Characterization of surface defects in niobium microwave cavities

Superconducting microwave cavities usually break down at localized regions of enhanced losses. Several such regions have been located during low temperature cavity measurements using a temperature mapping system. The regions are then isolated by cutting the cavities and analyzed under a SEM to determine their size and composition. The breakdown field for such defects is calculated using a mesh program and compared with experiment. The composition of defects gives clues to the origin and suggestions for elimination of defects.