A rapidly tunable superconducting resonator

Superconducting, high Q rf resonators which are continuously tunable over at least a factor of three in frequency have been designed for operation in the range of a few hundred megahertz. Prototypes of these resonators have been fabricated of OFHC copper and electroplated with lead. Rf decay times of 18 msec at 240 MHz have been achieved in these resonators; the rf losses which dominate the Q are found to take place in a thin dielectric layer on the superconducting lead surface. This loss mechanism decreases the decay time about a factor of 10 from the decay time expected from the measured rf resistance of the Pb surfaces. Preliminary work on rapid (less than 1 msec full range) tuning of high Q resonators, which may lead to a new technique of electromechanical energy conversion, is reported.