Experimental performance evaluation of prototype single-spoke resonator superconducting RF cavities

Abstract

The RF performance of prototype single-spoke resonator (SSR) superconducting radio-frequency cavities has been systematically evaluated to characterize their accelerating and mechanical properties. Vertical cryogenic tests were performed on SSR1 and SSR2 cavities to measure the intrinsic quality factor as a function of accelerating gradient, as well as to assess Lorentz force detuning (LFD) and helium pressure sensitivity. Both cavity types exhibited high quality factors at low accelerating fields, followed by gradual degradation with increasing field, consistent with typical field-dependent surface resistance behavior. The maximum achievable accelerating gradient of the higher-beta cavity was limited by thermal quenching. Mechanical characterization showed that the SSR2 cavity demonstrates enhanced stability, with reduced sensitivity to helium pressure fluctuations and Lorentz force detuning compared to the SSR1 cavity. These results confirm that both SSR1 and SSR2 cavities satisfy the RF and mechanical performance requirements for superconducting linac applications.