Improvements to power couplers for the LEP2 superconducting cavities

Abstract

Power couplers for the 352 MHz LEP2 superconducting RF cavities have been plagued by vacuum and electron outbursts which are attributed to multipacting. Processing of these couplers has been a lengthy operation which was often needed again after high power running even if only for a relatively short time. We report here on recent progress made in improved production methods of coupler parts and special treatment of surfaces, as well as practical tests and simulations of geometrical coupler modifications.