Influence of hydrogen on superconducting niobium cavities

Abstract

The influence of the solute hydrogen on rf properties of superconducting niobium cavities is investigated experimentally. Chemical polishing and too much electropolishing decrease the energy gap and rf breakdown fields. High-temperature vacuum firing in a UHV furnace decrease the residual loss and recovers the energy gap. Annealed cavities are, however, easily degraded not only by a short period of exposure to hydrogen, but also by a long term storage in air. Chemically polished cavities also show a great enhancement of the penetration depth λ0. These effects can be ascribed to hydrogen which is picked up from etchants or from atmosphere.