DC MAGNETIC HALL PROBE TECHNIQUE FOR CHARACTERIZATION OF THIN FILM AND MULTILAYER SUPERCONDUCTORS FOR ACCELERATING CAVITIES*

The best superconducting RF resonator Nb cavities used in particle accelerators can produce the accelerating gradients up to 45-50 MV/m. Further advances in the SRF accelerator technology demand even higher accelerating gradients and lower RF losses, which could be achieved using superconductors with critical fields higher than that of Nb, or multilayer (S-I-S) structures consisting of alternating thin layers of superconductor(S) and insulator(I) deposited on a bulk Nb. The measurements of the RF breakdown field of thin films and multilayers is an important problem requiring an experimental setup which can emulate the field configuration of SRF cavities on test flat samples. This work reports the development of a simple and efficient technique to measure the magnetic field of full flux penetration, B_p into bulk, thin film and multilayer superconductors.  The experimental setup contains a small superconducting solenoid which can produce a parallel surface magnetic field up to 500 mT and Hall probes to detect penetrated magnetic field across the superconducting sample. This system has been calibrated and used for the measurements on B_p on bulk Pb and Nb, Nb₃Sn thin film and Nb₃Sn/Al₂O₃ multilayer samples.