Design of a L-band cavity optimized for Robinson instability in the TTX-II storage ring

Abstract

Tsinghua Thomson Scattering X-ray Source Phase II is a Thomson scattering-based X-ray source currently under development at Accelerator Laboratory in Tsinghua University. The purpose of this paper is to design a L-band cavity for the storage ring and to study the coupled bunch instability induced by the HOMs of the cavity. The growth rates and tune shifts of the coupled bunch instability are calculated with approximation formulas and simulated with particle tracking code. The frequency of HOMs is optimized that the Landau damping can suppress the coupled bunch instability. A prototype cavity is manufactured and cold-tested. The HOM frequencies can be tuned away from beam spectrum, and the CBI instability can be easily suppressed with Landau damping. Without HOM dampers or feedback system, the HOMs can be tuned during design phase such that the CBI instability can be suppressed.