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3rd European Advanced Accelerator Concepts Workshop, EAAC 2017, La Biodola, Isola d'Elba, Italy, 24 Sep 2017 - 30 Sep 2017; Nuclear instruments & methods in physics research / A 909, 80 - 83 (2018). doi:10.1016/j.nima.2018.02.063, 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., Published by Elsevier, Amsterdam

This paper introduces a semi-analytic numerical approach (SANA) for the rapid computation of the transverse emittance of beams with finite energy spread in plasma wakefield accelerators in the blowout regime. The SANA method is used to model the beam emittance evolution when injected into and extracted from realistic plasma profiles. Results are compared to particle-in-cell simulations, establishing the accuracy and efficiency of the procedure. In addition, it is demonstrated that the tapering of vacuum-to-plasma and plasma-to-vacuum transitions is a viable method for the mitigation of emittance growth of beams during their injection and extraction from and into plasma cells.

We formulate a new procedure for modelling the transverse dynamics of relativistic electron beams with significant energy spread when injected into plasma-based accelerators operated in the blow-out regime. Quantities of physical interest, such as the emittance, are furnished directly from solution of phase space moment equations formed from the relativistic Vlasov equation. The moment equations are closed by an Ansatz, and solved analytically for prescribed wakefields. The accuracy of the analytic formulas is established by benchmarking against the results of a semi-analytic/numerical procedure which is described within the scope of this work, and results from a simulation with the 3D quasi-static PIC code HiPACE.

We use three-dimensional (3D) simulations with the particle-in-cell (PIC) code OSIRIS to demonstrate the theoretical production of high-quality electron bunches in beam-driven plasma wakefield accelerators (PWFA) by means of field-induced ionization injection. In these simulations, two realistic scenarios for PWFA have been considered: the FLASHForward project at DESY and the FACET experiment at SLAC. These two examples illustrate two different strategies for injection. The first one uses the transverse electric fields of the beam to induce injection, and the second constitutes a new method which utilizes only the wakefields to enable ionization and trapping of high quality electron bunches into beam driven plasma wakes. The produced bunches feature multi-kA peak currents, ~ 1 μ m transverse normalized emittances, uncorrelated energy spreads of ≤ 1 % on a GeV-energy scale, and few femtosecond bunch lengths.

We present simulations of injection of plasma electrons triggered by a negative gradient in the plasma-density profile for beam-driven plasma-wakefield acceleration. Studies show the potential of this trapping technique for the production of narrow-energy bandwidth, femtosecond, high-current electron beams with a small transverse normalised emittance in the hundred nm range. Moreover, the accelerated beams feature strong longitudinal phase-space correlations with sub-percent uncorrelated energy spreads. Tuning of density down-ramp injection is explored by scanning the slope and length of the downward transition. It is found that the mechanism causes particle trapping over a wide experimentally accessible parameter range. All simulations were performed in three spatial dimensions with the particle-in-cell code OSIRIS [1] . The investigated driver-beam properties and the plasma profile resemble expected experimental conditions at the FLASHForward facility at DESY.