University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
DESY, Hamburg, Germany
University of Hamburg, Hamburg, Germany
Pushing the limits of the accelerating field or quality factor of SRF cavities beyond pure Nb requires the implementation of specific inner surface treatments, which are yet to be studied and optimized. One of the fundamental challenges in exploring alternative materials is that only samples or cavity cuts can be fully characterized from a material point of view. On the other hand, complete cavities allow for the SRF characterization of the inner surface, while samples can usually only be analyzed using DC methods. To address this problem, a test resonator for samples, called "Quadrupole Resonator", was designed and operated at CERN and later at HZB. It allows for a full RF characterization of samples at frequencies of 0.42 GHz, 0.86 GHz, and 1.3 GHz, within a temperature range of 2-20 K and at magnetic fields up to 120 mT. This work presents the design process, which incorporated improvements motivated by mechanical and RF studies and experience, and the results from both warm and cold commissioning are discussed. More important, the results for the RF tests of a Nb sample after undergoing a series of heat treatments and an outlook of the further usage of the QPR is presented.
