Simulations and measurements of a heavily hom-damped multi-cell SRF cavity

After an initial cavity shape optimization [1] and cryomodule development [2] for an Ampere-class FEL ERL, we have simulated a complete 5-cell high-current (HC) cavity structure with six waveguide (WG) couplers for Higher Order Mode (HOM) damping and fundamental power coupling. MAFIA time-domain wakefield simulations have been used to calculate the cavities broadband HOM impedance spectra. Microwave Studio (MWS) has been used in addition to evaluate the external Q of the fundamental power coupler (FPC) and the R/Qs of the HOMs. A half scale 1497 MHz single-cell model cavity and a 5-cell copper cavity including dummy HOM WG loads were fabricated to bench measure and confirm the design performance. Details of the multi-beam wakefield simulations, the HOM damping measurements and multi-peak data fitting analysis techniques are presented.