Change of RF superconductivity parameters induced by heat treatment on niobium cavities

We have investigated the thermal quench evolution of a Niobium cavity, chemically polished, during ultra high vacuum annealings from 100 to 800/spl deg/C. Ten cavities have been tested before heat treatment (HT) and the results show a good agreement with the BCS theory for a diffuse reflection of the conduction electrons on the metal surface. All along the HT we have clearly identified at first the oxygen diffusion from the surface, followed by a cleaning phase of the RF surface and finally, above 800/spl deg/C, the appearance of a new contamination probably due to the furnace residual gases. All this events involve consequences for the quench position through the thermal conductivity.