Development of an Optimized Quadrupole Resonator at HZB

Current superconducting cavities are generally made of solid Niobium. A possibility to reduce cost as well as increase the quality factor and/or accelerating fields is to use thin film coated cavities. Apart from Niobium thin films, other substances such as Magnesium diboride, Niobium nitride and Niobium-tin are promising candidates. Measuring the RF-properties of superconducting thin films, specifically the surface resistance, with a high resolution at frequencies, magnetic field levels and operating temperature as realized in RF cavities, is needed to drive forward this development. Presently, only few setups exist capable of measuring the surface resistance of thin films samples with a resolution in the nano-ohm range at RF frequencies below 3 GHz. A dedicated test stand consisting of a quadrupole resonator is therefore being constructed at the Helmholtz Zentrum Berlin. Starting with the 400 MHz quadrupole resonator developed by CERN, the design was adapted and optimized to 433 MHz (making available the higher harmonic mode at 1.3 GHz for RF characterization of samples in the L-band) using simulation data obtained with CST Microwave Studio. A number of relevant figures of merit have been improved to provide a higher resolution, a lower peak electric field and less sensitivity to microphonics, enabling measurements with high resolution at high magnetic field levels.