Suppression of bunch destruction under resonant excitation of the plasma wakefield

Abstract

Plasma wakefield acceleration offers a compact and efficient method for generating high-brightness relativistic electron beams. Applications such as free-electron lasers and particle colliders demand high-quality bunches with stable, predictable profiles. However, previous studies have shown that a resonant sequence of electron bunches, where the spacing matches the plasma wavelength is prone to longitudinal instability, leading to progressive bunch destruction by gradual defocusing. In this work, we analyse the underlying mechanism of this instability, which arises from a phase shift between the bunch and the wake radial focusing force $F_r$ during the system’s evolution. We propose and validate, both numerically and analytically, a method to suppress the instability by shifting all bunches relative to the first into regions of the wakefield where $F_r$ is focusing and longitudinal derivative ${\partial }_z{F}_r\ne 0$ is maximized, ensuring stable propagation.