Laser wakefield acceleration with high-power, few-cycle mid-IR lasers

The study of laser wakefield electron acceleration (LWFA) using mid-IR laser drivers is a promising path for future laser driven electron accelerators, when compared to traditional near-IR laser drivers operating at 0.8-1 mu m central wavelength (lambda(laser)), as the necessary vector potential (a(0)) for electron injection can be achieved with smaller laser powers due to the linear dependence on lambda(laser). In this work, we perform 2D PIC simulations on LWFA using few-cycle, high power (5-15 TW) laser systems with lambda(laser) ranging from 0.88 to 10 mu m. Such fewcycle systems are currently under development, aiming at Gas High Harmonics Generation applications, where the favorable lambda(2)(laser) scaling extends the range of the XUV photon energies. We keep a(0) and n(e)/n(cr) (n(e) being the plasma density and n(cr) the critical density for each lambda(laser)) as common denominators in our simulations, allowing for comparisons between drivers with different lambda(laser), with respect to the accelerated electron beam energy, charge and conversion efficiency. While the electron energies are mainly dominated by the plasma dynamics, the laser to electron beam energy conversion efficiency shows significant enhancement with longer wavelength laser drivers. (c) 2018 Elsevier B.V. All rights reserved

Development of laser wakefield accelerators

This thesis investigates theoretically and experimentally the wakefield generation, elec- tron acceleration and x-ray emission in laser driven plasma wakefield acceleration. In preparation for a multi-stage laser accelerator with multiple laser, one of the Astra-Gemini laser pulses at 100 TW was used to reflect off a plasma mirror, a 125 μm Kapton foil. Its reflectivity of up to 70% and beam quality was measured. The beam was then self-guide it through a gas cell in preparation for a staged plasma wakefield accel- erator. These were one of the first measurements at such intensities of 4 × 1017 W cm−2 where the beam was injected into a gas cell. To test the usability of this beam to drive an accelerator stage, the guiding efficiency was measured and compared to particle-in- cell simulation. The simulations modelled the propagation of multi-Gaussian low beam quality laser beams at densities 0.25−0.75 × 1018 cm−3. Self-focusing of imperfect laser beams below the critical power is reported and simulation show potential 100s MeV en- ergy increase and a strong argument for beam quality optimisation is made by showing that the potential energy could be increased even further close to 1 GeV. The same Astra-Gemini laser at 150 TW was used to accelerate a bunch of elec- trons in a single gas cell and to optimise betatron radiation. The unique properties of the betatron radiation including a high peak photon flux of 7.5 ± 2.6 × 108 ph mrad−2 and a synchrotron spectrum with critical energy of 14.6 ± 1.3 keV was used in imaging industrial samples. The obtained data was post-processed to remove source based imaging artefacts such as bremsstrahlung hits obscuring the sample. The samples included a topography XCT sample for performance validation, a pouch cell battery and composite cylinder with a kink band failure. The results took advantage of phase- contrast enhancement show-casing its advantage compared to conventional XCT ma- chines. Finally, a machine learning algorithm, based on Bayesian optimisation, was im- plemented on the 5TW Astra laser to optimise electron and x-ray properties with 1Hz repetition rate. This work prepared the diagnostics and extracted the physical quantities used for the Gaussian process regression. It was used to investigate the optimisation process itself, the correlation of parameters for the enhancement of x- ray brightness with ionisation injection, based on N2 doped He-gas. A brilliance of 4.1 ± 1.0 × 1020 ph s−1 mm−2 mrad−2 0.1%BW−1 with a critical energy of 2.7 ± 0.3 keV can be reported at such low power as of 5.6 ± 0.2 TW. Furthermore, the reported energy of the electrons also exceeds similar laser power experiments.Open Acces

Laser wakefield acceleration with high-power, few-cycle mid-IR lasers

International audienceThe study of laser wakefield electron acceleration (LWFA) using mid-IR laser drivers is a promising path for future laser driven electron accelerators, when compared to traditional near-IR laser drivers operating at 0.8–1 μ m central wavelength ( λlaser ), as the necessary vector potential ( a0 ) for electron injection can be achieved with smaller laser powers due to the linear dependence on λlaser . In this work, we perform 2D PIC simulations on LWFA using few-cycle, high power (5–15 TW) laser systems with λlaser ranging from 0.88 to 10 μ m. Such few-cycle systems are currently under development, aiming at Gas High Harmonics Generation applications, where the favorable λlaser2 scaling extends the range of the XUV photon energies. We keep a0 and ne∕ncr ( ne being the plasma density and ncr the critical density for each λlaser ) as common denominators in our simulations, allowing for comparisons between drivers with different λlaser , with respect to the accelerated electron beam energy, charge and conversion efficiency. While the electron energies are mainly dominated by the plasma dynamics, the laser to electron beam energy conversion efficiency shows significant enhancement with longer wavelength laser drivers

Investigation of advanced electron bunch generation and diagnostics in the BOND laboratory at DESY

Laser driven plasma wakefield accelerators have been explored as a potential compact, reproducible source of relativistic electron bunches, utilising an electric field of many GV/m. Control over injection of electrons into the wakefield is of crucial importance in producing stable, mono-energetic electron bunches. Density tailoring of the target, to control the acceleration process, can also be used to improve the quality of the bunch. By using gas jets to provide tailored targets it is possible to provide good access for plasma diagnostics while also producing sharp density gradients for density down-ramp injection. OpenFOAM hydrodynamic simulations were used to investigate the possibility of producing tailored density targets in a supersonic gas jet. Particle-in-cell simulations of the resulting density profiles modelled the effect of the tailored density on the properties of the accelerated electron bunch. Here, we present the simulation results together with preliminary experimental measurements of electron and x-ray properties from LPWA experiments using gas jet targets and a 25 TW, 25 fs Ti:Sa laser system at DESY

FLASHForward - Beam-driven plasma wakefield acceleration at DESY

FLASHForward - Future-Oriented Wakefield-Accelerator Research and Development at FLASH - is a beam-driven plasma wakefield acceleration facility, currently under construction at DESY (Hamburg, Germany), aiming at the stable generation of electron beams exceeding 1 GeV with small energy spread and emittance

Future-oriented wakefield-accelerator research and development at FLASH

FLASHForward is a beam-driven plasma wakefield acceleration facility,currently under construction at DESY (Hamburg, Germany),aiming at the stable generation of electron beams of several \si{\GeV} with small energy spread and emittance.High-quality 1 GeV-class electron beams from the free-electron laser FLASH will act as the wake driver.The setup will allow studies on external injection as well as on various internal injection techniques, such as density-downramp or ionisation injection.With a triangular-shaped drive beam electron energies of up to 5 GeV from a few centimeters of plasma can be anticipated.Particle-In-Cell simulations are used to assess the feasibility of each technique and to predict properties of the accelerated electron bunches.In this contribution the physics case and the current status of FLASHForward will be reviewed.Concepts of the main components - the extraction beamline from the FLASH linac, the target area, the plasma cell and the post-plasma beam transport and diagnostics - will be described

FLASHForward - A Future-Oriented Wakefield-Accelerator Research and Development Facility at FLASH

FLASHForward is a beam-driven plasma wakefield acceleration facility, currently under construction at DESY (Hamburg, Germany), aiming at the stable generation of electron beams of several GeV with small energy spread and emittance. High-quality 1 GeV-class electron beams from the free-electron laser FLASH will act as the wake driver. The setup will allow studies of external injection as well as density-downramp injection. With a triangular-shaped driver beam electron energies of up to 5 GeV from a few centimeters of plasma can be anticipated. Particle-In-Cell simulations are used to assess the feasibility of each technique and to predict properties of the accelerated electron bunches. In this contribution the current status of FLASHForward, along with recent experimental developments and upcoming scientific plans, will be reviewed

Plasma Wakefield Accelerated Beams for Demonstration of FEL Gain at FLASHForward

FLASHForward is the Future-ORiented Wakefield Accelerator Research and Development project at the DESY free-electron laser (FEL) facility FLASH. It aims to produce high-quality, GeV-energy electron beams over a plasma cell of a few centimeters. The plasma is created by means of a 25 TW Ti:Sapphire laser system. The plasma wakefield will be driven by high-current-density electron beams extracted from the FLASH accelerator. The project focuses on the advancement of plasma-based particle acceleration technology through the exploration of both external and internal witness-beam injection schemes. Multiple conventional and cutting-edge diagnostic tools, suitable for diagnosis of short electron beams, are under development. The design of the post-plasma beamline sections will be finalized based on the result of these aforementioned diagnostics. In this paper, the status of the project, as well as the progress towards achieving its overarching goal of demonstrating FEL gain via plasma wakefield acceleration, is discussed