A Study of Surface Properties of Superconducting Materials for High Power Microwave Applications.

Abstract : We have investigated electric and magnetic critical field levels for Nb and Nb sub 3 Sn superconductors. Since the maximum power levesl for RF-Superconducting cavities seem to limited by maximum magnetic field capability, most of the work involved studies of the time dependence of flux penetration into Nb sub 3 Sn samples where maximum field limits are unknown. We find that the lower critical field (Hc sub 1) of Nb sub 3 Sn is about 600 gauss at low temperature and 2MHz frequency of applied field, but flux penetration occurs at very low level so that considerably higher field values will not lead to large power loss. Additional interesting effects are associated with Nb sub 3 Sn on Nb substrates which may also lead to increased peak power capability. Keywords: Superconducting RF, Nb3Sn Properties, Critical Fields Cavity loss mechanisms.