7th European Advanced Accelerator Conference

21 Sept 2025, 17:00 → 27 Sept 2025, 17:00 Europe/Rome

Hotel Hermitage, La Biodola Bay, Isola d'Elba, Italy

Ralph Assmann (GSI), Massimo Ferrario (Istituto Nazionale di Fisica Nucleare)

Registration, Student's Grant Application and Abstracts Submission are CLOSED.

The European Advanced Accelerator Conference has the mission to discuss and foster methods of beam acceleration with gradients beyond state of the art in operational facilities. The most cost effective and compact methods for generating high energy particle beams shall be reviewed and assessed. This includes diagnostics methods, timing technology, special needs for injectors, beam matching, beam dynamics with advanced accelerators and development of adequate simulations.

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Following the wake of the previous EAAC workshops we are happy to announce that the 7^th European Advanced Accelerator Conference (EAAC2025) will take place again in the island of Elba in Italy, September 21-27, 2025, in the premises of the Hotel Hermitage in the Biodola bay.

We are also glad to inform you that Prof. Patric Muggli (Max Planck Institute) has accepted to lead the Scientific Program Committee of EAAC2025. The community will be contacted soon for input to the conference program.

This conference is organized in the context and with sponsoring of the EU/I-FAST funded European Network for Novel Accelerators (EuroNNAc4), a network of more than 60 institutes and universities. Additional sponsors for EAAC2025 include at the moment CERN and INFN.

The conference will be followed (September 27) by a 1-day EuroNNAc4 Network Meeting by invitation only.

A special session on the EuPRAXIA Project will be included into the EAAC2025 scientific program. 

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Sunday 21 September

19:30 Welcome Cocktail

20:30 Dinner

Monday 22 September

1 Opening Remaks

Plenary Session

2 Beam-Driven Plasma-Wakefield Experiments at FACET II

The FACET-II facility at SLAC National Accelerator Laboratory conducts a broad science program based on the interaction of low-emittance high-current 10 GeV electron beams with lasers, plasmas and solids. FACET-II operates as a National User Facility while engaging a broad User community to develop and execute experimental proposals that advance the development of plasma wakefield accelerators. I will highlight recent breakthroughs achieved at FACET-II such as the generation of 100-kA class beams by laser-electron beam shaping, the demonstration of a brightness and energy transformer, and efficient plasma acceleration with percent-level field uniformity. The extreme beams delivered for plasma wakefield accelerator experiments have enabled additional opportunities such as the most precise measurements of quantum radiation reaction to date and extreme beam focusing by leveraging intense coherent transition radiation in the near field or plasma fields and these results will also be highlighted.

Speaker: Dr Mark Hogan (SLAC National Accelerator Laboratory)

3 KALDERA: A high-average power drive-laser for laser plasma acceleration

KALDERA is a novel TW-class Ti:Sapphie laser currently under development at DESY with the goal to drive a next-generation of high repetition-rate, high average-power laser-plasma accelerators. We report on the current development status of KALDERA and present commissioning results of the first 700 mJ / 100 Hz amplifier stage and its high power broadband multilayer-dielectric grating compressor supporting pulse lengths below 30 fs. We discuss the associated technology challenges concerning such as pump lasers, amplifier architecture (cooling concept) and broadband high-power pulse compression. Finally, we provde an outlook of the next development, which will deliver 100 TW peak power pulses at 100 Hz and repetition rate and beyond.

Speaker: Andreas Maier (DESY)

10:45 Coffee Break

Plenary Session

4 Multi-GeV laser wakefield electron acceleration in an all-optical plasma channel

Laser-plasma accelerators are a promising technology for compact drivers of linear colliders and secondary radiation sources. To maximize single-stage energy gain, the high-intensity drive laser pulse must be kept focused over several tens of centimeters through a sufficiently low-density plasma. Recently, we employed plasma channels based on the hydrodynamic expansion of optical field ionized plasmas (HOFI) [1-3] to form steep channels with appropriate matched spot-size at low plasma densities. Using the BELLA PW laser, we demonstrated high quality guiding of PW-class pulses through 30-cm-long channels [4]. By changing the channel length on a shot-by-shot basis, we observed laser coupling into high-order channel modes and their energy loss through mode filtering, followed by matched propagation of the fundamental mode, and nonlinear depletion of laser energy. Through localized ionization injection, we generated electron beams with single, quasimonoenegertic peaks up to 9.2 GeV and charge extending beyond 10 GeV. This work provides several key steps towards a 10-GeV-class LPA that is suitable for applications.

[1] R. Shalloo et al., Phys. Rev. E (2018)
[2] A. Picksley et al., Phys. Rev. E (2020)
[3] L. Feder et al., Phys. Rev. Research (2020)
[4] A. Picksley et al., Phys. Rev. Lett (2024)

Speaker: Alex Picksley (Lawrence Berkeley National Lab)

5 Femtosecond laser-induced plasma filaments for beam-driven plasma wakefield acceleration

Plasma-based acceleration technology can revolutionize particle accelerators, enabling the realization of compact systems capable of driving different user-oriented applications.
We propose developing a laser-based, high repetition rate (HRR), highly stable and tunable plasma filament stage for beam-driven plasma wakefield acceleration (PWFA) systems. The plasma filament, generated by a low-energy self-guided femtosecond laser pulse, is studied experimentally and theoretically in a low-pressure N2 gas environment.
Precise control of the plasma filament is crucial for plasma-based accelerators, and different techniques have been implemented to measure its density, temperature and dimensions. The measurements show the stable generation of a ≈4cm long channel with a ≈300μm diameter. The plasma density and temperature are ne≈1016cm−3 and Te≈1.3eV with a decay time of ≈8ns [1].
This technology can provide GeV-level electrons at HRR in a compact space, maintaining the high quality and brilliance of the LINAC-generated beams. This development aligns perfectly with the goals of the EuPRAXIA European project.
[1] Galletti, M., et al, Phys. Rev. E 111, 025202 – 2025, https://doi.org/10.1103/PhysRevE.111.025202

Speaker: Mario Galletti (Istituto Nazionale di Fisica Nucleare)

6 HALHF: a hybrid, asymmetric, linear Higgs factory using plasma- and RF-based acceleration

Plasma-wakefield acceleration holds great promise for particle physics due to its orders-of-magnitude higher accelerating gradients, which can result in significant cost reductions based on a sizeable reduction in footprint. However, plasma-based acceleration of positrons—required for an electron-positron collider—is much more difficult than for electrons. In 2023 a novel collider scheme, HALHF, was proposed that avoids positron acceleration in plasma, using a mixture of beam-driven plasma-wakefield acceleration to high energy for the electrons and RF acceleration to low energy for the positrons. Since first publication, an international collaboration has been built to progress the project towards a pre-CDR level. This process has led to the generation of new tools, for example to optimise the baseline collider design for total (build + run + carbon) cost, and has highlighted urgent topics for R&D, for example the plasma-heating and cell-cooling challenge. The status was recently submitted to the ESPPU process; the tools and insights developed are already proving beneficial to the 10 TeV collider effort in the US, and are expected to impact future plasma-based free-electron lasers and SFQED experiments. Here we present progress over the last two years and provide an outlook for the future.

Speaker: Richard D'Arcy (University of Oxford)

12:30 Lunch Break

16:00 Coffee Break

PS1: Plasma-based accelerators and ancillary components

Conveners: Mario Galletti (Istituto Nazionale di Fisica Nucleare), Sarah Schröder (Lawrence Berkeley National Laboratory)

7 The SPARTA project: designing a multistage plasma-accelerator facility

Plasma acceleration promises to make high-energy and high-power accelerator facilities, such as linear colliders, cheaper and more compact. However, many aspects of plasma accelerators are still at a relatively low technology readiness level (TRL). Maturing the technology requires near-term applications with moderate requirements in all but the core aspects, which in particular includes staging and stability. The SPARTA (Staging of Plasma Accelerators for Realizing Timely Applications) ERC project aims to provide technical solutions for both staging and stability, and to combine these into a design for a medium-scale multistage plasma-accelerator facility aimed at strong-field QED experiments. Solutions include nonlinear plasma lensing for achromatic transport, and passive stabilization mechanisms. Here, we give an overview of the motivations, solutions, aims and current progress of the SPARTA project.

Speaker: Dr Carl A. Lindstrøm (University of Oslo)

8 Energy and brightness booster stages for the UK XFEL

The UK XFEL project is pioneering a transformative approach to next-generation X-ray free-electron lasers (XFELs). It is committed to ensuring long-term scientific impact by exploring compact, efficient, and high-gradient plasma-based accelerators to enhance the machine’s beam energy and brightness reach as part of a future upgrade strategy. Among the most promising avenues, plasma-based acceleration stages offer a disruptive opportunity to develop ultra-compact, high-gradient electron energy and brightness boosters—crucial for pushing XFEL capabilities beyond conventional boundaries [1]. This contribution outlines a pathway for the self-consistent integration of advanced accelerator concepts into the UK XFEL facility design within the Conceptual Design and Options Analysis (CDOA) project, capitalising on the facility’s unique strengths and enabling completely novel research modalities through the combination of conventional and plasma-based accelerators. Preliminary start-to-end simulation results suggest that such booster stages could produce electron beams capable of generating very hard XFEL photons down to the 100 keV scale.

[1] Habib, A.F., et al. Nat Commun 14, 1054 (2023)

Speaker: Dr Ahmad Fahim Habib (University of Strathclyde, Glasgow, UK and Cockcroft Institute, Sci-Tech, Daresbury, UK.)

9 Collider-quality electron bunches from an all-optical plasma photoinjector

In recent years, plasma accelerators have advanced significantly toward producing beams suitable for colliders, aiming to replace conventional MV/m RF fields with GV/m fields of nonlinear plasma waves. Realizing a plasma-based collider requires electron bunches with high charge (hundreds of pC), low normalized emittance (~100 nm), and energy spread below 1%. Minimizing energy spread during acceleration involves flattening the accelerating field, which is achievable with a trapezoidal charge distribution.

We present a plasma photoinjector concept that enables collider-quality electron bunch generation using two-color ionization injection. The spatiotemporal control over the ionizing laser creates a moving ionization front inside a nonlinear plasma wave, generating an electron bunch with a current profile that flattens the accelerating field. Particle-in-cell (PIC) simulations of the ionization stage show the formation of an electron bunch with 220 pC charge and low emittance (ϵ_x = 171 nm-rad, ϵ_y = 76 nm-rad). Quasistatic PIC simulations of the acceleration stage show that this bunch is efficiently accelerated to 20 GeV over 2-meters with an energy spread below 1% and emittances of ϵ_x = 177 nm-rad and ϵ_y = 82 nm-rad. This high-quality electron bunch meets Snowmass collider requirements and establishes the feasibility of plasma photoinjectors for future collider applications.

Speaker: William Li (Brookhaven National Laboratory)

10 Exploitation of plasma wakefield acceleration at CLARA FEBE

Plasma wakefield acceleration (PWFA) has attracted great interest due to its large accelerating gradient, i.e. orders of magnitude higher than that in conventional accelerators. The purpose-built FEBE (Full Energy Beam Exploitation) beamline at CLARA facility at Daresbury lab will provide ultra-bright electron beams which enable us to exploit a wide range of PWFA experiments. In this talk, we will present the latest simulation results for the proposed PWFA experiments including the CLARA beam energy doubling, plasma beam dump and the betatron x-ray source.

Speaker: Guoxing Xia (Cockcroft Institute and the University of Manchester)

11 Resonant Emittance Mixing of Flat Beams in Plasma Accelerators

Plasma accelerators can sustain extremely high field gradients, making them strong candidates for future X-ray sources and compact linear colliders. Achieving the high luminosity required for collider applications necessitates the use of flat beams to minimize harmful beamstrahlung effects. However, we show that flat beams in plasma accelerators are susceptible to beam quality degradation due to emittance mixing, driven by transverse coupling in the wakefields. When a resonance arises between the horizontal and vertical betatron oscillations of beam particles within a coupled wakefield, the transverse emittances can fully exchange—resulting in a round beam. The impact of this resonance depends on its underlying mechanism and can be mitigated by appropriate design choices. In particular, using laser drivers or flat particle beam drivers can help suppress the resonance and preserve beam quality. These investigations are made possible by recent advances in high-performance, open-source simulation tools, which enable detailed studies of high-quality, high-energy electron beam acceleration in plasma wakefields. This study was published in [ S. Diederichs et al., Phys. Rev. Lett. 133, 2024].

Speaker: Maxence Thévenet (DESY)

12 Advancing Hybrid Laser- and Beam-Driven Plasma Accelerators: High-Energy and High-Quality Witness Beams

Hybrid laser- and electron beam-driven plasma wakefield accelerators (L-PWFAs) combine the compactness of laser wakefield acceleration (LWFA) with the beam quality and stability of particle-driven wakefield acceleration (PWFA). In this scheme, an LWFA stage generates a high-current electron bunch that drives a PWFA stage, where a witness bunch is internally injected and accelerated.
Our earlier experiments demonstrated witness beams with reduced divergence and energy spread—key for applications such as brilliant X-ray generation—but with limited energy gain, yielding transformer ratios below unity. In this work, we demonstrate high-quality witness beams with energies significantly exceeding that of the driver beam, reaching transformer ratios approaching 2. These advances are facilitated by precise control of plasma density and beam parameters, aided by advanced diagnostics: A few-cycle optical probe enables retrieval of the local plasma density and visualization of wakefield morphology changes due to driver depletion. These measurements are complemented by transition radiation diagnostics that allow relative localization of the driver and witness beams.
In conclusion, our PWFA stage acts as both an energy and beam quality transformer, enabling true gains in overall beam brightness, enhancing the potential for future applications like next-generation light sources.

Speaker: Moritz Foerster (LMU Munich)

18:20 Discussion & Closing Remarks

PS2: High gradient vacuum structures

Conveners: Evan Ericson (PSI/EPFL), Jom Luiten

13 Dielectric wakefields structures and their applications at CLARA facility

Accelerator user facility CLARA (Compact Linear Accelerator for Research and Applications) at Daresbury Laboratory is currently being commissioned. It comprises a 250MeV, 250pC linear accelerator and a dedicated beamline with the hutch for hosting a variety of user experiments including plasma and structure wakefield acceleration. Generation of drive-main bunch pairs for wakefield experiments is accomplished using masking technique and photoinjector pulse shaping.
Two dielectric wakefield structures are included in the machine layout: energy dechirper and streaker. Both are of similar design and can be used for either dechirping or streaking or as accelerating structures. We present first results of these structures commissioning and outline future plans including experiments on beam break-up instability suppression in collinear wakefield accelerators

Speaker: Yuri Saveliev (STFC, Daresbury Lab., ASTeC)

14 Controlling FEL bandwidth at SwissFEL using a dielectric wakefield structure

The bandwidth of a free-electron laser (FEL) is increased when the mean energy along the electron bunch varies. In this work, we demonstrate how a dielectric wakefield structure can be used to control the FEL bandwidth by manipulating the beam’s energy chirp prior to its injection into undulators. We compare simulations and measurements of the beam’s energy spread distribution and find reasonable agreement apart from when the structure is operated at gaps below 1 mm. Using the wakefield structure, we successfully reduce the beam's projected energy spread, leading to a narrower FEL bandwidth. Conversely, we also enhance the effect of an inverted chirp in the electron beam due to overcompression in the main linear accelerator, increasing the FEL bandwidth, showcasing the utility of the wakefield structure in tailoring FEL performance.

Speaker: Evan Ericson (PSI/EPFL)

15 Proposal to control BBU instability in SWFA by using adjustable rectangular dielectric waveguides

Structure wakefield acceleration (SWFA) is a promising novel acceleration method being explored to develop more compact and cost-effective future accelerators. In SWFA, a high-charge drive bunch travels through a structure, exciting strong wakefields that can be used to accelerate a trailing lower-charge main bunch. A major challenge in this scheme is beam break-up (BBU) instability, which can lead to beam losses, limiting the acceleration length and ultimately the beam energy gain. While several strategies have been proposed to address this issue, we present an alternative approach consisting of an array of rectangular dielectric waveguides with independently adjustable transverse positions. This arrangement enables section-by-section correction of transverse beam momentum and offset, offering a practical solution to mitigate BBU instability in SWFA schemes and improve their viability for future accelerator technologies. To test this concept, future experiments are being planned at the CLARA facility in Daresbury Laboratory.

Speaker: Beatriz Higuera Gonzalez (The Cockcroft Institute / The University of Manchester)

16 Energy Recovery in Beam-Driven Wakefield Accelerator.

An experiment at the Argonne Wakefield Accelerator toward implementing an energy recovery scheme in a beam-driven structure wakefield accelerator is in preparation. The experiment use a drive and locaing bunch to excite and turn of the wakefield. Such a configudation allows the generation of short THz pulse (below the one imposed by the structure group velocity) and could provide a phath the higher fields in SWFA. The experiment uses dielectric-lined waveguide in its first implementation. The experiment, expected outcome nd preliminary data will be discussed.

Speaker: Philippe Piot (Argonne National Laboratory)

17 High gradient electron injector for external injection for AWAKE Run 2C

AWAKE is constructing a new electron injector for external injection for Run 2C. One of the main goals of the experiment is to demonstrate external injection into a plasma wake field and emittance and energy spread control during acceleration. The injector consists of an S-band high gradient RF-gun and high-gradient X-band accelerating structures for velocity bunching and acceleration. The nominal beam has a bunch charge of 100 pC, a bunch length of 200 fs and an emittance below 2 um. This beam has to be focused down to 6 um in order fulfil the matching conditions during plasma acceleration. Additional requirements are a very good energy stability, a small energy spread and low longitudinal and transverse jitter. The status of this injector and its key-hardware will be presented.

Speaker: Steffen Doebert

18:00 Discussion & Closing Remarks

PS3: Laser technology

Conveners: Manuel Kirchen, Mariastefania De Vido (STFC Central Laser Facility)

18 High average power laser technologies for LPA-based FELs

In this paper, we present the state of the art laser technologies suitable for laser plasma accelerators as well as the roadmap to achieve average power scaling to the level required for future LPA-based FEL, in particular the flagship project of EuPRAXIA laser-driven machine.
We will present performance of operational performance of already operating 10 TW – 100 Hz laser systems using diode-pumped lasers as pumping lasers of TiSa amplifiers. We report on development of building blocks such as active mirror TiSa disk amplifiers and active cooling of gold-coated compression gratings in order to boost performance of such lasers to 50 TW – 100 Hz, available soon in laboratories, for example within EuAPPS project.
Furthermore we will report about technical strategies and the related developments which will enable to raise the performance of TiSa based CPA laser systems up to the PetaWatt peak power at 100 Hz repetition rate leading therefore to the delivery of an average power exceeding the kilowatt level. We will focus on developing the next generation of high average power compatible pulse compressors based on the use of dielectric-coated compression gratings.

Speaker: Christophe SIMON-BOISSON (THALES OPTRONIQUE SAS)

19 First Electron Beams from the High-Average-Power Laser-Plasma Accelerator KALDERA

Laser-plasma acceleration (LPA) is a promising technology for future compact accelerators. However, the low repetition rate (typically few Hz) of today’s high-power laser systems prevents reaching the average power required by applications and hinders the implementation of fast feedback systems to mitigate beam instabilities. To this end, DESY has established a dedicated research program on high-average-power LPA. Our flagship project KALDERA pursues the development of a new laser tailored to plasma acceleration. Based on Ti:Sa technology, the system will deliver pulses at 100 TW peak power at up to 1 kHz repetition rate and by that enable the application of active stabilisation techniques to enhance LPA performance. Here, we report on the development and commissioning of MAGMA, the first LPA powered by KALDERA. We demonstrate electron injection and acceleration to around 100 MeV at a repetition rate of 100 Hz, reaching into previously uncharted LPA territory.

Speaker: Manuel Kirchen

20 BEETLE: Laser plasma acceleration using a post-compressed industrial Yb-laser system with 1kW average power

Increasing the repetition rate of >100 MeV laser plasma accelerators to the kilohertz range is critical for many real-world applications. However, this requires drive lasers with pulse durations of tens of femtoseconds, pulse energies of hundreds of millijoules, and thus average power in the kilowatt range. Achieving this is challenging, especially with the Ti:sapphire technology widely used to drive such accelerators. However, industrial kW-level laser systems based on Ytterbium gain media do exist, and recently the compression of 200mJ laser pulses at 5kHz repetition rate to sub-40fs duration has been demonstrated using nonlinear post-compression in a gas-filled multi-pass cell.
In this contribution, we present the BEETLE project, which will use this laser system for laser plasma acceleration (LPA) at up to 5kHz repetition rate and 1kW average power of the drive laser. We give an overview of the project, the current status of the experimental setup and present an end-to-end simulation tool chain that allows us to simulate both the nonlinear spectral broadening and the plasma acceleration process itself. This enables a detailed design of the experimental setup, as well as studies of the LPA process using laser pulses with the complex temporal shape inherent in nonlinear post-compressed laser systems.

Speaker: Timo Eichner (Deutsches Elektronen-Synchrotron DESY)

21 Laser Stability Lessons Learned at ATLAS-3000

Laser-driven plasma-based particle acceleration has achieved impressive results over the last decades, demonstrating a large variety of experimental schemes. These studies were possible even though the available instrumentation mostly had prototype-like character, often introducing considerable jitter and drift in the experimental results. Currently, the interest in improving the reproducibility of plasma-based acceleration is growing in the community, with the prospect of facilitating explorative studies and enabling real-world applications.
In this endeavor, the properties of the laser driver, in particular its wavefront, have been shown to play a crucial role in the stability of laser-based acceleration. This also holds for ATLAS-3000, a petawatt laser system hosted at CALA in Garching. In this contribution, we characterize its fluctuations and systematically explore their possible origins as well as their effect on LWFA performance. This includes a detailed analysis of the frequency components present in the pointing jitter, the dynamics and origin of defocus fluctuations, as well as higher-order wavefront fluctuations driven by air turbulence. Special emphasis is put on the pre-focal region, where intensity fluctuations tend to be larger than in the focus itself. We hope that sharing our insights with the community will help address similar issues at other facilities.

Speaker: Johannes Zirkelbach

18:00 Discussion & Closing Remarks

PS4: Theory and simulations: HEP & staging

Conveners: Maxence Thévenet (DESY), Stefano Romeo (Istituto Nazionale di Fisica Nucleare)

22 Nonlinear interaction-point dynamics for plasma-accelerated beams

As the next generation of particle colliders stand to require an ever-increasing real-estate footprint, interest is growing in the potential to shrink the accelerator stage by taking advantage of the high accelerating gradients present in plasma-based accelerators.

The unique advantages of plasma accelerators come with unique challenges.
Radio-frequency accelerators offer symmetric acceleration of both electrons and positrons, while plasmas do not. Electrons can be accelerated in plasma to high energy with low emittance, wheras positrons experience emittance growth.
Additionally, conventional accelerators can accelerate flat beams to give low-disruption at the interaction-point (IP), while the tendency towards circular symmetry in plasmas struggle with this.

In this work, we use numerical simulation to explore the impact of colliding round beams, to what extent focussing optics can be used to shape the beams to reduce disruption at the IP, and the collision of asymmetric beams, where the positrons have a larger emittance than the electrons. We find that competitive luminosities can be obtained with high-disruption beams, and explore methods to optimise for beams with high emittance.

Speaker: Thomas Wilson (Heinrich Heine Universität)

23 All-optic In-plasma Staging of Laser-Wakefield Accelerators Using Density Tailoring

The staging of laser-driven plasma accelerators (LPAs) could open up energy frontiers, but achieving in- and out-coupling of laser pulses while preserving beam quality remains a challenge. In this work, we present an all-optical, in-plasma staging scheme that uses refraction in a transverse plasma density gradient to couple the incoming laser into the next LPA stage, eliminating the need for mirrors and magnets. This design can in principle support significant ion motion without substantial emittance degradation, making it well-suited for a broad energy range. With realistic 3D simulations using the quasistatic particle-in-cell code HiPACE++ on GPU, we observe 98% capture efficiency and 3 GeV energy gain in a second stage, driven by a ~10 J laser pulse guided by a hydrodynamic optical-field-ionized (HOFI) channel of matched spot size 37 microns. These results represent a significant step toward practical multistage plasma acceleration, paving the way for the generation of ultra-high-energy electron beams for a wide range of scientific and technological applications.

Speaker: Xingjian Hui

24 Design and challenges of the witness electron beam injection for AWAKE Run2c

The AWAKE experiment at CERN is developing a novel concept for high-gradient particle acceleration using plasma wakefields driven by high-energy proton bunches. After the successful completion of Run 2b which aimed to demonstrate the stabilisation of micro-bunches with a density step in the plasma source, the experiment started the preparation of its next phase Run 2c which focuses on accelerating high-quality electron beams suitable for particle physics experiments. Run 2c introduces a new modular two-stage configuration, where proton self-modulation and electron acceleration occur in two separate plasma sections. This approach allows independent optimization of each stage, but also introduces significant challenges in beam transport, alignment, and synchronization. In particular, electrons must be injected into the second plasma stage with micron-level precision in both position and beam size to ensure proper matching with the accelerating and focusing regions of the wakefield. Due to these tight injection requirements, the design of a new witness electron beamline for external injection and the design of the injection region itself have been particularly challenging and will be discussed in this contribution.

Speaker: Eleonora Belli (CERN / John Adams Institute, Oxford University)

25 Finding tolerances for the future diagnostics of AWAKE Run 2c

AWAKE is a plasma wakefield acceleration experiment where the wakefields are driven by a long, highly energetic proton bunch that undergoes the self-modulation instability (SMI). The objectives of Run 2c, due to start in 2029, are to demonstrate emittance control of the accelerated electron bunch. Planning for this next phase is under way and includes the design of specialized experimental diagnostics for the accelerated electron bunch.

The complex setup of Run 2c, comprising two ten-meter-long plasma sections, the injection of the witness electron beam into the self-modulated proton bunch in the middle, and two possible SMI seeding methods, is simulated here with both quasistatic and fully electromagnetic particle-in-cell codes. We show the numerical results of the baseline expectation as well as parameter scans that lead to a set of requirements for the electron bunch diagnostics. Such simulations represent a key source of information for the design of plasma-based acceleration experiments.

Speaker: Mariana Moreira (CERN)

26 Beyond Dephasing: Scalable laser-plasma accelerators via Traveling-wave electron acceleration

Traveling-wave electron acceleration (TWEAC) is a next-generation laser-plasma acceleration scheme that bypasses dephasing, pump depletion and diffraction limitations, offering a clear path toward compact accelerators beyond 10 GeV, making it a candidate for future compact accelerators based on existing CPA lasers. TWEAC utilizes two pulse-front tilted laser pulses whose propagation directions enclose a configurable angle. The accelerating cavity is created along their overlap region in the plasma and can move at the vacuum speed of light. The oblique laser geometry enables to constantly cycle different laser beam sections through the interaction region, hence providing quasi-stationary conditions of the wakefield driver. This approach decouples the need for staging from plasma physics, making the design of multiple stages rather a choice that follows the capabilities of the laser systems used.

We present recent results based on large scale 3D simulations conducted at OLCF's Frontier cluster using PIConGPU. For reaching linear, high-gradient cavities at high laser to electron beam energy efficiency we investigate TWEAC regimes featuring small-incident angle focal geometries in the range of 5 - 10°. In addition, we discuss current progress and challenges of maintaining steady-state accelerating conditions to high-energies.

Speaker: Alexander Debus (Helmholtz-Zentrum Dresden-Rossendorf)

18:00 Discussion & Closing Remarks

PS7: Beam diagnostics, instrumentation, Machine Learning: Diagnostics

Conveners: Alessio Del Dotto (Istituto Nazionale di Fisica Nucleare), Brigitte Cros (CNRS - LPGP - Universite Paris Saclay)

27 A Roadmap Towards Direct Imaging of Plasma Targets Using Computational X-ray Holography

Accurate, non-invasive diagnostics of laser-interacted plasma targets are essential for optimizing high-intensity laser experiments, including laser plasma acceleration (LPA). We present a novel approach based on computational X-ray holography to image targets such as hydrogen gas jets. This technique captures single-shot X-ray diffraction patterns in an in-line geometry, where phase contrast arises from the interaction of a divergent beam with the sample. These diffraction images are used to reconstruct spatial phase and, thereby, density distributions.

To solve the inverse problem from intensity-only measurements, we employ machine learning techniques capable of retrieving fine-scale features even in noisy, underdetermined conditions. As a proof of concept, we demonstrate reconstructions of laser-irradiated hydrogen jets, revealing hydrodynamic structure relevant for plasma tailoring and injection control. The approach is compatible with both external and compact plasma-based X-ray sources, enabling real-time, in-situ diagnostics in LPA platforms.

An additional application is proposed for inertial confinement fusion (ICF), where X-ray Free Electron Laser (XFEL)-based coherent diffraction imaging can image shock-compressed solid hydrogen. At the European XFEL’s HED-HIBEF instrument, this technique aims to resolve fuel compression from 20 μm down to sub-micron scales, addressing key challenges in high-gain ICF implosion diagnostics.

Speaker: Dr Ritz Aguilar (Helmholtz-Zentrum Dresden-Rossendorf)

28 Advanced Beam Diagnostics with PolariX TDS: Experimental 5D Reconstruction at SwissFEL

Next-generation accelerators, such as those employing plasma or laser wakefield acceleration techniques, demand precise characterization of the beam's properties, making accurate measurement of the five-dimensional (5D) phase space distribution essential. To meet this need, a novel transverse deflecting structure with adjustable polarization, known as the Polarizable X-band Transverse Deflector (PolariX TDS), has been developed through a collaboration between CERN, PSI, and DESY. By using this device, researchers at DESY have implemented a new tomographic algorithm capable of reconstructing the full 5D phase space of the electron beam. The PolariX TDS allows for beam streaking in a selected transverse direction by adjusting the polarization of the field inside the structure. When combined with a quadrupole scan, this functionality allows for complete 5D phase space reconstruction. This contribution presents measurements carried out at the Athos soft X-ray beamline of SwissFEL (PSI), showing the preparatory studies performed to apply this method at the Athos soft X-ray beamline at SwissFEL as well as showing first preliminary results towards the reconstruction of the 5D phase space under two different electron beam settings.

Speaker: Francesco Demurtas (Istituto Nazionale di Fisica Nucleare)

29 HELPMI: towards a data standard for laser-plasma experiments

The HELPMI project was a 2-year initiative to start the development of a F.A.I.R. data standard for laser-plasma experimental data. It was conducted by GSI, HI Jena and HZDR and subsidized by the Helmholtz Metadata Collaboration. The original aim was two-fold: building upon the extensible NeXus standard – being used for many experimental techniques in Photon and Neutron science – while keeping compatibility with openPMD, a meta-standard currently used for laser-plasma simulation data.
The partners have successfully extended the openPMD standard and its API to include arbitrary hierarchies (like NeXus), thereby allowing for full flexibility for either standard. They have created several showcase files, highlighting the potential of hdf5 containers along with a minimal Nexus standard compliance.
Regarding a metadata standardization, a collection of terms commonly used in laser-plasma experiments has been started. This can serve as a base for a future community-based “standard” list of terms. Furthermore, with contributions from HMC experts, this list was checked for existing definitions of terms in other scientific domains, since LPA is so far not part of e.g. the PaN community. After HELPMI, other projects like THRILL, Lasers4EU, DAPHNE4NFDI or UNLOCK will build upon the results and continue the work.

Speaker: Hans-Peter Schlenvoigt (Helmholtz-Zentrum Dresden - Rossendorf)

30 Development of an Electro-Optic Sampling Beam-Position Monitor at FACET-II

We report preliminary data from a prototype Electro-Optic Sampling Beam Position Monitor (EOS-BPM) at the FACET-II Facility at SLAC National Accelerator Laboratory. In EOS-BPM, a birefringence is induced in two electro-optic crystals on either side of the electron beam's trajectory as it passes by. Laser pulses traveling through each crystal pick up a spacially encoded polarization which is detected. The signal from each crystal provides a single-shot, non- destructive diagnostic of the relative time of arrival of the beam and, in two bunch operation, the longitudinal separation between the drive and witness bunches. By comparing the relative strengths of the signals on each crystal, the instrument can measure the transverse $x$ position of a bunch. We discuss how the installed prototype is currently being employed at FACET-II for plasma acceleration experiments and two bunch commissioning. We present preliminary results of the beam position monitor functionality of the prototype. Finally, we discuss work on an improved prototype capable of measuring bunch position in both transverse dimensions and with increased transverse resolution.

Speaker: Claire Hansel (University of Colorado Boulder)

31 Radiation Safety and Dose Monitoring in Plasma Accelerators

Plasma accelerators made huge advancements in recent years and with increasing repetition rate and average power start to become feasible for use in applications. This increase in power also requires more thinking in terms of radiation safety, especially since both photon and electron beams produced in plasma accelerators have very unique features compared to other beam sources. Here we present our findings of the radiation fields from the different plasma accelerators we have at Deutsches Elektronen-Synchrotron DESY and compare those to the radiation safety of our conventional accelerators on campus. Additionally, we present our radiation detector development programme and highlight several devices we have developed in recent years which are particularly well-suited for dose monitoring and characterizing the distinct radiation environments of advanced accelerator technologies.

Speaker: Dr Simon Bohlen (DESY)

32 Correlating post-wakefield acceleration laser spectra with electron beam spectra to bulid an indirect electron diagnostic

The driving laser's spectrum evolves during laser-wakefield acceleration due to the density and intensity gradients in the driven plasma wave. These density gradients also determine the accelerating fields experienced by injected electrons, and so the post-acceleration laser spectrum may be correlated with the electron spectrum, potentially allowing for its use as a non-disruptive diagnostic of the electron beam spectrum. This would be useful in any application that uses the electron beam in a disruptive way, including several methods of light generation and, of particular interest to the authors, radiation reaction studies.

The relationship is highly non-linear however, and so we make use of machine learning approaches and train a model using not only the laser and electron spectra, but also additional diagnostics measuring the post-acceleration laser energy and spot size. This approach is validated using idealised PIC simulation and then tested on real data from an inverse-Compton scattering experiment carried out at ELI-NP in April 2024. I will present on the method, its quality as an indirect diagnostic, and plans to improve it.

Speaker: Paul Gellersen (University of York)

18:40 General Discussion & Closing Remarks

Poster Session

33 An explicit algorithm in the quasi-static approximate PIC program QPAD

Plasma wakefield acceleration is a method that uses a driving particle beam or an intense laser to excite a wakefield in the plasma and uses the wakefield to accelerate another bunch of particles. In response to the need to simulate the plasma wakefield acceleration, large-scale parallel computing programs such as QuickPIC [1] and QPAD [2] have been developed. These programs use the quasi-static approximation PIC algorithm, while QPAD introduces the azimuthal Fourier decomposition on top of QuickPIC. Currently, both QuickPIC and QPAD use a predictor-corrector method to solve the field equations. In certain cases, multiple iterations are required to achieve convergence. Recently, T. Wang et al. [3] proposed a new explicit algorithm in the quasi-static approximation PIC code, thereby avoiding the need for iterative computation. We first developed an explicit algorithm within the azimuthal Fourier decomposition framework by analytically extracting implicit transverse magnetic terms from current derivatives using conserved quantities. In the explicit equation, the coefficients dynamically change during plasma solving, and their product with the transverse magnetic field quantity causes a modal nesting issue. The algorithm solves all-mode transverse magnetic equations via global matrix construction, enabling explicit quasi-static PIC with azimuthal Fourier decomposition.

Speaker: Ms Rong Tang (Beijing Normal University)

34 Beam Energy Deposition in Plasma Electrons during Wakefield Acceleration by Long Drivers

In this work, we investigate the energy transfer from a long proton bunch driver to the plasma in the context of the AWAKE experiment, using particle-in-cell simulations with OSIRIS. As the driver propagates through the plasma, it excites wakefields by displacing plasma electrons, which gain kinetic energy. This energy can dissipate through several mechanisms, including electromagnetic radiation. We analyse the correlation between the kinetic energy of plasma electrons and the longitudinal accelerating field. Initially, a linear relationship is observed; however, as the wake evolves, phase slippage (dephasing) introduces curvature into the wake structure. Multiple wake phases then contribute to the energy of individual plasma electron slices, breaking the simple linear scaling. We characterise this transition and quantify how dephasing affects the distribution of deposited energy.

Speaker: Carolina Amoedo (CERN)

35 Characterization of Secondary Radiation from LWFA in the EuAPS Project

Laser WakeField Acceleration (LWFA) is a useful mechanism for generating secondary radiation in a compact accelerator setup. Different types of radiation can be produced by the relativistic electrons accelerated in this process. Betatron X-ray radiation is emitted by the electrons due to their transverse oscillations in the plasma channel, while THz radiation is emitted when the electrons leave the plasma-vacuum boundary.
In this context, we present the results of different experimental campaigns carried out at the INFN Frascati and at the CLPU in Salamanca to characterize the secondary radiation from the LWFA process, in particular the expected parameters of the betatron radiation in the framework of the EuPRAXIA Advanced Photon Source (EuAPS) project.
The latter will be the first user dedicated betatron radiation source developed at the INFN Frascati; it is designed to produce photons with 1-10 keV critical energy operating at 1 Hz in the self-injection regime under highly non-linear laser-plasma interaction conditions.

Speaker: Federica Stocchi (Istituto Nazionale di Fisica Nucleare)

36 Controlling FEL bandwidth at SwissFEL using a dielectric wakefield structure

The bandwidth of a free-electron laser (FEL) is increased when the mean energy along the electron bunch varies. In this work, we demonstrate how a dielectric wakefield structure can be used to control the FEL bandwidth by manipulating the beam’s energy chirp prior to its injection into undulators. We compare simulations and measurements of the beam’s energy spread distribution and find reasonable agreement apart from when the structure is operated at gaps below 1 mm. Using the wakefield structure, we successfully reduce the beam's projected energy spread, leading to a narrower FEL bandwidth. Conversely, we also enhance the effect of an inverted chirp in the electron beam due to overcompression in the main linear accelerator, increasing the FEL bandwidth, showcasing the utility of the wakefield structure in tailoring FEL performance.

Speaker: Evan Ericson (PSI/EPFL)

37 Development of a Marx Generator Discharge Circuit for High-Current Plasma Capillary Discharges

In the context of plasma-based accelerators, one of the main advantages lies in their compactness and lower overall cost compared to conventional machines. Beyond acceleration, plasma can also be used to focus (plasma lens) and bend particle beams within compact structures such as discharge-based plasma capillaries.
Beam bending in such devices requires a tailored capillary geometry and a dedicated discharge circuit capable of delivering high currents — typically above 10 kA — through the plasma. In this work, we present the development of a new type of discharge system based on a Marx generator, specifically designed to deliver more than 50 kV and 15 kA into a 20 cm-long capillary.
Several discharge configurations have been tested to optimize the setup for this application. Spectroscopic diagnostics were employed to characterize the plasma parameters. Additionally, numerical simulations were conducted to estimate the resulting magnetic field distribution, and beam dynamics studies were performed to evaluate the guiding effect on a charged particle beam.

Speaker: Romain Demitra (Istituto Nazionale di Fisica Nucleare)

38 Driver distribution in a multistaged plasma-based accelerator facility

Plasma-wakefield accelerators have the potential to reduce cost and size for future accelerator-based projects. The recently initiated SPARTA project aims to design a multistage plasma-wakefield accelerator to accelerate electron bunches to high energy (~50 GeV), for use in strong-field quantum-electrodynamic experiments. We propose to use several beam-driven plasma stages which will require a delivery system of these beams that will drive the plasma wakes. For a train of drivers, all drivers need to be delayed by an appropriate amount of time in order to enter the plasma stage at the right time. The required delay is on the order of nano-seconds for each stage, which is quite challenging for high energy beams. By using a combination of RF-deflectors, dipoles, fast kickers and septum magnets, we show how an oscillating chicane can maximize the delay while keeping the required width of a beamline tunnel low.

Speaker: Daniel Kalvik (University of Oslo)

39 Electron beam setup for seeding of the self-modulation process of a long proton bunch in high density plasma for AWAKE Run 2b

The Advanced Wakefield Experiment (AWAKE) at CERN uses CERN SPS bunches to develop proton-driven plasma wakefield acceleration. However, to excite ~GV/m wakefields, the long SPS bunches must undergo self-modulation (SM) in plasma. SM is a beam-plasma instability and the instability can be seeded to ensure wakefield reproducibility. During Run 2a (2021–2022), AWAKE demonstrated SM seeding using wakefields driven by an electron bunch ahead of the proton bunch in plasma. In these experiments, the electron bunch length was shorter than the plasma wavelength, and asymmetry in the resulting SM was frequently observed, likely caused by beam misalignment. In this contribution, two approaches to improve the seeding process are investigated. First, challenges related to beam alignment are addressed, and strategies and potential solutions presented. Second, seeding with an electron bunch longer than the plasma wavelength is experimentally explored. This is interesting as higher plasma electron densities yield higher acceleration gradients, however, have shorter plasma wavelengths and sub-picosecond electron bunches needed for the seeding at these high densities are not readily available.

Speaker: Nikita Van Gils

40 Enhancing Electron Beam Quality Through Customized Density Gradients in Laser Wakefield Acceleration

The quality of electron beams produced by Laser Wakefield Acceleration (LWFA), is controlled through laser parameters and plasma density distribution during the injection and acceleration phases, and in some cases, a specific device providing beam selection or shaping to achieve the electron beam quality needed the envisaged application.

A major challenge in the generation of LWFA electron sources is reducing energy and transverse momentum spread to enhance spectral brightness, requiring advanced techniques to optimize beam quality.

We design plasma density profiles to control electron injection and acceleration, specifically to improve the electron beam phase space characteristics in a compact way. This poster presents our numerical study using Computational Fluid Dynamics (CFD) and Particle-In-Cell (PIC) simulations. These simulation results are in good agreement with experimental results obtained at Helmholtz-Zentrum Dresden-Rossendorf.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 871124 Laserlab-Europe, an was granted access to the HPC resources of TGCC and CINES under allocation 2023-A0170510062 (Virtual Laplace) made by GENCI.

Speaker: Lodewyk Steyn (LPGP - Universite Paris Saclay)

41 Experimental Generation of PWFA-suitable Bunch Current Profiles by Arc-like Bunch Compressors

Linear accelerators supplying beam-driven plasma-wakefield accelerators (PWFAs) often use chicane bunch compressors to generate the required bunch currents. Higher-harmonic radio-frequency (RF) cavities are typically employed to produce these current profiles, and the parameter range of the RF system might limit the current shaping capabilities. In contrast, arc-like bunch compressors, such as those employed in the MAX IV linac, naturally produce peaked current profiles via passive linearization, not requiring harmonic cavities. The PWFA-relevant capabilities of the linac have previously been investigated theoretically in simulations and experimentally inferred from energy spectra. This work demonstrates the generation of PWFA-suitable ramped current profiles at the MAX IV linac, measured with the recently commissioned transverse deflecting structure. Linearly up-/down-ramped current profiles can enable local flattening of the longitudinal (accelerating) electric field, providing uniform de-/acceleration of the driver and witness, respectively, benefiting final energy spread, gain, and efficiency. These results suggest high suitability of arc-like bunch compressors for future PWFA drivers.

Speaker: Dr Jonas Björklund Svensson (Lund University)

42 Experimental Observation of Space-Charge Field Screening of a Relativistic Particle Bunch in Plasma

The space-charge field of a relativistic bunch is screened in plasma due to the presence of mobile charge carriers. We experimentally investigate such screening by measuring the effect of dielectric wakefields driven by the bunch in an uncoated dielectric capillary where the plasma is confined. We show that the plasma screens the space-charge field when the distance between the bunch and the dielectric surface is much larger than the plasma skin depth, and that, otherwise, the effects of dielectric and plasma wakefields are present simultaneously [1].

[1] L. Verra et al., Phys. Rev. Lett. 133 035001 (2024)

Speaker: Livio Verra (Istituto Nazionale di Fisica Nucleare)

43 Experimental progress towards the Plasma-modulated plasma accelerator (P-MoPA)

Progress towards high-repetition (≥1kHz) GeV-scale electrons from a LWFA source is held back by the lack of laser sources capable of providing joule-level sub-100 fs pulses at high repetition rates. A possible trajectory is to replace Ti:sapphire lasers with Yb:YAG thin-disk lasers. The narrow bandwidth of Yb:YAG only allows direct compression to ∼1 ps, however. Although spectral broadening techniques are available, they are limited to approximately 100 mJ. The Plasma-Modulated Plasma Accelerator (P-MoPA) addresses this issue by utilizing a low-energy, sub-100-fs pulse to seed spectral modulation of a multi-joule picosecond pulse in a free-standing plasma waveguide. A resulting pulse train then resonantly drives a high-amplitude wakefield in a second plasma channel, accelerating electrons.

We describe the results of two experimental campaigns: (i) low-energy experiments at Oxford, which utilize filtered pulses from a Ti:sapphire laser to mimic the drive laser pulse, and (ii) high-energy experiments at the Centre for Advanced Laser Applications (CALA) with joule-scale thin-disk lasers. We demonstrate guiding of joule-level Yb:YAG pulses in a 60mm long plasma channel and the spectral broadening and compression of the "seed" pulse in an argon-filled Herriott cell. We then show the results of the modulation campaign.

Speaker: Sebastian Kalos (University of Oxford, Department of Physics)

44 Local plasma density measurements of a Discharge Plasma Source for AWAKE using Thomson Scattering

The development of scalable plasma sources is essential for future plasma wakefield acceleration (PWFA) applications. In this work, we present a pulsed-DC Discharge Plasma Source (DPS) developed for the AWAKE experiment at CERN, which requires a highly uniform electron density of $7×10^{14}$ cm$^{−3}$ maintained over tens to hundreds of meters. This DPS has already demonstrated to be compatible with AWAKE for the self-modulation of the proton bunch in different gases [1,2].
To assess the applicability of the DPS for electron acceleration, requiring an axial uniformity of better than 0.25%, we evaluate its uniformity by performing localised Thomson scattering [3] measurements on a 3-meter prototype. Time-resolved, axial and radial scans revealed a density uniformity within ±6% along the 3-meter length, excluding the cathode region. This spread approaches our diagnostic precision, highlighting the need for more precise diagnostics to assess whether the plasma axial uniformity meets AWAKE’s stringent requirements. These initial results demonstrate the DPS's potential for achieving the required uniformity and emphasise the importance of high-precision, local diagnostics for characterising plasma sources in next-generation PWFA experiments.

[1] C. Amoedo (The AWAKE Collaboration), in preparation (2025).
[2] Turner et al., PRL 134, 155001 (2025).
[3] Stollberg et al., PPCF 66, 024002 (2024)

Speaker: Carolina Amoedo (CERN)

45 Long-duration ion motion effects in beam-driven plasma-wakefield accelerators

High-repetition-rate operation of plasma-wakefield accelerators is essential for their suitability in the design of colliders and FELs. Energy remaining in the plasma after the wakefield acceleration event can limit the ultimate repetition rate of the plasma accelerator as the plasma takes time to relax to its initial state. This relaxation is limited by two ion-driven effects: their redistribution after the wakefield event and potential further collisional ionisation caused by this motion, as was observed at FACET [Nat. Commun 11, 1–11]. A tens-of-nanoseconds recovery of the original on-axis plasma density directly from ion motion was measured for standard FLASHForward operational settings [Nature 603, 58–62], prompting further investigations into possible ionisation effects. In this work, we investigated hydrogen and argon plasmas at a variety of working points with two different diagnostics: the pump-probe electron-beam-based technique and optical emission spectrometry. In some regimes, both diagnostics indicated additional ionisation happening on the nanoseconds-microseconds timescale, which elongated the recovery time. The dependency of the exact evolution rate of ion-motion-driven ionisation on the initial plasma conditions, namely plasma density and the degree of ionisation, was explored, which will inform the design of the highest repetition rate plasma sources for future colliders and FELs.

Speaker: Judita Beinortaitė (DESY)

46 Measurement of high-quality electron beams from Laser Wakefield Acceleration in a tailored plasma inside a gas cell.

A key challenge in Laser Wakefield Acceleration (LWFA) is to achieve electron beams having high spectral brightness, particularly with high charge and low energy spread. We address this challenge by tailoring density gradients in a gas cell. This provides a way to tune with a high precision the laser interaction with the plasma and enhance electron beam quality.

During experiments using the Helmholtz-Zentrum Dresden-Rossendorf DRACO laser facility,
using LWFA and ionization injection in a tailored plasma in a gas cell, we have consistently produced electron beams with high energy-divergence spectral brightness peaks of 8pC/MeV/mrad and divergence of 0.5 mrad. PIC simulations confirmed the effects resulting from the optimization of the plasma density profile.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 871124 Laserlab-Europe, and was granted access to the HPC resources of TGCC and CINES under allocation 2023-A0170510062 (Virtual Laplace) made by GENCI.

Speaker: Lodewyk Steyn (LPGP - Universite Paris Saclay)

47 Microbunching Instability Studies: a Semi-Analytical Insights for EuPRAXIA@SPARC_LAB

Microbunching instability (MBI) remains a critical challenge for high-brightness electron beams in linear accelerators, especially for free electron lasers (FEL). We present a comprehensive study of the MBI in the context of EuPRAXIA@SPARC_LAB, the first FEL user facility driven by plasma acceleration, focusing on both the emergence and the mitigation of MBI under various machine configurations. Our approach combines a semi-analytical model—based on the Huang–Kim formalism—to capture the evolution of current and energy modulations caused by longitudinal space charge and coherent synchrotron radiation effects, with an assessment of intrabeam scattering and Landau damping enhanced by the laser heater.
We complement this work with further studies of MBI, supported by FEL performance measurements, carried out at FERMI@Elettra, investigating dual stage compression schemes.

Speaker: Giovanni Campri (Istituto Nazionale di Fisica Nucleare)

48 Muon scattering tomography with laser-plasma-accelerator-driven muon source

Laser plasma accelerators (LPAs) can generate GeV-scale electron beams in ultra-compact footprints, making them ideal drivers for various secondary sources. Among these is muon generation, with various groups measuring LPA-driven muons recently. Muons are unstable, heavy elementary particles, that interact mostly by scattering off nuclei as they propagate through matter. This means that they can penetrate large and/or dense objects, with the scattering angle of the emerging muon carrying information about the elemental composition of traversed material. Properties of muon beams driven by an optimised LPA will be presented, along with first simulations of muon scattering tomography and object reconstruction using LPA-driven muons.

Speaker: Kristjan Poder (DESY)

49 Non-linear Inverse Compton Scattering Experiments using a Self-reflecting Plasma Mirror

Relativistic electrons colliding with an intense laser pulse will produce scattered photons through the non-linear Compton scattering (NLCS) process. Self-guided multi-GeV electrons that are accelerated in a gas jet interact at a small collision angle with the self-reflecting intense laser pulse. We describe recent PW-class experiments using a self-reflecting scheme to generate a bright and compact radiation source.

Speaker: Laurence Bradley

50 Nonlinear plasma lens for achromatic staging: follow-up on latest simulation and experiment

One core challenge of the SPARTA project [1] is to offer achromatic staging of plasma accelerators to reach high energies. We propose to achieve this through a specific lattice design, made of dipoles in combination with a novel concept: nonlinear active plasma lenses [2]. Originally motivated by an article on the Hall effect in a glow discharge [3], our idea is to shape the plasma lens discharge B-field distribution with an additional external magnet. The device is developed and manufactured at the University of Oslo. Its B-field currently is being characterised at CLEAR test facility, in combination with plasma hydrodynamic simulations in collaboration with DESY.

[1] European Commission, Staging of plasma accelerators for realizing timely applications (2023). URL https://doi.org/10.3030/101116161
[2] Drobniak, P., Adli, E., Anderson, H. B., Dyson, A., Mewes, S. M., Sjobak, K. N., ... & Lindstrøm, C. A. (2024). Development of a nonlinear plasma lens for achromatic beam transport. arXiv preprint arXiv:2411.00925.
[3] Kunkel, W. B. (1981). Hall effect in a plasma. American Journal of Physics, 49(8), 733-738.

Speaker: Pierre Drobniak (University of Oslo)

51 Physics Considerations for a Plasma Booster Stage for the European XFEL

The linac of the European XFEL accelerates high-quality electron bunches up to a maximum of 17.5 GeV, which undergo free-electron lasing in undulators at photon energies of up to 30 keV. A plasma accelerator stage could be used to significantly increase the electron bunch energy of the European XFEL cheaply and over a short distance. Towards this end we have developed models and performed the first beamtimes at the European XFEL in order to understand whether a twin-bunch structure suitable for plasma acceleration can be generated at the photocathode, then be accelerated and shaped in the following linac sections and bunch compressors. Promising first results from these studies will be presented alongside first considerations of a suitable plasma source, which must be scalable to high average powers. The high current (~5 kA) of an XFEL-derived plasma accelerator driver generates challenges for such a source, for example from ion motion and beam-induced ionisation. These effects will be explored and mitigation strategies proposed. Potential use cases for a plasma booster stage at the European XFEL will be presented.

Speaker: Dr Jonathan Wood (DESY)

52 Physics of transverse dynamics in a laser-plasma accelerator

Laser Wakefield Accelerators (LWFA) offer a promising solution for producing high-energy electron beams in compact setups. Beyond obtaining the required energy, the beam quality (emittance, energy spread, intensity) must also be optimized for LWFA to be considered an alternative to conventional accelerators. Achieving precise control of the transverse beam dynamics is one of the key challenges. This article thoroughly studies the physics governing the evolution of emittance and Twiss parameters within the plasma stage, on the density plateau, and in the up-ramp and down-ramp connections to conventional transport lines. Analytical and numerical analysis will be conducted using a toy model made of special quadrupoles, allowing numerical calculations to be sped up to a few seconds/minutes. Matching between plasma and transport lines will be extensively studied, clearly showing the dependence on initial conditions, and recommendations for the best realistic configurations will be provided

Speaker: Laury Batista (CEA Saclay)

53 Porous Foam: Bridging High-Energy-Density Physics and Complex System Sciences

Porous foams, composed of solid skeletons and vacuum pores, form intricate networks commonly observed in natural systems. The dynamics and pattern formation of waves and particles within these networks have become prominent topics in the study of complex systems. Given the widespread application of porous foams in high-energy-density physics, this talk will explore their potential as a platform for investigating complex system phenomena, such as branched flows and channeling radiation, under extreme conditions.

Speaker: Ke Jiang (Shenzhen Technology University)

54 Potential applications of Plasma-Modulated Plasma Accelerators.

Plasma-Modulated Plasma Accelerator (P-MoPA) can be driven by existing, efficient thin-disk lasers, accelerating electrons to GeV level energies at kHz-repetition-rate. Some aspects of the P-MoPA scheme have already been tested experimentally. Work to demonstrate in the lab the remaining key steps is being undertaken by the kHz Plasma Accelerator Collaboration (kPAC). Assuming that P-MoPA would operate as expected, we are assessing potential applications of P-MoPA. The long-term goal would be P-MoPA driven water window FEL. As a milestone would be a development of a Compton radiation source covering large range of photon energies from about 100 keV to few MeV. Such a source could be used for phase-contrast imaging over the whole range of photon energies covering micron level space resolution for biological objects as well as for high Z metals. On the other hand, transportable source of photons for absorption imaging would have applications for non-destructive inspection in many areas, such as security, manufacturing of critical machine parts and mining to identify rare-earth elements in ores. A separate direction would be to develop a THz radiation source which would only require a train of laser pulses obtained using the plasma modulator; no electron acceleration would ne needed.

Speaker: Roman Walczak (University of Oxford)

55 Progress on Investigating the Peeler Regime at JETi200

In this poster we present our recent progress on experimentally realizing the peeler mechanism to accelerate protons from silicon-based CH coated targets. Known for producing monoenergetic protons, abundant electrons and bright x-rays, the peeler is of general interest in laser-plasma field. The target is oriented longitudinally along the laser propagation direction. The laser pulse interacts with the target's front edge, peeling electrons and driving them forward. These electrons then pull out and accelerate protons at the rear edge. In preparation, the targetry process has commenced, and preliminary 3D-PIC simulations have been conducted to assess the feasibility of using the available femtosecond TW laser for this scheme.

Speaker: Israa Salaheldin (Helmholtz Institute-Jena)

56 Recent developments of a laser-driven ion acceleration beamline at SIOM

Laser driven ion acceleration provides a route to achieve high quality ion beams, which could be superior for specific applications. In this talk I will present recent development of a laser driven ion acceleration beam line based on a homemade table-top 200 TW laser system at Shanghai Institute of Optics and Fine Mechanics (SIOM). Our major motivation is the potential application of such pulsed ion sources.

Speaker: Prof. Jianhui Bin (Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences)

57 Synthetic Radiation Diagnostic in Hybrid LPWFA

We present a study of a radiation signal in laser-driven plasma wakefield accelerators (LPWFA) employing photo cathode injection. While experimentally observed and significant for timing calibration, its underlying physics remains elusive. Using a synthetic optical imaging plugin for PIConGPU we reproduce this signal in simulations for the first time, linking it to plasma structures and cavity dynamics. By analyzing the images alongside 3D, time-resolved particle distributions, we trace the formation of distinct scattering patterns, offering new perspectives on plasma dynamics.

Our synthetic diagnostic enables self-consistent imaging of plasma structures in laser-plasma accelerators. By integrating electromagnetic fields from the PIC simulation and propagating them via Fourier optics methods onto a virtual screen, we generate synthetic images that resemble experimental measurements. This approach allows direct comparison with experiments, providing insights into plasma dynamics and laser-plasma interactions.

These results highlight the potential of synthetic optical imaging to improve experimental diagnostics in laser-plasma accelerators, such as shadowgraphy, and to deepen our understanding of scattering processes in wakefield acceleration.

Speaker: Finn-Ole Carstens (Helmholtz-Zentrum Dresden - Rossendorf e. V.)

58 Temperature diagnostics for high-repetition-rate plasma accelerator sources

Electron-bunch-driven plasma-wakefield accelerators promise to revolutionize particle acceleration by providing compact and cost-effective energy boosters for electron linacs which could, for example, significantly enhance the photon energies produced by free-electron lasers. The FLASHForward facility at DESY has made substantial progress, demonstrating that accelerated electron bunches can maintain their charge, energy spread, and emittance during plasma acceleration. A major challenge remains in achieving high-repetition-rate operation, as is common in radio-frequency accelerators.

To be competitive with proposed linear collider schemes and currently operating FELs, average repetition rates on the order of 10 kHz are required. Therefore, identical plasma acceleration events must take place at high frequencies over a long period of time. One of the important challenges is to deal with the high heat load placed on the plasma cell by the plasma formation process and the driving beam, which are similar in terms of power deposition at FLASHForward. In this contribution we report on recent efforts to characterize the long-term heating effects arising in a discharge plasma source operated at repetition rates up to 1 kHz. We will present measurements of the time evolution of the discharge plasma source and discuss the implications of these results for sustained high-repetition-rate operation.

Speaker: Juan Pablo Díaz (DESY (Deutsches Elektronen Synchrotron))

59 The Linac-Extension Area at the Advanced Photon Source

The Linac-Extension Area (LEA) at the Advanced Photon Source (APS) in Argonne National Laboratory is an experimental facility located downstream of the APS injection linac. It accepts full-energy beam (up to 450 MeV currently) from the APS linac and supports accelerator R&D experiments. An upgraded photoinjector in the APS linac provides high-quality compressed beams to enable R&D on advanced acceleration techniques and next-generation light source concepts. This contribution discusses expected beam parameters, planned in-house experiments, collaboration opportunities, and the current status of the facility with its upgraded photocathode laser system.

Speaker: Philippe Piot (Argonne National Laboratory)

60 The NanoAc Collaboration: Toward a Proof-of-Principle for Laser Wakefield Acceleration in Nanostructured Solid-State Plasma

Solid-state plasma wakefield acceleration has recently garnered attention as a viable alternative for achieving unprecedented ultra-high acceleration gradients on the order of 1 TV/m or beyond. In this context, recent advancements in nanofabrication techniques have opened up the possibility of creating structured plasmas with tailored properties. For instance, the utilization of carbon nanotube (CNT) bundles holds great potential for generating stable plasmas with electron densities reaching as high as 10^{24} cm^{-3}, i.e., orders of magnitude higher than conventional gaseous plasmas. As part of a new collaborative effort called NanoAc, we have conducted Particle-In-Cell (PIC) simulations to investigate laser wakefield acceleration in nanostructured solid-state plasmas based on CNT arrays. Our results confirm the attainment of wakefields at the TV/m scale. Additionally, we observed self-injection, sub-femtosecond bunch formation, and electron acceleration in micrometre-scale targets, yielding kinetic energies of ~10 MeV. These findings open up promising possibilities to design novel ultra-compact accelerators and radiation sources. In this contribution, we present a summary of the work carried out by the NanoAc collaboration to date and discuss the preparation of future experimental tests in existing laser facilities.

Speaker: Javier Resta Lopez (ICMUV-University of Valencia)

61 Towards high-repetition-rate, application-driven LPAs for radiotherapy

The translation of laser-plasma accelerators (LPAs) from research facilities to clinical settings relies on both scalability and control. Bringing industrial, multi-kHz Yb lasers into the LPA landscape is a key step toward this goal, promising compact, tuneable electron sources for therapeutic applications, like FLASH radiotherapy.
Here, we present an integrated effort that combines the commissioning of a novel, kHz LPA with a machine learning-based simulation framework, designed to tailor the beam properties for optimised dose delivery. The optimisation routine navigates an hybrid workflow. It links computational fluid dynamics (CFD) for plasma source modelling, particle-in-cell (PIC) simulations for laser–plasma interaction and GEANT4 for dose deposition, to yield electron beams with specific spatial and temporal dose profiles. This simulation-led approach enables a precise plasma source design, assisting the experimental tuning and accelerating the system integration.
The simulation pipeline and the optimisation outcome are presented, alongside the first experimental results from the kHz Yb-laser-driven LPA under development. Together, these efforts represent a promising pathway toward application-driven, next-generation radiotherapy, enabled by industrial laser technology.

Speaker: Bonaventura Farace (DESY)

20:30 Dinner

Tuesday 23 September

Plenary Session

62 Resonant Excitation of Plasma Wakefields with a Train of Relativistic Particle Bunches

In the context of plasma wakefield acceleration, resonances can be exploited to generate large-amplitude wakefields, using a train of relativistic particle bunches with frequency content close to the plasma electron frequency, to accelerate a trailing bunch.
We show with experimental results and numerical simulations that the wakefields driven by individual successive bunches in overdense plasma superpose linearly, and that their amplitude increases along the train, under optimal coupling with plasma density oscillations. We also demonstrate that a train of bunches with increasing charge can be used to enhance the transformer ratio of the acceleration process, hence improving the energy transfer efficiency [1].

[1] L. Verra et al., submitted, https://doi.org/10.21203/rs.3.rs-6115160/v1

Speaker: Livio Verra (Istituto Nazionale di Fisica Nucleare)

63 Advanced diagnostics for high-peak current electron beams

The longitudinal structure of ultra-short electron bunches generated by Laser wakefield accelerators (LWFAs) is strongly shaped by the rapid injection dynamics and the interaction between the laser and the electron beam throughout the acceleration process. A detailed understanding of these bunch structures is essential for advancing compact FELs and further secondary light sources.

We present experimental results based on spectral single-shot measurements of broadband coherent transition radiation (UV to mid-IR, 250nm-11.35μm) from LWFA electron bunches passing through a metal foil. By analyzing the transition radiation spectra, we reconstruct electron bunch profiles including sensitivity and uniqueness properties. We show that electron bunches originating from different injection regimes exhibit complex longitudinal structures spanning multiple time scales — from the overall bunch envelope to sub-micrometer microstructures. These features vary with the injection regime and correlate with signatures in the electron spectrometer. Microstructures on the scale of the laser wavelength and its harmonics arise from laser–electron interactions during acceleration.

Speaker: Dr Alexander Debus (Helmholtz-Zentrum Dresden-Rossendorf)

10:40 Coffee Break

Plenary Session

64 High gradient X-band linac as a driver for PWFA user facility

The EuPRAXIA@SPARC_LAB project aims to develop a compact, high-brightness FEL user facility based on plasma wakefield acceleration (PWFA). To drive the plasma module, a normal-conducting RF linac employing X-band technology is foreseen. The linac features an S-band photoinjector followed by an X-band booster composed of sixteen 1.05 m-long traveling wave accelerating structures operating at 11.994 GHz. These structures are designed to sustain a minimum accelerating gradient of 60 MV/m to achieve the beam energy required for efficient plasma injection.
An extensive R&D program is underway at INFN-LNF to validate the X-band technology and confirm its suitability as a reliable driver for PWFA-based user facilities. This includes the design, fabrication, and testing of various RF components, along with the prototyping and qualification of the accelerating structures. Recently, two RF structure prototypes have been completed, and one has undergone preliminary high-power testing.
This contribution provides an overview of the ongoing and planned activities in X-band technology development, with a particular emphasis on the first high-power test results of the accelerating structure prototypes.

Speaker: Fabio Cardelli (Istituto Nazionale di Fisica Nucleare)

65 Stable laser-acceleration of high-flux proton beams from liquid sheets

Laser-plasma acceleration has enormous potential to provide compact sources of ultra-short ion beams. Several factors, such as the low shot-to-shot stability, large beam divergence and the difficulty of high-repetition rate operation, hamper their wider adoption. Recent work demonstrates an approach for overcoming these challenges using a novel liquid sheet target, developed at the SLAC National Accelerator Laboratory. These experiments, at the GEMINI TA2 laser facility (10 TW, 5 Hz), demonstrated stable acceleration of few MeV proton beams via target normal sheath acceleration with beam exhibiting high flux and low-divergence in comparison to proton beams from typical thin foil targets [1]. Supporting PIC simulations indicate that the presence of the low-density background vapour which surrounded the target plays an important role in the observed collimation of the proton beam through the generation of azimuthal magnetic fields which act to focus the proton beam. The measured proton beams are already suitable for applications requiring high proton flux and the platform can be extended to kHz repetition rates or higher laser energies extending the utility of the source to a wide range of applications.
[1] Streeter et al., Nat. Comms 16, 1004 (2025)

Speaker: Charlotte Palmer (Queen's University Belfast)

66 Measurement of directional muon beams generated at the Berkeley Lab Laser Accelerator

We report the detection of directional muon beams generated by a compact
petawatt-class laser-plasma wakefield accelerator (LPA). Multi-GeV electron bunches are generated and accelerated in a 30 cm plasma and subsequently converted into high-flux, directional muon beams through pair production in a high-Z target. Muons are unambiguously identified and characterized using a scintillator-based coincidence detection scheme. The results are benchmarked against a detailed Geant4 model of the experimental setup, showing excellent agreement with the data and indicating a production rate that significantly surpasses the cosmic muon background radiation. The demonstration of high-yield, directional muon beam production based on a compact laser-plasma wakefield accelerator paves the way for the development of portable muon
imaging applications with substantially reduced exposure times.

Speaker: Sarah Schroeder (Lawrence Berkeley National Laboratory)

12:30 Lunch Break

16:00 Coffee Break

PS1: Plasma-based accelerators and ancillary components

Conveners: Mario Galletti (Istituto Nazionale di Fisica Nucleare), Sarah Schröder (Lawrence Berkeley National Laboratory)

67 Towards better electrons for applications: tackling the energy, emittance and luminosity frontier

We present recent progress at the Center for Advanced Laser Applications (CALA) toward generating high-energy electron beams with minimal divergence and high stability. First, employing the petawatt (PW) laser ATLAS-3000, we aim to produce multi-GeV, precision-injected electron beams for a Breit–Wheeler pair creation experiment. Emphasis is placed on reliable performance in complex collision setups, favoring simpler target geometries such as gas jets and cells to enhance beam stability and energy. Second, we investigate the transformer ratio in a hybrid laser–plasma wakefield acceleration (LWFA)/particle beam-driven wakefield acceleration (PWFA) scheme, demonstrating internally injected, high-quality witness bunches at energies reaching twice that of the 750 MeV driver. These beams exhibit ultralow divergence and a few-percent energy spread, making them promising candidates as compact, table-top free-electron laser (FEL) drivers. Finally, we endeavor to implement a plasma-modulated plasma accelerator concept pioneered at Oxford using the picosecond, fully diode-pumped Yb:YAG CPA laser PFS. Ongoing efforts include integrated laser–target stabilization to ensure reliable electron-beam production, supporting the next generation of secondary radiation sources.

Speaker: Prof. Stefan Karsch (LMU München)

68 Direct Observation of electron shedding from a laser driven wakefield accelerator

Electron beams from a wakefield accelerator are usually assumed to be short, comparable to the plasma wavelength. Under certain conditions, as the electrons start to exit the accelerator, the plasma wavelength increases and the electrons are moved into the decelerating phase of the wakefield. At this point, the electrons start to lose energy, and a fraction of them are separated and lost from the beam, a process we call as "electron shedding."
Using femtosecond relativistic electron microscopy, we imaged the evolution in the longitudinal current density of the beam as it exits the accelerator. It is seen that an initially short electron beam lengthens to > 40 times the plasma period in the accelerating stage before losing electrons on the way. The process results from a modification of the energy distribution of the beam resulting in a lower useful charge and contributes to the formation of dark current, reducing its efficiency.

Speaker: Sheroy Tata (Weizmann Institute of Science)

69 Laser wakefield acceleration studies with experimental laser profiles using particle-in-cell simulations

The rapid evolution of advanced accelerator technology calls for high-fidelity computational models that can accurately reproduce experimental observations. Laser Wakefield Acceleration (LWFA) has emerged as a promising method for generating high-energy electron beams among the diverse high-gradient acceleration techniques. To accurately capture the complex physical dynamics observed in LWFA experiments, it is essential to incorporate realistic experimental laser profiles into simulations. In this work, we focus on implementing an experimentally realistic laser profile in the particle-in-cell (PIC) simulation framework SMILEI with azimuthal mode decomposition approximation. In this study, we used experimental input data from the PALLAS laser-plasma injector test facility, including intensity spatial and temporal laser profiles. The open-source Python library LASY is used to import the 3D experimental laser profiles and generate an input file for the PIC simulations. By integrating a realistic laser profile from the experiment, our study aims to bridge the gap between simulations and experimental results, providing deeper insights into the underlying physics of LWFA and trying to provide better tolerancing on laser driver pulse quality and control.

Speaker: Kalyani Swain (Laboratoire de Physique des 2 Infinis Irène Joliot-Curie-IJCLab-UMR9012, Bât. 100, 15 rue Georges Clémenceau, 91405 Orsay Cedex, France)

70 Dephasingless Laser-Wakefield Acceleration

Laser-wakefield accelerators (LWFA) deliver high quality, mono-energetic electron beams in a compact and reliable way. Yet, achieving multi-GeV electron bunches, without requiring additional laser beams or plasma channels, remains a challenge that may require changing our approach that will facilitate the acceleration of even more energetic electron beams. For that, LWFA must overcome challenges that limit the acceleration achievable in existing systems. The axiparabola, a long-focal-depth reflective optical element, has generated interest in its potential to overcome both the beam diffraction and the electron dephasing limitations of LWFA. This can be accomplished by combining the axiparabola with a manipulation of the spatio-temporal couplings (STCs) of the incoming beam.
In this talk, I will present our recent experimental results and the insights that they provide in the pursuit of dephasingless acceleration. These include the first experimental demonstration of the ability to tune the velocity of peak intensity via an axiparabola and STCs4, the first acceleration of electrons directly with an axiparabola-generated wakefield, and the first direct imaging of such a wakefield. The results are backed up by extensive simulations. These proof-of-concept results explore the novel regime of the axiparabola-generated wakefield and bring us closer to the eventual demonstration of dephasingless LWFA.

Speaker: Prof. Victor Malka (Weizmann Institute of Science)

71 Controlled Injection in a Laser Plasma Accelerator via an Optically Generated Waveguide Constriction

Following recent advances that have pushed LPA energy gains to the 10 GeV level, attention is beginning to shift toward enhancing beam quality, tunability, and reliability in this regime. In this context, we propose a novel scheme for controlling the injection of a high-quality electron bunch into a channel-guided laser-plasma accelerator. This all-optical technique, constricted waveguide injection, creates a highly tunable, controlled injection structure natively within a plasma waveguide, a key requirement for the efficient acceleration of high-quality multi-GeV electron beams. We describe a simple optical setup to tailor the plasma and present start-to-end simulations showing the injection structure formation and the generation of a 1.1 GeV electron beam with 10 pC of charge and 0.35% energy spread using 1 J of drive laser energy. We additionally discuss the scalability of the scheme to higher energies. Highly tunable tailored plasma sources, like those proposed here, enable fine control over the injection and acceleration processes and thus will be crucial for the development of application-focused laser-plasma accelerators.

Speaker: Dr Rob Shalloo (Deutsches Elektronen-Synchrotron (DESY))

72 Experimental generation of petawatt peak power electron beams via laser heater shaping at FACET-II

We report on the experimental generation of high-energy (10 GeV), ultra-short (fs-duration), ultra-high current (0.1 MA) electron beams with petawatt peak power at FACET-II [1]. These extreme beams enable the exploration of a new frontier of high-intensity beam-light and beam-matter interactions broadly relevant across fields ranging from advanced accelerators, laboratory astrophysics, strong field quantum electrodynamics and ultrafast quantum chemistry. We demonstrate our ability to generate and control the properties of these electron beams using a laser heater, which exploits the coherent interaction between a laser pulse and an electron beam in a magnetic undulator to shape the electron beam distribution. By tailoring the laser heater’s temporal profile, we can modulate the beam's current profile on-demand, creating designer electron beams for specific applications. We characterize the charge, peak current, and duration of these beams and show their use in initiating beam-induced ionization of gas targets relevant to advanced accelerator applications. The extreme beams generated in this work have already found applications in the FACET- II experimental program for studying plasma-based injection schemes and the transition between the nonlinear and wakeless regimes in beam-driven plasma wakefields.

[1] C. Emma et al., PRL 134, 085001 (2025)

Speaker: Claudio Emma (SLAC National Accelerator Laboratory)

18:20 Discussion & Closing Remarks

PS4: Theory and simulations: Methods

Conveners: Maxence Thévenet (DESY), Stefano Romeo (Istituto Nazionale di Fisica Nucleare)

73 ABEL: A Start-to-End Simulation and Optimisation Framework for Plasma-Based Accelerators and Colliders

The Adaptable Beginning-to-End Linac (ABEL) simulation framework offers a comprehensive solution for simulating and optimising plasma-based accelerators and colliders. ABEL’s modular, Python-based design unites diverse, specialised codes such as HiPACE++, Wake-T, ELEGANT, GUINEA-PIG, CLICopti and ImpactX under a single framework, enabling seamless transitions when simulating beamlines consisting of different components. Simplified models for transverse instabilities, radiation reactions, and ion motion built into ABEL also further allows for flexibility in balancing between simulation fidelity and computational fidelity. ABEL further integrates advanced diagnostic tools and robust Bayesian optimisation techniques to enhance machine design, performance evaluation and allow for global optimisation of the full programme cost.

Speaker: Dr Jian Bin Ben Chen (University of Oslo)

74 Modeling laser-wakefield accelerators using the time-averaged ponderomotive approximation in a Lorentz boosted frame

Future, high-fidelity simulations of multi-GeV-class Laser Wakefield Accelerators (LWFAs) will need to model the propagation of high-intensity laser drivers over meter-scale plasmas with high spatial and temporal resolutions, thus requiring high amounts of computational resources.

Various techniques have been devised over the years to reduce the computational cost of such simulations, including the time-averaged ponderomotive approximation, and the use of the Lorentz boosted frame technique.

In this presentation the combination of these two computational techniques will be discussed, highlighting the resulting significant reduction in the computational cost of LWFA simulations and the limitations of this approach.

The combination of the two techniques can potentially become essential for the modeling of a multi-TeV, LWFA-based collider.

Speaker: Francesco Massimo (LPGP - CNRS)

75 Mainstreaming Start-to-End Realistic Simulations in Plasma Accelerator Research

As plasma accelerators continue to mature, comprehensive simulations of all system components are increasingly essential for interpreting experimental results and designing credible concepts. Capturing the wide range of relevant physical mechanisms—including complex 3D effects—requires state-of-the-art simulation tools and seamless integration between them. In this contribution, we present a consistent set of simulation tools developed and employed at DESY to model the full plasma accelerator chain. This includes the formation and evolution of hydrodynamic optical-field-ionized (HOFI) waveguides, discharge capillaries, beam trapping and acceleration in plasma wakefields, as well as downstream RF and magnetic beamline transport. Our toolkit spans open-source codes capable of scaling from laptops to supercomputers—such as HYQUP, Wake-T and HiPACE++ and emphasizes their interoperability through shared data standards and interfaces. In particular, we highlight the adoption of the openPMD standard and LASY, a collaborative open-source Python library for handling laser pulses. We will also showcase production-level studies leveraging start-to-end simulations and discuss strategies for integrating simulations with experimental data.

Speaker: Maxence Thevenet (DESY)

76 Open boundary conditions for the time-averaged ponderomotive approximation in Particle-In-Cell codes

Fully kinetic Particle-In-Cell simulations of laser wakefield accelerators (LWFA) demand heavy computational resources mainly because of the wide range of time and space scales they have to cover: from the short laser cycle to the long plasma target.
The time-averaged ponderomotive approximation (TPA), also called the laser envelope model, is a very efficient way of reducing this disparity and thus the cost of LWFA simulations.

Over the last few years, this model has been improved and tailored for various LWFA schemes. The numerical dispersion of the highly parallelizable envelope equation solver has been improved, the model has been implemented in Cartesian and cylindrical geometries, and its capability of simulating tunnel ionization for LWFA has been demonstrated.

This presentation reviews the capabilities of the envelope model as they were implemented in the PIC code Smilei and reports, for the first time, the implementation of open boundary conditions for TPA in the form of Perfectly Matched Layers for the full wave equation for the laser complex envelope. This is a critical step towards the application of TPA to the accurate simulation of LWFA.

Speaker: Arnaud Beck (LLR - CNRS)

77 Galilean Electromagnetic (GEM) PIC code for highly efficient simulations of LWFA and PWFA

A novel method for simulating wakefield acceleration in plasmas is introduced. The newly developed GEM-PIC code is a fully electromagnetic, three-dimensional (3D) particle-in-cell (PIC) simulation tool that leverages a Galilean transformation of variables. This transformation effectively eliminates the vast scale disparity between the laser wavelength and the typical acceleration length in wakefield setups.

Similar to established quasi-static simulation codes, GEM-PIC employs a transformation to fast and slow variables: (\zeta = z - ct) for the fast coordinate and (\tau = t) for the slow time. However, unlike quasi-static approaches, GEM-PIC retains the complete set of Maxwell’s equations without approximation. This allows it to fully resolve electromagnetic wave propagation, including the laser pulse itself. Furthermore, GEM-PIC treats all particles equally and does not distinguish between beam and plasma particles, enabling a self-consistent modeling of particle trapping.

The GEM-PIC framework paves the way for ab initio simulations of laser pulse propagation and wakefield formation in extended plasma channels. It is also capable of modeling beam-driven wakefields and simulating the propagation of particle bunches through external magnetic fields—for instance, in transitions between plasma sections.

Speaker: Prof. Alexander Pukhov (University of Duesseldorf)

78 Recent progress on QuickPIC and QPAD

QuickPIC and QPAD are both parallel PIC codes that applies the quasi-static approximation. They can efficiently simulate both beam driven and laser driven plasma wake field accelerators with a speed that is much faster than the conventional PICs code without losing accuracy. QuickPIC is a 3D code in the Cartesian coordinates while QPAD is a branch of QuickPIC that applies azimuthal decomposition in cylindrical coordinates. In this work, we will introduce our recent developments on explicit solvers in both QuickPIC and QPAD. We will also introduce the progress on radiation module and the basic algorithm of a GPU + MPI version of QuickPIC.

Speaker: Weiming An (Beijing Normal University)

18:20 Discussion & Closing Remarks

PS5: Applications

Conveners: Felicie Albert (Lawrence Livermore National Laboratory), Jaroslav Nejdl (ELI Beamlines Facility, Extreme Light Infrastructure ERIC), Prof. Victor Malka (Weizmann Institute of Science)

79 Active energy compression of a laser-plasma accelerator

Laser-Plasma accelerators (LPAs) promise a compact alternative to modern RF-technology. However, the central energy jitter and energy spread, both on the percent-level, have so far prevented LPAs to drive real-world applications. Here, we experimentally demonstrate active energy compression of a laser-plasma accelerated electron beam. At the LUX experiment at DESY, a dipole chicane stretches the electron bunch in time thereby imprinting an energy-time correlation (chirp), which is subsequently removed with an RF cavity. Our setup reduces the variations in central beam energy as well as the energy spread by more than an order of magnitude to the permille-level. We demonstrate performance so far only attributed to modern RF based accelerators which opens the door for a variety of applications, such as compact plasma-based injectors for synchrotron storage rings.

Speaker: Andreas Maier (DESY)

80 Laser Wakefield Acceleration Experimental Area at the CLF Extreme Photonics Applications Centre

The Central Laser Facility are constructing the Extreme Photonics Applications Centre (EPAC), aiming to become operational as a user facility in 2027. EPAC will house a 10 Hz, 1 PW laser serving two independent experimental areas. The first area to come online is configured as a long focus beamline, predominantly for developing laser wakefield acceleration in gas targets. I will describe the design of this beamline, our plans for targetry and diagnostics, and our proposed operational model.
One of the goals for EPAC is to optimise secondary sources for applications, particularly x-ray imaging using ultrafast x-ray pulses. This will require the implementation of stabilisation strategies and machine learning techniques that have been demonstrated by the LWFA community in recent years. We have established a network of industrial users who are interested in using LWFA technology and I will highlight several areas we aim to explore with proof-of-principle campaigns.
Before starting full operations, we plan a period of beamline commissioning to establish reliable LWFA performance. I will outline our plan for these initial experimental campaigns and explain our facility priorities. Bringing EPAC online will be a collaborative effort with our users and we welcome involvement from all in the LWFA community.

Speaker: Daniel Symes

81 Field-deployable laser wakefield acceleration: Stable operation in conventional industrial settings beyond controlled laboratory environments

Laser wakefield accelerators (LWFAs) represent a transformative breakthrough in particle acceleration, achieving acceleration gradients 1,000 times higher than conventional radiofrequency-based accelerators. This revolutionary technology promises substantial reductions in the size and cost of accelerator-based systems, potentially paving the way for the next-generation compact light sources and high-energy particle colliders. However, despite their potential, state-of-the-art LWFAs remain primarily confined to laboratory settings due to environmental sensitivities, limiting their operational stability and flexibility in practical application scenarios. To address these challenges, we have developed a compact, transportable, containerized LWFA system, marking the successful demonstration of an LWFA operating stably outside a laboratory environment. The system maintained full-power operation for over 10 hours per day on approximately 150 days, and achieved stable electron beam generation for continuous 72 hours with a root-mean-square energy fluctuation of 1.4%. Currently, the system has been deployed to provide micro-focus, tens-of-MeV bremsstrahlung X-rays for mission-critical nondestructive testing applications of dense objects. Here, we present high-quality computed tomography imaging of a real nickel-alloy aeroengine turbine blade, achieving a spatial resolution better than 50 μm. This study marks a pivotal milestone in advancing LWFAs from research laboratory prototypes to practical, quasi-industrial-grade instruments, demonstrating their operational readiness for real-world applications.

Speaker: Jianfei Hua (Tsinghua University)

82 A compact portable X-Ray Source for Fast 3D Tomography Using Laser-Plasma Acceleration

The MULTISCAN 3D project aims to provide a technical solution to create 3D tomography systems capable of detecting threats invisible with current 2D technology. Laser-plasma acceleration appears to be a promising method, generating ultrashort and highly charged electron beams converted into versatile X-ray sources. Being flexible, laser-plasma accelerator offers multiple sources in a compact setup, which pave the path towards compact and fast 3D cargo container scan.
Here we present first demonstration of X-ray imaging with a highly compact (footprint < 9 m² ) transportable system capable of generating electrons and photons in the MeV range at repetition rates up to 10 Hz with charge reaching 1 nC. We profit a high divergence of optimized electron beams with Maxwellian energy spectra to convert it into compact X-ray beams with wide aperture. In addition to the principle of this technique, we demonstrate first tomography results obtained within the framework of the MULTISCAN 3D project. This achievement shows the feasibility of performing laser-plasma acceleration with a transportable system, significantly expanding the potential for applications.

Speaker: Lena Kononenko (Ecole Polytechnique)

83 Compact all-optical precision-tunable narrowband hard Compton X-ray source

Bright X-ray beams with narrow bandwidth and tunable energy can lead to various novel applications. Compact all-optical inverse Compton scattering X-ray sources show great potential as alternatives to large-scale synchrotron sources to democratise access to such beams. However, all-optical ICS sources are yet to demonstrate percent-level bandwidths, a key requirement for many applications. Here we show how an active plasma lens can be used to tailor the electron bunch-photon interaction, producing tunable X-ray and gamma beams with percent-level bandwidths. The central energy of the X-ray beam can be varied without any moving parts, allowing for precision-tuning the X-ray beam energy. These concepts form the basis of the APHEX source at DESY, which will be a precision-tunable high flux X-ray source for industrial and medical applications. First results from APHEX will be discussed along with potential applications for this unique source.

Speaker: Kristjan Poder (DESY)

84 Compact Beamline for Laser-Plasma-Based Radiotherapy

There has been growing interest in using very high energy (100-300 MeV) electrons for radiotherapy, both using conventional and plasma-based sources. While not as precise as ions, ultra-relativistic electrons offer a more favorable dose deposition profile than X-rays, potentially reducing the irradiation of healthy tissue. Laser-plasma sources of ions and electrons could offer cheaper and more compact alternatives to conventional sources, and recent advances have brought them closer to a relevant parameter range for radiotherapy. However, their energy spread often exceeds the stringent requirements of clinical radiotherapy. While further source optimization could partially bridge the gap, the particle transport system from source to target can also be used to tailor the final beam properties. This work outlines the design concept for a compact particle transport beamline that filters the particle energies and reduces the outgoing spatial and angular jitter, offering a step towards clinical implementations of laser-plasma particle sources for radiotherapy.

Speaker: Dr Jonas Björklund Svensson (Lund University)

18:20 Discussion & Closing Remarks

PS6: Ion acceleration and developments towards fusion

Conveners: Charlotte Palmer (Queen's University Belfast), Ulrich Schramm (Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Radiation Physics)

85 TNSA proton beam focussing in a low-density plasma behind the target

High-intensity lasers can accelerate protons through mechanisms such as target normal sheath acceleration, producing beams with picosecond pulse durations, high charge and low emittance. These beams are desirable for applications such as radiobiology, warm dense matter and radioisotope generation; however, for these applications to become viable, challenges that need to be addressed include reducing the high divergence of these sources (10s degrees) and achieving multi-Hz operation. Experiments have demonstrated that propagation of a proton beam through low-density media immediately behind the source can reduce the proton beam divergence by an order of magnitude, due to the generation of focussing magnetic fields [1]. This presentation will discuss recent experiments that have studied this focussing effect further using a multi-cm gas cell containing a low-density gas (10^16 – 10^17 cm^-3) behind a foil target, producing beams with a divergence below 3°. A low-density plasma behind a target, through using liquid sheet targets or a low-density gas behind a solid target, presents an opportunity for the development of simple, low-divergence, high-repetition-rate compatible proton sources, ideal for applications.

Speaker: Peter Parsons (Queen's University Belfast)

86 Towards a Stable and Application-Oriented Laser-Driven Proton Source at CALA

Over the last few years, research at the laser-driven ion acceleration (LION) beamline at the Centre for Advanced Laser Applications (CALA) in Garching near Munich has been established. The setup is powered by the Petawatt-class ATLAS-3000 Ti:Sa laser operating at 1 Hz. Currently, up to 13 J in 28 fs are focused to a 5 $\mu$m FWHM focal spot, reaching peak intensities $>10^{20}$ W/cm$^2$. To harness the high repetition rate of the laser system, a liquid leaf target system using water is implemented, routinely generating protons with maximum energies $>25$ MeV. First experiments were conducted to transport and focus these particles using an energy-selective doublet of permanent quadrupole magnets to a small focal spot on our application platform in air. For diagnostics, a set of electromagnetic pulse-resistant detectors based on the ionoacoustic principle is available. These are capable of diagnosing the three-dimensional properties of the particle bunch, including particle number, even at high repetition rates. Current projects focus on employing Machine Learning to optimize the proton source, supported by the "Tango Controls" software framework and a highly automated experimental setup in cooperation with leading expertise at CALA.

Speaker: Dr Sonja Gerlach (LMU Munich)

87 Efficient laser proton acceleration in the near critical density regime

Improved control of high intensity laser beam parameters on target recently enabled proton energies beyond 100 MeV, dose-controlled sample irradiation experiments, and the demonstration of seeded FEL light.
This presentation focuses on the chain of developments at the Petawatt laser DRACO that enabled systematic studies in the regime of relativistic target transparency for thin foil as well as cryogenic hydrogen targets. While both targets concepts yielded highest proton energies, the second was further improved to support 1 Hz repetition rate operation at 100TW class laser power. Here, flat jet geometries recently showed very promising energy and efficieny scaling for future applications.

References:
[1] F. Kroll, et al., Nature Physics 18, 316 (2022)
[2] M. Rehwald, et al., Nature Commun. 14, 4009 (2023)
[3] T. Ziegler, et al., Nature Physics 20, 1211 (2024)

Speaker: Ulrich Schramm (Helmholtz-Zentrum Dresden-Rossendorf)

88 Optical probing of plasma dynamics in intense laser interaction with nanostructured solids

Nanostructured solid targets have gained significant attention in high-intensity laser-plasma interaction due to their potential to improve laser absorption, enhance particle acceleration, and enable access to extreme-energy-density states [1].

However, experimentally probing the interaction dynamics and critical plasma properties remains challenging, as their evolution occurs on nanometer spatial and femtosecond temporal scales. Such measurements are particularly important for capturing the interaction of the leading picosecond pedestal and the steep rising edge of the amplified laser pulse, as they can pre-ionize and expand the target before the main peak of the laser[2]. The resulting pre-expansion can significantly alter the initial shape of the nanostructured target, adversely affecting laser absorption and particle acceleration. Accurately capturing these dynamics is essential for benchmarking plasma simulations and guiding the design of contrast-optimized targets.

Here, we present an optical pump-probe setup capable of resolving pre-plasma dynamics during the interaction of a 150 TW ultrashort pulse laser with nanostructured targets, with nanometric spatial and sub-picosecond temporal resolution. By combining scattering and Doppler spectrometry-based measurements [3], we characterize pre-plasma expansion, velocity, and particle acceleration under different laser contrast conditions. These measurements provide insights for understanding how modified nanostructure profiles of the target affect laser-plasma coupling and ion acceleration.

Speaker: ANKIT Dulat (Helmholtz-Zentrum Dresden-Rossendorf)

89 Modulations on Thomson parabolic-like ion-patterns caused by laser-matter produced ElectroMagnetic Pulses

When a high-intensity laser interacts with matter, many processes lead to the generation of intense electromagnetic fields, in a spectrum ranging from MHz to THz, known as electromagnetic pulses(EMPs). The effects of the EMPs on the instrumentation are long-time studied topic, especially in laser-driven ion acceleration or nuclear-fusion experiments.
We studied the evidence of such fields on the Thomson Parabola(TP) spectrometer used for the detection of the mass-to-charge ratio and energy spread of emitted ion beams in laser-matter interaction experiments. This detector separates particles by their mass-to-charge ratio and their energy using electrostatic and magnetostatic fields, producing characteristic parabolic traces. Spurious EMPs affect the static fields inside the TP, causing ripples in the particle traces. From the analysis of the ripples, we could retrieve the relative intensity and the temporal evolution of the intercepted EMP. In the same shot, we measured the electromagnetic signal captured by the TP-electrodes, which acts as a voltage variation between them, and the particle traces imaged in the detection plane of the TP.
This analysis leads to a temporal and spectral analysis of the emitted fields, giving a new tool for a deeper insight into the laser-plasma interaction dynamics and the generation of the EMPs.

Speaker: Francesco Filippi (ENEA)

90 Spin-polarized beams from plasma-based accelerators and prospects for nuclear fusion

In recent years, sources of polarized beams from laser-plasma interaction have gained significant interest in the accelerator community [1]. Possible applications of such beams range from basic research, e.g. deep-inelastic scattering, to enhanced energy production in fusion reactors. It was shown by Kulsrud et al. that in the case of the reaction $d + t\to \alpha + n$, the cross-section is increased by a factor of 1.5 [2]. Similar enhancements are expected for other reactions like proton-Boron fusion.
In this talk, we present the state-of-the-art for polarized beams from plasma-based accelerators. In particular, we discuss recent theoretical results like the acceleration of polarized Helium-3 using Laguerre-Gaussian laser pulses as well as the first successful acceleration of polarized beams using the PHELIX laser system [3].

[1] L. Reichwein et al., arXiv:2411.11621 (2024)
[2] R. M. Kulsrud et al., Phys. Rev. Lett. 49, 1248 (1982)
[3] C. Zheng et al., arXiv:2310.04184v2 (2024)

Speaker: Dr Lars Reichwein (Forschungszentrum Jülich)

18:20 Discussion & Closing Remarks

PS7: Beam diagnostics, instrumentation, Machine Learning

Conveners: Alessio Del Dotto (Istituto Nazionale di Fisica Nucleare), Brigitte Cros (CNRS - LPGP - Universite Paris Saclay)

91 Data-Driven Exploration of High Average Power Laser-Plasma Accelerators

Recent advances in high-power lasers approaching kilohertz repetition rates are pushing laser-plasma accelerators (LPAs) into the watt-level average-power regime, offering unprecedented statistical access to their intrinsic properties. In this talk, we outline how the Kaldera project at DESY employs fast diagnostic measurements to explore key performance aspects of high-average-power LPAs. We outline our real-time data-acquisition framework—designed to capture key experimental observables on every shot—and describe how scalable processing pipelines integrate these measurements with advanced modeling tools. We show how large, high-repetition-rate datasets can reveal sources of shot-to-shot variability and how, when combined with tailored real-time modeling techniques, they form the basis for efficient control and optimization. Finally, we will present recent results on data and machine-learing-driven operation at Magma–Kaldera’s high average power laser plasma accelerator.

Speaker: Sören Jalas

92 Active Sensing: Bayesian Measurement and Control

This work explores the application of Bayesian methods to enhance measurement and optimization in experimental physics, with a focus on laser-plasma interactions. Bayesian updates enable the integration of prior knowledge with new data, facilitating refined parameter estimation and uncertainty quantification. These methods have been employed to achieve the first single-shot measurement of complete spatio-temporal vector fields, providing a comprehensive characterization of petawatt laser pulses. Additionally, Bayesian Autocorrelation Spectroscopy (BAS) is introduced as an innovative technique for spectral measurements, leveraging prior information for rapid convergence. Finally, Bayesian optimization demonstrates exceptional efficiency in tuning laser wakefield accelerators, enabling precise control over electron beam properties through systematic exploration of parameter space.

Speaker: Andreas Döpp

93 Automated Bayesian Optimisation in Laser Plasma Acceleration

Bayesian Optimisation (BO) has shown great promise in optimising Laser Plasma Acceleration (LPA) experiments, even in the presence of substantial measurement noise. Notably, BO has demonstrated its ability to identify user-specified optima and generate tuning curves, effectively mapping an input space trajectory to a smooth variation of an observation parameter, such as mean energy. However, BO operates at an interesting intersection: the data acquisition rate in LPA experiments is fast by traditional BO standards (typically on the order of seconds), but slower compared to the needs of off-the-shelf gradient-based methods, which also struggle with high noise levels.
This talk will explore the practical challenges of applying BO to LPA experiments, focusing on the unique conditions and constraints presented by high-speed, noisy, and dynamic environments. Additionally, I will introduce a novel software framework designed to automate the optimisation process, effectively removing human intervention from the loop. By streamlining the optimisation into an end-to-end pipeline, this framework addresses the bottleneck of manual parameter adjustments. The automation of this process represents a crucial step toward real-time optimisation of LPA experiments.

Speaker: Christoph Marvin Eberle (LMU Munich)

94 Statistical analysis of sources of instability on electron beam quality in a laser plasma accelerator preparing for Bayesian optimization

Laser-electron accelerators emerge as novel, compact sources of high-quality relativistic electron beams. Their extremely high peak currents make them ideal for applications in fields such as material science, healthcare, and particle physics.
Each experimental application requires unique electron parameters. Additionally, all the input parameters are interconnected, resulting in a highly complex parameter space. This increases the cost in time and resources for preparing experiments. To address this issue, we have developed a semi-automated Bayesian optimization loop that adjusts six input parameters simultaneously to achieve optimal electron beam parameters.
However, the high nonlinearity of laser wakefield acceleration poses a challenge for automated optimization, as even minor fluctuations in input parameters can lead to significant changes in electron beam properties. To quantify and mitigate the effects of these statistical fluctuations, we have compiled an extensive dataset through systematic studies of their characteristics and influence on the electron beam quality.
Alongside demonstrating an initial prototype for semi-automated Bayesian optimization, this work will enhance the understanding of the underlying sources of instability in laser-plasma acceleration experiments, which are essential for more complex machine learning experiments.

Speaker: Franziska Marie Herrmann (Helmholtz-Zentrum Dresden-Rossendorf)

95 Advanced Controls and Machine Learning at FLASHForward

Plasma accelerators often constitute a high-noise environment with multiple, non-linear dependencies that make the setup and operation of such devices a difficult task. To address these challenges, Machine Learning methods have gained popularity in the field of plasma acceleration. In this contribution, we summarise the application of such techniques to the beam-driven plasma acceleration experiment FLASHForward at DESY, Hamburg. Examples include the automated tuning of the plasma stage via Bayesian Optimisation and the development of non-destructive, neural-network-based predictions of the resulting accelerated trailing-bunch spectra.

Speaker: Lewis Boulton

96 Machine Learning-Based Diagnostics and Control of Dielectric Laser Acceleration

Dielectric Laser Acceleration (DLA) is a promising technology for compact electron accelerators, capable of achieving accelerating gradients far beyond those of conventional radiofrequency cavities. Dielectric nanostructures are used to shape the near-fields of ultrashort laser pulses to accelerate electrons. However, introducing advanced laser shaping techniques, such as pulse front tilts or higher order dispersion, adds significant experimental and operational complexity. These setups involve many parameters that require precise control and optimization. Machine learning (ML) has proven to be a valuable tool in improving the performance of traditional accelerators. In this talk, we present the implementation of an ML-based control system for DLA experiments at the ARES facility at DESY. This system reconstructs and optimizes the laser pulse shape using diagnostic data from the post-DLA electron beam. A deep neural network built with PyTorch is trained on simulation data generated by a symplectic 6D tracking code. These simulations have been benchmarked against experimental results from interaction between electrons and laser pulses with different pulse shapes. We further refined hyperparameters for accurate reconstruction and evaluated DLA-specific structures and diagnostics to address ambiguities. Ultimately, this system serves as a virtual diagnostic to actively optimize DLA performance.

Speaker: Dr Thilo Egenolf (TU Darmstadt)

18:20 General Discussion & Closing Remarks

Poster Session

97 A hybrid accelerator to deliver therapeutic electron beams at high energies

Very High Energy Electrons (VHEE) are emerging as a cancer treatment commodity. Compared to protons, VHEE is less sensitive to inhomogeneities within the human body. This means they are less damaging to healthy tissue when treating dynamic organs such as the lungs, liver, and kidneys. VHEE have a range of penetration depths depending upon the energy, often ranging from 50 MeV to 250 MeV. Such beams can be generated using radiofrequency photoinjectors followed by tens of meters long copper-based booster linacs. We are envisaging a hybrid approach where high-brightness electron beams are generated using mature copper photoinjector technology and injected into a plasma module for further acceleration. The goal is proof of a compact VHEE radiotherapy machine within a meter. In this contribution, we will review therapeutic electron beams and discuss the layout of the hybrid VHEE machine and a technique developed to match the conventional electron source and the plasma accelerator.

Speaker: Oznur Apsimon (The University of Manchester)

98 An explicit algorithm for the quasi-static particle-in-cell program: QuickPIC

Plasma wakefield acceleration is a mechanism that utilizes intense particle beams to excite large-amplitude plasma wakefield in plasma, thereby accelerating charged particles. Its acceleration gradient exceeds that of the most advanced radio frequency acceleration techniques by several orders of magnitude, reaching GeV/m level. This technology lays the groundwork for constructing ultra-compact accelerators and radiation sources, and also enables the development of plasma-based free electron laser devices and ultra-high-energy positron-electron colliders. The quasi-static approximation Particle-in-Cell (PIC) code QuickPIC[1,2] is a large-scale parallel computing program capable of efficiently simulating the physics processes of plasma wakefield acceleration. It employs a predictive iteration method to solve the electromagnetic field equations, which may require multiple iterations to converge. Recently, another quasi-static approximation PIC code, WAND-PIC[3], proposed a new explicit algorithm for solving the equations without an iterative process. We have integrated this method into QuickPIC. To solve the new explicit magnetic field equations, the original spectral method based on fast Fourier transform is no longer applicable. Therefore, we have introduced a finite difference method-based Poisson solver into QuickPIC. Finally, we show a comparison of the computational results between the iterative and explicit algorithms in QuickPIC.

Speaker: Hainan Wang (Beijing Normal University)

99 Comparison of direct laser acceleration performance using radially polarized near infrared and long-wave infrared lasers

Direct laser acceleration with radially polarized lasers is an intriguing variant of laser-based particle acceleration that potentially offers GeV/cm-level gradients while avoiding the instabilities and complex beam dynamics associated with plasma-based accelerators. Currently, the performance of this method is primarily limited by the difficulty of generating high-power radially polarized beams. We propose the use of CO2-based long-wave infrared (LWIR) lasers as a driver for direct laser acceleration, as the polarization insensitivity of the gain medium allows for higher peak powers, since amplification can occur after polarization conversion. Additionally, the larger waist sizes and pulse lengths associated with a longer wavelength can improve electron beam injection efficiency. By comparing acceleration simulations using a near-infrared laser and an LWIR laser, we show that the injection efficiency is indeed improved by up to an order of magnitude using the LWIR laser. Furthermore, we show that even sub-TW LWIR lasers can provide MeV-level energy gains. Thus, radially polarized LWIR lasers show significant promise as a driver of a direct laser-driven demonstration accelerator.

Speaker: William Li (Brookhaven National Laboratory)

100 Correlating Light Emission and Wakefield Dissipation

In plasma wakefield acceleration, energy is tranferred from a driver to a witness bunch through the wakefields. Energy lost by the driver is stored in wakefields as kinetic energy of the oscillating electrons, and as potential energy of the electric and magnetic field. A witness bunch can be accelerated by the longitudinal electric field. Wakefield energy is eventually dissipated in the plasma. A part of this energy is emitted as light. We discuss the proportionality between the emitted light and wakefield amplitude. We correlate the measured light to energy deposited in the plasma by laser pulses and electron bunches with the amplitude of wakefields expected at the plasma entrance. We use these results to investigate the evolution of wakefields driven by a long relativistic proton bunch at AWAKE.

Speaker: Jan Mezger (Max-Planck Institute for Physics)

101 Design and tolerance studies of the Undulators for the EuPRAXIA@SPARC_LAB Free-Electron Laser lines

The EuPRAXIA@SPARC_LAB facility will be the first plasma-driven free-electron laser user facility and will host two different beamlines: the AQUA beamline, a SASE FEL designed to operate in the water window down to 3-4 nm, and the ARIA beamline, a seeded HGHG FEL operating in the VUV spectral range from 50 to 180 nm.
The beam driving these FELs is accelerated up to 1-1.2 GeV by an X-band normal conducting linear accelerator followed by a plasma wakefield acceleration stage.
The main FEL amplifier of AQUA consists of an array of ten APPLE-X permanent magnet undulator modules, each 2 m long and with a period length of 18 mm. The HGHG configuration for ARIA works with a modulator and four APPLE-X permanent magnet undulator modules with a period of 10 cm and 4.8 cm respectively.
The main design studies of such undulators are discussed, evaluating the tolerance of resistive wall wakefields, magnetic field errors and misalignments, as well as their impact on the FEL performance.

Speaker: Dr Michele Opromolla

102 Determining the matching codition of an electron beam to a plasma ion column

AWAKE aims to produce electron bunches with parameters suitable for fixed target experiments: 50-200GeV, percent level energy spread, and mm-mrad normalized emittance. The proton-driven plasma wakefield accelerator uses self-modulation of the long, narrow proton bunch to reach accelerating gradient of around 1GeV/m. To reach these parameters, the electron bunch must create its own blowout, i.e., its density must be larger than the plasma density. It must be matched to the focusing force of the ion column, and load wakefields driven by the proton bunch [1]. The plasma is created by ionization of a rubidium vapor by a backward-propagating laser pulse. We use numerical simulations to determine whether the matching condition could be determined experimentally, by measuring the energy spectrum of the bunch as a function of the relative timing between the bunch and laser pulse, without the proton bunch. Varying the delay, the bunch can enter the plasma focusing, at its waist, or defocusing. The beta function of the beam is around 4mm, delays of +/-60ps cover +/- two beta functions. Determining parameters for the matching condition would greatly simplify injection experiments in the presence of the proton bunch.

[1] V. K. Berglyd Olsen et al., PRAB 21, 011301 (2018)

Speaker: Marlene Turner (CERN)

103 Developing an ultra-short laser pulse for probing relativistic laser-plasma interactions

Ultra-short laser pulses are essential to resolve femtosecond-timescale dynamics in plasma-based particle accelerators. Presented here is a high-intensity hollow-core beam line designed to spectrally broaden an input spectrum by a factor three, with an output pulse energy of ~2 mJ. These pulses can then be compressed to ~10 fs and will be utilized to take crisp shadowgrams of plasma wave sub-structures in LWFAs and PWFAs and furthermore used as a photocathode injector laser in a PWFA.

The spectral broadening is based on the mechanism of self-phase modulation, which requires an intense, short laser pulse and a material with strong third-order nonlinearity.
Noble gases, with their comparatively high ionization levels and sufficiently large nonlinear refractive indices, are top candidates to act as nonlinear medium.
The required intensity for self-phase modulation is achieved by focusing the laser down to a smaller beam diameter.
A hollow-core fiber is used to maintain the small beam diameter over a longer distance and to clean the spatial profile of the pulse.

Challenges in designing such a hollow-core fiber beam line are spatial limitations, ionization de-focusing, laser induced damages on optics and self-focusing effects due to the high pulse intensity.

Speaker: Onur Bilen

104 Development of a high charge 10 GeV laser electron accelerator

Recent all-optical multi-GeV laser wakefield acceleration (LWFA) demonstrations have been enabled by University of Maryland's development of meter-scale supersonic gas jets and low-density plasma waveguides. This poster presents a review of our recent LWFA efforts, including gas jet development, experiments and simulations to benchmark plasma waveguide generation, a new 3-stage model for relativistic pulse propagation in meter-scale waveguides, and recent high efficiency LWFA experiments. These experiments demonstrate sub-milliradian divergence electron bunches with integrated charge >1nC above 1 GeV, and energy spectra including ≲ 10 pC features of ~10 GeV, representing a laser to electron conversion efficiency of at least ~30%.

Speaker: Ela Rockafellow (University of Maryland)

105 Development of an achromatic spectrometer for a laser-wakefield-accelerator experiment

The large gradients of plasma-wakefield accelerators promise to shorten accelerators and reduce their financial and environmental costs. For such accelerators, a key challenge is the transport of beams with high divergence and energy spread. Achromatic optics is a potential solution that would allow staging of plasma accelerators without beam-quality degradation. For this, a nonlinear plasma lens is being developped within the SPARTA project. As a first application of this lens, we aim to implement an achromatic spectrometer for electron bunches produced by a laser-wakefield accelerator. We report on progress in designing such an experiment.

Speaker: Felipe Peña (University of Oslo and Ludwig Maximilian University of Munich)

106 Electron-Positron Plasma Generation in Foam Targets

Electron-positron plasmas are fundamental to understanding some of the most energetic astrophysical phenomena and represent a unique state of matter. While they have been theoretically studied extensively, experimental studies remain limited due to the challenge of generating and confining such plasmas.
Numerous setups have been proposed to maximize pair yield [1]. With the advent of ultra-intense lasers, such as the 10 PW L4 laser at the ELI facility [2], the experimental realization of $e^-e^+$ plasmas is coming within reach. In recent years, foam targets have attracted significant interest in high-energy laser-plasma interactions [3] and are suitable for studying QED effects.
In our study, we consider a pre-ionized foam target with a Gaussian channel to guide a high-intensity laser pulse, generating high-energy electrons, using 2D PIC simulations A reflector placed behind the target reflects and intensifies the laser fields, enhancing pair production. We find that the production rate is highly sensitive to the reflector geometry and initial plasma profile. Additionally, we compare the resulting energy spectra with theoretical predictions, highlighting conditions for optimal pair production.

[1] A. Samsonov and A. Pukhov, arXiv:2409.09131 (2024)
[2] F.P. Condamine et al., PPCF 65, 015004 (2023)
[3] O.N. Rosmej et al., HPLSE 13, e3 (2025)

Speaker: Oliver Mathiak (Heinrich-Heine-Universität Düsseldorf)

107 Energy transfer in a proton-driven wakefield accelerator

Plasma-based accelerators support large field gradients, but reaching high energies requires that these gradients be sustained over long distances. The high energy of currently available proton sources offers the potential to accelerate a witness bunch to the energy frontier, avoiding the need to couple sequential plasma stages.

However, a proton driver presents its own unique challenges. The large proton mass means that the limiting factor at low energies is longitudinal dispersion of the driver, while the asymmetric plasma response arising from the mass difference between ions and electrons introduces additional constraints on the transformer ratio due to the positive driver charge. In this work, we investigate the efficiency with which energy can be transferred from a proton driver to a trailing witness, the scaling with driver energy, and the influence of the driver profile.

Speaker: Alexander Pukhov (uni duesseldorf)

108 Excitation of Wakefields in Carbon Nanotubes and Graphene Layers: Hydrodynamic Model and PIC simulations

Charged particles moving through carbon nanostructures may excite electromagnetic modes (plasmonic modes) due to the collective excitation of the electron gas in their surfaces. This effect might be a potential candidate to accelerate particles with ultra-high accelerating gradients. The plasmonic excitations can be studied by particle simulations and with analytical models. In this contribution, we firstly review the existing theory based on a linearised hydrodynamic model for a point-like charge propagating along a carbon nanotube and graphene layers. In this model, the electrons confined over the surfaces are treated as a two-dimensional plasma with additional contributions to the fluid momentum equation from specific solid-state properties of the electron gas. Then, we compare the plasmonic excitations derived from the hydrodynamic model with those obtained from Particle-in-Cell simulations. Finally, a comprehensive analysis is performed to explore the similarities, differences, and limitations of both methods.

Speaker: Pablo Martín-Luna

109 Experimental measurement of the saturation length of the Self-Modulation

A long, narrow bunch propagating in plasma is subject to the self-modulation (SM) instability, a transverse process. In the AWAKE experiment, we study the evolution of SM along the plasma by changing the length of plasma over which the bunch propagates. In particular, we observe the effect of the transverse wakefields on the bunch by measuring the size of the halo of defocused particles at a screen downstream from the plasma. We observe that the maximum radius of the halo changes with beam and plasma parameters. Numerical simulation results suggest that there is a correlation between the plasma length for which the halo is fully formed, and the plasma length for which the SM process saturates. We study this halo formation for different parameters, and compare it with numerical simulations results.

Speaker: Arthur Clairembaud (Max Planck Institüt für Physik)

110 First results of the E302 experiment at the FACET-II facility.

Plasma-wakefield accelerators are capable of sustaining accelerating fields on the GV/m scale, making them well-suited for shrinking the size and cost of future linear colliders. The recently proposed efficiency–instability relation sets an upper limit on the achievable power transfer efficiency from the driver to the trailing bunch if the stability of the transverse phase space of the trailing bunch is to be preserved. Examining the relation between efficiency and strength of transverse instabilities is a main objective in the E302 experiment which aims to identify, measure, and mitigate the beam-breakup (BBU) instability in beam-driven plasma-wakefield acceleration. We will discuss data taken during the first experimental shifts at the FACET-II facility at SLAC, Menlo Park, CA in April 2025. The shifts focused on (1) measuring the instability using the dipole spectrometer at FACET-II with parallel-to-point imaging, and (2) seeding a transverse offset between the trailing and driving bunches using a transverse deflecting cavity.

Speaker: Ole Gunnar Finnerud (The University of Oslo)

111 GPU-MPI Parallelization for QuickPIC, an Algorithm for Simulating Plasma Wake Field Acceleration

Plasma wake field acceleration (PWFA) is a new method for particle acceleration. It is potentially capable of reaching an accelerating gradient 1000 times the gradient of conventional accelerators. QuickPIC is a program for simulating PWFA. It can offer helpful insight on the construction and usage of plasma wake field accelerators, as well as some other plasma-related phenomena.
Considering that more and more supercomputers are equipped with GPUs, we need to make full use of these computing resources. This project attempts to develop a version of QuickPIC with GPU-MPI parallelization, based on the UPIC framework. We rewrite the subroutines in the classes part2d, fft2d, fpois2d, ufield2d and fdist2d, in the 2d loop of the program. In the end, this project realizes the running of QuickPIC on supercomputers with GPU clusters, and compares the efficiency and accuracy of the program running on CPUs and different numbers of GPUs. The results show the advantage of using GPUs over CPUs in PWFA simulation.

Speaker: Ms Yueran Tian (Beijing Normal University)

112 Independent Control of Electron Injection and Acceleration in a Laser Plasma Accelerator

Numerous studies have explored techniques to optimize electron beam properties, such as energy, energy-spread, charge, and divergence in a laser wakefield accelerator. Controlling electron injection and acceleration independently is key to producing high-quality beams in laser wakefield accelerators. We demonstrate such decoupling using one laser beam focusing in a gas medium thanks to a novel double-compartment gas cell with a modular design.

A nitrogen-doped hydrogen mixture in the first compartment enables ionization injection, while the interface between the two compartments supports density down-ramp injection, and pure hydrogen in the second compartment sustains laser guiding for efficient acceleration. The modular design allows customization of compartment lengths, interface geometry, and face diameters, providing precise control of the plasma density profile. This setup enables independent tuning of beam charge and energy, offering flexible control over key beam parameters.

Experiments at the DRACO laser facility (Helmholtz-Zentrum Dresden-Rossendorf) lead to the identification of many regimes (compartment sizes, pressures, and trigger timing) that generated quasi-monoenergetic electron beams with peak energies up to 300 MeV, FWHM charges up to 40 pC, energy spreads below 10%, and divergences under 1 mrad. These results highlight the potential of density-tailored, modular plasma targets for advanced beam manipulation in compact accelerators.

Speaker: Abhishek Panchal (CEA Paris-Saclay)

113 Laser post-compression for dephasingless laser-wakefield experiments of electron acceleration

Laser-wakefield electron acceleration (LWFA) is an important alternative to conventional accelerators, that was proposed by Tajima and Dawson [1]. To achieve higher electron energies, a new concept has been recently proposed based on laser fields with spatio-temporal coupling and focused by axiparabolic mirror. The aim is to have a long focal depth with phase-matched regime of wakefield acceleration [2].

As shown theoretically in [2], the electron energy gain obtained with phase-locked condition can be one order of magnitude or higher than with standard self-guided laser-plasma accelerators, at the same laser energy level, with gain increases when using shorter pulses.

We present our results intended to achieve shorter pulse durations by post-compressing [3] 27 fs, 1 J pulses from a Ti:Sa laser, based on self-phase modulation in fused silica. By characterizing the spatial and temporal profiles we can make further steps towards the usability of post-compressed high-power laser pulses in dephasingless LWFA experiments.

[1] Tajima, T. and Dawson, J. “Laser Electron Accelerator”, Phys. Rev. Lett. 43, 267-260 (1979)
[2] Caizergues, C. et al. “Phase-locked laser-wakefield electron acceleration”, Nat. Photonics 14, 475-479 (2020)
[3] Khazanov, E. et al. “Nonlinear compression of high-power laser pulses: compression after compressor approach,” Physics-Uspekhi 62(11), 1096-1124 (2019)

Speaker: Anda-Maria Talposi (Weizmann Institute of Science)

114 Machine learning-based optimisation of plasma density ramps at CLARA FEBE

Plasma wakefield acceleration (PWFA) offers acceleration gradients much larger than that in conventional accelerators. The Full Energy Beam Exploitation (FEBE), a new beamline attached to the Compact Linear Accelerator for Research and Applications (CLARA) at Daresbury Laboratory, has been designed as a dedicated test facility for users. By providing access to high-power lasers and electron beams, FEBE enables the validation of proof-of-principle experiments for innovative applications. In this work, we numerically investigate PWFA with a two-bunch configuration, i.e., the driver/witness bunch generated at CLARA FEBE, to enhance the beam quality of the accelerated witness bunch. Machine learning-based optimisation of the plasma density ramp, involving ramp position, peak density, and ramp sharpness, has been performed. Additional simulations validate and assess the trained model. Meanwhile, tolerance and sensitivity analyses are carried out to evaluate robustness and inform future proof-of-principle experiments.

Speaker: Jiaqi Zhang (University of Manchester)

115 Modelling of electro-optic sampling for the study of laser-wakefield acceleration

In the context of electron sources produced by laser-wakefield acceleration (LWFA), the temporal evolution of generated electron bunches is a key parameter. Detection of electrons' arrival time and longitudinal profile is needed to characterise the source. Among other diagnostic methods, electro-optic sampling enables to measure electron bunch distribution and arrival time non-destructively and in a single shot. It is a well-known approach for conventional accelerators, but the technique needs to be adapted to short-duration electron bunches obtained by laser-plasma acceleration. In this poster, I will present the results of analytical modelling of electro-optic diagnostics as well as a setup for a high-quality electron LWFA scheme.

Speaker: Oleksandra Khomyshyn (LPGP-CNRS-Université Paris-Saclay)

116 Optical control of betatron oscillation amplitude in a laser wakefield accelerator

One important application of laser wakefield acceleration is the production of bright x-ray beams generated from the betatron oscillations of electrons in the wake of a laser pulse. The amplitude of the betatron oscillations is directly correlated with key characteristics of the emitted x-ray radiation, such as flux, critical energy, and divergence. We experimentally demonstrate that a shock wave created by a heater beam can increase the amplitude of betatron oscillations with a degree of control, thereby improving the key parameters of the betatron radiation. The increase in the oscillation amplitude was inferred from electron and x-ray diagnostics, as well as through comparisons with particle-in-cell simulations. We observed the stability of the increased amplitude over series of more than 50 shots. The proposed method can be used independently or in conjunction with other techniques to enhance betatron x-ray sources produced by laser wakefield accelerators.

Speaker: Ivan Kargapolov (Weizmann Institute of Science)

117 Progress on the Flat beam PWFA experiment at AWA

A wakefield experiment at the Argonne Wakefield Accelerator (AWA) facility utilizes flat electron beams with highly asymmetric transverse emittances to drive plasma wakefields in the underdense regime. These beams create elliptical blowout structures, producing asymmetric transverse focusing forces. The experiment utilizes a compact 4-cm-long capillary discharge plasma source developed at UCLA. Analytic models of blowout ellipticity and matching conditions, supported by particle-in-cell simulations, guide the experiment's design. Engineering preparations including the use of windows for vacuum-gas separation, beam transport and diagnostics are discussed. The first beam runs involving flat beam generation and transport is also discussed.

Speaker: Pratik Manwani (University of California, Los Angeles)

118 Proton beam divergence measurements from radiation pressure driven shock acceleration

Laser-plasma ion acceleration is a well established field of research, with several mechanisms being exploited to produce high energy, short particle beams.

Scaling laws show that both the laser's vector potential, and the critical density scale favorably with laser wavelength. Hence the long wavelength ($\mathrm{9.2\mu m}$) $\mathrm{CO_{2}}$ laser at the Brookhaven National Laboratories is the ideal choice for exploring radiation pressure acceleration using gaseous targets.

The work carried out by the Imperial group at BNL has demonstrated steady ion production in the scenario where the laser interacts with the gas-jet from a supersonic nozzle.

Significant gains in the ion energies were obtained when employing the laser's pre-pulse to shape the target and form blast waves. This approach produced low divergence, $\sim$1MeV mono-energetic ion beams. The results are backed by PIC simulations which give insights on the acceleration dynamics.

Thanks to a short-pulse probe beam it was possible to accurately image the laser-target interaction using interferometry. An innovative proton spatial diagnostic, which allowed us to quantify the divergence of the ion beams, was also fielded.

Measuring particle divergence is a crucial first step towards optimising the coupling between beams and transport lines, which is essential for all applications of ion acceleration.

Speaker: Ginevra Casati (Imperial College London)

119 SHARP: A compact focusing system for medical applications using a diverging plasma lens

For cancer radiotherapy the ability to precisely irradiate a small spot deeply inside the patient while minimizing the radiation exposure to surrounding tissues is desired. This can be accomplished by a round beam sharply converging towards a single spot, requiring a large beam size in both planes at the exit of the focusing system. Achieving this over a short distance using only quadrupole lenses is challenging; but by using a linear active plasma lens (APL) in defocusing mode, the beam can be quickly and non-destructively enlarged before focusing using quadrupoles. The position of the irradiation spot can also be scanned in 3D space through changing magnet settings. We will also study the wakefield effects in the lens, which might be detrimental to the use of such a system for irradiation. The SHARP project will develop and test this concept. Such a system can be used with very high energy electrons (100s of MeV), creating a Bragg-peak like spot without requiring a bulky proton accelerator and gantry, enabling the use of novel accelerator technology for compact radiotherapy facilities. If successful, SHARP will enable precision conformal radiotherapy, spatial fractionation, and potentially be useful for FLASH therapy.

Speaker: Kyrre Ness Sjøbæk (University of Oslo)

120 Solving the external injection problem: H3$^+$Beams, High-quality High-gradient acceleration for HEP

The H3$^+$Beams project seeks to solve the many challenges of external injection from an RF-injector into a high-gradient LWFA structure, and to explore the physics of beam quality preservation in injection and staging.

Principal amongst the obstacles of injection from an RF-injector are the few-femtosecond synchronisation and bunch length requirements.
We address these through THz-driven bunch compression, were a laser-derived THz pulse provides a chirp to the RF-injector bunch. Subsequent compression in a magnetic arc leads to femtosecond temporal-locking between the laser and the (compressed) electron bunch. This temporal-locking is robust against RF injector jitter, and the timing jitter of the THz and LWFA drive laser.
Transverse focusing into the LWF channel is via PMQ triplets and plasma gradient lensing. Simulations indicate high preservation of bunch emittance and energy spread preservation.
Preliminary results in THz compression and temporal-locking will be discussed in detail, together with an overview of the full capability for GeV acceleration and beam quality preservation.

The project, a consortium of Lancaster, Liverpool, Manchester and Oxford Universities, and Daresbury National Laboratory, has been proposed for implementation on the CLARA electron beam facility. Discussion of wider engagement across Europe is welcomed, including potential for alternative host locations.

Speaker: Prof. Steven Jamison (Lancaster University)

121 Spectral characterization of hard X-rays emitted from a Laser Wakefield Accelerator

Laser-plasma-driven X-ray sources based on betatron oscillations and inverse Compton scattering offer unique properties, including femtosecond duration, milliradian divergence, and high photon flux. These very properties, however, impose limitations on their spectral characterization, particularly for single-shot detection of X-ray energies up to 100 keV. Conventional semiconductor and scintillator-based detectors face challenges due to limited quantum efficiency at higher energies and susceptibility to overexposure from intense photon fluxes. Our approach employs a filter pack comprising metallic elements of varying thicknesses and atomic numbers, paired with a pixelated CsI(Tl) scintillator array imaged onto a CCD camera. By analysing the spatially resolved transmission through the filter pack and solving the related inverse problem, we reconstruct the X-ray spectrum using probabilistic optimization algorithms. We validate the accuracy of this method by reconstructing spectra from conventional X-ray tubes and demonstrate that it is able to retrieve single-shot betatron spectra from laser-wakefield experiments without the need for assumptions about their spectral shape.

Speaker: Enes Travac (PhD)

122 Stable and High-Quality Laser Wakefield Positron Acceleration Scheme

Laser wakefield acceleration (LWFA) has the advantages of high acceleration gradient and compact scale, which is a promising candidate for the next generation of electron-positron colliders. However, high-quality positron acceleration mechanism based on LWFA is still absent. In this poster, we propose a stable, dephasing-resistant laser wakefield positron acceleration scheme to achieve low-energy-spread, low-emittance and high-charge positron acceleration. A bi-Gaussian laser pulse significantly shorter than the length of the blowout bucket is used, guided by a pre-formed plasma channel. This setup suppresses laser evolution and stabilizes wakefield structure, enabling consistent positron acceleration with low emittance and narrow energy spread. Additionally, the group velocity of the laser lower than the speed of the positron beam will cause the dephasing between the laser and the beam, resulting in changes in the accelerating field experienced by positrons. By optimizing the positron beam's current profile and initial distance from the laser, we can exploit dynamic beam loading, reducing or eliminating the dephasing-induced energy spread over tunable distances. Moreover, a scaling law is derived to show that a nC-level level positron beam can gain over 120 GeV through a <100 m single-stage acceleration using state-of-the-art laser facilities.

Speaker: Siqin Ding

123 Statistical analysis of sources of instability on electron beam quality in a laser plasma accelerator preparing for Bayesian optimization

Laser-electron accelerators emerge as novel, compact sources of high-quality relativistic electron beams. Their extremely high peak currents make them ideal for applications in fields such as material science, healthcare, and particle physics.
Each experimental application requires unique electron parameters. Additionally, all the input parameters are interconnected, resulting in a highly complex parameter space. This increases the cost in time and resources for preparing experiments. To address this issue, we have developed a semi-automated Bayesian optimization loop that adjusts six input parameters simultaneously to achieve optimal electron beam parameters.
However, the high nonlinearity of laser wakefield acceleration poses a challenge for automated optimization, as even minor fluctuations in input parameters can lead to significant changes in electron beam properties. To quantify and mitigate the effects of these statistical fluctuations, we have compiled an extensive dataset through systematic studies of their characteristics and influence on the electron beam quality.
Alongside demonstrating an initial prototype for semi-automated Bayesian optimization, this work will enhance the understanding of the underlying sources of instability in laser-plasma acceleration experiments, which are essential for more complex machine learning experiments.

Speaker: Franziska Marie Herrmann (Helmholtz-Zentrum Dresden-Rossendorf)

124 Tests of the fibre-optic FLASH beam monitor with laser-accelerated electron beams

Very High Energy Electron therapy has shown promising results for radiation therapy using shorter and higher energy electron bunches,100-250 MeV, then conventional electron therapy. One of the key challenges for VHEE is the need for a linear, non-perturbative beam monitor for these bunches. One of the authors, J. Bateman has developed the fibre-optic FLASH monitor (FOFM) [1], which images the Cherenkov radiation from an array of fibre optics to retrieve the charge and beam profile of an electron beam. This device was tested on the RF accelerator CLEAR, but never on a LWFA. Here we describe the results of the first experiments to demonstrate the operation of the FOFM monitor on a LWFA generated electron beam. The experiments were conducted on the recently upgraded 25 TW Ti:Sapphire laser at OPAL (Oxford Plasma Accelerator Laboratory) alongside commissioning of the accelerator.

[1] Bateman, J. J., Buchanan, E., Corsini, R., Farabolini, W., Korysko, P., Garbrecht Larsen, R., Malyzhenkov, A., Ortega Ruiz, I., Rieker, V., Gerbershagen, A., & Dosanjh, M. (2024). Development of a novel fibre optic beam profile and dose monitor for very high energy electron radiotherapy at ultrahigh dose rates. Physics in Medicine and Biology, 69(8). https://doi.org/10.1088/1361-6560/ad33a0

Speaker: Linus Feder

125 Towards improved control of laser-wakefield accelerators with multidimensional parameter scans

The quality of electron beams generated by laser wakefield accelerators (LWFAs) is constantly improving to the point where it is now possible to operate novel light sources such as free-electron lasers (FELs), as has been achieved at various facilities. However, this method is still limited by the fluctuations of the electron beam properties, which are difficult to control due to the non-linear nature of injection, cavity formation and laser propagation. This becomes increasingly difficult when aiming at X-ray FEL wavelengths.

We present an in-depth simulation study in which we have reconstructed an experimental LWFA setup with self-truncated ionisation injection (STII) as the injection mechanism using realistic 3D particle-in-cell (PIC) PIConGPU simulations combined with the automated workflow engine Snakemake. Based on the reconstruction, we have created a multidimensional mapping of electron beam parameters to laser and plasma parameters. With these results we present requirements for the laser and plasma configuration to ensure the appropriate onset and truncation of the injection process. In addition, a study of the spectral and longitudinal charge distribution on laser dispersion and focussing in the STII regime is presented. These results are confirmed with experimental observations obtained in a FEL campaign.

Speaker: Jessica Tiebel (HZDR)

20:30 Dinner

Wednesday 24 September

Plenary Session

126 First results from 10 PW electron acceleration experiments at ELI-NP

We will present the latest results of the commissioning campaign of the E6-10 PW experimental area of ELI-NP, dedicated to High-Field QED physics. The laser was operated up to nominal power (230J, 23fs) and by shooting onto a gas jet target via a long focal spherical mirror. Stable multi-GeV electron beam were obtained and used to generate intense and energetic photon beams via bremsstrahlung, inverse Compton scattering and betatron emission. We will detail the general layout, the laser parameters and its stability, the targets and the diagnostics that have been commissioned during those pioneer experiments. We will discuss shortly their relevance for radiation sources, QED physics and nuclear physics.
The E6 area is already available for users, with the first 2 campaigns set for the second part of this year.

Speaker: Petru Ghenuche (ELI-NP/IFIN-HH)

127 Overview of the hybrid LWFA-driven PWFA

Particle-driven wakefield acceleration (PWFA) promises the generation of high-brightness relativistic beams, as it allows dephasing-free acceleration and the implementation of various cold injection schemes, unlike laser-driven wakefield acceleration (LWFA). To keep the whole accelerator compact, generating the PWFA driver beam via LWFA is a promising concept [1] and the first proof of principle witness beam acceleration was demonstrated a few years ago [2]. Since then, efforts have focused on improving the quality (brightness), stability of the witness beam [3] and overcoming the initial driver energy. To address the first two aspects, various injection schemes have been experimentally tested, including density downramp [4] and plasma photocathode [5]. Additionally, the influence of the driver parameters has been investigated [6]. These studies reveal the significant impact of the driver beam charge on the wakefield generation and evolution, which is crucial for the witness beam acceleration. The presentation will provide an overview of these topics as well as a discussion on the next steps to be taken within the Hybrid Collaboration.

[1] PRL 104.195002 (2010)
[2] NatCommun 12,2895 (2021)
[3] Phxs.Rev.X 12.041016 (2022)
[4] Phys.Rev.Reasearch 3.L042005 (2021)
[5] P. Ufer et al. in preparation
[6] NJP 24.083034 (2022)

Speaker: Susanne Schoebel (Helmholtz-Zentrum Dresden-Rossendorf)

10:40 Coffee Break

Plenary Session

128 Laser Wakefield Accelerator Modelling with Variational Neural Networks

Laser-plasma accelerators produce electron beams whose properties depend on a complex, nonlinear relationship between numerous laser and plasma parameters. Neural networks offer a powerful tool for modelling this relationship using experimental datasets. In this talk, I will present results from training such models and using them to predict electron spectra prior to the onset of radiation reaction effects during nonlinear Compton scattering. The model architecture combines variational autoencoders, which learn a reduced representation of key diagnostics, with a fully connected neural network that maps these reduced parameters to the output spectra. I will also discuss ongoing efforts to extend this approach to other applications in laser-plasma experiments.

Speaker: Matthew Streeter (Queen's University Belfast)

12:30 Lunch Break

16:00 Coffee Break

PS1: Plasma-based accelerators and ancillary components

Conveners: Mario Galletti (Istituto Nazionale di Fisica Nucleare), Sarah Schröder (Lawrence Berkeley National Laboratory)

129 Progress towards demonstration of the plasma-modulated plasma accelerator (P-MoPA)

We describe recent results from our programme to develop high-repetition-rate, GeV-scale plasma-modulated plasma accelerators (P-MoPAs), which seeks to utilize advanced thin-disk lasers (TDLs) that can deliver joule-scale, picosecond-duration pulses, at kHz repetition rates.
A P-MoPA has three stages: (i) a modulator, in which a TDL pulse is guided in a hydrodynamic optical-field-ionized (HOFI) plasma channel and is spectrally modulated by the wake driven by a short, low-energy pulse; (ii) a compressor, which converts the spectrally-modulated drive pulse to a train of short pulses; and (iii) a resonantly-driven accelerator stage.
We describe the P-MoPA concept, and present simulations that establish the operating regime of P-MoPAs and predict acceleration to $\sim 2.5\,\mathrm{GeV}$ with a 5 J drive pulse.
We present the results of proof-of-principle experiments that demonstrate the operation of stage (iii) of a P-MoPA. These show resonant excitation of wakefields, with amplitudes in the range $3 – 10\,\mathrm{GV\,m}^{-1}$, by a train of $\sim 10$ pulses of total energy $\sim 1\,\mathrm{J}$ guided in a 110 mm long HOFI plasma channel.
We also describe progress towards demonstrating the stage (i) of a P-MoPA, i.e. spectral modulation of a picosecond-duration drive pulse by the low-amplitude wake driven by a short, low-energy seed pulse.

Speaker: Simon Hooker (University of Oxford)

130 Latest Results from the FLASHForward Experiment

The FLASHForward experiment at DESY uses high-quality electron bunches from the FLASH linac to perform fundamental plasma-wakefield-accelerator research. An overview of recent results will be provided in three areas: beam-quality preservation, energy efficient acceleration and repetition-rate limits. By precisely controlling the transverse properties of the witness bunch we demonstrate the preservation of the witness-bunch emittance $\epsilon_n$ during plasma acceleration for the first time. $\epsilon_n$ was preserved at 2.8 mm-mrad while maintaining > 20% instantaneous energy-transfer efficiency. To improve the overall energy-transfer efficiency, the acceleration distance must be increased. We will present the design and development of a new discharge plasma source which allowed us to accelerate a 1.2 GeV witness bunch by more than 0.5 GeV with per-cent-level energy spread. To further improve bunch quality, we have incorporated Bayesian optimisation techniques into our workflow and have demonstrated 0.25 GeV energy gain with < 0.2% energy spread. Finally, we further studied the ultimate repetition rate of plasma accelerators, which can be limited by secondary ionisation over tens or hundreds of nanoseconds driven by the hot plasma species left after the wakefield interaction.

Speaker: Dr Jonathan Wood (DESY)

131 Multi-GeV Witness Acceleration with High Field Uniformity at FACET-II

At the Facility for Advanced Accelerator Experimental Tests II (FACET-II) at SLAC, we are undertaking experiments in plasma wakefield acceleration using a 10 GeV electron beam configured as a drive and witness pair. We will share our progress towards the ultimate goal of doubling the energy of the 10 GeV witness bunch by PWFA, with high efficiency and while preserving beam quality. Our latest results demonstrate multi-GeV acceleration of the witness bunch, with energy gains exceeding 5 GeV and sub-percent energy spread, using a 40 cm long plasma source. Additionally, we have achieved near-complete charge capture of the witness bunch and are actively working to minimize emittance growth through careful control of the transverse properties of the bunches.

Speaker: Doug Storey (SLAC National Accelerator Laboratory)

132 Experimental Progress of PWFA in a Laser-Ionized Plasma Source FACET-II

To compete with conventional accelerators, collider and light source applications based on plasma wakefield acceleration need to be able to handle 10s of Joules of energy transfer between the drive beam, plasma, and witness beam at repetition rates exceeding 100 Hz. Scaling up to these parameters is challenging due to the large amount of heat deposited in the plasma source. To begin approaching this regime, we developed a laser ionized plasma source using a pair of diffractive optics to produce a meter-scale Bessel focus with a tailored axial intensity profile. Using this source, we demonstrate multi-Joule energy transfer between the drive beam and the plasma at SLAC’s FACET-II facility. Further, we discuss the transverse beam dynamics within the plasma and the alignment tolerance between the drive beam and the laser. Finally, we discuss future opportunities for using the plasma source to produce narrow plasmas for positron acceleration and ion channel lasers.

Speaker: Michael Litos (University of Colorado Boulder)

133 Experimental Validation of the EuPRAXIA@SPARC_LAB Nominal Working Point via RF Compression at SPARC_LAB

The EuPRAXIA@SPARC_LAB project is developing a compact high-brightness electron beam facility for plasma acceleration and advanced radiation sources. A central element is the definition and experimental validation of a nominal working point (WP) suitable for plasma injection. This WP relies on an innovative use of RF compression, achieved in two accelerating sections within the photoinjector, allowing for strong bunch length reduction while mitigating emittance growth. This scheme enables the generation of high-current, ultra-short electron bunches with low emittance and energy spread. The method has been experimentally tested at the SPARC_LAB facility, confirming its effectiveness and validating the beam dynamics design of the EuPRAXIA@SPARC_LAB WP. Results demonstrate the feasibility of achieving the required beam parameters with existing S-band technology, providing a solid foundation for the future implementation of the facility.

Speakers: Anna Giribono (Istituto Nazionale di Fisica Nucleare), Gilles Jacopo Silvi (Istituto Nazionale di Fisica Nucleare)

134 Laser Wakefield Electron Acceleration and Betatron Radiation from ZEUS

The Center for Ultrafast Optical Science (CUOS) at the University of Michigan has constructed a new high-power laser user facility called ZEUS (the Zettawatt-Equivalent Ultrashort Pulse Laser System), funded by the National Science Foundation (NSF). ZEUS currently operates at a power exceeding 2 petawatts, with a pulse duration of 25 femtoseconds and a repetition rate of one shot per minute. The facility includes three shielded target areas primarily dedicated to external user experiments. Recent results will be presented on system performance and laser wakefield electron acceleration, which has produced electron beams with energies up to 2.5 GeV, as well as on the study of betatron radiation and its application to high-resolution radiography in two energy ranges: 1–25 keV and 25–500 keV.

The ZEUS facility construction and operation is supported by the National Science Foundation under award 1935950 and 2126181, as well as by the AFOSR grant number FA9550- 22-1-0118 and the University of Michigan.

Speaker: Dr Anatoly Maksimchuk (University of MIchigan)

18:20 Discussion & Closing Remarks

PS4: Theory and simulations: Beams & applications

Conveners: Maxence Thévenet (DESY), Stefano Romeo (Istituto Nazionale di Fisica Nucleare)

135 Unlocking High-Dimensional Parameter Spaces: Bayesian Optimization in Beam-Driven Plasma Accelerators

Artificial intelligence (AI) has become a cornerstone in addressing complex optimization challenges across scientific domains. Among AI techniques, Bayesian optimization (BO) has proven particularly effective for navigating high-dimensional and computationally expensive parameter spaces.
Recent studies have demonstrated BO's ability to optimize electron beam properties to achieve small energy spreads, improve stability across experimental runs, and reduce computational costs through multi-fidelity approaches. Multi-objective BO further expands its capabilities by simultaneously optimizing competing objectives while dynamically adjusting simulation fidelity.
Bayesian optimization (BO) offers a powerful probabilistic framework for optimizing plasma wakefield acceleration systems while simultaneously uncovering underlying physics. By constructing surrogate models that capture parameter uncertainties, BO enables efficient exploration of complex, high-dimensional spaces. This approach facilitates data-driven discovery and validation of scaling laws governing beam energy and accelerator performance.
Notably, EuPRAXIA project can benefit of Bayesian Optimization techniques for beam-driven plasma acceleration schemes. This contribution highlights the transformative role of BO in plasma accelerator research and its potential to advance cutting-edge technologies and applications in EuPRAXIA.

Speaker: Alessio Del Dotto (Istituto Nazionale di Fisica Nucleare)

136 Microbunching Instability Studies: a Semi-Analytical Insights for EuPRAXIA@SPARC_LAB

Microbunching instability (MBI) remains a critical challenge for high-brightness electron beams in linear accelerators, especially for free electron lasers (FEL). We present a comprehensive study of the MBI in the context of EuPRAXIA@SPARC_LAB, the first FEL user facility driven by plasma acceleration, focusing on both the emergence and the mitigation of MBI under various machine configurations. Our approach combines a semi-analytical model—based on the Huang–Kim formalism—to capture the evolution of current and energy modulations caused by longitudinal space charge and coherent synchrotron radiation effects, with an assessment of intrabeam scattering and Landau damping enhanced by the laser heater.
We complement this work with further studies of MBI, supported by FEL performance measurements, carried out at FERMI@Elettra, investigating dual stage compression schemes.

Speaker: Giovanni Campri (Istituto Nazionale di Fisica Nucleare)

137 Acceleration-Induced Self-Interactions of Ultra-Short Electron Bunches

We present a theoretical description of the radiative and space-charge intra-bunch interaction of a compact charged bunch undergoing high-field acceleration relevant to LWFA, PWFA conditions. The effects during the process of acceleration are considered specifically, in contrast to previous work that assumes an instantaneous change in energy and examines the post-acceleration interaction with radiated fields.

For compact bunches (i.e. volume is < O(1)um^3) there is a significant modification to the space-charge and radiation field interactions within the bunch in the presence of high gradient acceleration, with the fields being asymmetric with respect to the centroid of the bunch. We find these effects to be significant for acceleration fields of order GV/m and charges exceeding 10pC, with potential to provide a mean energy loss on the order of 0.1-1% of the energy gained, and a head-tail energy difference of similar magnitude.

The model points to an inherent vacuum beam-loading process within compact bunches that is exacerbated rather than compensated by higher gradient acceleration fields.

Speaker: Ryan Mcguigan

138 Parametric mapping of the efficiency–instability relation in plasma-wakefield accelerators

High efficiency is essential for plasma-wakefield accelerators to be a cost-effective alternative for high-power applications, such as a linear collider. However, in a plasma-wakefield accelerator the beam-breakup instability can be seeded by a transverse offset between the driver and trailing bunch. This instability, which rapidly increases the oscillation amplitude of the trailing bunch, grows with higher power-transfer efficiency from the driver to the trailing bunch [V. Lebedev et al., Phys. Rev. Accel. Beams 21, 059901 (2018)]. We discuss the efficiency–instability relation with simulations using the 3D quasi-static PIC code HiPACE++. Using a grid of simulations, we examine the strength of the instability at different efficiencies across the parameters that contribute to the instability (beam loading, normalized wake radius) for a given plasma density. We find that the previously proposed efficiency–instability relation represents a lower limit on the strength of the instability for a given efficiency.

Speaker: Ole Gunnar Finnerud (The University of Oslo)

139 ML-enhanced start-to-end simulations of plasma acceleration facilities integrated with Geant4

Plasma acceleration is an emerging technology with transformative potential for accelerator and light source facilities, as well as applications in medical and nuclear physics. However, its broader adoption is hindered by the reliance on computationally intensive Particle-in-Cell (PIC) simulations, which require expert knowledge and multiple simulation tools.

Geant4 [1] is a widely used Monte Carlo (MC) toolkit to simulate various applications across high-energy, accelerator, nuclear, medical physics and space science. Despite its broad utility, Geant4 lacks native support for plasma acceleration modeling.

We present a novel mechanism of integration of a generic Machine Learning (ML) surrogate model [2], trained on PIC simulations, into Geant4 as a particle source. This approach enables the realistic generation and tracking of plasma-accelerated beams within complete experimental setups, effectively bridging PIC and MC methods. As a proof-of-concept, we showcase start-to-end simulations of the PALLAS laser-plasma accelerator facility [3-5], incorporating the full experimental setup within Geant4. This demonstrates the feasibility and flexibility of simulations for plasma acceleration applications within a single framework.

[1] S. Agostinelli et al., NIMA 506, 250-303 (2003).
[2] A. Sytov et al. arXiv2503.12154 (2025).
[3] G. Kane et al. arXiv2408.15845 (2024).
[4] P. Drobniak et al., PRAB 26, 091302 (2023).
[5] https://pallas.ijclab.in2p3.fr/.

Speaker: Alexei Sytov (Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara)

140 Synthetic Radiation Diagnostic in Hybrid LPWFA

We present a study of a radiation signal in laser-driven plasma wakefield accelerators (LPWFA) employing photo cathode injection. While experimentally observed and significant for timing calibration, its underlying physics remains elusive. Using a synthetic optical imaging plugin for PIConGPU we reproduce this signal in simulations for the first time, linking it to plasma structures and cavity dynamics. By analyzing the images alongside 3D, time-resolved particle distributions, we trace the formation of distinct scattering patterns, offering new perspectives on plasma dynamics.

Our synthetic diagnostic enables self-consistent imaging of plasma structures in laser-plasma accelerators. By integrating electromagnetic fields from the PIC simulation and propagating them via Fourier optics methods onto a virtual screen, we generate synthetic images that resemble experimental measurements. This approach allows direct comparison with experiments, providing insights into plasma dynamics and laser-plasma interactions.

These results highlight the potential of synthetic optical imaging to improve experimental diagnostics in laser-plasma accelerators, such as shadowgraphy, and to deepen our understanding of scattering processes in wakefield acceleration.

Speaker: Finn-Ole Carstens (Helmholtz-Zentrum Dresden - Rossendorf e. V.)

18:20 Discussion & Closing Remarks

PS5: Applications

Conveners: Felicie Albert (Lawrence Livermore National Laboratory), Jaroslav Nejdl (ELI Beamlines Facility, Extreme Light Infrastructure ERIC), Prof. Victor Malka (Weizmann Institute of Science)

141 Irradiation of cell cultures with laser-generated protons and X-rays

Laser-based particle sources allow for investigating biological effects of radiation at high instantaneous dose rates. We have run two experiments including the irradiation of monolayer cell cultures at total dose values of 3-12 Gy.
At the Laser Laboratory for Acceleration and Applications (L2A2) an X-ray source driven by a 35 fs pulsed laser with 1 mJ pulse energy at 1 kHz shot rate, focalized on a rotating copper plate, generates bremsstrahlung up to some tens of keV. It has been applied to 36 cell samples with a dose rate of about 100 mGy/s. An ionization chamber has been implemented for real-time dose control.
At the VEGA-3 laser of CLPU (1 PW, 27 J at 1 Hz pulse rate), a proton source developed by IGFAE has been combined with a magnetic energy selector from i3M to obtain a quasi-monoenergetic, 5 MeV beam which was guided through a thin vacuum window. Here, 27 cell samples have been exposed to proton pulses. For both campaigns, biological samples were prepared and analysed by local collaborators (IDIS, IBFG).

Funded by Generalitat Valenciana, ref. CIAICO/2022/008, and CLPU, experiment 00562-0101. Supported by the Government of Castilla y León, ref. CLP263P20, co-financed with FEDER funds.

Speaker: Dr Michael Seimetz (Instituto de Instrumentación para Imagen Molecular (i3M), CSIC-Universitat Politècnica de València)

142 Beam temporal structure of laser-driven VHEE beams affects biological response

Laser-Plasma Accelerators (LPAs) can reliably generate Very High Energy Electrons (VHEE, >50 MeV), a promising radiotherapy modality due to their favorable depth-dose profiles and potential for ultra-high dose-rates required for FLASH therapy. While most biological studies involving LPAs focus on beam energy and dose target, the temporal structure of radiation delivery, specifically the electron bunch repetition rate, remains unexplored. This timing parameter, tunable according to machine configuration, may play a critical role in shaping biological effects.

To investigate this aspect, we optimized a 150TW LPA to deliver electrons in the 50–100 MeV range, with an average charge exceeding 500 pC/shot and a dose of ~350 mGy/shot. We systematically varied the repetition rate (1-0.5-0.2-0.1 Hz), while keeping the electron energy and average dose constant. Biological effects were assessed in vitro (healthy fibroblasts, MRC5; colorectal cancer cells, HCT116) and in vivo (zebrafish embryos), using survival and developmental toxicity as endpoints.

Results showed that beam temporal structure strongly modulates biological response: higher repetition rates (1 Hz) reduced toxicity in healthy models, while tumor cells exhibited the opposite trend. These findings identify bunch repetition rate as a key accelerator parameter for tuning radiobiological outcomes, with direct implications for the development of LPA-based preclinical applications.

Speaker: Camilla Giaccaglia (Laboratoire d'Optique Appliquée - UMR7639 - ENSTA)

143 Progress update on the FACET-II Strong-Field QED program

The E-320 experiment at SLAC FACET-II aims to investigate Quantum Electrodynamics (QED) in the strong-field regime.
By colliding 10 GeV, high-quality electron beams with 10 TW NIR laser pulses it is aspired to probe the QED critical (Schwinger) intensity of 10E29 Wcm-2 in the electron rest frame.
In this regime, characterized by X = E/Ecr>1, quantum corrections to classical synchrotron radiation become important and the probability for electron-positron pair production is no longer exponentially suppressed.
A central objective of E-320 is to observe the transition from the perturbative (a0^2<<1) to the non-perturbative regime (a0^2>>1), characterized by the intensity parameter a0, while quantum effects are important (i.e., X ~ 1 ).
Here, qualitative changes are expected to be observed, such as e.g. a substantial red shift of the Compton edges in the electron or photon spectrum and eventually a transition to a quasi-continuous spectrum. We will report on recent progress and results in the E-320 research program as well as future plans and development efforts.

Speaker: Alexander Knetsch (SLAC National Accelerator Laboratory)

144 Recent progress in the LWFA-driven COXINEL FEL and its prospect towards shorter wavelengths lasing

Laser-plasma electron acceleration hit a turning point by the recent demonstrations of plasma-wakefield-driven FEL. Yet, there are still the remaining challenges to be resolved before such compact light sources ready for user applications. We present recent progress made by the HZDR-SOLEIL collaboration in seeded FEL using the COXINEL FEL-line powered by the HZDR laser-plasma accelerator. This platform facilitates a comprehensive and structured approach to the development of key components covering high-quality electron beam generation, advanced plasma-beam diagnostics and control, electron beam transport and FEL physics, all integrated in one laboratory. In particular, by exploiting strongly chirped electron beams, a new FEL scheme with red-shifted lasing was demonstrated, its spectral tunability was studied, while a careful analysis of the shape of the interference pattern of seed and FEL light revealed novel insight into the FEL process. Recent results on the LWFA stage show higher spectral-charge-density beyond 10 pC/MeV at improved stability aided with machine-learning-based optimization methods. Together with better control on beam phase-space during transport and on seed laser, higher FEL output of up to 50 nJ/pulse is achieved, well matching with simulations. This good agreement between experiments and simulations allows for parameter scaling towards shorter wavelengths down to EUV range.

Speaker: Arie Irman (Helmholtz Zentrum Dresden Rossendorf)

145 Ion channel formation for advanced betatron emission

A long ion channel has been proposed as a possible way to reduce the bandwidth of betatron radiation emitted in a plasma due to its wakeless nature; this allows to exclude longitudinal momentum variations from the photon energy dispersion, only retaining the transverse oscillations as plasma induced energy spreads. Although the concept of ion channel laser was proposed back in the nineties, no studies were published about the channel formation itself. In this contribution, we address the issue of depleting from electrons an already formed plasma column by means of a relativistic electron bunch, deriving some useful scaling laws supported by an extensive simulation campaign. Our studies aim at defining possible working points for a monochromatic betatron source in the framework of EuPRAXIA and the SL_betatest experiment at SPARC_LAB.

Speaker: Andrea Renato Rossi (Istituto Nazionale di Fisica Nucleare)

146 Development and commissioning of RadiaBeam ICS source

We report on the development, commissioning, and the first light from RadiaBeam Inverse Compton Scattering (ICS) source. This ICS source is driven by the C-band hybrid photoinjector, and 100 MeV high gradient C-band linac. The first light at 200 keV photon energy was detected and characterized. The machine modular design allows for multiple future upgrades, including energy upgrade, as well as a transition to the pulse train regime operations to enhance average power. However, this paper is mostly focused on the initial experimental resutls in a single shot regime, with the focus on the machine tunability, performance, and applications.

Speaker: Alex Murokh

18:20 Discussion & Closing Remarks

PS8: Plasma sources and related diagnostics

Conveners: Lucio Crincoli (Istituto Nazionale di Fisica Nucleare), Malte Kaluza (University of Jena, Helmholtz-Institute Jena)

147 Overview of scalable plasma source R&D for the AWKE project at CERN

Scalable plasma sources R&D for the AWAKE experiment at CERN focuses on two technologies as alternatives to the existing laser-ionised rubidium vapor plasma source: the Helicon Plasma Source (HPS) and the Discharge Plasma Source (DPS). The very stringent requirements of axial plasma electron density uniformity (n/n < 0.25%) and reproducibility are tackled thanks to a collaborative effort among several institutes addressing the source design and plasma characterization aspects. As a proof of principle of such alternative sources, a 10 m long DPS has been successfully tested for the self-modulation of a 400 GeV proton beam in the AWAKE experiment in May 2023. Since then, both sources have been operated and characterized in the different laboratories, implementing and comparing different plasma diagnostics.
This presentation will give an overview of the scalable plasma source R&D program within the AWAKE project timeline. Different characterization techniques used and corresponding results in terms of plasma electron density and temperature (spatially and/or temporally resolved) for the HPS and the DPS will be presented. Finally, we will discuss the next challenges for the sources design and diagnostics as well as the steps towards their length scalability.

Speaker: Alban Sublet

148 AWAKE Run 2b density step plasma source

The AWAKE experiment is now in its Run 2b phase. The main aim is to study the effect of a density step placed along the plasma to control the evolution of wakefields induced by a long proton bunch. Numerical simulation results predicted that, after saturation of the self-modulation process, wakefields maintain a larger amplitude with the step than in a uniform density plasma. A new rubidium vapor source has been designed, fabricated, and installed in 2023. It allows to impose a temperature, and thus a vapor density, and upon ionization, a plasma density step, up to 10% in relative height every 50cm over the first 4.5m of the source. Furthermore, in 2024 a number of movable screens were installed to allow to vary the plasma length by blocking the ionizing laser pulse at various positions, 1m apart along the source. The source is now under test with proton beam. In this contribution we will present the characteristics and the challenges of the new source, as well as the first applications to the propagation of the proton bunch in plasma.

Speaker: Michele Bergamaschi (Max-Planck-Institut für Physik/CERN)

149 Plasma density manipulation in gas-filled discharge capillaries designed for the EuPRAXIA project

In the field of particle accelerators, recent results obtained through the interaction between particle beams and plasmas in cm-scale short structures have demonstrated the capability to achieve high accelerating and focusing gradients while preserving electron beam quality. In this context, the EuPRAXIA project represents the worldwide first high energy plasma-based accelerator that can provide beam quality and user areas using both electron beams and laser pulses to interact with plasmas. For future applications, to achieve high energies, the challenge in the coming years will be to study solutions capable of lengthening plasma sources to the m-scale with tailored plasma density profiles optimizing the matching with particle beams.
For this purpose, gas-filled discharge capillaries are designed for plasma acceleration experiments. These discharge-induced plasma sources are used for both accelerating and focusing sections and can be designed, in terms of geometry, gas distribution and HV sources, to control the properties of plasmas interacting with particle beams. We present a study concerning the possibility of modulating the longitudinal plasma profiles required for large sources to be used in the EuPRAXIA project, based on both the geometric characteristics of the structure and the use of laser pulses capable of controlling the plasma formation process.

Speaker: Angelo Biagioni (Istituto Nazionale di Fisica Nucleare)

150 A kHz length scalable plasma for the ALiVE proton driven plasma accelerators

The ALiVE concept for a Higgs factory using single stage proton driven plasma acceleration of lepton bunches requires a plasma with electron density matching the driver bunch size and length matching the driver depletion length. This results in a plasma with an electron density of up to 10^15 cm^-3 and a length of hundreds of meters. An energy and cost efficient way to create long plasmas use a double pulse (ignition+heating) direct current electric discharge. This generated plasmas in noble gases with lengths up to 20m.

The ALIVE concept brings new constrains to the plasma due to the possibility of field ionisation and ion motion caused by the intense lepton bunch being accelerated. These lead to the choice of plasmas generated from alkali vapours of medium ion mass which combine a low/high first/second ionisation potentials with a sufficient ion mass to reduce ion motion. Alkalis also reduce the required electric power. The high repetition rate (～15 kHz) requires a new electric circuit topology to mitigate the resulting plasma ion drift. Further power reduction may be achieved by partial plasma axial confinement using a solenoid magnetic field.

The plasma source development plan will be presented.

Speaker: Nelson Lopes (IST)

151 Advanced ceramic plasma discharge capillary for high repetition rate operation

In view of future applications of plasma-based particle accelerators, within the fields of high-energy physics and new light sources, the capability of plasma sources to operate at high repetition rates is crucial. In particular for gas-filled plasma discharge capillaries, which allow direct control over plasma properties, a key aspect is the longevity of the material, subject to erosion due to the heat flux delivered by high voltage plasma discharges. In this regard, we present an innovative design of discharge capillaries based on the use of different ceramic materials, which can sustain high voltage plasma discharges at high repetition rate and, moreover, be easily machined for the complex geometries required for plasma-based accelerators. Experimental campaigns are carried out at 10–150 Hz, assessing the longevity of ceramic capillaries by means of different diagnostic techniques. In addition, numerical simulations are performed to analyze the heat transfer within the whole plasma source. Results from experimental and numerical analysis highlight the capability of ceramic capillaries to preserve plasma properties and the integrity of the source during long-term plasma discharge operation at high repetition rate. In particular, we demonstrate the suitability of the proposed solution for the operative range of 100–400 Hz, foreseen for EuPRAXIA@SPARC_LAB project.

Speaker: Lucio Crincoli (Istituto Nazionale di Fisica Nucleare)

152 Curved hydrodynamic optical-field-ionised waveguides

Curved plasma waveguides have been proposed as a means to: guide fresh laser pulses into multistage plasma accelerators [1, 2], replace plasma mirror tapes used to eject depleted laser pulses [3], and to bend electron bunches for radiation generation [4-6]. However, all curved channel experiments so far have employed discharge capillaries, which are prone to laser damage especially at high pulse repetition rates.

In contrast, hydrodynamic optical-field ionized (HOFI) channels are free-standing and hence immune to laser damage. Furthermore, they have been demonstrated to operate at kHz repetition rates [7-10]. We will describe experiments and simulations on the formation and operation of curved HOFI channels. Particle-in-cell simulations show, for a parameter regime relevant to PW-scale facilities, that curved HOFI channels can be used to introduce a fresh laser drive pulse in a staged laser-wakefield accelerator. A 100% electron capture efficiency can be achieved between stages although the asymmetric sheath fields led to emittance blow-up. We have demonstrated experimentally that introduction of the appropriate phase modulation can curve the trajectory of the channel-forming Bessel beam by more than 10 laser spot sizes in a distance of 120 mm. We will also present the results of experiments to generate curved HOFI channels.

Speaker: Darren Zeming Chan (University of Oxford)

153 Laser Pulse Tailoring for HOFI Waveguide Generation

Extended depth of focus optics or axioptics are becoming increasingly important for many areas of high-power laser-matter interactions. Rather than focusing light to a single longitudinal point, like a parabolic mirror, these optics focus light to a line segment along the optical axis, allowing for the generation of extended regions of high laser intensity. Optics for generating such intensity structures include the axicon, the axilens, and the more recently proposed axiparabola.

Axioptics are routinely used to form optical waveguides in laser-plasma accelerators, in order to prevent diffraction of the drive laser and boost the electron beam energy to the multi-GeV level. They have also been proposed as a key optical element in the application of flying focus techniques to mitigate dephasing in laser-plasma accelerators. Efficient tailoring of the longitudinal intensity profile can be challenging, with the achievable peak intensity being reduced by deleterious effects such as chromaticity in diffractive optics or by misalignment in complex off-axis solutions.

Here we present theory and simulations detailing an alternative approach to the generation of foci with an extended region of high intensity for HOFI plasma channel formation and present recent experimental results employing custom optical elements that demonstrate this approach in the laboratory.

Speaker: Anna Puchert (DESY)

18:40 Discussion & Closing Remarks

PS9: Particle physics applications: proposals, ESPP input, sustainability

Conveners: Marlene Turner (CERN), Rajeev Pattathil (Rutherford Appleton Laboratory)

154 Transition of CLARA facility at Daresbury Laboratory to user facility for novel acceleration

The Compact Linear Accelerator for Research and Applications (CLARA) at Daresbury Laboratory has been fully installed and is currently undergoing beam commissioning. The Full Energy Beam Exploitation beamline will combine a 250 MeV FEL quality electron beam with a 100 TW class laser and will support exploitation of the CLARA beam for advanced acceleration experiments and research. This includes plasma based and structure-based acceleration, with laser and beam drivers. FEBE has been designed to provide flexibility in both electron and laser beam delivery. We present an overview of capabilities of FEBE including: targeted electron beam parameters, a broad range of beam and laser diagnostic systems, TW laser parameters and integration, and the optical timing and synchronisation system. Finally,the potential for supporting experiments aimed at overcoming some of the pressing novel acceleration challenges e.g. beam quality perseveration, stability and synchronisation, staging, etc. will be discussed. We will give an update on the status of beam and laser commissioning, preparations for beamtime call and the transition of CLARA to operational user facility. User operation of the CLARA facility is expected to begin early 2026.

Speaker: Deepa Angal-Kalinin (STFC, Daresbury Laboratory)

155 The program of AWAKE towards high-energy electrons for particle physics experiments

AWAKE at CERN has moved from a proof-of-concept experiment to a facility that develops the proton-driven plasma wakefield acceleration technology to be ready for proposing first particle physics applications in the 2030’s. To this aim, the experiment will be significantly upgraded during CERN’s Long Shutdown 3 (2026-2028) to demonstrate the acceleration of electrons to energies up to 10 GeV in a single 10-m long plasma source, while controlling the beam quality and to demonstrate the scalability of the process. We present the well-defined roadmap, the scientifc program and challenges of the experiment starting in 2029, where a 150 MeV, 100 pC charge, 200 fs long electron bunch is externally injected into a 10m-long accelerator plasma source. In addition the development of scalable discharge and helicon plasma sources to hundreds of meters length, necessary to reach high energies, is shown. The relevance of the AWAKE developments for other plasma-based accelerator projects as well as first possible particle physics applications are highlighted.

Speaker: Edda Gschwendtner

156 Advanced modeling tools for 10 TeV wakefield colliders

In the wake of the recent community discussions and reports, a new study group has been formed to develop end-to-end design concepts of colliders based on wakefield acceleration technologies [1]. The study group is organized in a number of working groups, including a working group on “simulations/computing/AI”. We will report on the activities of this working group, and on the open modeling tools, AI/ML techniques and simulation ecosystem that are being organized and fostered. We will also report on selected collaborations that develop integrated software ecosystems and standards, including the Collaboration for Advanced Modeling of Particle Accelerators (CAMPA) and the newly developed community Particle Accelerator Lattice Standard (PALS) [2].

[1] S. Gessner et al., arXiv:2503.20214 (2025)
[2] https://github.com/campa-consortium/pals

Speaker: Jean-Luc Vay

157 Transverse tolerances in colliders based on the plasma-wakefield acceleration blow-out regime

We report on recent progress in transverse instabilities and transverse tolerances for colliders based on the plasma-wakefield acceleration in the blow-out regime. In this regime, the transverse fields provide both strong focusing and strong deflection via transverse wakefields. The deflection effect of the wakefields on the main beam leads to limitations on the acceleration efficiency, if not mitigated. Ion motion and energy spread may mitigate the instability. With linac start-to-end simulations, using the recently developed ABEL framework, we demonstrate that the instability and emittance growth may be sufficiently mitigated for the colliding beams in the HALHF concept. Independent of wakefield effects, the strong focusing fields lead to very tight tolerances for the drive-beam jitter. We show that the tolerances are greatly loosened by applying external magnetic fields to guide the drive-beam propagation in the plasma.

Speaker: Erik Adli (University of Oslo, Norway)

158 Toward a Multi-TeV Linear Collider Based on Structure Wakefield Acceleration

Beam-driven structure wakefield acceleration represents a compelling technology for future energy-frontier machines: it can accelerate any particle species and is implemented in two primary configurations—two-beam acceleration (TBA) and collinear wakefield acceleration (CWA). The TBA approach has demonstrated exceptional performance, with accelerating gradients approaching 500 MV/m achieved experimentally, offering the potential for dramatically more compact high-energy accelerators. This contribution discusses the use of the TBA implementation as a fundamental building block for a multi-TeV scale e⁺/e⁻ collider, examining the technological progress supporting such a concept, remaining challenges, and the pathway toward realizing next-generation particle physics discoveries at unprecedented energy scales.

Speaker: Philippe Piot (Argonne National Laboratory)

159 Report from PWFA-Linac Working Group of the 10 TeV Wakefield Collider Design Study

The 10 TeV Wakefield Collider Design Study [1] aims to produce a self-consistent, start-to-end design of a 10 TeV-center-of-mass linear collider based on wakefields technology. One of the considered options for driving the main linac is beam-driven plasma wakefield acceleration (PWFA). The goal of the PWFA-Linac Working Group is to identify the main challenges and showstoppers, and to define a set of global metrics to optimize the proposed solutions.
We summarize the recent discussions and present some basic considerations on the PWFA Linac design.

[1] S. Gessner et al., arXiv:2503.20214 (2025)

Speaker: Livio Verra (Istituto Nazionale di Fisica Nucleare)

160 ALiVE: Proton-driven plasma wakefield acceleration for collider applications

Current hadron accelerators can deliver energies far beyond those of lepton acceleration schemes, but this energy is divided among the partons. Plasma wakefield acceleration offers a method to transfer energy from a drive beam to a witness, allowing existing proton accelerators to be transformed into lepton machines. Relatively little civil engineering would be required due to the high gradients which plasma offers, and the re-use of existing infrastructure makes this scheme extremely attractive. The application of this concept to a Higgs factory driven by 400 GeV protons was recently proposed [Farmer, Caldwell and Pukhov, NJP (2024)]. In the present work, we discuss the ongoing efforts to address the challenges to realising such a scheme, including options for a suitable proton source, and possible upgrade paths for particle physics applications beyond a Higgs factory.

Speaker: Alexander Pukhov (uni duesseldorf)

18:40 Discussion & Closing Remarks

Poster Session

161 Acceleration-Induced Self-Interactions of Ultra-Short Electron Bunches

We present a theoretical description of the radiative and space-charge intra-bunch interaction of a compact charged bunch undergoing high-field acceleration relevant to LWFA, PWFA conditions. The effects during the process of acceleration are considered specifically, in contrast to previous work that assumes an instantaneous change in energy and examines the post-acceleration interaction with radiated fields.

For compact bunches (i.e. volume is < O(1)um^3) there is a significant modification to the space-charge and radiation field interactions within the bunch in the presence of high gradient acceleration, with the fields being asymmetric with respect to the centroid of the bunch. We find these effects to be significant for acceleration fields of order GV/m and charges exceeding 10pC, with potential to provide a mean energy loss on the order of 0.1-1% of the energy gained, and a head-tail energy difference of similar magnitude.

The model points to an inherent vacuum beam-loading process within compact bunches that is exacerbated rather than compensated by higher gradient acceleration fields.

Speaker: Ryan Mcguigan

162 Advanced Beam Diagnostics with PolariX TDS: Experimental 5D Reconstruction at SwissFEL

Next-generation accelerators, such as those employing plasma or laser wakefield acceleration techniques, demand precise characterization of the beam's properties, making accurate measurement of the five-dimensional (5D) phase space distribution essential. To meet this need, a novel transverse deflecting structure with adjustable polarization, known as the Polarizable X-band Transverse Deflector (PolariX TDS), has been developed through a collaboration between CERN, PSI, and DESY. By using this device, researchers at DESY have implemented a new tomographic algorithm capable of reconstructing the full 5D phase space of the electron beam. The PolariX TDS allows for beam streaking in a selected transverse direction by adjusting the polarization of the field inside the structure. When combined with a quadrupole scan, this functionality allows for complete 5D phase space reconstruction. This contribution presents measurements carried out at the Athos soft X-ray beamline of SwissFEL (PSI), showing the preparatory studies performed to apply this method at the Athos soft X-ray beamline at SwissFEL as well as showing first preliminary results towards the reconstruction of the 5D phase space under two different electron beam settings.

Speaker: Francesco Demurtas (Istituto Nazionale di Fisica Nucleare)

163 All-optic In-plasma Staging of Laser-Wakefield Accelerators Using Density Tailoring

The staging of laser-driven plasma accelerators (LPAs) could open up energy frontiers, but achieving in- and out-coupling of laser pulses while preserving beam quality remains a challenge. In this work, we present an all-optical, in-plasma staging scheme that uses refraction in a transverse plasma density gradient to couple the incoming laser into the next LPA stage, eliminating the need for mirrors and magnets. This design can in principle support significant ion motion without substantial emittance degradation, making it well-suited for a broad energy range. With realistic 3D simulations using the quasistatic particle-in-cell code HiPACE++ on GPU, we observe 98% capture efficiency and 3 GeV energy gain in a second stage, driven by a ~10 J laser pulse guided by a hydrodynamic optical-field-ionized (HOFI) channel of matched spot size 37 microns. These results represent a significant step toward practical multistage plasma acceleration, paving the way for the generation of ultra-high-energy electron beams for a wide range of scientific and technological applications.

Speaker: Xingjian Hui

164 Bayesian optimisation of second harmonic light generation from plasma apertures modelled in particle-in-cell simulations.

Interest in generating higher-order structured light with orbital angular momentum at high intensities (IL ≥ 1018 Wcm-2) has been developing recently due to the ability to exercise control over the spatio-temporal profile and polarization of the resultant light. Potential applications of such light include laser-driven particle acceleration and radiation generation.

When an intense laser pulse interacts with a micron-scale target with a preformed aperture on the order of the laser focal spot, intense light at the fundamental mode, ωL, and higher harmonics frequencies of the laser are produced with distinct spatial structure.

Generation of structured 2ωL light using this novel technique has been demonstrated using particle-in-cell (PIC) simulations varying aperture diameter and thickness of the target yielding a conversion efficiency from the fundamental mode of the laser, ωL to 2ωL of ~ 3 – 5 %.

We have developed a new code called BISHOP which uses Bayesian optimization to tune the 2ωL conversion efficiency simulated by the PIC code EPOCH across a multi-dimensional parameter space. The optimisation shows strong sensitivity to target density and a matching condition between aperture size and the laser spot size. We discuss the underlying reasons for these dependencies and experimental routes to achieve similar conditions.

Speaker: Radhika Nayli (University of Strathclyde)

165 Correlating post-wakefield acceleration laser spectra with electron beam spectra to bulid an indirect electron diagnostic

The driving laser's spectrum evolves during laser-wakefield acceleration due to the density and intensity gradients in the driven plasma wave. These density gradients also determine the accelerating fields experienced by injected electrons, and so the post-acceleration laser spectrum may be correlated with the electron spectrum, potentially allowing for its use as a non-disruptive diagnostic of the electron beam spectrum. This would be useful in any application that uses the electron beam in a disruptive way, including several methods of light generation and, of particular interest to the authors, radiation reaction studies.

The relationship is highly non-linear however, and so we make use of machine learning approaches and train a model using not only the laser and electron spectra, but also additional diagnostics measuring the post-acceleration laser energy and spot size. This approach is validated using idealised PIC simulation and then tested on real data from an inverse-Compton scattering experiment carried out at ELI-NP in April 2024. I will present on the method, its quality as an indirect diagnostic, and plans to improve it.

Speaker: Paul Gellersen (University of York)

166 Curved hydrodynamic optical-field-ionised waveguides

Curved plasma waveguides have been proposed as a means to: guide fresh laser pulses into multistage plasma accelerators [1, 2], replace plasma mirror tapes used to eject depleted laser pulses [3], and to bend electron bunches for radiation generation [4-6]. However, all curved channel experiments so far have employed discharge capillaries, which are prone to laser damage especially at high pulse repetition rates.

In contrast, hydrodynamic optical-field ionized (HOFI) channels are free-standing and hence immune to laser damage. Furthermore, they have been demonstrated to operate at kHz repetition rates [7-10]. We will describe experiments and simulations on the formation and operation of curved HOFI channels. Particle-in-cell simulations show, for a parameter regime relevant to PW-scale facilities, that curved HOFI channels can be used to introduce a fresh laser drive pulse in a staged laser-wakefield accelerator. A 100% electron capture efficiency can be achieved between stages although the asymmetric sheath fields led to emittance blow-up. We have demonstrated experimentally that introduction of the appropriate phase modulation can curve the trajectory of the channel-forming Bessel beam by more than 10 laser spot sizes in a distance of 120 mm. We will also present the results of experiments to generate curved HOFI channels.

Speaker: Darren Zeming Chan (University of Oxford)

167 Development of gas targets for laser-plasma accelerators

Laser-plasma acceleration experiments require the implementation of gas target technology (a system delivering specific gas with a pre-defined density profile inside a high-vacuum environment). The generated particle beams and radiation in these experiments strongly depend on the choice of optimal density profile formed in a gas target. Here we present the development of gas targets suitable for various laser-plasma experiments driven by high-intensity ultra-short laser pulses at high repetition rates. Hydrodynamic simulations of the neutral gas flow are implemented to design the targets. Then, the target characterization is performed by interferometric measurement and tomographic reconstruction of the density profile. To improve the stability of the interactions, the targets are optimized to work in a continuous flow operation regime. We investigate the conical and slit supersonic nozzles. These nozzles are tested with a differential pumping system. Then, the novel extended length nozzles and dual-stage target designs are presented.

Speaker: Sebastian Lorenz (The Extreme Light Infrastructure ERIC)

168 Enhancing light-matter interaction with nanostructured targets

In the high-power laser-matter interaction, two main components are the laser pulse and the target. By adjusting one of them, the results can be tailored to a specific application. Nano and micro structured targets are being studied for applications of high intensity laser-matter interaction for more than 30 years and take many forms: gratings, wires, dots, spheres, tubes. With the help of such structured targets, we can modify the laser interaction to improve the particle acceleration, by increasing the surface area and through volumetric heating, resulting in higher proton energies or increased X-ray flux, high energy density matter creation and terabar pressures.
Metallic (gold and nickel) nanowires and nanotubes were fabricated in the Target Laboratory from ELI-NP by electrochemical methods, using porous alumina as a template. These targets were used in 1 PW laser experiment to study the x-ray emission and proton acceleration, with an experimental set-up employing a single plasma mirror for contract enhancement, and for diagnostics: radiochromic films and Thompson parabola for ion detection, and CsI scintillators for photon detectors. Proton and ion results, as well as photon and electron signals will be presented from the nanostructured targets, in comparison to flat targets.

Speaker: Stefania-Cristina Ionescu

169 Experimental capabilities at the ARCTURUS laser laboratory - versatile development and diagnostics platform for advanced plasma-based accelerator experiments

The experimental area at the ARCTURUS laser laboratory at Heinrich Heine University Düsseldorf (HHU) provides a versatile research and development platform, designed for supporting flexible configurations of advanced laser-driven and hybrid laser- and electron beam-driven plasma accelerator concepts, as well as offering a test-bed for novel diagnostic approaches.
The experimental setup has already enabled a series of laser-driven plasma accelerator experiments and has seen continuous additions and refinements in complementary diagnostics abilities.
We provide an overview of the currently implemented diagnostics and their prospective development paths, including online main laser monitoring before and after the laser-plasma interaction, probe laser plasma interferometry, various plasma wave shadowgraphy methods, spatial and spectrally resolved plasma-light metrology, electron and dose characterisation methods as well as secondary radiation monitors.
Future experiments at ARCTURUS laboratory are furthermore envisioned to be developed in a community-driven and collaborative approach.

Speaker: Thomas Heinemann (Heinrich-Heine-University Düsseldorf)

170 Experimental measurement of the saturation length of the Self-Modulation

A long, narrow bunch propagating in plasma is subject to the self-modulation (SM) instability, a transverse process. In the AWAKE experiment, we study the evolution of SM along the plasma by changing the length of plasma over which the bunch propagates. In particular, we observe the effect of the transverse wakefields on the bunch by measuring the size of the halo of defocused particles at a screen downstream from the plasma. We observe that the maximum radius of the halo changes with beam and plasma parameters. Numerical simulation results suggest that there is a correlation between the plasma length for which the halo is fully formed, and the plasma length for which the SM process saturates. We study this halo formation for different parameters, and compare it with numerical simulations results.

Speaker: Arthur Clairembaud (Max Planck Institüt für Physik)

171 Experimental progress towards the Plasma-modulated plasma accelerator (P-MoPA)

Progress towards high-repetition (≥1kHz) GeV-scale electrons from a LWFA source is held back by the lack of laser sources capable of providing joule-level sub-100 fs pulses at high repetition rates. A possible trajectory is to replace Ti:sapphire lasers with Yb:YAG thin-disk lasers. The narrow bandwidth of Yb:YAG only allows direct compression to ∼1 ps, however. Although spectral broadening techniques are available, they are limited to approximately 100 mJ. The Plasma-Modulated Plasma Accelerator (P-MoPA) addresses this issue by utilizing a low-energy, sub-100-fs pulse to seed spectral modulation of a multi-joule picosecond pulse in a free-standing plasma waveguide. A resulting pulse train then resonantly drives a high-amplitude wakefield in a second plasma channel, accelerating electrons.

We describe the results of two experimental campaigns: (i) low-energy experiments at Oxford, which utilize filtered pulses from a Ti:sapphire laser to mimic the drive laser pulse, and (ii) high-energy experiments at the Centre for Advanced Laser Applications (CALA) with joule-scale thin-disk lasers. We demonstrate guiding of joule-level Yb:YAG pulses in a 60mm long plasma channel and the spectral broadening and compression of the "seed" pulse in an argon-filled Herriott cell. We then show the results of the modulation campaign.

Speaker: Sebastian Kalos (University of Oxford, Department of Physics)

172 Gas jet characterization methods for laser plasma wakefield accelerators

The dynamics of laser wakefield acceleration processes are strongly coupled to the underlying plasma density profile, which, in turn, directly scales with the target’s initial gas density distribution. Hence, a precise and reliable characterization of gas targets is an indispensable prerequisite for optimizing the performance of plasma-based accelerators. We present a comparative study of gas target characterization methods employing light sources across different wavelength regimes. Several de Laval nozzles generating gas jets with densities ranging from 10^17 to 10^19 cm^-3 were investigated. By integrating diagnostics across multiple regimes, we aim to develop a comprehensive understanding of important gas target characteristics, facilitating improved control over accelerating and matching conditions in plasma-based accelerator experiments. Additionally, further ideas for improved data collection and analysis are discussed.

Speaker: Natascha Thomas (Heinrich-Heine-University Düsseldorf)

173 HD and MHD Plasma Simulations inside Discharge Capillaries with PLUTO

Simulations play a key role in the design of plasma sources, employed for plasma-based accelerators and other applications, and it is important to have alternative codes, for simulating the dynamics of the plasma. We propose an open source code, PLUTO, which allows to perform 3D, hydrodynamic (HD) and magneto-hydrodynamic (MHD) simulations of gas-filled plasma discharge capillaries. We demonstrated its functionality and its versatility for testing different geometries for the capillary and parameters for the gas injection and discharge generation. Even if it lacks an ionization module, PLUTO results to be useful to analyze the behavior of the neutral gas, filling the capillary before ionization, and assess the plasma evolution after ionization, by implementing the time-dependent magnetic field created by the discharge.

Speaker: Marco Pitti (Istituto Nazionale di Fisica Nucleare)

174 In vivo whole-thorax irradiation in mice with laser-driven VHEE

Laser-Plasma Accelerators (LPAs) provide a compact source of ultra-short, high-dose-rate electron beams through acceleration gradients >100 GV/m. Capable of producing Very High Energy Electrons (VHEEs, >50 MeV), LPAs represent a promising alternative to conventional accelerators for preclinical radiotherapy, particularly due to their unique temporal structure and potential for FLASH-like delivery.

We report the successful whole-thorax irradiation of mice using a laser-driven VHEE beam (50-100 MeV) from the 150 TW LPA at the Laboratoire d’Optique Appliquée, aiming to assess fibrosis development, a key marker of late lung toxicity. A dedicated beamline was developed for this complex in vivo experiment, with passive beam expansion and shaping to conform the dose to the lung volume while sparing surrounding organs at risk. The protocol replicates that of the 2014 study by Favaudon et al., which first revealed the FLASH effect.

This benchmark experiment demonstrates the feasibility of performing complex, organ-specific irradiations with LPA-based VHEEs and provides a critical reference for situating laser-driven VHEE delivery between conventional and FLASH modalities.

Speaker: Camilla Giaccaglia (Laboratoire d'Optique Appliquée - UMR7639 - ENSTA)

175 Jitter study on the phase control approach of the high power RF supply in EuPRAXIA

This work presents a jitter study of the fast intra-pulse feedback loop for klystron-driven RF power stations in SPARC_LAB. To meet the rigorous RF stability demands of next-generation accelerators, such as the EuPRAXIA facility, the LLRF system in SPARC_LAB has undergone a comprehensive upgrade. The requirement for phase jitter in plasma wakefield acceleration and seeded free-electron laser (FEL) experiments is sub-10 fs timing precision. A feedback loop is implemented to control this, and the original loop—operational since 2008—achieved a reduction in phase jitter from hundreds of femtoseconds to tens of femtoseconds for S-band klystrons. As part of this upgrade, the S-band system was further enhanced through several modifications, including the replacement of the fast phase shifter, an upgrade of the error amplifier, and the introduction of a slow feedback loop. Recent results on the S-band system show that the jitter can be reduced to less than 20 fs. Long-term measurements have been performed to further investigate the factors that impact loop performance. These measurements represent a significant step toward achieving sub-femtosecond RF stability, which is crucial for novel plasma accelerator facilities.

Speaker: Xianghe Fang (LNF-INFN)

176 Laser fields reconstructor for initialization of experimental laser profiles in Particle In Cell simulations

Particle-in-cell (PIC) simulations are a well-established tool to study and predict the outcomes of a Laser Plasma Accelerator experiment, but the results are often hindered by the initialization of highly idealized laser profiles. In this work, we present the development of a Laser Pulse reconstructor For Particle In Cell simulations (LP4PIC), a Python package to retrieve experimental laser fields to be initialized in a FBPIC simulation. The retrieval of fields from fluence measurements is based on an improved Gerchberg-Saxton algorithm (GSa), taking in input a measurement before the focusing element and a series of focal scan measurements to retrieve the aberration phase. The propagator, on which is based the GSa, simulating the focusing of a given mirror solves the Fourier transformed Helmholtz equation. LP4PIC is also provided with functions to simulate the focusing of an input profile, analytical or from measurements, through phase/absorption plates, eventually providing aberration coefficients, and to give an estimation of aberration coefficients corresponding to the GSa retrieved phase. The so-rebuilt fields are finally initialized in a FBPIC simulation through a proper custom interface. Features and characteristics of LP4PIC will be shown through examples, also in terms of PIC simulations results.

Speaker: Federico Avella (Istituto Nazionale di Ottica - CNR)

177 Laser-Driven Very High Energy Electrons for Femtosecond-Scale Irradiation of In Vitro Cell Lines

Laser-driven plasma accelerators offer a compact, cost-effective alternative to conventional radiofrequency accelerators, capable of generating very high energy and ultra-high dose-rate radiation sources that induce unique cellular responses. We report on the characterisation of laser-driven, very high energy electrons and the response of seven in vitro cell lines to this radiation source.

High-charge electron beams (~nC) were generated using a laser-driven wakefield accelerator, depositing doses up to 3Gy per pulse across cm² areas. Electron beam durations were estimated to be on the order of tens of femtoseconds, equating to unprecedented dose-rates > $10^{13}$ Gy/s.

Exposure of in vitro cell samples to this radiation source resulted in significantly different responses compared to conventional x-ray irradiation. Notably, we observed a statistically significant increase in RBE (1.40 ± 0.08 at 50% survival) in one healthy and one cancerous cell line, alongside a reduction in the relative radioresistance of the cancer cells.

Recent experiments have shown similar results, observed across the seven different in vitro cell lines, indicating a universal response to this radiation source. Dose profiles obtained from radiochromic films and Monte Carlo simulations demonstrated good longitudinal and transverse uniformity, further establishing this radiation source as an exciting, novel approach to radiobiology research.

Speaker: Hannah Maguire (Queen's University Belfast)

178 Laser-Plasma Micro-accelerator for Health and Energy Applications in the framework of SAMOTHRACE project

High-intensity laser interactions with solid targets enable the generation of compact and energetic ion beams. When irradiated with laser intensities exceeding 10¹⁸ W/cm², target materials are rapidly ionized, leading to the formation of relativistic electron populations and strong transient electrostatic fields capable of driving efficient ion acceleration. Target Normal Sheath Acceleration (TNSA) is one of the most robust and widely adopted mechanisms for laser-driven ion acceleration. It can efficiently accelerate protons and ions to tens of MeV, enabling the development of compact, high-brightness ion sources.
In this context, the WP1-Spoke5 of the SAMOTHRACE ecosystem focuses on developing a compact laser-driven ion accelerator for medical and energy applications. This contribution presents the technological development and current implementation status of the miniaturized ion accelerator. It is composed by an ion target station that supports up to 900 targets at 3 Hz, with sub-micrometer positioning accuracy and full EMP compatibility. Ion diagnostics based on a Thomson Parabola Spectrometer (TPS), optimized for detecting protons up to 70 MeV will operate in low- and high-energy configurations, achieving energy resolutions of 2–5%. The micro-accelerator will be installed at the I-LUCE (INFN–Laser indUCEed radiation production) facility at INFN-LNS.

Speaker: Carmen Altana (Istituto Nazionale di Fisica Nucleare)

179 Less is more: unconventional Compton source optimisation for soft- and hard x-rays

In inverse Compton scattering (ICS), tunable and narrowband x-rays are produced by collisions between relativistic electron bunches and intense laser pulses. In conventional Compton source designs, the x-ray photon energy is tuned by varying the electron energy, which has the drawback of reduced brilliance at soft x-ray energies. Additionally, to achieve sufficient x-ray flux, high bunch charges are utilized, which lead to reduced coherence and high background radiation. In this presentation we discuss two ideas which run counter to the conventional approaches while resulting in a significantly improved performance, in particular at soft x-ray energies. First, by decreasing the electron emission area in the photogun, the electron bunch charge can be decreased without loss of x-ray flux, while gaining x-ray coherence. Second, by changing the laser interaction angle, rather than the electron energy, the x-ray energy can be varied by several orders of magnitude, whilst maintaining the favourable properties of the high energy electrons. This makes Compton scattering a viable source for soft x-rays. We provide an analytical framework to analyse these concepts and investigate their limits. We propose a photocathode-based ICS beamline providing high-brilliance x-rays, continuously tunable from soft to hard photon energies.

Speaker: Coen Sweers (Eindhoven University of Technology)

180 Measurement of transverse profile in novel accelerators

The measurement of transverse profiles is key to determining central parameters of the electron beam. Additionally, transverse profile monitors are used in conjunction with an RF deflecting structure to measure bunch length and slice emittance. A transverse deflecting structure and a dipole can be used to measure the longitudinal phase space. This is of particular interest behind an undulator in a free electron laser, where information on the FEL process and the resulting radiation can be deduced from the measurement of the electron beam.
Novel acceleration techniques impose specific challenges on the instrumentation, but ultimately, the methods are the same as in radio frequency accelerators.
I will therefore present recent advances in profile measurements in SwissFEL and the Swiss Light Source, including scintillating screens, wire scanners, and imaging and interference techniques for synchrotron radiation from dipole magnets.

Speaker: Rasmus Ischebeck (PSI)

181 Multi-GeV Electron Beams from Self-Waveguided Laser Wakefield Acceleration in ELBA at ELI Beamlines

We present recent high-power guiding and laser wakefield acceleration results from the ELBA at ELI Beamlines, utilizing the L3 laser system delivering 13 J, 30 fs pulses at 0.2 Hz. In these experiments, self-waveguiding was employed to generate 20 cm plasma channels in helium above an ELBA-developed supersonic gas jet. The channel forming beam was split from the drive beam post-compression and focused with an off-axis reflective axicon—used for the first time in self-waveguiding experiments—to generate the plasma/neutral prepared index structure for the ~2-3 ns delayed, 11.4 J self-waveguiding LWFA drive pulse. This all-reflective optical setup allowed efficient guiding and stable acceleration of electron beams to energies approaching 5 GeV and is suitable for 3.3 Hz repetition rate. This new implementation of self-waveguided LWFA demonstrates a robust and compact approach compatible with single-laser, single-compressor platforms. ELBA is a fully operational user beamline capable of delivering multi-GeV-class electron beams, including 5 GeV-level outputs, for a range of experiments in advanced laser-plasma acceleration and secondary source development.

Speaker: Jiří Šišma (ELI Beamlines)

182 Optimisation of Inverse Compton Scattering via spatio-temporal tailoring of the scattering pulse

All-optical high-energy X-ray (HEX) beam sources based on Inverse Compton Scattering (ICS) are a promising and innovative alternative to conventional sources, enabling the generation of X-ray beams with percent-level bandwidth. These X-rays are generated by colliding a laser pulse with relativistic electron beams from a laser-plasma accelerator. Although a low HEX bandwidth is essential for many applications, current all-optical ICS sources still exhibit bandwidths of tens of percent. In this work, we present experimental results demonstrating the use of a 'Flying Focus' scheme to achieve spatio-temporal shaping of the scattering pulse. In this scheme, a chirped laser pulse and a chromatic focusing system are combined to make different frequencies focus at different positions. This allows the high-intensity region of the laser to interact with the electron beam over distances longer beyond previously published limits. Such focus optimisation—crucial to precisely match the laser pulse with the electron beam—can lead to a significant reduction in the X-rays bandwidth and an increase in the photon yield. This advancement paves the way for tunable, compact X-rays sources applicable in fields such as non-destructive testing of large or dense objects and k-edge subtraction imaging.

Speaker: Cristina Mariani (Deutsches Elektronen-Synchrotron DESY)

183 Plasma formation via electron-beam driver ionization at SLAC FACET-II

Electron-driven plasma wakefield accelerators offer an advantageous environment for realizing advanced ionization-injection schemes, such as “Trojan Horse” plasma photocathodes [1]. Plasma photocathodes utilize a synchronized laser pulse to release electrons from a dopant species directly inside the wake structure. In comparison to laser drivers, the substantially lower peak electric field of electron drivers facilitates the retention of a dopant species that can, in turn, be accessed for injection already with comparatively low-power laser pulses. Plasma photocathodes therefore promise to generate ultra-cold electron beams with emittances on the order of ~10 nm-rad.
The “E310: Trojan Horse-II” experiment at the Facility for Advanced Accelerator Experimental Tests II (FACET-II) at SLAC National Accelerator Laboratory utilizes a 10 GeV electron driver and employs a gas mixture of hydrogen and helium. The hydrogen component can either be pre-ionized by a dedicated laser pulse or self-ionized by the FACET drive beam, however, ideally without compromising the helium dopant reservoir for selective ionization injection.
We present results from first systematic ionization tests in the context of the E310 experiment and discuss the employed experimental methods. An overview of the E310 program is given in a talk.

[1] A. F. Habib et al. “Plasma Photocathodes”. Ann. Phys. 2023

Speaker: Edgar Anton Hartmann (Heinrich-Heine-University Düsseldorf)

184 Probing Nanostructures for a Novel Inertial Fusion Energy Ansatz with X-rays from a Laser-Driven Plasma-Wakefield Accelerator

Nuclear fusion represents one of the most promising and at the same time challenging pathways toward a sustainable and reliable energy production. A novel inertial fusion concept proposes the use of nanostructured targets in the form of arrays of thin rods that are irradiated by high-intensity laser pulses. The resulting rapid electron expulsion triggers a Coulomb explosion that accelerates nuclei to high energies, potentially enabling efficient heating and compression of solid fusion fuel. Experimental validation of this approach is crucial, but the underlying dynamics unfold on femtosecond time scales and nanometer length scales, posing significant diagnostic challenges.
This work investigates the feasibility of probing these targets during the laser-target interaction using laser-driven plasma-wakefield accelerators for X-ray generation, delivering ultrashort and high-brightness pulses via either betatron radiation or inverse Compton scattering. We want to explore possibilities to use these radiation sources for small-angle X-ray scattering or coherent diffraction imaging to probe the interaction at the nano target.

Speaker: Maurice Zeuner (LMU Munich)

185 Progress and perspectives of the “E310: Trojan Horse-II” program at SLAC FACET-II

Plasma photocathodes utilize a comparatively low-power laser pulse to release and inject electrons directly inside an electron-driven plasma wakefield via selective ionization of a dopant gas or ion species. This injection process is therefore largely decoupled from wake formation and driver evolution dynamics. Also known as “Trojan Horse” injectors, plasma photocathodes promise a pathway towards controlled production of ultra-high brightness electron beams with emittances on the order of ~10 nm rad and kA peak-currents [1].
We report on recent progress and perspectives of the “E310: Trojan Horse-II” experimental program at the Facility for Advanced Accelerator Experimental Tests II (FACET-II) at SLAC National Accelerator Laboratory, which utilizes a 10 GeV electron driver and a mixture of hydrogen and helium for wake formation and injection, respectively.
We will provide an overview of principal experimental design aspects and discuss further advancements of the experimental setup towards implementing plasma photocathodes under various injection geometries. Experimental results from first ionization tests will be presented on a dedicated poster.

[1] A. F. Habib et al. “Plasma Photocathodes”. Ann. Phys. 2023

Speaker: Edgar Anton Hartmann (Heinrich-Heine-University Düsseldorf)

186 Radiation Safety Challenges and Detector Solutions for Plasma Accelerators

Plasma accelerators produce both electron and photon beams with unique characteristics compared to traditional beam sources. As advancements in repetition rate and average power continue, radiation shielding and monitoring become increasingly critical. This poster highlights the distinctive radiation features of plasma accelerators and presents detector developments at Deutsches Elektronen-Synchrotron (DESY) specifically designed for monitoring these radiation fields. By comparing our findings with those from conventional accelerators and free-electron lasers, we provide insights into the evolving needs for radiation safety and dose monitoring. This comparison also offers an outlook on the techniques and advancements required to enable the safe adoption of plasma accelerators for practical applications.

Speaker: Dr Simon Bohlen (DESY)

187 Stable 1.5 GeV range electron beams in a centimeter pre-formed axiparabola driven plasma waveguide with a 50 TW laser power

Today’s laser-plasma accelerators produce electric fields of ~100 GV/m — over 1000 times those in conventional accelerators — shrinking their size from large facilities to compact tabletop laboratories. Recent LWFA advances have demonstrated high-quality femtosecond relativistic electron bunches accelerated to GeV energies within a few centimeters of plasma. Research on plasma waveguides to sustain large accelerating fields over longer distances is advancing rapidly, offering new prospects for scaling up energy and beam quality.

We present results on generating stable multi-GeV electron beams using laser wakefield acceleration assisted by a pre-formed axiparabola-driven plasma waveguide. Experiments at Weizmann Institute of Science accelerated electrons to peak energies exceeding 1.5 GeV using a 50 TW Ti:Sapphire laser power. We achieved reproducible stable high-energy continuous electron spectra and quasi-monoenergetic beams at 1 GeV, maintained over multiple days. A detailed investigation revealed strong dependence of energy and stability on key parameters, including the guiding channel’s density gradient profile matched to the laser spot size, channel length, and injection mechanism. We discuss these results in light of theoretical models for laser guiding and wakefield evolution, highlighting strategies to optimize plasma channel design for next-generation laser-driven electron accelerators.

Speaker: Arujash Mohanty (Weizmann Institute of Science)

188 The plasma injector for Petra IV: Conceptual Design Report

We present the conceptual design of an alternative injector system based on laser-plasma accelerator technology, aimed at delivering high-quality electron bunches to PETRA IV—the upcoming 4th-generation synchrotron light source at DESY. The proposed design features a laser-plasma accelerator capable of producing 6 GeV electron bunches with state-of-the-art energy spread and stability (~1%), followed by an X-band energy compression beamline that reduces energy deviations to the sub-permille level. This enables efficient charge injection into the PETRA IV storage ring. Powered by the Petawatt-class upgrade of DESY’s flagship laser, KALDERA, the plasma injector system offers a promising solution for top-up injection, significantly alleviating the load on the conventional RF injector chain. Looking ahead, continued advancements in high-efficiency, high-power laser drivers operating at high repetition rates could allow the plasma-based injector to fully replace the RF system—ultimately reducing the injector’s spatial footprint and energy consumption. The Report can be found at [A. Martinez de la Ossa et al., DESY, 2024 https://doi.org/10.3204/PUBDB-2024-06078 ].

Speaker: Maxence Thévenet (DESY)

189 Ultrafast Electron Scattering & Imaging Using MeV Electrons

Going higher electron beam energy had been one of the major factors improving electron microscope performance. The ‘holy grail’ of electron microscope – 1 Å resolution was first demonstrated in 1990s with a 1.2 MeV electron microscope. The introduction of aberration-correction electron optics and cold field-emission electron source led to the demise of MV electron microscope. To meet the challenge of ultrafast science & imaging bio-samples in physiological environments, there is renewed interest in going higher electron beam energy. The MeV ultrafast electron diffraction (MeV-UED) is the first step of the renaissance of MeV electron scattering. MeV-UED opened a new paradigm due to its capability of following dynamics on femtoseconds scale with the high spatial resolution and sensitivity. MeV-UED had broad and transformative impact to ultrafast science, such as the first ultrafast structure dynamics of 2-D materials, light-induced transient states, and the first direct imaging of fundamental chemical processes: canonical interception & ring-opening. In this talk, I will first discuss the latest advancements of MeV-UED technology and science, such as hydrogen bond structure dynamics in liquid water and simultaneous observation of both electronic and nuclear dynamics. the advanced accelerator technologies needed to enable MeV-UEM will be explored.

Speaker: Xijie Wang (University of Duisburg-Essen & TU-Dotmund)

190 Wakefield mitigation in the High-Energy EuPRAXIA@SPARC_LAB LAB X-Band Linac

EuPRAXIA@SPARC_LAB aims to be the first European research infrastructure to demonstrate the application of a plasma accelerator. The project is currently in the technical design report preparation phase. This facility combines a high-brightness electron beam in the GeV range, produced by an X-band linac, with a powerful 0.5 PW-class laser system, by utilizing a sophisticated “particle-driven configuration” to achieve highly efficient particle acceleration. This method involves an RF injector system consisting of an S-band photoinjector and an X-band linac. In the typical operating scenario, the system is designed to handle a witness beam with a charge of 30 pC and a driver beam with a charge of 200 pC. These beams are longitudinally compressed within the photoinjector and boosted in energy in the X-band linac. This work reports on beam dynamics studies devoted to investigating and comparing several methods to mitigate wakefields contributions in the X-band linac due to residual machine misalignments regarding beam quality preservation. Dedicated simulations will be performed implementing Dispersion-Free Steering (DFS) and Wakefield-Free Steering (WFS) correction algorithms with the RF track code, aimed at minimizing trajectory deviations and mitigating transverse emittance dilution, thus ensuring the beam quality required for efficient plasma injection.

Speaker: Gilles Jacopo Silvi (Istituto Nazionale di Fisica Nucleare)

20:30 Dinner

Thursday 25 September

Plenary Session

191 Recent progress on laser-driven Very High Energy Electron radiotherapy

Radiotherapy is one of the mainstream methods for cancer treatment. In recent years, the use of very high energy electron beams (VHEE, generally with energies between 50MeV and 300MeV) for deep tumor radiotherapy has been very active in international research. Due to its superior dose deposition characteristics compared to traditional X-rays and its pencil beam scanning capability comparable to ion beams, it is considered to be a very promising new type of radiotherapy method in the future. The use of ultra-high gradient laser wakefield acceleration (LWFA) can further reduce the size and cost of such electron radiotherapy devices, making them more attractive in the field of radiotherapy. This talk will introduce our team's recent progress in the LWFA-based VHEE radiotherapy studies, including the development of high-reliability industrial-grade ultra-short ultra-intense laser systems as well as high-stability laser wakefield accelerators, experimental studies on irradiation of tumors in small animals, and the new design of a LWFA-based VHEE prototype for radiotherapy.

Speaker: Yang Wan (Zhengzhou University)

192 Physics and Application of the ELI betatron radiation source

The realization of compact, broadband X-ray sources is one of the most promising applications of laser-plasma accelerators (LPAs). State-of-the-art LPA-based X-ray sources currently deliver photon fluxes exceeding 10¹¹ photons per shot [1]. In this contribution, we present a summary of compact X-ray sources offered to user applications at the ELI Beamlines facility. One of the key developments is the Gammatron beamline [2], which generates a collimated, bright, and partially coherent X-ray beam suitable for a wide range of multidisciplinary applications. Furthermore, we introduce a novel optical probing technique allowing precise characterization of low-density gas targets used in LPAs [3].
A second LPA-based X-ray source, the Betatron source, is currently under development at the ELI Plasma Physics Platform (P3) [4]. This source is specifically designed to serve as a back lighter for laser-matter interaction studies, High energy density (HED) physics & Inertial fusion energy (IFE) experiments and advanced investigations in plasma physics.

References
1. S. Fourmaux, et al., Opt. Express 28.3,3147-3158 (2020)
2. U. Chaulagain, et al., Photonics, 9.11 (2022).
3. M. Raclavsky et al., Opt. Letters 49.9 2253-2256 (2024).
4. U. Chaulagain et al., SPIE Conf. Proc. (2018)

Speaker: Uddhab Chaulagain (ELI beamlines)

193 Laser driven proton acceleration from imploded gas targets

Advances in short-pulse near-infrared laser technology have significantly expanded access to the relativistic regime of laser–plasma interactions, enabling new approaches for compact, high-energy proton acceleration. A primary objective is to produce stable, high-charge proton beams suitable for applications such as proton radiography, hadron therapy, and medical isotope generation. Proton acceleration with near-critical density (NCD) gas targets offer promising energy scaling and operation at high repetition rate.

In this work, we present experimental results demonstrating efficient proton acceleration using optically tailored hydrogen gas targets. Femtosecond laser pulses are used in distinct, implosion geometries in order to attain a transient, near-critical density region. By tailoring the gas density profile and optimizing the focal geometry, we achieved stable proton beam generation. Our findings exemplify the role of laser-shaped density gradients in achieving proton acceleration and provide a robust platform for exploring NCD-driven acceleration mechanisms under well-controlled experimental conditions.

Speaker: Santhosh Krishnamurthy (Weizmann Institute of Science)

10:40 Coffee Break

Plenary Session

194 Development of high peak and high pulse rate drivers for accelerators: opportunities and challenges

High peak power lasers are ideal drivers for compact, high-brightness particle and radiation sources.
Day-to-day application of laser-driven sources in fields such as industry, healthcare and security requires drivers operating at high pulse rates with high reliability and reproducibility.
This talk will provide an overview of current and emerging laser driver technologies and an analysis of technical opportunities and limitations. Notable laser systems and development projects will also be discussed.

Speaker: Mariastefania De Vido (STFC Central Laser Facility)

195 Modelization of Plasma Accelerators in the Exascale Era

Plasma accelerators have demonstrated significant milestones, from producing 10 GeV electron beams in wakefield acceleration, high-gain free-electron laser operation, energy boosting of electrons, to reaching stable (ultra-short, nC-class) proton acceleration that enable studies of ultrahigh dose-rate radiobiology. Now, the community is setting sight on integrating plasma acceleration deep into future particle colliders and applications, such as a potential 10 TeV center-of-mass collider, Higgs factory, injection into rings for next-generation light sources, stable high-repetition rate operations, among others, which continue to set demanding research challenges on particle beam quality, repetition rate and reliability.
This presentation will discuss the current capabilities and latest trends in modeling plasma accelerators and integrated modeling of beamlines with plasma elements. With a need for detailed kinetic modeling from design to operations, a comprehensive and coordinated approach is needed to cover and optimize anything from the source to the end of the beam’s lifetime. An important enabler are new technologies from Exascale Computing, providing (GPU) accelerated computing for accelerator and plasma physicists from laptops to supercomputers. Advances in open source modeling ecosystems and coupling to AI/ML with standardized data exchange now enable user-friendly model-building for integrated accelerators, combining theory, kinetic modeling and fast surrogate models.

Speaker: Dr Axel Huebl (Lawrence Berkeley National Laboratory)

196 Meter-scale supersonic gas jets for multi-GeV laser-plasma accelerators

Recent ~10 GeV laser wakefield acceleration (LWFA) experiments have been made possible by low-density hydrodynamic plasma waveguides generated by femtosecond Bessel beams in meter-scale supersonic gas jets. Such jets and Bessel beam optics will likely be critical components in next-generation experiments surpassing 10 GeV. Here I describe our gas jet and Bessel beam development, along with detailed measurements of waveguide evolution. These have led to understanding of the self-waveguiding process in low density gas channels and the first all-optical multi-GeV waveguide-based electron accelerator, directly leading to the ~10 GeV results. Our jet designs provide longitudinal control of the gas density and species composition, essential for controlling electron injection, rephasing, and optimizing energy gain in channel-guided LWFA. I will also present results from recent ELI-Beamlines experiments demonstrating density upramps, injection from optical shocks, and the use of funnel mouthed waveguides for improved laser coupling and laser-to-electron efficiency.

Speaker: Bo Miao (University of Maryland, College Park)

12:30 Lunch Break

16:00 Coffee Break

PS1: Plasma-based accelerators and ancillary components

Conveners: Mario Galletti (Istituto Nazionale di Fisica Nucleare), Sarah Schröder (Lawrence Berkeley National Laboratory)

197 Progress on the Flat beam PWFA experiment at AWA

A wakefield experiment at the Argonne Wakefield Accelerator (AWA) facility utilizes flat electron beams with highly asymmetric transverse emittances to drive plasma wakefields in the underdense regime. These beams create elliptical blowout structures, producing asymmetric transverse focusing forces. The experiment utilizes a compact 4-cm-long capillary discharge plasma source developed at UCLA. Analytic models of blowout ellipticity and matching conditions, supported by particle-in-cell simulations, guide the experiment's design. Engineering preparations including the use of windows for vacuum-gas separation, beam transport and diagnostics are discussed. The first beam runs involving flat beam generation and transport is also discussed.

Speaker: Pratik Manwani (University of California, Los Angeles)

198 Slice Emittance Preservation and Focus Control in a Passive Plasma Lens

Strongly focusing plasma lenses have been proposed to mitigate chromatic aberrations in the high-strength focusing systems needed to accommodate the small beam sizes associated with plasma-based accelerators and collider final foci. Active plasma lenses focus using the azimuthal magnetic field generated by an electric discharge through a plasma. Emittance preservation with such lenses has been shown for low-charge bunches under certain conditions, but their compatibility with high-brightness beams, which are needed for applications but are likely to generate a beam-quality-spoiling plasma wakes, has not. Passive plasma lenses are a promising route for focusing high-brightness beams, as a plasma wake is required to generate the transverse fields required for focusing. Operation of such passive plasma lenses has been experimentally demonstrated, but their ability to preserve beam quality has not. In this work, we show experimentally that passive plasma lenses can preserve FEL-quality transverse slice emittance while focusing two orders of magnitude more strongly than quadrupole magnets.

Speaker: Dr Jonas Björklund Svensson (Lund University)

199 Experimental study of the growth of hosing instability

The hosing instability, a significant concern for accelerator applications, poses limitations on achieving high energy gain over long distances. Understanding and mitigating this instability is crucial for advancing accelerator technologies. The AWAKE experiment at CERN offers a unique opportunity to investigate the hosing instability in a plasma wakefield accelerator using a long proton bunch driver. The recent upgrade of the AWAKE plasma source enhances the capability to study the dynamic evolution of this instability. Not only is it possible to study the hosing evolution along the drive bunch, but it is also possible to observe the growth along the plasma. In this contribution, we present the initial findings that delineate the conditions under which hosing occurs, and its impact on beam quality.

Speaker: Michele Bergamaschi (Max-Planck-Institut für Physik/CERN)

200 GeV Compton photons generated by self-aligned collisions with a plasma mirror

Current multi petawatt laser systems allow unprecedented experimental tests of quantum electrodynamics (QED) in all-optical schemes. In this work we demonstrate experimentally that a single-laser beam Compton scattering arrangement leads to GeV energy photons [Matheron et al. 2024]. The collisions between a reproducible nC, multi-GeV electron beam and the unspent laser by the plasma accelerator via a plasma mirror have a characteristic 100% success rate. The obtained photon energies represent several orders of magnitude increase over the initial seminal results of [Ta Phuoc et al. 2012]. We will discuss the results obtained at Apollon and ELI-NP laser facilities together with their impact for precise investigations of strong-field QED processes and photon sources development.

Speaker: Petru Ghenuche (ELI-NP/IFIN-HH)

201 All-optical, self-aligned Compton source using a PW-scale laser-wakefield accelerator and a plasma mirror

We will report on an experimental campaign to explore inverse Compton scattering using the 1PW experimental area E5 at ELI-NP. Laser pulses containing up to 20 J were focused into a gas jet to accelerate electrons beams to GeV energies via laser wakefield acceleration. The residual laser exiting the plasma accelerator was then back-reflected onto the electron beam using a tape-based plasma mirror to drive inverse Compton scattering. This all-optical geometry using a single laser pulse yielded successful collisions on every shot due to the self-alignment of the wakefield electrons and the driving laser pulse also acting as scattering beam. The process was diagnosed through measurements of the profile and spectrum of the generated electron and gamma beams. We will present details of the experimental setup and a preliminary analysis of the results.

Speaker: Elias Gerstmayr (Queen's University Belfast)

202 Laser wakefield acceleration in a carbon nanotube-based plasma

Laser wakefield acceleration (LWFA) has been evidenced by a capability of reaching acceleration gradients ranging from tens to hundreds of GV/m, thereby reducing the footprint and cost of accelerators. Carbon nanotubes (CNTs), featuring high plasma density (>10$^{19}$ cm$^{-3}$) and the ability to tailor plasma density effectively, have emerged as a novel solid-state plasma source. Recent numerical studies suggest that using CNT-based structures can enhance the acceleration gradient to the TV/m regime, offering unique advantages for compact medical accelerators. In this work, we modelled the structure of a hollow solid-state plasma which is composed of carbon nanotube bundles. An intense laser pulse is injected into this channel, where self-injected electrons achieve TeV/m-scale acceleration, as simulated using a particle-in-cell (PIC) code. Energy gain and beam quality of the electron bunches, such as charge absorbed, energy spread, and emittance, are optimised by tuning the plasma density, geometric properties of the carbon nanotubes, and laser parameters.

Speaker: Jiaqi Zhang (University of Manchester)

18:20 Discussion & Closing Remarks

PS2: High gradient vacuum structures

Conveners: Evan Ericson (PSI/EPFL), Jom Luiten

203 Towards three-dimensional confinement of the electron beam inside dielectric laser accelerators

In dielectric laser acceleration (DLA), well known accelerator concepts are applied at a much smaller length scale. While classical accelerators use radiofrequency cavities, dielectric laser accelerators utilize dielectric nano-structures driven by strong infrared femtosecond laser pulses. Due to the high damage threshold of dielectric materials, acceleration gradients up to one or two orders of magnitude larger can be obtained. In addition to high acceleration gradients, the electron beam needs to be confined inside the narrow acceleration channel to maximize transmission. This can be achieved by employing alternating phase focusing (APF), a scheme also adapted from classical accelerators. By combining these approaches and utilizing a scanning electron, we recently demonstrated the coherent acceleration of electrons from 28.4 to 40.7 keV in a 500 µm long structure [1]. However, due to the two-dimensional design process and the lithography structure fabrication, the APF control was limited to one of the transverse directions. In this talk, we present how this principle can be expanded to full three-dimensional confinement by using multiple layers of dielectric materials. We will show first measurements of simple guiding structures and revisit the old two-dimensional designs to investigate the effect of top-illumination.

[1] Chlouba et al., Nature 622, 476 (2023)

Speaker: Manuel Konrad (Chair for Laserphysics, Friedrich-Alexander-Universität Erlangen-Nürnberg)

204 The Ultracold Electron Source as an Injector for high bunch charge Dielectric Laser Acceleration

The potential of Dielectric Laser Accelerators [1] is currently limited due to the low bunch charges typically achieved. This is because the small lateral sizes of the accelerating structures pose strict requirements on the injection beam. A bunched low emittance beam is thus required for reasonable injection efficiency. We propose a compact low-energy design of an electron injector based on the Ultracold Electron Source [2, 3] and a novel permanent magnet lens designed through genetic optimization. Simulations indicate a beam waist in the order of 1 um and bunch length of 1ps at a bunch charge of 1 fC can be attained without a linac. This can potentially increase the bunch charge of Dielectric Laser Accelerators by several orders of magnitude.

1. R. Joel England et al., Dielectric laser accelerators, Rev. Mod. Phys. 86, 1337
2. J. G. H. Franssen et al., Compact ultracold electron source based on a grating magneto-optical trap, Phys. Rev. Accel. Beams 22, 023401
3. T. C. H. de Raadt et al., Subpicosecond Ultracold Electron Source, Phys. Rev. Lett. 130, 205001

Speaker: Ameya Patwardhan (Eindhoven University of Technology)

205 Terahertz-driven compression for femtosecond bunching and laser-electron temporal locking of relativistic electron beams.

We demonstrate the application of THz-frequency acceleration in the control of the chirp of an electron beam supplied by an RF linac injector. An ultrafast Ti:Sapphire laser drives the THz source, enabling a direct link between laser and electron beam timing and temporal-locking between laser and electron bunch arrival time. The accelerating structures high drive frequency results in a high temporal gradient of the accelerating field. The resulting strong chirp allows compression of the injected bunches to the few-femtosecond level.
Experimentally, multi-cycle THz is generated through optical rectification of wafer-stack periodically poled lithium niobate sources. A sub-picosecond electron bunch interacted with the ~20 MeV/m gradient accelerating THz field, in a velocity-matched dielectric-lined waveguide. Compression of the experimental observed electron time-energy phase space with a modelled magnetic chicane demonstrates a compression factor of over 20, providing bunch durations <20 femtoseconds. The compressed electron-bunch arrival time is correlated with the THz drive laser, and sub-20fs temporal locking between drive laser and compressed electron beam is shown to be achievable even with the energy and time jitter present in RF accelerator, despite the >100 fs RF-laser time jitter. The techniques demonstrate a route to external injection of RF-injector into high-gradient plasma accelerators.

Speaker: Mr Christopher T. Shaw (University of Lancaster, The Cockcroft Institute)

17:20 Discussion & Closing remarks

PS4: Theory and simulations: LPA

Conveners: Maxence Thévenet (DESY), Stefano Romeo (Istituto Nazionale di Fisica Nucleare)

206 On an analytical optimization of plasma density profiles for downramp injection in LWFA

We propose and test a multi-step preliminary analytical procedure that tailors the initial density $\widetilde{n_0}$ of a cold diluted collisionless plasma to a very short and intense plane-wave laser pulse travelling in the $z$ direction, so as to maximize the early laser wakefield acceleration (LWFA) of bunches of plasma electrons self-injected in the plasma wave (PW) by the first wave-breaking (WB) at the density down-ramp. The procedure partially inverts the determination of the motion of the plasma electrons for a given pulse and (for simplicity, slowly varying) $\widetilde{n_0}(Z)$: the motion of every infinitesimal layer of electrons having coordinate $z\!=\!Z\!>\!0$ for $t\!\le\!0$ is determined using a fully relativistic multi-stream plane model (encompassing the Lorentz-Maxwell equations) that is valid as long as the pulse depletion can be negleted; up to WB, its equations reduce to a family (parametrized by $Z$) of decoupled pairs of Hamilton equations for a 1-dimensional system where $\xi=ct\!-\!z$ replaces time $t$ as the independent variable. We apply the procedure to a Gaussian laser pulse with $l_{fwhm}=10.5\lambda$ and $a_0=2$; using the latter and two associated $\widetilde{n_0}(Z)$ as inputs, we then determine the detailed plasma dynamics by FB-PIC simulations, confirming the predicted maximal acceleration in the early LWFA stages.

Speaker: Gaetano Fiore (Istituto Nazionale di Fisica Nucleare)

207 Algorithmic optimization of ionization injection in laser wakefield acceleration

Narrow energy spread beams with high spectral density and minimal dark current are critical for a wide range of applications. We report results from both experiments and simulations aimed at optimising these key parameters using laser wakefield accelerators. A fully automated experiment using Bayesian optimisation, controlling only the laser focal position and spectral phase, was used to achieve low energy spread electron beams with minimal dark current above 20 MeV. High fidelity simulations that closely match the experiment reveal the key role played by spectral phase terms in optimising accelerator performance. In particular, third-order dispersion plays a vital role in maximising beam charge, with a slight positive skew increasing the wake amplitude at the moment of injection. Simulations are further used to explore optimal trade-offs between beam parameters for the experimentally studied case and for next generation laser wakefield acceleration systems.

Speaker: Michael Backhouse

208 Physics of transverse dynamics in a laser-plasma accelerator

Laser Wakefield Accelerators (LWFA) offer a promising solution for producing high-energy electron beams in compact setups. Beyond obtaining the required energy, the beam quality (emittance, energy spread, intensity) must also be optimized for LWFA to be considered an alternative to conventional accelerators. Achieving precise control of the transverse beam dynamics is one of the key challenges. This article thoroughly studies the physics governing the evolution of emittance and Twiss parameters within the plasma stage, on the density plateau, and in the up-ramp and down-ramp connections to conventional transport lines. Analytical and numerical analysis will be conducted using a toy model made of special quadrupoles, allowing numerical calculations to be sped up to a few seconds/minutes. Matching between plasma and transport lines will be extensively studied, clearly showing the dependence on initial conditions, and recommendations for the best realistic configurations will be provided.

Speaker: Laury Batista (CEA Saclay)

209 Towards improved control of laser-wakefield accelerators with multidimensional parameter scans

The quality of electron beams generated by laser wakefield accelerators (LWFAs) is constantly improving to the point where it is now possible to operate novel light sources such as free-electron lasers (FELs), as has been achieved at various facilities. However, this method is still limited by the fluctuations of the electron beam properties, which are difficult to control due to the non-linear nature of injection, cavity formation and laser propagation. This becomes increasingly difficult when aiming at X-ray FEL wavelengths.

We present an in-depth simulation study in which we have reconstructed an experimental LWFA setup with self-truncated ionisation injection (STII) as the injection mechanism using realistic 3D particle-in-cell (PIC) PIConGPU simulations combined with the automated workflow engine Snakemake. Based on the reconstruction, we have created a multidimensional mapping of electron beam parameters to laser and plasma parameters. With these results we present requirements for the laser and plasma configuration to ensure the appropriate onset and truncation of the injection process. In addition, a study of the spectral and longitudinal charge distribution on laser dispersion and focussing in the STII regime is presented. These results are confirmed with experimental observations obtained in a FEL campaign.

Speaker: Jessica Tiebel (HZDR)

210 Start-to-End Simulations for the Extreme Photonics Application Centre

The Extreme Photonics Application Centre (EPAC) will house a 1 PW, 10 Hz repetition rate laser: performing laser-plasma experiments for both academic and industrial communities. Accurate modelling of the laser, of the laser-plasma interaction, and of radiation propagation is essential for experiment design in large-scale user facilities, where access to the beam is highly sought after. To address this, we are building a toolkit, vEPAC, which aims to leverage existing open-source simulation tools and combine them with an intuitive wrapper to perform start-to-end simulations for a number of applications. We will present the design approach for this toolkit, along with test cases showing beam tracking of an LWFA output and radiography with a simulated source.

Speaker: Oliver Finlay (Central Laser Facility)

211 Exascale Plasma Accelerator Simulations with PIConGPU

We present PIConGPU as an enabling simulation tool for recent advances in plasma acceleration. The transition to Exascale capabilities as enabled new opportunities and capabilities to study plasma accelerators at unprecedented resolution and physical detail. We present recent studies on both laser-driven ion acceleration as well as laser- and plasma-driven electron acceleration and potential applications from compact free electron lasers to fusion schemes. We conclude by introdcuing important work on data harmonization and complex workflows enabling new capabilities for optimization of particle accelerators, better diagnostics and more realistic simulations.

Speaker: Michael Bussmann (HZDR)

18:20 Discussion & Closing Remarks

PS5: Applications

Conveners: Felicie Albert (Lawrence Livermore National Laboratory), Jaroslav Nejdl (ELI Beamlines Facility, Extreme Light Infrastructure ERIC), Prof. Victor Malka (Weizmann Institute of Science)

212 3D Theory of the Ion Channel Laser

The ion channel laser (ICL) is similar to the free electron laser (FEL) but utilizes the electric field from a blowout regime plasma wake rather than the magnetic field from an undulator to oscillate particles. Compared to the FEL, the ICL can lase with much larger energy spread beams and in much shorter distances, making it an attractive candidate for a future compact plasma accelerator driven coherent light source. We present a novel full 3D theory of the ICL accounting for numerous effects including transverse guided mode shape, diffraction, frequency and Betatron phase detuning, and nonzero spread in energy and undulator parameter. This theory is used to predict the gain, radiation mode profile, gain bandwidth, and emittance and energy spread constraints of the ion channel laser.

U.S. Department of Energy, Office of Science, Office of High Energy Physics, Award Number DE-SC001796; National Science Foundation Grant Number PHY-2047083

Speaker: Claire Hansel (University of Colorado Boulder)

213 Smart*Light: an X-band LINAC-based Compton x-ray source with continuous tunability

At Eindhoven University of Technology, a tabletop x-ray source based on inverse Compton scattering (ICS) has recently been commissioned. In the ICS process monochromatic x-rays are produced by colliding relativistic electron bunches with intense laser pulses. This compact and tunable source holds the promise of a performance in between small-scale x-ray tubes and large-scale synchrotron light sources, making advanced x-ray diagnostics accessible to a wider range of applications. The beamline utilizes a 100 kV DC photo-electron gun in combination with an X-band linear accelerator. The X-band LINAC is based on a design for the CERN Compact Linear Collider (CLIC), but adapted to allow for the injection of subrelativistic electrons. After acceleration the electron bunches collide with femtosecond laser pulses, producing x-ray photons with energies which are continuously tunable between a few and 40 keV. In this presentation we present the design and the successful commissioning of Smart*Light. We discuss the measured characteristics of the x-ray beam, which are in full agreement with theoretical expectations, and we present results from the first demonstration experiments.

Speaker: Jom Luiten

214 Progress in Plasma Accelerator R&D at the BELLA Center: From Early Applications to Collider-Relevant Studies

The BELLA Center at LBNL facilitates four independent laser-plasma accelerator systems and a high-repetition rate fiber laser laboratory, enabling a comprehensive research program spanning critical system development, early applications and collider-relevant studies. Recent advancements in ancillary components, including active stabilization systems and plasma sources, have enabled significant milestone experiments, such as robust free-electron laser operation [1] and high-quality 10 GeV-level electron beam generation in a single stage [2] as well as early application experiments in nuclear science [3] and muon production [4]. This contribution provides an overview of the BELLA Center's cutting-edge infrastructure with its diverse scientific capabilities, outlining future research directions and highlighting recent scientific results.

[1] S. Barber et al. (accepted in PRL)
[2] A. Picksley et al. PRL 133 (25), 255001 (2024)
[3] R. Jacob et al. PRL 134 (5), 052504 (2025)
[4] D. Terzani et al. PRAB (in review with PRAB)

Speaker: Sarah Schroeder (Lawrence Berkeley National Laboratory)

215 A fast neutron source driven by an 80W average-power laser and its application in radiobiology

A laser-based neutron source was commissioned using the 1kHz repetition rate SYLOS3 laser of ELI-ALPS, delivering 80mJ, sub-10 fs laser pulses on a heavy water sheet. The accelerated deuterons induced a 2H + 2H fusion reaction on a rotating disk of deuterated polyethylene, resulting in neutrons with a mean kinetic energy of 3.5MeV in the forward direction. We maximized the neutron yield per laser shot by tuning the dispersion, and hence the temporal shape of the laser pulse. At the optimum neutron yield of $7\times 10^4$ neutron/shot, the cutoff energy of the forward accelerated deuterons well exceeded 2MeV, while its average power was around 4W. However, due to the degradation of the surface of the deuterated polyethylene disk, the yield continued to drop continuously over 4 hours of operation. The average neutron flux on target exceeded $2\times10^7$ neutron/cm2/s, while the flux rate of a neutron pulse was estimated around $10^{12}$ neutron/cm2/s.
In an irradiation session of four hours, a total of 1.6 Gy dose was delivered on zebrafish embryos. The density of apoptotic cells as well as double-strand breaks in the zebrafish embryos was similar to that of the control group irradiated with cyclotron-generated neutrons. However, photomotor responses showed differences.

Speaker: Karoly Osvay (University of Szeged)

216 Design of a Water-Window Free-Electron Laser Using the Two-Beam Acceleration Scheme

Two-beam acceleration (TBA), pioneered at CERN, has witnessed breakthrough achievements over the last five years. Accelerating fields approaching 400 MV/m have been routinely produced experimentally. These achievements are bolstering efforts to explore the use of TBA to drive hard X-ray free-electron lasers based on future light source (FLS) concepts. As a first demonstration, a scaled-down version of this concept could support a water-window FEL operating in the 2.3-4.4 nm spectral range, enabling unique biological imaging capabilities. This contribution discusses progress toward the realization of such a free-electron laser and options for its implementation at Argonne National Laboratory. Start-to-end simulations of the concept will be presented along with its compelling scientific case for structural biology and materials science applications.

Speaker: Philippe Piot (Argonne National Laboratory)

217 Optimisation of Inverse Compton Scattering via spatio-temporal tailoring of the scattering pulse

All-optical high-energy X-ray (HEX) beam sources based on Inverse Compton Scattering (ICS) are a promising and innovative alternative to conventional sources, enabling the generation of X-ray beams with percent-level bandwidth. These X-rays are generated by colliding a laser pulse with relativistic electron beams from a laser-plasma accelerator. Although a low HEX bandwidth is essential for many applications, current all-optical ICS sources still exhibit bandwidths of tens of percent. In this work, we present experimental results demonstrating the use of a 'Flying Focus' scheme to achieve spatio-temporal shaping of the scattering pulse. In this scheme, a chirped laser pulse and a chromatic focusing system are combined to make different frequencies focus at different positions. This allows the high-intensity region of the laser to interact with the electron beam over distances longer beyond previously published limits. Such focus optimisation—crucial to precisely match the laser pulse with the electron beam—can lead to a significant reduction in the X-rays bandwidth and an increase in the photon yield. This advancement paves the way for tunable, compact X-rays sources applicable in fields such as non-destructive testing of large or dense objects and k-edge subtraction imaging.

Speaker: Cristina Mariani (Deutsches Elektronen-Synchrotron DESY)

18:20 Discussion & Closing Remarks

PS8: Plasma sources and related diagnostics

Conveners: Lucio Crincoli (Istituto Nazionale di Fisica Nucleare), Malte Kaluza (University of Jena, Helmholtz-Institute Jena)

218 Temperature effects in a plasma-wakefield accelerator

Plasma-wakefield acceleration holds great promise for photon science and particle physics due to its extremely high accelerating gradients. However, plasma accelerators must also be capable of operating at very high repetition rates—orders of magnitude beyond the state of the art—to meet the brilliance and luminosity demands of users. Recent results from FLASHForward demonstrated that operation at the required MHz rates are possible in principle; the next step is to operate at (or close to) this rate in practice. However, doing so will result in the deposition of enormous amounts of beam power in the plasma, likely leading to far-from-equilibrium plasma conditions that must subsequently relax via multi-scale physics before the next acceleration event. Unfortunately relatively little is known about how this beam power evolves in the plasma and to the plasma stage over long (ns-μs) timescales and how the resulting background temperature increase will modify the subsequent plasma-electron and -ion response. Here we present novel numerical and experimental concepts to describe and map the key thermodynamics of state-of-the-art plasma accelerators, which is required to inform the design of future high-repetition-rate and high-average-power plasma accelerators, such as FLASHForward and HALHF.

Speaker: Ibrahim Najmudin (University of Oxford)

219 Diagnostics for plasma ion and electron heat flow

Plasma-based accelerators have the potential to reduce the size, cost, and carbon footprint for a wide variety of applications, including light sources and linear colliders, due to the ultra-high electric-field strengths that can be sustained in the accelerating structure. However, the nonlinear processes typically involved with this mechanism place stringent demands on the plasma’s initial
conditions, as shot to shot fluctuations in parameters such as density and temperature potentially lead to large instabilities in the accelerated electron beams. This problem is increasingly relevant as research pushes towards higher repetition rates, resulting in significant heat deposition in to the plasma medium and the target substrate. In the High-average-power Plasma-accelerator
Experimentation (HiPE) Laboratory in Oxford, we are developing a set of diagnostics to map the
energy deposition and transport in beam- and laser-driven plasma-wakefield accelerators. We aim to show that the most important plasma parameters—temperature and density profiles of the plasma electrons and ions, as well as heat load on the materials used to produce and contain the plasma—can be obtained using minimally invasive all-optical techniques that can be transported to plasma-accelerator facilities for parasitic measurements during experimentation.

Speaker: James Cowley

220 Measurement of the radius of a plasma column in presence of a relativistic proton bunch

To reach large accelerating gradients, an important requirement for a plasma wakefield accelerator is to produce a uniform plasma density. The creation and characterization of the density can be challenging. Demeter et al. showed that the schlieren imaging technique is well suited to determine the geometrical properties of the AWAKE, 10m-long plasma column of Rubidium vapor. We describe an experimental investigation of the effect on the plasma of a relativistic proton bunch driving wakefields using an improved version of this diagnostic.

The schlieren imaging with near resonant probe light yields estimates of the radius of the plasma column of excited rubidium atoms ionized by an ultra-short, terawatt laser pulse. Moreover, this measurement is adequate to observe the effect on the plasma radius of the wakefields driven by the proton bunch.

Speaker: Dr Lucas Ranc (Max Planck Institut for Physics, Munich)

221 Experimental Progress of Passive Plasma Lens at FACET-II

The thin, underdense, passive plasma lens comprises a sub-millimeter scale, laser-ionized plasma in the outflow of a supersonic gas jet. It promises compact, strong, tunable, axisymmetric focusing of intense electron beams and is ideally suited for matching beams into and out of plasma wakefield accelerator stages. It can also be used for reducing divergence of high-brightness plasma-injected beams as they exit the plasma source. Results from experiments at SLAC’s FACET-II facility will be presented demonstrating strong focusing of a 10 GeV electron beam to a small waist in vacuum downstream of the plasma lens.

Speaker: Michael Litos (University of Colorado Boulder)

222 Visualizing plasma waves and long-living soliton-like structures in a laser wakefield accelerator

In LWFA, the driving laser generates a high-amplitude plasma wave producing the electric field structure, which can trap and accelerate electron pulses. For a detailed investigation of the formation and evolution of the wave and the acceleration process we use a synchronized, ultra-short (few-cycle), ultra-broadband laser pulse, which probes the interaction region. In transverse geometry, shadowgraphic snapshots of the plasma can be taken [2]. Applying a linear chirp to the probe pulse and using a spatially resolving spectrometer allowed us to record short movies of the interaction during one single laser shot. In addition to visualizing the plasma wakefield, this technique also allowed us to observe and study the evolution and the lifetime of soliton-like structures generated during the interaction and emitting broad band electro-magnetic radiation. The experimental results will be presented and compared to numerical simulations pointing towards the origin of these structures.

Speaker: Malte Kaluza (University of Jena, Helmholtz-Institute Jena)

223 Single-mode laser guiding in non-parabolic plasma channels for high-energy electron acceleration

The discovery of laser wakefield acceleration in gaseous plasma was a major milestone that could lead to a significant reduction of size and cost of large electron accelerators. For higher-energy laser-driven electron acceleration guiding plasma channels were proposed, which are
matched to the laser pulse parameters. A parabolic density profile is
needed for guiding a Gaussian beam, which is difficult to realize experimentally. The realistic channel profiles can be described
by higher order polynomial functions which are not optimal for guiding due to the development of undesired distortions in the laser intensity envelope. However, here we show that for non-parabolic
plasma channels well-defined matching conditions exist, which we call mode matching. This leads to the guiding of the fundamental mode only in the acceleration regime, where the plasma electron density is modulated by the high-intensity laser pulse. In this way we eliminate two deteriorating
factors of laser wakefield acceleration, namely the mode dispersion and energy leakage. We apply this new matching condition for single-mode guiding in quasi-3D simulations to show that 10 GeV energies can be reached in a distance of less than 15 cm.

Speaker: Zsolt Lécz

18:20 Discussion & Closing Remarks

PS3: Laser technology

Conveners: Manuel Kirchen, Mariastefania De Vido (STFC Central Laser Facility)

224 The TAF-project: Synchronized High Power Laser Experiments @ HI Jena

A new target area is set up at the Helmholtz Institute Jena. One central aspect are combined experiments with the laser systems JETi200 and POLARIS. Additionally, a new dedicated probe laser system, JETi ONE, was installed giving the opportunity to investigate laser-plasma interactions with few-cycle laser pulse ranging from the visible to the mid infrared spectrum. To synchronize these three laser systems a timing system was installed just recently. A status of the overall project and planed experiments will be presented.

Speaker: Alexander Sävert (Helmholtz Institut Jena)

225 Research opportunities at Brookhaven's Accelerator Test Facility supported by multi-wavelength lasers combined with an electron beam

Brookhaven’s Accelerator Test Facility (ATF) offers users access to a broad array of advanced research capabilities, including an RF photocathode electron LINAC, a femtosecond Ti:Sapphire laser, and a high-peak-power long-wave infrared (LWIR) laser. These systems can be synchronized for integrated experiments or operated independently, supporting R&D in next-generation accelerator and laser technologies, and exploration of diverse regimes of laser/e-beam/plasma interactions.
The ATF’s pioneering work in developing sub-picosecond, multi-terawatt LWIR laser systems is opening new frontiers in strong-field physics, particularly in low-density regimes of laser-plasma interactions.
In our talk, we will present short-term plans for the development of a 20-TW, 500 fs, 9-μm laser system. This laser is ideally suited for driving plasma bubbles at electron densities of approximately 10¹⁶ cm-3. Such conditions are optimal for investigating precision external electron injection into plasma cavities, a key step toward generating low-emittance electron beams for compact laser wakefield accelerators with wide-ranging scientific and industrial applications.
Additionally, we will explore the prospects of high-repetition-rate lasers with the same pulse format and of LWIR laser systems exceeding 100 TW. Through its ponderomotive effect, such laser could rival the performance of multi-petawatt near-infrared lasers, opening the door to a new class of strong-field experiments and applications.

Speaker: William Li (BNL)

226 The ARCTURUS Laser Laboratory: Advanced Plasma-Based Acceleration and Ultrabright Beam Applications

The ARCTURUS laser laboratory at Heinrich Heine University Düsseldorf (HHU) is undergoing a renewed phase of development, with a sharpened focus on plasma-based electron acceleration. At the heart of the facility is the ARCTURUS system, a 150 TW, multi-pulse laser capable of delivering synchronised high-power and probe pulses into a radiation-shielded experimental area. This infrastructure supports multiple beamlines, offering a flexible development platform for complex multi-stage accelerator setups and advanced diagnostics.
Initial experimental campaigns have successfully demonstrated the generation of energetic electron bunches via laser wakefield acceleration (LWFA), with simultaneous characterisation of associated dosing effects on electronic components - an application directly relevant to space radiation hardness testing, but also for medical treatments of superficial cancers.
Our primary development trajectory centres on a hybrid plasma wakefield acceleration scheme, in which an LWFA-produced electron beam powers a second, beam-driven plasma wakefield accelerator (PWFA) stage. This configuration combines the compactness and synchronisation benefits of LWFA with the enhanced energy output and beam quality prospects of PWFA. We outline the current and future development plans as ARCTURUS is envisaged to serve as a versatile testbed for advancing next-generation plasma accelerator technologies aimed at high-brightness electron-bunch production and secondary radiation sources, including FEL applications

Speaker: Mirela Cerchez

18:30 Discussion & Closing remarks

20:30 Social dinner

Friday 26 September

Plenary Session

227 Wakefield-Based Diagnostics for High-Brightness Beams: From FELs to Plasma Accelerators

High-resolution temporal diagnostics are essential for the development and optimization of next-generation high-brightness accelerators. This talk presents recent advances in wakefield-based diagnostics which enable single-shot, femtosecond-resolved measurements of ultra-short electron bunches. These diagnostics, based on the time-dependent transverse kick induced by beam-driven wakefields in dielectric or corrugated structures, have been successfully demonstrated at X-ray free-electron lasers (XFELs) as compact, cost-effective tools for beam and photon diagnostics. We will highlight their current use at SwissFEL, design and implementation strategies, and discuss ongoing efforts to adapt and deploy them in plasma-based accelerators, where robustness, synchronization, and compactness are essential.

Speaker: Dr Paolo Craievich (Paul Scherrer Institut)

228 Efficient high energy and high-repetition-rate proton acceleration from cryogenic hydrogen foil targets

Laser plasma-based ion accelerators have not yet reached their full potential in producing high radiation doses at high particle energies, mainly due to the lack of a suitable high-repetition-rate targets that also provide adequate control of the plasma conditions. Cryogenic solid gas jet targets are being developed to fill this gap, as they combine many favourable properties for studying advanced laser ion acceleration regimes, such as low solid density, single ion species composition and ease of probing in experiments, with repetition-rated operation capability by being self-replenishing and debris-free.

In a recent experiment, a new foil-like geometry of this cryogenic hydrogen jet target is implemented to accelerate proton bunches at 1 Hz repetition rate. Using the Draco PW laser at intrinsic contrast and significantly reduced laser energy, we report stable, continuous acceleration of ion beams over thousands of consecutive shots. Despite the low laser energy of only 1.6 J, we observe maximum proton energies of up to 50 MeV, indicating a very high acceleration efficiency. This combination of tens of MeV proton energies with very modest laser parameters marks a significant step forward towards developing laser driven ion sources for scientific and industrial applications.

Speaker: Stefan Assenbaum (Helmholtz-Zentrum Dresden-Rossendorf)

10:40 Coffee Break

Plenary Session

229 Simulations of the plasma injector for PETRA IV

DESY is pursuing an ambitious laser-plasma injector option for its future flagship high-energy synchrotron light source PETRA IV. Operating at 6 GeV the PETRA IV Plasma Injector will deliver low emittance electron bunches to support all foreseen operation modes. This talk will cover start-to-end simulations of the LPA injector, injection efficiency and charge accumulation in the storage ring, and implications for its commissioning.

Speaker: Sergey Antipov

230 Advancing PWFA and PWFA-FEL research in China, including FEL Lasing

Overview of the major efforts on PWFA/LWFA from two national accelerator lab in China ( IHEP in Beijing, and SARI in Shanghai), including test facilities construction and latest experimental progress on PWFA driven XFEL, including XFEL lasing.

Speaker: Wei lu

12:30 Lunch Break

16:00 Coffee Break

Plenary Session

Awards Session

231 Closing Remaks

20:30 Dinner

Saturday 27 September

EuroNNAc4 Yearly Network Meeting