Observation and cure of severe Q-degradation of superconducting niobium cavities

Abstract

Abstract The observed Q -degradation of a superconducting 3 GHz niobium cavity of the Darmstadt electron linear accelerator S-DALINAC made from high purity material with RRR = 280 is described. It is shown, that the effect is due to hydrogen contamination of the material and can be explained by precipitation of the hydride phase Nb 4 H 3 during cooldown of the cavity. The conditions influencing the amount of precipitation are reported. Heating of the cavity in UHV is one possible way of cure and has been applied successfully to S-DALINAC cavities, as it is shown in this paper.