Investigation of Superconducting Niobium Cavities at S-Band

This paper describes the investigation of superconducting Nb cavities at S-band frequencies. The TE011and TM011cavities 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 TE011cavity had a measured Qo(4.2°K) 324 × 106and a residual Qres ≈ 6.97 × 109, whereas the TM011cavity had a Qo(4.2°K) ≈ 89 × 106and a residualQres ≃ 425 × 106. These results correspond to a surface resistance of R(4.2°K)/f2= 0.29 μΩ/GHz2. High level measurements were limited at a critical RF field Hacc= 15.5 G in the TM011mode and Hacc= 290 G in the TE011mode.