Proximity breakdown of hydrides in superconducting niobium cavities

TL;DR

This paper proposes that proximity-coupled niobium hydrides cause the high field Q-slope in superconducting niobium cavities, offering a potential explanation for a long-standing unexplained phenomenon affecting particle accelerators.

Contribution

It introduces a novel mechanism involving niobium hydrides to explain the high field Q-slope in superconducting niobium cavities, linking material properties to performance issues.

Findings

Proximity-coupled niobium hydrides can explain the high field Q-slope.

The mechanism may affect other niobium-based superconducting devices.

Hydride presence correlates with surface degradation in 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 yet unexplained even though an empirical cure is known. Here we propose a mechanism based on the presence of proximity-coupled niobium hydrides, which can explain this effect. Furthermore, the same mechanism can be present in any surface-sensitive experiments or superconducting devices involving niobium.