The role of near-surface dislocations in the high magnetic field performance ofsuperconducting niobium cavities

Abstract

Quantitative analysis of the near-surface dislocation content performed using electronbackscattered diffraction for samples cut from niobium cavities limited by the ‘high fieldQ-slope’ effect show a high dislocation content, as well as a pronouncedchange in the near-surface dislocation content caused by the100–120 °C annealing when such annealing has a healing effect on the high fieldQ-slope. We propose a model for the sharp degradation of the cavityQ athigh field for niobium cavities based on dislocation-assisted magnetic flux entry at surface magneticfields lower than those expected for ideal niobium. It is proposed that the elimination of the high fieldQ-slopeby 100–120 °C annealing is caused by vacancy-assisted dislocation climb in the near-surface region.