Higher Order Modes Damping Analysis for the SPX Deflecting Cavity Cyromodule

A single-cell superconducting deflecting cavity operating at 2.815 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source (APS) upgrade. A cryomodule of 4 such cavities will be needed to produce the required 2-MV deflecting voltage. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. The damping of the LOM/HOM below the beampipe cutoff has been analyzed in the single cavity geometry and shown to meet the design requirements. The HOM above the beampipe cutoff in the 4-cavity cyromodule, however, may result in cross coupling which may affect the HOM damping and potentially be trapped between the cavities which could produce RF heating to the beamline bellows. We have evaluated the HOM damping in the 4-cavity cryomodule using the parallel finite element EM code suite ACE3P developed at SLAC. We will present the results of the cryomodule analysis in this paper