Theoretical and experimental studies of plasma generation. Tailoring plasmas for wakefield accelerators

Plasma targets required for wakefield acceleration rely on establishing specific electron density distributions in longitudinal and sometimes transverse direction to allow for control over the quality of accelerated electron bunches. The complex fragmentation dynamics of molecular gases in strong electric fields can have a crucial impact on target as well as injection properties in plasma wakefield acceleration. The importance of dissociative fragmentation during ionisation will be discussed in this contribution on the example of hydrogen. Especially in complex scenarios, in which multiple gas-species can be involved, the strength of the plasma generating source may be adjusted to accommodate for the species-specific ionisation thresholds to e.g. generate strong gradient down ramps. To predict the theoretical electron density distribution across the target, we compute the ionisation behaviour based on rate equations and ADK theory in strong electric fields. Here, the fragmentation dynamics governed by various dissociation and ionisation pathways play a crucial role in generating specific profiles. Results from these methods are benchmarked experimentally employing a multi-TW short-pulse laser. The developed understanding of the underlying processes of plasma generation allows for tailoring the electron density distribution by manipulating the focusing geometry and thus spatial laser-intensity evolution

FLASHForward X-2: Beam quality preservation in a plasma booster

Staging of plasma-wakefield accelerators is essential to utilise them in particle physics or other applications requiring high energy beams.Quality preservation in external beam injection is one of the key missing milestones towards this goal.This and other topics related to the plasma booster will be studied at FLASHForward, a unique beam-driven plasma wakefield acceleration facility currently under construction at DESY (Hamburg, Germany),in the frame of the FLASHForward X-2 experiment.High-quality 1 GeV-class electron beams with $\mu m$-emittances from the free-electron laser FLASH will be utilised to generate driver-witness pairsby using a mask in a dispersive section.Alternatively, it is possible to generate two independent bunches directly in the photocathode electron-gun by using a double-pulse laser.In this contribution, the physics case and the current status of the FLASHForward X-2 experiment will be reviewed.The experimental installation will be described, with a focus on the electron beam line.Electron beam dynamics and Particle-in-Cell simulations will be presente

FLASHForward X-2: Towards beam quality preservation in a plasma booster

Beam quality preservation in the external injection scheme is one of the key missing milestones towards staging of plasma-wakefield accelerators, a prerequisite for their utilisation in particle physics or other applications requiring high energy beams. This topic will be studied at FLASHForward, a unique beam-driven plasma wakefield acceleration facility currently under construction at DESY (Hamburg, Germany), in the frame of the FLASHForward X-2 experiment. High-quality 1 GeV-class electron beams from the free-electron laser FLASH with m-emittances, kA-scale currents, and less than 100 fs durations will be utilised to generate driver–witness pairs by using a mask in a dispersive section. In this contribution the physics case and the current status of the FLASHForward X-2 experiment are reviewed. The experimental installation is described, with a focus on the electron beamline. Electron beam dynamics and particle-in-cell simulations are presented

FLASHForward X-1: High-brightness electron beams from a plasma cathode

The beam-driven FLASHForward experiment 1 (X-1) aims at the generation of high-brightness electron bunches for photon science applications in several centimeters of plasma, with the plasma acting both as a cathode and accelerator.The 1 GeV electron-bunch with a peak current of 2.5 kA and a synchronized TW-laser system makes FLASHForward a unique facility[1] to study controlled electron-injection into plasma wakes.With density downramp injection, witness bunches of ~1 kA peak current at emittances well below 1 µm are achievable[2]. The sharp plasma density gradients are produced by means of controlled gas flow[3] or by localized laser ionization transverse to the electron-beam orbit[4]. Precise laser-to-electron-beam synchronization enables controlled injection as e.g. the Trojan Horse scheme[5], which is predicted to support sub-0.1-µm-emittance witness bunches.experimental installation status, planning, and prospects of the FLASHForward X-1 experiments are presented

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