Field-dependent surface resistance for superconducting niobium accelerating cavities -- condensed overview of weak superconducting defect model

Abstract

Small (compared to coherence length) weak superconducting defects when located at the surface, combined with the proximity and percolation effects, are claimed responsible for various observations with superconducting rf accelerating cavities with non-constant Q-value, such as "Q-slope" and "Q-drop", the role of temperature, the result of "nitrogen doping" and its relation to the free path, and the influence of the static external magnetic field. The Ginzburg-Landau equations are used to confirm the results.