Design of a Balloon-Shaped Superconducting Single Spoke Resonator

We have investigated designs for a superconducting single spoke resonator with a resonant frequency of 325 MHz and an optimum beta of 0.51. In this paper, we suggest a balloon variant of a spoke cavity having an end-wall structure, which has a distinct advantage from the viewpoint of multipacting suppression. We determined the geometric parameters of the balloon-shaped single spoke resonator through electromagnetic, multipacting, and mechanical simulations. In addition, we discuss the resonant frequency shifts caused by the cavity processing, the power coupling, and the cavity tuning.