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

TL;DR

This paper investigates how weak superconducting defects at the surface of niobium cavities influence their surface resistance and quality factor behavior, using theoretical modeling to explain phenomena like Q-slope and Q-drop.

Contribution

It introduces a condensed weak superconducting defect model that explains surface resistance variations in niobium cavities through Ginzburg-Landau equations.

Findings

Weak defects cause non-constant Q-value phenomena.

Temperature and nitrogen doping effects are explained by defect interactions.

External magnetic fields influence surface resistance via defect behavior.

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.