CERN, Geneva, Switzerland
MPI-K, Heidelberg, Germany
Cockcroft Institute, Warrington, Cheshire, United Kingdom
The surface resistance of superconducting samples can be derived from the heat dissipation under RF exposure. This requires challenging and sometimes opposing design constraints. The samples shall be small and easily exchangeable. The RF magnetic field on the sample surface shall be large and homogeneous. It must not be limited by the host cavity. A calorimetric technique enables precise measurements and has therefore recently gained much interest. One of the devices exploiting this technique at multiple frequencies is the Quadrupole Resonator. Its measurement capabilities and limitations are discussed and compared with similar devices. Results on bulk niobium and niobium film on copper samples are presented. It is shown how different contributions to the surface resistance depend on temperature, applied RF magnetic field and frequency. Furthermore measurements of the maximum RF magnetic field as a function of temperature and frequency in pulsed and CW operation are presented.
