CRYO-COOLED SAPPHIRE OSCILLATOR OPERATING ABOVE 35K

摘要

We present preliminary design features for a second generation thennomechanically compensated sapphire resonator. Developed a few years ago, the "77K CSO" resonator showed a quality factor Q = 2 × 10~(6) at an operating temperature of 85K, enabling a frequency stability of δiff < 1×10~(13). The new design promises a frequency stability of parts in 10~(15) with cooling provided by a cryocooler consuming several hundred watts or less. Optimization of the resonator design for a temperature of 40K results in a mechanical tuning rate requirement (MHz/micron) reduced by a factor of 8, allowing for reduced EM fields at the surface of the sapphire and reduced sensitivity to mechanical deformation. This optimized EM design is implemented in a self-assembling mechanical design flint allows easy disassembly for cleaning, together with a first-order cancellation for expected mechanisms of physical creep. The new design is expected to share the very short thermal time constants characteristic of the 10K and 77K CSO resonators, thus allowing effective compensation of rapid temperature fluctuations.