage is applied at the hollow cathode. Here, the anode was grounded in this experiment. Thereafter, an electron beam is formed by applying the pulsed (AC) or the steady-state (DC) voltage between the extraction electrode and the anode. In this presentation, evaluations on the characteristics of a hollow cathode plasma and initial results of electron beam formation are reported.

[1] R. Mavrodineanu, Hollow Cathode Discharges - Analytical Applications, Journal of Research of the National Bureau of Standards. 89, (1984)

Speaker: H. Nakamura (EPS 2019)

596 P4.3020 Phase mixing of Langmuir wave in a warm multi-component plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3020.pdf

An analytical study on the space-time evolution of normal electrostatic modes in warm multicomponent plasma is presented. Multi-component plasma can be comprised of electrons, ions, dusts etc. Immobile dust grains can be either positively or negatively charged. [1] In this work, they are considered to be distributed uniformly over space with constant density. In a fluid description, a nonlinear analysis of the basic fluid-Maxwell's equations of ions and electrons confirms that the excited Langmuir wave can break even at arbitrarily low amplitude due to phase-mixing.[2] When multi-component plasma is perturbed from the equilibrium, both electrons and ions respond to the perturbation. But due to the positive charge, heavier mass and lower mobility, ions respond differently than electrons. They (electrons and ions) redistribute themselves in such a way, that the plasma becomes spatially inhomogeneous. This spatial inhomogeneity drives the excited Langmuir wave to phase-mixing. The nature of the dust-charge as well as the amount of dust grains present in the system can significantly influence the phase-mixing process. The approximate time when the phase-mixing occurs, is also evaluated analytically. The phase-mixing time is also found to increase with the temperature.

References :
[1] Introduction to Dusty Plasma Physics, Institute of Physics, Bristol, 2002.
[2] Phys. Rev. Lett. 82, (1999) 1867.

Speaker: S. Pramanik (EPS 2019)

597 P4.3021 Deposition and characterization of SiOx-like thin films from HMDSO mixtures plasmas

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3021.pdf

Plasma polymerization of organosilanes is a valuable method for depositing both inorganicSiO2-like films, which have found many applications in microelectronics and optics, and polymer-like SiOxfilms, suitable for barrier films in food packaging and corrosion protection layers.In this work, SiOx-like films were deposited on silicon and on aluminum substrates startingfrom HMDSO as precursor with different reactive gases (O2and/or Ar) [1]. Thin film mor-phology depends on growth process, two different chemical vapour deposition techniques hasbeen employed: Plasma Assisted Supersonic Jet Deposition (PASJD) and Plasma EnhancedCVD (PECVD). The former is a technique which splits the deposition process into two steps:the precursor dissociation by a radio frequency (RF) inductively coupled plasma (ICP) and thenanoparticles acceleration and assembly on a substrate by means of a supersonic inseminatedjet [2]. The latter is one of the techniques allowing industrial-scale deposition of high-qualitycoatings. The reacting gases are also ionized by an RF inductively coupled discharge and thesubstrate is placed within a diffuse plasma region.Correlation between different operating conditions (such as the effect of HMDSO/O2ratio, totaltreatment pressure and growth time) and the resulting surface properties were also discussed.The structure and bondings in the deposited films were studied by means of Fourier transforminfrared (FTIR) spectroscopy. The thickness of the deposited films was deduced applying amask on the substrate and measuring the surface roughness with a mechanical profilometer.Films morphology and nano-structures were analyzed by scanning electron microscopy (SEM).Thermal annealing was performed, the effects induced on film composition and chemical struc-ture were therefore evaluated.The capability of controlling the film composition by varying operating conditions opens inter-esting perspectives. A potential research direction of this study worth exploring is to electro-chemically reduce the SiOx-like films to obtain a nano- or fine micro-structured surface layer,providing a novel Black-Silicon fabrication process.

References
[1] Wavhal, D.S., Zhang, J., Steen, M.L. and Fisher, E.R.,Plasma Processes and Polymers,3(3), 276-287 (2006)
[2] Biganzoli, I., Fumagalli, F., Di Fonzo, F., Barni, R. and Riccardi, C.,Journal of Modern Physics,3(10), (2012)

Speaker: C. Carra

598 P4.3022 Improvement of bond strength on dental materials using low temperature multi-gas plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3022.pdf

Zirconia shows excellent dental applications such as crowns and bridges. When adhering a zirconia crown to a tooth, the abutment tooth needs to be prepared a large amount and thus the bonding area on the abutment tooth becomes small. For this reason, bond strength is important factor for keeping the application in the oral cavity or abutment tooth. In recent years, low temperature plasma has been attracted as a new surface treatment method in dental field. Effectiveness of low temperature plasma in improving the bond strength of zirconia has been reported[1]. However, effective irradiation conditions and its mechanism have not been clarified. The purpose of this study is to assess the effects of surface treatment by various gas atmospheric low temperature plasma and to find the effective gas species for improving the bond strength on zirconia using multi gas plasma jet.
Zirconia pieces (15 mm x 15 mm x 3 mm) polished with waterproof abrasive paper was used in this study. Atmospheric low temperature plasma generated by N2, CO2, O2, Air and Ar was irradiated from 3 mm above zirconia pieces for 10 s. After plasmatreatment, zirconia pieces and stainless rods were bonded by resin cement. The bonding area was φ3 mm. Next, these samples immersed in water at 37±2°C for 24 h. Untreated group and sandblasting treatment group were used as control.
The bond strength was 9.75 MPain the untreated group, and 18.5 MPa in the sandblast treatment group. In any plasma treatment, the bond strength was increased compared with the control group. Especially, N2 plasma treatment showed high bond strength equivalent to sandblasting treatment. These results indicate the effectiveness of atmospheric low temperature plasma treatment for adhesion improvement of zirconia. In addition, to understand the mechanism the surface of zirconia pieces after plasma treatment was observed using AFM and XPS.

[1] Y. Itoet al., J.Prosthodont Res.,60, 289-93(2016).

Speaker: Y. Abe

599 P4.4001 Relaxation of strongly magnetized non-neutral electron plasmas

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4001.pdf

The dynamics of a pure electron plasma confined by strong magnetic fields in a Malmberg-Penning trap is analogous to the vortex flow in an inviscid two-dimensional fluid. In fact, in the guiding-center approximation the transverse electron evolution is dictated by the drift-Poisson equations which are isomorphic to the Euler equations that describe the vorticity field in an ideal fluid. As a consequence, the effects of the collisions between electrons are negligible in such devices and the plasma never reaches the thermodynamic equilibrium. Instead, it relaxes through Landau damping to a complex nonequilibrium stationary state. A theory is presented which allows us to quantitatively predict the final stationary state achieved by the plasma [1]. Nonequilibrium phase transitions are observed as the initial conditions are varied. Theoretical estimates of the location in the parameter space of these transitions are also discussed. All the theoretical results are compared with explicit molecular dynamics simulations.

References
[1] R. Pakter and Y. Levin, Phys. Rev. Lett., 121, 020602 (2018).

Speaker: R. Pakter (EPS 2019)

600 P4.4004 Ion acceleration in a non-equilibrium plasma flow expanding from a magnetic mirror

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4004.pdf

The formation of the ambipolar potential profile in a plasma flow expanding from a mirror magnetic trap is a challenging problem in plasma physics [1-6]. Here we focus on a particular case of non-equilibrium plasma with hot electrons expanding from a gas dynamic trap that is important for a number of applications [7-10]. The main feature of such a plasma is that the electron velocity distribution is isotropic inside the trap and near the magnetic throat but acquire strong anisotropy with the density decrease in the expansion region. We consider a transition from quasi-gasdynamic to fully kinetic regime inside the expander. The analysis of ion acceleration by a self-consistent ambipolar potential profile is performed for a wide range of the plasma parameters and magnetic fields.
The work is supported by Russian Foundation for Basic Research (projects no. 17-02-00173 and 18-32-00419).

References
[1] I. K. Konkashbaev , I. S. Landman, and F. R. Ulinich, JETP, 47, 501 (1978)
[2] A. V. Turlapov, V. E. Semenov, Phys. Rev. E, 57, 5937 (1998)
[3] D. D. Ryutov, Fusion Science and Technologies, 47, 148 (2005)
[4] A. V. Arefiev, B. N. Breizman, Physics of Plasmas, 15, 042109 (2008)
[5] D. I. Skovorodin, A. D. Beklemishev, Physics of Plasmas, 1771, 030029 (2016)
[6] D. I. Skovorodin, Physics of Plasmas, 26, 012503 (2019) [7] R. Geller, Electron cyclotron resonance ion sources and ECR plasmas, ISN, Grenoble (1996)
[8] P. A. Bagryansky, A. G. Shalashov, E. D. Gospodchikov et al. Phys. Rev. Lett. 114, 205001 (2015)
[9] N. I. Chkhalo, N. N. Salashchenko et al. J. Micro/Nanolithography, MEMS, and MOEMS 11, 021123 (2012)
[10] I. S. Abramov, E. D. Gospodchikov, A. G. Shalashov, Physics of Plasmas 24, 073511 (2017)

Speaker: I. Abramov (EPS 2019)

601 P4.4005 Nonlinear anomalous skin effect in the inductively coupled plasma (ICP)

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4005.pdf

The skin effect is the basic mechanism which governs the distribution of the electromagnetic field as well as of electron heating and power absorption in the ICP plasma. Recent interest in ICPs operating at low gas pressure (0.1-50 mTorr) has prompted intensive studies of the anomalous skin effect - mechanisms of the screening of the penetrated electromagnetic field, anomalous power absorption and electron heating due to the resonant interaction of the wave with thermal electrons in the low pressure collisionless plasma. In spite of the great progress in the investigations of the ICP plasma sources in the regimes corresponding to the anomalous skin effect, there are numerous experimental results which reveal that plasma heating by the external high frequency electric fields and power absorption was unexpectedly intensive and exceed the predictions of the existing theory of the anomalous skin effect.
We found that the observed anomalously strong power absorption and heating of electrons originate from the short-scale instabilities of the parametric type which are excited by the oscillating current formed by the oscillatory motion of electrons relative to the practically immobile ions. In our report we present the linear and nonlinear theory of the parametric instabilities which develop in the skin layer and of the resulted anomalous electron heating and anomalous absorption of the pumping wave.

Speaker: V.V. Mykhaylenko (EPS 2019)

602 P4.4006 Plasma potential profile shaping using strongly emissive cathodes in a plasma column

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4006.pdf

The control of plasma potential profile in plasmas is crucial for various applications ranging from space propulsion [1], the development of plasma centrifuges [2] or the mitigation of turbulent transport by sheared flows [3].
We report here a detailed experimental investigation of the plasma potential control using emissive cathodes in a moderately magnetized plasma column [4]. Negatively biased hot emissive cathodes are inserted in a low pressure Argon plasma column confined by a moderate axial magnetic field (from 35 to 600 G) with ionisation rates ranging from 2 to 30%. When injecting strong electron currents in the plasma from the emissive cathodes, we demonstrate the ability of our setup to control the plasma potential and the plasma density radial profiles - in particular the plasma potential decreases at radii at which emissive cathodes are inserted. The experimental plasma potential profiles are compared to theoretical computations assuming ambipolar transport in the presence of strong electron beams imposed by the emissive cathodes.
Controlled shaping of the plasma potential profile also allows a direct control of the plasma rotation profile - the dominant drive being the electric and diamagnetic drifts. We demonstrate that the amplitude, the direction and the shear profile of the plasma column rotation may be controlled at will using strongly emissive cathodes. Experimental plasma flow profiles are in excellent agreement with the electric drift computed from the controlled plasma potential profile, taking into account finite Larmor radius effects as well as friction between ions and neutrals.
The scheme proposed here complements previous studies using concentric rings, end plates or grids used to shape the plasma potential. References
[1] Goebel D. M. and Katz I., Fundamentals of Electric Propulsion: Ion and Hall Thrusters, Wiley (2008)
[2] Gueroult, R. et al., Plasma Sources Sci. Technol., 25, 35024 (2016).
[3] Terry P. W., Rev. Mod. Phys. 72, 109 (2000).
[4] Plihon, N. et al., J. Plasma Phys., 81, 345810102 (2015).

Speaker: N. Plihon (EPS 2019)

603 P4.4007 Magnetic nulls from the topological perspective

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4007.pdf

Magnetic nulls in 3 dimensional fields appear in the solar corona, in planetary fields and in fusion concepts such as the polywell and Field Reversed Configuration (FRC). These points where the field vanishes are topologically stable and are hotspots for magnetic reconnection. We analyze these nulls, their motion and coalescence in topologically nontrivial analytical vector fields.
Being the zeroes of a continuous vector field, magnetic nulls are governed a topological index theorem. This theorem states that the index of an isolated null equals the degree of the mapping from a surface enclosing the null to the unit sphere. If a surface encloses more than one null, then the de- lated to the origin gree of the mapping from this surface to the sphere equals the sum of the indices of the nulls enclosed.
We relate the properties of these mappings to the eigenvectors of the matrix of partial derivatives, which is the conventional method of analyzing 3D null points [1], and show that type A nulls carry negative topological index and type B nulls positive.
We describe the construction of the isotropic field, whose integral curves are lines where the field points in one unique direction. As a configuration changes, the nulls must move along these curves of constant direction. As such, this foliation of space provides an elegant method of tracking the nulls. We demonstrate this by tracking the locations of the null points around a localized, finite energy analytical vector field as we change the magnitude and direction of an applied guide field in a configuration that is topologically similar to a planetary field embedded in a guide field, or the field of an FRC configuration.

References
[1] Parnell, C. E., et al. "The structure of three-dimensional magnetic neutral points." Physics of Plasmas 3.3 (1996): 759-770.

Speaker: C.B. Smiet (EPS 2019)

604 P4.4008 Turbulence-induced transport dynamo mechanism

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4008.pdf

Random motions of particles have an interesting property to break the magnetic field lines, and can induce a net transport flow crossing the field lines. The transport flow deserves special attention from the dynamo-theoretical point of view. By definition, the cross field diffusion velocity describes a relative one to the field line, and has a capability to generate a magnetic field in nearly frozen-in plasmas[1,2], accompanying a net change of the magnetic flux[3]. It turns out that classical diffusion due to the short range ion-electron can give rise to the magnetic change comparable to the resistive diffusion, whereas, for example, the Bohm type anomalous diffusion due to the drift turbulence can give rise to a much higher magnetic field amplification[4,5]. This dynamo mechanism by the transport flow is quite different from the conventional mean-field dynamo theory, which is based on average coupling of turbulent velocity and magnetic fluctuations [6]. The magnetic amplification by a transport flow can only be effective in a non-uniform plasma. To sustain such a flow, this mechanism requires a source and a sink. Ionization and recombination of atoms or molecules can play such roles to maintain the density profile, going through the recycling processes. In fact, in a fusion machine, recycling processes of neutrals have been known to be essential to sustain the particle confinement times[7]. In this paper, the possibility and implications of the magnetic field generation by the transport flows induced by turbulence are discussed in the context of laboratory astrophysics.

[1] T .G. Cowling, Magnetohydrodynamics, Chap5, p86, Adam Hilgar, Bristol (1976).
[2] H. Bondi and T. Gold, "On the generation of magnetism", Month.,Not. R. Soc. 110, 607 (1950).
[3] C.-M. Ryu and M. Yu, Phys. Scr. 57(5),"Magnetic field enhanced by diffusive flow", 601 (1998).
[4] T.-Y.Lee and C.-M. Ryu, "Amplification of axially symmetric magnetic field by Bohm particle diffusion", Phys. Plasmas 11, 5462 (2004),
[5] T.-Y. Lee, and C.-M. Ryu, J. Phys. D: App Phys. 40, "Magnetic field induction by Bohm plasma diffusion", (19), 5912 (2007).
[6] A. Brandenburg, "Advances in mean-field dynamo theory and applications to astrophysical turbulence ", J. Plasma Phys. 84(4) , 735840404 (2018).
[7] E. S. Marmar,"Recycling processes in tokamaks", J. Nucl. Mater. 59, 450 (1078).

Speaker: C. Ryu (EPS 2019)

605 P4.4009 Weibel and Biermann fields simulated self-consistently in laser-plasma interaction

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4009.pdf

The Biermann battery [1], driven by the perpendicular temperature and pressure gradients, is often dominant source of magnetic fields generated in laser-plasma experiments. A detailed study of Biermann generated magnetic fields in collisionless systems has been carried out [2] in an expanding plasma bubble, showing that for large system sizes (L/d_e >=100), where d_e is the electron inertial length, the Weibel instability dominates as the major source of magnetic field. However, these Weibel generated magnetic fields have yet to be demonstrated in the context of laser-plasma interaction.
We model, using ab initio PIC [3] simulations, the interaction of a short (~ps) high intensity laser pulse, thus generating a collisionless system. We demonstrate the first 3D kinetic simulation of the Biermann battery which is self-consistently driven by laser-plasma interaction. We have shown that when the laser hits the plasma, target electrons are heated and expand away from the front side of the target. The expansion causes a density gradient and the heating causes a temperature gradient, which are perpendicular to each other. As a result, a toroidal magnetic field is generated.
Although the length scale of the 3D simulation is too small for the Weibel instability to dominate, we also carry out 2D simulations with a target of sufficiently large gradient scale length, L, and observe Weibel filaments. The expanding hot energetic electron population generated by the laser produces an anisotropy in the velocity distribution. This anisotropy provides the free energy that drives the Weibel instability that appears on the surfaces of the target and dominates over the Biermann battery field.

References
[1] J. A. Stamper et al, PRL 26, 1012 (1971)
[2] K. M. Schoeffler et al, POP 23, 056304 (2016)
[3] R. A Fonseca et al, Lec. Notes Comput. Sci. 2331, 342 (2002)

Speaker: N. Shukla (EPS 2019)

606 P4.4010 Large amplitude quasi-periodic structures mediated via coherent large-amplitude oscillations and in 3D MagnetoHydroDynamics

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4010.pdf

Within the framework of MagnetoHydroDynamics, a strong interplay exists between flow and magnetic fields. This interplay is known to lead to several interesting phenomena such as nonlinear non-dispersive Alfven waves, recurrence phenomena and magnetic re-connection, to name a few. Using a set of divergence free sinusoidal flow fields (e.g., Arnold-Beltrami-Childress, Taylor-Green, Orszag-Tang etc) as initial flow profile we numerically integrate a self-
consistent set of 3D, weakly compressible MHD equations [1] to study non-dispersive nonlinear Alfven waves over a wide range of parameters [2]. It is inferred that these nonlinear Alfven waves generate coherent large-amplitude oscillations between kinetic and magnetic energies.

Followed by this, we identify a novel phenomena called "Recurrence", within the premise of single fluid MHD equations for initial flow fields which are chaotic [3]. Even though it appears counter-intuitive, the strong nonlinearity of the problem allows a selected initial flow fields to quasi-periodically reconstruct its structures despite the fact that its structure is completely distorted during the evolution of the plasma. Such magnetic recurrence phenomena mediated by a dynamical energy exchange between magnetic and velocity fields via a reconnection process (Fig. 1) is believed to have wide applications in controlling the disruption in the magnetically confined plasmas. After demonstrating the numerical convergence, we attempt possible explanation using a simple Hamiltonian field model.

References
[1] R. Mukherjee, R. Ganesh, V. Saini, U. Maurya, N. Vydyanathan and B. Sharma, IEEE Conference Proceedings of 25th International Conference on High Performance Computing Workshops (HiPCW), 2018; arXiv:1810.12707
[2] R. Mukherjee, R. Ganesh and A. Sen, arXiv:1811.00744
[3] R. Mukherjee, R. Ganesh and A. Sen, Physics of Plasmas 26, 022101 (2019); arXiv:1811.00754

Speaker: R. Mukherjee (EPS 2019)

607 P4.4011 Self-organized criticality uncorrelated pulses and intermittency

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4011.pdf

Self-organized criticality (SOC) is a well-known paradigm for explaining power law probability distributions and frequency spectra in astrophysical, space and laboratory plasmas [1, 2]. By contrast, in the scrape-off layer of magnetically confined fusion plasmas and other turbulent systems, probability distributions with exponential tails and Lorentzian frequency spectra are observed [3, 4]. These observations are well explained by a stochastic model consisting of a superposition of exponential pulses, arriving according to a stationary Poisson process, called the filtered Poisson process (FPP) [3, 4].
Connections between SOC and the FPP were made as early as one of the original SOC publications [5], where power-law distributed event durations and power-law frequency spectra were explained based on viewing a SOC time series as a sequence of uncorrelated pulses. However, this result relies on an erroneous, yet often repeated conclusion [6]. As exponential waiting times are often observed in SOC models, Poisson distributions (stationary and otherwise) have been invoked as well [1, 7], although a careful definition of 'waiting time' is required [7].
In this contribution, the connection between the FPP and SOC is discussed. As both event duration times and waiting times are explicit parts of the FPP formulation, the difference between these and time spent above a threshold are discussed and compared to the SOC notion of event duration. It is argued that without power-law inputs, pink-noise spectra are not found in the FPP and it is only in the limit of infinite pulse overlap that power law distributed times above a threshold appear. In this limit, the FPP is identical to an Ornstein-Uhlenbeck process [8], which leads naturally to fractional brownian motion, an often studied process in the context of SOC [1, 2]. Unfortunately, in this limit any advantage of using the FPP formulation disappears. The FPP is thus argued to be incompatible with the SOC paradigm.

References
[1] M. J. Aschwanden et. al., Space Sci Rev 198, 47 (2016) [2] A. S. Sharma et. al., Space Sci Rev 198, 167 (2016)
[3] A. Theodorsen, O. E. Garcia and M. Rypdal, Phys Scr 92, 054002 (2017)
[4] O. E. Garcia et. al., Phys Plasmas 23, 052308 (2016)
[5] P. Bak, C. Tang and K. Wiesenfeld, Phys Rev A 38, 364 (1988)
[6] O. E. Garcia and A. Theodorsen, Phys Plasmas 24, 032309 (2017)
[7] R. S·nchez, D. E. Newman and B. A. Carreras, Phys Rev Lett 88, 068302 (2002) [8] A. Theodorsen and O. E. Garcia, Phys Rev E 97, 012110 (2018)

Speaker: A. Theodorsen (EPS 2019)

608 P4.4012 Identification of magnetosonic modes in Galactic turbulence

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4012.pdf

We have detected the first observational evidence of magnetosonic modes in the Cygnus X region, with our novel method, the signature from polarization analysis (SPA). The region dominated by the magnetosonic modes overlap to a high degree with the enhanced gamma ray emission, completely in line with the predictions from the cosmic ray transport theory. Through comparison with the spectrum at other wavelengths, our results provide a new perspective in understanding star formation processes, which is intimately linked to turbulence properties as widely acknowledged. The method I am going to present, SPA, sheds light on the hitherto unknown plasma modes composition of the Galactic turbulence, and marks the onset of a new era in the study of interstellar turbulence and accordingly our understanding of cosmic ray transport and star formation.

Speaker: H. Yan (EPS 2019)

609 P4.4013 Instability Threshold of Alfven Waves in a Non-Ideal

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4013.pdf

A system of the modified quantum fluid equations has been used for the investigation of Alfven wave dispersion properties in a non-ideal astrophysical plasma medium. The dispersion relation is derived by perturbation method in the presence of dissipative effects, self-gravitational, quantum potentials and electromagnetic forces. The results show that the presence of the resistivity and quantum force can lead to the instability of the system. The instability of the waves is increased with decreasing in the wavelengths. Although, quantum aspects play an important role in the short wavelengths, nevertheless, in the long wavelengths, quantum effects are negligible. The assumptions and results of the present study are one of the fundamental interests in the study of astrophysical plasmas such as molecular-clouds.

Speaker: N. Morshedian (EPS 2019)

610 P4.4014 Particle-in-cell simulations of pair discharges at pulsar polar caps

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4014.pdf

When subject to the rotationally induced electric field of pulsar polar caps, electrons and positrons are accelerated along the magnetic field, producing gamma-ray curvature radiation. The emitted gamma-rays, in turn, are absorbed by the magnetic field, converting to new electron-positron pairs. The repetition of this process leads to a cascade of elementary particles that are the source of pulsar magnetospheric plasma. The final number of particles created in pair cascades and their connection with pulsar radio emission remains an open problem. Obtaining numerical models of pulsar pair discharges is a challenging endeavor and one that was only addressed in simplified one-dimensional simulations.
In this work, we present two-dimensional particle-in-cell simulations of pair discharges near pulsar polar caps, including the Quantum Electrodynamics effects responsible for gamma-ray and pair production processes from first principles. These simulations allow studying the time dependence and distribution in altitudes and latitudes of pair cascades while resolving the relevant plasma electrodynamic scales. We analyze the particle spectra and discuss the constraints that our simulations put on pair production rates for use in global pulsar simulations, underlining the differences to previous models with simplified prescriptions. We also estimate the fraction of gamma-rays that escapes the polar cap and contributes to the flux of polar gamma-rays in Fermi data.

Speaker: F. Cruz (EPS 2019)

611 P4.4015 Dynamical frequency modulation as a signature of cyclotron emission of a transiting object in radio signal from its host star

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4015.pdf

We present modelling a dynamical spectrum of a host star's cyclotron emission which came through a magnetically active (auroral) region of a planetary magnetosphere. The model for the local planetary emission is based on a horseshoe-type cyclotron instability [1,2]. A full electromagnetic modelling of a signal which propagated through the instability in the local magnetosphere is done. We use 1D geometrical setting but 3D fields in our model to account for initial circular polarization in the star's radio emission since it is characteristic for cyclotron maser radiation. The resultant frequency time dependence (dynamical spectrum) has a periodic modulated character. We suggest that seeing such dynamical spectrum can be an indication of a dipole magnetic field present at the planet, and compare to available observational results.

MTW acknowledges support of Royal Society of Edinburgh's Cormack Vacation Research Scholarship 2018, which enabled him to work on this research as a summer project".

[1] I. Vorgul, B.J. Kellett, R.A. Cairns, R. Bingham, K. Ronald, D.C. Speirs, S.L. McConville, K.M. Gillespie and A.D.R. Phelps, `Cyclotron maser emission: Stars, planets and laboratory', Physics of Plasmas. 18, 5, (2011)

Speaker: M.T. Whyte (EPS 2019)

612 P4.4016 Analytical model of a current sheet at a magnetosheath's boundary in a collisionless plasma

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4016.pdf

We suggest and investigate in detail an analytical model of a quasi-stationary current sheet in a collisionless plasma describing the boundary of a magnetosheath formed by the solar (stellar) wind [1]. The model significantly expands the scope of the magnetohydrodynamic approach and is based on a consistent kinetic description of the inhomogeneous anisotropic momentum distribution functions of electrons and ions with different effective temperatures.
Using the method developed in [2], we find exact one-dimensional solutions to the Vlasov-Maxwell equations with electron and ion distribution functions in the form of a Maxwellian function multiplyed by a Heavyside step function of the particle generalized momentum, which includes the vector potential. We analyze in detail possible monotonic profiles of the magnetic field and number density of plasma species, and localized structure of the current density, which are all expressed by the error and the exponential functions of the vector potential.
We present various examples of one-, two- and three-component current sheets formed by the electrons and one or two fractions of energetic protons, including the cases of the same and opposite directions of their currents. For all these sheets we explicitly find the widths of different components of the current and describe their asymmetry, as well as the anisotropy degree of the particle momentum distributions. The widths and the values of electron and proton current components depend on gyroradii, number density and effective temperature of particles.
The model allows us to give a qualitative description of the inhomogeneous current structure in the bow shock and the magnetopause for a broad class of objects, including the heliospheric shock layer, the planetary magnetospheres modified by an incident stellar wind, the boundary layers of the magnetic clouds filled with plasma and moving from a star through the surrounding plasma of its wind, the high coronal magnetic loops immersed in the wind on the late spectral class stars. We give estimates of current sheet parameters in these cases and use the analytical solutions for the interpretation of observational data.

References
[1] V. V. Kocharovsky, Vl. V. Kocharovsky, V. Yu. Martyanov, A. A. Nechaev, Astron. Lett. (2019). Submitted.
[2] V. V. Kocharovsky, Vl. V. Kocharovsky, V. Yu. Martyanov, S. V. Tarasov, Phys. Uspekhi, 59, 1165 (2016).

Speaker: A.A. Nechaev (EPS 2019)

613 P4.4017 Numerical simulations of kinetic plasma turbulence in the low plasma beta regime

See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.4017.pdf

We present numerical results from high-resolution hybrid kinetic and full PIC kinetic simulations of plasma turbulence, following the development of the energy cascade from large magnetohydrodynamic scales down to electron characteristic scales. By considering the low plasma beta regime we use our results for interpreting MMS observations in the Earth's magnetosheath and predicting Parker Solar Probe observations in the solar corona
We explore a regime of plasma turbulence where the electron plasma beta is low, so that there is a clear separation between the electron inertial length and the electron gyroradius. This is typical of environments where the ions are much hotter than the electrons, e.g., the Earth's magnetosheath and the solar corona, as well as regions downstream of collisionless shocks. In such range of scales, recent theoretical models predict a different behaviour in the nonlinear interaction of dispersive wave modes with respect to what typically observed in the solar wind (e.g., polarization characteristic of inertial kinetic Alfvén waves). We also extend our analysis to scales around and smaller than the electron gyroradius, where hints of a further steepening of the magnetic and electric field spectra have been recently observed by the NASA's Magnetospheric Multiscale mission, although not yet supported by theoretical models.
Our numerical simulations exhibit a remarkable quantitative agreement with recent observations by MMS in the magnetosheath, allowing us to investigate simultaneously the spectral break around ion scales and the two spectral breaks at electron scales, the magnetic compressibility, and the nature of fluctuations at kinetic scales, by employing a new kind of analysis which takes into account the local plasma properties. Moreover, they allow us to provide predictions for observations by NASA's Parker Solar Probe mission in the solar corona.

Speaker: D. Burgess

614 P4.3014 Nanoparticles de-agglomeration in non-equilibrium low-pressure radiofrequency plasma

See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P4.3014.pdf

This contribution describes an interesting phenomenon concerning the interaction between a non-equilibrium low-pressure radiofrequency plasma and aggregated particles injected into it. This phenomenon is related to the particle de-agglomeration when they are injected in a plasma. In order to develop nanoparticle metrology diagnostics in "dry environment", a unique experimental device has been developed, composed of a low-pressure radiofrequency plasma reactor and a nanoparticle injector allowing the characterization of nanoparticles by non-intrusive metrology diagnostics. The particles injected into the plasma gas phase are trapped and levitate within the chamber. The average size of the nanoparticles obtained by the developed methods are in general smaller than the average size given by the manufacturer, but in quite good agreement with those (in the reactor) given by transmission electron microscopy. The injection of the particles is regarded by mean of a fast camera. We observed that during the injection, the particles de-agglomeration ration reaches up to 90%). The analysis of particles by metrology methods in plasma makes it possible not to analyze the aggregates, but the primary particles. This phenomenon opens many ways in particular for toxicity control and presence of so-called nanoparticles (less than 100nm) in ingredients from, for example, the pharmaceutical or cosmetic industry. Moreover it allows the study of the interactions between plasma and aggregated particles.

Speaker: M. Hénault (EPS 2019)

16:00 Coffee Break

BPIF

Convener: M. Vranic (GoLP/IPFN - Instituto Superior Tecnico)

615 I4.203 Exascale laser plasma physics - from computational speed to predictions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.203.pdf

Since the very beginning, simulations have been an integral part of laser plasma research. With the advance of high-power lasers, non-linear effects on ultra-short time scales require extensive control in experimental setups, theoretical assumptions and simulation stability alike. For the latter, Particle-in-Cell simulations have been established as a scalable method to cover kinetic effects with long-range potentials at affordable computational costs.

Within the next years, supercomputers with the capability of calculating an ExaFlop/s will emerge for the scientific community. In order to fit in a power-envelope of approximately 10 MW per system, traditional computing architectures are replaced with highly parallel, RISC architectures that demanded a reinvention of our algorithms for a higher degree of parallelism. Driven by the urge to exploit these computational advances for precise modeling efforts, zerocost methodological abstraction, cross-discipline collaboration, and the urgent need for reproducibility in simulation methods initiate a dawn of open source science and shared, dataintensive workflows.

Since 2013, the PIConGPU community converts that immense computational potential into robust predictions for laser plasma interaction within an open environment. We present our contemporary approaches to laser plasma modeling, starting from fast turn-around simulations to modeling of multi-physics effects to experimental uncertainty approximation, charging current and future challenges in our domain. Especially for high energy density plasmas, full-geometry runs in wide parameter spaces drive our long-term strategic developments, involving proper initial conditions under realistic laser contrasts and profiles, and stable modeling under extreme conditions such as X-FEL probe beams.

Speaker: A. Huebl (EPS 2019)

616 I4.204 Novel regimes of high-intensity laser-plasma interactions enabled by extreme magnetic fields

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.204.pdf

Newly constructed laser facilities such as ELI NP and ELI Beamlines are expected to deliver unprecedented laser intensities, making it possible to probe new regimes of light-matter interactions in laboratory conditions. One such regime is where a laser-irradiated solid material becomes relativistically transparent and enables laser propagation though an otherwise prohibitively dense electron population. We found that a collective electron response to the laser pulse results in a MA-level current that sustains previously inaccessible quasi-static magnetic fields with a strength reaching a MT [1, 2]. This magnetic field qualitatively alters the electron dynamics in the propagating laser pulse, making it possible to
- Accelerate electrons to GeV energies over just tens of laser wavelengths [3];
- Induce efficient and directed -ray emission at intensities as low as 5 x 10^22 W/cm^2, with over 10^12 multi-MeV photons in a 30 fs bunch [1];
- Produce proton accelerating structures that generate dense mono-energetic beams with 200 MeV in energy and tens of nC of charge [4].
Using 3D kinetic simulations, we found that structured targets with a pre-filled lower density channel are essential for generating the magnetic fields in a controlled way. These targets mitigate plasma cavitation, thus extending the volumetric laser-plasma interaction for longer laser beams (e.g. 150 fs long L4 beam at ELI Beamlines). We also found that structured targets can aid the detection of the extreme magnetic fields using XFEL beams by reducing the effect of the relativistic transparency for the probing x-ray photons [5].
This work was supported by NSF (No. 1632777), AFOSR (No. FA9550-17-1-0382), DOE (DE-AC02-05CH11231), and XSEDE.

References
[1] D. Stark, T. Toncian, and A. Arefiev, Phys. Rev. Lett. 116, 185003 (2016)
[2] O. Jansen, T. Wang, D. Stark, E. d'Humieres, T. Toncian, and A. Arefiev, PPCF 60, 054006 (2018)
[3] Z. Gong, F. Mackenroth, T. Wang, X. Q. Yan, T. Toncian, and A. Arefiev, arXiv:1811.00425 (2018)
[4] A. Arefiev, Z. Gong, T. Toncian, and S. S. Bulanov, arXiv:1807.07629 (2018)
[5] T. Wang, T. Toncian, M. S. Wei, and A. Arefiev, Phys. Plasmas 26, 013105 (2019)

Speaker: A. Arefiev (EPS 2019)

617 O4.206 Production of collimated gamma ray beams for e- e+ pair creation.

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.206.pdf

Despite being one of the most basic process of quantum electrodynamics (QED), and being responsible of the universe opacity to high energy photons [1], the electron-positron pair production by two photons collision (gamma-gamma -> e-e+, linear Breit-Wheeler [2] process, LBW) has never been observed directly in the laboratory.
However, increasing available intensity at laser facilities make possible to create high brilliance MeV ray sources that could be used to observe this process for the first time [3].
We propose [4] to detect e+ produced by LBW using two crossing ray beams (see Fig. 1). Those sources could be created in typical laser-solid experiments: some target e- are accelerated from laser field and their propagation near a high Z atomic nuclei in the material can produce gamma rays through the Bremsstrahlung process. However, e- and gamma propagation in a high Z material can also produce background e-e+ pairs through the Trident (e-Z -> e-Ze-e+) and Bethe-Heitler (gammaZ -> Ze-e+) processes.
In this work, a semi-analytical model to estimate LBW pair production, and a complete simulation setup (using hydrodynamics, Particle-In-Cell and Monte Carlo codes) have been developed to simulate LBW and background e+ production.
These tools could be used to investigate pair plasma jets in Active Galactic Nuclei [5], and further developments could help to test more advanced theoretical predictions [6] or measure the LBW cross section (widely used in QED) for the first time.

References
[1] R. Ruffini, G. Vereshchagin, and S. S. Xue, Phys. Reports 487, 1 (2010).
[2] G. Breit and J. A. Wheeler, Physical Review 46, 1087 (1934).
[3] O. J. Pike et al., Nature Photonics 8, 434 (2014). X. Ribeyre et al., Phys. Rev. E 93, 013201 (2016).
I. Drebot, et al., Phys. Rev. Accel. Beams 20, 043402 (2017). J. Yu et al., ArXiv:1805.04707 (2018).
[4] X. Ribeyre et al., Plasma Phys. Control. Fusion 59, 014024 (2017).
[5] X. Ribeyre et al., Plasma Phys. Control. Fusion 60, 104001 (2018).
[6] A. Hartin, Pramana - J Phys 69, 1159 (2007).

Speaker: L. Esnault (EPS 2019)

618 O4.207 Can quantum stochastic effects be detected in ultra-intense laser-plasma interactions?

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.207.pdf

When an ultra-intense laser pulse interacts with plasma, the accelerated electrons experience the back-radiation reaction due to the emission of electromagnetic radiation, and this has recently been experimentally evidenced [1]. The results suggest that both the quantum and classical nature of the back-radiation reaction have been detected. However, the situation is more subtle in the case of a laser-plasma interaction in which the laser plasma heating as well as the collective plasma effects may drastically effect the importance (and therefore the detection) of the quantum stochastic nature of the emitted radiation [2]. Our study is within the realm of radiation pressure acceleration (RPA) regimes involving thick targets. First, via QED-PIC numerical simulations performed with the EPOCH code, we show that the importance of the quantum stochastic heating strongly depends on the laser parameters such as polarisation and temporal profile. In doing so, via analytical criteria, we can deduce a range of laser-plasma parameters for which high-field phenomena triggered by quantum stochastic heating could be detected. Secondly, we demonstrate that the quantum stochastic heating induces an electrostatic instability at the front of the laser-piston [3] due to the enhancement of the electron heating of backward-directed electrons, which results in a peak in the ion energy spectrum as well as a decrease of the oscillations of the the longitudinal electric field. Initial conditions to obtain an optimal ion energy spectra are shown. Through this process, quantum stochastic heating improves the energy spread of the ion beam via RPA, in ultraintense laser-plasma interactions and could be relevant for Laboratory astrophysics.

[1] J. M. Cole et al. Phys. Rev. X 8, 011020 (2018); K. Poder et al. Phys. Rev. X 8, 031004 (2018).
[2] N. Neitz and A. Di Piazza Phys. Rev. Lett 111, 054802 (2013); C. P. Ridgers et al. J. Plasma Phys. 83, 715830502 (2017); F. Niel et al. Phys. Rev. E 97, 043209 (2018).
[3] T. Schlegel et al. Phys. Plasmas 16, 083103 (2009); A. P. L. Robinson et al. Plasma Phys. Controlled Fusion 51, 024004 (2009).

Speaker: R. Capdessus (EPS 2019)

619 O4.208 Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interactions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.208.pdf

The interaction of intense electromagnetic waves with plasmas is a rich research topic. Magnetic fields play a crucial role in this context and there are several processes that can lead to the generation and amplification of these fields. Recent experiments, for instance, demonstrated the generation large-scale magnetic fields [1] due to hot electron currents in underdense plasmas, and determined the turbulent [2] dynamics of intense magnetic fields in laser-solid interactions.
In this work we explore a novel mechanism to drive the Weibel instability in laser-plasma interactions using theory and full scale particle-in.cell simulations in two- and three-dimensions with the code OSIRIS [3]. We show that intense laser pulses interacting with sub-quarter-critical density plasmas can lead to anisotropic heating, if stimulated Raman scattering (SRS) grows. Electron heating, due to wavebreaking of the SRS excited plasma waves, will be preferential in the propagation direction of the excited plasma waves, creating a temperature anisotropy behind the laser. The direction of the scattered waves has a dependence on the plasma temperature, as Landau damping can prevent small wavelength waves to grow. We find a good agreement between the observed magnetic field growth rate and characteristics with theoretical predictions of the Weibel instability due to temperature anisotropy.
We also argue that this setup can be used to investigate the long-time evolution of the Weibel instability in laboratory, as the evolution of the Weibel generated magnetic fields can be related to the time delay of the laser passage for the region. This is of great relevance to understand the structure of collisionless shocks in astrophysical objects, in particular, gamma-ray bursts [4, 5].

References
[1] A. Flacco, et al., Nature Physics 11, 409 (2015).
[2] G. Chatterjee, et al., Nat. Comms. 8, 15970 (2017).
[3] R. Fonseca, et al., Lecture Notes in Computer Science 2331, 342 (2002)
[4] M. V. Medvedev, et al., The Astrophysical Journal Letters 618, L75 (2005).
[5] U. Keshet, et al., The Astrophysical Journal Letters 693, L127 (2009).

Speaker: T. Silva (EPS 2019)

620 O4.209 Advanced multi-dimensional simulations on parametric instabilities in in- homogeneous plasmas relevant to inertial confinement fusion

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.209.pdf

Parametric instabilities in two- and three-dimensional configurations in inhomogeneous plasmas have been studied on a wide range of parameter space ranging from direct-drive scheme to shock ignition. These include the nonlinear evolutions of stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and two-plasmon decay (TPD), and interactions among them. In 2D particle-in-cell (PIC) simulations [1], we have demonstrated a clear transition from TPD dominant regime to SRS dominant regime near the quarter-critical density as the laser intensity increases from direct-drive regime to shock ignition. Instability nature changes from absolute TPD/SRS to convective SRS. The relevant hot-electron generation is discussed based on a simple particle acceleration model [2]. Hot electron fraction is shown to have a peak near the convective SRS threshold. And the effective hot electron temperature is about 90keV when TPD is dominant, and is shown to have a bi-Maxwellian distribution with Th1=90keV (dominated by TPD) and Th2=54keV (dominated by SRS) when in shock ignition regime. The behavious of SRS and TPD were recently observed by experiments [3]. Next, we have performed more realistic 3D PIC simulations to study interactions among SRS, TPD, and SBS [4]. Especially, we observed when the laser power is high enough (above some certain threshold), stimulated Raman sidescattering (SRSS) occurs ubiquitously in a wide range of density regions, and finally scattered out of plasma with a large exit angle. The situation may be found in a single laser speckle. Thus, we simulated this effect on 3D configuration. SRSS grows to an intensity comparable with the laser beam when excited. It has a weak competition with Raman backward scattering, while both of them can suppress TPD. It is also observed that SRSS has few influences on SBS occurred at low density regions. Also, differences of parametric instabilities in 2D and 3D PIC simulations are discussed.

References
[1] C. Z. Xiao, Z. J. Liu, C. Y. Zheng, and X. T. He, Phys. Plasmas 23, 022704 (2016).
[2] C. Z. Xiao et al., submitted.
[3] M. J. Rosenberg et al., Phys. Rev. Lett. 120, 055001 (2018).
[4] C. Z. Xiao, H. B. Zhuo, Y. Yin, Z. J. Liu, C. Y. Zheng, Y. Zhao, and X. T. He, Plasma Phys. Control. Fusion 60, 025020 (2018).

Speaker: C. Xiao (EPS 2019)

BSAP

Convener: K. Ferriere (IRAP/OMP)

621 I4.403 Particle acceleration in relativistic magnetospheres

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.403.pdf

Rapidly rotating neutrons stars and black holes are the central engines of some of the most extreme astrophysical phenomena such as gamma-ray bursts, pulsars, X-ray binaries, binary mergers or active galactic nuclei. The activity of these compact objects is often associated with the creation and the launching of a relativistic magnetized plasmas accompanied by efficient particle acceleration and non-thermal radiation, but the underlying physical mechanisms are still poorly understood. The particle-in-cell method is well-suited to model these processes from first principles. Recent numerical simulations have clearly established that relativistic magnetic reconnection within the magnetosphere of pulsars and black holes plays a crucial role in dissipating magnetic energy which is then efficiently channeled into energetic particles and high-energy radiation. Results will be discussed in the context of gamma-ray pulsars, merging binary neutron stars and weakly accreting Kerr black holes.

Speaker: B. Cerutti (EPS 2019)

622 I4.404 Cosmic ray propagation in the Galaxy: the role of self-confinement

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.404.pdf

Understanding the transport of charged particles in the Galaxy is fundamental to solve the mystery of the origin of Galactic cosmic rays (CR) and to asses their role in several Galactic processes. Recent results from direct experiments, especially AMS-02 and PAMELA, are revealing a fine structure in the CR spectrum which is difficult to explain in the standard picture of Galactic propagation. Some of these features could be understood when the self generated turbulence is taken into account. When CR propagate through a plasma they can trigger the streaming instability which produces resonant Alfvén waves modifying the diffusive properties of the plasma and changing the CR transport itself in a complex non-linear fashion. In this talk I will highlight the role of this self-generated turbulence in several context of the CR journey: during the escape from their sources, close to molecular clouds and during the escape from the Galactic disk.

Speaker: G. Morlino (EPS 2019)

623 O4.401 The Spectral Web of the super-Alfvénic rotational instability in accretion disks: an alternative to the MRI paradigm!

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.401.pdf

The recently developed theory of the Spectral Web [1, 2] is a method to compute the full complex spectrum of stationary plasmas together with a connecting structure. This permits to consider the enormous diversity of MHD waves and instabilities of rotating tokamaks and astrophysical plasmas from a single unifying view point.
Presently, the Spectral Web approach is applied to explore the non-axisymmetric rotational instabilities of accretion disks about black holes and neutron stars. These modes are driven by the extremely super-Alfvénic equilibrium flows which are symmetry breaking through the dominant Doppler shift mOmega. Here, m is the toroidal mode number and Omega is the angular rotation frequency of the disk. The spectrum of complex modes becomes a very intricate interplay between the real frequencies of the four Dopplershifted forward and backward Alfv¥en and slow continua (Omega±A,S = mOmega ± w A,S) and the closely associated complex frequencies of the non-axisymmetric (m different from 0) instabilities. The latter appear as infinite sequences 'emitted' from the continua along paths in the complex w-plane provided by the Spectral Web method. Due to the closeness of the continua, the resulting modes exhibit extreme localization in the radial direction.
This is in complete contrast to the standard axisymmetric (m = 0) magnetorotational instabilities (MRIs) [3], where the continua w A,S are not Doppler shifted and they do not interact with the MRIs since they are located far away from them in the complex w-plane. Consequently, the MRIs form a finite sequence of unstable eigenvalues, which turn into stable waves when approaching the real axis. Hence, the modes do not have the extreme radial localization that is exhibited by the non-axisymmetric modes. Since the very reason of accretion is generally considered to be the turbulence caused by the magneto-rotational instabilities, it is clear that the non-axisymmetric super-Alfvénic rotational instabilities provide a relevant alternative.

[1] J. P. Goedbloed, Phys. Plasmas 25, 032109 & 25, 032109 (2018).
[2] Hans Goedbloed, Rony Keppens and Stefaan Poedts, Magnetohydrodynamics of Laboratory and Astrophysical Plasmas (Cambridge University Press, 2019).
[3] S. A. Balbus and J. F. Hawley, Astrophys. J. 376, 214 (1991).

Speaker: H. Goedbloed (EPS 2019)

624 O4.402 On the influence of particle acceleration on the structure of low-Mach astrophysical shocks

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.402.pdf

Cosmic rays are charged particles, moving at relativistic speeds after being accelerated through interaction with astrophysical shocks. This process, known as diffusive shock accleration, or Fermi acceleration, involves the particle repeatedly crossing the shock, picking up speed each time it is reflecte by the local magnetic field. So far, computer models of this particle-shock interaction have focussed primarily on highmach shocks, such as supernovae and stellar wind collisions. Here we concentrate instead on low-Mach shocks, such as those that occur when galaxy clusters collide. These shocks are characterised by a combination of a low sonic-Mach number and a high plasma-beta. Previous results showed that these shocks are capable of accelerating particles and may contribute to the cosmic ray spectrum. We now continue this work using a combined particle-in-cell (PIC) and magnetohydordynamics (MHD) approach. This involves plitting the plasma into two components. The first, which comprises the majority of the local plasma behaves as a thermal plasma and can be simulated using MHD. The scond, much smaller component behaves nonthermally and is modelled using PIC. The two components interact self-consistently with each oher through the local electromagnetic field. This approach allows us to simulate a much larger physical volume than would be possible with the more traditional PIC-only approach. Our results show that for these low-Mach, high-beta shocks, the particle acceleration process has a significant influence on the local plasma. Local instabilities, triggered by the interaction between the non-thermal particles and the magnetic field, change both the Mach-number of the shock, as well as the angle between the shock surface and the magnetic field to the point where it may well inhibit the injection of non-thermal particles into the local medium, effectively cutting off the acceleration process.

Speaker: A. van Marle (EPS 2019)

625 O4.403 Properties of Alfven and magnetosonic modes in compressively driven turbulence

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.403.pdf

The properties of magnetohydrodynamic (MHD) turbulence have significant implications for astrophysical phenomena like cosmic ray scattering. We study properties of MHD modes by decomposing data of MHD simulations into linear MHD eigenmodes - namely the Alfvén, slow, and fast modes. Some earlier studies have shown the differences in the turbulent spectrum and anisotropy characteristics of these different modes [1, 2]. However, several open questions still remain. We vary the nature of the turbulence in our simulations by varying the forcing from solenoidal to compressive, while also varying the plasma beta and Mach number. We find that the proportion of the magnetosonic (fast and slow) modes in the mode mixture increases with increasing fraction of compressive forcing and higher plasma beta. As a result, the compressible magnetosonic modes can become the dominant fraction in the MHD mode mixture. The Alfvén mode shows the well-known anisotropic Goldreich-Sridhar spectrum characteristics. We also find a transition from strong to weak Alfvénic turbulence at low Alfvén Mach numbers. In cases where the fast mode is strong, the isotropic nature of the fast mode cascade is verified with higher resolution and better diagnostics compared to previous studies. These results also indicate that there can be significant coupling between the different MHD modes depending on which mode is dominant. This study motivates the development of a better theory of magnetosonic modes turbulence.

References
[1] Jungyeon Cho and A. Lazarian, Physical Review Letters 88, 245001 (2002)
[2] Jungyeon Cho and A. Lazarian, Mon. Not. R. Astron. Soc. 345, 325-339 (2003)

Speaker: K. Makwana (EPS 2019)

626 O4.404 Particle Transport Energisation and Loss in the Alfvénic Inner Magnetosphere

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.404.pdf

Observations recorded from NASA's Van Allen Probes have revealed the prevalence of a broad spectrum of Alfvénic field fluctuations in the inner magnetosphere. The properties of these waves in the inhomogeneous plasma of his region of near-Earth space give rise to a number of resonant and non-resonant interactions between the waves and the plasma that lead to the transport of relativistic electrons across magnetic field-lines, the loss of the same through the magnetopause and to the atmosphere, as well as the extraction and energisation of ionospheric plasmas into the magnetosphere. Transport coefficients and simulations for observed wave spectra along with features of the observed particle distributions and measurements of magnetospheric particle pressures suggest that these processes are competitive with the traditional mechanisms invoked for particle transport, energisation and loss in Earth's inner magnetosphere. We present an overview of these observations and associated physics to demonstrate how important these 'new' processes may be for explaining global variations in near-earth space during geomagnetically active times.

Speaker: C.C. Chaston (EPS 2019)

MCF

Convener: G. Pautasso

627 I4.105 The effect of high-Z material injection on runaway electron dynamics

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.105.pdf

Developing a disruption & runaway electron (RE) mitigation strategy that robustly scales to ITER and beyond is a major challenge. The dynamics is governed by a complex interplay of effects such as the atomic physics and penetration of the high-Z material injected for mitigation, quench dynamics (MHD), kinetic physics, and quantum mechanics. The EUROfusion consortium is executing a coordinated research program to better understand the generation [1,2], control [3] and mitigation [4] of disruption-born REs following massive material injection.
RE studies on ASDEX Upgrade and TCV are carried out using massive gas injection (MGI) of neon, argon and krypton. The injection of high-Z materials mixed with deuterium is a promising mitigation strategy for ITER. A 1:4 argon-deuterium mixture has prevented RE beam formation in the commonly used RE scenario on ASDEX Upgrade. TCV demonstrated RE beam control up to a pre-disruption elongation of k~1.5. Our results indicate that increasing elongation has no significant impact on RE physics and the main challenge is position control.
The scaling of the initial runaway current on plasma- and injection parameters, as well as the subsequent dissipation is analysed using 1D disruption-runaway simulations [5,6] along with state-of-the-art full-f kinetic models7. The high-Z dissipation model [7] was validated using experimental data from multiple European tokamaks. Full-f kinetic simulations were carried out for the first time for the complete duration of the thermal & current quench. These simulations show that an abrupt delivery of high-Z material (e.g. executed by SPI) is expected to significantly decrease the RE generation rate compared to slower injections methods (such as MGI).

References
[1] G. PAUTASSO ET AL. Plasma Physics and Controlled Fusion, 59 (1):014046 (2017).
[2] J. MLYNAR ET AL. Plasma Physics and Controlled Fusion, 61 (1):014010 (2019).
[3] D. CARNEVALE ET AL. Plasma Physics and Controlled Fusion, 61 (1):014036 (2018).
[4] G. PAPP ET AL. IAEA-FEC, IAEA-CN-234-0502:EX/9 (2016).
[5] G. PAPP ET AL. Nuclear Fusion, 53 (12):123017 (2013).
[6] E. FABLE ET AL. Nuclear Fusion, 56 (2):026012 (2016).
[7] L. HESSLOW ET AL. Plasma Physics and Controlled Fusion, 60 (7):074010 (2018).

Speaker: G. Papp (EPS 2019)

628 I4.106 Shattered pellet injection research on DIII-D in support of ITER Disruption Mitigation System development

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.106.pdf

Recent advances in shattered pellet injection (SPI) in the DIII-D tokamak have led to improved understanding of several critical issues for the ITER Disruption Mitigation System. Infrared thermography shows elevated thermal quench heat loads indicative of radiation asymmetries peaked near the injection source. However these elevated heat loads, which are broadly centered around the injection port, indicate a peaking factor of <1.4 and remain below values predicted to cause melting in ITER [1]. Ballistic penetration of solid pellet fragments is thought to play a role in the initial mixing of injected particles, as shown by injecting along a shallow trajectory in which the shattered pellet misses the plasma core. This shallow SPI is observed to have reduced performance, comparable to that of equivalent massive gas injection, suggesting the importance of maximizing the initial penetration of particles, which would favor equatorial injection over upper port injection in ITER. The net particle assimilation from SPI is characterized across a wide range of plasma scenarios, and is found to depend predominantly on the plasma thermal energy, with Ohmic dissipation of the poloidal magnetic energy becoming important for sustaining the electron density later in the current quench (CQ). Increasing injection quantities by firing multiple pellets demonstrates the ability to further increase the density using simultaneous injections. CQ densities initially increase linearly with total injection quantity, indicating constant assimilation fraction, although saturation at higher quantities may occur. These assimilation data are in good agreement with energy balance models which account for ablation shielding of the pellet fragments and non-coronal radiation rates.

References
[1] M. Sugihara et al., Nucl. Fusion 47, 337 (2007)
Work supported by US DOE under DE-FC02-04ER54698, DE-AC05-00OR22725, DE-FG0207ER54917, and DE-AC52-07NA27344.

Speaker: D. Shiraki (EPS 2019)

629 O4.109 Experimental and modelling study of locked mode dynamics prior to disruptions in high performance JET plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.109.pdf

The presence of Error Fields (EFs) in magnetic fusion devices can affect energy confinement and plasma stability by braking plasma rotation, by inducing fast particle losses and being amplified when exploring high- regimes. The resulting EF Locked Modes (LMs) can be stabilized by NBI injection through the rotation shielding mechanism. However, the NBI is switched off to exit H-mode and to terminate the plasma discharge. Therefore, the rotation shielding effect is lost during these phases and an EF LM could be triggered. This contribution presents a characterization of the LM dynamics prior to the termination phase of high performance JET plasmas. The JET tokamak is a suitable device for performing this study being subject to an intrinsic EF, associated with asymmetries in the poloidal field coils [1], and with the NBI terminated when the real-time protection system detects the possibility of a plasma disruption. This study is carried out through a statistical analysis of magnetics and ECE data, which reveals that the n=1 mode is more prone to lock at the intrinsic EF toroidal location. The mode locking mechanism has been modelled by the RFXlocking code [2], which solves the torque balance equation considering the electromagnetic, the viscous and the toroidal viscosity torques. EF correction experiments performed in 2006 show that EF correction coils can spin up EF LMs, and can be thus exploited to avoid disruptions induced by LM.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

[1] Fishpool G.M. and Haynes P.S. 1994 Nucl. Fusion 34 109, [2] P. Zanca et al 2015 Nucl. Fusion 55 043020

Speaker: L. Piron (EPS 2019)

630 O4.110 Simulation of disruptions in EAST tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.110.pdf

Disruptions are one of the fundamental issues to be tackled in future tokamaks [1], due to significant eddy and halo currents in the conducting structures producing substantial electromagnetic forces and torques thanks to the interaction with the magnetic field. It is hence fundamental to have reliable modelling tools able to make prediction for future devices. The EAST tokamak [2] is equipped with fully superconducting poloidal and toroidal field coils and is designed and constructed to investigate the physical and engineering issues under steady state and long pulse operation for support of future fusion reactors. It is an ideal test-bed for the model validation, owing to its unique feature of having significant 3D current density patterns in the conducting structures during VDEs [3]. This is due to the presence of toroidally segmented stabilizing plates facing the plasma, in which significant "zig-zag" stabilizing currents may flow. In this paper, we show that the CarMa0NL code [4] is able to reproduce with remarkable accuracy the experimentally measured time traces of currents flowing in various parts of the tokamak during a disruption. The capability of the code of coupling an axisymmetric plasma with conductors with arbitrary 3D geometry allows us to demonstrate that in the events considered the halo currents do not contribute significantly to the currents measured in the supports, which are due mainly to eddy currents induced by plasma motion.

[1] T. Hender et al, Nucl. Fusion 47 (2007) S128
[2] Y.X. Wan et al, Proc. 21st Int. Conf. on Fusion Energy (Chengdu, China, 2006) (Vienna: IAEA)
[3] S.L. Chen, F. Villone et al., Nucl. Fusion 55 (2015) 013010
[4] F. Villone et al., Plasma Phys. Control. Fusion 55 (2013) 09500

Speaker: F. Villone (EPS 2019)

631 O4.111 Free-boundary simulations of MHD plasma instabilities in tokamaks

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.111.pdf

The growing need for a fundamental understanding of complex MHD phenomena in diverted tokamaks requires the development of more sophisticated and highly demanding codes. The numerical MHD code JOREK-STARWALL is adapted and applied to the simulation of free-boundary instabilities. The investigation of this type of instabilities requires a special treatment for the plasma boundary conditions for the magnetic field, where the interaction of the plasma with the vacuum and the surrounding conducting structures needs to be taken into account. In this work, the modelling of the electromagnetic plasma-wall-vacuum interaction is reviewed and generalized for time-varying coil currents and for the so-called halo currents.

The adapted JOREK-STARWALL code is applied to realistic plasma geometries in order to study the physics of two particular free-boundary instabilities: Edge Localized Modes (ELMs) triggered by vertical position oscillations and Vertical Displacement Events (VDEs). Two major results are obtained: 1. The triggering of ELMs during vertical position oscillations is for the first time reproduced with self-consistent simulations. These allow for the investigation of the physical mechanism underlying this phenomenon. The simulations reveal that for the ITER tokamak, these triggered ELMs are mainly due to an increase in the plasma edge current due to the vertical plasma motion [1]. 2. For VDEs, several benchmarks are performed with other existing MHD codes showing a good agreement and therefore allowing the performance of ITER simulations to estimate the expected amount of halo currents in ITER. Additionally, preliminary toroidally asymmetric VDE simulations are presented.

[1] F.J. Artola et al, Non-linear magnetohydrodynamic simulations of edge localised mode triggering via vertical position oscillations in ITER, Nuclear Fusion 58 (9) (2018) 096018.

Speaker: F.J. Artola (EPS 2019)

632 O4.112 Analysis of MHD stability and active mode control on KSTAR for disruption prediction and avoidance

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.112.pdf

Long-pulse plasma operation at high normalized beta up to 4 (exceeding the n = 1 ideal MHD no-wall stability limit) in KSTAR is presently limited by tearing instabilities rather than resistive wall modes that are computed to be stabilized by kinetic MHD effects. H-mode plasma operation during the 2018 KSTAR device campaign also produced discharges having strong m/n = 2/1 tearing instabilities at N lower than the idealMHD no-wall beta limit. The magnitude of the strongly unstable mode exceeded 30 G which consequently reduced plasma confinement and toroidal plasma rotation significantly. Mode stability alteration was attempted by varying plasma heating, safety factor, collisionality, and rotation profile. The experiment confirmed that an extended duration of the electron cyclotron heating (ECH) at the initial phase of the discharge plays a critical role in mode destabilization. To study destabilizing mechanisms that affect the mode growth, the stability of the observed tearing modes is computed by using the resistive DCON code and the M3D-C1 code. Equilibrium reconstructions that include constraints from Thomson scattering, charge exchange spectroscopy, motional Stark effect diagnostic data, and allowing fast particle pressure are used as input for reliable computation of stability. The classical tearing stability index, from resistive DCON is compared to modes from significantly higher normalized beta plasmas and the result indicates that their stability is governed by different physical mechanisms. In preparation for long-pulse plasma operation at higher beta utilizing increased plasma heating power in 2019, a resistive wall mode (RWM) active feedback control algorithm has been completed and enabled on KSTAR. To accurately determine the dominant n-component produced by RWMs, an algorithm has been developed that includes magnetic sensor compensation of the prompt applied field and the field from the induced current on the passive conductors. Use of multiple toroidal sensor arrays is enabled by modifying the sensor toroidal angles assumed in mode decomposition to include the effect of varied mode helicities in the outboard region where the mode measurement is made. This analysis on stability, transport, and control provides the required foundation for disruption prediction and avoidance research on KSTAR.
This work is supported by US DOE Grant DE-SC0016614.

Speaker: Y. Park (EPS 2019)

MCF

Convener: R. Ding

633 I4.103 Modelling radiative power exhaust towards future fusion devices

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.103.pdf

Power exhaust in future electricity producing fusion device like DEMO features difficulties which, compared to ITER, are harder to tackle in terms of operational control requiring an improved physics understanding. For a given power loss density Ploss/R the plasma facing components need to withstand a maximum heat flux not exceeding 5MW/m^2 in steady state on timescales lasting days or weeks. To achieve this, a pronounced detached divertor regime is to be exploited with low divertor temperatures Te,div < 1-2 eV [1]. For a DEMO sized device a total dissipated fraction fdiss=Pdiss/Ploss close to 95% or higher is required to reduce the total target heat load. The amount of achievable radiation loss in the scrape-off layer (SOL) is limited by the amount of removable pressure inside the SOL [2]. In DEMO, Pdiss must not only cover the diverted plasma and SOL regions, but also part of the confined region to reduce upstream pressure. Validated numerical models like SOLPS-ITER including neutral kinetics and SOL drifts & currents are required to accurately predict such exhaust regimes in varying geometries [3]. A numerical model must be scalable to qualify detachment criteria bridging the gap towards ITER and DEMO exhaust operational regimes. To clarify the role of machine size (Rmaj) on critical numerical parameters (e.g. anomalous transport), similarity experiments on power exhaust for JET and ASDEX-Upgrade (AUG) have been undertaken. A N2-seeded partially detached H-mode JET discharge in vertical target configuration was performed (2.5MA/2.7T, PNBI=20.6MW). SOLPSITER model constraints were derived from diagnostic JET divertor characterization. An AUG N2seeded similarity discharge matching the SOL q|| was obtained by controlling Pheat/R, Te,div and q95 (0.8MA/2.5T, PNBI=10MW). A similar SOLPS-ITER model has been setup to the matched AUG discharge to quantify remaining discrepancies to the JET case. The results highlight the criticality of other model parameters like neutral conductance to match accurately the total divertor pressure.

[1] M. Wischmeier et al., J. Nucl. Mater. 463, 22 (2015);
[2] C. S. Pitcher and S. P. C., Plasma Phys. Control. Fusion 39, 779 (1997);
[3] S. Wiesen et al., Nucl. Mater. Energy 12, 3 (2017)

Speaker: S. Wiesen (EPS 2019)

634 I4.104 Progress Toward Divertor Detachment in TCV H-mode Discharges

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I4.104.pdf

The operation of future high-power density fusion reactors such as ITER and DEMO requires avoiding damaging plasma-facing surfaces and good core confinement. The former requirement necessitates operating in the detached divertor regime, and the latter is met by operating in the high confinement (H-) mode. Recent experiments on the TCV tokamak have explored access to H-mode and divertor detachment in neutral beam heated ELMy and ELM-free scenarios in conventional and alternative divertor configurations using fuelling and N2 seeding. The impact of the divertor geometry on detachment access was explored in variations of the single null configuration where the poloidal flux expansion at the outer divertor ranged from 3.5 to 10 and the major radius from 0.75m to 1.03m. The approach toward detachment and its evolution has been extensively diagnosed to characterise the divertor particle and power loads, radiation losses and spectral line emission profiles. This work builds on previously reported studies of ohmic H-modes where Ne injection was applied, resulting in a reduction in divertor power and particle loads [1]. The heating power required to enter H-mode was measured in a range of divertor configurations, finding that, in the vicinity of the minimum of the PL-H/ne curve, the threshold power is largely independent of the poloidal flux expansion and major radius of the outer divertor. A factor 2 reduction in the outer divertor power load was achieved in ELM-free (using N2 seeding and D2 fuelling) and ELMy scenarios (using N2 seeding only). No significant reduction in the outer divertor particle flux was observed in the ELM-free scenarios, compared with ~30% reduction in the most strongly detached ELMy cases, which is thought to be due to a reduction in the particle source in the divertor due to ionization, which is also observed in L-mode [2]. Unlike L-mode plasmas, a broadening of the emission profiles after the onset of detachment is not observed. The deposited ELM heat flux is found to decrease with increasing seeding. Nevertheless, at all depths of detachment explored, ELMs led to attachment of the divertor followed by prompt re-detachment following the ELM. Increasing poloidal flux expansion was found to result in a deeper detachment. These observations will be interpreted via SOLPS-ITER simulations.

Work supported by RCUK [grant number EP/I501045] and Euratom.

[1] R. A. Pitts et al., J. Nucl. Mater 266-269 648-653 (1999) [2] K. Verhaegh et al., NME 12 112-117 (2017)

Speaker: J. Harrison (EPS 2019)

635 O4.105 Energy Transport and Dissipation in DIII-D Detached Divertor Plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.105.pdf

A comprehensive diagnostic set compared against 2D modeling has provided new insight into energy transport and dissipation processes in detached plasmas and their scaling to future devices. Experiments and modeling reveal a detached divertor plasma dominated by plasma convection from the X-point towards the target. While a significant fraction, ~1/3, of the convection is carried by ionization-driven parallel flow, a larger part is carried by ExB plasma drift in the
poloidal direction driven by the radial Te gradient and the resulting radial electric field. This plasma flow allows utilization of the entire divertor volume for dissipation with a hierarchy of radiative processes including higher charge states of the intrinsic carbon impurity, CIV, dominating near the X-point with additional contributions from CIII and CII extending down the divertor leg towards the target. Near the target, Ly-alpha radiation from the deuterium fuel, including a large contribution from plasma recombination, is dominant, but deuterium molecular radiation from the Lyman-Werner bands may also contribute a fraction of the observed radiative dissipation. A power scan carried out to examine scaling of the detached divertor towards color is towards power densities expected in future devices found the upstream separatrix density to increase with the parallel heat flux density as q parallel ^1/2 . Near complete radiative dissipation was achieved even as into the divertor near the X-point was increased from 130 MW/m^2 to 350 MW/m^2 with the power scan. At the higher power levels, radial transport was found to increase the width of the heat flux channel, lambda q, both in the midplane and divertor profiles. This increase in lambda q stands in contrast to the ITPA scaling which found no power dependence in attached plasmas and may be a manifestation of MHD ballooning stability limits being reached at high power. The result of this broadening is a divertor density that does not increase with power as might otherwise be expected. These results, poloidal expansion of the radiating volume due to convection and radial expansion of the divertor plasma at higher power, imply an optimistic scaling of heat flux dissipation in future devices. These observations were made possible by an extensive diagnostic set that included bolometry and VUV spectroscopy for energy balance, Thomson Scattering at the midplane and divertor for plasma profiles and Coherence Imaging Spectroscopy (CIS) for plasma flow, Fig. 1. Interpretation of these data was made possible by the multiple physics processes employed in the 2D fluid code UEDGE, including realistic 2D geometry, comprehensive atomic physics processes and full ExB plasma drifts.

Speaker: A. Leonard (EPS 2019)

636 O4.106 Turbulence driven widening of the near-SOL power width in H-Mode discharges at ASDEX Upgrade

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.106.pdf

Operation of tokamaks with H-Mode characteristics and at high densities is generally foreseen for future high-power fusion systems, including ITER. The ease of access to divertor detachment via impurity seeding scales to first order proportional to (n_sep/n_GW)^2 lambda_q/rho_s,pol [1] with lambda_q being the power width, rho_s,pol = Sqrt(T_sep m_D/e/B_pol), T_sep and n_sep the separatrix temperature and density, respectively. Divertor heat flux data from infra red (IR) from various tokamaks in H-Mode regime scales approximately like rho_s,pol. However, the IR based scaling comes with the restrictions that only low-gas-puff discharges were considered. Here, we extend the low edge density data base with high density plasmas reaching the H-mode density limit by using Thomson-Scattering to measure the electron temperature decay length which will set the near-SOL power width through parallel heat conduction, lambda_Te ~ 7/2 lambda_q. As the principal result we present a generalized power width scaling which reads as lambda_q proportional to rho_s,pol (1 + 2.8alpha_t^1.8) where alpha_t describes a normalized collisionality (alpha_t = 3 10^-18 R q^2 n Z_eff T^-2). The parameter alpha_t describes the relative importance of the interchange effect on drift-wave turbulence as proposed by Scott[2] and is found for our data base to be about inversely proportional to the diamagnetic parameter alpha_d in [3]. This new scaling shows (a) in the limit of low edge densities (alpha_t ~0.15) accurate agreement to the IR based scaling and (b) at elevated separatrix densities (alpha_t ~0.8) that the power width is broadened by a factor of about three albeit accompanied by a confinement degradation to near L-Mode levels. We show that the confinement degradation is dominated by a reduction of the pedestal top pressure. Importantly, plasmas with higher shaping (higher triangularity) show a reduced confinement degradation at the same separatrix densities. We will present the experimental data base, new scaling results and discuss implications for ITER.

References
[1] R.J.Goldston et al, Nuclear Fusion 57, 055015 (2017)
[2] B.D. Scott, Physics of Plasmas 12, 062314 (2005)
[3] B.N.Rogers, J.F.Drake, A.Zeiler, Phys. Rev. Lett. Vol.81, p.4396 (1998)

Speaker: T.H. Eich (EPS 2019)

637 O4.107 Integrated operation in achieving steady-state H-mode plasma on EAST

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.107.pdf

A 100 sec long-pulse steady-state H-mode plasma with good energy confinement (H98(y,2) ~ 1.1) has been successfully achieved on EAST using RF heating and current drive. Recent EAST experiments with improved hardware capabilities have demonstrated steady-state fully non-inductive scenarios with extension of fusion performance (Betap~2.5 & N~2.0, H98(y,2) ~ 1.2, <ne>/nGW~0.8, fBS~50% at q95~6.8) through integrated control of the wall conditioning and recycling, plasma configuration, divertor heat flux, particle and impurity control, and the effective coupling of multiple RF heating and current drive (H&CD) sources. This steady-state scenario was characterized with fully non-inductive current drive at high density with low rotation and high-frequency, small-amplitude edge localized modes (ELMs), and stable control of heat and particle exhaust using various technologies (e.g. RMP) on the ITER-like tungsten divertor. The optimization of the X-point, plasma shape, the outer gap and local gas puffing near the lower hybrid wave (LHW) antenna were integrated with global parameters of BT, line averaged electron density <ne> for high LHW current drive efficiency, and on-axis deposition of ECH in the long pulse operation. The benefits of using ECRH to avoid tungsten accumulation in the core plasma, and enhancement of H&CD by the synergistic effect of ECH and LHW were demonstrated. A higher energy confinement is observed at higher performance with favourable toroidal field direction. In addition, reduction of the peak divertor heat flux was successfully demonstrated using active radiation feedback control. Towards the next goal (400s long pulse H-mode operations with ~50% bootstrap current fraction) on EAST, an integrated control of the current density profile, the pressure profile and the radiative divertor will be addressed in the near future.

Speaker: X. Gong (EPS 2019)

638 O4.108 Divertor Power Load Studies in ASDEX Upgrade and TCV

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O4.108.pdf

In recent years the focus of tokamak fusion research onto power exhaust increased showing that first wall power load is one of the major challenges in realizing a power plant. Unmitigated divertor power loads in next step fusion devices like ITER are projected to exceed material limits making significant impurity seeding necessary. Furthermore, scenarios without large type-I edge localized modes (ELMs) are desired for a future reactor. Two possible regimes, among others, are the operation with negative triangularity and type-I ELM suppression or mitigation using an external magnetic perturbation (MP) field. Shaping the plasma to negative triangularity was pioneered at TCV showing improved core confinement in L-mode, a natural ELM free regime, compared to positive triangularity. ELM suppression by an external MP is studied in most of today's tokamaks. However, steady state power exhaust under these conditions is an open field of research. The divertor power load characterization in both regimes is presented. Experiments in TCV were conducted in L-mode performing a scan of the upper triangularity from -0.28 to 0.47 with both magnetic drift directions and in deuterium and helium. These experiments exhibit a correlation between upper triangularity and scrape-off layer power falloff length. With decreasing triangularity a narrowing of the power fall-off length is observed with the smallest values at negative triangularity. This shows that the power fall-off length is possibly narrower in a negative triangularity reactor than expected from multi-machine scaling laws derived from data with positive triangularity and without dedicated triangularity variations. A recently established empirical scaling from ASDEX Upgrade L-mode is extended towards TCV. No direct effect of the machine size on the power fall-off length is observed. Experiments in ASDEX Upgrade were conducted characterizing the effect of an external MP on divertor power load. The application of a non-axisymmetric MP leads to a toroidal variation of heat flux in both L- and H-mode plasmas. It is shown that the toroidally averaged heat flux profiles are described by a 1D diffusive model and are comparable to heat flux profiles without MP. Plasma discharges with an increased density have a reduced toroidal heat flux variation. The local decrease of plasma temperature in the divertor caused by the increased density is the identified reason. Also, previous studies reported that heat load caused by ELMs correlates with pedestal pressure. This correlation is confirmed in presence of a MP. However, the external MP affects the toroidal position of the heat load caused by ELMs.

Speaker: M. Faitsch (EPS 2019)

20:00 Social Dinner

Friday, 12 July

Plenary Session

Convener: S. Brezinsek (Forschungszentrum Jülich)

639 I5.012 Plasma techniques for nanostructured materials

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.012.pdf

Nanostructured materials are revolutionizing many fields of science and technology and are finding their way in many commercial products. Their interest is due to the fact that nanostructured films present functional (tribological, biological, electrical, optical) properties which are new, or of superior quality, compared to non-nanostructured ones. Indeed, plasma sources are essential for the synthesis of new molecules yielding very high purity materials, allowing in addition the control of formation and transport of the synthesized building blocks for the nanofabrication of thin layers and multilayer composited films, as well as the synthesis of nanoparticles (NPs). A large variety of nanostructured materials and their applications have been already demonstrated in different fields. So far, plasma-based methods have been employed for the precursor dissociation, the most relevant of which is the expanding thermal jet (1995) enabling purity control of the growth process, and more recently, the Pulsed Laser Deposition (PLD) technique working at ultra-high vacuum has been developed to control both purity and nanostructured morphology. A novel technique was designed to assemble high purity materials at the nanoscale over a larger area and higher flexibility, allowing to work with many kind of chemicals, and less severe operational conditions due to the possibility of working at higher pressures. The method is based on a non-thermal supersonic plasma jet where independent control over plasma chemistry, dissociation and molecule aggregation, nanoparticle assembly and film growth, are achieved by fluidodynamic segregation of the two processes in a unique remote plasma configuraton. The method for producing nanostructured films and NPs with controlled morphology, particularly of a hierarchically organized type, is suitable to a scale-up for industrial processing. The technique denominated Plasma Assisted Supersonic Jet Deposition (PA-SJD) is the segmentation of the gas phase material synthesis in two separate steps: Chemistry control in a reactive cold plasma environment of several precursors; and secondly, nucleation and assembling of the building blocks by means of a supersonic inseminated plasma jet where particle collisions can be controlled. By acting on the jet parameters, the active control of the synthesis of NPs is able to produce cluster sizes varying from few nm to 100 nm. These nanomaterials (NPs and films) have a broad range of applications in diverse fields such as photovoltaics, photoelectrochemistry, energy storage, photonics and biomedicine.

Speaker: C. Riccardi (EPS 2019)

640 I5.013 The ITER Research Plan and supporting R&D in present experiments

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.013.pdf

The primary aim of the ITER Research Plan (IRP) is to define the plan of research and development and of the exploitation of the facility necessary to meet the ITER mission goals. The IRP is divided into two main phases after first plasma demonstration: operation in H/He plasmas (Pre-Fusion Plasma Operation (PFPO)) and in DD/DT plasmas (Fusion Plasma Operation (FPO)). These two main phases are subdivided into experimental campaigns, separated by further assembly phases, in which the tokamak ancillary systems (heating and current drive, fuelling, etc.) are progressively implemented to their baseline configurations to be completed before FPO ("Staged Approach"). The IRP describes the objectives of each operational campaign consistent with the available tokamak systems, details the experimental plan to achieve them (including options), and identifies the main risks of the experimental plan to achieve the objectives of each phase and corresponding mitigation actions. The main physics objectives of the two initial experimental campaigns (PFPO-1 and PFPO-2) are the achievement of high confinement plasmas (H-mode) and the demonstration of plasma operation up to the ITER design values for plasma current (15 MA) and toroidal field (5.3T) in L-mode plasmas. These experiments will characterize for the first time energy and particle confinement in a tokamak plasma at the reactor scale, to compare with the extrapolations made on the basis of present experiments that have been used for the ITER design. This will determine the operational range for H-mode operation in H/He plasmas in ITER and allow an initial assessment of core-edge integration and plasma-wall interactions in ITER. It is anticipated that operation will be limited to plasma currents/fields ~50% of the design values in H mode. Important issues for these initial phases concern the demonstration of disruption mitigation by shattered pellet injection, H-mode operation at low values of current and field (5 MA/1.8T to 7.5 MA/2.65T) and the optimum plasma species to perform the H-mode experiments (H, He or mixed H-He); the required R&D to address the open issues will be described. The FPO campaigns cover a long operational period from the start of DD plasma operation, with the principal objectives being the demonstration of the Q = 10 inductive operation and Q = 5 operation with in-principle steady-state conditions. The experimental plan to proceed from DD towards DT plasmas builds on the results expected to be achieved in PFPO. It includes a verification of the L-mode 15 MA development path demonstrated in PFPO and the initial expansion of the H-mode operational space in DD plasmas from low values of current and toroidal field. This is followed by a gradual evolution toward DT plasmas with increasing T content plasmas leading to a demonstration of Q = 10 operation for a duration of 50 s. The details of the experimental path depend on the changes of plasma parameters with increasing currents, fields and T concentration with the optimum path providing a gradual assessment of physics and resolution of integration issues and tuning of plasma control schemes as the fusion power builds up, for which R&D is required. This initial phase is then followed by experimental campaigns focused on increasing the burn length of the inductive Q = 10 scenario towards the objective of 300-500s and the development of the in-principle stady-state Q = 5 scenarios where the optimization of the pressure and plasma current profiles will be a main focus of the experimental programme. In both cases, scenario integration issues associated with high Q operation will explore the new regime of dominant self-heating for the first time. The open R&D physics and operational issues regarding the achievement of high Q fusion performance for pulse durations from 300 s up to 3000s will be discussed.

Speaker: A. Loarte (EPS 2019)

10:10 Coffee Break

BPIF

Convener: P. Muggli (Max-Planck-Institut für Physik)

641 I5.201 High quality laser-plasma acceleration with the Resonant Multi-Pulse Ionization injection scheme

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.201.pdf

The production of high-quality electron bunches in Laser Wake Field Acceleration [1] relies on the possibility to inject ultra-low emittance bunches in the plasma wave. A new bunch injection scheme (Resonant Multi-Pulse Ionization, ReMPI) has been conceived and studied in which electrons extracted by ionization are trapped by a large-amplitude plasma wave driven by a train of resonant ultrashort pulses [2]. Such a train of pulses can be obtained in very efficient, compact and stable way, by phase manipulation in the front-end [3]. The ReMPI injection scheme relies on currently available laser technology [4] and is being considered for implementation of future compact X-ray free electron laser schemes [5]. Simulations show that high-quality electron bunches with energy up tp 5 GeV, with normalized emittance below 0.1 mm◊mrad and energy spread below 1% can be obtained with a single stage.

References
[1] T. Tajima and J. M. Dawson, Laser Electron Accelerator, Phys. Rev. Lett. 43, 267 (1979)
[2] P. Tomassini et al., The Resonant Multi-Pulse Ionization injection, Physics of Plasmas 24, 103120 (2017)
[3] L. Labate et al., Quasi Lossless Pulse Train generation by Early Amplitude division, submitted
[4] L.A. Gizzi,A viable laser driver for a user plasma accelerator, NIM-A 909 58-66 (2017)
[5] EuPRAXIA collaboration, http://www.eupraxia-project.eu/

Speaker: P. Tomassini (EPS 2019)

642 I5.202 Optimizing Direct Laser Acceleration

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.202.pdf

Modern laser technology and the realization of high-intensity, short-pulse laser systems using Chirped-Pulse Amplification has led to the development of novel laser-based acceleration schemes. For high-intensity, picosecond duration pulses, where the pulse duration exceeds the plasma period, the laser pulse will expel nearly all of the electrons within the focal volume, creating an ion channel. Electrons that become trapped in the ion channel will gain energy directly from the laser field through the v X B force through a process known as Direct Laser Acceleration (DLA). Here, we present experimental measurements of electrons accelerated by the Omega Extended Performance (EP) laser system, through the interaction of a with 1 ps laser pulse with an underdense CH plasma plume. These results demonstrate the existence of an optimal plasma density for electron acceleration by DLA, producing electron beams with energies up to a record 0.6 GeV and 10s of nC charge. Two-dimensional PIC simulations conducted using the EPOCH code, with conditions designed to match Omega EP, confirm DLA as the dominant acceleration mechanism. Particle tracking enables further investigation into the dynamic role of quasi-static channel fields on electron energy enhancement, beam pointing and divergence, elucidating the mechanisms and action of DLA at different plasma densities and pulse durations. Electron beams generated by this scheme could be used to obtain brilliant, spatially coherent X-rays with the capability to be accurately synchronized to short pulse laser-initiated events and for experimental verification of the two-photon Breit-Wheeler process.

Speaker: A.E. Hussein (EPS 2019)

643 O5.201 Petawatt laser guiding and electron beam acceleration to 7.8 GeV in a laser heated capillary discharge waveguide at BELLA

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.201.pdf

We present modeling and experimental results concerning the guiding of relativistically intense laser pulses with peak power of 0.85 PW over a distance of 15 diffraction lengths. Laser guiding was achieved by increasing the focusing strength of a capillary discharge waveguide using laser inverse Bremsstrahlung heating. This allowed for the production of electron beams in a laser-plasma accelerator with quasi-monoenergetic peaks up to 7.8 GeV, double the energy that was previously demonstrated. Charge was 5 pC at 7.8 GeV and up to 62 pC in 6 GeV peaks, and typical beam divergence was 0.2 mrad.

(*) Now at Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany

Speaker: C. Benedetti (EPS 2019)

644 O5.202 Production of isolated CEP-tunable subcycle pulses in laser-driven wakes

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.202.pdf

Intense, ultra-short electromagnetic pulses are enabling applications such as the control of motion in solids and the observation of reaction dynamics at the electronic level. While both high-intensity and carrier envelope phase (CEP) tunability are crucial, they are hard to obtain with current methods. Laser-plasma methods, e.g. [1, 2], are scalable alternatives which, however, are either not CEP-tunable or require a controllable CEP-stable high-intensity laser.
Here, we propose a new scheme for the generation of intense, isolated, CEP-tunable, subcyclepulses by laser-driven wakes. It relies on the interaction of a low-intensity, CEP-stable, longwavelength seed pulse with a wake driven by an intense, not necessarily CEP-stable pump laser pulse. We show through 3D particle-in-cell (PIC) simulations that a seed pulse with wavelength longer than the plasma skin depth, c/pe, can extract energy from the leading density spike of the wake. As a result of localized amplification, an intense subcycle pulse is formed. Through a parametric study with 2D PIC simulations we show that the subcycle pulse is CEP-tunable by varying either the CEP of the seed pulse or the delay between the seed and pump pulses. Moreover, we show that we can control the subcycle pulse intensity, mean frequency and spectral range by varying the plasma density and pump laser intensity. In particular, relativistic intensity subcycle pulses can be obtained in the mid-IR regime, which are hard to obtain by other means.

References
[1] Z. Nie et. al, Nature Photonics 12, 489 (2018). [2] I. Thiele et al., arXiv:1806.04976 (2018).

Speaker: E. Siminos (EPS 2019)

645 O5.203 Collimated electron bunches from relativistic laser solid interaction

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.203.pdf

We demonstrated efficient electron acceleration in the plasma channel with injection through the breaking of plasma waves generated by parametric instabilities. It was shown experimentally that in the case of optimal preplasma parameters femtosecond laser pulse with an intensity of 5x10^18 W/cm^2 and an energy of 50 mJ generates a collimated electron bunch having divergence of 50 mrad, exponential spectrum with the slope of ~2 MeV and charge of tens of pC [1]. The charge was confirmed measuring neutron yield from Be(g,n) photonuclear reaction with threshold of 1.7 MeV.
This bunch was produced using arbitrary sharp L ~ 0.5 gradient at the vicinity of 0.1-0.5 critical density and a long tail of teneous preplasma. We successfully formed such a gradient by an additional nanosecond laser pulse with intensity of 5x10^12 W/cm^2 [2]. The reflected pulse creates plasma channel that serves for the DLA of electrons. Finally, well collimated bunch of high energy electrons emerges with mean electron energy well above the ponderomotive energy of the femtosecond pulse. Additional calculations showed that L~0.5 is the optimal scale length for the considered mechanism of electron acceleration.
Simulations of a test electron's motion in the complex electromagnetic field consisting of the laser pulse and static azimuthal electric and magnetic fields showed that an electron acquires maximum energy at the channel exit if its initial energy amounts to several hundred keV and it is injected at the instant of the maximal field of the laser pulse. Plasma waves of the hybrid SRS-TPD instability are capable of injecting electrons with required energies in the channel. This instability generates two groups of waves: one moves along the plasma surface and the other - approximately in the perpendicular direction toward lower densities. Analysis of electron's trajectories obtained from the PIC-modeling showed that the first group of waves accelerates electrons, while the field of the second group pushes electrons into the plasma channel. These waves were evidenced experimentally and numerically from the scattered 3/2w_0 harmonic.

1. I.Tsymbalov et al., submitted to Plasma Physics & Controlled Fusion, 2019. 2. K.Ivanov et al, Phys. Plasmas 24 063109 (2017)

Speaker: A. Savel'ev (EPS 2019)

646 O5.204 Nonlinear dynamics of plasma grating in a static ponderomotive potential

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.204.pdf

The plasma devices can stand for much larger energy fluency than solid optical devices. Thus plasma devices become a hot topic recently, as the laser power is promoted to Petawatt order. Plasma grating is one of these appealing plasma devices. Plasma grating can act as laser polarizer and waveplate for both long, moderately intense laser[1, 2, 3] and short, superintense laser[4]. And it also can be used as photonic crystal[5]. On the surface of solid target, it is generated as plasma hologram for ultraintense laser[6]. It is also used for coupling the laser into surface plasma wave instead of solid grating[7].
The growth of the plasma grating is thought to be brought by the deepening of the ion velocity. Its collapse is also believed to be induced by the X-type breaking of the grating[8, 9]. Forslund et al. compares the momentum of ions with initial velocity distribution to the maximum possible thermal potential, to explain the X-type breaking[10].
Here in this work, we analyze the plasma grating grows in a static ponderomotive potential generated by two identical counterpropagating lasers. The details of the building and collapsing process are shown with both fluid and PIC simulation. The mechanism is discussed in details. We find good agreement between fluid and PIC simulation.

References
[1] P. Michel, et al. Phys. Rev. Lett.113, 205001 (2014)
[2] D. Turnbull et al. Phys. Rev. Lett. 116, 205001 (2016)
[3] D. Turnbull et al. Phys. Rev. Lett. 118, 015001 (2017)
[4] G. Lehmann and K. H. Spatschek, Phys. Rev. E 97, 063201 (2018)
[5] G. Lehmann and K. H. Spatschek, Phys. Rev. Lett. 116, 225002 (2016)
[6] A. Leblanc et al. Nat. Phys. 13, 440 (2017)
[7] S. MonchocÈ et al. Phys. Rev. Lett. 112, 145008 (2014)
[8] D. W. Forslund, J. M. Kindel, and E. L. Lindman, Phys. Fluids 18, 1017 (1975)
[9] A. A. Andreev et al. Phys. Plasmas 13, 053110 (2006)
[10] D. W. Forslund et al. Phys Fluids 22, 462 (1979)

Speaker: H. Peng (EPS 2019)

BSAP

Convener: D. Burgess

647 I5.401 Magnetic reconnection in AGN disks and jets

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.401.pdf

Turbulent fast magnetic reconnection can be an important mechanism for accelerating particles to relativistic velocities and produce very-high-energy (gamma-ray and neutrino) emission in the magnetized regions of galactic and extragalactic black hole sources. In this talk, we discuss this process in the framework of accretion disks and relativistic jets of Active Galactic Nuclei (AGNs). We summarize recent results of our group on multidimensional numerical generalrelativistic magnetohydrodynamical (GRMHD) and special relativistic MHD (SRMHD) simulations, including radiative transfer calculations and the injection of test particles, in order to understand this acceleration process and the resulting non-thermal emission both in the relativistic jets and accretion flows of these sources. Fast turbulent reconnection is naturally driven in these systems by MHD instabilities like the magnetorotational, Parker-Rayleigh-Taylor, and current-driven kink instabilities. We will also present the resulting magnetic reconnection rates, the power spectrum of the accelerated particles, and the non-thermal gamma-ray and neutrino emissions we obtain for these systems.

Speaker: L.H. Kadowaki (EPS 2019)

648 O5.401 Opportunities for plasma physics experiments on the new lunar orbiting manned international space station

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.401.pdf

In 2023 the first element of a new international space station is to be launched. The Lunar Orbital Platform-Gateway (LOP-G), or Deep Space Gateway (DSG) will orbit the Moon rather than the Earth [1]. The purpose of the Gateway is to acclimatise crew and technology for long durations and radiation exposure of deep-space missions far from the Earth.
The Gateway will offer the opportunity to deploy additional plasma instrumentation on ‘cube’ or ‘nano’ satellites. Previous work [2] has shown how features like the lunar crustal magnetic anomalies can be used as natural laboratory-type experiments in space due tothe number of in-situ missions thathave made observations and thefixed footprint of the magnetic fieldsources.
The Gateway will offer the opportunity to conduct active and passive plasma physics experiments in a low density, collisionless plasma environment. Active plasma experiments are also being considered.
In this presentation I will outline some interesting ideas and topics that will take advantage of this opportunity to investigate plasmas far from equilibrium.

References
[1] NASA updates Lunar Gateway plans. (Sept (2018).
[2] Bamford, R. A., et al. ApJ 830.2 (2016): 146.

Speaker: R.A. Bamford (EPS 2019)

649 O5.402 Linear and Nonlinear Physics of Tenuous Beam-Plasmas Instabilities

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.402.pdf

Astrophysical plasmas are ubiquitous and differ from laboratory plasmas in key aspects. They are typically cold (k_B T<<m_e c^2), collisionless, and usually contain relativistic sub-populations. To study the evolution of such plasmas, it is necessary to employ a fully kinetic treatment.
Particle-in-cell (PIC) algorithms combine Eulerian and Lagrangian methods to efficiently solve for the full evolution of plasmas. Due to numerical heating in PIC algorithms, exploring nonlinear and long term (e.g., millions of omega_p^-1 ) evolution is inaccurate and unreliable.
We developed the SHARP algorithms [1] (1D, 1D3V, and 2D3V), which uses higher-order interpolation to great improve energy conservation while exactly conserving both the charge and the total momentum. This enables reliable explorations of the nonlinear evolution of astrophysical plasmas. The talk will prominently features this novel PIC simulations of the linear and nonlinear evolution of tenuous beam-plasmas instabilities (within inhomogeneous [2] and homogeneous [3] background plasmas) driven by pair beams that result from the propagation of TeV photons from Blazars [4].

References
[1] Shalaby, M., Broderick, A. E., Chang, P., et al. 2017, ApJ, 841, 52
[2] Shalaby, M., Broderick, A. E., Chang, P., et al. 2018, ApJ, 859, 45
[3] Shalaby, M., Broderick, A. E., Chang, P., et al. 2017, ApJ, 848, 81
[4] Broderick, A. E., Chang, P., & Pfrommer, C. 2012, ApJ, 752, 22

Speaker: M. Shalaby (EPS 2019)

LTPD

Convener: A. Michau (LSPM CNRS)

650 I5.301 Atmospheric pressure helium plasma as a tool for interacting with cells and pathogens

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.301.pdf

This contribution reviews recent activity of the Padova group on the use of helium plasmas in plasma medicine. Following the initial emphasis on disinfection of the cornea [1], the research activity has developed along several research lines, which cover the topics of wound healing, cancer treatment and non-thermal coagulation.
Plasma source characterization from the physical and chemical point of view has been performed, comparing two different sources: a RF source for indirect plasma treatment [2] and a Dielectric Barrier Discharge jet for direct treatment, specifically designed for non-thermal blood coagulation applications. The comparison has included an assessment of disinfection properties. The specificity of helium as working gas has been emphasized by mass spectrometry measurements, which hint to the importance of metastable excited states.
The wound healing activity has seen a set of in vitro tests, which have shown the ability of a RF indirect treatment to stimulate cell proliferation and migration, processes which are related to an increase of intracellular Reactive Oxygen Species (ROS) level [3]. Subsequently, an in vivo study on large animals (sheep) has been performed, showing the ability of the plasma treatment to significantly reduce bacterial charge on the wound, to reduce inflammation, to promote the regeneration of cutaneous annexes, such as hair follicles and glands, and to lead to an anticipated induction of blood vessel formation.
The work on cancer treatment has been carried out in vitro, using primary cells cultivated from tissue samples of patients affected by laryngeal and lung cancer. The plasma treatment has been shown to lead to an increased ROS level in cells, with a stronger effect observed in cancer cells than in healthy ones. As a consequence, apoptosis is induced in a remarkable fraction of cancer cells, with a preferential effect with respect to healthy ones. This result could be enhanced by combining the plasma treatment with incubation with a molecule known to increase the ROS level in cells.
Finally, results of a project on non-thermal blood coagulation induced by the direct interaction with a helium plasma jet will be reported. In vitro studies have shown that the applications of the plasma indeed accelerates coagulation. The result has been confirmed by in-vivo tests on animal models.

References
[1] E. Martines, P. Brun, P. Brun, et al., Clinical Plasma Medicine 1, 17 (2013).
[2] E. Martines, M. Zuin, R. Cavazzana, et al., New J. Phys. 11, 115014 (2009).
[3] P. Brun, S. Pathak, I. Castagliuolo, et al., PLOS ONE 9, e104397 (2014).

Speaker: E. Martines (EPS 2019)

651 I5.302 Magnetic fields in dusty plasmas: pattern formation particle growth and other recent studies in the Magnetized Dusty Plasma Experiment

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.302.pdf

For over a decade, it has been postulated that the addition of a magnetic field can have a profound influence on the properties of a complex/dusty plasma. The Magnetized Dusty Plasma Experiment (MDPX) device at Auburn University is the most recent facility to study dusty plasmas in strongly magnetized plasmas. The MDPX device is a flexible, high magnetic field research instrument with a mission to serve as an open access, multi-user facility for the dusty plasma and basic plasma research communities. In a strong magnetic field, the transport of ions and electrons in the plasma will be modified. This changes how the microparticles become charged and modifies the Debye screening of the microparticles by the surrounding plasma, thus altering the inter-particle interactions within the plasma. In particular, under conditions when the magnetic field is sufficiently large, B >= 0.5 T, a variety of emergent phenomena are observed including a new type of imposed spatial ordering, significantly modified particle charging, significant modification of wave properties, and a strong coupling between ion and microparticle transport. This presentation will focus on recent studies with a specific emphasis on studies of imposed ordering of the dust particles and modification of particle growth at high magnetic field. Time permitting, other recent work on optical measurements and modeling of the plasma will be presented.

This work is supported with funding from the U.S. Department of Energy and the National Science Foundation (Physics Division and EPSCoR Office).

Speaker: E. Thomas (EPS 2019)

652 O5.301 Dissipative factors effect on the efficiency of the plasma acceleration in electromagnetic accelerator of rail type

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.301.pdf

The electromagnetic rail accelerators (railguns) with plasma armature are an interesting object for the plasma physics. The acceleration of the plasma (or a solid body ahead of plasma armature) in railguns are due to electromagnetic interaction of the electrical current in plasma and magnetic field (generated by current and from external source). In theory there is no limit on achievable velocity. But in reality there is a velocity ceiling of about 6 km/s. Different dissipative factors are responsible for the limiting of the achievable velocity. In the report the different factors will be analyzed.
One of it is the effect of current leakage through shock-compressed layer. Our experimental and theoretical investigations of the plasma armature motion in a channel of an electromagnetic rail accelerator (railgun) filled with an inert gas will be presented. The model of the plasma armature acceleration takes into account the force of the gas pressure in the shock-compressed layer and the drag force resulting from a capture of a part of the erosive mass by the plasma armature. It is shown that in the case of considerable gas ionization after the shock wave the discharge current flows partly through the conducting shock-compressed layer. This leads to a decrease in the current in the plasma armature, and, hence, in the ampere force. As a consequence, an acceleration crisis occurs and the maximum velocities of the plasma armature becomes limited. Comparison of the experimental and theoretical data on the shock wave velocity in the channel shows that they are in good agreement.
The report will summarize the dissipative factors affecting plasma acceleration and based on the analysis the parameters of achievable plasma jets will be presented. Such application of the railguns can be interesting in terms of construction of new plasma engines for the satellites.
The work was partly supported by Russian Foundation for Basic Research (grant RFBR 18-08-01503).

Speaker: S. Poniaev (EPS 2019)

653 O5.302 Dynamics of the gas discharge sustained by the powerful radiation of 0.67 THz gyrotron

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.302.pdf

At present, the THz frequency range is still the least studied from the point of view of gas discharge physics. The study of the discharge, sustained by the powerful focused beams of THz radiation, has become possible recently due to the development of powerful sources in this range (FELs and gyrotrons) and is of interest both from a fundamental research and from possible applications.
This paper presents the results of studies of the discharge dynamics sustained by the gyrotron radiation (40 kW@0.67 THz). The discharge propagation velocity towards electromagnetic radiation was measured in various gases and their mixtures (helium-argon, argon, krypton, nitrogen). It was shown that the discharge propagation velocity in noble gases decreases with an increase in the atomic mass of the gas (from helium to krypton).
The dependence of the discharge propagation velocity in wide gas pressure ranges (0.1 - 2 atm) was investigated. It was shown that in all gases the discharge propagation velocity decreased with an increase in pressure value and for noble gases was at the level of 10^5-10^6 cm/s, and in nitrogen - 10^4-10^5 cm/s. The dynamics of the discharge glow in various ranges (from VUV to IR) was investigated. The presence of a powerful recombination afterglow at the end of a heating radiation pulse in a low-pressure discharge (less than 100 Torr) in noble gases and an afterglow in a high-pressure discharge in nitrogen, which is associated with excited metastable states (A^3Sigma_u+) of the nitrogen molecule, is shown.

Speaker: A. Sidorov (EPS 2019)

654 O5.303 Concentric double hollow grid cathode discharges

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.303.pdf

Multiple complex space-charge structures in unmagnetized low temperature plasmas, such as fireballs or inverted fireballs, arise from ionization phenomena near electrodes or due to local constraints [1,2]. The generation of such complex space-charge structures is often accompanied by plasma instabilities. [3,4]. Recently strong emphasis has been laid on the dynamics of such individual structures generated on various geometrical electrode configurations [5]. We present a new system, consisting of two concentric spherical hollow grids with aligned orifices, investigated by Langmuir probes and non-linear dynamics analysis. Negative biases of this system lead to the formation of two complex space charge structures on the orifices (Fig. 1).
The overall dynamics of the current-voltage characteristic (I-V trace) of each discharge is characterized by strong oscillatory behaviour with various waveforms correlated with jumps in the static I-V trace. Space-resolved measurements through the two aligned orifices of the two grids show a peak increase of electron temperature and particle density inside the two space-charge structures. The effects of the biases and Ar pressure on the overall spatial distribution of all plasma parameters are investigated. Two important working points of the concentric double hollow grid cathode discharges are revealed which could make this configuration suitable as an electron source.

References
[1] C.T. Teodorescu-Soare et al., Int. J. Mass Spectrometry 436 (2019), 83-90.
[2] D.G. Dimitriu et al., Plasma Sources Sci. Technol 22 (2013) 035007.
[3] R.L. Stenzel et al., Phys. Plasmas 19 (2012) 082105/082106/082107/082108.
[4] D.G. Dimitriu et al., Phys. Plasmas 22 (2015) 113511.
[5] C.T. Teodorescu-Soare et al., Physica Scripta 91 (2016), 034002.

Speaker: C. Ionita-Schrittwieser (EPS 2019)

655 O5.304 Energy bands selection in two-color temperature diagnostic in Z-pinch dynamic hohlraum of Julong-1

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.304.pdf

Z-pinch dynamic hohlraum (ZPDH) is one of the promising approaches to generate high energy density X-ray to be applicated in inertial confinement fusion, radiation physics and opacity measurements. The quality of the hohlraum radiation field can be characterized by radiation temperature. Brightness temperature provides an integration of the radiation power spectrum over a whole photon energy range, while color temperature is a characteristic quantity of the spectrum shape, which can give the spectrum intensities at different photon energies, providing more insights about the blackbody radiation filed. A suit of multi-channel spectrometer is prepared to be mounted on the Julong-1 facility in China with a peak current of about 8 MA and a rise time of about 70 ns. Multilayer mirrors are used as dispersion elements at different energy bands and photodiodes or photomultipliers are used as detectors in the spectrometer. It will be used to measure the color temperature of the ZPDH using the two-color method. In this method, the ratio of the fluxes of the power spectrum integrated in two different energy bands is used to infer the temperature, as shown in Fig. 1. The energy bands selection is one of the most important questions during the spectrometer design, as the flux ratio may be sensitive to different radiation temperature ranges which are actually unknown. To overcome this difficulty, four energy bands are selected to form six kinds of combinations with each one fit for a temperature range, finally realizing a full cover of the possible temperature scope. Every combination is firstly selected by the maximum flux ratio sensitivity as shown in Fig. 2, which is defined as the derivative of the flux ratio to temperature. In addition, dynamic range, effect of energy band width and uncertainty of this method are also investigated, with which the final optimized energy band combinations are determined.

Speaker: Q. Yi (EPS 2019)

MCF

Convener: R. Panek (Institute of Plasma Physics ASCR| Prague)

656 I5.101 Progress of physics understanding for long pulse high-performance plasmas on EAST towards steady-state operation of ITER and CFETR

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.101.pdf

Significant progress has been achieved along the China's roadmap towards tokamak based fusion energy production. The three-pronged approach towards the Chinese Fusion Engineering Test Reactor (CFETR) will be reported.
Recently, EAST achieved the first demonstration of 100s time scale steady-state H-mode operation with good control of impurity, core/edge MHD stability, heat exhaust using an ITER-like tungsten divertor and pure RF power. Thereafter, with an increase by 20% in heating power, the long-pulse fusion performance was nearly doubled taking advantage of several synergistic effects: electron heating using on-axis Electron Cyclotron Heating (ECH) enhances heating and current drive from Lower Hybrid Waves (LHW) injection, increasing confinement and enabling fully non-inductive operation at higher density (GW ~80%) and higher poloidal beta (P ~2.5). Higher density and poloidal beta increase the bootstrap current fraction and self-consistently broaden current density profile, leading to further increase in confinement. The physics process (RF synergy, core-edge integration, confinement properties, etc.) of the steady-state operation will be illustrated for experiments performed with the following plasma parameters: toroidal magnetic field BT=2.5T, q95~6.6, elongation k=1.6, poloidal beta P ~2, normalized beta N ~1.6, and bootstrap current fraction BS ~50%, maintained for up to 21s with zero-loop voltage. Small ELMs facilitate the RF power coupling in H-mode phase and reduce divertor sputtering/erosion. Zero/low NBI torque, high performance experiments on EAST offer unique contributions to ITER and DEMO.
These results provide key data for validation of heat exhaust, transport and current drive models, and enhance confidence in the fusion performance predictions for CFETR. Recently, a self-consistent steady-state scenario extrapolating the EAST results has been developed using the intergraded modelling. At present, CFETR physics design focuses on optimization of a third-evolution machine: R=7m, a=2m, Bt=6.5-7T, Ip=13MA. Furthermore, a new National Mega Science Project has been recently launched, in support of the engineering development of CFETR and a future DEMO.

Speaker: J. Huang (EPS 2019)

657 I5.102 Paths towards new quasi-axisymmetric stellarator designs

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.102.pdf

Lausanne, Switzerland An extensive study of quasi-axisymmetric equilibria has been conducted, from which a highly promising magnetic field design has been found by exploiting ROSE (Rose Optimizes Stellarator Equilibria) [1] - an optimization code for 3D magnetic plasma equilibria. The results of this design study and the characteristics of the new configuration [2] are presented. Quasi-axisymmetric fields have small neoclassical particle losses thanks to a magnetic field strength which is independent of the toroidal Boozer coordinate. This toroidal symmetry causes quasi-axisymmetric stellarators to share many neoclassical properties with tokamaks such as a substantial bootstrap current, which produces positive rotational transform and thus helps to confine the plasma. In addition to the advantage of steady-state operation, there is experimental evidence that sufficient vacuum rotational transform can prevent certain types of disruptions - a major challenge for tokamaks.
The ROSE code optimizes the plasma boundary calculated with VMEC based on a set of physical and engineering criteria. Various aspect ratios, number of field periods and rotational-transform profiles have been investigated. As an evaluation of the design, the bootstrap current [3], ideal MHD stability [4], fast-particle losses [5], and the existence of islands [6] are examined. To the best of our knowledge, we have obtained better fast-particle loss-fraction rates than any previous quasi-axisymmetric configuration.
This study could form the basis of the design of a compact, MHD-stable, two-field-period stellarator with particularly good fast-particle confinement. As an extension to the optimization, which mainly concerned plasma physical properties, a new approach will also be presented that includes coil properties in the optimization procedure, which is one of the most demanding issues in stellarator design.

[1] M. Drevlak, et al., Nucl. Fusion, 59 (2018) 016010
[2] S. Henneberg, et al., Nucl. Fusion, 59 (2019) 026014
[3] Y. Turkin, et al., Phys. Plasmas 18 (2011) 022505
[4] C. Schwab, Phys. Fluids 5 (1993) 3195
[5] M. Drevlak, et al., Nucl. Fusion 54 (2014) 073002
[6] J. Loizu, et al., Phys.Plasmas 23 (2016) 112505

Speaker: S.A. Henneberg (EPS 2019)

658 O5.101 Ramping up RF power and increasing pulse length in the full tungsten environment of WEST

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.101.pdf

WEST is a full tungsten (W) superconducting tokamak with a major radius of 2.5 m, an aspect ratio of 5 and a nominal magnetic field of 3.7T. WEST programme aims at power exhaust studies on the ITER-like actively cooled tungsten divertor and at bulk plasma performance in discharges reaching 1000s.
So far up to 5.3 MW of LHCD and 1.4 MW of ICRH have been injected in L mode plasmas. In these conditions, the central electron temperature reaches 5 keV (at n_e of 3.5x10^19 m^-3) with a radiated fraction of ~50% with LHCD and between 60 to 100% with ICRH. In the plasma edge, Doppler reflectometry measures a radial electric field well reaching -12kV/m as the power crossing the separatrix increases, though still below the L to H power scaling law [1].
Repetitive and reliable long L-mode discharges (~ 30 s) were achieved, accumulating ~ 20 minutes of plasma over two days. They were performed on the actively cooled upper divertor using 2.7 MW LHCD power with I_P= 400 kA, B_T=3.7 T, n_e = 3.2x10^19 m^-3. The plasma radiation and density remained constant, indicating the absence of W accumulation. During N2 seeding, an increase of the core temperature was measured.
Using the 1.5D METIS code [2], the plasma composition is inferred thanks to synthetic diagnostics (bolometer, SXR, etc) [3]. The LHCD power deposition and current drive efficiency are modelled thanks to the 3D C3PO/LUKE code [4]. The ICRH absorption is modelled thanks to EVE/AQL [5]. The respective core W transport contributions: turbulent vs neoclassic; diffusion vs convection, are obtained thanks to NEO [6] and QuaLiKiz [7].

[1] Martin Y et al 2008
[2] Artaud JF et al, Nuclear Fusion 2018
[3] Vézinet D et al, Nuclear Fusion 2016
[4] Peysson Y et al, Phys. of Plasmas 2008
[5] Dumont R et al, Nuclear Fusion 2013
[6] Belli E et al, Plas. Phys. and Cont. Fus. 2012
[7] Bourdelle C et al, Plas. Phys. and Cont. Fus. 2016

Speaker: C. Bourdelle (EPS 2019)

659 O5.102 Modelling of three-ion ICRF schemes with PION

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.102.pdf

Ion Cyclotron Resonance Frequency (ICRF) heating is one of the auxiliary heating methods which will be used in ITER. A detailed assessment of ICRF schemes available in the non-active phase of ITER operation was recently carried out [1]. As a result, the ICRF scenarios considered for ITER also include the so-called three-ion ICRF heating schemes in addition to standard minority and majority ion heating. They provide new ways to couple ICRF waves in the core plasma for efficient heating and fast ion studies. Such scenarios have been a focus of intensive research from the theoretical, numerical and experimental point of view [2], and they are also planned for the future JET D-T (DTE2) campaign. In the present work, we analyse discharges carried out with three-ion ICRF schemes on JET and ASDEX Upgrade tokamaks using the ICRF modelling code PION [3]. PION computes the ICRF power absorption and the distribution functions of the resonant ions in a self-consistent way. It also includes a simplified model for taking finite-orbit-width effects of the resonant ions into account. Prior to this work, PION has been extensively compared against experimental data for a large variety of minority and majority ion heating schemes on JET, AUG, DIII-D and Tore Supra. We show that despite its relatively simple models, PION reproduces the main features observed in the experiments using three-ion ICRF schemes on JET and AUG. They include strong ion cyclotron damping by the third ion species despite their very low concentration, strong ICRF acceleration of resonant ions, and the dependence of the resonant ion distribution function on experimental parameters. This increases our confidence in using PION for modelling the performance of three-ion ICRF schemes in JET DTE2 and ITER [4].

References
[1] M. Schneider et al., EPJ Web. Conf. 157, 03046 (2017).
[2] Ye.O. Kazakov et al., Proc. 27th IAEA Fusion Energy Conf., EX/8-1 (2018) and references therein.
[3] L.-G. Eriksson, T. Hellsten and U. Willén, Nucl. Fusion 33, 1037 (1993).
[4] I.L. Arbina et al., this conference.

Speaker: M. Mantsinen (EPS 2019)

660 O5.103 EC assisted start-up experiment and predictions for the next generation fusion experiments

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.103.pdf

For an efficient and robust use of Electron Cyclotron (EC) to assist the start-up phase of the plasma in large tokamaks with superconductive coils, it is necessary to develop appropriate models capable of predicting from present experiments to future scenarios (as for ITER, JT60SA and DEMO). Experience gained on TCV and FTU tokamaks has highlighted the relevance of a correct and consistent evaluation of the EC absorbed power together with the role of impurity and magnetic configuration in the early stage of the discharge. The code BKD0, one of the existing codes for start-up study, is a predictive 0D model for the burnthough phase, which includes the calculation of the EC absorption computed by the beamtracing code GRAY and an impurity model. A benchmark activity between BKD0 and DYON codes was successfully carried out for the simplified ITER case (ohmic). BKD0 validation has been based on experiments performed on FTU (circular, full metallic wall) and characterized by the injection of 400kW in first ordinary (OM1) and in second harmonic extraordinary (XM2) modes, similarly to what is foreseen in ITER. BKD0 reproduces successfully the FTU operational window at low toroidal electric field, showing that a factor 5 in neutral prefill can be sustained by a low level of EC power, injected as OM1. More recently, experiments on TCV (with carbon wall) have been carried out to test the BKD0 impurity model in presence of Ar. The EC assisted start-up experiments were focused on reproducing the JT-60SA configuration (82.7 GHz, XM2, toroidal electric field of 0.7 V/m). BKD0 reproduces the 400kW threshold of EC power needed for plasma initiation, that increases with addition of Ar in D2 prefill, and infers the impurity content at startup, thus confirming the validity of the model included in the code. An iterative procedure has been implemented which couples BKD0 with the CREATE-BD magnetic model for JT-60SA, integrating and optimizing the active circuit currents and considering eddy currents in the passive structures for developing the plasma breakdown scenario. Based on these results, BKD0 is able to extrapolate the operational parameters for the next generation fusion experiments like ITER, JT-60SA and DEMO, providing values of, e.g. the required EC power or neutral gas composition and pressure, for the optimization of the ECRH in different experimental conditions.

Speaker: D. Ricci (EPS 2019)

661 O5.104 High fusion power in tritium rich scenario in JET

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/O5.104.pdf

Series of isotope control experiments in H/D mixtures on JET [1] have shown that NBI fuelling species has only a weak effect on the core isotope composition, which remains determined by the edge H/D ratio and therefore by the injected gas. The analysis of the core particle transport of the ion components revealed a fast isotope mixing ubiquitous in plasmas with dominant ITG turbulence [2-4]. Fast isotope mixing offers an opportunity to significantly boost the fusion power in JET DTE2 campaign in a variant of a hybrid scenario [5,6] with unbalanced (tritium rich) D/T isotope composition and pure D-NBI heating, as opposed to the symmetric 50/50 D/T mixture and combined D- and T-NBI. High PDT brings substantial benefits to the physics goals of DTE2, such as investigation of alpha particle physics and demonstration of the alpha heating.
Thermonuclear fusion reactivity reduces as the plasma composition deviates from the balanced 50/50, although injection of fast deuterium into thermal tritium plasma greatly enhances the beam-target fusion, due to the large cross-section of D-_fast>T reactions and increased number of the tritium targets. In the parameters space of JET hybrid scenarios that gives a net increase of the total number of fusion reactions, with larger gain at higher tritium concentrations.
Further to the NBI fast-thermal reactions, the low expected D/T ratio (nD/ne 35%) enables the usage of deuterium fundamental harmonic ICRH heating scheme which further boosts the fusion power, as, unlike in 2nd harmonic schemes, it avoids accelerating fuel ions to energies well above the peak of the DT cross section (~120keV). The fundamental D minority heating demonstrated the highest Qfus=0.22 in DTE1 (1997) for a 4 second stationary state plasma [7]. In the proposed scenario, part of the ICRH power will also be absorbed by the fast D-NB ions and the intrinsic Be impurity as the resonant species in a three-ion heating scheme [8]. TOMCAT and TORIC simulations have shown that the fractions of the total ICRH power absorbed by the individual components depend on the exact plasma D/T composition, with more power going to the thermal and fast deuterium in more T-rich plasmas. Therefore, larger D/T imbalance also provides larger boost to the fusion reactivity from the ICRH heating.
Combination of the NBI beam-target reactions with the ICRH effects in the proposed scenario has the potential of boosting the fusion power significantly over an otherwise similar hybrid plasma with nD=nT. This contribution will present the present status of development for this scenario, modelling results and extrapolations to DT.

[1] King D.B. et al, 44th EPS (Belfast, 26-30 June 2017) http://ocs.ciemat.es/EPS2017PAP/pdf/O3.112.pdf
[2] M Maslov et al 2018 Nucl. Fusion 58 076022;
[3] C Bourdelle et al 2018 Nucl. Fusion 58 076028
[4] M Marin et al, 45th EPS (Prague, 2-6 July 2018) http://ocs.ciemat.es/EPS2018PAP/pdf/O2.102.pdf
[5] L Garzotti et al, 27th IAEA FEC, Ahmedabad, India (21-26th October, 2018)
[6] J Garcia et al, 27th IAEA FEC, Ahmedabad, India (21-26th October, 2018)
[7] D.F.H. Start et al, Phys. Rev. Letters, 1998, vol. 80, num. 21
[8] J. Ongena et al, EPJ Web. Conf. 157, 02006 (2017)

Speaker: M. Maslov (EPS 2019)

BSAP-MCF

Convener: A. Alonso (Laboratorio Nacional de Fusi__n - CIEMAT)

662 I5.J601 Plasma filament dynamics in different toroidal magnetic configurations

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.J601.pdf

Filaments detaching from the edge of tokamak plasmas are well known. They are generated by pressure driven instability and driven outward by polarization due to the magnetic field curvature and gradient. Similar structures are also commonly observed in the edge and island divertor of the Wendelstein 7-X stellarator. Given the complex 3D geometry of the device and long connection length to the divertors considerable differences are expected in the filament dynamics. Local measurements are insufficient, therefore a multi-diagnostic approach is adopted: local measurement by an alkali Beam Emission Spectroscopy (BES) diagnostic and toroidally distributed information from 10 video cameras.
Indeed long-range correlations are seen all around the machine indicating that filaments are non-local and thus a quasi-2D treatment is inappropriate both in measurement and theory. In the LFS edge region filaments propagate outward similarly to tokamaks. As they cross the island separatrix their movement appears to be more complex. Filaments appear to extend to more than one toroidal turn and appear on the outboard side of the island as well where the polarisation electric field, and thus the radial drift is likely reversed.
Filament activity is affected by edge plasma conditions where in some cases periodic oscillations resembling the I-phase in tokamaks appear. The talk presents analysis of these structures in different stellarator magnetic configurations and their role in edge and island transport. These observations are compared to comparable data from alkali and heating BES data on various tokamak experiments (EAST, KSTAR, COMPASS) where in some cases 2D BES measurements are also available in the SOL and edge.

Speaker: S. Zoletnik (EPS 2019)

663 I5.J602 Interaction of Alfvénic modes and turbulence investigated in a self-consistent gyrokinetic framework

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.J602.pdf

Tokamak plasmas are examples of complex systems where multiple spatial and temporal scales are intrinsically linked. Microturbulence, meso-scale zonal structures (ZS, like zerofrequency zonal flows and geodesic acoustic modes) and macroscopic MHD instabilities like Alfvénic modes (AM), mutually interact either due to the modification of the equilibrium profiles, or by direct coupling via wave-wave nonlinear interaction. In particular, a strong interest recently raised in understanding the generation of ZS by AM, due to the strong implications in modifying the turbulent transport. The gyrokinetic global particle-in-cell code ORB5 [1, 2] was developed for turbulence studies, extended to its electromagnetic multi-species version, and verified and benchmarked for the linear dynamics of mictroturbulence modes, ZS and AM. The importance of the kinetic electron effects in the ZS dynamics has also been emphasized with ORB5 [3]. Recent simulations with ORB5, have investigated the nonlinear dynamics of AM [4], the self-consistent interaction of AM and turbulence, and in particular the competition of the generation of ZS by turbulence and by AM [5]. In this work, the mechanisms of generation and saturation of the ZS will be described. In particular, the wave-particle nonlinearity, the wave-wave nonlinearity, the effect of turbulence on AMs, the effect of AMs on turbulence, for example via ZS generation, will be studied separately and in self-consistent simulations. Comparisons with other models like the gyrokinetic Eulerian code GENE [6] will also be shown.

References
[1] S. Jolliet, et al. Comput. Phys. Commun. 177, 409 (2007)
[2] A. Bottino, et al. Plasma Phys. Controlled Fusion 53, 124027 (2011)
[3] I. Novikau, et al., Phys. Plasmas 24, 122117 (2017)
[4] A. Biancalani, et al., Plasma Phys. Controlled Fusion 59, 054004 (2017)
[5] A. Biancalani, et al., IAEA Fusion Energy Conference, Ahmedabad (India), Oct. 22th-27th, 2018, TH/P2-9
[6] F. Jenko, et al., Phys. Plasmas 7, 1904 (2000)

Speaker: A. Biancalani (EPS 2019)

12:40 Lunch

Poster P5

664 P5.1001 Overview Progress and Plans for the Compact Toroidal Hybrid Experiment

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1001.pdf

The Compact Toroidal Hybrid (CTH) is an l=2, m=5 torsatron/tokamak hybrid (R=0.75m, a~0.2m, and |B|<=0.5T) with the ability to vary the confining magnetic field configuration and generate rotational transform profiles that are tokamak-like with ohmically driven plasma current for disruption and MHD studies. The main goals of the CTH experiment are to study disruptive behavior as a function of applied 3D magnetic shaping, and to test and advance the V3FIT reconstruction code and NIMROD modeling of CTH. Past and recent disruption studies will be overviewed and their relevance to tokamaks and quasi-axisymmetric stellarators discussed. Current new diagnostic development for the experiment includes an upgrade to the interferometer, new spectroscopic studies, and coherence imaging of plasma flows. CTH also serves as a test bed for diagnostic development for our collaborations on the larger facilities like DIII-D and W7-X. These facility collaborations will be briefly summarized along with a new research direction to explore low temperature plasmas on magnetic surfaces.

*This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610 and NSF EPSCoR program OIA-1655280 .

Speaker: D. Maurer (EPS 2019)

665 P5.1002 Modelling multi-modal Resistive Wall Mode feedback control in JT-60SA perspective high beta scenarios

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1002.pdf

The forthcoming device JT-60SA, under construction in Naka (Japan), is particularly well equipped for studying Advanced Tokamak scenarios with high N and a non-negligible fraction of energetic particles from neutral bean injectors [1][2]. These plasmas are prone to exhibit kink-like ideal MHD instabilities; one or more Resistive Wall Modes (RWM) in particular can be potentially unstable when operating beyond the no-wall pressure limit [3]. While a synergy of wave-particle resonances and active control will play a role in stabilizing RWMs, the present work focuses on the latter. An advanced modelling tool has been developed based on the CarMa code [4][5] which includes a detailed description of the passive stabilizing plate and active coils. As an improvement of previous results, simultaneous stabilization of the most unstable RWMs (n=1,2) is demonstrated, discussing the capabilities and limits of the feedback system. Different configurations of active coils are compared, taking advantage of the flexibility granted by the 18 independent power supplies. A realistic controller for the RWM loop is discussed and implemented in the model, combined with accurate positioning of magnetic sensors on the stabilizing plate and vacuum vessel. The performance of the mode-control algorithm is assessed by analyzing the eigenvalues of the closed-loop system. The development of the time simulation, describing mode dynamics, is also described.

[1] Shirai, H., et al. Nuclear Fusion, 2017, 57.10: 102002.
[2] Giruzzi, G., et al. Nuclear Fusion, 2017, 57.8: 085001.
[3] Bolzonella, T., et al. "Recent studies in support to MHD stability and control on JT-60SA." 39th EPS Conference on
Plasma Physics and 16th International Congress on Plasma Physics. European Physical Society, 2012.
[4] Portone, A., et al. Plasma Phys. Contr. Fusion, 2008, 50, 085004.
[5] Pigatto, L., et al. "Resistive Wall Mode physics and control challenges in JT-60SA high beta-N scenarios." 27th IAEA
Fusion Energy Conference. IAEA, 2018.

Speaker: L. Pigatto (EPS 2019)

666 P5.1003 ITER disruption simulations with realistic plasma and conductors modelling

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1003.pdf

Disruptions are one of the major concerns in ITER and other future tokamaks [1]. In addition to heat, particle flux, and energetic electrons impacting the first wall, significant electromagnetic loads will arise, due to the interaction of eddy and halo currents in the conducting structures with the magnetic field. Reliable modelling tools able to make predictions for future devices are hence fundamental. Two aspects must be considered for a suitable modelling of disruptions. First, a detailed model of plasma is needed, to describe its (possibly unstable) modes of evolution. Here, we use the M3D-C1 code [2], an implicit 3D extended-MHD code that uses high-order C1 continuous finite elements. The second point is an accurate description of the conducting structures surrounding the plasma, whose geometry affects the plasma evolution itself and the actual value of electromagnetic loads. We use the CarMa0NL code [3], to treat an axisymmetric plasma in the evolving equilibrium limit with arbitrary conducting structures, and the CARIDDI code [4], a 3D volumetric eddy currents computational tool. In this paper, we first compare the results of M3D-C1 and CarMa0NL for axisymmetric disruptions, showing that, despite the substantially different assumptions made in the two codes, the predictions are very close, hence increasing confidence in the reliability of the results. Secondly, we describe a coupling scheme between M3D-C1 and CARIDDI, which allows us to use M3D-C1 plasma evolution, in the presence of simplified but realistic wall geometry, as input to subsequent electromagnetic computations made by CARIDDI with a detailed description of the structures. The final aim is to use this coupling scheme also for asymmetric disruptions (AVDEs), in order to quantify the sideway forces expected in ITER.

This work was supported in part by F4E (contract F4E-OPE-0891) and by U.S. DoE Award No. DE-AC02-09CH11466 and the DoE SciDAC Center for Tokamak Transient Simulations.

[1] T. Hender et al, Nucl. Fusion 47 (2007) S128
[2] S.C. Jardin, N. Ferraro, et al., Comput. Sci. & Disc., 5, 014002 (2012)
[3] F. Villone et al., Plasma Phys. Control. Fusion 55 (2013) 09500
[4] R. Albanese, G. Rubinacci, IEE Proc. A 135 (1988) 457

Speaker: N. Isernia (EPS 2019)

667 P5.1004 Effects of control voltage saturation and sensor noise on the RWM feedback in ITER

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1004.pdf

Active control of the n = 1 (n is the toroidal mode number) resistive wall mode (RWM) is numerically studied, taking into account (i) recent design of the plasma equilibrium for the ITER 9 MA steady state scenario, and (ii) two important control aspects towards realistic modeling of the RWM feedback for ITER, namely the control power saturation issue and the presence of sensor signal noise. This is the first such attempt where both the aforementioned factors are included into investigation. The large L/R response time of the active coils in ITER results in a significant reduction of the open-loop RWM growth rate, when the active coils act as passive conductors. For a typical RWM, the linear flux-to-voltage control scheme yields complex closed loop eigenvalue (in the absence of plasma flow and drift kinetic effects), before the mode is fully stabilized by feedback. Without sensor signal noise, the RWM feedback system can tolerate a low level of control voltage saturation, typically in the order of 1 V in ITER. The presence of high-frequency sensor signal noise, however, can significantly increase the tolerable level of control power saturation. For a plasma close to the ITER target, and with the feedback gain well beyond the critical value for the linear closed loop stability, the tolerable voltage saturation level is predicted to be about 4 V at the sensor signal noise level (standard deviation) of 0.25 Gauss, and about 40 V at noise level of 1 Gauss.

Speaker: S. Wang (EPS 2019)

668 P5.1005 Aspect on equilibrium calculation of ITER configuration in Tokamaks

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1005.pdf

In this work, we have constructed an ITER con guration, which is generated by currents owing within the plasma and currents owing in external coils. The plasma current density takes the form j_φ (r; z) = - ar - bR^2/r or other H-mode current pro le inside the plasma, and is zero in the surrounding vacuum. We use Green's function method to compute the plasma current contribution, together with a homogeneous solution to the Grad-Shafranov equation, to construct the full solution. Matching with the constant boundary condition on the last closed flux surface is performed to determine the homogeneous solution. Then the total solution in the full space is obtained. We can also obtain the value of external coils current by the homogeneous solution.

Speaker: T. Xu (EPS 2019)

669 P5.1006 Design of the Massive Gas Injection system for JT-60SA

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1006.pdf

Disruption mitigation is one of the main research topics on the way to ITER and future Tokamak fusion power plants. Therefore, extensive studies have to be carried out on large Tokamaks to understand the physics and to develop the necessary technologies. JT-60SA, which will go into operation in 2020, will be a primary machine for this research. It will be equipped with a Massive Gas Injection (MGI) system to conduct disruption mitigation experiments in the first research phases. This MGI system will consist of two fast valves with integrated reservoirs (1000 cm³), which will be installed inside the vacuum vessel behind the stabilizing plate. The toroidally opposite locations in upper oblique position minimize the distance between the valves and the q=2 surface and maximizes the distance between the two injection spots. This setup allows investigation of radiation asymmetries, heat load and force mitigation in various plasma scenarios, runaway electron mitigation and gas propagation into hot plasmas. The close proximity of the valves to the plasma is especially beneficial for unstable scenarios like runaway beam mitigation. Each valve will be able to hold up to 7500 Pa*m³ of mitigation gas, that can be injected within milliseconds. Due to their location inside the vacuum vessel, the valves must be compatible with in-vessel conditions (magnetic field, elevated temperature, radiation and vacuum). Hence, a spring-driven valve with piezoelectric actuation was chosen as design basis. It is foreseen to inject a large variety of different noble gases and gas mixtures with H2/D2. A gas preparation system was specifically designed to allow mixing of different gases and fast filling of the MGI valves internal voluminal, while still complying with high safety standards regarding high pressures and explosion prevention. Finally, the vacuum feedthroughs were designed to preserve the different electric potentials of the machine and the vacuum conditions of the cryostat while allowing high pressure gas supply and 120 V trigger voltage to the MGI valves. This contribution presents the detailed designs of the MGI valves, the gas preparation system and the vacuum feedthroughs together with the results of the design analysis.

Speaker: M. Dibon (EPS 2019)

670 P5.1007 The New Compact Torus Injection System on KTX device

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1007.pdf

A new compact torus injection (KTX-CTI) system is being developed on Keda Torus eXperiment (KTX), which is a newly built medium size reversed field pinch device. The KTXCTI is a three-meter long linear device designed to inject compact torus (CT) into KTX at a high speed of over 100km/s. The tangential injection angle is 25°with respect to the major radius direction at the CT entry location in the middle plane shown in Fig. 1, and the maximum injection mass of CT is 50 μg for hydrogen, which is about 30% of the KTX plasma particle inventory. The KTX-CTI includes the vacuum vessel, centre solenoid, the fast gas valves, FPGA timing system, pulse power supplies and CT exclusive diagnostics. Currently, the KTXCTI is in the engineering commissioning. CTs injected with KTX-CTI have tangential momentum, it is possible to induce and to sustain toroidal rotation of the KTX plasma due to the momentum transfer from the CT to KTX plasma. In addition, a small amount of helicity can also be injected for the single helicity mode (SH) research, which is expected to improve the confinement for reversed field pinch plasma. As an advanced fuelling system with very high penetration speed about two orders higher than common fuelling, the KTX-CTI will be used as a prototype device prepared for central fuelling of China Fusion Engineering Test Reactor (CFETR) in the future.

*This work is supported by the National Magnetic Confinement Fusion Science Program of China under grant nos. 2017YFE0301700.

Speaker: C. Chen (EPS 2019)

671 P5.1008 Toroidal field ripple-induced NBI energetic particle losses in JT-60SA

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1008.pdf

JT-60SA is large device (R_0/a=3.0/1.1) which will use neutral beam (NB) injection as the main actuator to reach the desired plasma temperature and performance[1]. In total, the NBI system provides 34MW of power, of which 10 (24) MW is injected at the energy of 500 (85) keV. The geometry features both parallel and perpendicular injection. The toroidal field (TF) system has 18 coils, producing a field B_tor =2.28 T at the magnetic axis. At the plasma edge, the finite number of TF coils results in a 3D feature known as the TF ripple.This distortion of the magnetic field impacts on fast ion confinement and this effect has already been investigated for ITER because it can lead to loss of power delivered to the plasma and excessive heat fluxes to the wall [2, 3]. The same issue is relevant also for DEMO because of the potential occurrence of unwanted heat fluxes to the wall and loss of power deliver to the plasma. It is therefore mandatory to increase our confidence and prepare the validation of existing models against relevant experiments. For the JT-60SA case, the Biot-Savart law integrator BioSaw [4] has been used to calculate the TF ripple (Δ = (Bmax-Bmin)/(Bmax+Bmin)) - from the geometry of the TF coil. This value has been found to be <1 % inside the plasma separatrix. The 3D non-axisymmetric magnetic field is then applied to JT-60 SA reference scenarios to study the impact of this deformation of the magnetic field on NBI-injected particles orbit using the ASCOT Monte Carlo code. This work builds upon previous axisymmetric ASCOT simulations of JT-60 SA NBI injection [5]. In the inductive case here presented, an increase of the losses (both the prompt losses and the pitch-scattering losses) is documented: the axisymmetric case shows almost no losses during the slowing-down, while ripple can increase fast particle losses and then the power reaching different regions of the first wall. The orbit can be perturbed and the drifts sum up instead of cancel out (e.g. the super bananas get lost because the grad(B) drift). Lost particles where those which were ionized at rho>0.8, which is the area where the magnetic field is mostly perturbed. The region where these particles hit the wall is just below the midplane, around θ=-20 degrees. In the case of low-energy (85 keV), particles get lost also to the lower divertor region. The quantification of the power linked to 3D energetic particle losses will help the tuning of the experimental scenarios.

[1] H. Shirai et al., Nucl. Fusion 57 (2017) 102002
[2] K. Shinohara. et al, Fusion Eng. Des. 84, 24 (2009)
[3] Kurki-Suonio T. et al., NF 49 (2009)
[4] Akaslompolo S. et al., FED 98 (2015)
[5] Vallar M. et al., 44th EPS conference, P1.149 (2017)

Speaker: M. Vallar (EPS 2019)

672 P5.1009 The effect of parallel magnetic field fluctuations on pressure driven MHD instabilities in toroidal plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1009.pdf

Analytic derivation and numerical calculation of pressure driven MHD instabilities in toroidal plasmas is notoriously difficult. Instability is determined by apparently weak effects in the toroidal metric tensor. A classical example is the m = n = 1 internal kink mode, where previous numerical and analytic results obtained in a cylinder were shown [M. N. Bussac et al, Phys. Rev. Lett. 35, 1638 (1975)] to be exactly cancelled by toroidal corrections, even in the limit of infinite aspect ratio. With such lessons well learnt by many MHD code and analysis developers, there are now new generations of gyro-kinetic codes (e.g. EUTERPE [1], GTC [2], LIGKA [3], ORB5 [4]) that are being deployed to model MHD instabilities. Some of these codes are, or have been, only partially electromagnetic. It is usually assumed that the perturbed vector potential is parallel to the equilibrium field (so that the perturbed parallel magnetic field is nearly zero), though in some codes the parallel magnetic potential assumption is deployed together with a change to the equilibrium magnetic field that is consistent with an effective adiabatic parallel magnetic field. Similar such reduced models are also assumed in some non-linear MHD codes deployed for the study of edge localised modes (e.g. JOREK [5]), and non-linear kinetic-MHD codes (e.g. HXMGC [6]). The present contribution investigates the impact of code-relevant models for the parallel magnetic field on pressure driven instabilities in axisymmetric toroidal equilibria. The work therefore provides analytic benchmarks for codes that are not yet fully electromagnetic. For example, for the case where the parallel magnetic field is not compensated, it is shown that neglecting parallel field fluctuations allows the drive for pressure driven instabilities to be artificially absorbed by the energy required to perturb the magnetic curvature. While ballooning modes in tokamaks are only weakly affected by the neglect of the parallel magnetic field, the internal kink mode, infernal modes and interchange modes are strongly, or entirely, stabilised by neglecting B . For example, for interchange modes, the effect is dominant if the ballooning parameter > 4(1 - q2r ), where qr = m/n is the rational safety factor of the main mode, and is the local inverse aspect ratio. The effect in a cylinder, reverse field pinch, and the core of the tokamak is seen to be particularly important.

References
[1] M. Cole et al, Phys. Plasmas 21, 072123 (2014)
[2] J. McClenaghan et al, Phys. Plasmas 21, 122519 (2014)
[3] Ph. Lauber et al, J. Comp. Phys. 226, 447 (2007)
[4] A. Biancalani et al, Phys. Plasmas 23, 012108 (2016)
[5] G.T.A Huysmans and O. Czarny Nucl. Fusion 47 659 (2007)
[6] S. Briguglio et al, Phys. Plasmas 2, 3711 (1995)

Speaker: J.P. Graves (EPS 2019)

673 P5.1010 ITER 15 MA DT scenarios with maximum expansion of poloidal magnetic flux on divertor target plates

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1010.pdf

An increase of the poloidal flux expansion near the divertor target plates reduces the heat flux on the plates. A study has been performed with the goal to design and simulate with the DINA code [1] an ITER 15 MA DT scenario (Q = 10, Pfus = 500 MW) with a plasma configuration during the burn having a maximum expansion of the poloidal magnetic flux on the divertor vertical plates. A new feedback controller was designed with the purpose of feedback control (during the plasma current flattop) of the distance between the separatrix and "1 cm SOL" near the outer target plate (Delta_out), simultaneously with feedback control of the nominal set of plasma parameters (six plasma-wall "gaps" and plasma current). To obtain the maximum value of the parameter Delta_out, the target value of this parameter used in the feedback control was increased until the current in the PF4 coil hits the design limit (55 kA). Feedback control of the distance between the inner (with lower X-point) and outer (with upper X-point) separatrices in the plasma outboard region was also performed at the plasma current flattop with the target minimum value of 4.5 cm.
In the scenario considered, relative to scenarios with the nominal magnetic configuration, the values of Delta_out and Delta_in (the distance between the separatrix and "1 cm SOL" near the inner divertor target plate) are increased during the plasma current flattop by about 80% and 40%, respectively. The heat fluxes on the divertor vertical plates are reduced correspondingly. However, the poloidal flux expansion requires a higher value of current in the CS1 coils than that in the nominal scenarios. This leads to a decrease of the burn duration (limited by the maximum current in these coils). In the scenario with the fast plasma current ramp-up (during 50 s, limited by the allowable value of the magnetic field on the PF6 conductor of 6.4 T), the duration of burn is about 386 s (taking into account 1 MA of current driven by NBI).

[1] R.R. Khayrutdinov and V.E. Lukash. Journal of Comp. Physics, 107(2), 106 (1993)

Speaker: V. Lukash (EPS 2019)

674 P5.1011 L-mode plasmas analyses in view of realistic ramp-up predictions for JT-60SA and ITER

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1011.pdf

Predicting plasma performance is an essential activity for assessing future campaigns in present day tokamaks as well as in future devices as ITER or JT-60SA. In particular, predictions for the ramp-up phase are of special importance, as successful plasmas in the flat-top phase critically depend on the initial configuration. This is particularly the case for the so-called advanced scenarios for which the plasma shape, flux consumption reduction or the control of the q profile during the ramp-up is mandatory [1-3]. However, the prediction and simulation of the plasma behavior during the ramp-up is a complex activity due to the combination of several challenges involving for instance, the lack of a heat transport model valid close to the separatrix or the inadequacy of neoclassical resistivity in the prediction of q profiles. Therefore a precise computation of the turbulent transport and current diffusion in L-mode is needed in order to accurately predict the q profile evolution in ECRH assisted ramp-ups.

In this contribution, L-mode analyses have been performed combining plasmas from different tokamaks in order to assess and to provide a credible modelling framework for the predictions of ramp-up phase for JT-60SA and the initial phase of ITER for which ECRH is planned to be used. We have compared two turbulent transport models (CDBM [4] and TGLF [5] in CRONOS [6]) in order to evaluate their predictive capabilities. To this end we have run simulations of the ramp-up phase in a JET plasma without auxiliary heating and in a flat-top L-mode TCV plasma with applied ECRH. Parameter scans in Zeff and in the edge electron temperature (within the experimental uncertainties) have been performed in order to assess the simulation sensitivity to these quantities. We have found a good prediction of the q profile and li evolutions in JET ramp-up if the edge electron temperature is well captured. Indeed our sensitivity scan showed a strong impact of the edge electron temperature on the q profile and li evolutions. In both tokamaks, results with CDBM showed better agreement with experimental measurements. Elements explaining the good prediction using this relative simple transport model and the impact for JT-60SA and ITER ramp-up will be given.

[1] Imbeaux et al. 2011 Nucl. Fusion
[2] Voitsekhovitch et al. 2010 PPCF
[3] Wakatsuki et al. 2015, PPCF
[4] Itoh et al. 1993, 1994, PPCF
[5] Staebler et al. 2005 Phys. of Plasmas
[6] J.-F. Artaud et al. 2010 Nucl. Fusion

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: J. Morales (EPS 2019)

675 P5.1012 Reassessment of steady state operation in ITER with NBI and EC heating and current drive

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1012.pdf

The parametric Operational Space (OS) for Steady-State (SS) operation [1] in ITER has been reassessed by global analysis taking into account the baseline design of the Neutral Beam Injection (NBI) and EC H&CD systems and their foreseen upgrades (up to P_NBI = 49.5 MW and with P_EC = 30 MW, where up to 40 MW upgrade is possible). The analysis has been carried out for so-called Type-II SS scenarios, which exclusively use NBI and EC for heating and current drive H&CD and for which no internal transport barriers are assumed [2, 3]. The obtained OSs determine the choice of plasma current, density, H&CD specifications (power levels, injection geometries, etc.) and required energy confinement to achieve a given fusion gain, Q=P_fus/(P_EC+P_NB). From these OSs a set of Operational Points (OP) with fusion gain Q=5 with various H&CD specifications have been selected for more detailed MHD stability and 1.5-D transport and current drive analysis including sensitivity studies. Self-consistent 1.5-D transport simulations have been carried out for these selected OPs during the steady-state current flat-top phase. The 1.5-D simulations take into account the contribution of the fast particles pressure as well as bootstrap and externally driven currents. Sensitivity studies to current and pressure profiles have been performed by variation of NBI & EC specifications and the consequences for ideal MHD stability evaluated including diamagnetic effects. These studies allow the determination of the optimum operational conditions for the achievement of MHD stable plasmas to demonstrate the Q = 5 steady-state goal in ITER in terms of plasma current, density, NBI and EC specifications, as well as the capability of the H&CD systems to ensure MHD stability and the assessment of other integration issues, such as divertor power load control. The capability of the ITER CS/PF magnets' system to support these scenarios is found to be adequate [4] and will be described in the paper.

[1] A.R. Polevoi, et al, "Assessment of Operational Space for Long-pulse Scenarios in ITER", P2.187, EPS2010
[2] A.R. Polevoi, et al, Nucl. Fusion 45 (2005) 1451-1456
[3] C. Gormezano, et al, Nucl. Fusion 47 (2007) S285-S336
[4] S.H. Kim, et al, (2019), submitted to NF

Speaker: A.R. Polevoi (EPS 2019)

676 P5.1013 Effect of shaping on turbulent transport in JT-60SA

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1013.pdf

Plasma shaping is known to affect the properties of micro instabilities that cause outwards radial transport of heat and particles in tokamaks. In particular, the elongation has been observed to have a stabilizing effect on the ion-temperature-gradient (ITG) instability in low-β plasmas, whilst increased triangularity can have varied effects on confinement [1-3]. The effect of shaping in high-β, high-β' plasmas such as those expected in JT-60SA advanced scenarios is less documented and is the focus of this work.
Here we use the local δ f -gyrokinetic code GS2 [4] to extend an earlier modelling study [5] of the tokamak JT-60SA and investigate the ideal plasma shaping parameters for the machine in two different scenarios - one low (1.4%) β and one high (3.7%) β plasma equilibrium. We confirm, using electrostatic simulations with both kinetic ions and electrons, that the low-β plasma exhibits monotonic stabilization with increasing elongation, whilst the effect of triangularity varies with κ (destabilizing and stabilizing at low and high κ, respectively). However, the analysis of the high-β plasma shows that moderate increases in elongation (up to κ~1.4) have a destabilizing effect; beyond this elongation is again stabilizing.
To explain this observation, we use a simplified Miller parametrization for the poloidal cross section to determine how an interaction between β' and κ is responsible for this behaviour. In particular, increasing κ at large β
' increases the local magnetic shear (destabilizing) but also the perpendicular wavenumber (stabilizing). The competition between these two effects leads to the observed peak in maximum growth rates as a function of κ. We also present results from electromagnetic simulations for the high-β equilibrium.

[1] H. Weisen et al., Nucl. Fusion 37 (1997), 1741.
[2] Y. Camenen et al., Nucl. Fusion 47 (2007), 510.
[3] J. Ball, F.I. Parra, M. Landreman, and M. Barnes, Nucl. Fusion 58 (2018), 026003.
[4] M. Kotschenreuther, G. Rewoldt and W.M. Tang, Comp. Phys. Comm. 88 (1995), 128-140.
[5] M. Nakata et al., Plasma Fusion Res. 9 (2014), 1403029.

Speaker: O. Beeke (EPS 2019)

677 P5.1014 Beam-plasma system as reduced model for energetic particle ITER relevant transport

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1014.pdf

With the aim of finding and validating reduced models able to reproduce the relevant features of the energetic particle interacting with the Alfvénic spectrum, we define a mapping procedure (based on the resonance rule) between the reduced radial profile of the burning plasma scenario and the velocity space of the beam-plasma system [1, 2, 3]. The map is defined around a single reference resonance, resulting in a linear (local) relation, and then extended to the multiple mode case. This technique is applied to the reduced ITER 15MA beseline scenario analysed in Ref.[4] (see also Ref.[5]), in the presence of the least damped 27 toroidal Alfvén eigenmodes. Mode saturation and energetic particle redistribution are analysed, and avalanche effects on the spectral evolution and domino (convective) transport well emerges from simulations in agreement to Ref.[4]. This outlines the importance of the stable (sub dominant) component spectrum. Moreover, quasi-linear equations are mapped in the radial dimension and numerically integrated for the addressed multi mode case. The obtained quasi-linear profiles differ from non-linear simulations since they clearly do not reproduce avalanche phenomena and outer redistribution of energetic particles.

** Work carried out within the framework of EUROfusion as Enabling Research Projects: NAT (AWP17-ENR-MFE-MPG-01) and MET (CfP-AWP19-ENR-01-ENEA-05) **

[1] N. Carlevaro, M.V. Falessi, G. Montani, F. Zonca, J. Plasma Phys. 81, 495810515 (2015)
[2] N. Carlevaro, A.V. Milovanov, M.V. Falessi, G. Montani, D. Terzani, F. Zonca, Entropy 18, 143 (2016)
[3] L. Chen, F. Zonca, Rev. Mod. Phys. 88, 015008 (2016) [4] M. Schneller, Ph. Lauber and S. Briguglio, Plasma Phys. Control. Fusion 58, 014019 (2016)
[5] Ph. Lauber, Plasma Phys. Control. Fusion 57, 054011 (2015)

Speaker: N. Carlevaro (EPS 2019)

678 P5.1015 Structure generation of the edge radial current during the L-H transition on JT-60U

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1015.pdf

In this study, we analyzed the structure generation of the edge radial current (j_r) by means of Poisson's equation with a measured E_r data (CXRS diagnostic) in JT-60U NBI heating plasmas [1-4]. About 200 ms after the start of NBI heating, a slow L-H transition takes place, which evolves into a fully-developed H-mode spending a few 100ms. During this slow transition process, a smooth decrease in D emission, increase in the edge line-averaged electron density and steepening of ion temperature take place. The Er-well bottom value at ~3 cm inside the LCFS becomes large up to -40 kV/m as a similar time-scale of the change in the density [5], while the jr shows a local Max. value of 0.01-0.02 A/m^2 just after a slow L-H transition and its broader radial structure propagates toward plasma core region in the time-scale of ~100ms as seen in the pedestal development. On the other hand, we found that a localized jr structure with positive or negative polarities of its absolute peak value of 0.4-0.5 A/m^2 occurred spontaneously during the later ELM-free H-phase at which a complex multi-stage E_r-transition was seen with a fast time-scale. This observation suggests a co-existence of the non-linear physical mechanism for the j_r generation at the plasma edge region in terms of its variation in the time-scale and radial structure. Comparison with a theoretical model, including fast-ion loss current due to the ripple loss effect, is also discussed.

[1] K. Itoh and S-I. Itoh, Plasma Phys. Control. Fusion 38, 1-49 (1996).
[2] M. N. Rosenbluth and F. L. Hinton, Phys. Rev. Lett. 80, 724-727 (1998).
[3] M. Honda, et al., Journal of the Physical Society of Japan 80, 114502 (2011).
[4] T. Kobayashi, et al. Sci. Rep. 6, 30720 (2016).
[5] K. Kamiya, et al., Phys. Rev. Lett. 105, 045004 (2010).

Speaker: K. Kamiya (EPS 2019)

679 P5.1016 Guiding centre simulation of neoclassical impurity transport in the pedestal region

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1016.pdf

The neoclassical impurity transport in the pedestal region of a tokamak plasma is studied with non-local guiding center particle simulations, employing the code HAGIS with a Monte Carlo collisions model. The simulations are done in two steps, assuming the trace limit for the impurity ions. First the parallel velocity of the main ions (D) is obtained for given density and temperature profiles from a simulation with D-D collisions neglecting the collisions with impurities. Then the simulation for the impurity ions is made, where only the collisions between impurities and main ions are included, since the particle transport is caused by these collisions. HAGIS is a δf code, the evolution of δf = f - f_0 is calculated from the change of f_0 along the orbits (with full radial motion) and the contribution from the collisions. For the main ions f_0 is chosen as a Maxwellian centred at v = 0, while for the impurity ions f_0 is a shifted Maxwellian centred at the parallel velocity of the main ions. Thus in both steps f_0 is invariant to the collisions. In the simulations the radial interval 0.8 <= ρ_pol <= 0.999 is covered, where ρ_pol is defined by ρ_pol^2 = ψ/ψ_edge with ψ_axis = 0. The poloidal and radial variations of density, temperature, and parallel velocity and the radial particle flux are obtained. We determine the deviation of the parallel impurity velocity from that of the main ions and we find an in-out density asymmetry as seen in the experiments. We also find an up-down density asymmetry, which is caused by the friction between impurity and main ions and which is necessary for radial transport. The radial transport in the pedestal is found to be reduced compared to the usual neoclassical expression. No poloidal electric field is included, so the poloidal variation of the radial flux is equal to that of the magnetic particle drift: the flux is inwards above the midplane and outwards below the midplane (for ion drift directed downwards). For trace impurities this is generally true, since the poloidal electric field is small, except for the field caused by the centrifugal force, which does not produce a net radial transport.

Speaker: A. Bergmann (EPS 2019)

680 P5.1017 Electron temperature fluctuation measurements of pedestal fluctuations in I-mode at ASDEX Upgrade and Alcator C-Mod

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1017.pdf

I-mode is a naturally ELM-free improved confinement regime which exhibits high energy confinement and a temperature pedestal, but low particle confinement and a density profile similar to L-mode [1]. The weakly coherent mode (WCM) occurs in the pedestal region of Imode plasmas at both ASDEX Upgrade (AUG) and Alcator C-Mod, but the role of the WCM in particle and heat transport remains an open question. In this work, temperature fluctuations in the pedestal of I-mode plasmas are studied through correlation electron cyclotron emission (CECE) at AUG and C-Mod. The electron temperature fluctuation level of the WCM has been measured in C-Mod at 1-2% [2] and in AUG at 2.3% [3]. The optical depth of some CECE measurements at AUG is marginal and therefore the contribution of density fluctuations is studied as part of this work. In addition, a finite phase between density and temperature fluctuations (nT phase) has been observed at AUG using a reflectometer along the same line of sight as the CECE system. Comparison between the two devices and nT phase observations may provide insight into the effect of the edge fluctuations on density and temperature transport.

This work is supported by the EUROfusion Consortium (No 633053), and by US DoE under Grants DE-SC0006419, DE-FC02-99ER54512-CMOD, and DE- SC0017381.

[1] D.G. Whyte et al, Nucl. Fusion 50 (2010) 105005
[2] A.E. White et al., Nucl. Fusion 51 (2011) 1130005
[3] T. Happel et al., Nuclear Materials and Energy 18 (2019) 159-165

Speaker: R. Bielajew (EPS 2019)

681 P5.1018 Impact of an inward particle flux inducing the coherent fluctuation on pedestal dynamics in toroidal plasmas

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1018.pdf

In the transition from low (L) to high (H) confinement regime a transport barrier usually develops in a narrow layer and so called pedestal of high temperature and density gradients forms at tokamak plasma edge [1]. The accumulation of energy and particles inside the pedestal normally leads to an explosive relaxation of the gradients through edge localized mode (ELM) onset. The gradients then intrinsically develop
again until a next ELM onset under a variety of physics mechanisms. This is a typical self-organization process of edge gradients in magnetic confinement fusion plasmas
[2]. Understanding the pedestal dynamics and relaxation mechanism in the inter-ELM phases is essential for advance of the pedestal nonlinear physics.
In the recent experiments of the HL-2A tokamak, the pedestal dynamics has been investigated in detail [3]. The increases of density and its gradient were observed in the edge transport barrier prior to each ELM onset in a series. An inward particle flux inducing the coherent fluctuation mode (f=30-70 kHz) was found to be responsible for such changes. The characteristics of the coherent fluctuation, including frequency, wave vector and propagation velocity were identified. The mode localizes in the pedestal, leads to the rapid increase of density gradient, and has strong nonlinear interaction with the turbulence. The impact of the inward particle flux in the particle balance and increases of pedestal density is also discussed.

This work is supported by NSFC under the grant Nos. 11875017, 11875020, 11320101005, the National Key R&D Program of China under the grant No. 2017YFE0301203 and the National Magnetic Confinement Fusion Science Program of China under grant Nos. 2015GB104003 and 2015GB106005.

[1] F. Wagner, et al 1982 Phys. Rev. Lett. 49 1408
[2] A. Loarte, et al 2003 Plasma Phys. Control. Fusion 45 1549
[3] J. Cheng, et al., the 27th IAEA-FEC, 22-27 October, 2018, India, EX/P5-6

Speaker: J. Cheng (EPS 2019)

682 P5.1019 The effect of pacing pellets on ELMs W impurity behaviour and pedestal characteristics in high-power JET-ILW H-mode plasmas

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1019.pdf

Sustained ELMy H-mode operation at high heating power (~ 32 MW) in JET-ILW requires gas puffing to control radiation from high-Z impurities (W, Ni) by increasing their rate of removal by ELMs, as well as core ICRH heating to mitigate their accumulation and sweeping of the strike points to avoid overheating of the target material [1]. If the gas puffing rate is insufficient, the radiated power increases, causing an H/L-transition and impurity accumulation. A deleterious effect of the gas puffing is to reduce the pedestal temperature [2, 3] and the overall confinement compared to that in similar JET-C pulses at the same power.

Partially replacing some of the gas fuelling by injection of small, ELM-pacing pellets, thereby reducing the particle throughput by ~30%, extends the duration of the high-performance phase and enhances the overall confinement compared to that achieved with gas fuelling alone [1, 4]. Analysis of SXR, bolometry and Z_eff data shows the total radiation is dominated by that from W [5]. Hence, an estimate of the W flushing efficiency, i.e. the fraction removed per ELM, can be evaluated from fast bolometric measurements [6]. This, and a similar measure estimating the inter-ELM W ingress, can be used to quantify the net effect of the ELMs on the W content. By classifying the ELMs as either pellet-triggered or natural events, their flushing efficiency, as well as the post-ELM pedestal characteristics and ELM sputtered impurity influxes (W, Be), determined from visible divertor spectroscopy, can been compared between ELM types.

So far, no statistically significant difference in the W flushing efficiency between the pellet triggered and natural ELMs has been found. However, the smaller, irregular ELMs induced by pellets sputter less impurities per ELM from the divertor targets, which reduces the resulting impurity influx into the confined plasma and the net rate of increase of W contamination. Use of pellet fuelling can thereby extend the period of high-performance, ELMy H-mode operation and enhance the overall confinement beyond that achievable with gas puff fuelling alone.

[1] Garzotti L. et al., IAEA FEC `18;
[2] Giroud C. et al., Nucl. Fusion 53 (2013) 113025;
[3] Maggi C. et al., Nucl. Fusion 55 (2015) 113031;
[4] Kim H-T et al., Nucl. Fus. 58 (2018) 036020;
[5] Sertoli, M. RSI 89 (2018) 113501;
[6] Fedorczack N. et al., J. Nucl. Mat. 463 85-90.

Speaker: A.R. Field (EPS 2019)

683 P5.1020 Analysis of W transport in ASDEX Upgrade during various pedestal activities

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1020.pdf

Edge transport barrier (ETB or pedestal) regime is often associated with transient relaxations (Edge Localized Modes or ELMs) of the plasma. These periodic bursts of particles and energy can significantly erode and damage the materials (eg. Tungsten, W) of the tokamak vessel. Any high-Z impurities remaining confined in the plasma may potentially contribute to decrease the overall confinement time by radiating part of the heating power mostly via line-emission radiation (and Bremsstrahlung at higher temperatures). When impurities accumulate in the core, they can eventually cause the disruption of the plasma and the abrupt end of the confinement.

We compare results from recent ASDEX Upgrade experiments in various ELMs regimes (type I or type III). Spectroscopic measurements give an indication of the W source evolution with heating and ELM activity. Measurements from the grazing incidence spectrometer [1] are analysed in order to assess the W content of the confined plasma in colder (~1.5 keV) and warmer (~>2.5keV) regions. Both ELMs cycles maintain a constant impurity level but type III discharges exhibit much less W content due to decreased physical sputtering. RMPs (Resonant Magnetic Perturbation coils) alter the plasma edges and decrease the peaking of the W-content through plasma rotation breaking. Tomographic reconstructions [2] of the Soft X-Ray (SXR) emission are used to assess the effect of plasma rotation on the degree of poloidal asymmetry [3] in the distribution of the tungsten. Planned experiments in ASDEX Upgrade dedicated to W transport studies are introduced.

[1] T. Pütterich et al. J. Phys. B: At. Mol. Opt. Phys. 38 (2005) 3071-3082
[2] T. Odstrcil et al. Rev. Sci. Instrum. 87, 123505 (2016);
[3] T. Odstrcil et al. 2018 Plasma Phys. Control. Fusion 60 014003

Speaker: F. Jaulmes (EPS 2019)

684 P5.1021 Investigation of pedestal stability in edge plasma region of the COMPASS tokamak

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1021.pdf

Electron density and temperature profile measurements are important for magnetic confinement fusion research performed on tokamaks. One of the research areas these measurements help to understand is physics of edge transport barrier (pedestal) formation, which is closely related to plasma performance in the H-mode regime. Investigation of the pedestal stability can provide an important insight into the edge plasma behaviour trying to understand the magnetohydrodynamic (MHD) activity including edge localised modes (ELM) instabilities. Several experimental points for dierent COMPASS discharge scenarios were analysed using ideal MHD codes, HELENA and ELITE/MISHKA, concentrated on the H-mode performance evaluation and analysing the behaviour of the peeling-ballooning boundary in order to characterize ELMs and their triggering mechanism. Essential input for the analysis of electron density and temperature profiles is provided by the Thomson scattering (TS) diagnostics system of the COMPASS tokamak. Recent progress in the data processing of the COMPASS TS diagnostics suggested several improvements in order to optimize the data processing code and improve its reliability, thus, improving the precision of the pedestal stability analysis.

Speaker: M. Sos (EPS 2019)

685 P5.1022 Pedestal instabilities in between ELMs at ASDEX Upgrade

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1022.pdf

The High confinement mode (H-mode) edge pedestal, a narrow region (~1.5 cm width) with steep pressure gradient just inside the last closed flux surface, is prone to various instabilities. Instabilities include intermittently occurring Edge Localised Modes (ELMs) but also other more continuous modes that occur in between ELM crashes. With imaging of the electron cyclotron emission (ECE-I) we identify and diagnose an instability in the low-frequency part of the spectrum, that occurs before the ELM crash [1, 2]. The radial resolution of ECE allows for its localisation near the pedestal top [1]. The poloidal propagation of the mode, as measured by ECE-I, correlates with the plasma rotation at the location of the mode. The radial electric field, calculated from charge exchange recombination spectroscopy (CXRS) measurements using the radial force balance is such that the observed mode propagates with respect to the E_r = 0 reference frame in the electron diamagnetic direction with no measurable phase velocity. A database has been assembled to investigate dependencies on plasma parameters [2]. Within this database, the frequency of detected instability decreases with increase in Neutral Beam Injection (NBI) heating power. We attribute this trend to the increase in the toroidal rotation with NBI. Simultaneously, an increase in heating power leads to an increase of global β_p which leads to an increase in the pedestal pressure. In the literature (as shown in [3]) the pedestal width ∆ scales as ∆~sqrt(β_p,ped). Therefore, if the pedestal widens with β_p,ped in our cases, instabilities may move radially inward towards lower E_r. Hence, their frequency decreases. The two contributions appear combined within the examined database. In order to confirm the contribution from the toroidal rotation, we first examine the behaviour of mode frequency with NBI heating power from the upcoming reverse I_p/B_t campaign at ASDEX Upgrade. In this configuration, the mode frequency should increase with the increase in NBI heating. Second, to disentangle the contribution from the core rotation due to the NBI heating and contribution from the β_p,ped we analyse discharges heated with the ECRH power only. The frequency and mode numbers are then compared with plasma parameters and correlated with the pedestal width.

[1] B. Vanovac et al 2018 Nucl. Fusion 58 112011
[2] B. Vanovac 2019 PhD Thesis, Chapter 8, TU/e
[3] M. N. A. Beurskens et al 2011 Physics of Plasmas 18 056120

Speaker: B. Vanovac (EPS 2019)

686 P5.1023 Observations of pedestal impurity transport with 3D fields in ITER-baseline-shape DIII-D plasmas

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1023.pdf

Recent results on DIII-D show that low-field-side RMPs improve the robustness of discharges to high-Z impurity injection. Experiments were performed in H-mode ITER-baseline-shape discharges for three cases: 1. ELMy - q95 = 4.1, 2. RMP ELM-suppressed - q95 = 4.1, and 3. RMP with ELMs - q95 = 3.5. For each case above, impurities were injected with either the laser blow off (W and Al) or gas valve (Ar) systems. W injection into ELMy discharges led to a rapid increase in impurity emission, halting of ELMs, and the radiative collapse of the plasma. W injection into discharges with RMPs--either ELMy or ELM-suppressed--did not lead to an increase in radiation or a decrease in plasma temperature. For Al and Ar impurity injection the charge exchange recombination (CER) diagnostic measured spatially (ΔR~8 mm) and temporally (Δt~2.5 ms) resolved emission in the pedestal region of the plasma. These measurements are used in conjunction with the STRAHL transport code to determine the particle convective velocity and diffusion coefficients. For the discharges with RMPs, after the initial Al density rise from the LBO injection, the Al density decreases at a steady rate in the pedestal. However, for the ELMy cases, the Al density continues to increase after the initial rise and only decreases during ELMs. This indicates a lack of outward diffusion of impurities in the inter-ELM period of the ELMy discharges that is maintained in the discharges with RMPs. The ELMy discharges, without RMPs to enhance radial transport, go ELM-free due to the increased impurity accumulation and radiation with the higher particle confinement and thus differ from the other discharges.

*Supported by US DOE under DEAC52-07NA27344, and DE-FC02-04ER54698.

Speaker: B.S. Victor (EPS 2019)

687 P5.1025 Effects of dust on plasma discharges during tokamaks start-up phase

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1025.pdf

Dust in tokamaks is unlike to be mobilized prior to the beginning of plasma discharges, then dust presence in the vessel during the start-up phase of discharges is not considered an issue. Problems could arise due to the presence of magnetic dust [1,2,3] that are more likely to fly in the vessel volume during stat-up phase [4] and could interfere with the plasma discharge [5]. In fact the presence of dust in the early phase of discharges can induce a shift of the optimal loop-voltage vs. gas pressure curve during breakdown phase (i.e. shift in the Paschen's curve), or perturb the plasma resistivity, through the perturbation of Z_eff, leading to a change of the current rise time and a limitation in the plasma current plateau during start-up. In the perspective of the use of stainless steel for the ITER diagnostic first wall [6] and RAFM steel in future fusion plants [7], the presence of magnetic dust could not be negligible.

In this work we propose a model to describe the start-up phase of plasma discharges in presence of solid metallic particles (dust). Examples on how the presence of dust can interfere with the current rump-up phase for relevant dust densities and dust nature scenarios, being dust generally composed by different materials, is presented.

[1] D. Ivanova, M. Rubel, V. Philipps, et al., Phys. Scripta T138, 014025 (2009).
[2] A.N. Novokhatsky, A.E. Gorodetsky, V.K. Gusev, et al. Proc. 38th EPS Conference on Plasma Physics, 27 June-1 July 2011, Strasbourg, France, Vol. 35G, P5.066.
[3] M. De Angeli, L. Laguardia, G. Maddaluno, et al. Nucl. Fusion 55, 123005 (2015).
[4] M. De Angeli, E. Lazzaro, P. Tolias, S. Ratynskaia, et al., submitted to Nucl. Fusion.
[5] J. Winter, Phys. Plasmas 7, 3862 (2000).
[6] R.A Pitts, B. Bazylev, J. Linke, et al. J. Nucl. Mater. 463, 748 (2015).
[7] K. Sugiyama, K. Schmid, W. Jacob, Nucl. Mater. Energy 8, 1 (2016).

Speaker: M. De Angeli (EPS 2019)

688 P5.1026 ELM suppression and recycling reduction by BN & B injection in KSTAR

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1026.pdf

Long periods of ELM quiescence <= 5sec were observed with BN injection into KSTAR ELMy H-modes with an innovative Impurity Powder Dropper (IPD) [1]. In addition, divertor D_α emission was substantially reduced with boron B injection into ELMy H-modes, indicating improved recycling control. In both cases, there was no adverse impact on plasma stored energy. A new mode at ~ 180 kHz frequency appeared in Beam Emission Spectroscopy data, suggesting a modification to the edge transport with active impurity injection.
The powders were dropped into 0.5 MA plasmas with 1.5 MW auxiliary heating and of duration 10-20 s. Photodiode signals and real-color fast camera images show the powders entering the plasma. A series of 2.5 mg doses of BN, delivered in 0.1 s bursts, was observed to eventually reduce the ELM amplitude and frequency without changing the stored energy or plasma density. Analysis of the BES data during the ELM-free phase showed increased coherent mode activity near 180 kHz, corroborated by magnetics data. A continuous BN dose of 2.5 mg/s for 10 s reduced the ELM amplitude and frequency, but did not result in ELM quiescence. In addition, several 2.5 mg doses of B during a single discharge reduced recycling as evidenced by the reduced baseline D_α level during the following shot. A 10 mg dose of B resulted in a disruption. Signatures of each of these effects and the effect on plasma profiles and discharge characteristics will be presented. In addition, these results will be compared with IPDs used for similar experiments on ASDEX-Upgrade [2,3], EAST [4], and DIII-D [5].

*Supported in part by U.S. Dept. of Energy under contract DE-AC02-09CH11466

[1] A. Nagy et al., Rev. Sci. Instrum. 89, 10K121 (2018).
[2] A. Bortolon et al., submitted to Nuclear Materials and Energy (2018).
[3] R. Lunsford et al., Nuclear Fusion, in preparation (2019).
[4] Z. Sun et al., Nuclear Fusion, in preparation (2019).
[5] A. Bortolon, Bull. Am. Phys. Soc. (2018).

Speaker: E. Gilson (EPS 2019)

689 P5.1027 The impact of modeling the separatrix in 3D slab edge simulations

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1027.pdf

Edge simulations until recently focussed on simulating only the scrape-off layer (SOL) and including appropriate boundary conditions to the numerical domain to mimic effects like the presence of a separatrix on the inner radial boundary. To a large extent, flux-driven 3D simulations have had considerable success in recovering the statistical behaviour of plasma fluctuations in the SOL [1]. However, explicitly incorporating a separatrix is a non-tivial addition to the already complex physics of edge transport, and needs a detailed study. It provides insights into how cross-field transport is balanced across the separatrix via parallel transport in the open fieldline region. The separatrix also plays an important role in some of the instabilities common to the edge like filamentation, and in shear flows. In this paper, slab simulations with a separatrix are compared to slab simulations where the separatrix is absent. The differences observed in the transport of the two cases is crucial to singling out and understanding the role of the separatrix. In these simulations, it is seen that the separatrix triggers a strong velocity gradient which possibly plays a role in establishing global poloidal flows. Filamentation is also seen to occur in the vicinity of the separatrix, which poses new questions about the physical description of filamentation with respect to the separatrix - whether the ingredients of filamentation are unique to the presence of a separatrix, or if filamentation (as reproduced in simulation without a separatrix) is independent of the separatrix. This paper describes the analysis of these simulations performed using the TOKAM3X fluid code [2], and outlines the role of the separatrix for an electrostatic isothermal edge plasma.

[1] J. Anderson et al, Physics of Plasmas (1994-present) 21, 122306 (2014)
[2] P. Tamain et al, J. Comp. Phys., 321, 606-623 (2016)

Speaker: W. Gracias (EPS 2019)

690 P5.1028 Research on beam emission spectroscopy combined HL-2A tokamak real experimental data with spectra simulation code

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1028.pdf

A beam emission spectroscopy (BES) diagnostic system has been developed on HL-2A tokomak. Combined with motional stark effect (MSE) diagnostics, the BES could assess the radial electric field and the safety factor, which plays an important role in plasma control and impurity transport processes. A Simulation of Spectra (SOS) code has been developed for spectra simulations based on various tokamak devices' real conditions. It can be used for designing visible spectral diagnostics system and predicting its performance. In this paper, based on the HL-2A real experimental running parameters, it used the SOS code to simulate BES and MSE spectra. The spectra were consistent with experimental data fitting results. The Simulation of Spectra code was also able to get the safety factor and other parameters. The results reveal that this code could be used to design similar diagnostic systems for ITER in the future.

Speaker: J. Wu (EPS 2019)

691 P5.1029 Three-dimensional plasma edge transport and divertor flux modeling for the application of resonant magnetic perturbations in EAST

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1029.pdf

The three-dimensional edge plasma transport with resonant magnetic perturbations (RMPs) in EAST is simulated with plasma responses being considered. This work is motivated by the significance of understanding plasma responses for optimizing edge localized mode (ELM) control and steady-state divertor flux control by RMPs[1].
The modeling is carried out by the full 3D plasma fluid and kinetic neutral transport code EMC3-EIRENE[2, 3]. The plasma responses are simulated by the linear magnetohydrodynamic (MHD) code MARS-F[4]. The modeling results are compared to that of the vacuum assumption, in which a full penetration of the perturbation was assumed. The total particle and heat fluxes deposited on divertor targets and the fraction on each target plate are changed after the plasma responses being considered. For evaluating the integrating effect of a rigid rotating RMPs, the toroidal averaged heat flux profiles along the target are compared. After including the plasma response in the modeling, the changes of the peak value and the width of the profile indicate the ratio of the heat flux deposited on the original strike line to that on the secondary strike line is also changed. The prediction by the 3D magnetic topology modeling shows that the field line penetration depth could play an important role in the divertor power load distribution[5]. The modeling results also show that the changes of the relative velocity of edge plasma flows in adjacent helical flux tubes are caused by plasma response included RMP fields. It also indicates the change of 3D magnetic topology thus its influences on 3D plasma edge transport is crutial for understanding the physics mentioned at the beginning.

[1] Y. Sun et al., 2016 Phys. Rev. Lett., 117 115001
[2] Y. Feng et al., 1999 J. Nucl. Mater., 812 266
[3] D. Reiter et al., 2005 Fusion Sci. Technol., 47 172
[4] Y. Liu et al., 2010 Phys. Plasmas, 17 122502
[5] M. Jia et al., 2018 Nucl. Fusion, 58 046015

Speaker: M. Jia (EPS 2019)

692 P5.1030 0D model of vapour shielding and its application for liquid material targets

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1030.pdf

Intense heat loads on the plasma-facing components (PFC) of tokamaks during transient events such as Type I ELMs and disruptions may result in melting and evaporation of the materials. The evaporated impurity cloud ionizes and serves as a shield reducing heat loads on the PFC. Since accurate estimates of the power fluxes to the divertor targets are crucial for ITER and future DEMO design, shielding physics is intensively studied on linear plasma devices such as Magnum-PSI and QSPA. Moreover, development of liquid metal divertor concepts for tokamaks as a possible alternative to a fully metallic first wall also requires taking the shielding effects into account.
Experiments with Li and Sn aimed to study liquid metal response to the extreme plasma heat loads and associated shielding effects are conducted extensively on Magnum-PSI and Pilot-PSI devices [1]. However, a consistent theory of the vapour shielding is yet to be developed. In this work we present a new 0D model of shielding including an extensive set of processes involved. Singly ionized species of background plasma and evaporated material are considered. We take into account elastic collisions between all the participating particles, volumetric ionization and recombination, radiation, and plasma-surface interaction processes. The surface temperature evaluation is governed by 1D thermal conductivity equation.
The model is applied to experiments on Sn and Li vapour shielding [1]. The role of different processes controlling the target surface temperature is discussed. Stability of steadysate solution with respect to perturbations of vapour density and temperature is investigated. Estimations of Li vapour shielding in fusion relevant case of hydrogen plasma are given.

This work is supported by Russian Foundation for Basic Research grant 18-3220114\18.

[1] T.W. Morgan, P. Rindt et al. Plasma Physics and Controlled Fusion, V. 60, 2017, P. 014025.

Speaker: E. Marenkov (EPS 2019)

693 P5.1031 Study of the two null nearby divertor magnetic configuration at EAST

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1031.pdf

Two of the biggest challenges for future fusion reactors are the power dissipation and erosion of diverter targets. Alternative configurations such as Snowflake [1] (SF) and the Quasi-snowflake family (QSF), including Two Null nearby divertor [2] (TNND), have the aim of controlling and optimising the magnetic flux expansion and the connection length. These can reduce the peak power flux and the temperature at the strike points enhancing the recombinations in the divertor region, in order to access the detachment state. The EAST tokamak is capable of pursuing advanced exhaust experiments with alternative magnetic configurations. The preliminary experiments dedicated to TNND were conducted at EAST with the aim of testing the potential of this alternative configurations, by moving the secondary x-point during the discharge evolution with the results of a increase of ~30% of connection length and a factor ~4 in the flux expansion, compared with the Single Null initial case. In this contribution the impact of distance between the two nulls of TNND, is investigated via the 3D edge plasma fluid and neutral particle transport code EMC3EIRENE [3]. A predictive study has been done to compare two TNND with different position of the second null and similar characteristic to the experimental one, studying the effect of second null's position on the power exhaust. The Peak power load in the TNND cases, in function of density and power entering the SOL, compared with a reference Single Null magnetic configuration, shown a significative reduction thanks to a lower value of Bp/ Btot in the divertor region. Instead the fraction of recombinations near the targets is negligible for the whole cases, although TNND's fraction is greater than SN case, at the same density.

[1]Ryutov D.D,. et al, Phys Plasmas 15 (2008) 092501
[2]G. Calabrò, et al., Nucl. Fusion 55 (2015) 083005
[3]Y. Feng, et al., Contrib. Plasma Phys. 54(4-6), 426-431 (2014)

Speaker: C. Meineri (EPS 2019)

694 P5.1032 Predicting Scrape-Off Layer profiles and filamentary transport for reactor relevant devices

See full abstract:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1032.pdf

In magnetic confinement devices, boundary turbulence is responsible for transporting plasma and energy from the well-confined region towards the material surfaces where it can severely harm reactor relevant machines. It is therefore essential to develop a solid understanding of the mechanisms behind the transport in the edge of the plasma. Large fluctuations, often called filaments, dominate the particle transport in the edge and determine the erosion of the plasma facing components in steady state conditions. A statistical framework that relates the fundamental physics of Scrape-Off Layer (SOL) L-mode and inter-ELM filaments with the profiles they generate is presented. This work will discuss the theoretical and numerical work aimed at understanding statistics and dynamics of plasma filaments, which represent the basis for the statistical framework. The framework predicts that radially accelerating filaments, less efficient parallel exhaust (e.g. due to interaction with neutrals) and a statistical distribution of the radial velocities can contribute to induce flatter profiles in the far SOL and therefore enhance plasma-wall interactions. Also, profile broadening at high fuelling rates, potentially harmful for ITER, can be caused by interactions with neutrals in the divertor or at the wall or by a significant radial acceleration of the filaments. The mechanisms governing the interaction of pairs of filaments, as well as the dynamics of high beta, inter-ELM like, filaments were investigated and employed to improve the statistical framework. The results of the framework are backed up by experimental comparison with measurements taken on JET and MAST. Advanced machine learning algorithms were developed and deployed, including convolutional neural networks applied to filament identification in images, techniques that have an interest that goes beyond the validation of the statistical framework. In all cases treated, the theoretical prediction matched the experimental data within errorbars.

Work supported by RCUK [grant number EP/I501045] and Euratom.

Speaker: F. Militello (EPS 2019)

695 P5.1033 Characterization of the scrape-off layer and pedestal conditions at JET using density profile measurements by reflectometry

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1033.pdf

The edge electron density at the midplane is a very important interface parameter between core (associated with fusion performance) and divertor plasma (able to control power exhaust). The separatrix density is also essential to assess the pedestal stability and has been observed to be related with the plasma energy confinement, with a significant impact on the Edge Localized Mode (ELM) dynamics. Previous studies indicate that divertor conditions and the separatrix density are correlated influencing even the core plasma confinement (e.g. [1]). Mechanisms such as confinement degradation with gas fuelling, the role of neutrals and the importance of the separatrix density are however not fully understood.
Measurements of the midplane density with high temporal and spatial resolution are therefore instrumental. A reflectometry diagnostic is available at JET that provides density measurements with the required temporal and spatial resolution. A large dataset of measurements is available that enables to estimate physics relevant parameters characterizing the density profile such as pedestal density, pedestal width, separatrix density and scrape-off layer (SOL) width.
In this work, a set of different density profile models are presented as possibilities to expand to the SOL the commonly used modified hyperbolic tangent (mtanh) function. Different SOL models were compared, ranging from simple linear slopes to polynomials and exponentials. A database was established with discharges selected to offer a wide variation of global parameters such as plasma confinement or discharge conditions as impurity seeding, fuelling rate and divertor configuration. Initial results on the correlations between the plasma parameters characterizing the density profile and the selected discharge parameters will be presented. Taking advantage of the high temporal resolution of the reflectometry measurements (down to 15 μs) the evolution along the ELM cycle was also studied. Encouraging results were obtained that allow the determination of the time scales for ELM crash and recovery based on the evolution of parameters such as pedestal and SOL width and separatrix density.

1. M. N. A. Beurskens et al., Plasma Physics and Controlled Fusion 55, 124043, DOI 10.1088/0741-3335/ 55/12/124043 (2013).

Speaker: D. Nina (EPS 2019)

696 P5.1034 Non-linear hybrid kinetic-MHD simulations of ELMs in the ASDEX Upgrade tokamak

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1034.pdf

Recent experiments have shown that Edge Localized Modes (ELMs) can have a strong impact on the fast-ion population, causing significant losses and/or acceleration [1, 2]. These findings motivate a kinetic study of the interplay between fast-ions and ELMs. For this purpose, the 3D hybrid kinetic-MHD code MEGA [3] has been applied to a diagnosed ASDEX Upgrade case [4]. Large type I ELMs have been obtained using both the standard and extended MHD model in a fully 3D geometry, including the X-point and scrape-off layer (SOL) region. Standard MHD simulations reveal that high (n~30) ballooning modes dominate the linear phase. A saturated phase is obtained, in which lower n modes have grown due to non-linear couplings between different harmonics. These results are compared against extended MHD simulations, including ion diamagnetic drifts and neoclassical flows, the latter recently being implemented in MEGA. Preliminary results of the dependence of the mode stability on the NBI fast-ion distribution will be discussed.

[1] M. Garcia-Munoz et al., Nucl. Fusion 53 (2013), 123008.
[2] J. Galdon-Quiroga et al., Phys. Rev. Lett. 121 (2018), 025002.
[3] Y. Todo et al., Phys. Plasmas 5 (1998), 1321.
[4] A. F. Mink et al., Nucl. Fusion 58 (2018), 026011.
§ H. Meyer et al, Nucl. Fusion 57 (2017), 102014.

Speaker: J. Dominguez-Palacios

697 P5.1035 Comparison of H-mode pedestal characteristics in SAS and open divertor configurations on DIII-D

See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1035.pdf

The Small Angle Slot (SAS) divertor installed on DIII-D combines high closure with small incidence angle to achieve detachment over the entire divertor at low density. Experiments on DIII-D comparing divertor detachment and other divertor characteristics of the SAS configuration to an otherwise identical open divertor configuration also revealed differences in the H-mode pedestal characteristics and overall plasma performance. Density scans in otherwise matched discharges in the SAS and open divertor configurations were obtained over a range of neutral beam heating powers with the Bx∇B drift direction both toward and away from the X-point.
With the Bx∇B drift away from the X-point, SAS discharges showed improved energy confinement at a given pedestal density, n_e^PED, with higher temperature and reduced thermal diffusivity from the top of the H-mode pedestal inwards, compared the open divertor configuration. At a given n_e^PED, pedestal density profiles are similar in the two divertor configurations, but the SAS discharges have wider and higher temperature pedestals with the top of the temperature pedestal shifted inwards relative to the density pedestal. For this Bx∇B drift direction, the pedestal pressure increases with density in the SAS configuration while it is reduced with density for the open divertor. Both configurations show a strong decrease in pedestal temperature and pressure above a density where a high radiation zone reaches the X-point region, although the density at which this occurs is significantly higher for the SAS case.
With the Bx∇B drift toward the X-point the SAS and open divertor have similar pedestal structure with pedestal pressure increasing with density. In comparison to the other Bx∇B drift direction pedestal temperature profiles are higher and wider and separatrix density is reduced.
These discharges have relatively weak shaping and high density and as a result lie along the ballooning mode branch of pedestal peeling-ballooning stability. In this regime the critical pressure gradient is strongly affected by the level of diamagnetic stabilization making the pedestal stability limit sensitive to the relationship between the pedestal density and temperature profiles. In the open divertor case with Bx∇B drift away from the X-point the diamagnetic stabilization is weakened with increasing density resulting in the reduced critical gradient and pedestal pressure while in the SAS case diamagnetic stabilization improves with density. This affect was dramatically demonstrated in a SAS discharge in which Ne injection improved the core ion confinement resulting in a strong increase in pedestal ion temperature resulting in improved ballooning mode diamagnetic stabilization and critical pressure gradient. Although significant differences were seen in the pedestal pressures for a given density in the different divertor configurations and Bx∇B drift directions the fact that plasma shape and other discharge characteristics where matched resulted in the usual form for the EPED1 model[1] predicting similar pressures for all cases. However the pedestal widths were consistent with the scaling used in EPED1 indicating that the model would predict the results if the relationship between the pedestal density, temperature, and impurity profiles were included.

[1] P.B. Snyder, et al., Nucl. Fusion 51 (2011) 103016

Work supported by US DOE under DE-FC02-04ER54698, DE-AC02-09CH11466 and DE-AC05-00OR22725

Speaker: T.H. Osborne (EPS 2019)

698 P5.1036 Systems Studies of Double Null Divertor Models

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1036.pdf

As conceptual design options for a demonstration fusion power plant (DEMO) are explored it is important to understand the design space for possible non-ITER like design options. The power exhaust is a key design driver for a fusion power plant, and puts strong constraints on the size of the machine. One candidate for an alternative design is a double null divertor configuration which provides better power and heat flux management[1, 2], but involves decreased space in the first wall for blanket technologies and greater design complexity with more demanding remote handling considerations[3].
A tool for understanding large integrated technology problems is a systems code, such as PROCESS[4]. The systems code models all important plant systems and allows for the fast evaluation of consistent scenarios which can therefore also be used to explore alternative designs for baseline design options, with the need for later extensive detailed studies. In this work we will use the PROCESS system code to analyse the effect of double null divertors, and explore advantages and disadvantages in employing this divertor technology on the exhaust power handling, plasma physics and blanket systems within the power plant.
The greatest benefits of double null are achieved by operating in a regime in which the power across the separatrix is shared nearly evenly into both the upper and lower divertors, known as a connected double null. But, this configuration is not easily controlled due to vertical displacements. A proposed method of overcoming these issues is driving a cyclic vertical motion in the plasma, which leads to a continuous wobbling of the power and heat loads on the upper and lower divertor targets[5]. We assume operation in the regime of cyclic motion and present the constraints put on the DN divertor design by the wobbling of the heat loads. This assumes the technological challenges of achieving meaningful control for load sharing can be overcome.

[1] T.W. Petrie et al, Journal of Nuclear Materials 290-293 (2001) 935-939
[2] G. De Temmerman et al, Plasma Phys. Control. Fusion 52 (2010) 095005
[3] R. Kemp et al, Fusion. Eng. Des. 136 (2018) 970-974
[4] M. Kovari et al, Fusion Eng. Des. 89 (12) (2014) 3054-3069
[5] R. Wenninger et al, 26th IAEA Fusion Energy Conference (2016)

Speaker: A. Pearce (EPS 2019)

699 P5.1037 Initial studies of liquid lithium divertor operation in T-15

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1037.pdf

The power and particle exhaust are among the key problems to be solved for successful operation of ITER and DEMO [1]. The conventional solid plasma-facing component (PFC) solution suffers from numerous drawbacks such as material erosion and degradation under severe power, charged particle and neutron fluxes, possible damage caused by transient events such as Type I ELMs and disruptions. An alternative PFC concept involves using liquid metal (LM) as the divertor target material combined with the tungsten first wall [1]. Among the LM options considered lithium is the most promising one due to its low Z, gettering capabilities and overall positive influence on the plasma discharge. However, a high sputtering yield of the liquid lithium PFC combined with intense evaporation limit the range of the surface temperature over which it can be used without producing significant core plasma dilution, unless specific divertor designs such as the lithium vapour box [2] are implemented. In the present study we investigate the regimes of the capillary porous structure (CPS) based liquid lithium divertor operation in the T-15 tokamak, using the SOLPS4.3 2D transport code. The simulation setup is close to the one used in [3]. Two possible cases are considered: i) both target plates are made of the actively cooled CPS filled with liquid lithium; ii) only the outer target is, whereas the inner one is made of tungsten. The local surface temperature of the CPS targets is assumed to depend linearly on the heat flux (i.e. 2D effects are neglected), the proportionality factor is defied via 3D finite element modeling and verified experimentally. Various values of the power fluxes from the core region to the edge, the hydrogen fueling rates and the recycling conditions at the surface of PFCs are considered. Since lithium is a relatively inefficient radiator, injection of radiating impurity (neon) for additional heat flux dissipation is also considered. The operational window of the parameters varied is defined, where both the target heat loads are manageable and the lithium influx into the core plasma is acceptable.

1. Brezinsek S. et al. Nucl. Fusion. 2017. Vol. 57, P. 116041.
2. Goldston R.J., Myers R., Schwartz J. Phys. Scr. 2016. Vol. T167, P. 014017.
3. Pshenov A.A., Kukushkin A.S. Plasma Phys. Reports. 2018. Vol. 44, P. 641-651.

Speaker: A.A. Pshenov (EPS 2019)

700 P5.1038 Simulation of nonresonant stellarator divertor

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1038.pdf

The nested magnetic surfaces that confine a fusion plasma can be designed to be bounded by a limiter or a divertor. For a limiter, confining surfaces extend until they intercept a part of the surrounding structure. For a divertor, an outermost confining magnetic surface exists which is well separated from the surrounding structures. The only designs that are thought to be fusion relevant have divertors that direct field lines from the plasma edge into chambers where the particle exhaust can be pumped and the residual heat exhaust can be handled. The topological properties of magnetic field lines just outside the outermost confining surface determine much of the physics of divertors. Axisymmetric tokamak divertors are well-known, and the outermost confining surface is defined by a sharp separatrix. The topology of the magnetic field lines associated with a stellarator divertor is far more subtle. Related subtleties arise in tokamak divertors when subjected to sufficiently strong non-axisymmetric perturbations. An efficient simulation method for carrying out topological studies of nonaxisymmetric divertors was recently developed [A. H. Boozer and A. Punjabi, Phys. Plasmas 25, 092505 (2018)]. This method uses the ideas of Hamiltonian mechanics, including symplectic invariant, cantori, and turnstiles, to explore the magnetic topology to understand the physics of divertor configurations in both stellarators and tokamaks, and in particular nonresonant stellarator divertors. Results of this study on the width of the footprint, loss rate of magnetic flux, and the decay of confinement will be presented. The study aims to find the scaling laws that govern the loss of magnetic flux; and whether the scaling laws are universal in nature [A. H. Boozer and A. Punjabi, Phys. Plasmas 23, 102513 (2016)].

This work is supported by the U.S. DoE Grant No. DE-FG02-04ER54793 to Hampton University and DEFG02-95ER5433 to Columbia University. The research used NERSC resources, supported by the Office of Science under Contract No. DE-AC02-05CH11231.

Speaker: A. Punjabi (EPS 2019)

701 P5.1039 Study of nitrogen seeded plasma in JET in preparation of JT60SA

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1039.pdf

The operational conditions of DEMO require a high density and a high fraction of power radiated in the Scrape-Off Layer in order to fullfill the strict limits imposed by the material and the necessity to work in detached conditions. Indeed, almost the 95% of the input power must be radiated [1]. Various experiments in JET and ASDEX Upgrade have shown the possibility to work in high radiating scenarios, with a power fraction higher than the 75% by inserting external impurities as nitrogen or neon[2]. In the framework of the worldwide fusion community, JT60SA plays a crucial role in support of ITER in order to define possible scenarios of DEMO. In particular, one of the mission stems in the investigation of the feasibility of high density and high radiating scenarios, as in the Scenario 3[3], with a CFC tiles in the first phase and then with Tungsten wall in the second phase. These experiments shall give a deeper insight in the definition of both divertor and detachment conditions in presence of external impurity, as well as to provide a wide range of well diagnosed discharged necessary for the code validation[3]. In this contribution we present the study on a high triangularity N_2 seeded plasma in JET used as a reference for the study of the divertor conditions of the Scenario 3 of JT60SA. First of all, a benchmark of the simulation of SOLPS-ITER[4] with experimental data will be discussed by comparing the outputs of the code with different diagnostics as the High Resolution Thompson Scattering for the upstream conditions and Langmuir probe for the target. Therefore, the behaviour of SOL plasma and the stability of the detachment in high radiating scenario are investigated by changing the upstream density and the N_2 seeding rate.

[1] Wenninger R. P., et al., (2014) Nuclear Fusion 54 114003 ISSN 0029-5515
[2] Bernert M., (2017) Nuclear Materials and Energy 12 111-118 ISSN 2352-1791
[3] JT-60SA Research Plan, Version 4, September 2018
[4] S.Wiesen, et al., (2015) Journal of Nuclear Materials, 463, 480-484 1

Speaker: G. Rubino (EPS 2019)

702 P5.1040 Observations of 3D magnetic perturbation effects on divertor heat flux distribution induced by LHW using the infrared camera on EAST

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1040.pdf

Previous experimental results from the Experimental Advanced Superconducting Tokamak (EAST) have shown that the lower hybrid wave (LHW) can induce a 3D magnetic topology change at the plasma boundary, thus affect significantly the edge plasma transport and divertor heat flux distribution [1, 2]. To investigate further the 3D effects on the interaction between the plasma and the first wall on EAST, a middle-waveband wide-angle infra-red (IR)/visible integrated endoscope diagnostic system has been developed to measure the surface temperature distribution on important inner components like the upper & lower divertors and LHW protection guide limiter etc., simultaneously. Splitting of the original strike line, which characterised as appearance of multiple peaks in the heat flux distribution profile along the divertor target, has been observed during the application of LHW. A temperature measurement method using a proposed nonlinear emissivity of the divertor target plate is developed to obtain more accurate heat flux results.
In this paper, the effects of LHW on the heat flux distribution will be discussed. A numerical model using field-line tracing method for modeling of three-dimensional magnetic field topology change induced by the LHW on EAST is presented. The topological structure is calculated in the vacuum paradigm. The modeling result predicts the toroidal dependence of the strike line splitting on the divertor target, which has been observed by using the IR camera, as well as various divertor probes located at different toroidal cross sections.

[1] Y. Liang et al., Phys Rev Lett 110, 235002 (2013).
[2] J. Li et al., Nature Physics 9, 817 (2013).
[3] K. F. Gan et al., Rev Sci Instrum 84, 023505 (2013).

Speaker: S. Shu (EPS 2019)

703 P5.1041 Analysis of inter-ELM bursts in the JET scrape-off layer

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1041.pdf

Edge localized modes (ELMs) are typically considered as major concerns for the main chamber wall. However, other smaller but more frequent events, so called inter-ELM bursts, which appear between type-I ELMs, could also harm the plasma-facing components. Although they only occasionally appear in the JET scrape-off layer in the majority of the discharges, they became frequent [1] in a discharge series, where the effect of fuelling on plasma parameters was studied. These plasmas were in the middle of the JET operation space (B_t=2.2 T, I_p=2.2 MA, P_NBI=13.5 MW, P_ICRH~1-2 MW), had high triangularity and the strike points were placed close to the pumping duct in the corner of the divertor. The bursts were detected as huge (n_e~1-1.5 x 1019 m-3) complex and multi-peaked density perturbations in the Lithium beam emission spectroscopy diagnostic signals observing the top of the machine. However, they did not appear in the Beryllium II line spectroscopy signals monitoring plasma-wall interaction in the divertor at the bottom of JET. This might suggest that they load the main chamber wall. In this contribution a possible explanation to the complex structure of this type of inter-ELM bursts is provided: the assumption that several filaments are simultaneously released at the outer midplane, corresponding to a ballooning-like structure, is shown to fit to the observations. They extend along the field lines and propagate radially outwards passing the observation window of the Lithium beam diagnostic. The effect of fuelling level on burst statistics is characterized. An estimation of the filament velocity and shape is provided. Burst properties are compared to the observations done in ASDEX Upgrade [2].

[1] B. Tal et. al., TTF Seville (2018)
[2] P. Hennequin et. al., EPS Belfast (2017), P1.167

Speaker: B. Tal (EPS 2019)

704 P5.1042 Lithium influence on edge plasma parameters at T-11M tokamak

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1042.pdf

Liquid lithium is considered as a material for plasma facing components (PFCs) of fusion devices. Its properties have been widely studied at present. In particular, the lithium program of T-11M tokamak is focused on solving the technological problems of creating a stationary tokamak with plasma-facing components from liquid lithium. As a part of this program edge plasma parameters were investigated using a Mach probe at different temperatures and positions of lithium limiters.
The first experiments with the probe were carried out with one vertical and longitudinal lithium limiter inserted in the vacuum chamber of T-11M. In this case radial distributions of ion saturation current and the electron temperature for L-mode had a maximum at r = 4 cm (distance from the wall of vacuum chamber) which may be due to the formation of a magnetic island near the vertical limiter. This effect was not observed in the H-mode, which may be connected with the weaker interaction of the edge plasma with the vertical limiter.
In addition, this effect disappeared when second longitudinal limiter was installed, which can be considered as a result of the symmetrization of the collector system.
In order to study the effect of lithium on edge plasma parameters, the radial distributions of the electron temperature and the ion saturation current were compared for hot and cold lithium limiters. The hot limiters corresponded to an enhanced intake of lithium into the edge plasma. As a result, a flat electron temperature profile was observed with hot limiters. The electron pressure remained constant for cold and hot limiters. This can be explained by the fact that hydrogen recycling decreases with increasing of the lithium amount in the edge plasma.

Speaker: I. Vasina (EPS 2019)

705 P5.1043 Drift effects in SOLPS-ITER simulations for the TCV divertor upgrade

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1043.pdf

The effect of the upcoming TCV divertor upgrade on the distribution of neutrals and the onset of detachment is studied using 2D transport simulations. The divertor upgrade is centered around the installation of a gas baffle to form a closed divertor chamber [1]. SOLPS-ITER simulations predict that the baffle geometry selected to be installed in TCV in 2019 will increase the divertor neutral density by a factor 5 and the neutral compression by an order of magnitude for typical TCV single null, Ohmic heated, scenarios, significantly facilitating access to deeper detachment [2].
As the conditions for the onset of detachment depend on the power entering each divertor leg, its simulation requires defining correct inboard/outboard power asymmetry that is, to large extent, determined by scrape-off layer drifts. The inclusion of such drift effects in transport codes remains to date numerically challenging. Such an attempt, that includes self-consistent electric fields and full drift effects, is presented. Drift simulations in which the targets detach are found to be numerically more stable as radial gradients in the target temperature profiles are reduced and thus the local radial electric fields are decreased.
Comparison to unbaffled well-diagnosed TCV experiments is made and quantitative predictions for future baffled experiments are described employing synthetic diagnostics. TCV operation with baffles will not only enhance our understanding of the role of neutrals for detachment but also provide a direct test of the SOLPS-ITER model for initial ITER operation and beyond.

References
[1] A. Fasoli, and the TCV team, TCV Heating and Divertor Upgrades, Fusion Energy Conference 2018
[2] M. Wensing et al., SOLPS-ITER simulations of the TCV divertor upgrade, to be submitted to Plasma Phys.
Contr. F.

Speaker: M. Wensing (EPS 2019)

706 P5.1044 Link between stability of edge plasma and two-layer convection

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1044.pdf

In magnetic confinement devices, the boundary turbulence is characterised by intermittent ejection of coherent filamentary structures. These filaments transport plasma from the well-confined core region, through the Scrape-Off Layer (SOL), towards the material surfaces. This results in increased plasma-wall interaction, which has the potential to damage plasma-facing components and shorten the lifetime of the device. It is therefore essential to develop a full understanding of the mechanisms behind the transport in the edge of the plasma.
A good candidate for the mechanism responsible for the scrape-off layer fluctuations is the interchange instability. SOL interchange models have been studied extensively both theoretically and numerically, and have provided useful insight into the dynamics of SOL plasma. Subsequently, motivated by the concept that filaments are generated in the core region before being ejected into the SOL, the simple SOL models have been extended to consider a configuration composed of the two regions (core and SOL) connected at the interface. The two regions exhibit distinct dynamics parallel to the magnetic field. In the core, field lines are considered periodic in the parallel direction, while in the SOL, the field lines end with a Debye sheath at a material surface. The presence of the sheath provides a sink for plasma particles and energy. Mathematically, this is represented by the inclusion of parallel loss terms in the SOL region. Although such two-region models have become fairly standard in numerical modelling of filament generation, their linear stability properties have not been explored.
The fundamental mechanism of interchange drive in edge plasma has been compared to that of buoyancy drive in neutral fluids, with reference to Rayleigh­-Bénard convection in particular. Indeed, simple SOL interchange models can be viewed as a modified convection problem. By extension, there is a similar analogy between two-region plasma models and two-layer convection. Two layer convection has attracted considerable attention because of its interesting theoretical aspects and a variety of possible convection modes. One of these is the possibility of the onset of two distinct unstable modes at the same value of Rayleigh number.
In this contribution address we investigate whether a similar situation can occur in the two-region plasma models through a linear stability analysis of a two dimensional interchange model that includes a simple description of open and closed field line regions based on the sheath dissipation closure.

Speaker: F. Wilczynski (EPS 2019)

707 P5.1045 Simulation of the radiative control and QSF configuration on EAST by the SOLEDGE2D-EIRENE code

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1045.pdf

AST has implemented the feedback control of the radiated power to protect divertor target plates from overheating in H-mode long pulse discharges [1]. Since now, by the real-time control system it has been obtained a radiative fraction up to 40%, and it was found the neon (Ne) gas one of the best choices as the additional radiator. In order to analyze the transfer process in scrape-off layer (SOL) and impurity behavior in the scenario of radiative control, the edge code SOLEDGE2D-EIRNE [2]. In this article, two typical upper-single null (USN) tungsten divertor discharges were modeled: an Hmode discharge in radiative feedback control phase (neon seeding) with = 0.8, and one without neon seeding with <= 0.5 used as the reference pulse. The experimental data without neon seeding show a nearly uniform radiation emission distribution in the different regions (main plasma and divertor region). For the neon seeding phase, the change of the radiated emission also shows a uniform increment both in the main plasma and the divertor region. This kind of distribution can be caused by various factors: a lot of seeded light impurity may be transported into main plasma or to an increment of core accumulation of heavy impurities like tungsten. In the modeling situation, the low edge electron temperature is one of the possible reasons to allow more Ne particles into separatrix but results also suggested that heavy impurity might increase. However, whether the neon seeding causes an additional sputter of W still needs more study. Modeling results confirm that the additional neon gas injection provides the reduction of the divertor peak power fluxes, mitigates the power load on the divertor region, which is consistent with the diagnostic data from Langmiur probe. The Quasi-snowflake (QSF) discharge on EAST has been also simulated to assess the effectiveness of neon seeding for this configuration. Based on this simulation result of an existing non-seeded discharge, a prediction of the neon seeding phase with the same configuration is done to estimate the neon transport process under the upper QSF shape.

References
[1] K. Wu, et al., Achievement of radiative feedback control for long-pulse operation in EAST tokamak, Nuclear Fusion 58 (2018) 056019
[2] H. Bufferand, et al., Near wall plasma simulation using penalization technique with the transport code SolEdge2D-Eirene, Journal of Nuclear Materials 438 (2013) S445S448

Speaker: K. Wu (EPS 2019)

708 P5.1046 Experimental investigations of MARFE and detached plasma on J-TEXT tokamak

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1046.pdf

Multifaceted asymmetric radiation as well as strong poloidal asymmetry of the electron density from the edge, dubbed as `MARFE', has been observed in high electron density Ohmically heated plasmas on J-TEXT tokamak. While the plasma density increasing further, it is found that the MARFE sometimes moves poloidally and evolves into the poloidally symmetric structure with strong radiation at edge, named as "detached plasma" or "detachment". The evolution of MARFE into detachment only occurs in discharges with high safety factor (q_a>5). The physical process from MARFE to detachment has been investigated. It is found that the energy balance between perpendicular loss and parallel transport is critical. While the balance saturates, the MARFE stay at the high field side. Otherwise, the MARFE moves along poloidal direction and evolves into detachment. In addition, the stability of MARFE could be affected by electrode biasing at edge. Here, the ExB poloidal flow acts the dominant role. More details will be discussed in the meeting.

Speaker: G. Zhuang (EPS 2019)

709 P5.1047 Finite beta effects on the island bundle diverter of CFQS

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1047.pdf

CFQS is a new stellarator program proposed in China with the magnetic configuration of the quasi-axisymmetry. This program is an international joint project (NSJP) conducted by NIFS (National Institute for Fusion Science), Japan and SWJTU (Southwest Jiaotong University), Chengdu China. The number of toroidal period is 2 and the major radius of the device is 1 m. The magnetic strength is 1 T targeting an ECH plasma with high electron temperature.
Magnetic configuration of CFQS is designed based on the CHS-qa design [1], which was completed in NIFS for the succeeding program to the CHS experiment. The quasi-axisymmetry was successfully designed for CHS-qa giving strongly improved neo-classical transport. The design of modular coils for the device was also completed with the engineering supporting structure design. However, the work for the magnetic divertor configuration was not sufficiently done except a preliminary study of magnetic field line structures outside the last closed magnetic surface.
For CFQS, a special type of the island divertor configuration is studied more intensively. This island divertor has very large islands surrounding the core confinement region with a clear interface of magnetic separatrix [2]. However, the formation of islands strongly depends on the rotational transform, which changes very much with the bootstrap current. Because the quasi-axisymmetric stellarator has a large bootstrap current similar to standard tokamaks, it is important to study the effect of plasma beta on the island divertor. In this paper, we show various conditions of the formation of the island bundle divertor (IDB) and will propose the possible scenarios of high beta experiment with IBD in CFQS.

[1] S. Okamura, et. al., Nucl. Fusion 41 (2001) 1865.
[2] S. Okamura, et. al., EPS conference 2018, paper P5.1034.

Speaker: S. Okamura (EPS 2019)

710 P5.1048 Field line escape pattern in a poloidally diverted tokamaks

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1048.pdf

To simulate magnetic configuration in tokamaks like ITER, we use a wires model consisting of electric currents in five parallel infinite wires to obtain double-null magnetic surfaces with specific choices of magnetic axis position, triangularity and elongation. This model reproduces quite well the ITER configuration and it can delineate dynamical properties of open and closed field lines near the separatrix. Comparing to numerical equilibria reconstructions to simulate plasma in the presence of poloidal divertors, which are time-consuming, this model is faster and versatile, reproducing ITER like magnetic topology. Due to the flexibility of the wires model we can consider different effects of perturbing magnetic field lines near the separatrix. One of them is to include a perturbing error field, due to asymmetries on the external coils[1,2]. Moreover, we include magnetic perturbations caused by external coils, similar to correction coils installed at the tokamak DIII-D and those that will be installed at ITER[3,4,5]. We integrate numerically the field line differential equations to obtain the deposition patterns of magnetic field line in the divertor plate. We show that the results agree with those observed in sophisticated simulation codes.

References
[1] Reiman A. Physics of Plasmas 3, 906, 1996.
[2] Kroetz, T. et al. J. of Plasma Physics, 79, 751, 2013
[3] Evans, T.E., et al. Physics of Plasmas , 9, 4957, 2002.
[4] Foussat., A. et al. IEEE. Trans. Appl. SUpercond. 30, 402, 2010.
[5] Martins, C.G.L., et al. Physics of Plasmas, 21, 082506, 2014.

Speaker: M. Roberto (EPS 2019)

711 P5.1049 Effect of plasma parameters on molecular penetration in fusion plasma during SMBI

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1049.pdf

The penetration depth of neutrals in fusion plasma determines the fueling efficiency of the applied puffing method. Experiments have proven higher efficiency of SMBI (supersonic molecular beam injection)[1] compare to GP (gas puffing), that can be explained by a high direct velocity of molecules and domination of convection transport in the former case.
In this paper, we investigated the variation of molecules penetration depth for different injection rates and plasma conditions. 2D simulations of supersonic molecular beam injection were performed using the HESEL/neutral model [2,3]. The model allows for studying plasma-neutral interaction in the edge/SOL region in a dynamical, self-consistent manner.
Simulations demonstrated linear increasing of penetration depth for increasing of injection flux, as well as an inverse ratio from plasma density and temperature. Dependances of penetartion depth as a function of the beam and plasma parameters are presented at the work. Fueling efficiency and effect of SMBI on plasma edge dynamics were estimated for different injection scenaries. Results of simulations are qualitatively compared with existing experimental data on KSTAR tokamak for experiments with SMBI in L-mode dicharges.

References
[1] Y. Lianghua, New Developments in nuclear fusion research, (2006)
[2] A.H. Nielsen et al, Plasma Physics and Controlled Fusion, 59 (2017)
[3] A.S. Trysøe et al, Plasma Physics and Controlled Fusion, 58 (2016)

Speaker: G. Avdeeva (EPS 2019)

712 P5.1050 Estimation of the Kubo number at the edge and SOL region of KSTAR

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1050.pdf

The Kubo number is estimated based on the correlation analysis of the density fluctuations measured by the 2D beam emission spectroscopy system in KSTAR. The Kubo number defined as an autocorrelation time of the fluctuating quantities normalized by the eddy turn over time characterizes significance of the nonlinear interactions of the turbulent plasma [1]. If the Kubo number is larger than the unity, the nonlinear interaction is strong, and the turbulence of the plasma is considered to be strong. For the strong turbulence, the quasilinear approximation is invalid since the nonlinear terms cannot be ignored. The Kubo number is estimated in the L-mode, ELMy and ELM-suppressed H-mode plasma at the edge and SOL region of KSTAR. To extract the nonlinear interaction time from the 2D(radial and poloidal) fluctuating density measurements, we assume that the level of density fluctuations follows the Boltzmann response; while the phases between the density and electrostatic potential are not constrained to allow finite turbulence induced transport.

Reference
[1] J.A. Krommes, "Fundamental Statistical Descriptions of Plasma Turbulence in Magnetic Fields", Physics Reports, vol. 360, April 2002.

Speaker: W. Lee (EPS 2019)

713 P5.1051 Cold background plasma characterization during Runaway Electron mitigation experiments in the JET tokamak

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1051.pdf

Disruptions are a major threat to future tokamaks like ITER and beyond. In addition to heat and electromagnetic (EM) loads, disruptions also generate runaway electron (RE), tens of MeVs electron beams which may damage plasma facing. The current ITER disruption mitigation strategy is first to mitigate disruption heat/EM loads and then mitigate the RE beam using Shattered Pellet Injection (SPI) systems.
During the past JET experiments, the ineffectiveness of Massive Gas Injection (MGI) to mitigate RE beam was observed[a]. This poor efficiency is suspected to be caused by the shallow penetration of MGI due to the presence of a cold dense background (BG) plasma. The characteristics of the BG plasma are poorly known as most of the conventional diagnostics cannot measure low electron temperature during post-disruption phase.
Assuming a parabolic electron temperature profile of BG plasma, the profile parameters are estimated using VUV spectroscopy with the help of a synthetic spectrum constructed from ADAS Photon-Emissivity Coefficient[b] (PEC) data. For various BG plasma electron densities (1.10^18 - ­3.10^19 m-^2) and runaway currents (0.4-1.11 MA), temperature profiles retain similar shape and the peak value lies between 5-20 eV. This is hotter than on smaller machines (1-2 eV in DIII-D[c]) and may explain the poor efficiency of MGI on RE beam mitigation at JET. No obvious increase or decrease of the temperature during the RE beam phase for a given pulse is clearly observed. A decrease of temperature with increasing maximum runaway current IRE is observed for a given flat-top plasma current. Higher electron temperatures are only observed in lower density BG plasmas and higher density plasmas tend to have lower Te.
By making a power balance of RE beam and BG plasma system, a 0D model based on experimental data will be proposed to explain the interaction of RE beam with the BG plasma.

References
[a] Reux, C. et al. 59th meeting of the APS Division of Plasma Physics ­ October 2017
[b] Summers, H. P. (2004) The ADAS User Manual, version 2.6 http://www.adas.ac.uk
[c] Hollmann et al, Nuclear Fusion 2013

Speaker: S. Sridhar (EPS 2019)

714 P5.1052 The influence of edge sheared radial electric fields on edge-SOL coupling in the TJ-II stellarator

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1052.pdf

The radial electric field (Er) is a crucial parameter to control transport both in tokamaks and in stellarators. Its local value is result of the interplay between neoclassical (NC) and turbulent mechanisms. In stellarators, the edge radial electric field changes its sign in a continuous manner during the electron (Er > 0) to the ion root (Er < 0) transition [2]. Therefore, stellarators are unique laboratories to investigate the connection between radial electric fields and edge-SOL (Scrape-Off Layer) coupling. It has been shown recently that turbulence is not only locally suppressed by sheared flows, but also affected by radial transport or spreading of turbulence [2]. The propagation of turbulence from the edge to the SOL was shown to decrease when the E × B shearing rate exceeded a threshold, reducing turbulence penetration into the SOL and thus affecting its profile. To further explore the impact of the radial electric field (or its gradient) on turbulence and the edge-SOL coupling, the Er profile was modified slowly during the electron-ion root transition in the TJ-II stellarator. This was done by increasing the line average density in a continuous manner in ECRH heated plasma. This allows us to study, with unprecedented detail, the impact of Er on edge-SOL turbulence propagation and its effect on local plasma parameters. This work highlights the role of the radial electric field on regulating turbulence and the level of edge-SOL coupling. As the turbulence spreading is an important factor in setting the SOL width, results reported here provides a route to better understanding and controlling power exhaust in reactor-relevant scenarios.

References
[1] C. S. Chang, S. Ku, A. Loarte et al., Nucl. Fusion 57(11):116023,2017
[2] G. Grenfell et al. Nucl. Fusion 59(1):016018,2018

Speaker: G.G. Grenfell (EPS 2019)

715 P5.1053 Measurement of edge ion temperature in W7-X with island divertor by retarding field analyzer

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1053.pdf

Measurement of edge ion temperature is critical to understand the underlying physics of the island configuration effect on the plasma transport. Here, the Ti profile at the plasma boundary has been successfully measured on W7-X during the last experimental campaign OP1.2b by a retarding field analyzer (RFA) probe. The RFA probe head was mounted on the front-end of a multipurpose manipulate (MPM) located at the middle plane of W7-X. The edge ion temperature profile has been studied by slightly varying the edge island size by changing the control coil current Icc, ECRH heating power PECRH and plasma density in the standard configuration (EIM+252). The experimental observations show that in the EIM+252 configuration, an ion temperature shoulder has been observed near the location where a sudden change of the field line connection length appears in the scrape-off-larger (SOL) region. The ion temperature measured at the edge shoulder region (Tish) decreased when the island width was expanded. For a fixed control coil current, Tish increases gradually with the increase of the ECRH heating power. A decrease of Tish was also observed when the central line-integrated electron density, nel , increases from 7×10^19 m^-2 to 9×10^19 m^-2. Nitrogen seeding injection from the upper horizontal divertor port M51 was performed on W7-X, a significant reduction and flattening in the edge ion temperature profile has been observed. In addition, the edge ion-to-electron temperature ratio tau_i/e has been calculated which gradually increases with the major
radius from the edge plasma to the far SOL region. An extended two-point model including upstream ion temperature is introduced to understand the experimental measurement. The edge plasma parameters are also reconstructed by a much more complete 3D simulation code, EMC3/EIRENE, and compared with the RFA measurement. This work may help to understand the plasma transport in the island configuration in the W7-X stellarator.

Speaker: Y. Li (EPS 2019)

716 P5.1054 Investigation of the toroidal propagation of lithium injected by laser blow-off into TJ-II plasmas to measure edge ion temperature

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1054.pdf

Wall conditioning in TJ-II, is regularly performed by Glow Discharge deposition of B films and Li evaporation from ovens located inside the vacuum chamber [1]. In order to tests in-situ, real-time conditioning techniques, a Nd-YAG laser (normally used for Laser Blow-Off studies [2] and LIBS [3]) is used to ablate lithium off the inner wall of the chamber, in line with previous attempts using Li powder droppers [4] or DOLLOP [5]. For this purpose, the laser beam is focussed onto the vacuum chamber wall directly opposite its entry window while laser spot power density is controlled by varying the position of a focussing lens.
The Li source, highly localized both in position and time, opens up the possibility for transport studies at the plasma periphery in TJ-II. This is possible because the laser-ablated Li is quickly ionized by the plasma and transported along the field lines. In its toroidal travel, collisions with plasma particles lead to the thermalization of the initially cold Li+ ions. This equilibration process can be followed by time-of-flight (TOF) measurements at different distances from the source. Li+ emission monitors (at 538 nm), X-ray detectors and bolometers are used to collect plasma radiation. The goal of this work is to demonstrate the viability of injecting Li, using a Nd-YAG laser, to study its subsequent toroidal propagation. It should be noted that ion temperature, Ti, measurements at the periphery of fusion plasmas have traditionally been obtained using passive spectroscopy [6], ion sensitive probe (ISP) diagnostics [7] or retarding field analysers (RFA) [8]. Here, it is hypothesized that an alternative method for measuring Ti at the plasma periphery could be developed, which simultaneously allowing localized condition of the wall that is in close contact with the plasma.

References
[1] D. Tafalla et al., Fusion Eng. Design 85 915 (2010)
[2] B. Zurro et al., Nucl. Fusion 51 063015 (2011)
[3] B. López-Miranda et al., Rev. Sci. Instrum. 87 11D811 (2016)
[4] S.M. Kaye et al., Nuclear Fusion, 55 104002 (2015)
[5] D. K. Mansfield et al., Nucl. Fusion 41 12 (2001)
[6] A. Baciero et al., Rev. Sci. Instrum. 72 971 (2001)
[7] N. E. Zumi et al., J. Nucl. Materials 313-316 696-700 (2003)
[8] R. A. Pitts et al., Rev. Sci. Instrum. 74 11 (2003)

Speaker: B. López-Miranda (EPS 2019)

717 P5.1055 Generation of suprathermal ions in ECR heated plasmas in the stellarator TJ-II

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1055.pdf

The majority ions present in Electron Cyclotron Resonance (ECR) heated plasmas in the stellarator TJ-II are heated through collisions with electrons. Since there is no direct heating of plasma ions in this device their thermal distribution is expected to be Maxwellian. However, during recent experiments in TJ-II a population of suprathermal ions, with energies in the range 600 - 1000 eV and with a non-Maxwellian distribution, was observed during the ECR only heating phase [1]. A possible explanation to this phenomenon is a reduction of the power that triggers the parametric decay instability (PDI) when certain conditions of the density profile, magnetic field and turbulence are fulfilled, as explained in [2]. It is considered that one of the daughter waves from this PDI may heat resonant ions and give rise to the non-Maxwellian distribution. ECR plasmas in TJ-II are created and maintained by two gyrotron systems that deliver microwaves at two symmetric positions in the plasma that are separated 56º toroidaly. This work presents a series of experiments in which one gyrotron is modulated while the second is operated continuously during the whole discharge. This produces two clearly separated phases: one with full power, the other with half power. It is observed that suprathermal ions are generated when full power is applied. In addition, when a cryogenic pellet is injected during a full power phase, in order to modify the plasma density profile, it is found that suprethermal ions are absent from the ion flux, measured with a neutral particle analyser (NPA), immediately after the pellet injection. Finally, the radial extent of the suprathermal ion population is investigated by changing the NPA line-of-sight.

References
[1] J.M. Fontdecaba et al. ECA Vol. 42A 45th EPS Conference on Plasma Physics 2 6 July 2018
[2] E.Z. Gusakov and A.Yu. Popov Physical Review Letters 105 115003 (2010)

Speaker: J. Fontdecaba (EPS 2019)

718 P5.1056 The injection of cryogenic pellet series in the stellarator TJ-II

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1056.pdf

Cryogenic pellet injection (PI) is a well established fuelling tool used on most mediumand large-sized magnetically confined plasma devices. PI technologies are mature and such systems are earmarked as critical items for future reactors. Nonetheless, despite significant progress over recent decades, a complete comprehension of pellet penetration, ablation, and enhanced ablation, as well as of subsequent particle drift/diffusion remains to be achieved. Indeed, understanding these is essential to improve codes and to optimize core fuelling. An issue that has come to the fore with the recent start of operation of the Wendelstein 7-X, a superconducting stellarator, is continuous central particle fuelling [1]. In this case a series of pellets is employed, in which initial pellets cool the plasma outer regions thereby facilitating deeper penetration, and high fuelling efficiencies, for later pellets. In this paper, we report on short series of pellets injected into the TJ-II, a medium-sized stellarator device. This is done in order to elucidate on the effect of an initial small plasma edge-cooling pellet on the penetration depth and fuelling efficiency of subsequent larger fuelling pellet(s).
A PI system is used for low-field side injections into the TJ-II [2]. It is a four-pellet system equipped with a cryogenic refrigerator for in-situ hydrogen pellet formation. Moreover, its flexibility permits separation times between injected pellets to be varied ( 50 ms). The TJ-II is also fitted with a wide range of diagnostics, thereby making it a powerful tool for pellet physics studies [2, 3]. Previous pellet injection studies on this device revealed a strong penetration depth/fuelling efficiency relationship [2]. In this work, series of pellets, containing between ~5x10^18 and ~2x10^19 hydrogen atoms, are injected into its plasmas heated by either electron cyclotron resonance (ECRH), or neutral beam injection (NBI), heating. Furthermore, series of pellets, with different pellet separation times, are injected in order to determine how penetration depth and fuelling efficiencies depend on this time separation. For instance, it is seen that plasma cooling and subsequent recovery are heating type dependant, being significantly transient, for NBI heated plasma. Finally, the use of a small cooling pellet is seen to significantly modify fuelling efficiency, this depending on separation times.

References
[1] J. Baldzuhn et al., in preparation (2019).
[2] K. J. McCarthy et al., Nucl. Fusion 57 (2017) 056039.
[3] N. Panadero et al., Nucl. Fusion 58 (2018) 026025.

Speaker: K.J. McCarthy (EPS 2019)

719 P5.1057 Neutral beam injection on Wendelstein 7-X: beam transmission shine through and effect of plasma current

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1057.pdf

This work presents details of the Wendelstein W7-X stellarator Neutral-Beam-Injector (NBI) system, and its effect on the beam dump, duct, heat efficiency and plasma current. During the last stellarator W7-X operation phase, the first of two NBI injectors (NI21) was taken into operation. It was equipped with two hydrogen sources with a neutral power before the duct of 2×1.7MW and a maximum pulse-length of 6.5s. A second NBI system (NI20) is in preparation for the next experimental campaign and each injector can be equipped with a total of four sources each. NI21 was commissioned first as it was calculated that the current drive is opposite to the bootstrap current in the standard magnetic field configuration [2]. NI20 will be symmetrically oriented to NI21 and drives current in the direction of the bootstrap current. One source of NI21 was installed at a location optimized for maximum port transmission and another source at a location for maximum heating efficiency [1]. The predictions for the heat load on the port liner and the beam dump are compared with the experimental findings for operating NI21 into the empty torus and into W7-X plasmas. In addition, the effects of NI operation on the overall plasma current are assessed.

References
[1] N. Rust et al., Fusion Eng. And Design 86 (2011)
[2] Schmidt et al., 31st EPS Conference on Plasma Phys. London, 2004, Vol. 28G, P-1.200

Speaker: N. Rust (EPS 2019)

720 P5.1058 ECCD-driven temperature crashes at W7-X stellarator

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1058.pdf

The optimized stellarator W7-X generates its rotational transform by means of 70 superconducting coils. Therefore, no toroidal current is necessary for plasma confinement. Up to 10 gyrotrons can be used for electron cyclotron current drive (ECRH) and, in case of oblique beam injection, it is possible to drive a net current (electron cyclotron current drive or ECCD). The ECCD is a flexible tool, which could be used to guarantee safe divertor operation, because residual plasma currents of several tens of kA can lead to a shift of the strike line on the divertor targets [1] or locally affects MHD stability. Due to the low toroidal current, W7-X itself is a perfect testbed for ECCD experiments. Since the ECRH and ECCD deposition is well localized, a relevant local change of the rotational transform (ι) is possible, thus producing low order rational values. Such values are associated with repetitive crashes of the electron temperature that were observed during ECCD experiments. In such experiments, with strong current drive, even a total loss of plasma confinement was observed. Toroidal current modeling shows that in these case with coECCD, ι = 1 was reached on a time scale of hundreds of milliseconds and resistive MHD calculations suggest the existence of a double tearing mode, corresponding to two neighboring flux surfaces with ι = 1. In this work, an overview of the effects these crashes have on the plasma is presented, in order to evaluate the effect of crashes on discharge performances. A first attempt of mode analysis, using magnetic diagnostics, soft x-rays tomography and ECE, is presented to verify the theoretical predictions.

[1] Gao , "ECCD effects on the divertor power distributions on W7-X", this conference

Speaker: M. Zanini (EPS 2019)

721 P5.1059 Turbulent fluctuations in the edge of the W7-X as measured by the alkali beam emission spectroscopy

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1059.pdf

Early turbulence measurements in W7-X stellarator by means of poloidal correlation reflectometry [1] have revealed some important characteristics of turbulent density fluctuations such as the perpendicular ExB velocity and the decorrelation times in low density (0.6 10^19 - 2 10^19 m^-3) discharges. In a more recent study [2], the 3D filamentary structure of turbulent fluctuations in the edge / SOL plasma has been observed using fast visible cameras. The observed filaments have large correlation times (≈ 200 s) and rotate poloidally with a advection velocity consisted with a radial electric field of Er ≈ 5000 V/m. The poloidal mode number has been also estimated as being between 10 and 20. In the present contribution we present a systematic study of the fluctuation data measured by the alkali beam emission spectroscopy diagnostics in the 2018 W7-X campaign. The main focus is on the statistical analysis of intermittent filamentary structures. We show the variation of the distribution functions, the waiting times and the filament correlation times as a function of the radial position in different W7-X configurations and different densities. Using the conditional average technique the radial propagation velocity can also be estimated.

References
[1] A. Kramer-Flecken et al., Nuclear Fusion 57, 066023 (2017)
[2] G. Kocsis et al., 43rd European Physical Society Conference on Plasma Physics (EPS), (2018)

Speaker: A. Bencze (EPS 2019)

722 P5.1060 Slow modulation of SOL turbulence on W7X as measured by A-BES diagnostics

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1060.pdf

Various low frequency (~200 Hz) edge fluctuations were observed on the W7X stellarator. ELM-like events in ''high iota'' discharges[1] were seen on multiple diagnostics and an oscillation in the gradient of the light profile of the A-BES signal during FTM configurations. This profile variation is in strong correlation with a well-localized modulation of the fluctuation power in the 5-20 kHz band which was observed only in SOL channels without any precursor. In this study we examine multiple shots with a focus on the changes in plasma parameters and investigate the occurence of this phenomenon in various configurations. We create density reconstructions to observe changes in the actual profile. Cross-spectrum and cross-phase analysis are conducted to uncover the radial and temporal characteristics of these oscillations, particularly looking for intermittency. Conditional averaging technique is used to uncover systematic characteristic during these periods. We compare the results to other diagnostics especially various magnetic coils to investigate if there is any coupled fluctuations in plasma current.

Reference
[1] G. A. Wurden et al., Quasi-continuous low frequency edge fluctuations in the W7-X stellarator, 45th EPS Conference on
Plasma Physics (2018)

Speaker: A. Buzás (EPS 2019)

723 P5.1061 Edge radial profile measurement of magnetic fluctuations using 3D pick up coils and a differential coil on W7-X

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1061.pdf

Measurement of the edge radial profile of magnetic fluctuation is a basic and crucial method to investigate the edge turbulence and transport. A set of pick up coils, located in the combined probe head and mounted on the multi-purpose manipulator, has been used to measure the magnetic fluctuation in the scrape-off layer (SOL) during the experimental campaign OP1.2 of Wendelstein 7-X (W7-X). The 3D coil measured the evolving toroidal, radial and poloidal magnetic fluctuations at various radial positions near the SOL. Two branches of magnetic fluctuations which peak at 10 kHz and 60 kHz were observed in standard divertor configuration (EJM+252). Those peaked magnetic fluctuations became stronger and had boarder spectrums when the probe approached the last closed flux surface. Meanwhile, a broadband fluctuation appeared with frequencies up to around 250 kHz, sharing some similarities to the measurement of the Langmuir probe near the SOL region. To measure fluctuations more locally, a differential coil that obtains higher sensitivity to the position of fluctuation source was equipped beside the 3D coil. Those 10 kHz and 60 kHz modes observed from 3D coil measurements are weak on the differential coil measurement. Instead, a 40 kHz fluctuation appeared and showed no correlations with the same frequency fluctuations on the 3D coil. It indicates that this 40 kHz mode is not strong but far closer to the plasma periphery. A rough estimation to the fluctuation source position was made via the power density evolution at corresponding frequencies under a current sheet and differential coil model. In addition, some distinct behaviors on the magnetic fluctuation spectrum have been observed on both the 3D coil and differential coil under different configurations, suggesting a magnetic topology dependence of the magnetic fluctuations.

Speaker: Z. Huang (EPS 2019)

724 P5.1062 Propagation of turbulent filaments in the SOL of Wendelstein 7-X

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1062.pdf

In the Wendelstein 7-X Scrape-Off Layer (SOL), turbulent (radial) transport is assumed to play an important role for heat and particle transport to the divertor due to the generally long connection lengths of a few 100 m. The existence of large magnetic islands at the plasma edge results in a complex three-dimensional magnetic field in the SOL which can be very wide and feature flat temperature and density profiles with small temperature and density gradients. The inherent three-dimensionality make experimental investigations of turbulent transport in W7-X SOL challenging. Here, we employ both reciprocating and divertor Langmuir probes to investigate the spatio-temporal dynamics of turbulent filaments. Probe arrays on the Multi-Purpose Manipulator (MPM) in the outer mid-plane provide turbulence characteristics such as correlation lengths, life times, and propagation velocities. Using the magnetic flexibility of W7-X and the reciprocating motion of the MPM, the role of magnetic islands for plasma turbulence can be assessed. We find that the presence of islands can significantly affect (reduce) the radial turbulent transport. Exploiting the magnetic connection between the MPM and divertor Langmuir probes, the 3D (radial, poloidal, parallel) dynamics of filaments can be assessed by correlating the fluctuation data from both diagnostics. The role of plasma conditions (heating, density) and the effect of toroidal plasma currents on the edge magnetic topology is explored.

Speaker: C. Killer (EPS 2019)

725 P5.1063 Diffusion Dominated Transport for a Wide Range of Different Impurity Species Observed at Wendelstein 7-X

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1063.pdf

This paper reports on trends for impurity transport with respect to different impurity species as observed in hydrogen plasmas of W7-X. Measurements of the impurity transport times τ_I [1] show a very similar impurity transport behaviour for a wide range of different impurities under the variation of the atomic number Z as well as the atomic charge q and the
charge to mass ratio q/M. The observed marginal effect of the impurity mass and charge state on the transport properties of highly charged impurities is in agreement with theoretic expectations of anomalous, diffusion dominated impurity transport [2], supporting recent experimental findings of anomalous transport with large impurity diffusivities in W7-X plasmas [3,4]. We note that neoclassical transport calculations predict a pronounced Z dependence of the impurity convection v. In addition, the neoclassical diffusivities are predicted to be more than one order of magnitude smaller than the observed ones.
The combination of weak Z dependence and high diffusivities is beneficial for avoiding impurity accumulation in the planed long pulse operations of W7-X, especially for the high Z materials, including tungsten.

References
[1] A. Langenberg, N.A. Pablant, Th. Wegner et al. Rev. Scient. Instrum. 89 10G101 (2018)
[2] P. Helander and A. Zocco, Plasma Phys. Control. Fusion 60 084006 (2018)
[3] B. Geiger, Th. Wegner, C. Beidler et al. Nucl. Fusion 59 046009 (2019)
[4] A. Langenberg, N.A. Pablant, O. Marchuk et al. Nucl. Fusion 57 086013 (2017)

Speaker: A. Langenberg (EPS 2019)

726 P5.1064 Shrinking of resonant manifold under flow shear at the stellarator TJ-K

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1064.pdf

Since in magnetically confined fusion plasmas the evolution of transport barriers at the transition from the low to high confinement regime is accompanied by E × B shear flows, their interrelation with transport producing drift-wave (DW) turbulence has attracted much interest. In the Hasegawa-Mima model the redistribution of energy in DW turbulence is described by quadratically non-linear three-wave interactions [1], which are limited by resonance conditions in wavenumber and frequency domain according to the DW dispersion relation. The set of coupling modes can be understood as resonant manifold [2]. Gürcan et al. showed theoretically that in a sheared flow field the resonant manifold, among which potential structures associated with zonal flows, are persistent coupling partners, shrinks in time [3]. In the present work, the phenomenon of manifold shrinking is addressed experimentally at the stellarator TJ-K.
To this end, the DW dominated turbulence in TJ-K plasmas is measured simultaneously by an array consisting of 128 Langmuir probes, with 32 tips aligned to each of four neighboring fluxsurfaces within a poloidal cross-section. Frequency-wavenumber bispectral analysis of potential fluctuations is carried out, temporally triggered to the occurrence of large amplitude zonal (poloidally averaged) potential events. This way, the analysis is constricted to coupling drift modes being subject to the DW dispersion relation. The time dependence of the frequency decomposition for conditional analyses is maintained by using a wavelet decomposition. This allows to temporally correlate the change in the behavior of poloidal mode coupling with naturally occurring zonal flows.
The bispectrum essentially represents the coupling manifolds, where an effective mode number is defined to measure the extent. When a shear flow persists, i.e. during the occurrence of the ZF, the effective mode number decreases. This is considered as the shrinking of the manifold. A shrinking of the manifold forces the DWs to couple into lower wavenumber modes an thus favoring large scale structures as described by the straining out process of turbulent vortices.

References
[1] A. Hasegawa and K. Mima, Physics of Fluids 21, 87 (1978).
[2] W. Horton and A. Hasegawa, Chaos: An Interdisciplinary Journal of Nonlinear Science 4, 227 (1994).
[3] Ö. D. Gürcan, Physical Review Letters 109, 155006 (2012).

Speaker: T. Ullmann (EPS 2019)

727 P5.1065 Studies on carbon content and transport with Charge Exchange Spectroscopy on W7-X

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1065.pdf

The first absolute impurity density profiles of the optimised stellarator Wendelstein 7X (W7-X) plasma core will be presented and investigated under different operating scenarios. The profiles are derived from the Charge Exchange Recombination Spectroscopy (CXRS) diagnostic that observes the Neutral Beam Injection (NBI) which is well-suited for determining spatially resolved profiles of fully-stripped low-Z impurities across the entire plasma radius. Understanding the confinement of impurity ions can help optimise the stellarator configuration in order to control their effect on plasma radiation and subsequent power losses. This work concentrates on carbon, the main intrsinsic impurity in W7-X, although the radiation of other low-Z impurities, such as oxygen and boron is also measured.
The carbon density profiles and their evolution are investigated in different magnetic configurations, densities and heating scenarios with different NBI and ECRH power ratios. Of particular interest are discharges with pure NBI heating phases or with very low ECRH power, where indications of unusually high impurity confinement times have been observed.
If impurity transport is dominated by neoclassical effects, the carbon profile measurements could give important insight into the optimisation of W7-X. The impurity transport modeling code STRAHL is used to determine the transport coefficients (diffusivity and radial convective velocity) from the measurements which are then compared with neoclassical predictions.

Speaker: L. Vanó (EPS 2019)

728 P5.1066 A heuristic Dimits shift prediction using reduced tertiary instability analysis

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1066.pdf

An intriguing phenomenon, likely to be of relevance in future fusion devices operating at or near beyond the threshold of marginal ITG-stability, is the Dimits upshift, where close above the linear threshold stabilising zonal flow shear nearly complete suppress these modes. The general features of this phenomenon are broadly understood, but a quantitative predictions of, among other things, the size of the upshift is lacking. Recently however, St-Onge presented a simple but efficient heuristic prediction that yielded good results for a simple modified Terry-Horton system.
As an intermediary step on the path to extending this prediction to full gyrokinetics, an analytically tractable strongly driven, local gyrokinetic limit with both linear drive and nonlinear zonal-drift wave interactions is presented. After supplying additional damping to artificially push the system to the Dimits regime, St-Onge's method can be slightly modified to produce a Dimits shift prediction which continues to impress when compared with results from fully nonlinear simulations. The consistency and robustness of the prediction across a wide selection of parameter choices and damping operators indicates that it may continue to be applicable even in full gyrokinetics, something ongoing Z-pinch studies intend to investigate.

Speaker: A. Hallenbert (EPS 2019)

729 P5.1067 Observation of drift effects on W7-X divertor heat and particle fluxes

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1067.pdf

Particle drifts are known to affect the fluxes of heat and particles to plasma-facing components of both tokamaks and stellarators. Here we present results from the first dedicated study of edge drift effects in W7-X scrape-off layer plasmas. In these experiments, similar discharges were repeated with forward and reversed magnetic field in order to isolate the effects of drifts that would reverse in response to a field reversal. We find that drifts are responsible for asymmetric distributions of heat flux on upper and lower divertor targets, driving radial discrepancies of 3 cm or more in the positions of the strike lines. Up-down asymmetries are also observed in downstream temperature, particle flux, and net current flow through the targets, each with different characteristic distributions and degrees of asymmetry. Furthermore, the nature of the asymmetries is observed to change substantially with core plasma density. Overall, for the magnetic configuration tested, we have found that almost all of the up-down asymmetry can be attributed to drift effects.

Speaker: K. Hammond (EPS 2019)

730 P5.1068 Study of runaway electron transport with the fractional diffusion model and comparison with experiments on COMPASS

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1068.pdf

Runaway electrons (RE) represent one of the main obstacles to the successful operation of ITER [1]. During plasma diruptions, the structure of magnetic surfaces is broken and large regions of stochastic magnetic field are created; however, the rapidly reforming magnetic flux tubes are able to trap RE for a long time [2]. The magnetic configuration inside the plasma volume consists of intact magnetic surfaces alternated with magnetic islands and stochastic layers, which make the usual diffusive approach inadequate to the study of transport. When different degrees of magnetic stochasticity are present in the plasma volume, the fractional diffusion model should be used instead. The generalization of the diffusive model leads to a fractional order time derivative, which introduces a temporal non-locality in the system [3]. The average over the finite drift orbits of the electrons introduces an energy-dependent factor in the diffusion coefficient [4]. The fractional diffusion model can be used to study RE transport in tokamaks, by calculating the diffusion coefficient corresponding to the magnetic configuration and by solving the fractional diffusion equation. This model has been applied to the study of RE transport in COMPASS, to evaluate the effect of MHD perturbations, with a particular focus on magnetic islands, on the RE beam confinement. The evidence of a coupled dynamics of runaways and magnetic islands has been observed [5], and the use of resonat magnetic perturbations (RMP) has proved to affect RE losses [6][7], but a complete understanding of this complicated dynamics is missing. The purpose of this study is to provide an interpretation of these phenomena within the framework of the fractional diffusive model.

References
[1] T.C. Hender et al., Nucl. Fusion 47 S128 (2007)
[2] A.H. Boozer, Phys. Plasmas 23 082514 (2016)
[3] D. del-Castillo-Negrete, Phys. Plasmas 13 082308 (2006)
[4] T. Hauff & F. Jenko, Phys. Plasmas 16 102308 (2009)
[5] O. Ficker et al., Nucl. Fusion 57 076002 (2017)
[6] J. Mlynar et al., Plasma Phys. Control. Fusion 61 014010 (2018)
[7] M. Gobbin et al., Plasma Phys. Control. Fusion 60 014036 (2017)

Speaker: A. Casolari (EPS 2019)

731 P5.1069 Inner versus outer ExB shear layer: an attempt to radially localize the L-H transition

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1069.pdf

The importance of the E × B flow shear in the transition from the low (L-) to the high (H-) confinement mode is well and widely appreciated [1]. At the edge of tokamaks, the E × B velocity profile shows two shear layers: the "inner" one is located within the confined region and is related to the ion pressure gradient while the "outer" layer is influenced by the plasma potential in the SOL, which is set by the divertor sheath. Both edge shear layers can in principle trigger the L-H transition but it is not yet clear which is the dominant one.
In this work, a direct radial localization of the turbulence suppression at the L-H transition via Doppler Reflectometry (DR) is attempted. Discharges with repetitive L-H-L dithers at a frequency of 200 Hz have been designed to measure the turbulence level at different radial locations by varying the DR sampling frequency. An initial turbulence suppression at ρ = 0.975 could be identified and is located, based on the associated evaluations of the v_E×B profile, at the inner shear layer. However, the v_E×B profile from DR does not agree with the Charge Exchange Recombination Spectroscopy (CXRS) evaluations. This discrepancy is interpreted by the influence of strongly intermittent events on the DR signal.

References
[1] H. Biglari et al., Physics of Fluids B: Plasma Physics, vol. 2, 1-4 pp, 1990

Speaker: M. Cavedon (EPS 2019)

732 P5.1071 Neoclassical simulations of tungsten impurities in JET plasmas using the total-f gyrokinetic code XGCa

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1071.pdf

The neoclassical tungsten impurity transport is studied with the gyrokinetic neoclassical code XGCa [1,2] in whole volume JET plasma, from magnetic axis to scrape-off layer (SOL). Instead of simulating all 74 tungsten charge states, they are bundled and treated as several separate species. It is found, in a model JET plasma, that the general direction of the radial tungsten transport can be partly understood from a single tungsten species study. However, the interaction between different charge states is significant in determining the level of transport, hence a trace impurity approximation or a single tungsten species study may not yield sensible physics results. It is also found that the low-Z tungsten particles can move radially inward from SOL into core region, while the high-Z tungsten particles move inwardly from separatrix to pedestal and outwardly from core to the pedestal top where they accumulate. Poloidally asymmetric tungsten distribution of each bundle is found to be an important factor in understanding their neoclassical transport behavior. A realistic JET-ILW plasma is under investigation and its results will be presented. Optimized plasma and magnetic equilibrium that minimizes the high-Z tungsten in-flux into the core will also be studied. If time permits, preliminary turbulence simulation will be presented. These could help giving insight into the issue of W transport compared to other simulations performed when splitting turbulence (with quasi-linear models) and neoclassical transport, as the ones recently performed by Casson et al. [3].

References
[1] R. Hager, E. Yoon, S. Ku, E. D'Azevedo, P. Worley, and C. S. Chang, "A fully non-linear multi-species fokker planck landau collision operator for simulation of fusion plasma," Journal of Computational Physics 315, 644 ­ 660 (2016).
[2] R. Hager and C. S. Chang, "Gyrokinetic neoclassical study of the bootstrap current in the tokamak edge pedestal with fully non-linear coulomb collisions," Physics of Plasmas 23, 042503 (2016).
[3] F. Casson, H. Patten, C. Bourdelle, S. Breton, J. Citrin, F. Koechl, and et al., "Predictive multi-channel flux-driven modelling to optimise icrh tungsten control in jet," 27th IAEA Fusion Energy Conference (FEC 2018).

Speaker: J. Dominski (EPS 2019)

733 P5.1072 Short wavelength ion temperature gradient mode in tokamak plasmas with hollow density profile

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1072.pdf

The short wavelength ion temperature gradient (SWITG) driven instability in tokamak plasmas with hollow density profiles is numerically investigated by using the gyrokinetic integral eigenmode equation. It is found that for the hollow density profile (negative R / L_n , ), there exists a critical ion temperature gradient R / L_Tic above which the SWITG mode is unstable, and that R / L_Tic for negative R / L_n is somewhat higher (lower) than that for positive R / L_n in the moderate (steep) density gradient region. In addition, the effect of temperature ratio on the SWITG mode has been investigated, indicating the SWITG mode is harder to be excited in hot ion plasmas than that in hot electron ones. Besides, two critical R / L_Ti (positive and negative) exist in hot electron plasmas. In particular, it is found that non-adiabatic electron response can stabilize the SWITG mode, which is different from the conventional long wavelength ITG mode. Moreover, when the nonadiabatic electron is considered, the eigenfunctions have broad structures along the magnetic field line and have oscillatory tails with a periodicity about π.

Speaker: H. Du (EPS 2019)

734 P5.1073 Impurity transport driven by parallel velocity shear turbulence in hydrogen isotope plasmas

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1073.pdf

Turbulent impurity transport driven by parallel velocity shear (PVS) turbulence in hydrogen isotope plasmas is studied using the gyrokinetic theory in a slab configuration with weak magnetic shear. The quasi-linear impurity flux written in terms of diffusion and convection is analytically derived. It is found that PVS turbulence leads to an inward impurity convection. For high temperature helium ash from deuterium (D) and tritium (T) reaction, the turbulent impurity flux could be outward because the impurity diffusion dominates over the inward convection. Therefore, PVS turbulence might be beneficial for removing high temperature helium ash in future burning plasmas. Moreover, both the outward flux and diffusivity of helium ash are enhanced by increasing PVS, but reduced by decreasing the temperature of helium ash. For fully ionized light impurities with finite concentration and the trace heavy metal impurities, the stronger sheared parallel velocity as well as the steeper parallel velocity profile, the more serious accumulation of impurity. Thus, PVS turbulence might be a partial explanation for experimental observation of impurity accumulation in the neutral beam heated plasmas. While, the increase of the electron density gradient may be favorable for stabilizing the PVS mode and easing the accumulation of impurities from plasma-wall interaction or external injection. Furthermore, isotopic effects (increasing the effective hydrogen isotope mass number) are favorable for both removing helium ash and easing the accumulation of heavy metal impurities induced by PVS turbulence. Implications of these theoretical results to the future burning plasmas are discussed.

Speaker: W. Guo (EPS 2019)

735 P5.1074 JET 1D tokamak plasma profile database construction for training neural network surrogate transport models

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1074.pdf

The most widely accepted models for plasma turbulent transport are based on gyrokinetic (GK) theory, but the computational times of full nonlinear GK codes prohibit their use for applications such as experimental scenario optimization and control-oriented modelling. Reduced formulations of these equations have resulted in quasilinear turbulent transport models, such as QuaLiKiz [1, 2], which has improved their speed by a factor of 106 compared to full nonlinear GK codes, but is still too slow for the desired application. Recent work has applied neural network (NN) regressions to emulate the reduced models, showing promising results in terms of bridging this gap [3, 4]. This study extends previous work done on the NN regression of QuaLiKiz by including additional input parameters, such as plasma rotation via Mtor and E × B shear, Shafranov shift via MHD, and a heavy impurity species to disentangle main ion dilution from Zeff. This is intended to capture a larger variety of plasma scenarios and improve the applicability of the NN predictions. In order to reduce the training set to a computationally viable size, experimental plasma profiles were extracted from the JET tokamak plasma device and
fitted using Gaussian Process Regression techniques [5], which rigourously accounts for experimental uncertainties. These techniques have also been applied to preparing integrated model inputs and improving their uncertainty quantification [6], further demonstrating their suitability for large-scale data extraction. The primary use of this database is to sufficiently populate a training set to perform exploratory modelling, while remaining focused to the capabilities of the
experimental device. This database can be extended using the developed workflows to include multiple plasma devices, further enhancing the capabilities of the NN regression.

References
[1] J. Citrin et al., Plasma Physics and Controlled Fusion 59, 12 (2017)
[2] C. Bourdelle et al., Plasma Physics and Controlled Fusion 58, 1 (2016)
[3] F. Felici et al, Nuclear Fusion 58, 9 (2018)
[4] J. Citrin et al., Nuclear Fusion 55, 9 (2015)
[5] M.A. Chilenski et al., Nuclear Fusion 55, 2 (2015)
[6] A. Ho et al., Nuclear Fusion, accepted (2019)

Speaker: A. Ho (EPS 2019)

736 P5.1075 Investigation of strong isotope effect in energy confinement for high density FT-2 tokamak discharges

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1075.pdf

In contrast to theory expectations, the hydrogen isotope effect results in the improvement of tokamak energy confinement in numerous experiments as the hydrogen isotope mass increases, which has remained a long-standing puzzle [1]. This effect is beneficial and important for the success of Iter, where a fuel mixture of deuterium and tritium will be used. Explanation of the effect involves the delicate balance of microturbulence and large-scale flows, with an effect on particle confinement that has been demonstrated in FT-2 tokamak [2] for various pairs of similar hydrogen (H) and deuterium (D) Ohmic discharges with modest central electron density varying in the range (2.3 - 4)×10^19 m^-3. Recently the strong difference in energy confinement between hydrogen and deuterium plasmas has been demonstrated in the FT-2 tokamak [3] in high density regimes of <ne> ~ (7-9)×10^19 m^-3, Te 600 ÷ 700 eV, Ti ≈ 200 eV. In a particular series of Ohmic discharges performed in H and D plasmas the difference of energy confinement time increased as plasma density was increased, based on calculations using measured kinetic profiles. Close to the operational density limit (<ne>~ 9×10^19 m^-3) the energy confinement time in D was twice as high as in H. In the present paper the detailed analysis of density and temperature profiles in high density D and H discharges is performed. It is shown that improvement of confinement in D-discharge is accompanied by the steepening of the electron density profile at the edge and a flattening in the central region, which demonstrates distinct features of an Ohmic H-mode. Using experimentally obtained profiles gyrokinetic modeling of drift instabilities for these highdensity discharges is carried out using GENE and ELMFIRE codes. Reasonable agreement of gyrokinetic calculations with experimental results (behavior of the thermal diffusivity estimated from the ASTRA modeling and turbulence spectra provided by reflectometry) is demonstrated.

Refrences
[1] C F Maggi et al 2018 Plasma Phys. Control. Fusion 60 014045
[2] P. Niskala, et al., 2018 Nuclear Fusion 58, 112006.
[3] D V Kouprienko et al., 45th EPS Conference on Plasma Physics, P4.1097 (2018)

Speaker: D. Kouprienko (EPS 2019)

737 P5.1076 Linear stability of the inner core of JET plasmas using gyrokinetic simulations

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1076.pdf

Transport of tungsten (W) in the central part of ITER is expected to be determined by neoclassical and turbulent processes, which strongly depend on the main ion density, temperature, and rotation profiles. Thus, to predict the W core transport behaviour, one needs to know the transport processes determining the density and temperature gradients of the main ions.

In the central zone near the magnetic axis, r/a<0.3, turbulence is close to marginality. In this region, key questions for ITER are 1) whether turbulent diffusion is sufficiently large to offset the neoclassical (inward) pinch of W, 2) if yes, up to which radius and how sensitive this is to the background gradients. An auxiliary question is to which degree standard quasi-linear models such as QuaLiKiz or TGLF are valid in the central zone.

To start providing an answer to these questions, linear gyrokinetic simulations are first performed in the central zone of a JET hybrid H-mode plasma using the gyrokinetic code GKW in the local approximation limit. The studied JET pulse corresponds to the operating phase with Carbon plasma facing components. For this plasma, there are high quality core profile measurements for electron and main ions (Thomson scattering and charge exchange spectroscopy) and the discharge has no sawteeth and no other significant MHD activity. Following this initial modelling, the main ion temperature gradient will be scanned around the experimental value to determine the threshold at which significant turbulent transport can be triggered and its sensitivity to other parameters will be assessed (magnetic shear, Te/Ti, etc.). The simulations will include electromagnetic perturbations, magnetic shear, collisions, plasma beta effects, and will include three species (deuterium, electron, and carbon). The next step will be to perform non-linear gyrokinetic simulations of the same plasma by GKW code and compare the results with quasilinear simulations by QuaLiKiz code to test the validity of the quasi-linear approximation in the central zone (r/a<0.3) of tokamak plasmas.

Speaker: N. Kumar (EPS 2019)

738 P5.1077 Preliminary research on the reversal transport barrier in HL-2A H-mode discharges

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1077.pdf

In the common transport model, the anomalous transport is believed to be attributed to the plasma turbulence. The ExB shearing flow suppress the turbulence to reduce the radial
transport. The formation of the transport barrier makes a very strong ExB shear to achieve the high confinement state (H-mode). The radial correlation length of the turbulence is interrupted, which is the important mechanism to lower the radial transport. In addition, the existence of zonal flows will play an important role to improve the confinement. From the generation of poloidal flow from the Reynolds stress theory, the turbulence accumulation in the radial direction will lead to the poloidal acceleration. The transport barrier could be treated as a solid wall to change the radial flux to the poloidal direction. In this phenomenological opinion, the transport barrier could also reflect radial flux to the inward direction. The inward flux caused by long live mode (LLM) due to the tremendous changes of the cross phase between poloidal
electric field and electron density are observed in certain radial region on HL-2A discharges. The correlation between the edge and core LLM signals indicates the inward transport
originates from the electrical field instead of plasma density, which indicates the electrostatic potential structure is the key to forming the inward transport. The preliminary research on the reversal transport barrier is detailly provided in this poster.

References
[1] M. Shats. et al Phys. Rev. Let. 79 (1997) 2690.
[2] K. Toi. et al Plasma Phys. Control. Fusion 44 (2002) A237.
[3] J. Boedo. et al Nucl. Fusion 40 (2000) 1397. Y.Xu. et al Phys. Rev. Lett. 97 (2006) 165003.
[4] D. Kong. et al Nuclear Fusion 58 (2018) 034003.
[5] P.W. Terry. et al Phys. Rev. Let. 87 (2001).
[6] H.G. Shen. et al Phys. Plasmas 23 (2016) 042305.
[7] R.B. Zhang. et al Plasma. Phys. Control. Fusion. 56 (2014) 095007.
[8] L.M. Yu. et al Nucl. Fusion 57 (2017).

Speaker: T. Lan (EPS 2019)

739 P5.1078 The comparison of ion and electron anomalous heat conductivities in T-10 plasma

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1078.pdf

The aim of this work is the determination of parametric dependencies of anomalous ion and electron heat conductivities in whole operational space of the T-10 tokamak. Verified experimental data base of plasma parameters, heat fluxes, and transport coefficients is made. It allow us to perform a background for transport analysis. Heat conductivities are determined from the steady state equation of heat flux continuity for ions and electrons:
[see equation on full abstract] (1)
where χ_e,i ­ heat conductivity of electrons or ions, n_e,i - electron or ion density, T_e,i - electron or ion temperature, Γ_e,i - particle flux of electrons or ions, P_e,i - heat sources and sinks. Anomalous heat conductivities χ_e^an ≈ χ_e and χ_i^an = χ_i - χ_i^neo obtained from (1) is analyzed in T-10 discharges with different plasma parameters. It is shown that χ_e^an and χ_i^an have different dependencies on averaged density n¯e, effective charge Z_eff, and plasma current I_pl. These dependencies lead to the fact that the increase of ion heat conductivity corresponds to the decrease of electron one, and vice versa. In discharges with ECR-heating it is shown that χ_i^an grows in r/a = 0.5 - 0.8 region in discharges with on-axis ECRH and does not change with off-axis ECRH. For electron anomalous heat conductivity the well known result is obtained - the values of χ_e^an increases outside the region where auxiliary heating power is absorbed (see for example [1]).

References
[1] V. Erckmann, U. Gasparino. Electron cyclotron resonance heating and current drive in toroidal fusion plasmas. Plasma Phys. Controlled Fusion 36, 1869 (1994).

Speaker: M. Nurgaliev (EPS 2019)

740 P5.1079 A mechanism of neoclassical tearing modes onset by drift wave turbulence

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1079.pdf

The evolution of neoclassical tearing modes (NTMs) in the presence of electrostatic drift wave turbulence is investigated. In contrast with anomalous transport effect induced by turbulence on NTMs, a new mechanism that turbulence-driven current can affect the onset threshold of NTMs significantly is suggested. Turbulence acts as a source or sink to exchange energy with NTMs. The turbulence-driven current can change the parallel current in magnetic islands and affect the evolution of NTMs, depending on the direction of turbulence intensity gradient. When the turbulence intensity gradient is negative, the turbulence-driven current enhances the onset threshold of NTMs. When the turbulence intensity gradient is positive, it can reduce or even overcome the stabilizing effect of neoclassical polarization current, leading to a small onset threshold of NTMs. This implies that NTMs can appear without noticeable magnetohydrodynamics (MHD) events.

References
[1] Huishan Cai, 2019 Nucl. Fusion 59 026009

Speaker: H. Cai

741 P5.1080 Toroidal rotation prediction of ITB H-mode JET plasmas using CRONOS code

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1080.pdf

This work uses an integrated predictive simulation code CRONOS to simulate plasma profiles of JET discharge. Simulations are carried out with ion and electron temperatures, electron density and toroidal velocity profiles predicted both individually and simultaneously. Core transport models used in these simulations is a combination of an anomalous transport model semi-empirical Mixed Bohm/gyro-Bohm (Mixed B/gB) or the gyro-Landau fluid (GLF23) that includes ITB effects and a neoclassical transport model NCLASS. A simple linear pedestal model is used based on an international scaling to estimate the top of pedestal. Time evolution of plasma temperatures, density and toroidal velocity profiles of JET optimized shear discharge 40542 are compared between experimental measurements and simulation results. Qualitatively, ITB formations are identified and evaluated. Quantitatively, statistical analysis including root mean square errors (RMSE) and offsets are used for comparison. Additionally, roles of toroidal rotation on ITB formation and plasma performance are investigated.

Speaker: J. Promping (EPS 2019)

742 P5.1081 Revisiting H D T studies of L-H transition in JET

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1081.pdf

Much of the information on the isotope scaling of the L-H transition power threshold, P_LH, in JET is derived from early experiments in Hydrogen (H), Deuterium (D) and Tritium (T) with C wall (JET-C) [1]. More recent experiments have studied P_LH(H) and P_LH(D) in JET-C [2,3] and JET-ILW [4], and have shown considerable variability in P_LH associated with divertor geometry, divertor strike point configuration, Carbon vs. ILW, Neutral Beam Injection (NBI) vs. Radio Frequency heating (RF) and plasma current or q_95, particularly for Hydrogen. Here we consider the dataset with toroidal field B_tor=1.8 T of all L-H transition experiments at JET, to see what we can learn about the isotope scaling of the L-H power threshold. It contains the only n_e scan for all 3 isotopes in the old data.
Reanalysing the old P_LH data, and using P_Martin = 0.0488 n_e20^0.717 B_t^0.803 S^0.941 [5] as a convenient metric, we find that P_LH^Old(D, RF) = P_Martin, while P_LH^Old(H, RF & NBI) = 1.6 P_Martin. In Tritium the data is in a very narrow density range, (1.5-1.8)×10^19 m-3, lowest n_e with NBI, higher with RF, with different slopes, so the n_e scaling of P_LH^Old(T) is quite uncertain, with P_LH^Old(T) values falling between (0.67-0.9)P_Martin. In the JET-ILW P_LH^ILW(H, RF + NBI) = 2.6 P_Martin for the configuration (strike points in corners of divertor) most similar to the old one, but we lack data in D at this field and shape.
For scaling to high field it is especially important to investigate the low field point, which can heavily influence extrapolations. One implication of this study is that we should create a P_LH(D) dataset at 1.8 T in Corner configuration and consider studying P_LH(T) in Corner at 1.8 T in a broad density range in the forthcoming isotope campaigns at JET.

References
[1] E. Righi et al, Nucl. Fusion, 39, 309 (1999);
[2] Y Andrew et al, Plasma Phys. Control. Fusion 48 479 (2006);
[3] L. D. Horton et al, 26th EPS Conf. Contr. Fusion and Plasma Physics, Maastricht P1.021(1999);
[4] C Maggi et al Nucl. Fusion 54 023007 (2014);
[5] Y Martin et al J. Phys. Conf. Ser. 123 012033(2008)

Speaker: E.R. Solano (EPS 2019)

743 P5.1082 First results of the particle and heat flux transport study in the spherical tokamak Globus-M2

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1082.pdf

The presentation is devoted to particle and heat flux study in the Globus-M2 tokamak [1]. Globus-M2 is a spherical tokamak with the major radius R = 0.36 m and the minor radius a = 0.24 m (aspect ratio A = 1.5), and is the upgraded version of the Globus-M tokamak [2]. The upgrade allows increasing the plasma current I_P up to 500 kA and a toroidal magnetic field B_T up to 1 T. The aim of the study was to determine the effectiveness of thermal insulation in a compact spherical machine with neutral beam heating for the new experimental conditions. The first measured results of the electron temperature and density, the ion temperature and the total stored plasma energy for OH and NBI modes are presented and used for calculations. The calculations were carried out using the ASTRA code [3]. The main attention is paid to the safety factor influence on the particle and energy confinement in the modes with early NBI started at the current ramp up phase.

References
[1] Minaev V.B. et al, 2017, Nucl. Fusion, 57 066047;
[2] Gusev V.K. et al, 1999, Tech. Phys. 44;
[3] Pereverzev G. and Yushmanov P. N., 2002, Max-Plank IPP Report, 5/98.

Speaker: A. Telnova (EPS 2019)

744 P5.1083 The role of the edge barrier in the penetration of impurities in the JET ELMy H-mode plasmas

See the full abstract here: http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1083.pdf

Increasing the heating power in both baseline and hybrid JET H-mode scenarios modifies the edge kinetic profiles in a way that progressively reduces the neoclassical inward velocity of impurities [1]. Along this path JET approaches the situation expected in ITER where heavy impurities should be repelled at the H mode barrier by a strong neoclassical barrier associated with a "favorable" combination of density and ion temperature profiles. Such finding has motivated the extension of the impurity modeling activities of the core to the edge [2], in the direction of an integrated core-edge description of the impurity behavior that incorporates the way medium and high Z impurities penetrate into the plasma core of JET as ELM frequency and heating power vary. Full predictive modeling includes simulations by means of integrated JETTO-SANCO-Edge2D, available in the JINTRAC suite of codes [3], with two impurities (Ne, W). Modeling has focused on the simulation of a high power (32 MW) "hybrid" discharge in which traces of Ne have been puffed for diagnostic purposes, in particular to provide ELM resolved Ne density profiles in the edge barrier region. The EDWM model [4] for the turbulent transport in the core and NCLASS for the neoclassical transport have been adopted. For the ELM description we have assumed a heuristic model with either ad hoc enhancements of heat and particle diffusivities or an ad hoc burst of the outward radial velocity in the barrier. In this way the impact of convective versus diffusive transport during an ELM event has also been investigated. Transport in the barrier region outside the ELM event is also described heuristically imposing neoclassical transport and an ad hoc turbulent transport multiplier. The ELM frequency has been artificially varied in order to replicate the experimental evidence according to which an increased main gas fueling leads to an increase of the ELM frequency and to a decrease of the concentration of any type of impurities. The paper presents the results of ELM frequency and density scan and a comparison with JETTO-SANCO core only simulations featuring QualiKiz [5] and NEO [6] for turbulent and Neoclassicla transport respectively.
[1] Valisa M et al Proc. 44th EPS Conf.2017 http://ocs.ciemat.es/EPS2017PAP/pdf/P4.174.pdf [2] F Koechl et al Pl. Phys. Contr. Fus. 60, (2018) [3] Romanelli M et al Plasma Fusion Res. 9, 3403023. [4] Strand P I et al 31th EPS Conf. , London 2004, EPS(2004), Vol. 28. [5] Bourdelle C et al Phys Pl. 14 112501(2017) [6] E. A. Belli and J. Candy, Pl Phys. Contr. Fus, 50 (2008), 1, (2009) 75018; c) Plasma Phys. Control. Fusion, 54 2012), 15015 ____
*See the author list of "Overview of the JET preparation for Deuterium-Tritium Operation" by E. Joffrin et al. to be publ. in Nuclear Fusion Special issue: overview and summary reports from the 27th Fusion Energy Conference (Ahmedabad, India, 22-27 October 2018)

Speaker: M. Valisa (EPS 2019)

745 P5.1084 Comparison of the ion heat transport properties of ASDEX Upgrade H-mode plasmas with theory-based transport models

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1084.pdf

Heat transport in tokamaks is widely believed to be dominated by turbulence associated with gradient-driven modes. As a consequence, temperature profiles tend to clamp to a critical logarithmic gradient, weakly reacting to additional heating. The extent of this so-called "profile stiffness" is, however, different depending on several plasma parameters, according to theory and to experimental observations in several tokamaks. Moreover, in a given plasma it's different for Ti and Te. Theory-based modelling is necessary to be able to interpret and order the experimental evidences, where it is often impossible to disentangle the effects of different plasma parameters: first, because they cannot always be scanned separately; secondly, they can affect both the stiffness and the critical gradient length. In this contribution, we consider a set of recent experiments in ASDEX Upgrade [1] where the ion heat transport properties have been investigated by using the on-axis and off-axis possibilities of the neutral beam injection system, applied in combination with two different levels of background electron cyclotron resonance heating. These well diagnosed experiments provide an excellent opportunity of validation for state-of-the-art transport models. We use two broadly used quasi-linear transport models, TGLF-SAT1 and QuaLiKiz, to predict the experimental profiles with varying Te/Ti. The RABBIT code, newly implemented in ASTRA, allows to have a fast, yet accurate and energy-resolved reconstruction of the fast-ion distribution function in presence of Neutral Beam Injection. This also enables us to test the impact on the predictions when the fast-ion population in ASTRA is evolved self-consistently with the modelled profiles. The quasi-linear effects of fast-ion stabilization of turbulence beyond dilution are then compared to those predicted with gyrokinetic linear and non-linear simulations.

Speaker: G. Tardini (EPS 2019)

746 P5.1085 Tungsten core transport in 30s WEST L-mode plasma with RF heating

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1085.pdf

W (Tungsten) accumulation in the core plasma could cause largely increased radiation because of its high cooling rate, which severely restricts long-pulse operation. In this context, WEST has achieved 30s L-mode pulses without any sign of W accumulation. The discharges were performed on the upper divertor in a full W environment, with LHCD power reaching 2.8MW and a constant central line-integrated electron density of 3.2x10^19m^-2. The radiated power was 50% of the total RF heating power and this fraction remained constant over 30s.
To explain why there is no W accumulation in these long pulses, core W transport is analyzed. Based on the experimental analysis, within ρ <0.4, a proxy of the W peaking is correlated to the proxy of neoclassical pinch to diffusion ratio, R/Lne - 0.5 R/LTe [1], hence the neoclassical convection plays the dominant role. The impurity content is reconstructed using METIS [2] constrained thanks to iterations with synthetic diagnostics for SXR, bolometer and Bremsstrahlung emission. The respective core W transport contributions: turbulent vs neoclassical and diffusion vs convection, are obtained thanks to NEO [3] and QuaLiKiz [4].
In addition, in these long pulses, during the phase of N2 seeding which is used to investigate the ammonia production, an increase of the core temperature was measured. The mechanism of this improvement is investigated using METIS and QuaLiKiz.

[1] Angioni C et al, Nucl. Fusion 2014
[2] Artaud J.F et al, Nucl. Fusion 2018
[3] Belli E et al, Plas. Phys. and Cont. Fus. 2012
[4] Bourdelle C et al, Plas. Phys. and Cont. Fus. 2016

Speaker: X. Yang (EPS 2019)

747 P5.1086 Heat Transport Analysis for the High-betan Discharge on EAST

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1086.pdf

Recent experiments on the EAST tokamak have extended the high-βN scenario towards the steady-state burning plasma regime by combination of NBI heating and LHW injection to obtain ~100% non-inductively-driven operation. By employing a very broad current profile, the negative magnetic shear leads to a high normalized beta (β𝑁~2.4) and the energy confinement factor reaches about 1.0.
The ion temperature of the discharge discussed in this paper is slightly higher than the electron temperature. The ion and electron temperature both become strongly peaked in the core during the higher N phase and leads to the ITB formation. The LHW deposit position moves outward with the increasing auxiliary heating power which leads to an off-axis total current profile. The negative magnetic shear results in the escalating q0 and q𝑚𝑖𝑛(q0~4, q𝑚𝑖𝑛~3.5), while q95 remains around 7 in spite of the βN increasing. The bootstrap current faction is 20% and completely non-inductive driven current occurs when βN reaches 2.3.
The electron and ion thermal diffusivities derived from TRANSP code increase systematically with higher central electron heating and remain well above the neoclassical level. The χi and χe shows different relationship with βN during the typical discharge. Gyrokinetic simulation by GTC code is taken out to study the turbulence change with the βN changing for the typical high-βN discharge.

References:
1. B.N. Wan et al 2017 Nucl. Fusion 57 102019
2. X. Gao, et al 2017 Nucl. Fusion, 57 056021.
3. H. Doerk et al 2018 Nucl. Fusion 58 016044
4. G. L. Falchetto et al 2003 Phys of Plasmas 10 1424
5. M. J. Pueschel et al 2008 Phys. Plasmas 15 102310

Speaker: X. Zhang (EPS 2019)

748 P5.1087 Impact of 3D magnetic perturbations on turbulent transport in tokamak limited plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1087.pdf

A tokamak has theoretically a toroidally symmetric magnetic field. However, the magnetic field is never perfectly homogeneous in the toroidal direction. The 2 most common reasons for non axisymmetric fields are engineering limitations and voluntary perturbations applied by additional coils for control purposes. The latter are planned to be used in ITER to mitigate and/or suppress Edge Localized Modes (ELMs) via Resonant Magnetic Perturbations (RMPs). Experiments on current machines have shown the capability of RMPs to achieve their purpose but have also demonstrated an impact on the edge plasma equilibrium as well as on turbulence. One of the concerns for futur devices is the consequences on the heat load distribution at the targets. If the impact of RMPs has been studied through MHD and 2D transport simulations, self-consistent modelling of their impact on turbulent transport remains to be done.
In this presentation, we use the 3D fluid turbulence edge plasma code TOKAM3X to investigate the response of the plasma to simple 3D RMP-like perturbations. Although TOKAM3X has the capability to solve full fluid-drift equations in complex geometries, we restrict ourselves as a first step to an isothermal model in an idealized circular limited geometry. The response of the equilibrium to the perturbation is neglected assuming the common vacuum approximation.
In a limiter tokamak geometry, with a single mode perturbation, we have performed a scan in perturbation amplitude, comparing resulting simulations with a reference case without perturbation. Pertrubed simulations exhibit of drop of the particle content reminiscent of the pump-out observed in experiments. The amplitude of the pump-out is of the order of 5 to 10 % for perturbations of the order of 10^(−4). Experimental trends are also recovered in the response of the radial electric field which is not impacted in open field lines but decreases by a factor of 2 in the closed field lines region. On the other hand, key features of turbulence are only moderately impacted, even though one can observe a change in the poloidal distribution of the turbulent flux which becomes less ballooned. The physical mechanisms explaining these observations are then discussed. Finally, first simulations with more realistic and complex perturbation patterns are presented.

Speaker: B. Luce (EPS 2019)

749 P5.1088 Integrated modelling of tokamak plasma confinement

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1088.pdf

The design of future fusion reactors and their operational scenarios require accurate estimates of the plasma confinement, which is a key parameter for the evaluation of the fusion performance. We are developing a new model that integrates different elements describing the main physics phenomena which determine plasma confinement. We use the ASTRA transport code, which thanks to its modularity allows us to make use of different models to simulate transport in each plasma region. In particular, we are coupling to ASTRA a new pedestal transport model [1], based on empirical observations. For core transport we use the TGLF turbulent transport model, and NCLASS is used for neoclassical transport. We also coupled a simple scrape-offlayer model to ASTRA [2], which provides the boundary conditions at the separatrix, which are a function of the main engineering parameters. By this way no experimental data needs to be imposed at the boundary, and the only inputs of the model are the magnetic field, the plasma current, the heating power, the fueling rate, and the plasma geometry. In the modelling workflow, first a scan in pedestal pressure is performed, by changing the pedestal width. Then the pedestal top pressure is determined using the MISHKA MHD stability code. This modelling framework is tested by simulating ASDEX Upgrade discharges. We show comparisons with experimental fuelling and power scans. The changes of the pedestal structure and the gradients in the plasma core, due to the different combinations of fuelling and heating power, are well captured by the model. We also show that the modelled pedestal height, the energy confinement time and the stored energy, are in agreement with the experimental measurements, and more accurate with respect to the prediction of scaling laws. However, the predictions of the model are sensitive to the plasma core pressure, which has a strong impact on the pedestal stability and on the stored energy, and depends on the reliability of the TGLF transport model. The long term goal is to obtain a robust model which can be used to identify important hidden dependencies affecting global plasma confinement, which are difficult to capture by statistical regressions on global parameters.

References
[1] P.A. Schneider et al., Nuclear Fusion 53.7 (2013), p. 073039.
[2] A. Kallenbach et al., Nuclear Materials and Energy 18 (2019), pp. 166-174.

Speaker: T. Luda di Cortemiglia (EPS 2019)

750 P5.1089 Simulations of blob dynamics in the edge of tokamak T-15

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1089.pdf

Turbulent dynamics of tokamak edge plasma related to convective motion of filamentary structures, or blobs, plays an important role in determining the heat and particle fluxes coming from core plasma to the first wall of the machine [1]. Combined with the problem of plasmasurface interaction and tritium retention in the plasma facing components of a tokamak, this makes prediction of the areas of preferential contact between blobs and the tokamak first wall a highly important issue.
Computer simulations of blob dynamics in turbulent codes, such as HESEL, GBS, BOUT++, TOKAM3X and others [1, 2], are widely used in theoretical studies of blob dynamics nowadays. In these works, it is frequently assumed that blobs propagate in background plasma with either homogeneous or inhomogeneous model profiles. In tokamaks, however, the edge plasma parameters can have intricate profiles both across and along the magnetic field lines, which has to have impact on dynamics of filaments in the edge of these machines.
In this contribution, we numerically investigate dynamics of blobs in the edge of the T-15 tokamak, presently constructed at the National Research Center "Kurchatov Institute". For simulations, we employ the code written in the BOUT++ framework [3], taking into account the realistic magnetic geometry of the tokamak and the spatial distributions of the edge plasma profiles obtained by using the 2D transport code SOLPS4.3. Specific routines that allow interpolating data between the BOUT++ and SOLPS computational grids and to pre/post-process them are developed. For the analysis of filament dynamics, two distinct scenarios of T-15 operation with low and high edge plasma densities are chosen. The first modeling results of blob motion in the edge of the T-15 tokamak in these operational regimes are demonstrated and discussed.

The study was funded by the Russian Foundation for Basic Research (RFBR) project 18-3200208 mol_a.

References
[1] D. A. D'Ippolito, J. R. Myra, and S. J. Zweben, Phys. Plasmas 18, 060501 (2011).
[2] S. I. Krasheninnikov, D. A. D'Ippolito, and J. R. Myra, J. Plasma Phys. 74, 679 (2008).
[3] B. D. Dudson, M. V. Umansky, X. Q. Xu, et al., Comp. Phys. Comm. J. R. J. Plasma Phys. 180, 1467 (2009).

Speaker: A. Lyashenko (EPS 2019)

751 P5.1090 Studies of poloidal rotation of plasma density turbulence with HIBP in the T-10 tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1090.pdf

An ExB drift poloidal rotation is now considered as an effective mechanism to suppress the plasma instabilities [1]. So, the direct radial electric field Er studies are important ingredient for understanding the role of E_r x B_t shear poloidal rotation in the turbulence suppression. In the -10 tokamak, the mean values of E_r were retrieved via plasma electric potential measured by heavy ion beam probe (HIBP) [2]. On top of that, recent advances in the T-10 HIBP allows us to measure simultaneously the plasma potential and density fluctuations within the frequency domain up to 250 kHz in 5 poloidally shifted sample volumes with the 5-slits energy analyser [3] in the plasma core (0.07 m < r < 0.2 m). Cross-phase θ_ij between density fluctuations in two sample volumes poloidally shifted at Δx_ij, each observed by corresponding analyzer entrance slits with numbers i and j, gives the information on the poloidal turbulence rotation velocity: V_turb =Δxij∙2πf/θij, i, j = 1-5, ixj [4]. The ohmic plasmas with m, B_t = 2.2 T, I_pl = 230 kA, n_e = 1x1019 m -3 were studied. For the stochastic low-frequency fluctuations (SLF) [5] with f_SLF =0-30 kHz, V_SLF ~ 2.5-3 km/s is directed towards the ion diamagnetic drift. For the low-frequency quasi-coherent fluctuations (LFQC) [6], f_LFQC =50200 kHz, V_LFQC ~ -10-15 km/s is directed towards the electron diamagnetic drift. It has been shown that E_r = - 60 V/cm, so E_r X B_t rotation velocity V_ExB equals to ~ -3 km/s and directed to the electron diamagnetic drift. The effect of EC heating on the ExB and turbulence rotation will be also presented.

References
[1] Burrell K.H., Phys. Plasmas 4 (1997) 1499
[2] Melnikov A.V. et al., Rev. Sci. Instrum. 66 (1995) 317
[3] Melnikov A.V. et al., Nucl. Fusion 57 (2017) 115001
[4] Eliseev L.G. et al., Plasma Fusion Res. 7 (2012) 2402064
[5] Vershkov V.A. et al., Nucl. Fusion 45 (2005) S203
[6] Vershkov V.A. et al., Nucl. Fusion 57 (2017) 102017

Speaker: A.V. Melnikov (EPS 2019)

752 P5.1092 Plasma edge current fluctuation measurements during the ELM cycle with the atomic beam probe at COMPASS

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1092.pdf

The evolution of the edge plasma current in magnetically confined plasmas is identified as a critical parameter of Edge Localized Mode (ELM) destabilization. While the plasma pressure gradient, the other critical parameter, is routinely measured with high spatial and temporal resolution on fusion experiments, the plasma edge current measurement capabilities are limited. The Atomic Beam Probe (ABP [1][2]) is an extension of the widely used Alkali atomic beam emission spectroscopy diagnostic [3] offering a novel solution for plasma edge current measurement. The atomic beam, which is injected into the plasma, is ionized due to the collisions with the plasma particles. The ions originating from the beam follow a curved path in the magnetic field and might hit the wall of the machine. The impact location and the number of ions carry information about the toroidal plasma current distribution, the density profile and the electric potential in the plasma. The capabilities of the diagnostic technique have been demonstrated at COMPASS [4]: measurements were carried out with 1-2 mA lithium and sodium beam, beam modulation up to 100 kHz, beam size reduction to 5 mm (beam current reduced to 50 µA), and in various scenarios (1 - 1.38 T, 150 - 300 kA). Along with experimental work, extensive ion orbit modelling efforts have been made in order to interpret the results. The measurement location in the modelled plane was identified matching the modelled and the measured ion distribution on the 100 ms timescale, while radially localized and poloidally extended current fluctuations have been applied to the equilibrium profiles in the model to match the measured fluctuations on the 100 µs timescale. First experimental results will be presented demonstrating the linear response of the detector to current changes and the ion distribution movement during the ELM cycle. Parallel fast density and current fluctuation measurements will also be shown, emphasizing the unique capabilities of the combined BES and ABP diagnostic.

[1] P. Hacek et al., Review of Scientific Instruments 89, 113506 (2018)
[2] D. I. Refy et al., Accepted at RSI (2019)
[3] G. Anda et al., Lithium beam diagnostic system on the COMPASS tokamak. Fus. Eng. Des. 108 (2016)
[4] R. Panek et al., Plasma Phys. Control. Fusion 58 014015 (2016)

Speaker: D. Réfy (EPS 2019)

753 P5.1093 Role of electrostatic fluctuations in the loss of runaway electrons in ADITYA-U tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1093.pdf

Formation of relativistic runaway electrons (REs) beam during plasma disruption, which can seriously damage the first wall, is a major threat to the safety of large tokamaks like ITER. In order to suppress the disruption-generated runaway beam, techniques such as massive gas injection, resonant magnetic perturbations etc. are tried out, but their adequacy are yet to be fully established [1]. Hence a better understanding of REs loss mechanism is crucial for the development of better RE mitigation schemes. The dependence of RE loss on magnetic as well as edge electrostatic fluctuations have been studied in ADITYA-U [2] tokamak (minor radius, a=25 cm and major radius, R=75 cm). The studied discharges have: plasma current 80-­120 kA, chord-averaged electron density ~ (1-­4) × 10^19 m^-3, chord-averaged electron temperature ~ 200-­500 eV and toroidal magnetic field ~ 0.75 - 1.2 T. Earlier in ADITYA tokamak it had been observed that the overlapping of two MHD islands (m/n=2/1 & 3/1) significantly enhances the radial RE transport [4], whereas the RE transport is reduced when good magnetic surfaces stay between the islands. In addition to that, it has been observed that the turbulent electrostatic fluctuations in the edge of ADITYA-U also play a dominant role in the RE loss mechanism. The edge electrostatic fluctuations are suppressed by the periodic gas puffs and it has been shown that it leads to substantial decrease in HXR flux intensity signifying reduction in RE loss. The HXR flux intensity decreases by >80% during the suppression of turbulent electrostatic fluctuations in edge plasma after the injection of gas puff. In this paper, we present the experimental observations demonstrating the strong effect of electrostatic fluctuations on RE dynamics in the edge region of ADITYA-U tokamak. The study provides a basis to explore the possibility of a new RE mitigation scheme based on enhancing seed RE loss with the assistance of external electrostatic perturbations.

[1] Allen H Boozer (2019) Plasma Phys. Control. Fusion 61 024002
[2] Tanna, R, Raj, Harshita , J.Ghosh, et.al , (2019) Nucl. Fusion, Accepted Manuscript
[3] Harshita Raj , J.Ghosh, et al, (2018) Nucl. Fusion 58 076004

Speaker: H. Raj (EPS 2019)

754 P5.1094 Particle-In-Cell simulation of parallel blob dynamics in the near scrape-off-layer plasma of a generic medium-size tokamak with divertors

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1094.pdf

Blob transport is subject to intense study in fusion energy research for the understanding and prediction of particle and heat fluxes onto the plasma-facing components (PFC) [1]. Blobs originate around the separatrix at the outer midplane, forming filaments which expand and propagate in the parallel and, respectively, perpendicular (outwards) direction, with respect to the total magnetic field. Although considerable work has been done to address the perpendicular (radial and poloidal) transport in the scrape-off-layer (SOL) plasma, both experimentally and numerically, the dynamics of these filaments along the flux tube did not receive sufficient investigative attention. Up to now, flux tube dynamics simulations assumed constant temperatures, forced Maxwellian-distributed species and/or no divertor physics. Experimentally, mean parallel flows can only be estimated by using Mach probes [2]. We have studied the evolution of a blob along a magnetic field line in the near scrape-off-layer (SOL) plasma of a generic diverted medium-size tokamak (MST) and its contribution to the recorded heat flux at the divertors, using the 1D3V PIC BIT1 code [3]. We have observed that most of the blob's hot electrons are immediately screened by the cold electrons of the SOL plasma and that they can reach the two divertors depending on the density of the SOL plasma, due to Coulomb collisions. Secondly, we showed, in terms of density, that a SOL plasma can be built by a train of blobs shot in vacuum when ion-recycling at the divertors is activated (i.e. ions touching the divertors become neutrals, with 99% probability). In this case, the built SOL plasma is made of cold electrons due to the inelastic collision between the blob's electrons and the neutrals formed by recycling, and of cold ions formed by the ionization of slow neutrals or by charge-exchange between blob's ions and the slow neutrals.

References
[1] H.W. Müller et al., Nuclear Fusion 51 (2011), 073023.
[2] B. LaBombard et al., Nuclear Fusion 44 (2004), 1047.
[3] D. Tskhakaya, Plasma Phys. Control. Fusion 59 (2017), 114001.

Speaker: R.W. Schrittwieser (EPS 2019)

755 P5.1095 Sonic-flow gyrokinetic simulations with a unified treatment of all length scales

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1095.pdf

Tokamak turbulence exhibits interaction on all length scales, but standard gyrokinetic treatments consider global scale flows and gyroscale flows separately, and assume a separation between these length scales. However, the use of a small-vorticity ordering [1, 2] allows for the presence of large, time-varying flows on large length scales, whilst providing a unified treatment including shorter length scales near and below the gyroradius. We present the numerical implementation of the resulting implicit gyrokinetic equations, and provide an interpretation of their meaning, as well as alternative numerical schemes.
The implicit dependences take the form of partial time derivatives of the E × B flow. These are analogous to those found in the V^ll formulation of gyrokinetics for electromagnetic perturbations. We show that we are able to solve our implicit equations with an iterative scheme, where the first iteration uses equations that are analogous to the small-flow limit. The Poisson solver (using the same numerical scheme [3] as the ORB5 code) is capable of solving 3D global tokamak geometry but is used here for slab and cylindrical cases. We present simulation results that demonstrate the effects of sonic flows.
Additionally, we show the differences between the distribution functions for the small-flow and sonic-flow formalisms.

References
[1] A.M. Dimits, Physics of Plasmas 17, 055901 (2010)
[2] B.F. McMillan and A.Y. Sharma, Physics of Plasmas 23, 092504 (2016)
[3] J. Dominski, B.F. McMillan, S. Brunner, G. Merlo, T.-M. Tran and L. Villard, Physics of Plasmas 24, 022308 (2017)

Speaker: A.Y. Sharma (EPS 2019)

756 P5.1096 Simulation of turbulent plasma toroidal rotation evolution with ECR heating switch-on in tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1096.pdf

This paper continues our research on nonlinear low-frequency turbulent convection and associated anomalous cross-field transport processes of tokamak core plasmas [1]- [4]. Numerical simulations are performed with code CONTRA-C, which is developed in the frame of simplified cylindrical model for tokamaks [2]. The dynamic of toroidal momentum in this model is governed by several processes: viscosity, Reynolds' stress and external momentum sources and sinks (e.g. neutral beam injection). Viscosity term is divergent at the plasma core region, but also includes momentum exchange between plasma core and SOL region at the simulation domain boundary. Reynolds' stress governs the kinetic energy exchange between toroidal rotation and fluctuations. This term does not change the toroidal momentum integral, but affects toroidal rotation profile. The example of interplay between viscosity and Reynolds' stress is self-consistent toroidal rotation maintenance in some tokamak ohmic regimes [4]. In this paper temporal evolution and radial profiles of toroidal momentum and plasma potential are simulated and analyzed for tokamak regimes with ECR heating switch-on. Special attention is paid to regimes with conditions for ITB formation near major rational magnetic surfaces [3].

References
[1] V.P. Pastukhov, N.V. Chudin and D.V. Smirnov, Plasma Physics and Controlled Fusion 53, 054015 (2011)
[2] V.P. Pastukhov and D.V. Smirnov, Plasma Phys. Reports 42, 307 (2016)
[3] V.P. Pastukhov and D.V. Smirnov, Proceedings of 44th EPS Conference on Plasma Physics, report P2.173 (http://ocs.ciemat.es/EPS2017PAP/pdf/P2.173.pdf)
[4] V.P. Pastukhov and D.V. Smirnov, Proceedings of 45th EPS Conference on Plasma Physics, report

Speaker: D. Smirnov (EPS 2019)

757 P5.1097 Density turbulence modification by gradient control in W7-X

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1097.pdf

The Wendelstein 7-X superconducting stellarator at IPP Greifswald has a neoclassically optimized magnetic field, such that turbulent transport can be a major loss channel. Its variable three-dimensional field geometry is expected from analytical and numerical models to provide venues to modify both spatial localization and strength of turbulent mode activity. Turbulence in W7-X has therefore been experimentally investigated in the recently completed experimental campaign that demonstrated long pulse operation at high density and triple product.
This contribution focuses on results from the phase contrast imaging (PCI) diagnostic, which provides poloidally resolved (k⊥ρs ≈ 1) density fluctuation measurements along a line of sight through the magnetic axis. The system is a collaboration between the MIT PSFC and IPP and has been in operation for the last operation phase OP1.2 (2017-2018).
While ion-scale density turbulence is regularly observed in the core plasma which scales well in magnitude with the diamagnetic energy over a wide range of discharge scenarios, several remarkable exceptions are found. In particular, a transient increase of the diamagnetic energy with a simultaneous reduction of density fluctuations are observed in discharge scenario in which the equilibrium temperature and density profiles undergo changes in magnitude and location of maximum gradient lengths. This is the case after pellet injections (hydrogen ice or tracer impurity), and after rapid changes in heating power from both the electron cyclotron heating and neutral beam injection systems. The PCI frequency-wavenumber-spectra are then significantly modified, displaying multiple phase velocities which suggests the coexistence of turbulent modes. This is supported by reflectometer data and radially resolved impurity transport experiments, which indicate radial localization of this feature.
Gyrokinetic simulations (both linear and non linear) further support these findings by showing that growth rates are minimized when the ion temperature and density gradients are of similar amplitude and spatially overlap.

Speaker: A. Von Stechow (EPS 2019)

758 P5.1098 Effects of magnetic island on ExB shear flow structure and plasma self-driven current in tokamaks

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1098.pdf

Global gyrokinetic simulations with self-consistent coupling of neoclassical and turbulent dynamics show that turbulence can significantly affect plasma self-driven mean current generation in tokamaks. The current amplitude, profile and phase space structure can all be modified. Turbulence can significantly reduce the current generation in collisionless regime, generate current profile corrugation near rational magnetic surface and nonlocally drive current in the linearly stable region ­ all these are expected to have a radical impact on broad tokamak physics. Both electron parallel acceleration and residual stress from turbulence play crucial roles in turbulence-induced current generation. The magnetic island is found to strongly change ExB shear flow structure and current generation in the island region. It is shown that charge separation due to electron parallel transport induced finite electron density flattening in the O-point generate a strong radially localized ExB shear layer, which may facilitate the formation of a transport barrier near the resonant magnetic surface by decoupling plasma inside the shear layer from the outside. On the other hand, turbulence self-generated zonal flow shows a helical structure akin to the island in large island case, namely, a poloidal ExB shear flow on the perturbed magnetic surfaces, which may prevent the turbulence developed in the outside of the island from spreading into the O-point. The parallel mean current is also largely modified in the island region by both neoclassical and turbulent effects. Its impact on island evolution will be discussed.

Speaker: W. Wang (EPS 2019)

759 P5.1099 From Lawson to burning plasmas: a multi-fluid analysis

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1099.pdf

A standard figure of merit for magnetic-confinement nuclear fusion experiments is expressed through the Lawson criterion [1]. The criterion gives the value for the "triple product" of plasma density, temperature and energy confinement time that must be reached in order for the plasma to ignite, i.e. to continue producing fusion power without any input heating power. Experimental parameters can easily be compared with Lawson's value. However, this evaluation of plasma performance is inaccurate because of the extreme simplifying assumptions made in the derivation of the Lawson criterion, namely, the 0D geometry and the single-fluid plasma model. The Lawson criterion was improved in recent work, where one-dimensional geometry and multifluid (ions, electrons and alphas) physics were included in the model, accounting for physical equilibration times and different energy confinement times between species [2]. Both steadystate (Lawson-like) and time-dependent calculations were considered, with particular emphasis on the heating power needed to bootstrap a plasma to ignition. A further drawback of the Lawson criterion is that it expresses performance in terms of ignition. A much more meaningful measure for the performance of current and future experiment is expressed in terms of the gain factor Q (ratio between total fusion power and external heating power, with the burning plasma state corresponding to Q=5). Of particular interest for the next generation of experiments is the introduction of no-alpha parameters, which give a formal, physics-based procedure to compare pure deuterium plasma discharges with future deuterium-tritium discharges [3].

References
[1] J. D. Lawson, Proc. Phys. Soc. London Sect. B 70, 6 (1957)
[2] L. Guazzotto and R. Betti, Tokamak Two-Fluid Ignition Conditions, Phys. Plasmas 24, 082504 (2017)
[3] L. Guazzotto and R. Betti, Two-Fluid Burning-Plasma Analysis for Magnetic Confinement Fusion Devices, submitted for publication

Speaker: L. Guazzotto (EPS 2019)

760 P5.1100 Three-dimensional geometric integrator for charged particle orbits in toroidal fusion devices

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1100.pdf

A three-dimensional integrator for guiding center orbits of charged particles in toroidal fusion devices with 3D field geometry is described. The integrator uses a representation of the electromagnetic field by low order polynomials on a 3D tetrahedal grid and is intrinsically designed to preserve the total energy, perpendicular adiabatic invariant, and the phase space volume accurately for any grid size. Thus, it belongs to the class of geometric integrators. The integrator is designed for usage in Monte Carlo (MC) procedures to simulate particle distribution functions where a box counting method (calculation of dwell time within spatial cells) is used for the evaluation of macroscopic plasma parameters. Such a computation is needed, e.g., for the evaluation of plasma response currents and charges caused by external non-axisymmetric electromagnetic perturbations in tokamaks as well as for kinetic modeling of edge transport in devices with 3D field geometry. This geometric integrator is more efficient in evaluation of dwell times than a solution of guiding center equations with a high order adaptive ODE integrator, while keeping roughly the same speed for orbit computations, because dwell times and the particle's coordinates and velocities at boundaries of spatial cells are intrinsically available without additional efforts for tracing the intersections with cell boundaries. Similar to the 2D geometric integrator of Ref. [1] also the 3D geometric integrator is less sensitive to inaccurate representation of the electromagnetic field resulting from statistical noise in plasma response currents and charges computed by a MC method within a feedback loop. Artificial numerical diffusion which can arise in presence of perturbations is extensively discussed. It can be shown that the use of field aligned coordinates is beneficial and that such a diffusion scales inversely with the grid size and thus can be kept well below neoclassical values.

References
[1] S.V. Kasilov, A.M. Runov, W. Kernbichler, Computer Physics Communications 207, (2016), 282­286

Speaker: M. Eder (EPS 2019)

761 P5.1101 Numerical study of linear dynamics of a confined plasma by a spherical tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1101.pdf

The study of plasma dynamics is the main tool for both the description and control of Tokamak devices for thermonuclear fusion systems, which has been carried out mainly by computational simulation techniques. The magnetohydrodynamic (MHD) equilibrium of the plasma is the starting point for the study of macroinstabilities, which is obtained from the solution of the force balance equation. For axially symmetric systems, the force balance equation leads to theGrad-Shafranov equation [1]. In this work, we present the results of the numerical study of linear dynamics of a confined plasma by a spherical Tokamak of aspect ratio A ∼ 1.6. This study is carried out in two sequential stages: (i) numerical solution of the Grad-Shafranov equation in the poloidal plane, using the finite difference method and the successive over-relaxation scheme (SOR) as is described in reference [2], and (ii) simulation of the plasma dynamics in the linear regime by using the MHD model, starting from the perturbation of the equilibrium state. For this stage, a fourth order finite difference scheme for the spatial derivatives is used, and the Runge-Kutta algorithm is implemented as the temporal integrator. In order to guarantee the fulfillment of the equation ∇ · B = 0 in each time step, the restricted flow transport scheme is implemented [3]. For the MHD equilibrium state, the poloidal magnetic flux, pressure, safety factor and magnetic field profiles are presented. For the perturbed state, the results show that the perturbations are located mainly in the outer edge of the plasma; however, some poloidal modes move toward the central zone around the magnetic axis.

References
[1] V.D. Shafranov. Soviet Phys. JETP, 6, 1013 (1958)
[2] J.E. López, E. A. Orozco and V. D. Dougar-Zhabon, J. Phys. Conf. Ser., 1159 (1), 012017 (2019).
[3] C.R. Evans and J.F. Hawley. The Astrophysical Journal, 332:659-677, (1998)

Speaker: J.E. LÌ_pez (EPS 2019)

762 P5.1102 Density profiles in low collisionality FTU plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1102.pdf

FTU offers the unique opportunity to explore a broad range of collisionality [1] expressed as ν_eff = 0.1 Zeff 〈ne〉 R / 〈Te〉^2.
This work is devoted to study the dependence of the electron density profiles and peaking in a low collisionality regime, more interesting for comparison with other tokamaks [2]. With respect to those indeed, FTU features a wider scale of magnetic fields and densities. This allows to analyse the behaviour of the electron density profiles as a function of magnetic field and plasma current, investigating also more factors, such as: wall conditioning, plasma temperature.

[1] C. Mazzotta et al., Highly collisional regimes in FTU. Proceedings of the 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland (UK). Paper P2.179 (2017). Vol. 41F ISBN: 979-10-96389-07
[2] C. Angioni et al., Plasma Phys. Control. Fus. 51 (2009) 124017

Speaker: C. Mazzotta (EPS 2019)

763 P5.1103 Cylindrical vs toroidal Single Helical states in the low aspect- ratio RELAX device

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1103.pdf

The RELAX device is a low aspect- ratio ( with R/a=2 where R and a are the major and minor radius of the torus) Reverse Field Pinch (RFP) in which on-axis resonant helical modes with m=1 and n=4 (m and n being the poloidal and toroidal mode numbers respectively) are observed during the so called Single Helical (SH) states, i.e. states in which the plasma shows (at least in some time windows) an helical saturated dominant perturbation. These states have been predicted by numerical 3D visco-resistive MHD simulations and afterwards detected in almost all RFP's. The SH states can also be studied and characterized, as shown recently, within a cylindrical relaxation theory which assumes as global invariant the plasma volume integrated magnetic helicity weighted over the helical flux of the dominant mode. In this paper we compare the predictions of the cylindrical relaxed states with the solutions that can be obtained by using the VMEC helical equilibrium solver and also with the states obtained by the 3D MHD MIPS code. Both the VMEC and MIPS solutions are fully taking into account the toroidal geometry, so it would be interesting to check to which extent the toroidal effects modify the cylindrically symmetric relaxed states. Furthermore we will check if the global helicity related invariants hypothesized within the cylindrical theory are well reproduced by the time dependent nonlinear simulations.

Speaker: R. Paccagnella (EPS 2019)

764 P5.1105 Design of neutron and gamma ray measurements for the start-up phase of the DTT tokamak

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.1105.pdf

The Divertor Tokamak Test (DTT) facility, which is under design for construction in Frascati (Italy), will produce neutron yield up to 1.3*10^17 n/s at full power (H-mode scenario). This calls for an accurate design and selection of the 2.5 MeV neutron diagnostic systems and detectors which can give the fill exploitation of the high neutron fluxes. Measurements of 14 MeV neutrons (which are about 1% of the total yield) due to triton burn-up will also be performed.
DTT will reach its best performances after a preliminary phase needed to assess and improve the machine parameters. Here we present the neutron and gamma ray diagnostics systems which are under design for the initial start-up phase of DTT. The design work benefits from the experience gathered by the community on high power tokamak such as JET. These systems, also called day-1 diagnostics, are:
i) Neutron flux monitors which measure the 2.5 and 14 MeV neutron yield
ii) Hard x-ray monitors for measurements of the bremsstrahlung radiation produced by runway electrons in the 1-40 MeV energy range
iii) Neutron/Gamma camera for the reconstruction of the neutron and gamma ray emission profile of the plasma.
A brief description of the nuclear diagnostics which are under study for the so called exploitation phase of DTT will also be given. Although these systems will be needed only in a second phase during the operation of DDT at full power, it is crucial to study and design them from the beginning for integration issues.

Speaker: M. Angelone (EPS 2019)

765 P5.2001 Energy deposition and ion stopping in inertial confinement fusion plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2001.pdf

Investigation of interaction processes of ion beams with dense plasmas is one of the key problems in physics of inertial confinement fusion driven by heavy ion beams [1]. The stopping power is an important quantity used to describe the interaction of particle beams with matter. In the field of particle-driven inertial confinement fusion, interaction of highly charged ions with dense plasmas is of special interest [2-3]. Consequently, knowledge of dynamical characteristics of plasma ions in the ICF, such as the implosion time, energy deposition, penetration depth and the effective range in the plasma will enable us to calculate the design of thermonuclear target more accurately. In this work, the Monte Carlo method is used for simulation of ion trajectories in a dense plasma of inertial confinement fusion [4]. The main advantage of calculations by the Monte Carlo method is that they allows us to take into account any physical process directly, for example, local and non-local inelastic energy losses, binding energy between atoms, charge transfer collisions, etc. Moreover, it is possible to obtain accurate solutions for multi-target and multi-layered complex geometry, which allows us to simulate actual interactions with the plasma ion beam. The values of energy deposition, energy partition, and implosion time in a wide range of densities and temperatures for inertial confinement fusion applications have been calculated. The obtained results for energy loss of particles and other energetic characteristics in dense plasma are compared with the available experimental data and theoretical results of other authors [5].
1. R. Davidson (Ed.) Frontiers of High Energy Density Physics, Washington; D.C.: Natl. Acad. Press, (2003). 2. D.H.H.Hoffmann, K. Weyrich, H. Wahl et al, Phys. Rev. A 42, 2313 (1990) 3. D.O. Gericke and M. Schlanges, Phys.Rev. E 60, 904 (1999) 4. S.K. Kodanova, T. S. Ramazanov, M. K. Issanova, N.K. Bastykova, R.I. Golyatina, S.A. Maiorov, J. Phys.: Conf. Ser. 946, 012014 (2018) 5. L.S. Brown, D.L Preston, and R.L. Singleton Jr., Phys. Rev. E 86, 016406 (2012)

Speaker: M. Issanova (EPS 2019)

766 P5.2002 Interaction of plasma flows and magnetic field with the formation of shock waves in nested arrays

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2002.pdf

The results of plasma compression studies of nested wire and fiber arrays with current flowing through them are presented in this work. Experiments were made on the Angara-51 installation with current up to 4 MA. The current implosion of nested arrays represents a unique opportunity to simulate the interaction of a plasma flow with a magnetic field. Inside the volume of such an array, there is a collision of the supersonic plasma flow from the external wire array produced by the current flowing through it with the magnetic field generated by a part of the total discharge current flowing through the inner array. Various plasma flow regimes in the space between the inner and outer arrays were obtained: subAlfven (V_r<V_A), super-Alfven (V_r > V_A) and the regime with the formation of a transition region: a shock wave (SW) between the arrays, depending on the ratio of the radii of the nested arrays. The dependence of these flow regimes on the plasma formation rate of the inner and outer arrays is shown. The obtained experimental results are compared with the simulations of the plasma motion between the arrays using the three-dimensional radiationmagnetohydrodynamic code MARPLE. A possible scenario for the interaction of plasma in the nested arrays is proposed. At certain parameters of the nested arrays, a shell, quasiclosed in the azimuthal direction, is formed around the inner array. At the same time, the plasma of the outer array surrounds the inner one and stabilizes its compression. The suppression of MRT instabilities during plasma compression of the inner array leads to the formation of a stable, compact Z-pinch and the generation of a short-time soft X-ray pulse. Further optimization of the parameters of the nested arrays of mixed composition will be carried out by reducing the fraction of current flowing through the trailing mass by varying the number of fibers and their mass in the outer array. The research is carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University and supercomputers at Joint Supercomputer Center of the RAS (JSCC RAS).

This work was carried out with the partial financial support of the Russian Foundation for Basic Research under grants No. 18-29-21005, No. 18-02-00170.

Speaker: A.V. Branitskiy (EPS 2019)

767 P5.2003 New Prism EOS and opacity tables with NLTE atomic kinetics

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2003.pdf

We present new features of PROPACEOS, a code that generates equation-of-state (EOS) and opacity tables for radiation-hydrodynamics and spectroscopic simulations. In addition to existing capabilities to produce tables for LTE and optically thin NLTE plasmas, these new features allow PROPACEOS to perform calculations that include other effect of NLTE atomic kinetics. The primary purpose of this development is to facilitate efficient spectroscopic simulations for short-pulse laser experiments. The simulations are based on post-processing of PIC calculations and focus on the analysis of K-alpha/K-beta emission signatures. PROPACEOS can now produce emissivity and opacity databases on a grid with up to six independent parameters, for example: plasma temperature, plasma density, and hot electron parameters. Hot electron distributions are specified in terms of analytic functions. We will also discuss new capabilities that allow for computing opacities for optically thick NLTE plasmas. We will present simulation results relevant to ongoing experiments on Omega EP laser facility.

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Fusion Energy Sciences (FES) under Award Number DE-SC0018105

Speaker: I.E. Golovkin (EPS 2019)

768 P5.2004 Dynamical structure factor of non-ideal ions in dense quantum plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2004.pdf

Advances on dense plasma diagnostics using X-ray scattering techniques [1] have allowed one to gain insight into the ionic dynamics at extreme conditions. As a result, properties such as the ion acoustic dispersion and corresponding sound velocity in dense plasmas and warm dense matter can be probed experimentally. This development of experimental diagnostic capabilities has motivated the theoretical investigation of the ionic dynamical structure factor (DSF) [2, 3, 4]. For the understanding of the DSF of strongly coupled ions in dense plasmas and in warm dense matter, an accurate analysis of the effects related to quantum degeneracy and electronic correlations is needed. Therefore, in this work, we present the results of an investigation of the impact of electronic correlations on the DSF of non-ideal ions.
The DSF of ions was computed using a screened ion potential in molecular dynamics simulation, where the screening by electrons was calculated on the basis of liner response theory. In order to take into account the electronic correlations, we used the Singwi-Tosi-Land-Sjölander ansatz (STLS) [5, 6]. The range of plasma parameters at which the STLS approximation is applicable for the description of the screening was defined in our recent work [7]. The analysis of the impact of the electronic correlations on the ionic DSF has been done by comparing the STLS potential based results to the MD data obtained using the screened ion potential in random phase approximation (i.e., neglecting electronic correlations). Additionally, the applicability of the Yukawa model for the description of the ionic DSF in dense quantum plasmas is discussed.

References
[1] E. E. McBride et.al., Rev. Sci. Instrum. 89, 10F104 (2018).
[2] T. G. White et.al., Phys. Rev. Lett. 111, 175002 (2013)
[3] H. R. Rüter and R. Redmer, Phys. Rev. Lett. 112,145007(2014).
[4] J. Vorberger et.al., Phys. Rev. Lett. 109, 225001 (2012).
[5] K.S. Singwi, M.P. Tosi, R.H. Land, and A. Sjölandar, Phys. Rev. 176, 589 (1968).
[6] S. Tanaka and S. Ichimaru, J. Phys. Soc. Jpn. 55, 2278 (1986).
[7] Zh. Moldabekov, S. Groth, T. Dornheim, H. Kählert, M. Bonitz, and T. S. Ramazanov, Phys. Rev. E 98, 023207 (2018).

Speaker: Z. Moldabekov (EPS 2019)

769 P5.2005 Equilibration of electron-hole plasma during the formation of warm dense matter

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2005.pdf

The recent advent of the XFEL allowed us to follow ultrafast electron dynamics in the HED matter. We used femtosecond pulses from the PAL-XFEL to measure the ultrafast changes in the X-ray absorption of Cu nanofoil excited by intense laser pulses. Upon exposure to laser irradiation, significant portions of both the s/p and d electrons are excited, and the strongly perturbed copper evolves into warm dense matter with temperatures of a few eV. In this contribution, we present the results of measurements of the X-ray absorption spectra below the copper L_3 edge with 150 fs resolutions. The data visualize the creation and annihilation of holes in the highly excited Cu d band. Comparison of the experiment with the predicted absorption based on the two-temperature-model enabled the initial nonequilibrium durations to be determined at a stage at which the TTM is non-applicable. This investigation allows us to quantify the lifetimes and the decay speed of d holes in warm dense copper, which are a few orders longer and slower, respectively, than known values. It raises an issue of the fast thermalization concept and the widely used two-temperature model to describe the nascent stage of intensively photoinduced material responses.

It has been supported by the National Research Foundation (NRF2016R1A2B4009631) of Korea.

Speaker: B. Cho (EPS 2019)

770 P5.2006 Kinetic effects in high-energy-density plasmas

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2006.pdf

Experiments are indicative of substantial kinetic effects in high-energy-density plasmas during the course of a spherical implosion. The effects appear as the plasma mean-free-path grows relative to the background scale making standard rad-hydro single-fluid description invalid. To understand their mechanics and implications it is convenient to consider the thermal and suprathermal particles separately. For the former, sharp gradients can drive the inter-ion-species diffusion, so the fuel composition no longer remains constant unlike what the standard, single-fluid codes assume [1-4]. Atomic mix at interfaces is, fundamentally, due to the same diffusion process. For the latter, the mean-free-path is much larger than that of their thermal counterparts, so their distribution function may be far from Maxwellian, even if thermal ions are nearly equilibrated. It is these suprathermal, or tail, ions that fuse in subignited implosions. Their distribution is thus the key to proper interpretation of nuclear diagnostics employed in HEDP experiments in general and to correct fusion yield prediction in particular [5]. Furthermore, suprathermal electron distribution shows similar behavior, affecting the X-ray diagnostics [6]. Basic mechanisms behind and practical consequences of these groups of effects in ideal and non-ideal HED plasmas will be discussed.

[1] G. Kagan and X.-Z. Tang "Electro-diffusion in a Plasma with Two Ion Species" Physics of Plasmas 19 (2012) 082709 [2] G. Kagan and X.-Z. Tang "Thermo-diffusion in Inertially Confined Plasmas" Physics Letters A 378 (2014) 1531 [3] G. Kagan, S. D. Baalrud and J. Daligault "Influence of Coupling on Thermal Forces and Dynamic Friction in Plasmas with Multiple Ion Species" Physics of Plasmas 24 (2017) 072705 [4] G. Kagan and S. D. Baalrud "Transport Formulas for Multi-component Plasmas Within the Effective Potential Theory Framework" https://arxiv.org/abs/1611.09872 [5] G. Kagan, D. Svyatskiy et al. "Self-similar Structure and Experimental Signatures of Suprathermal Ion Distribution in Inertial Confinement Fusion Implosions" Physical Review Letters 115 (2015) 105002 [6] G. Kagan, O. L. Landen et al. "Inference of the electron temperature in ICF implosions from the hard X-ray spectral continuum" Contributions to Plasma Physics (2018) 1

Speaker: G. Kagan (EPS 2019)

771 P5.2007 SPECT3D Imaging and Spectral Analysis Package

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2007.pdf

SPECT3D is a collisional-radiative spectral analysis package designed to compute detailed emission, absorption, or x-ray scattering spectra, filtered images, XRD signals, and other synthetic diagnostics. The spectra and images are computed for virtual detectors by post-processing the results of hydrodynamics simulations in 1D, 2D, and 3D geometries. SPECT3D can account for a variety of instrumental response effects so that direct comparisons between simulations and experimental measurements can be made. We will present new features of SPECT3D and highlight their application to the analysis of HEDP experiments. Recent additions to SPECT3D include an updated version of Prism's Atomic Database that incorporates NIST atomic data version 5.0 and improves the consistency for modeling He- and Li-like satellite transitions. X-Ray Thompson scattering calculation times have been improved for the RPA model, and multi-threading has been added for the short characteristics method. Future development plans for SPECT3D will also be discussed.

Speaker: S. Kulkarni (EPS 2019)

772 P5.2009 Hydrodynamic simulations of laser/plasma interactions via ALE methods

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2009.pdf

Hydrodynamic simulations of laser-produced plasmas represent a useful tool both for theoreticians and experimentalists allowing them to investigate processes during laser-plasma interaction, which are often impossible to observe directly during the experiments. They allow not only interpretation of experimental results, but are also often used for designing of the experimental setup or detailed analysis of particular processes during the experiment.
Here, we are mainly interested in the application of the Arbitrary Lagrangian-Eulerian (ALE) numerical methods, benefiting from the computational mesh moving with the fluid in a Lagrangian manner, while enforcing its geometric quality by a regular mesh smoothing mechanism. This type of methods is very convenient for simulations of laser/target simulations and is relatively simply extendable for additional physical models needed for suitable results, such as realistic equations of state [1], absorption of laser beam [2], heat conductivity model [3], cylindrical geometry, two-temperature model, phase transition model, etc.
The described models have been implemented in the framework of PALE (Prague ALE) hydrodynamic code, allowing a large range of hydrodynamic simulations related to laser/target interactions, see [4] for several examples. Here, the performance of the code is verified on selected realistic numerical tests.

References
[1] M. Zeman, M. Holec, and P. Vachal. HerEOS: A framework for consistent treatment of the equation of state in ALE hydrodynamics. Computers & Mathematics with Applications, 2019. In press.
[2] J. Nikl, M. Kucharik, J. Limpouch, R. Liska, and S. Weber. Wave-based laser absorption method for high-order transport-hydrodynamic codes. Advances in Computational Mathematics, 2019. In press.
[3] R. Liska and M. Kucharik. Arbitrary Lagrangian Eulerian method for compressible plasma simulations. In M. Fila, A. Handlovicova, K. Mikula, M. Medved, P. Quittner, and D. Sevcovic, editors, Proceedings of EQUADIFF 11, International Conference on Differential Equations, pages 213­222. STU, 2007. ISBN 97880-227-2624-5.
[4] R. Liska, M. Kucharik, J. Limpouch, O. Renner, P. Vachal, L. Bednarik, and J. Velechovsky. ALE methods for simulations of laser-produced plasmas. In Jaroslav Fort, Jirí Fürst, Jan Halama, Raphaèl Herbin, and Florence Hubert, editors, Finite Volumes for Complex Applications VI Problems & Perspectives, volume 4 of Springer Proceedings in Mathematics, pages 857­873. Springer, 2011.

Speaker: M. Kucharik (EPS 2019)

773 P5.2010 Modelling of the non-local transport of energy in laser plasmas with high-order numerical methods

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2010.pdf

The description of the energy transport processes in the laser plasma is crucial for capturing the dynamics of the laser­target interaction relevant to shock ignition [1] and pre-pulses of ultra-intense lasers [2]. The diffusion approximation of the heat and radiation transport become inadequate even for the laser intensities 1015 W/cm2 in many cases [3]. The non-local nature of the transport phenomena must be considered due to long mean-free-paths of the heated electron species compared to the characteristic length of the plasma temperature variations. The shift in the physical models of plasmas must be reflected in the numerical treatment of the problem too. The high-order finite element methods present a favourable option. We have proposed such method recently [4] and continue in the effort towards better modelling and understanding of the non-local phenomena by means of numerical simulations.

References
[1] D. Batani, L. Antonelli, G. Folpini, Y. Maheut, L. Giuffrida, G. Malka, Ph. Nicolai, X. Ribeyre, M. Richetta, T. Levato, F. Baffigi, P. Koester, L. Labate, L.A. Gizzi, J. Nejdl, M. Sawicka, D. Margarone, A. Velyhan, M. Krus, O. Renner, M. Smid, E. Krousky, J. Skala, J. Ullschmied R. Dudzak, Ch. Spindloe, T. O'Dell, R.de Angelis, F. Consoliand T. Vinci, M. Rosinski, J. Badziak an T. Pisarczyk, Z. Kalinowska, T. Chodukowski, Y.J. Rhee, A. Marocchino, A. Schiavi, and S. Atzeni. Generation of high pressure shocks relevant to the shock-ignition intensity regime. Phys. Plasmas, 21:032710, 2014.
[2] M. Holec, J. Nikl, M. Vranic, and S. Weber. The effect of pre-plasma formation under nonlocal transport conditions for ultra-relativistic laser-plasma interaction. Plasma Physics and Controlled Fusion, 60(4):044019, 2018.
[3] A. V. Brantov and V. Yu. Bychenkov. Nonlocal transport in hot plasma. Part I. Plasma Physics Reports, 39(9):698­744, 2013.
[4] M. Holec, J. Nikl, and S. Weber. Nonlocal transport hydrodynamic model for laser heated plasmas. Physics of Plasmas, 25(3):032704, 2018.

Speaker: J. Nikl (EPS 2019)

774 P5.2012 Using the Bayes Inference Engine to study the deceleration-phase of Rayleigh-Taylor growth rates in laser-driven cylindrical implosions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2012.pdf

Hydrodynamic instabilities, such as the Rayleigh-Taylor (R.-T.) instability develop in high energy density, inertial confinement fusion (ICF) experiments. These instabilities degrade the implosion due to mixing of the fuel. We study R.-T. modes in ICF implosions in order to better understand how they evolve in time. To improve our data analysis, we use the Bayes Inference Engine (BIE). The BIE is a computational framework that takes an iterative forward modeling approach to perform statistical inference.
We use the BIE to create a parameterized model of these 2D implosions. This model accounts for blur, alignment and illumination. The parameters are optimized to obtain maximum likelihood estimates for the time-dependent amplitude of the R.-T. modes, the returned solution considers weighted statistical likelihood and prior information.
This technique has helped improve our ability to quantify uncertainties, establish sensible error bars and guide the refinement of our experimental techniques. When applied to our data analysis the BIE can be used to confirm the symmetry of the implosion and understand all asymmetries to be a result of parallax, as well as, improve our error bars and establish a more statistically significant model moving forward.

Work supported by the National Nuclear Security Administration, performed by Los Alamos National Laboratory, operated by Triad National Security, LLC, under contract 89233218CNA000001 LA-UR-19-21647

1. 1 K.M. Hanson and G.S. Cunningham, Maximum Entropy and Bayesian Methods, Springer, Dordrecht, pp. 125-134 (1996)

Speaker: C. Fiedler Kawaguchi (EPS 2019)

775 P5.2014 Prospects for Magnetic Indirect Drive Inertial Confinement Fusion

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2014.pdf

Experimental, theoretical, simulation, and technological advances over the past 30 years are motivating a reassessment of the Magnetic Indirect Drive (MID) approach to Inertial Confinement Fusion (ICF). In this concept,1,2 a radiation source drives a hohlraum to temperatures required to implode a capsule symmetrically and create a high (>200 MJ) neutron yield. The advances start with a new concept for a pulsed-power driver3 that creates high amounts of radiation that can be coupled into a hohlraum.1 The capsule uses a liquid layer of deuterium-tritium fuel instead of the conventional cryogenic layer of DT used in current experiments.4 The liquid-layer approach is inherently low convergence (convergence ratio of 12-20) so that hydrodynamic instabilities and symmetry issues are greatly reduced. Experiments at the National Ignition Facility (NIF) demonstrated the basic robustness of this approach5-8 Advances in target fabrication98 are creating higher quality capsules with the foam matrix needed to support the liquid DT. Using an indirect-drive hohlraum leverages ten years of experience at NIF using laser-driven hohlraums. This experience shows where capsule/hohlraum issues remain and where modeling gaps remain. We outline the main physics concerns of the MID approach. These include symmetry control, the very important issue of minimum case-to-capsule ratio (CCR),10 radiation coupling into the hohlraum, and pulse-shaping of the radiation drive.

References
1 T. W. L. Sanford, R. E. Olson, R. L. Bowers, et al., Phys. Rev. Lett. 83 5511 (1999).
2 R. E. Olson, G. A. Chandler, M. S. Derson, et al., Fusion Technology 35 260 (1999).
3 W. A. Stygar, et al., Physical Review Special Topics 18 110401 (2015).
4 R. E. Olson and R. J. Leeper, Phys. Plasmas 0 092705 (2013).
5 R. E. Olson, J. L. Kline, R. J. Leeper, A. B. Zylstra, et al., Phys. Rev. Lett. 117 245001 (2016).
6 A. B. Zylstra, S. A. Yi, B. M. Haines, R. E. Olson, et al., Phys. Plasmas 25 056304 (2018).
7 R. E. Olson, R. J. Leeper, S. H. Batha, et al., submitted to Nuclear Fusion (2019).
8 B. M. Haines, R. E. Olson, W. Sweet, S. A. Yi, et al., Phys. Plasmas 26 012727 (2019).
9 T. Braun, et al. Fusion SciSci. Technol. 73 229 (2016).
10 A. B. Zylstra, S. A. Yi, S. MacLaren, J. Kline, et al., Phys. Plasmas 25 102704 (2018).

Speaker: S.H. Batha (EPS 2019)

776 P5.2015 VISRAD 3-D target design and radiation simulation code

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2015.pdf

The 3-D view factor code VISRAD is widely used in designing HEDP experiments at major laser and pulsed-power facilities, including NIF, OMEGA, OMEGA-EP, ORION, LMJ, Z, and PLX. It simulates target designs by generating a 3-D grid of surface elements, utilizing a variety of 3-D primitives and surface removal algorithms, and can be used to compute the radiation flux throughout the surface element grid by computing element-to-element view factors and solving power balance equations. Target set-up and beam pointing are facilitated by allowing users to specify positions and angular orientations using a variety of coordinates systems (e.g., that of any laser beam, target component, or diagnostic port). Analytic modeling for laser beam spatial profiles for OMEGA DPPs and NIF CPPs is used to compute laser intensity profiles throughout the grid of surface elements. We will discuss recent improvements to the software package and plans for future developments.

Speaker: V.N. Golovkina (EPS 2019)

777 P5.2016 Experimental research of the plasma behavior in the key regions of ICF Hohlraum in SG-series laser facilities

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2016.pdf

Laser-driven high-Z hohlraum is used to provide intense x-ray radiation source for driving the capsule implosion in indirect-dirve inertial confinement fusion (ICF). With the campaigns of hohlraum energetics and implosion physics in NIF, the lack of advanced knowledge on laser-hohlraum coupling process has shown the complexity of hohlraum environment. Recently, several experiments have been planed and been done for the research of plasma behavior in the key regions of ICF hohlraum in Shenguang (SG) laser facilities. Under a laser intensity and width close to those of an ignition main pulse, the movement of a high-Z plasma bubble has been studied uing gas-filled open-end gold hohlraums. Under a quasi-2d environment, the plasmas evolution and the dynamic effect in different regions of the hohlraum, including around the LEH, in the gas, or in the bubble, have been preliminary understood by developing 4 Thomson scattering technique. Furthermore, the detailed mix state around the gold bubble-gas interface, which is the key region of the hohlraum, will be studied by a novel method in next step.

Speaker: Z. Li (EPS 2019)

778 P5.2017 Validation of radiation-hydrodynamic code DUED using high-precision OMEGA and NIF experiments on exploding pusher implosions

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2017.pdf

Exploding pusher targets, i.e. gas-filled, large aspect-ratio shells, driven by a strong lasergenerated shock, are widely used as pulsed sources of neutrons and fast charged particles. Due to small convergence ratio, exploding pushers are little affected by fluid instabilities and are weakly sensitive to irradiation nonuniformities. Development of high space- and time-resolution neutron and X-ray diagnostics allows for detailed comparison of experimental data with simulations, and for validation of simulation models. In particular, we refer to simulations with the DUED code of a series of direct-drive experiments performed at the OMEGA laser (reported in Refs [1, 2], and others currently being analyzed) and two indirect-drive NIF shots [3]. Comparisons provided evidence for the transition from a nearly fluid behaviour to a kinetic one, as the implosion Knudsen number Kn (ratio of ion mean-free path to compressed gas radius) becomes comparable or larger than one [1]. Agreement between predicted and measured observables worsens as Kn grows. Ion separation effects occur also for Kn < 1, i.e. in a quasi-hydrodynamic regime [2]. Here we show that in the quasi-hydrodynamic limit simulations reproduce DD and DT reaction yields, bang times, burn-widths, burn radii, compressed fuel radius, reaction-averaged ion temperatures. (For gas fills also containing 3He, the delay between D-3He bang time, instead, is not predicted.) Instrumental to the achievement of such an agreement was the introduction of ion viscosity, of a smooth transition between ion viscosity and artificial viscosity, of an appropriate limiter for momentum flux, of bulk fluid motion in the Monte Carlo neutron synthetic diagnostics. The sensitivity of the results to the shell opacity model has also been tested.

Work supported in part by Eurofusion projects AWP17-ENR-IFE-CEA-01 and ENR-IFE19.CEA-01.

References
[1] M. J. Rosenberg et al., Phys. Rev. Lett. 112, 185001 (2014)
[2] H. Sio et al., Phys. Rev. Lett. 122, 035001 (2019)
[3] S. Le Pape et al., Phys. Rev. Lett. 112, 225002 (2014)

Speaker: S. Atzeni (EPS 2019)

779 P5.2018 A new MJ-class pulsed-power facility for HEDP experiments

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2018.pdf

We describe a newly commissioned pulsed-power machine, "M3", for driving high energy density physics experiments at First Light Fusion. 2.5 MJ of stored electrical energy is discharged in 2 us, generating currents of up to 14 MA into a low-inductance load. The primary purpose of M3 is to launch high velocity projectiles for driving shocks into targets. The machine architecture consists of a 125 uF bipolar capacitor bank, with a maximum relative charge of 200 kV. The capacitors discharge via 92 multi-channel ball gap switches into 6 parallel plate transmission lines, which feed the current into the vacuum target chamber. Machine current is monitored with several in-fibre Faraday rotation probes. The diagnostic suite consists of imaging and streaked VISAR, laser backlighting and selfemission imaging onto fast optical framing and streak cameras, and optical and IR pyrometry. We also present data on initial M3 experiments that have been focussed on projectile launch techniques.

Speaker: G.C. Burdiak (EPS 2019)

780 P5.2019 A study of beam hosing in different regimes

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2019.pdf

Beam hosing is a transverse beam-plasma instability that causes the centroid of a beam to oscillate with increasing amplitude and can therefore lead to the disruption of the beam as it propagates in plasma [1, 2, 3]. This instability can jeopardize those novel accelerator concepts which are based on plasma wakefields driven by long particle beams (where long is with respect to the plasma skin depth). The AWAKE experiment, for example, has recently demonstrated one such concept using a long proton beam as the driver [4]. Besides the successful acceleration of injected electrons, however, the experiment also enabled the observation of short-wavelength (at the plasma wavelength pe) beam hosing under particular experimental conditions [5].
Simulation results indicate that the hosing instability can be suppressed by seeding the selfmodulation instability [6] (a competing transverse instability) at a high enough level [6, 7] in the linear plasma wakefield excitation regime. It is not clear, however, whether some slowergrowing, longer-wavelength modes of hosing (which find analogy in long-wavelength laser hosing [8]) are as effectively suppressed.
Using particle-in-cell simulations in conjunction with experimental data, this work will show how beam hosing can be observed in two different regimes: one where this instability develops on its own, and one where it develops while coupling to the self-modulation instability [9]. In addition, this work will investigate the long-wavelength regime of beam hosing through theory and simulations.

References
[1] E. P. Lee, Phys. Fluids 21, 1327 (1978)
[2] H. L. Buchanan, Phys. Fluids 30, 221 (1987)
[3] D. H. Whittum, W. M. Sharp, S. S. Yu, M. Lampe, and G. Joyce, Phys. Rev. Lett. 67, 991 (1991)
[4] E. Adli, et al. (the AWAKE collaboration), Nature 561, 363-367 (2018)
[5] M. Hüther, et al. (the AWAKE collaboration) (private communication)
[6] N. Kumar, A. Pukhov, and K. V. Lotov, Phys. Rev. Lett. 104, 255003 (2010)
[7] J. Vieira, W. B. Mori, and P. Muggli, Phys. Rev. Lett. 112, 205001 (2014)
[8] B. J. Duda, R. G. Hemker, K. C. Tzeng, and W. B. Mori, Phys. Rev. Lett. 83, 1978 (1999)
[9] C. B. Schroeder, C. Benedetti, E. Esarey, F. J. Grüner, and W. P. Leemans, Phys. Rev. E 86, 026402 (2013)

Speaker: M. Moreira (EPS 2019)

781 P5.2020 Parametric tolerance study of trojan horse plasma wakefield acceleration scheme

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2020.pdf

A promising scheme for plasma wakefield acceleration is the hybrid plasma acceleration mechanism, which is experimentally connected to world-wide programs at various accelerator facilities. This scheme may lead to extremely high quality electron bunches, which can be used to drive ultrabright light sources such as free electron lasers. The big challenge for plasma acceleration is to produce electron bunches with high quality in terms of low emittance, energy spread and high brightness. To overcome this challenge, the Trojan Horse scheme [1,2,3,4] is used for production of designer electron beams.
This work explores the Trojan Horse mechanism in a parametric study by variation of the injector laser pulse by intensity, spot size and relative spatiotemporal synchronization and alignment. These parameters define output electron witness beam parameters and its quality. This sensitivity study shows a high robustness of the scheme, which is promising for a wider key prospect of the approach, namely the development of compact plasma accelerators to produce electron beams with unprecedented emittance and brightness in order to power freeelectron lasers.

References
[1] B. Hidding, G. Pretzler, J. B. Rosenzweig, T. Königstein, D. Schiller, and D. L. Bruhwiler, Phys. Rev. Lett. 108, 035 001(2012).
[2] Y. Xi, B. Hidding, D. Bruhwiler, G. Pretzler, and J. B. Rosenzweig, Phys. Rev. ST Accel. Beams 16, 031 303(2013).
[3] B. Hidding, G. Manahan, O. Karger, A. Knetsch, G. Wittig, D. Jaroszynski, et al., Journal of Physics B: Atomic,Molecular and Optical Physics 47, 234010 (2014).
[4] G.G. Manahan, A.F. Habib, P. Scherkl, et al., Nat. Commun. 8, 15705 (2017).

Speaker: R.A. Altuijri (EPS 2019)

782 P5.2021 Genetic algorithm controlled 2D laser wakefield acceleration simulations

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2021.pdf

One of the most promising technologies to form the next generation of compact particle accelerators is plasma acceleration, providing accelerating distances up to 3 orders of magnitude shorter than conventional accelerators. Recent progress has been tremendous but improving beam quality still remains as a grand-challenge in the field, as numerical simulations remain the only way to capture all self-consistent dynamics of the laser and plasma. Beam quality often depends on specific aspects of the plasma density and laser pulse profiles, which cannot be retrieved by purely analytical models alone, thus requiring extensive parameter scans, which can be very expensive computationally. Here we show a technique that can be used to reduce the computing time required to determine the optimal conditions to control and optimize specific properties of the accelerated beams.
Recent experiments employed genetic algorithms to control plasma-based accelerators [1]. Here, instead, we will employ this technique to optimize accelerators from laser wakefield simulations. We implemented a genetic algorithm in ZPIC, a fully relativistic particle-in-cell educational code [2]. The algorithm is fully automated, launching several simulations in parallel. Some studies were already performed in 1D [3], but here we focus on the results from two-dimensional simulations. Specifically, we considered the role of aberrations on the laser driver wavefronts, parametrized by Zernike polynomials. We present optimization studies of laser plasma accelerators, towards beam energy control (more particles in a predetermined energy range), higher radiation production and shorter acceleration lengths. In each of these cases, we found the optimized beam to be significantly different from a regular Gaussian beam, even when optimizing the latter for focus and phase. The increase in the different optimization problems ranged from 10% in the acceleration minimization to 30% in radiation production.

References
[1] Z.-H. He, B. Hou, V. Levailly, J. Nees, K. Krushelnick and A. Thomas, Nature communications, 6 (2015)
[2] https://github.com/zambzamb/zpic
[3] B. Malaca, J. Vieira, R. Fonseca, 45th EPS Conference on Plasma Physics Proceedings (2018)

Speaker: B.F. Malaca (EPS 2019)

783 P5.2022 OSIRIS 4.0: A state of the art framework for kinetic plasma simulations

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2022.pdf

The OSIRIS [1] Electromagnetic particle-in-cell (EM-PIC) code has been widely used in the numerical modeling of many astrophysical and laboratory scenarios. Since the release of version 4.0, the framework has been continuously developed to support multiple hardware architectures, and to extend the base algorithm, allowing the code to address an increasingly wider range of problems, all from a common code base. In this work we give an overview of the current status of the OSIRIS framework, describing the multiple simulation modes available (Quasi-3D, PGC, QED, Shearing and spherical geometries, etc.), and the multiple hardware configurations supported (ARM, KNL, CUDA, etc.). We will also focus on new features being introduced into the code, such as spectral and hybrid field solvers, and alternative charge conservation schemes. Finally, we will discuss some of the software engineering aspects allowing for the development and maintenance of a large code base, and the collaboration of a continuously growing development team.
This work was partially supported by Fundaação para a Ciência e Tecnologia (FCT), Portugal, through grant no. PTDC/FIS-PLA/2940/2014.

Reference
[1] R. A. Fonseca et al., Lecture Notes in Computer Science 2331, 342-351 (2002)

Speaker: R.A. Fonseca (EPS 2019)

784 P5.2023 The ZPIC educational code suite

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.2023.pdf

Particle-in-Cell (PIC) codes are used in almost all areas of plasma physics, such as fusion energy research, plasma accelerators, space physics, ion propulsion, and plasma processing, and many other areas. In this work, we present the recent developments of the ZPIC educational code suite, a new initiative to foster training in plasma physics using computer simulations. ZPIC includes a set 1D/2D fully relativistic electromagnetic PIC codes (with both finite difference and spectral field solvers), as well as 1D electrostatic. These codes are completely self-contained and require only a standard laptop/desktop computer with a C99 compiler to be run. The code suite also includes Python interfaces for all the codes, allowing for simulations to be totally controlled from within this environment. Using this feature we have developed a set of Jupyter (Python) notebooks with well-documented example problems, that can be used to illustrate several textbook and advanced plasma mechanisms and including instructions for parameter space exploration. We also invite contributions to this repository of test problems that will be made freely available to the community provided the notebooks comply with the format defined by the ZPIC team.
The code suite is freely available and hosted on GitHub at: https://github.com/zambzamb/zpic

Speaker: R. Calado (EPS 2019)

785 P5.3001 Studies on the plasma parameters and electron heating mechanism in RF biased inductive discharges

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3001.pdf

Studies on the plasma parameters and electron heating mechanism were investigated in the RF biased inductively coupled plasmas (ICPs), which are widely used and studied in various industrial plasma processes and laboratory research, by using careful plasma diagnostic techniques. In RF biased ICP (ICP+CCP), as the RF bias power was increased, plasma density increased at the high ICP power and decreased at the low ICP power. This change in the plasma density suggests that the RF bias affects the plasma parameters, as well as the self-bias voltage and can be explained by the global model. Plasma uniformity was changed by the non-uniform power deposition of the RF bias and the uniformity was enhanced by the RF bias power. Electron heating mechanism by the ICP (inductive field) and the RF bias (capacitive field) was investigated. It was observed that with small RF bias powers in the ICP, the EEDF evolved from bi-Maxwellian distribution to Maxwellian distribution by an enhanced plasma bulk heating, and the collisionless sheath heating was weak. In the capacitive RF bias dominant regime, however, high energy electrons by the RF bias were heated on the EEDFs in the presence of the ICP and the collisionless heating mechanism of the high energy electrons transited from the anomalous skin effect by the ICP to the capacitive coupled collisionless heating by the electron bounce resonance in the RF biased ICP. As a study on the observation of the collisionless heating by the inductive field, the EEDFs with applying the ICP power were measured in the CCP. A significant heating of low energy electrons was seen in the E mode and it indicates that collisionless heating in the skin layer is an important electron heating mechanism of low pressure ICP, even when the discharge is in E mode. This Experiment was also preformed in the electro-negative gas (Ar/O2) and it was found that the Ohmic heating is inefficient with O2 gas pressure due to the decreased bulk electric field by the negative ions. The combined effect of collisionless heating by capacitive and induced electric fields was also investigated in the Ar/O2 RF biased ICP.

Speaker: H. Lee (EPS 2019)

786 P5.3002 Study of As spectral lines for discharge diagnostic purpose

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3002.pdf

This work is devoted to the diagnostic of high frequency electrodeless light sources (HFEDL) for their use in high precision atomic absorption analyzers. The arsenic discharge is studied. The diagnostic technique consists of the line profiles measurements by means of Fourier transform spectrometer and Jobin Yvon SPEX 1000M spectrometer with further deconvolution and real (without instrumental function) profile obtaining by means of ill posed inverse task solution[1]. Special attention is devoted to the 189.042nm; 193.7nm and 197.262nm of As spectralline shapes. The spectral lines were analyzed in detail in dependence on the discharge power.
Within the framework of this work the influence of the instrumental function on the form and FWHM(full width at half maximum) of the lines profiles and were analyzed. The neglecting the instrument function, in the case of low pressure or cold plasma when instrument function is on the same order that experimental profile, gives huge error for the FWHM estimation and consequently for discharge temperature estimation.[2]

Acknowledgements
The research was partly supported by project ,,Atomic physics, optical technology and medical physics (LU IAPS) "

References
[1] G. Revalde, N. Zorina, A. Skudra, Multicomponent line profile restoring by means of illposed inverse task solution, Journal of Physics: Conference Series, Vol. 810(1), Article number 012056, 2017
[2] N. Zorina, Deconvolution of the spectral line profiles for the plasma temperature estimation, Nuclear Inst. and Methods in Physics Research A 623 (2010) p. 763-765

Speaker: N. Zorina (EPS 2019)

787 P5.3003 Study of particle flow generated by 70-kV 30-ns vacuum surface flashover

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3003.pdf

In this work we study plasma beams generated by 70-kV 30-ns vacuum surface flashover discharge. The aim of the work was to compare parameters of particle flows at different values of discharge current and reveal the dependence of particle flow power on current. We used a pulsed generator with coaxial glycerol-filled pulse-forming line. Maximum voltage is 70 kV, width of current first half wave is 30 ns. We used polymethyl methacrylate (PMMA), polytetrafluorethylene (PTFE) and polyethylene (PE) as samples. Also, potassium chloride (KCl) single crystals were used as model objects. We measured full energy of the plasma flow, ionic current, velocity of ions, and thrust at 2 values of discharge current (3 and 5 kA). Alteration of current was performed by the redesigning of the forming line. We obtained plasma bunches with energy up to 0.1 J for PE, PTFE and KCl at frequency of 100 pps. We show that as the discharge current increases, the ions velocity doesn't change significantly. Velocity of ion component of the plasma beam for both cases is up to 500 km/s. Meanwhile, the increase of full energy of the plasma flow is mainly due to increase in total mass of the bunch of particles. Average mass velocity of ions was calculated from values of thrust. Average velocity increased twice for PMMA and 1.5 times for KCl as the current was raised up to 5 kA.

Speaker: I.F. Punanov (EPS 2019)

788 P5.3004 Suppression of the ion drag force in strongly magnetised plasmas

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3004.pdf

The ion drag force is one of the dominant forces determining the motion of dust particles in tokamak edge plasmas. We might expect that, in the same way that current onto a dust grain is suppressed by strong magnetic fields [1], the momentum flux will be also. However, the ion drag models employed by dust transport codes are magnetic field independent [2]. We use the monte carlo dust-plasma interaction code DiMPl [3] to consider the case of a dust particle immersed in a plasma flowing parallel to a magnetic field, and evaluate the ion drag force at different magnetic field strengths. Preliminary results show significant supression at fields for which the ion gyroradius is comparable to the dust radius, as shown in Figure 1.
Characterisation of the dependence of the drag force on magnetic field strength for a range of flow speeds, dust radii, and dust potentials is presented. Comparison is made with the widely-employed `hybrid' ion drag model of Khrapak et al. [4], along with semi-analytic models of collection and deflection of charged particles by a dust grain in a magnetic field.

References
[1] J. Rubinstein and J. G. Laframboise (1982). Theory of a spherical probe in a collisionless magnetoplasma. Physics of Fluids, 25(7), 1174âA ¸S1182. https://doi.org/10.1063/1.863886
[2] A. Jarvinen, M. Sertoli, M. Bacharis, A. Uccello, G. Matthews, E. Lazzaro, and J. Flanagan (2016). Comparison of dust transport modelling codes in a tokamak plasma. Physics of Plasmas, 23(10), 102506.
[3] L. Simons, J. T. Holgate, D. M. Thomas and M. Coppins, Floating potential of spherical probes in weakly collisional magnetised plasmas (in preparation).
[4] S. A. Khrapak, A. V. Ivlev, S. K. Zhdanov, and G. E. Morfill (2005). Hybrid approach to the ion drag force. Physics of Plasmas, 12(4), 1-8. https://doi.org/10.1063/1.1867995

Speaker: L.T. James (EPS 2019)

789 P5.3005 Surface plastic of micro-scale tungsten powder for additive manufacturing by thermal plasmas processing

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3005.pdf

The surface of tungsten powder with irregular shape was treated by thermal plasmas and the thermodynamics and dynamics behavior of powder particles in the plasma was monitored by the particle online monitor of DPV2000. The morphologies of the plasma plastic powders was observed by Scanning Electron Microscope (SEM). The results show that the temperature and velocity of tungsten particles decreased with the increasing of axial distance away out of the plasma generator. The morphology of that presented a regular spherical shape and its interior was densified after plasma plastic processing.

This work is supported by National Natural Science Foundation of China (Nos. 11805058, 11535003) and Sichuan Science and Technology Program (No. 2019YFG0444).

References
[1] Kobayashi N, Kawakami Y, Kamada K, et al. Spherical submicron-size copper powders coagulated from a vapor phase in RF induction thermal plasma [J]. Thin Solid Films, 2008, 516(13): 4402-4406.
[2] Liu X p, Wang K s, Hu P, et al. Spheroidization of molybdenum powder by radio frequency thermal plasma [J]. Int. J. Miner. Metall. Mater., 2015, 22(11): 1212-1218.
[3] Wang J J, Hao J J, Guo Z M, et al. Preparation of spherical tungsten and titanium powders by RF induction
plasma processing [J]. Rare Met., 2015, 34(6): 431-435.

Speaker: L. Chen (EPS 2019)

790 P5.3006 Temperature regimes of plasma sputtering cell for deactivation of nuclear power plants constructions

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3006.pdf

One of the current nuclear industry problems is irradiated reactor graphite deactivation during decommissioning of nuclear power plants, as well as findings of effective method for decontaminating of nuclear power equipment internal surfaces sedimented with radionuclides from reactor water during operation. Important sub-task in this way is removal of the 14C isotope (half-life of 5730 years) from irradiated graphite. Experimental studies of the spatial localization of 14C isotope inside of the irradiated graphite balk [1] showed that considerable amounts of 14C isotope may be concentrated at or in close vicinity under the bulk surface. We propose a new approach for the surface decontamination of irradiated reactor graphite or nuclear power plant structures: nano- and micro-sized radioactive contaminants by sputtering in inert gas plasma discharge and diffusively transferred to the metal collector, the liquid radioactive wastes are not formed, and the radionuclides to be removed are condensed in a compact solid form [2]. The direct current plasma discharge is ignited in argon at a pressure of P ~ 0.1-1 bar, collector flat tantalum plate (as anode of 1 mm thick covered with 10 mm ceramics) is set at 1 mm above the flat surface of the graphite bulk cathode. We have calculated the temperature distribution in three media: graphite cathode thickness 60 cm), argon plasma (1 mm), anode (10 mm). The Table shows the surface temperature of the cathode TK and the anode TA, depending on the discharge input power density and equivalent current density at 600V discharge voltage. The external boundary surfaces of said anode and cathode are cooled and maintained at 300K.

Acknowledgement
The work was supported by the RFBR grant No.18-32-00679- mol_a

1. LaBrier, Daniel, Dunzik-Gougar, Mary Lou, Journal of Nuclear Materials, v. 448, I. 1-3, p. 113-120, 2014
2. A.S. Petrovskaya, A.B. Tsyganov, A.Yu. Kladkov, S.V. Surov, M.R. Stakhiv, Surface Deactivation of the Nuclear Power Plants Constructions by a New Plasma Method, IEEE International Conference on Electrical Engineering and Photonics 2018, https://ieeexplore.ieee.org/document/8564400

Speaker: A. Petrovskaya (EPS 2019)

791 P5.3007 The Development of Test-Device based on Surface Discharge for Imitation of Erosion Monitoring Process in the Fusion Reactors

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3007.pdf

The implementation of thermonuclear technology requires the development and formation of the reliable, long-lived nuclear fusion systems that will be able to guarantee the safe operation. Meanwhile, interaction plasma with divertor and the reactor first-wall elements leads to damage of their surfaces via erosion process and to generation dusty in the reactor zone [1]. The dust accumulation in reactor can cause an explosion. Thus, it is necessary to study such type process in order to limit undesirable implications.
To check the erosion and deposition processes in the reactor, a non-contact method with high spatial resolution and high accuracy in geometry measurements is required. According to [2], these measurements can be realized by using means dual wavelength speckle interferometry providing record of topogram. The method works with optical rough surfaces and has good precision (100 nm). Although high-quality topogram might be obtained by the approach, there are a lot of factors that negatively influence on the recording process. Therefore, to develop a reliable interferometer for real conditions, we have to spend a lot of time for hardware debugging. Thus, to shorten a design period, it is necessary to represent erosion in reactor via imitation. In order to inspect erosion process under normal condition in air, a gas-discharge test-device based on the removable electrode systems with the colliding surface discharges [3] was proposed. In contrast to [3], the electrode system has a high-resistive, diffusely reflecting coating on a fiber-glass plastic, dielectric barrier. The presence of diffusely reflecting coating has two consequences. Firstly, the coating provides registration of quality speckle-interferograms. Secondly, the colliding surface discharges are excited in the porous medium of the reflecting layer. In experiment, the surface discharge due to heating of electrode system evaporates the bonding medium of fiberglass plastic. As a result, the erosion zone with area of about several square centimeters and depth from ten micron to 0.1 mm forms. So, the test-device allowed us to observe both thermal deformation of electrode system and surface erosion of dielectric barrier. The device may be useful for testing of digital speckle-interferometers in the study of plasma-wall interaction.

References
[1] Coenen J.W. et al. (2017). Nuclear Materials and Energy, V.12 - P.307-312.
[2] Franson M. (1980). Optics of speckles. Moscow: Mir.[In Russian]
[3] Ivchenko A.V., et al. (2012). Europhysics Conference Abstracts, V.36F-4p

Speaker: A.V. Ivchenko (EPS 2019)

792 P5.3008 The spectrum correction filter for Deuterium-Halogen Light by Reactive Electron Beam Evaporation with Ion-Assisted Deposition

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3008.pdf

This study describes the specification, design and fabrication technology of the modified source spectrum filter for the combination of deuterium and halogen lamps light source system. The filter is modified and eliminated. The resulting Alpha deuterium line produces a smoother spectrum of light sources over a wide range of wavelengths. The filter will be simulated to obtain a better tolerance for film thickness, and the multilayer film coated by ion source assisted electron beam evaporation for processing, with automatic optical monitoring system to control the thickness, and control the each film layer thickness precisely. The corresponding optical and mechanical properties of multilayer optical thin film were investigated by in-situ optical monitoring, spectrometer, ellipsometry, and Scanning Electron Microscope(SEM).

Speaker: H. Chen (EPS 2019)

793 P5.3009 The thermodynamic and transport properties of metals in warm dense matter regime

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3009.pdf

In this work, using the chemical model of the atomic plasma "3+" proposed in [1], we present a joint calculation of the composition, equation of state and transport properties of metal vapors in warm dense matter regime within the unified approach The Helmholtz free energy of dense atomic metal vapors describe the mixture of free non-ideal electrons and ions and atoms immersed in jellium. Given the presence of jellium, we named this model the "3+" model. Jellium is constituted by tails of wave functions of bound electrons. Jellium provides the appearance of collective quantum energy--cohesion. Jellium does not change the balance and the electroneutrality equations. The main feature of jellium is its collectivity and the ability to conduct the current. The interaction between free charges is described in nearest neighbor approximation (NNA). We show that the corrections for the charge-charge interaction and interatomic interaction compensate each other by calculating the composition and the equation of state. The equation of state and electrical conductivity were calculated in warm dense matter regime for various group of metals: from low-melting posttransition (Al, Pb, Ga) to refractory metals (Be, Mo, Ta, W). The obtained results are compared with data of physical and numerical experiments [2-5]. Calculations in the framework of the "3+" model show a good agreement with both physical and numerical experiments. We calculated also the critical point parameters (density, temperature, pressure and electrical conductivity) for various groups of metals.

References
1. A.L. Khomkin, A.S. Shumikhin, J. Exp. Theor. Phys. 124, 1001 (2017).
2. A.W. DeSilva, A.D. Rakhel, Contrib. Plasma Physics 45, 236 (2005).
3. M. French, T.R. Mattsson, Phys. Rev. B 90, 165113 (2014). 4. A.M. Kondratyev, V.N. Korobenko, A.D. Rakhel, JETP 127, 1074 (2018).
5. D. Li et al, Sci. Rep. 4, 5898 (2015).

Speaker: A. Shumikhin (EPS 2019)

794 P5.3010 Theoretical and experimental study of THz discharge threshold in various gases.

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3010.pdf

In spite of the well-studied microwave discharge and laser, the discharge in the beams of the THz frequency band remains practically unexplored, including the gas breakdown threshold. Nowadays, there is a significant progress in the study of the THz discharge, associated primarily with the development of sources of the high-power coherent radiation in the terahertz and sub-terahertz range -- gyrotrons and free electron lasers. The result of theoretical and experimental research of breakdown by powerful THz and subTHz radiation of gyrotron in various gases (Ar, Kr, Xe, N2, O2, Air) are presented in this work.
Experimental data were carried out in two setups. In both cases focused beam of THz emission used. In the first setup heating radiation were provided by gyrotron working in pulsed regime and generating radiation with a frequency of 670 GHz with power of 40 kW and maximum radiation intensity 10 MW/cm^2. In the second setup we used gyrotron with 250 GHz radiation frequency with power up to 250 kW and maximum intensity 5MW/cm^2. Discharge was studied in various gases (both for noble and molecular) in pressure range from 1 to 1500 Torr.
Calculation of breakdown threshold in heavy gases were based on Raizer discharge theory [1]. So we assumed that intensity of electrical field does not affect on electron diffusion and determined only by gas pressure. Calculation of breakdown electrical field for molecular gases (Air, N2) provided by using previous measured and calculated values of ionization frequency and diffusion coefficient which were carried out for static electric fields [2] by replacing it to effective electric field. In calculation we supposed that electrons were heated by numerous collisions. In case of electronegative gases the electron detachment were also taken into account. In conclusion the experimental and theoretical results were compared.

1. A. I. Vyskrebentsev, Yu. P. Raizer, Journal of Applied Mechanics and Technical Physics, 14, I, pp 32-38 (1973).
2. K.H. Wagner ," Ionization, Electron-Attachment, - Detachment, and Charge-Transfer in Oxygen and Air", Z. Physik 241,258-270 (1971)

Speaker: A. Veselov (EPS 2019)

795 P5.3011 Time dependent kinetic flux limiters during ELMs in ITER Scrape-Off-Layer

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3011.pdf

The divertor targets in tokamaks are constantly bombarded with high-energy neutral and charged particles and such violent events can pose a serious threat to the long-time resistance of the divertor materials. The wall erosion, caused by the bombardment, releases impurities, that migrate towards the bulk plasma and due to the effects, the plasma state is deteriorated [1]. In order to keep the limits of wall erosion, it is important to estimate the plasma characteristics in the Scrape-off Layer (SOL) i.e the region outside the last closed magnetic surface (separatrix). This is a complex region where many processes such as low collisionality, geometrical effects, physical and chemical reactions, can cause deviation of the parallel transport from the classical one during time. However, the transient heat loads such as ELMs (Edge-Localized modes) occur in tokamak edge during H-mode confinement lead to a significant loss of stored plasma energy [1]. Once the ELM-driven plasma pulse has crossed the magnetic separatrix, it travels mainly parallel to the magnetic field lines and ends up hitting the divertor plate.
Most of the studies are focused on the problem of the transition between a hot plasma and a material surface. The effects caused by the wall erosion represent the boundary conditions in regions of plasma-surface interaction and the limiting expressions for the parallel heat flux and viscosity. The formulation of boundary conditions (BCs) and their time dependence is an interesting and important task for plasma edge studies.
The aim of this work is to derive time-dependent BCs at the PWT of Type I ELMs state from the kinetic simulation in ITER tokamak. This contribution describes the first results of efforts to address this issue for ITER simulations under high performance conditions using the 1D3V electrostatic parallel Particle-in-Cell (PIC) code BIT1 [2]. As a first approximation plasmasurface interaction processes are not included in this model. The burning plasma conditions correspond to the ITER Q = 10, 15 MA baseline at q95 = 3, for which the poloidal length of the 1D SOL is 20 m from inner to outer target. Typical upstream separatrix parameters of ne ~ 3 - 5 1e^19 m^-3, Te ~ 100 - 150 eV and Ti ~ 200 - 300 eV are assumed. Inclined magnetic fields at the targets of (~5º) are included, as are the particle collisions, with a total of 3.4. 10^5 poloidal grid cells giving shortening factors of 20. Secondary electron emission at the tungsten targets is neglected. In the first instance, a SOL flux tube just outside the separatrix is considered. A typical simulation requires up to 60 days running massively parallel 11522304 cores of the EU Marconi super-computer. The duration of the ELM pulse is taken to be between 100-200 µs. In a later stage of the work, these will be used as boundary conditions for calculations of ELM target heat loads using the SOLPS-ITER [3]code.

References
[1] D. Tskhakaya and S. Kuhn, Contrib. Plasma Phys., 44, 5-6 (564-570), (2004);
[2] D. Tskhakaya et al., Plasma Phys. Control. Fusion, 59, 114001 (19pp), (2017);
[3] X. Bonnin et al., Plasma and Fusion Research, 11, 1403102, (2016).

Speaker: I. Vasileska (EPS 2019)

796 P5.3012 Tomographic reconstruction of the visible emission of NIO1 negative ion beam

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3012.pdf

Neutral beam injectors (NBIs) are one of the most important additional heating devices both in present and in future nuclear fusion experiments. In order to heat the plasma at the high temperatures required, several critical aspects need to be fulfilled in the design of future NBI. In particular, one issue is the maximization of the spatial uniformity of the extracted beam, which is a strict requirement for ITER NBI [1]. This information can be achieved by the tomographic reconstruction of the beam emission profile, using a sufficient number of suitably arranged cameras.
The aim of this contribution is to present the tomographic diagnostic of the extracted beam of the NIO1 experiment [2], which is a small-size radio-frequency driven negative ion source. The tomographic system is composed of three visible cameras and the inversion is obtained by the simultaneous algebraic reconstruction technique [3]. The surface of the beam cross-section is divided into pixels and the employed algorithm reconstructs the emissivity profile of each pixel. The reconstruction of the experimental data is capable of showing the 3x3 matrix of the extracted beamlets in different experimental conditions using a 40x40 pixel matrix. Using the information collected by this non-invasive diagnostic, it is possible to characterize the main beam properties, such as the beam uniformity and aiming. Moreover, a correlation between the source physics and the extracted beam behaviour is performed.
Furthermore, an estimation of the divergence is achieved by reconstructing the beam profile at different positions along its propagation direction.

References
[1] R.S. Hemsworth, Overview of the design of the ITER heating neutral beam injectors, New J. Phys., 19, 025005, doi:10.1088/1367-2630/19/2/025005 (2017).
[2] M. Cavenago et al., Improvements of the versatile multiaperture negative ion source NIO1, AIP Conference Proceedings 1869, 030007, doi:10.1063/1.4995727 (2017).
[3] M. Brombin et al., The tomographic diagnostic of ITER neutral beam injector, Nucl. Fusion 53, 053009, doi:10.1088/0029-5515/53/5/053009 (2013).

Speaker: M. Ugoletti (EPS 2019)

797 P5.3013 Towards a universal collision-free sheath solution with warm ions

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3013.pdf

Speaker: S. Kuhn (EPS 2019)

798 P5.3014 Transport properties and phase separation in binary dusty plasmas under microgravity

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3014.pdf

Dusty plasmas typically contain one species of monodisperse dust particles. Experiments under microgravity conditions allow to study the dynamics of individual particles in three dimensionally extended systems. Adding a second species of monodisperse particles of different size allows to study phase separation processes. Such binary systems exhibit phase separation even for small relative size disparities of about 3%. There, fluorescent particles have been used for one of the species. A video microscopy setup consisting of two cameras equipped with appropriate filters then allows to distinguish between the species despite of their small size disparity. A pair of example images is shown in fig. 1. The time between the injection of the mixed particles into the plasma and their complete separation is of the order of 10 s. As it is possible to track individual particles, the particle flux J can be obtained and the dynamics of the phase separation process can be studied. The diffusion coefficient D is calculated according to Fick's first law J=−D∇n, where n is the particle number density. The particle species separate with about 0.2 mm/s typically, whereas the particles also perform vortex-like flows on the order of 1 mm/s. Therefore, strategies have to be found to separate these two effects. Furthermore, the presented measurements were performed on parabolic flights and particle motion caused by residual gravity must be taken into account. In this contribution, different data analysis approaches are shown. This work was financially supported by DLR under grant no. 50WM1638.
Figure 1: Inverted snapshot of a cloud of particles with diameters of 6.84 and 7.12 microns, respectively, during the
phase separation process. Camera 1 observes all particles while camera 2 observes only the larger particles.

Speaker: S. Schütt (EPS 2019)

799 P5.3015 Vibrational excitation of the electronic ground state of H2 via electron-impact excitation and radiative decay

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3015.pdf

Electron-impact excitation of the singlet states of H2 will either lead to dissociation through the excited singlet spectrum, or radiative decays to the vibrational levels of the ground electronic state. Decays to bound levels are one of the dominant processes by which vibrationally-excited H2 is formed in plasmas, which is of considerable importance as excitation cross sections depend strongly on the initial vibrational state of the molecule. Cascades to continuum levels, on the other hand, are an important process for dissociation of H2.
As with many vibrationally-dependent processes in e-H2 scattering, the previously available theoretical data has been almost entirely produced using the impact-parameter method, which is known to be inaccurate except at high incident energies [1]. The present calculations [2], which have been performed using the adiabatic-nuclei convergent closecoupling method, are a significant improvement in accuracy over the previous theoretical data.
In Fig. 1 we present the cross sections for electron-impact excitation and radiative decay to the bound and continuum (dissociative) vibrational levels from all vi = 0–14 initial vibrational levels of H2. There is a strong dependence on the initial vibrational state, particularly for the decays leading to dissociation, where there is a significant enhancement in the cross section for scattering on the higher levels.

References
[1] R. Celiberto et al, At. Data Nucl. Data Tables 77, 161 (2001)
[2] L. H. Scarlett et al, Plasma Sources Sci. Technol. 28, 025004 (2019)

Speaker: D. Fursa (EPS 2019)

800 P5.3016 Visualization of dissociative recombination of positive ions in surface dielectric barrier discharge

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3016.pdf

To understand dissociative recombination (DR) of positive ions at plasma-metallic walls is a key to control plasmas in fusion edge plasma, material processing and plasma bio-medicine. Especially, a product of DR would generate ozone (O3) as both positive effects (sterilization of germs) and negative effects (toxic to sensitive organs of human being) in plasma bio-medicine. DR has been verified in surface dielectric barrier discharge (SDBD) plasma generated by a sputtered-type flexible copper clad laminates (FCCL) Kapton ENA with thickness 25 and 150 m, thickness of exposed electrode = 2 and 8.6 μm for the exposed electrode peak to peak voltage of 5 kV_pp and frequency of 16 kHz. An isotropic undercutting was observed by focused ion beam-scanning electron microscope (FIB-SEM), which seems to be caused by SDBD plasma etching on exposed metallic cathode surface.

Speaker: I. Park (EPS 2019)

801 P5.3018 Voids in plasmas containing interacting variable charge dust grains

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3018.pdf

A nonlinear model of void formation is proposed that includes the dust grain charge variation along with the grain-grain interaction and the effect of neutral density. It is found that the extension of the void decreases if the dust particulate charge is taken into account. Moreover, for bigger dust grains, it is seen that the wave-like structure recedes when charge variation is dealt with. Furthermore, as the grain-grain distance is inversely proportional to density, the grain-grain interaction gets more important for a denser dust population and is to be included in momentum equation. Grain-grain interaction affects the depth of the void as well as the secondary depletion rings. Finally, increasing neutral density leads to widening of depletion rings and to the appearance of new ones.

Speaker: N. El amine (EPS 2019)

802 P5.3019 Waves and instabilities in dusty plasmas at Phobos and Deimos

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3019.pdf

Waves and instabilities in a near-surface plasma above Phobos and Deimos are discussed. It is shown that the disturbance of the isotropy of the distribution function of electrons in dusty plasma above the surface of Mars satellites is associated with the movement of the solar wind relative to photoelectrons and charged dust particles. It leads to the development of instability and excitation of high-frequency waves with frequencies in the range of Langmuir and electromagnetic waves. In addition, the propagation of dust acoustic waves is possible. Dust acoustic waves can be excited, for example, in the vicinity of the terminators of the Mars satellites. Solutions in the form of dust acoustic solitons corresponding to the parameters of dusty plasma systems over the illuminated parts of Phobos and Deimos are found. The regions of possible Mach numbers and amplitudes of solitons are determined. This work was supported by the Program No. 28 of Basic Research of the Presidium of the Russian Academy of Sciences «Cosmos: Studies of Fundamental Processes and Their Interconnections», as well as the Russian Foundation for Basic Research (Project No. 18-02-00341-a). T.I. Morozova acknowledges the support of the Foundation for the advancement of theoretical physics and mathematics "BASIS".

Speaker: T.I. Morozova (EPS 2019)

803 P5.3020 LIBS in a low temperature plasma for the detection of airborne asbestos

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.3020.pdf

Forbidden in french constructions since 1997, asbestos remains present in most of the buildings constructed before this date. Thus, during work or in case of degradation, asbestos fibres can be emitted in air. The smaller the asbestos particles, the longer they stay in suspension in air, increasing the hazard of inhaling them.
The current determination of airborne asbestos presence in France follows a long and cumbersome normative protocol (NF X 43-050), with an analysis carried out on a Transmission Electron Microscope at laboratory after air filtration on-site. Such a protocol induces wasting time between the sampling and the results delayed not less than 48 hours and therefore prevents for the intervention on-site-on-time. Thus, the demand of a real-time measurement increases, even if it is only an alert technique.
The PLASMIANTE project aims to develop an apparatus able, on-site and in near-real-time, to analyse the particles present in an air sample and to identify the presence of asbestos. The device will sample air and send the particles in a reactor in which they will be trapped in a low-temperature argon plasma. Among several diagnostics that will be applied directly on the particles in suspension in the plasma, Laser Induced Breakdown Spectroscopy will be used to identify the presence of asbestos in the samples.
In this study, we present the first results of LIBS applied to particles of asbestos, building materials and mixtures in suspension in a low temperature plasma.

Speaker: C. Duée

804 P5.4001 Transformation and radiation processes in turbulent plasma in the presence of convective cells

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4001.pdf

The process of plasma radiation is studied when the transformation of an longitudinal Langmuir wave into the transverse electromagnetic wave occurs. The transformation takes place on turbulent plasma fluctuations in the presence of upper hybrid pump wave parametric instability. We consider the parametric decay of such wave into the daughter upper hybrid wave and modified convective cells. It is shown that the main contribution to the correlator of electron density which defines the value of transformation coefficient is given by low-frequency plasma oscillations (convective cells).
Notice must be taken that convective modes arise in magnetized plasma with a small ratio of the plasma pressure to the magnetic pressure, and can occur in the ionospheric plasma.
The transformation coefficient is calculated. We demonstrate the dominant role of the pump wave term which is essentially depend on the pump wave amplitude and frequency. For typical ionospheric plasma parameters in the F layer at about 250 km, we show that the pump wave term can exceed by several orders of magnitude the analogous one for the case of stable plasma ( the parametric instability is absent ) when the level of plasma density fluctuations is determined by the thermal noise.
The intensity of transverse waves radiation from turbulent plasma is calculated and its dependence on convective cells frequency and damping rate is obtained.

Speaker: V.G. Panchenko (EPS 2019)

805 P5.4002 Studying the photoemissive sheath using an EM-PIC code

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4002.pdf

We would be reporting about the preliminary results of the analysis using Particle In Cell (PIC) simulation on properties of photoemissive sheath in the presence of a magnetic field. Our present investigation reveals that the photoemission from a wall can induce electron twostream instability (ETSI) within the photoemission sheath region and the Electron Velocity Distribution Function (EVDF) can become highly non-Maxwellian which is usually treated as a Maxwellian. This raises a fundamental question about the behavior of the electron distribution function near a photoemissive sheath. As the cases where the photoemissive sheath can occur is abundant in nature, including the lunar surface and the surface of airless astrophysical bodies, we hope to answer some fundamental questions regarding the sheath physics. In what follows we shall present an analysis of our PIC simulation of a photoemissive sheath with crossed electric field and magnetic field.

Speaker: S. Changmai (EPS 2019)

806 P5.4003 Stimulated Raman scattering of the multi-Gaussian beam in a relativistic plasma

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4003.pdf

In the present work, the non-linear propagation of multi-Gaussian beam, consisting of coherent Gaussian beams with similar distribution [1], has been studied in collision-less plasma in the relativistic regime. We investigated the stimulated Raman scattering (parametric instability) of electromagnetic wave pulse and the evolution of its spot size. A theory of stimulated Raman scattering is developed by the composition of the hydrodynamic model and Maxwell's equations. We drive mode structure equation governing the amplitude mode, from which the fundamental mode and the Eigenvalue are found. The equations are coupled with low-frequency electron and ion plasma oscillations. It is observed that in the transition from weak to strong relativistic plasma, the growth rate for stimulated Raman scattering (SRS) instability is reduced. However, the presence of strong axially external magnetic field can further supress the SRS instability [2]. Numerically, we obtained the frequency shift and the growth rate of scattered off EM wave. The effect of eccentric displacement on the evolution of spot size has been uncovered by using WKB approximation and non-paraxial theory. It has been observed that the relativistic non-linearity strongly depends on the eccentric displacement as the beam possesses different radial intensity distributions for its different value. Oscillating focusing as well as defocusing has been observed in different cases.

Reference
[1] Wang, Y., Yuan, C., Jia, J., Gao, R., Hong, Y., Yao, J., ... & Wu, J. (2017). Propagation characters of multiGaussian beam with large eccentric displacement in collisionless plasma: Higher order paraxial theory. Physics of Plasmas, 24(6), 062306.
[2] Pan, K. Q., Guo, L., Li, Z. C., Yang, D., Li, S. W., Jiang, S. E., ... & He, X. T. (2019). Stimulated Raman scattering instability of a left-handed circularly polarized laser in strongly axially magnetized plasmas. Physics of Plasmas, 26(1), 012108.

Speaker: M. Dwivedi (EPS 2019)

807 P5.4004 To control the angular momentum of trapped electrons in tapered foam target

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4004.pdf

We have developed an analytical model to control the angular momentum of electrons trapped in ultra-relativistic laser-plasma interaction. The energy coupling from laser to plasma can be enhanced by using the foam target which regulates the near-critical density more efficiently in the medium. When laser is incident on the target, the ponderomotive force and self-generated electromagnetic fields associated with the laser affect the electrons. Owing to the tapered geometry of medium, the laser wavefront confronts hollow cone which results in an openmouth bubble. Inside the bubble, electrons are assumed to be accelerated in laser-piston regime [1] where the relativistic electrons form a density peak sheath at the head of laser pulse. When the electrostatic field overcomes the ponderomotive force the electrons start reflecting from the peak sheath. The reflected electrons follow the path of inner lining of the bubble and induce transverse self-injection. Non-linear scattering of laser field results the radiation reaction force which causes the self-injection of electrons in the laser pulse. The incident laser pulse carries large spin and orbital angular momentum which can be transferred to the particles via direct laser acceleration regime. The angular momentum associated with the energetic particle beams gives an additional degree of freedom which has potential applications in different fields such as condensed-matter spectroscopy and new electron microscopes [2].

References:
[1] Schlegel, T., Naumova, N., Tikhonchuk, V. T., Labaune, C., Sokolov, I. V., & Mourou, G. (2009). Relativistic laser piston model: Ponderomotive ion acceleration in dense plasmas using ultraintense laser pulses. Physics of Plasmas, 16(8), 083103.
[2] Taira, Y., Hayakawa, T., & Katoh, M. (2017). Gamma-ray vortices from nonlinear inverse Thomson scattering of circularly polarized light. Scientific reports, 7(1), 5018.

Speaker: S. Punia (EPS 2019)

808 P5.4005 The role of dielectric function local field corrections in the plasma transport properties description in the linear response theory

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4005.pdf

Within the linear response theory in the formulation of Zubarev [1, 2] the modification of electron-ion and electron-electron correlation functions is made with the account of local field corrections in the dielectric function [3]. Recently the Chebyshev polynomial expansion of the Fermi distribution functions was suggested [4, 5]. Using this method, the electron-electron correlation functions were reduced to frequency and momentum two-dimensional integrals for the arbitrary electron degeneracy. The calculations were performed in the random phase approximation (RPA) for the dielectric function. The proposed approximation provides more accurate consideration of the inter-particle correlations effects in a strong collisions area. The results for hydrogen fully ionized plasma transport coefficients are compared with those obtained in RPA.

References
[1] D. N. Zubarev, Nonequilibrium Statistical Mechanics (Plenum, New York, 1974).
[2] G. Röpke, Physica A 121, 92 (1983).
[3] S. Ichimaru, H. Iyetomi and S. Tanaka. Phys.Rep. 149, 91 (1987).
[4] V. S. Karakhtanov, The EPS Conference on Plasma Physics, Leuven, Belgium, 2016,
http://ocs.ciemat.es/EPS2016PAP/pdf/P5.102.pdf
[5] V. S. Karakhtanov, The EPS Conference on Plasma Physics, Belfast, Northern Ireland, UK, 2017, http://ocs.ciemat.es/EPS2017PAP/pdf/P5.406.pdf

Speaker: V. Karakhtanov (EPS 2019)

809 P5.4006 Teaching plasma physics with the open-source PIC code SMILEI

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4006.pdf

SMILEI [1,2] is an open-source, collaborative Particle-In-Cell (PIC) code co-developed by plasma physicists and high-performance computing (HPC) specialists. Thanks to its userfriendly (Python) interface, built-in diagnostics and visualization tools, SMILEI can be used not only for research but also as a teaching platform.
Over the last years, various practical trainings have been proposed to students at the Bachelor, Master and post-graduate levels. These exercises address numerical analysis, highperformance computing, and of course plasma physics: streaming instabilities, collisionless to collisional processes, laser-plasma interaction, particle acceleration, QED processes under extreme light conditions, astrophysics, etc.
This poster gives an overview of the various topics taught with the SMILEI PIC code as well as of the open-access material (online tutorial and lecture notes, input files and postprocessing tools, virtual machines) offered to the plasma community to introduce - in a practical and interactive way - plasma physics and numerical simulation to students.

[1] Derouillat et al., SMILEI: A collaborative, open-source, multi-purpose particle-in-cell code for plasma simulation, Comp. Phys. Comm. 222, 351 (2018); www.maisondelasimulation.fr/smilei.
[2] Beck et al., Adaptive SIMD optimizations in particle-in-cell codes with fine-grain particle sorting, https://arxiv.org/abs/1810.03949.

Speaker: T. Vinci (EPS 2019)

810 P5.4007 Ion Acoustic Supersolitons in a Plasma Consisting of Nonthermally Distributed Electrons and Positrons

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4007.pdf

Supersolitons are qualitatively different solitary structures from conventional solitons in terms of the potential profile and the phase portrait of the corresponding dynamical system. It has been established that the existence of a soliton after the formation of double layer confirms the existence of a sequence of supersolitons after the formation of double layer [1]. According to Dubinov & Kolotkov [2], the separatrix corresponding to a supersoliton envelopes one or several inner separatrices and several equilibrium points, whereas the separatrix corresponding to a conventional soliton encloses only one non-saddle equilibrium point. In the present paper, using the Sagdeev pseudo-potential approach, we have investigated the ion acoustic (IA) solitary structures in a collisionless unmagnetized plasma consisting of adiabatic warm ions, Cairns [3] distributed nonthermal electrons and positrons. We have drawn the existence domains of solitary structures with respect to the nonthermal parameter of electrons. In a parameter regime, we have found the existence of positive potential solitons after the formation of positive potential double layer and consequently the system supports positive potential supersolitons. To confirm the existence of positive potential supersolitons we have showed the phase portraits of the dynamical system of the corresponding IA solitary structures. With the help of phase portraits, we have observed that there exists a critical value Mcr of the Mach number M such that the system supports supersolitons just after the formation of double layer (at M=MDL) up to the Mach number Mcr, whereas for M>Mcr, the system supports solitons after the formation of double layer and there is no qualitative difference between the solitons for M>Mcr and the conventional solitons. Consequently, there must be a smooth transition of solitary structures, viz., soliton before the formation of double layer double layer supersoliton soliton after the formation of double layer. We have explained the mechanism of such transition process by plotting the equilibrium points of the corresponding dynamical system.

References:
[1] A. Paul, A. Bandyopadhyay, and K. P. Das, Phys. Plasmas 24, 013707 (2017).
[2] A. E. Dubinov and D. Y. Kolotkov, Plasma Phys. Rep. 38, 909 (2012).
[3] R. A. Cairns, A. A. Mamun, R. Bingham, R. O. Dendy, R. Bostrm, P. K. Shukla, and C. M. C. Nairn, Geophys. Res. Lett. 22, 2709 (1995).

Speaker: A. Paul (EPS 2019)

811 P5.4008 Ion temperature effects on the coexistence regions of positive and negative solitons in a negative ion plasma with superthermal electrons

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4008.pdf

Negative ion plasmas are observed in space and astrophysical environment (D and F layers of Earth's Ionosphere, Titan's atmosphere, Cometary comae) and in laboratory plasmas (e.g. plasmas processing reactors). In such plasmas, propagation of ion acoustic solitary waves have been observed experimentally in laboratory by Ludwig et al. [1] and Adhikany et al. [2].
Theoretical and experimental investigations of the propagation of ion acoustic waves have shown that positive and negative solitons can exist in a negative ion plasma; see for example Kumar and Mishra [3] and Rouhani and Abbasi [4]. From these and previous studies, it is known that only positive solitons propagate at low fractions of negative ion density to positive ion density f, positive and negative solitons coexist at middle values of f and only negative solitons survive at high ratios of f. However no deep investigation of the coexistence regions of positive and negative solitons has been reported yet, particularly the effects of ion temperatures on existence of these regions. Using the pseudopotential method, we have carried out analytical calculations followed by numerical analysis and investigated the effects of ions temperatures on the solitons coexistence regions in a negative ion plasma composed of adiabatic ions and kappa distributed electrons. Our results show that the existence of the above mentioned three regions strongly depend on the ions temperatures. It is found that coexistence regions may vary depending on ion temperatures and other plasma parameters.

References
[1] G. O. Ludwig, J. L. Ferreira and Y. Nakamura, "Observation of ion -acoustic rarefaction solitons in a multicomponent plasma with negative ions," Physical Review Letters, pp. 275 - 279, 1984.
[2] N. Adhikany, M. Deka and H. Bailung, "Observation of rarefactive ion acoustic solitary waves in dusty plasma containing negative ions," Physics of Plasmas, p. 063701(2009), 2009.
[3] K. Kumar and M. K. Mishra, "Large amplitude ion-acoustic solitons in warm negative ion plasmas with superthermal electrons," AIP Advances, vol. 7, p. 115114(2017), 2017.
[4] M. R. Rouhani and Z. E. Abbasi, "Characteristics of ion acoustic waves in a negative ion plasma with superthermal electrons," Physics of Plasmas, vol. 19, p. 112307(2012), 2012.

Speaker: X. Mushinzimana (EPS 2019)

812 P5.4009 Nonlinear oscillations in a protoplanetary disk

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4009.pdf

In a protoplanetary disk (PPD) system, the magneto-rotational instability (MRI) driven turbulence produces a strong electric field in the neutral co-moving frame when the ionization degree is low [2]. This electric field leads to plasma heating at some parts of a weakly ionized protoplanetary disk, which results in an asymmetric electron distribution that can be represented by Davydov distribution function [1, 3]. In this work, we investigate how this asymmetry in electron distribution plays a significant role in the behavior of electrostatic solitary waves (ESW) that are produced in the PPD. We derive the electron density from Davydov function and incorporate it into the Poisson's equation which gives a Sagdeev potential that is very similar to that of the Maxwell distribution when the asymmetry is very small. We further look into the case where we find out the domain of soliton existence when the asymmetry becomes large.

Reference:
1. B Davydov, Phys Z Sowjet 8, 59 (1935)
2. Inutsuka, S., & Sano, T., ApJL, 628, L155 (2005)
3. Okuzumi and Inutsuka, The Astrophysical Journal, 800:47 (19pp) (2015)

Speaker: M. Khusroo (EPS 2019)

813 P5.4010 Ion versus electron heating in the nonlinear phase of the collisionless MRI

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4010.pdf

The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in several astrophysical scenarios, like accretion disks around black holes [1]. The MRI has been widely studied using MHD models and simulations, in order to understand the behavior of astrophysical fluids in a state of differential rotation. In radiatively inefficient accretion flow (RIAF) models for accretion onto compact objects, the accretion proceeds via a hot, low-density plasma with the proton temperature larger than the electron temperature [2, 3]. In order to maintain the two-temperature flow characteristic of RIAF models, the typical collision rate must be much smaller than the accretion rate. This suggests that the standard MHD approach may be insufficient, and a kinetic description is required instead.
Leveraging on our recent results [4] obtained in 2D pair plasma configuration, we present our recent studies on collisionless MRI in electron-ion high- plasma. Increasing the mass ratio of our simulations, we show the development of an enhanced ion heating during the nonlinear phase of collisionless MRI (channel flows). In particular, we claim a mass ratio dependence of the temperature ratio of the two plasma species, with Ti/Te (mi/me)1/2. We will explore the mechanism responsible for this effect, identified as the compression of the current sheets formed during the nonlinear MRI. We support our assumptions with a theoretical model for kinetic compression of current sheets, giving a quantitative prediction of the electric and magnetic fields acceleration on the trapped particles during the compression phase.

References
[1] S. A. Balbus, J. F. Hawley, Astrophys. J., 376, 214 (1991)
[2] R. Narayan, I. Yi, Astrophys. J. Lett., 428, L13 (1994)
[3] E. Quataert, Astronomische Nachrichten, 324, 435 (2003)
[4] G. Inchingolo, et al., Astrophys. J., 859, 149 (2018)
[5] S. J. Squire, et al., J. of Plasma Phys., 83, 6 (2017)
[6] M. W. Kunz, et al., Phys. Rev. Lett., 117, 235101 (2016)
[7] M. Hoshino, Astrophys. J., 733, 118 (2013)
[8] M. A. Riquelme, et al., Astrophys. J. 755, 50 (2012)
[9] M. A. Riquelme, et al., Astrophys. J. 800, 1 (2015)

Speaker: G. Inchingolo (EPS 2019)

814 P5.4011 On frequency of ion cyclotron radiation in connection with its observability

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4011.pdf

Magnetic activity of distant objects can manifest itself in electron cyclotron emission. While it was detected from a large number of stellar objects (including pulsars) and brown dwarfs, not detection does not necessarily mean it does not happen. Being a highly directed radiation, it leaves the magnetospheres shaped as hollow cones centered around magnetic poles, which rotate with the object and get detected when the beam points towards the Earth.
Ion cyclotron emission, also expected to happen on the same objects, would be directed differently and hence could provide an alternative root to detecting the objects' magnetic activities. The expected frequency of radiation though is much lower then for electron cyclotron emission, if expecing it to be close to ion cyclotron frequency, which makes it more difficult to detect.
Here we analyse the range of frequencies which can be expected from ion cyclotron radio emission, based on a horseshoe-shaped magnetically confined velocity distribution function Since coming out at a different frequency and direction from those of electron cyclotron emission from the same object, it can be observable even when the electron cyclotron
signals were not detected from that object. We analyse the possibilities of such detection based on expected frequency of radiation. Ion cyclotron maser instability based on magnetic confinement is considered2, and the results show that the frequency of ion cyclotron emission can be significantly different from the local cyclotron frequency. Some combinations of parameters provide up to ten times higher frequency of the emission, when the radiation direction is substantially different from normal to the beam. This is in line with some observations, and suggests a number of instruments will be capable of detecting such emission from Brown Dwarfs.

1 I. Vorgul et al, Phys. Plasmas, 12, 122903 (2005)

Speaker: C.R. Straub (EPS 2019)

815 P5.4013 Spatiotemporal wave dynamics in the transition to defect-mediated dust acoustic turbulence wave

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4013.pdf

Under increasing driving and through modulation instability, the transition from the ordered wave to the weakly disordered wave state occurs in various nonlinear waves. The emergence of fluctuating topological defects at the sites with null amplitude and undefined phase leads to the name of defect-mediated turbulence (DMT) for the weakly disordered state. The recent study in an acoustic-type travelling wave demonstrated that defect filaments winded by helical waveforms named as acoustic vortices (AVs), through pairwise generation and annihilation, are the singular objects for characterizing the dynamical behaviour of DMT. In this work, the spatiotemporal waveform dynamics in the transition from the plane wave to DMT is experimentally investigated in 3D traveling dust acoustic waves. It is found that with increasing effective driving, the transition onsets from the stable single AV state, through the unstable single AV state, to the multiple AVs state. The correlation of waveform undulation, AVs motion, and the broadening of power spectrum is also unravelled.

[1] Y. Y. Tsai and L. I, Phys. Rev. E 90, 013106 (2014)

Speaker: J. Tsai (EPS 2019)

816 P5.4014 Onset of wave turbulence in dust acoustic waves

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4014.pdf

In this work, wave turbulence transition from a stable plane wave to wave turbulence through intermediate weakly disordered state is investigated in self-excited 3D dust acoustic waves, composed of negatively charged particles suspended in low pressure RF discharges, through direct observing dust density fluctuations over a large area. Through wavelet transform, we demonstrate the extraction of three dimensional local turbulent sites (LTSs) associated with multi-mode excitation in spatiotemporal domains, from the ordered background in the xyt space. LTSs with high frequency bandwidth are found intermittently emerging around defect filaments with extremely low amplitude and decaying in the ordered background in the weakly disordered state. During the transition, LTSs rapidly spread and cluster around high amplitude sites with increasing LTS volume fraction, and eventually forming one percolating large cluster with other sparse ones, evidencing that wave turbulence transition is a type of percolation transition, similar to laminar-turbulent transition in hydrodynamic flows.

Speaker: W. Chen (EPS 2019)

817 P5.4015 Scattering of lower hybrid radio frequency waves by cylindrical turbulent structures in the plasma edge in tokamaks

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4015.pdf

Lower hybrid (LH) radio frequency (RF) waves are used in fusion tokamak devices to generate non-inductively toroidal currents. LH waves are effective in imparting toroidal momentum to electrons in the core of the confined plasma. Since the LH waves are generated by wave guide structures near the wall of a tokamak, the waves have to propagate through a turbulent plasma in the edge region before coupling to the core. It is especially important to quantify the effect of this plasma region on the propagation characteristics of the LH waves, since fusion reactors like ITER will have an extended edge region. Structures in the plasma edge like filaments and blobs which have highly varying density fluctuations compared to the background density, span radial spatial scales that are comparable to the LH wavelength. We study the scattering of the LH waves by the filamentary structures using Maxwell's equations, in which the plasma permittivity is given by the cold plasma dispersion tensor. The collisional absorption of LH waves in the edge region is included by a modification to the elements of the dispersion tensor. The filaments are assumed to be cylindrical with the axis predominantly aligned along the direction of the toroidal magnetic field. Our studies are both analytical and numerical [1,2] and show that these structures can lead to reflection, refraction, diffraction, and side-scattering of both an incident LH plane wave and a Gaussian beam. We will present a variety of different density variations and collisional absorption rates in plasmas with filamentary structures of varying sizes. The changes in the spectral properties of the LH waves will also be discussed.

References
[1] S. I. Valvis and others "Scattering of radio frequency waves by cylindrical filaments with general orientation relative to the magnetic field", Journal of Plasma Physics vol. 84, 745840604 (2018)
[2] Z. C. Ioannidis, A. K. Ram, K. Hizanidis, and I. G. Tigelis, "Computational studies on scattering of radio frequency waves by density filaments in fusion plasmas", Physics of Plasmas 24, 102115 (2017)

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053 (except author A.K.R.). The views and opinions expressed herein do not necessarily reflect those of the European Commission. A.K.R. is supported by the US Department of Energy grant nos. DE-FG02-91ER-54109 and DE-FC02-01ER54648.

Speaker: S. Valvis (EPS 2019)

818 P5.4016 Study of quasi-static equilibrium fluctuation and confinement in a currentless toroidal device using two different plasma sources in the presence of plasma flow

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4016.pdf

A currentless toroidal device (CTD) is one in which plasma is confined by the application of toroidal and vertical magnetic field only resulting in absence of a conventional effective rotational transform. Such devices provide a simple and well diagnosable test-bed for studies related to equilibrium, fluctuations and particle confinement for Tokamak edge. The device BETA at the Institute for Plasma Research (IPR) is one such CTD with a plasma major radius of 45 cm and minor radius of 15 cm and a maximum toroidal field of 0.1 Tesla. Quasi-static equilibrium in a CTD is controlled by the nature of fluctuation and flow [1, 2]. As observed in hot cathode discharges studied earlier [1, 2], density gradient provide fluctuation in the plasma and hence the instabilities [2], whereas radial electric field provides poloidal flow. Thus, the conditions are akin to Tokamak edge.
In addition to hot cathode source, Microwave plasma source is also available for producing plasma. The hot cathode source uses thermionic emission of electron to produce the plasma and the discharge is struck between grounded wall and the hot cathode. Plasma produced by Microwave source involves launching of Microwave of frequency of around 2.45 GHz with average launched power of around 1 kW. It has been observed that using these two sources in tandem in the presence of an external vertical field, can provide a control over density profile [3]. This helps in controlling the density gradient on the outboard side and hence controlling the nature of instabilities. Additionally, the presence of flows significantly affects the nature of quasi-static equilibrium and fluctuation. The detailed experimental study of controlling the nature of plasma profiles using two sources and external vertical field in presence of flows will presented.

References
[1] T. S. Goud, Thesis, Institute for Plasma Research, Gandhinagar, Gujarat, India (2012).
[2] Umesh Kumar, Shekar G Thatipamula, R. Ganesh, Y. C. Saxena and D. Raju, Phys. Plasmas 23, 102301
(2016).
[3] Umesh Kumar, R. Ganesh, K. Sathyanarayana, Y. C. Saxena, S. G. Thatipamula, D. Raju , Manuscript under
preparation, (2019)

Speaker: U. Kumar (EPS 2019)

819 P5.4017 Propagation of Alfven Waves in a Two Ion Species Plasma

See full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/P5.4017.pdf

Understanding the behavior of plasma waves in mixed-species plasmas is important for explaining many observations seen in both space and laboratory plasmas. The addition of a second ion species in a magnetized plasma introduces new behavior in the propagation of waves in the ion cyclotron region, such as the ion-ion hybrid cutoff frequency for parallel propagating shear Alfven waves [1]. Previous experiments on the Large Plasma Device (LAPD) have demonstrated the existence of a propagation gap for shear waves between the ion cyclotron frequencies of the two ion species [2], while more recent work has expanded the range of plasma conditions in which this was observed. Additionally, the ion-ion hybrid cutoff is documented for various mix ratios in order to determine its viability as a diagnostic for the ratio of ion densities. `

[1] Buchsbaum, S. J. (1960), Resonance in a plasma with two ion species, Phys. Fluids, 3, 418, doi:10.1063/1.1706052
[2] Vincena, S. T., W. A. Farmer, J. E. Maggs, and G. J. Morales (2011), Laboratory realization of an ion-ion hybrid Alfvén wave resonator, Geophys. Res. Lett., 38, L11101, doi:10.1029/2011GL047399.

Speaker: J. Robertson (EPS 2019)

16:00 Coffee Break

Plenary Session

Convener: G. Giruzzi (IRFM! CEA (France))

820 I5.014 The shock ignition approach to laser fusion: status and progress

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.014.pdf

Direct-drive "Shock Ignition" is an interesting alternative to the classical approach to ICF investigated on NIF and could relax the problems met on the pathway to ignition. In the conventional approach, hot electrons (HE) are dangerous because they induce target preheating making compression more difficult. In SI, however, HE generated by the final laser spike at the end of compression, when the accumulated target <rho r> is large enough, may increase lasertarget coupling and strengthen the shock with a positive impact. Hence, their characterization is crucial for assessing SI feasibility. Within the Enabling Research EUROfusion Project "Preparation and Realization of European Shock Ignition Experiments", we are conducting experiments in Europe and the US to contribute answering these open questions.
At the PALS laboratory in Prague we characterized HE produced by high-energy laser pulses of 300 ps at 1st and 3rd harmonics of the iodine laser (wavelength = 1315/438 nm, focused to intensities 9x10^15 / 2x10^16 W/cm^2). We studied the correlation of HE and Stimulated Raman Scattering (SRS) and assessed the impact of HE on target preheating and on shock dynamics. Results were compared to advanced hydro simulations done with the code CHIC that takes into account parametric instabilities and HE in a self-consistent way. At the Omega EP facility in Rochester, we characterized HE by X-ray imaging and spectroscopy and evaluated their impact on preheating and shock dynamics by time-resolved X-ray radiography. Finally, the addition of an external magnetic field (MIFED device) affected HE trajectories affecting their capability of penetrating into the target. A significant effort was also done to optimize diagnostics, including time-resolved X-ray radiography (experiments at LULI and GEKKO), shock breakout diagnostics (LIL facility) and X-ray phase contrast imaging (Phelix laser).
This work contributed to our understanding of SI physics but also to consolidate a European research network on IS, serving as preparation for future experiments to be done on the LMJ/PETAL laser facility at the relevant energy scale.

Speaker: D. Batani (EPS 2019)

821 I5.015 Interplay between MHD and turbulence in plasma

See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.015.pdf

Interplay between MHD and turbulence is interesting topics in magnetically confined plasma and solar plasma. The fast reconnection of magnetic field in the solar flare is well known but the mechanism is not well understood. Turbulence in the current sheet is a strong candidate to explain the fast reconnection in solar flare is one of the mystery in solar flare [1,2]. In magnetically confined plasma, MHD instability and electrostatic turbulence have been studied independently. No coupling between the electrostatic turbulence and MHD instability is assumed. However, recently the experimental observations below suggest the coupling and interplay between MHD and turbulence in magnetically confined toroidal plasmas. 1) Turbulence spreading into the magnetic island [3]. 2) Self-organized change in topology and turbulence in magnetic island [4]. 3) Flow damping by stochastic magnetic field [5]. 4) Trigger mechanism for the MHD bursts [6]. 5) Impact of MHD bursts on the ion velocity distribution and potential [7,8]. 6) Turbulence exhausts at the MHD burst event [9]. In this plenary talk, the experimental evidence of the interplay between MHD and turbulence in toroidal plasma is presented. For example, in the heat pulse experiment in DIII-D tokamak plasma, the heat pulse propagates earlier than heat pulse at the X-point but later at the O-point of the magnetic island. This is due to that the turbulence is spreading from the X-point to O-point of the magnetic island faster than the heat pulse determined by the transport time scale inside the magnetic island. A self-regulated oscillation of the topology and transport inside the magnetic island is observed due to the interplay between the MHD and turbulence.

References
[1] K. Shibata and S. Tanuma, Earth Planets Space 53, (2001) 473.
[2] N. Nishizuka and K. Shibata, Phys. Rev. Lett. 110, (2013) 051101.
[3] K.Ida et. al., Phys Rev Lett 120 (2018) 245001.
[4] K.Ida et. al., Sci. Rep. 5 (2015) 16165.
[5] K.Ida et. al., Nature Communications 6 (2015) 5816.
[6] K.Ida et. al., Sci. Rep. 8 (2018) 2804.
[7] K.Ida et. al., Sci. Rep. 6 (2016) 36217.
[8] K.Ida et. al., Phys Plasmas 24 (2017) 122502.
[9] K.Ida et. al., Nucl Fusion 58 (2018) 112008.

Speaker: K. Ida (EPS 2019)

Prize Presentation

Closing Ceremony