Proximity breakdown of hydrides in superconducting niobium cavities

Abstract

Many modern and proposed future particle accelerators rely on superconducting radio frequency cavities made of bulk niobium as primary particle accelerating structures. Such cavities suffer from the anomalous field dependence of their quality factors Q0. High field degradation—so-called ‘high field Q-slope’—is so far unexplained even though an empirical cure is known. Here, we propose a mechanism based on the presence of proximity-coupled niobium hydrides that can explain this effect. Furthermore, the same mechanism can be present in any surface-sensitive experiments or superconducting devices involving niobium.