Acceleration of electron bunches in a plasma channel implies a matched beam spot size at the micron level: this property, together with generally low values for slice emittance and energy spread (and large peak current), boosts the rho pierce parameter value up to order of 10^-2 or even more. Upon leaving plasma channel, due to prompt electrons divergence, rho is reduced quickly so that...
Laser-plasma accelerators are promising candidates to drive a next generation of compact FELs. The LUX plasma accelerator, developed and operated in a collaboration of Hamburg University and DESY, recently demonstrated the generation of spontaneous undulator radiation from a laser-plasma electron beam. A future upgrade of the beamline, currently under commissioning, will include the cryogenic...
A proposal for building a Free Electron Laser, EuPRAXIA@SPARC_LAB, at the Laboratori Nazionali di Frascati, is at present under consideration [1]. This FEL facility will exploit plasma acceleration to produce ultra-bright photon pulses with durations of few femtoseconds down to a wavelength between 2 and 4 nm, in the so called โwater windowโ.
The photon beamline we designed will deliver the...
Here we report on beam quality optimization in a stable and robust nanocoulomb-class laser wakefield accelerator. The self-truncated ionization injection scheme enables precise control over the amount of injected charges up to 0.5 nC (FWHM) at a quasi-monoenergetic peak. Stable operation of the accelerator is achieved, enabling us to study key parameters in statistical data-sets. Employing the...
Proof-of-concept experiments in AWAKE Run 1 have demonstrated electron acceleration in a proton-driven wakefield$^1$. A high momentum proton beam can drive a wakefield over long distances and overcome some limitations of lepton-driven schemes, which are susceptible to energy depletion. AWAKE Run 2 aims to preserve the beam quality of an injected electron beam throughout acceleration, and...
In an initially uniform plasma, the lifetime of a weakly nonlinear plasma wave excited by a short driver is limited by the ion dynamics. The wakefield contains a slowly varying radial component, which results in a perturbation of the ion density profile and consequent destruction of the plasma wave. We suggest a novel method of quantitative characterization of the plasma wave lifetime in...
We propose a method to generate isolated relativistic terahertz (THz) pulses using a high-power laser irradiating a mirco-plasma-waveguide (MPW). When the laser pulse enters the MPW, high charge electron bunches are produced and accelerated to 100 MeV by the transverse magnetic modes. A substantial part of the electron energy is transferred to THz emission through coherent diffraction...
The interaction of both linearly and circularly polarized laser pulses with high-Z solid targets is investigated through PIC simulations, using the SMILEI particle-in-cell code that features a thoroughly benchmarked relativistic collisional module. Even though circular polarization (CP) mitigates collisionless hot-electron acceleration processes compared with linear polarization, inverse...
AWAKE (the Advanced WAKefield Experiment at CERN) aimed to demonstrate the first controllable self-modulation of a long ultrarelativistic proton beam in plasma and acceleration of electrons in the wakefield from the resulting train of microbunches. The experiment fully completed these tasks in 2017 and 2018. Three main diagnostics: OTR, CTR screens and imaging stations measured longitudinal...
Spontaneous undulator radiation emission, after the COXINEL line using a Laser Plasma acceleration (LPA) source, has been observed. The line enables to manipulate the electron beam phase space such as emittance, dispersion and energy spread along a 10 m long transport. The large divergence is handled at a very early stage to mitigate the chromatic emittance, using high gradient permanent...
At FLASHForward, the plasma wakefield is driven by a high-current-density electron beams extracted from the FLASH superconducting radiofrequency (RF) accelerator. Therefore, FLASHForward is in a unique position for studying and providing insight for the design study of next-generation light sources and high energy physics facilities such as EuPRAXIA, which aim to provide industrial beam...
The ARES (Accelerator Research experiment at SINBAD) Linac at SINBAD (Short and INnovative Bunches and Accelerators at DESY) facility at DESY aims to produce high brightness ultrashort electron bunches (sub fs to few fs) at around 100 MeV, suitable for injection into novel accelerators e.g. dielectric Laser acceleration (DLA) and Laser Driven Wakefield acceleration (LWFA). The external...
The proton driven plasma wakefield acceleration experiment AWAKE at CERN demonstrated basic electron capturing and acceleration using a rather long electron bunch spreading out over several plasma wavelengths. For the second phase of the experiment, the aim is to inject a short electron bunch with appropriate emittance and charge to achieve full capture and emittance preservation of the...
We present the work on development of the millimeter wavelength accelerating structure. It consists of cylindrical cavities with the operating frequency of 96 GHz. The structure will be excited by the picosecond electron beam from the photocathode RF gun. In order to define exact both structure and exciting beam parameters, analytical estimations and simulations of the structure excitation...
We investigate possibilities that dielectric accelerator structures, excited by fs lasers, offer for X-ray free electron lasers. The present scheme uses a dielectric laser accelerator to modulate an electron beam to create a pulse train of short (100 as) X-ray pulses in the undulators of SwissFEL. The implementation of such a scheme would be enabled by using the experimental chamber installed...
THz radiation is the most important portion of the electromagnetic spectrum in terms of multi disciplinary use in basic science and technology. Beyond the numerous applications, a great interest is its potential for future, compact linear accelerators. Conventional high brightness radio-frequency accelerating structures operate with 30-50 MV/m gradients; terahertz-driven accelerating...
A central challenge for next generation accelerator facilities (Linear Colliders and FELs) is to operate at high wall plug efficiency. However, the fraction of energy that can be transfer from the accelerating fields to the charge particle bunch is limited by beam loading. This is true for advanced acceleration schemes, Structure Wakefield Acceleration (SWFA), Plasma Wakefield Acceleration...
Laser-plasma accelerators [1] may become a compact, affordable and powerful alternative for delivering relativistic electron beams of relevance for medical treatment and imaging [2] to fundamental researches related to high-energy physics [3]. However, a main obstacle for this approach to fulfill its promise, for some of the applications, is the beam quality with large divergence and emittance...
Plasma-wakefield acceleration is a promising technique for future accelerators in that it can deliver significantly higher (factor of ~100-1000) accelerating fields compared to conventional RF accelerators, and also be used to generate beams of ultralow (โฒ0.1 mm mrad) normalized emittance. However, many challenges remain to be overcome, one of which is the hose instability, where a witness...
Laser wakefield accelerators can provide a very compact source of electron beams, which combined with intense laser pulses can result in a versatile X-ray source. Of particular interest for medical imaging are X-rays in the 50-100 keV energy range, high enough energy to penetrate through human-sized objects. Highly collimated beams with such energies form the basis of an all optical Thomson...
High intensity ultra-short laser pulses interacting with thin solid targets are able to produce energetic proton and ion beams by means of extremely large accelerating fields. The process starts with the emission of fast electrons that, escaping the target, set an electrostatic potential, responsible for the subsequent acceleration of heavier particles. The characterization of such electrons...
The transverse gradient undulator (TGU) scheme is a viable option to compensate for the challenging properties of the LWFA electron beam, in terms of beam divergence and energy spread, to enable FELs amplification. At Karlsruhe Institute of Technology (KIT, Germany), a 40-period superconducting TGU has been designed and built. In this contribution, we report on the first test operation of...
A hybrid laser plasma accelerator (HLPA) has been developed to produce low divergence ($<$ 100 mrad), high charge ($>$ 60 nC) electron beams with energies greater than 150 MeV. The HLPA, driven by ps, kJ class lasers, uses an interplay between self-modulated laser wakefield acceleration and direct laser acceleration to trap and accelerate electrons through up to 10 mm of plasma. The resulting...
Controlled guiding of laser pulses at relativistic intensities in plasmas over distances exceeding the diffraction length is a crucial requirement of a Laser Plasma Accelerator Stage (LPAS) for achieving high quality electron beams. A new hybrid guiding scheme is proposed, in which first a laser pre-pulse (I ~ 1016 W/cm2) guided through a dielectric capillary ionizes and...
Operation of modern particle accelerators require high brightness beam and sensitive diagnostic system in order to monitories and characterize the beam during the acceleration and transport.
A turn-key high level software has been designed to fully characterise the 6D beam phase space and the trajectory in order to help operator during commissioning with an easily scalable suite for any high...
Ultra high-gradient accelerating structures are needed for the next generation of compact light sources. In the framework of the Compact Light XLS project, we are studying a high harmonic traveling-wave accelerating structure operating at a frequency of 35.982 GHz, in order to linearize the longitudinal space phase. In this paper, we propose a new analytical approach for the estimation of the...
Recent high RF power experiments show that hard structures, fabricated without high-temperature processes, achieve a better high gradient performance in terms of accelerating gradients. Two three-cell standing-wave accelerating structures, designed to operate in the pi-mode at 11.424 GHz, have been successfully built and cold tested. In order to guarantee a vacuum envelope and mechanically...
The design, installation and operation of AWAKE (run1) infrastructure and equipment took place from 2013 until 2019. This was the first PWA facility of this large scale, which influences many choices regarding infrastructure and design. Lessons learnt from designing, installing and running the AWAKE facility's infrastructure are shown, and are extrapolated to show how they could be implemented...
The two-photon (linear) Breit-Wheeler mechanism is the simplest process through which light can be converted into matter. Despite its simplicity only the multi-photon (non-linear) process has yet been measured definitively. The linear process remains elusive as the production threshold of $2 m_e c^2 \approx 1\,\mathrm{MeV}$ is comparatively high for two photons and requires two bright sources...
The plasma source during AWAKE run 1 consists of a 10 meter long rubidium vapor source ionized by a laser pulse from a 4 TW titanium:sapphire system focused to a mm spot size. Because the plasma column geometry can have an effect on the formation of the proton driven plasma wakefields when the plasma skin depth approaches the size of the plasma column, the geometry needs to be understood. ...
The bandwidth of Thomson sources are determined, amongst others, by the bandwidth- and the length of the laser pulse and the energy spread of the electrons. Here we show that if the electron bunch's energy spread is correlated, that the emitted radiation's bandwidth can be decreased by chirping the laser pulse. The instantaneous laser frequency is given by
\begin{equation}
\frac{\partial...
Advanced accelerator concepts usually address linear acceleration schemes. Storage rings, however, are often superior to linear machines regarding repetition rate, stability and efficiency. The radiative energy loss per turn in an electron storage ring is compensated by radiofrequency resonators with a wavelength of the order of 1 meter, which corresponds to the spacing between consecutive...
Accelerators based on LWFA are of great interest for a new generation of compact machines. Choosing external injection of the probe beam in LWFA has the advantage that a well-controlled and fully characterized beam can be injected. The matching of electron bunches into an accelerating wakefield makes high demands on the electron beam quality. The electron beam size must be extremely small to...
With the help of 3D numerical simulations, we demonstrate the possibility to accelerate a high number of electrons (tens of nC) to tens or even hundreds of MeVs using relativistic laser pulses ($\sim 10^{22}$ W/cm${}^2$) grazingly incident on solid targets. It is shown that in this regime, the electrons are accelerated mostly efficiently at some distance from the target, and the key factor in...
Guiding high-intensity laser pulses over long distances through low density plasma ($\sim 1 \times 10^{17} \ \rm{cm^{-3}}$) is one of the key challenges to create laser plasma accelerators for high energy physics and industrial applications. We recently demonstrated that low density channels suitable for such guiding could be generated by the hydrodynamic expansion of optical-field-ionised...
The continuous development of high power lasers (I > 10$^{22}$ W/cm$^{2}$) allow to accelerate multi-species charged particles to higher and higher energies. For this new interaction regime nowadays it become crucial to develop diagnostic systems for comprehensive characterisation of plasma processes and ion acceleration phenomena for the range of energies not explored before.
The main goal...
Intensities of the Purcell-Smith radiation from DLA-compatible grating and pillar structures are calculated numerically using the finite-element method. Geometric parameters are scanned in search of resonant radiation enhancement [1].
[1] Yi Yang et al, Maximal spontaneous photon emission and energy loss from free electrons, Nature Physics 14, 894โ899 (2018)
Resonant wakefield excitation in two-beam electron-positron collider by a long train of relativistic electron bunches is difficult because it is difficult to support homogeneous and stationary plasma in experiment. In [1-5] the mechanism has been found of resonant plasma wakefield excitation by a nonresonant train of short electron bunches. The frequency synchronization results by defocusing...
Dielectric laser driven particle acceleration (DLA) is one of the candidates for novel high-gradient technologies to reduce the footprint of large scale particle acceleration facilities. On the other hand these devices can be used to interact with the particle beams of state-of-the-art photon science machines, especially with FELs, to manipulate the longitudinal phase space in a compact and...
Charged particle acceleration using solid-state nanostructures is attracting new attention in recent years as a method of achieving ultra-high acceleration gradients, in principle of up to ~1 TV/m [1]. The use of carbon nanotubes (CNT) has the potential to enable limitations of using natural crystals, e.g. in channeling aperture and thermo-mechanical robustness, to be overcome. In this work,...
The AWAKE project aims to accelerate electrons through proton driven plasma wakefields. The transverse extend of the wakefields is given by the plasma density and is of the order of one millimeter. With external injection, the exact position of the electron bunch in the wakefields determines the acceleration energy and the captured charge. The pointing jitter of the electron beam is of the...
The Relativistic Electron Gun for Atomic Exploration (REGAE) is a small accelerator located at DESY in Hamburg. The machine was designed and built to provide ultra-short electron bunches on the order of 10 fs, used as probe pulses for time-resolved electron diffraction experiments. Recently, REGAE has been upgraded and connected to the ANGUS high-power laser system. With this new...
The AWAKE experiment at CERN [1] recently demonstrated the world's first acceleration of electrons in a proton-driven plasma wakefield accelerator [2]. Such accelerators show great promise for a new generation of linear e-p colliders using GV/m accelerating fields. Effectively driving a wakefield in AWAKE requires 100-fold self-modulation of the 12 cm Super Proton Synchrotron (SPS) proton beam...
In the AWAKE experiment, a train of micro-bunches resonantly drives high-gradient wakefields in which electrons have been accelerated up to 2 GeV. The micro-bunches result from the 400 GeV CERN SPS proton beam self-modulating in a pre-formed plasma through a self-modulation (SM) process. Initial transverse wakefields focus and defocus the bunch at the scale of the plasma wavelength. When not...
Precise control over the longitudinal phase space (LPS) of electron bunches in accelerators can be of interest for example for bunch-compression, where in the ideal case a completely linear LPS is needed to reach maximum compression. We present a compact and completely passive way to alter the LPS of a given electron bunch in a way that arbitrary, pre-defined shapes can be achieved. The...
In modern experiments on plasma wakefield acceleration, relativistic electron bunches (or laser pulses) excite plasma wakes with energy density comparable to the rest energy density of plasma electrons. Breaking of such wake in a radially bounded plasma is followed by its energy redistribution between hot electrons, electric fields and radial ion motion and leads to plasma column expansion via...
Controlling the injection and trapping of electrons into plasma wakefields is key to improving the beam quality and reproducibility of accelerated beams. Injecting electrons into a narrow $(ฯ_r โช ฮป_p)$ transverse region of the wakefield is fundamental to achieving low beam emittance. Brief $(T_{inj} โช L_{acc} / c)$ injection into a short $(ฯ_z โช ฮป_p)$ longitudinal region yields low energy...
The recent installation of a double plasma mirror in the experimental area of the Lund High-Power Laser facility now allows the study of laser-plasma interactions with stable, pre-pulse and pedestal-free laser pulses. Such a regime of high contrast (10e-8 at 1 ps before the pulse peak) ensures that targets with nm-scale thicknesses can be irradiated without forming a pre-plasma at their...
In this talk, I will discuss a diagnostic method for the electron plasma density and temperature based on the exploitation of wideband THz pulses. I will present the model accompanying the diagnostic method showing its utility to characterize the plasma density and temperature profile along a symmetry axis. This diagnostic is particularly interesting for plasma-acceleration schemes or...
During its first experimental run (2016-2018), AWAKE [1] reached two important milestones: the demonstration of the seeded self-modulation of the 400 GeV/c proton bunch delivered by the CERN Super Proton Synchrotron [2,3], and the acceleration of externally injected electrons from 19 MeV to 2 GeV [4]. The goal of the second run (starting in 2021) is to accelerate an electron bunch with a...
The Advanced Wakefield Experiment AWAKE develops the first plasma wakefield accelerator with a high-energy proton bunch as driver [1]. The 400 GeV bunch from CERN SPS propagates through a 10 m long rubidium plasma, ionized by a 4 TW laser pulse co-propagating with the proton bunch. The relativistic ionization front seeds a self-modulation process. The seeded self-modulation (SSM) transforms...
To overcome dephasing and pulse depletion while maintaining a high average accelerating gradient, staging multiple 10 GeV level Laser Wakefield Accelerators has been proposed. To minimise the total length of a staged accelerator laser beams must be introduced at an angle to the beamline. A convenient solution to reflect the intense laser pulse on to the beamline is to use a thin, moveable tape...
Laser wakefield accelerators are highly tuneable sources of radiation with a correspondingly varied number of potential applications, including ultrafast imaging, high energy physics and radiation therapy. The Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) is a facility designed to allow proof of concept investigations towards the realisation of next generation laser...
Beam driven wakefield acceleration in plasmas is one of the most promising candidates for novel, compact accelerators. Several aspects of this acceleration scheme can be optimised by transverse and longitudinal shaping of the bunch that drives the wake and of the bunch that is accelerated in the wake. The ratio between acceleration of the witness and deceleration of the driver, the transformer...
In a variety of electron accelerator based light sources relativistic electron bunches propagate through an undulator and emit intense narrow band radiation. Here, we propose new types of short period undulators, which are based on the alternating electromagnetic field pattern of THz-driven surface plasmon polaritons in sub-wavelength structures. Analytic undulator models are derived and...
Additive manufacturing techniques such as stereolithography can simplify prototyping of novel accelerator components.ย
A precise knowledge of the permittivity of the material is essential to the design of dielectric accelerating structures.
We present here measurements of the permittivity of commercially available polymers, as well as tests for vacuum compatibility.
Dielectric laser acceleration (DLA) is one of the advanced concepts for more compact accelerators. DLA gratings have apertures within the range of optical wavelengths. Wakefields limit the beam intensities of relativistic electrons required for possible applications. Particle tracking is needed to study the intensity limitations due to nonlinear laser fields in combination with wakefields. For...
Using newly available compact laser technology [1] one can produce 100 PW-class laser pulses with a single-cycle duration on the femtosecond timescale. With a fs intense laser one can produce a coherent X-ray pulse that is also compressed, well into the hard X-ray regime. Prof. T.Tajima suggested [2, 3] utilizing these coherent X-rays to drive the acceleration of particles. Such X-rays are...
Plasma-based waveguides are currently employed for laser wakefield acceleration to extend the focal region
of laser beams. Indeed, a parabolic transverse plasma density profile can be formed in a dielectric capillary as a thermal consequence of a gas discharge.
In this work, we report on a new ray tracing model, based on the Zemax software, able to simulate
the envelope of ...
