Proximity breakdown of hydrides in superconducting niobium cavities

Abstract

Many modern and proposed future particle accelerators rely on superconducting\nradio frequency cavities made of bulk niobium as primary particle accelerating\nstructures. Such cavities suffer from the anomalous field dependence of their\nquality factors Q0. High field degradation - so-called high field Q-slope - is\nyet unexplained even though an empirical cure is known. Here we propose a\nmechanism based on the presence of proximity-coupled niobium hydrides, which\ncan explain this effect. Furthermore, the same mechanism can be present in any\nsurface-sensitive experiments or superconducting devices involving niobium.\n