Kugeler, O.; Neumann, A.; Voronenko, S.; Anders, W.; Knobloch, J.; Schuster, M.; Frahm, A.; Klauke, S.; Pflückhahn, D.; Rotterdam, S.: Manipulating the Intrinsic Quality Factor by Thermal Cycling and Magnetic Fields. In: Proceedings SRF 2009, 14th International Conference on RF Superconductivity, DBB Forum, Berlin September 20 - 25, 2009Berlin: Helmholtz-Zentrum, 2009 (HZB-Bericht 2), p. 352-354
Abstract:
For CW applications of superconducting cavities, obtaining a high quality factor is an important issue, since the required cryogenic power drops inversely proportional to Q0. Q0 is limited by BCS-losses and static losses, i.e. impurities and trapped magnetic flux. With sufficient magnetic shielding for TESLA type cavities, typical values of 2*1010 are being achieved at 1.8K operating temperature. The flux trapping was monitored by cooling the cavity at different ambient magnetic fields. In another experiment we have observed a significant increase in the Q0 value of up to 50% when subjecting the cavity to an additional cryogenic cooling cycle. Quantitative results are being presented and possible explanations for the effects are being discussed.