Investigation of Superconducting Niobium Cavities at S-Band

Abstract

This paper describes the investigation of superconducting Nb cavities at S-band frequencies. The TE ₀₁₁ and TM ₀₁₁ 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 TE ₀₁₁ cavity had a measured Q _o (4.2°K) 324 × 10 ⁶ and a residual Qres ≈ 6.97 × 10 ⁹ , whereas the TM ₀₁₁ cavity had a Q _o (4.2°K) ≈ 89 × 10 ⁶ and a residual ^Q res ≃ 425 × 10 ⁶ . These results correspond to a surface resistance of R(4.2°K)/f ² = 0.29 μΩ/GHz ² . High level measurements were limited at a critical RF field H ^ac _c = 15.5 G in the TM ₀₁₁ mode and H ^ac _c = 290 G in the TE ₀₁₁ mode.