A Novel Bimodal Radio-frequency Cavity with Independent Tuning and Effective Higher-Order Mode Damping for Advanced Synchrotron Light Sources

Abstract: Double radio-frequency (RF) systems, comprising both fundamental and harmonic cavities, are essential in advanced synchrotron light sources for lengthening beam bunches, thereby increasing the Touschek lifetime and reducing intrabeam scattering. RF cavities must incorporate effective higher-order mode (HOM) damping to mitigate coupled bunch instabilities (CBI). Additionally, a compact design is crucial for fitting within the limited straight sections of storage rings. This paper presents a novel coaxial bimodal cavity that simultaneously delivers fundamental and harmonic voltages, allowing independent operation of both modes and effective HOM damping. It offers a more compact and efficient alternative to conventional separate cavities. A prototype cavity design was developed, featuring resonant frequencies of 166.6 MHz for the fundamental mode and 499.8 MHz for the third harmonic mode. Simulation results indicate the successful implementation of a bimodal RF cavity, featuring independent frequency tuning, separate RF drives, and effective HOM damping. This work offers a compact and efficient solution for implementing double-frequency RF systems in advanced synchrotron light sources.