Simulation study of higher-order-mode damping of storage ring cavities

We present studies of a higher-order-mode damping device, which employs a circular waveguide to coaxial transition (CWCT). The waveguide is double-ridged. A properly shaped back cavity at the far end allows broadband coupling to a coaxial window. Configurations of CWCTs with either symmetric or asymmetric ridge depth are both optimized with the HFSS code. HFSS calculations have also been performed to examine CWCT damping effects on a pillbox cavity. The lowest order anti-symmetric modes are shown to be much more effectively damped by the asymmetric CWCT. However, relative merits of the symmetric and asymmetric CWCTs depend on other factors such as the cavity configuration.