Investigation of Superconducting Niobium Cavities at S-Band

This paper describes the investigation of superconducting Nb cavities at S-band frequencies. The TE011 and TM011 cavities were machined by Varian Associates from solid billets of electron-beam-melted niobium and chemically polished to remove all work-damaged material. At low power levels, the TE011 cavity had a measured Qo(4.2??K) ?? 324 ?? 106 and a residual Qres ?? 6.97 ?? 109, whereas the TM011 cavity had a Qo(4.2??K) ?? 89 ?? 106 and a residual Qres ?? 425 ?? 106 . These results correspond to a surface resistance of R(4.2??K)/f2 = 0.29 ????/GHz2. High level measurements were limited at a critical RF field Hacc = 15.5 G in the TM011 mode and Hacc = 290 G in the TE011 mode.