A SUPERCONDUCTING HYDROGEN MASER RESONATOR MADE FROM ELECTROPHORETIC YBA2CU3O7-DELTA

A compact loop-gap hydrogen maser resonator has been constructed by electrophoretic deposition of YBa2Cu3O7-delta (YBCO) onto silver. The resonator is tuned to operate at the hyperfine transition frequency of hydrogen (1.42 GHz). This device is considered to be the first step towards a superconducting cavity for a compact hydrogen maser to be used in the Global Positioning System (GPS). The required miniaturization of the resonator reduces its Q value. This effect can be compensated for by the low surface resistance of YBCO at 77 K. Large and curved polycrystalline YBCO layers can be obtained by the electrophoretic deposition technique. In this contribution we report on the construction and the test of three loop-gap resonators which are prepared for the High Temperature Superconductor Space Experiment (HTSSE). The loop-gap electrodes are the lossiest parts of such a resonator. In a first step these electrodes with a surface of 150 cm2 were covered with YBCO. The Q values of the resonators at 77 K ranged between 2.3 10(4) and 3.1 10(4) and exceed the minimum requirement for a later maser application. They correspond to a surface resistance between 0.7 and 1.4 m-OMEGA which is a factor of 3 to 5 below the equivalent value of copper. The cavities can be excited in a higher order mode (HOM) at 4.3 GHz whose field distribution is still sensitive to the superconducting electrodes. Thus the experimental requirements for the HTSSE project can be fulfilled.