COMPARISON OF HIGH GRADIENT PERFORMANCE IN VARYING CAVITY GEOMETRIES

Five types of CLIC prototype TW accelerator structures were high-gradient tested at KEK, up to 100 MV/m level. The ramping speed of each processing and the resultant breakdown rate were compared among them. From this comparison, it was found that the ramping speed of the structures with opening ports for HOM damping with magnetic coupling became slow and the resultant breakdown rate became high. This indicates the role of the magnetic field on vacuum breakdowns in copper structure at the region around 100 MV/m. In this paper, we review such processing characteristics and the final high gradient performance of the recent structures. One of the structures showed frequent breakdowns in two particular regions of the structure, indicating a mechanism reflecting not only the geometry or material characteristics but the local features acquired after completion or even during the running.