Title: RF Losses due to incomplete Meissner-Ochsenfeld effect: difference between bulk Nb and Nb/Cu
Author: Enzo Palmieri
Institution: Legnaro National Laboratories of INFN and University of Padua
Abstract: Experimentally it is found that for Nb/Cu Sputtered Resonators, conrary to bulk Niobium Cavities the residual resistance due to magnetic flux trapped into the superconductor is independent of the magnetic induction intensity B at the moment of cooling. Because of the large demagnetization factor of the extended surface of a resonator, an incomplete Meissner-Ochsenfeld effect happens, favouring the trapping into the superconductor of any external fied present during the cooling phase as for instance the earth magnetic field or its unscreened fraction.
For Bulk Nb cavities the trapped vortexes dissipate energy since depinned by radiofrequency, while for Nb sputtered cavities the vortexes are frozen on pinning centers and there is no flow resistance.