Effect of the cooldown velocity on the performance of superconducting cavities

The medium temperature heat treatment of superconducting radio frequency cavities is investigated to asses their use in an upgrade of the European X-ray Free ElectronLaser. For the medium temperature heat treatment, which alters the cavity’s surface, the question is, which influences on the performance of cavities do exist. The objectiveis, the investigation into the effects of the cooldown velocity on the cavity performance. To investigate whether this influence exists, an analytical tool, has been developed, toacquire the cooldown velocity. Furthermore, with the use of this tool the investigation of this dependency was started. The conclusion of the analysis is that the quality factor andresidual resistance are depended on the cooldown velocity. The accelerating gradient and quench limits of the cavities seem to be unaffected. The strength of this degradation of thecavities quality factor is observed to be lower than 15%. This could allow the use of these cavities even if this degradation is unavoidable during the cooldown of the cryomodulesat the European XFEL.