Injection tolerances and self-matching in a quasilinear wakefield accelerator

TL;DR

This paper investigates how injection tolerances and plasma response in a quasilinear wakefield accelerator affect beam quality, revealing broad tolerances for witness bunch radius due to self-matching physics and establishing constraints on initial bunch parameters.

Contribution

It introduces a figure of merit for beam quality in quasilinear wakefield accelerators and analyzes the impact of injection parameters and plasma response on emittance growth.

Findings

Broad tolerances for witness bunch radius due to self-matching

Constraints on initial bunch parameters for optimal beam quality

Development of a figure of merit for high-energy applications

Abstract

Particle acceleration in a quasilinear plasma wake provides access to high acceleration gradients while avoiding self-trapping of the background electrons. However, the plasma response to the externally injected witness bunch leads to a variation of the focussing fields along the bunch length, which can lead to a emittance growth. In order to investigate the impact of this emittance growth on the overall beam quality, we develop a single figure of merit based on a potential high-energy application for the AWAKE experiment at CERN. We show that the development of such a figure of merit naturally gives rise to constraints on both the tunability and stability of the initial witness bunch parameters. It is further shown that the unique physics of the quasilinear wake gives rise to broad tolerances for the witness bunch radius at the injection point, as the plasma wakefields self-match to the witness bunch.