High-temperature annealing of superconducting cavities fabricated from high purity niobium

Surface cleaning of superconducting cavities by high-temperature annealing (HTA) under UHV conditions is considered to be an effective means to achieve both high Qo values and high accelerating fields, which are essential for linear collider applications as well as for upgrading of electron accelerators for nuclear physics research. Suppression of defect induced quenching by the use of high purity niobium has brought surface magnetic fields beyond 100 mT within reach. However, field emission loading has become a significant field limitation. Recent dc field emission studies have shown that the number of field emitters can be reduced drastically by HTA above 1100%C. The authors have investigated the influence of HTA on the performance of superconducting S-band single-cell cavities fabricated from niobium of high thermal conductivity, which has been postpurified by solid state gettering. Peak surface magnetic and electric fields up to 97 mT and 59 MV/m respectively, have been achieved