HIGH FIELD Q-SLOPE AND THE BAKING EFFECT

The performance of SRF cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing RF losses (high-field Q-slope), in the absence of field emission, which are often mitigated by a low temperature (100-140 °C, 12-48h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field Q-slope will be presented for cavities that had been heat treated at high temperature in the presence of a small partial pressure of nitrogen. Improvement of the cavity performances have been obtained, while surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments