Superconducting bar-loaded resonator for electron accelerator application

Superconducting rf structures hitherto used for electron accelerator application have been plagued by multipactoring problems. For storage ring application, where operating frequencies are likely to be restricted to the UHF band (e.g., 500 MHZ), multipactoring may impose even more severe limitations in performance. In the course of searching for an rf structure with more favorable multipacting properties, it was decided to investigate the "ridged easitron". The cavity design is a variation of the crossbar structure. A rectangular ridged waveguide is loaded with a pair of bars at half-wave-length intervals. All the bars are oriented parallel to the beam plane and the ridge runs along the (waveguide) walls that intercept the bars. Rf properties measured in model copper cavities are discussed. Test results are presented on the superconducting performance and multi-pactoring behavior of a 2-cell S-band Niobium cavity operating in the standing wave, π-mode.