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 ${Q}_{\text{ext}}$ values agreed well with calculations.
Highlights
A deflecting/crabbing cavity uses the first dipole mode for operation, which has important applications in particle accelerators
Time−domain result Frequency−domain result dipole beam the range of R=30 to R=10, and the wake impedance dependence on the angle φ needs to be investigated in the asymmetric cavity
Asymmetric cavity geometry has been adopted in a number of superconducting deflecting cavity designs
Summary
A deflecting/crabbing cavity uses the first dipole mode for operation, which has important applications in particle accelerators. Wakefield characterization is a critical issue given that most superconducting deflecting cavities operate in high-current accelerator facilities. The TM-type deflecting cavity operates at TM110y-like mode, which has been implemented at the KEKB B-factory [8,9]. In a TM-type deflecting cavity, the squashed cell could either separate the polarizations of the dipole modes and make the damping task easier [17,18], or it could enhance the figures of merit of the deflecting mode and achieve a higher deflecting gradient [19]. Symmetry breaking increases the difficulty in characterizing wakefields, which is very crucial given that most SC deflecting cavities operate in high-beam-current accelerator facilities. The wake impedance cannot be directly calculated in terms of cavity mode parameters in many cases.
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