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.