Wakefield characterization in an asymmetric superconducting deflecting cavity

Abstract

Nonaxially symmetric superconducting deflecting cavities are under development for a variety of purposes, but breaking the symmetry adds more complexity to wakefield characterization. This paper considers the influence of cavity asymmetry on the wakefield. Based on the TM-type deflecting cavity, we investigated how the polarized cell and the damper coupling affect the wake impedances. An improved method to characterize the wake impedances in asymmetric cavities is proposed by combining the time-domain and frequency-domain calculations. Compared to conventional methods, the new method decomposes the wake potential in terms of beam moments, which provides more information about the wakefield, and significantly reduces the simulation time with better accuracy. Using this method, we analyzed the wakefield of the deflecting cavity and the wakefield coupling between the cavities for the advanced photon source. Bench measurements were performed on a fabricated copper prototype; the measured mode field distributions and the Q_{ext} values agreed well with calculations.