THERMOMETRIC STUDY OF ELECTRON-EMISSION IN A 1.3 GHZ SUPERCONDUCTING CAVITY

A 768-thermometer temperature mapping system with 40 ms total readout time was used for field emission studies on a single-cell 1.3 GHz niob ium cavity, immersed in superfluid helium. Any significant change in t he excitation function Q(E) of the cavity (quality factor as function of accelerating field) could be associated with a modification in the temperature map. The energy deposition by field-emitted electrons was studied as a function of position on the cavity surface. The removal o f field emitters by high peak power processing (HPP) was clearly visib le on the temperature map. HPP improved the attainable gradient but in several cases reduced the low-field Q of the cavity, probably due to surface contamination by material evaporated from the processed emitte r.