Positron Acceleration in Plasma Wakefields

TL;DR

This paper reviews the challenges and progress in accelerating positrons in plasma wakefields, highlighting the inherent charge asymmetry issues and potential strategies to improve beam quality for collider applications.

Contribution

It provides a comprehensive overview of historical and current positron acceleration schemes in plasma wakefields, introduces a new metric for efficiency, and discusses future mitigation strategies.

Findings

Positron acceleration schemes are below collider requirements.

Electron motion causes non-uniform fields degrading beam quality.

Mitigation strategies are discussed for future improvements.

Abstract

Plasma acceleration has emerged as a promising technology for future particle accelerators, particularly linear colliders. Significant progress has been made in recent decades toward high-efficiency and high-quality acceleration of electrons in plasmas. However, this progress does not generalize to acceleration of positrons, as plasmas are inherently charge asymmetric. Here, we present a comprehensive review of historical and current efforts to accelerate positrons using plasma wakefields. Proposed schemes that aim to increase the energy efficiency and beam quality are summarised and quantitatively compared. A dimensionless metric that scales with the luminosity-per-beam power is introduced, indicating that positron-acceleration schemes are currently below the ultimate requirement for colliders. The primary issue is electron motion; the high mobility of plasma electrons compared to plasma ions, which leads to non-uniform accelerating and focusing fields that degrade the beam quality of the positron bunch, particularly for high efficiency acceleration. Finally, we discuss possible mitigation strategies and directions for future research.