On electrical breakdown in superconducting accelerating cavities

Recent results on electron loading in superconducting cavities are presented and are compared with observations in DC field emission. It is shown that electron loading is the main obstacle to achieving accelerating fields higher than 10 MV/m. Multipactor electron loading, which may limit the accelerating fields, can be processed away, but processing times might be long. There exists experimental evidence that accelerating fields of 10 MV/m can be reproducibly obtained in storage-ring accelerating multicell structures. New diagnostic tools developed for superconducting RF cavities have contributed to the knowledge of electron emission in broad areas. Experimental results in DC and RF field emission are very similar. A simple statistical model, with an exponential increase of the number of emitters toward lower β values, may explain the frequency dependence of field-emission electron loading observed so far