Superconducting Niobium Cavity Measurements at SLAC

The program of measurements at SLAC on superconducting niobium cavities is described. Results for TE and TM mode X-band cavities are presented. An RF magnetic breakdown field of 960 gauss and Q values greater than 1011 were measured for an electron beam welded TE011 mode cavity at 10.5 GHz. The best result for a TM mode cavity was a Q of 1.4 × 109 and a breakdown field of 360 gauss, limited probably by the quality of the electron beam weld. Data on the effect of exposure to air and to nitrogen are presented.