High Q sapphire loaded superconducting cavities and application to ultrastable clocks

Several superconducting cavity stabilized oscillator (SCSO) systems with exceptional frequency stability and very low phase noise have been developed during the past decade. Limitations are mainly related to the coefficient of thermal expansion of the cavity, temperature dependence of the surface reactance of the superconductor, and mechanical deformations.Braginsky et al. (1981) have shown that the very low loss tangent of sapphire, the low coefficient of thermal expansion, and the high Young's modulus, makes a sapphire dielectric resonator (SDR) suitable as an extremely stable frequency standard. The present investigation is concerned with a practical configuration for a sapphire loaded superconducting cavity (SLOSC) resonator. The described device should be suitable for use as a high precision secondary frequency standard. Applications for such a standard are to be found in gravitational radiation detection by Doppler tracking of spacecraft and in VLBI radio astronomy. A use in laboratory tests for relativistic timing effects might even be feasible.