Design of a HOM-Damped 166.6 MHz Compact Quarter-Wave beta=1 Superconducting Cavity for High Energy Photon Source

TL;DR

This paper presents the design and development of a compact, HOM-damped 166.6 MHz superconducting cavity with excellent RF and mechanical properties for the High Energy Photon Source, enhancing stability and performance of the accelerator.

Contribution

It introduces a novel HOM-damped superconducting cavity design at 166.6 MHz with a ferrite damper and detailed mechanical and RF optimization for HEPS.

Findings

Successful development of a proof-of-principle cavity

Achievement of low HOM impedance below instability thresholds

Design of a two-cavity string with proper component transitions

Abstract

Superconducting cavities with low RF frequencies and heavy damping of higher order modes (HOM) are desired for the main accelerator of High Energy Photon Source (HEPS), a 6 GeV synchrotron light source promising ultralow emittance currently under construction in Beijing. A compact 166.6 MHz superconducting cavity was proposed adopting a quarter-wave beta=1 geometry. Based on the successful development of a proof-of-principle cavity, a HOM-damped 166.6 MHz compact superconducting cavity was subsequently designed. A ferrite damper was installed on the beam pipe to reduce HOM impedance below the stringent threshold of coupled-bunch instabilities. Being compact, RF field heating on the cavity vacuum seal was carefully examined against quenching the NbTi flange. The cavity was later dressed with a helium vessel and the tuning mechanism was also realized. Excellent RF and mechanical properties were eventually achieved. Finally, the two-cavity string was designed to ensure smooth transitions among components and proper shielding of synchrotron light. This paper presents a complete design of a fully dressed HOM-damped low-frequency beta=1 superconducting cavity for HEPS.