Studies of high order modes in asymmetric dual-axis cavity

Abstract

Electron-beam current in superconducting radiofrequency energy recovery linear accelerators (SCRF ERLs) is limited by beam break-up (BBU) instabilities disrupting beam transport and energy recuperation. The instabilities originate from the accumulation of high order modes (HOMs) in the cavity and positive feedback between the beam and HOMs which is especially evident in multi-pass ERLs. Overcoming the beam current limitations due to BBU instabilities is one of the challenges in accelerator science. A dual-axis asymmetric SCRF ERL has been proposed as a possible way to drive a high average current electron beam for next-generation light sources and beam cooling in electron-ion colliders (EICs). In this work, detailed studies on HOMs in the asymmetric dual axis cavity were carried out. The asymmetric field distribution of HOMs (i.e., confinement to one or another axis) has been demonstrated and their excitation from different axes has been studied. The results confirm the numerical predictions and theory developed to describe the asymmetric dual axis cavity.