Toward a plasma-based accelerator at high beam energy with high beam charge and high beam quality

Abstract

From plasma-wakefield acceleration as a physics experiment toward a plasma-based accelerator as a user facility, the beam physics issues remaining to be solved are still numerous. Providing beams with high energy, charge, and quality simultaneously, not only within the plasma but also at the user doorstep itself, is the main concern. Despite its tremendous efficiency in particle acceleration, the wakefield displays a complex 3D profile which, associated to the beam-loading field induced by the accelerated beam itself, makes the acceleration of high charge to high energy often incompatible with high beam quality. Beam extraction from the plasma without quality degradation for a transfer either to the next plasma stage or to the user application is another difficulty to consider. This article presents the substantial studies carried out and the different innovative methods employed for tackling all these different issues. Efforts focused on achieving the challenging beam parameters targeted by the EuPRAXIA accelerator facility project. The lessons learned at the end of these in-depth simulations and optimizations are highlighted. The sensitivity to different error sources is also estimated to point out the critical components of such an accelerator. Finally, the needs in terms of laser and plasma parameters are provided.

Electron Sources for Accelerators

“…A single RF pulse accelerates hundreds of bunches spaced by a few nanoseconds. Collider designs based on plasma wakefield acceleration techniques plan for a very different pulse format, with equidistant pulses at tens of kHz repetition rates [29]. An electron source for such accelerators would therefore need to be able to provide high brightness electron beams capable of being efficiently squeezed into the micrometersize accelerating region, at high repetition rates.…”

Predicting the transverse emittance of space charge dominated beams using the phase advance scan technique and a fully connected neural network

“…Beam brightness is important for many accelerator applications, such as ultrafast electron diffraction [1], free electron lasers [2] and the operation of new compact accelerator concepts in general (e.g. [3][4][5][6]). A common definition of brightness is [7]…”

Electron Beam Transport in Plasma-Accelerator-Driven Free-Electron Lasers in the Presence of Coherent Synchrotron Radiation and Microbunching Instability

“…Nevertheless, in spite of lower bunch charges, the beam charge density in plasma accelerators can still be very high. Moreover, schemes for the reduction of the SES at the entrance of the undulator are being pursued to achieve more efficient lasing [26][27][28][29][30]. Since the MBI gain is proportional to the bunch peak current and inversely proportional to the transverse beam sizes, and since Landau damping becomes less effective for low SES values relative to the beam energy, it is worth paying attention to the growth of the instability in the switchyard line downstream of a plasma accelerator, which is the motivation for the present study.…”

“…The MBI in the switchyard is, thus, analyzed as a function of the momentum compaction or longitudinal transport matrix term (R 56 ) of the line, while for the initial uncorrelated energy spread in the range of 10-300 keV, beam energies of 1 and 5 GeV are considered. While the root-mean-square (RMS) value of the total energy spread of the plasma-accelerated beam could be 1%, which is commonly the case when non-linear correlations in the beam's longitudinal phase space appear, the slice energy spread (SES) (i.e., the energy spread evaluated along a short portion of the bunch, for example the slice duration < fs) could be much smaller [30]. The case of SES~100 keV at 1 GeV beam energy reflects state-of-the art manipulation of the electron beam before entering the undulator.…”

“…Lower SES values of tens of keV are most likely out of the present scope of plasma accelerators. The aim of this paper is two-fold: to point out potential showstoppers in lasing due to the MBI in cases of super-cold beams, as specified in [30]; to mimic a stronger source of instability at the entrance of the switchyard due to causes such as pre-bunched beams (either in terms of the energy or density, or both). Finally, the highest energy of 5 GeV is used to identify any scaling of the instability strength and of the optics prescriptions used to counteract it with beam energy.…”