Keckert, S.; Kleindienst, R.; Knobloch, J.; Kugeler, O.; Tikhonov, D.; Ackermann, W.; De Gersem, H.; Wenskat, M.; Jiang, X.; Sezgin, Ö.; Vogel, M.: Mitigation of Parasitic Losses in the Quadrupole Resonator Enabling Direct Measurements of Low Residual Resistances of SRF Samples. In: Frank Zimmermann ... [Ed.] : IPAC2022 : Proceedings of the 13th International Particle Accelerator Conference, organized by the Synchrotron Light Research Institute (SLRI) in Nakhon Ratchasima, Thailand and hosted at the IMPACT Exhibition and Convention Center in Bangkok, Thailand, 12–17 June 2022Geneva: JACoW, 2022. - ISBN 978-3-95450-227-1, p. TUPOTK005/1-4
https://accelconf.web.cern.ch/ipac2022/papers/tupotk005.pdf
Open Accesn Version
Abstract:
The quadrupole resonator (QPR) is a dedicated sample-test cavity for the RF characterization of superconducting samples in a wide temperature, RF field and frequency range. Its main purpose are high resolution measurements of the surface resistance with direct access to the residual resistance thanks to the low frequency of the first operating quadrupole mode. Besides the wellknown high resolution of the QPR, a bias of measurement data towards higher values has been observed, especially at higher harmonic quadrupole modes. Numerical studies show that this can be explained by parasitic RF losses on the adapter flange used to mount samples into the QPR. Coating several micrometer of niobium on those surfaces of the stainless steel flange that are exposed to the RF fields significantly reduced this bias, enabling a direct measurement of a residual resistance smaller than 5 nΩ at 2 K and 413 MHz.