Reliability and Reproducibility of the Cryogenic Sapphire Oscillator Technology

TL;DR

The paper reports on the development, improved stability, and reliable long-term operation of cryogenic sapphire oscillators, demonstrating their suitability for high-precision scientific applications over a decade.

Contribution

It presents advancements in the stability, power efficiency, and reproducibility of cryogenic sapphire oscillators over ten years, enabling their use in critical scientific fields.

Findings

Short-term stability improved by a factor of 3-10

Reproducible frequency stability over multiple units

Unattended operation with maintenance every two years

Abstract

The cryogenic sapphire oscillator (CSO) is a highly specialized machine, which delivers a reference signal exhibiting the lowest frequency fluctuations. For the best units, the Allan deviation (ADEV) is <1e-15 for integration time between 1 and 10,000 s, with a drift <1e-14 in one day.The oscillator is based on a sapphire monocrystal resonating at 10 GHz in a whispering-gallery mode, cooled at 6 K for highest Q-factor and zero thermal coefficient. We report on the progress accomplished implementing eleven CSOs in about 10 years since the first sample delivered to the ESA station in Argentina. Short-term stability is improved by a factor of 3-10, depending on the integration time, and the refrigerator's electric power is reduced to 3 kW. Frequency stability and overall performances are reproducible, with unattended operation between scheduled maintenance every two years. The CSO is suitable to scientific applications requiring extreme frequency stability with reliable long-term operation. For example, the flywheel for primary frequency standards, the ground segment of GNSS, astrometry, VLBI, and radio astronomy stations.