On the role of electrons in RF breakdown

Measurements on two types of S-band single-cell cavities are reported. In these investigations our interest has been directed toward questions concerning the location and mechanisms of magnetic field breakdown in these cavities. The results show that in TM modes the surface electric fields are an important factor in the initiation of rf breakdown. Among the mechanisms for rf breakdown are: localized heating initiated by multipacting electrons, deterioration of the superconducting properties through the impact of electrons, and inherent inhomogeneities in the surface. In order to reduce the electron loading and subsequent field limitation, careful treatments have been applied to the surface. In doing this fields of 81 mT in an electron free mode and 40 mT and 25 MV/m in TM modes were attained in one type of cavity. In the other type cavity 67 mT and 38 MV/m have been attained.