High sapphire loaded superconducting cavities and application to ultrastable clocks

This paper describes the microwave properties of a sapphire loaded super conducting cavity resonator. We report measurements of energy confinement, evanescent field scale lengths, and radiation losses. We report high quality factors, in excess of 10⁹at cryogenic temperatures, for a resonator based on a sapphire element mounted inside a superconducting cavity. Resonators of this type have potentially valuable applications as ultrahigh stability oscillators, high Q filters and as low phase noise frequency sources.