HZB, Berlin, Germany
The systematic research on superconducting thin films requires dedicated testing equipment. The Quadrupole Resonator (QPR) is a specialized tool to characterize the superconducting properties of circular samples. A calorimetric measurement of the RF surface losses allows the surface resistance to be measured with sub nano-ohm resolution. This measurement can be performed over a wide temperature and magnetic field range, at frequencies of 433, 866 and 1300 MHz. The system at Helmholtz-Zentrum Berlin (HZB) is based on a resonator built at CERN and has been optimized to lower peak electric fields and an improved resolution. An alternative calorimetry chamber has been designed in order to provide flat samples for coating and to ease changing of samples. Furthermore it enables exchangeability of samples between the QPRs at HZB and CERN. With this poster the design and first measurements of the new calorimetry chamber is presented.
HZB, Berlin, Germany
Recent cavity results with niobium have demonstrated the necessity of a good understanding of both the BCS and residual resistance. For a complete picture, and comparison with theory, it is essential that one can measure the RF properties as a function of applied magnetic field, temperature, frequency and ambient magnetic field. Standard cavity measurements are limited in their ability to change all parameters freely and in a controlled manner. On the other hand, most sample measurement setups operate at fairly high frequency, where the surface resistance is always BCS dominated. The quadrupole resonator, originally developed at CERN, is ideally suited for RF characterization of samples at frequencies of 400 and 1300 MHz, between which many of today’s SRF cavities operate. We report on a modified version of the QPR with improved RF figures of merit for high-field operation. Experimental challenges in the commissioning run and alternate designs towards a simpler sample change are shown alongside measurement results of a large grain niobium sample.
