A superconducting hydrogen maser resonator made from electrophoretic YBa/sub 2/Cu/sub 3/O/sub 7- delta /

The construction and test of three loop-gap resonators which are being prepared for the high-temperature superconductor space experiment (HTSSE) are discussed. The loop-gap electrodes are the lossiest parts of such a resonator. In a first step these electrodes, with a surface of 150 cm/sup 2/, were covered with YBCO. The Q values of the resonators at 77 K ranged between 2.3*10/sup 4/ and 3.1*10/sup 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 three to five below the equivalent value of copper. The cavities can be excited in a higher-order mode (HOM) at 4.3 GHz with a field distribution that is still sensitive to the superconducting electrodes. Thus, the experimental requirements for the HTSSE project can be fulfilled.