Analysis of the Cool Down Related Cavity Performance of the European XFEL Vertical Acceptance Tests

Abstract

For the European X-Ray Free Electron Laser (XFEL) cavity production, the cold radio-frequency (RF) test of the cavities at 2K after delivery from the two vendors was the mandatory acceptance test. It has been previously reported, that the cool down dynamics of a cavity across T$_c$ has a significant influence on the observed intrinsic quality factor Q$_0$, which is a measure of the losses on the inner cavity surface. A total number of 367 cool downs is used to analyze this correlation and we show that such a correlation is not observed during the European XFEL cavity production