Intrinsic energy spread and bunch length growth in plasma-based accelerators due to betatron motion

TL;DR

This paper analyzes how betatron motion in plasma-based accelerators causes intrinsic energy spread and bunch length growth, affecting beam quality, and offers theoretical insights and mitigation strategies validated by simulations.

Contribution

It provides an analytical theory describing betatron-induced energy spread and bunch length growth in PBAs, validated with simulations, and offers guidelines for improving beam quality.

Findings

Betatron motion significantly contributes to energy spread.

Theoretical predictions match particle-in-cell simulation results.

Mitigation strategies can improve beam quality in PBAs.

Abstract

Plasma-based accelerators (PBAs), having demonstrated the production of GeV electron beams in only centimetre scales, offer a path towards a new generation of highly compact and cost-effective particle accelerators. However, achieving the required beam quality, particularly on the energy spread for applications such as free-electron lasers, remains a challenge. Here we investigate fundamental sources of energy spread and bunch length in PBAs which arise from the betatron motion of beam electrons. We present an analytical theory, validated against particle-in-cell simulations, which accurately describes these phenomena. Significant impact on the beam quality is predicted for certain configurations, explaining previously observed limitations on the achievable bunch length and energy spread. Guidelines for mitigating these contributions towards high-quality beams are deduced.