QUENCH STUDIES IN LARGE AND FINE GRAIN Nb CAVITIES

Quenches without radiation are sometimes observed at accelerating fields between 25 and 40 MV/m in niobium SRF cavities. The cause for this limitation is not well un- derstood. This work presents results from vertical tests of seven 1.3 GHz single-cell cavities performing above 25 MV/m. Studies were carried out on both fine grain and large grain cavities in ILC and Cornell Reentrant shape ge- ometries. The quenches were located by triangulation us- ing Cornell oscillating superleak transducers and then cav- ities were optically inspected to determine the surface con- ditions of the cavity at the quench location. Optical in- spection images are presented as well as 3D recreations of quench spots generated using a surface mold and a confocal microscope.