Use of the titanium solid state gettering process for the improvement of the performance of superconducting r.f. cavities

It is well known that the low-temperature thermal conductivity of niobium is mainly influenced by the interstitial impurity content of oxygen, nitrogen, hydrogen and carbon. Solid state gettering by materials with a higher affinity to gaseous impurities at elevated temperatures tends to improve the thermal properties of the material. In this paper, the use of titanium as a getter material is described and the effects of the treatment at different temperatures and for varying durations of time on the thermal conductivity of niobium are presented. Improvements of the thermal conductivity at 4.2 K by a factor of 15 corresponding to a value of 160 W m−1 K−1 have been obtained. Measurements on single-cell and multi-cell niobium r.f. cavities at 1500 MHz before and after treatment with titanium are reported. These measurements clearly show an improved performance of these cavities. Residual Q values as high as 1.7 × 1011 and accelerating gradients of Eacc = 11.9 MV m−1 have been measured.