Instabilities in Linear Accelerators

TL;DR

This paper discusses the nature of wakefields induced by charged particle beams in linear accelerators, their effects on beam stability, and potential mitigation techniques, with a focus on cylindrical geometries and resonant modes.

Contribution

It provides a fundamental analysis of wakefields in linear accelerators and explores their impact on beam dynamics, including instabilities and mitigation strategies.

Findings

Wakefields induce both longitudinal and transverse fields affecting beam stability

Analysis of resonant modes in cylindrical geometries

Discussion of mitigation strategies for beam breakup instabilities

Abstract

As a charged particle beam moves through perfectly conducting structures with varying cross-sectional boundaries - such as RF cavities, tapers, bellows, kickers, ... - it induces both longitudinal and transverse electromagnetic fields called wakefields. In this lecture, we explore the fundamental characteristics of wakefields and illustrate key concepts using simple cases in cylindrical geometry, including a perfectly conducting pipe and the resonant modes of an RF cavity. Finally, we examine how wakefields influence beam dynamics in a LINAC, focusing on beam breakup instabilities and potential mitigation strategies.