The Joint Accelerator Conferences Website (JACoW) is an international collaboration that publishes the proceedings of accelerator conferences held around the world.
TY - UNPB AU - Miyazaki, A. ED - Schaa, Volker RW ED - He, Yuan ED - Li, Lu ED - Zhao, Ning TI - The role of cool down dynamics on the performance on Nb/Cu cavities– HIE-ISOLDE resonator as an example J2 - Proc. of SRF2017, Lanzhou, China, July 17-21, 2017 C1 - Lanzhou, China T2 - International Conference on RF Superconductivity T3 - 18 LA - english AB - The High intensity and Energy upgrade of the ISOLDE facility (HIE-ISOLDE) is operated by superconducting quarter-wave resonators (QWR) made of a thin Nb film sputtered on a Cu substrate (Nb/Cu).The intrinsic quality factor of these cavities strongly depend on the thermal gradient (less than 1K) between top and bottom of the cavity as pointed out by P. Zhang in SRF15. Although the best cavity performance can be achieved by careful cool down, the physics of this phenomenon is not fully understood. In this study, possible hypotheses and experimental efforts are presented. A similar phenomenon has been reported on the elliptical bulk Nb cavities, and its physics was interpreted as flux expulsion efficiency. Since Nb/Cu QWR is insensitive to the flux expulsion, the thermoelectrically induced magnetic field due to Nb/Cu bi-metal structure is supposed to be the most promising hypothesis instead. Some of the model calculations and experiments to measure such a thermoelectric effect are explained. Recent findings showed that thermal gradient does not only affect the residual resistance but also temperature-dependent resistance. A result on a seamless QWR without welding will be also shown. PB - JACoW CP - Geneva, Switzerland ER -