Temperature mapping results on the high-field Q-slope of 1500 MHz single cell superconducting radiofrequency cavities baked in-situ at 400 C

The heat treatment of a niobium cavity between 100degC - 120degC for 48 hours substantially improves cavity performance, presumably by healing the nature of the oxide- metal interface, although the nature of the healing is not yet understood. The heat treatment at higher temperatures is found to deteriorate the performance. Our tests on 1500 MHz single cell cavities are always equipped with a temperature mapping system [1] consisting of 700 thermometers. The effect of heat treatment at various temperatures has been studied in detail using the temperature mapping system. In this article we report on several interesting findings from studies of a 400degC heat treatment.