Design, Construction, and Performance of the NRC CsVI Primary Cesium Clocks

Abstract

Three primary cesium clocks with a one-metre microwave interaction length have been constructed at the National Research Council of Canada. Based on a design similar to that of CsV, the 2.1 m NRC primary cesium clock, they have bi-directional beam capability, a resonance line width of about 100 Hz, and embody improvements to the cesium ovens, detectors, and dipole magnetic-state selectors which lead to a lifetime, estimated from cesium consumption, of about 25 years. In operation as secondary clocks from late 1978 until December 1979, and subsequently as primary clocks, they provide an accuracy and stability comparable to those of CsV. Long-term frequency stability is better than 1 × 10^-14, and short-term frequency stability at beam currents normally used for continuous clock operation of about 2.5 to 3 pA is about 1 × 10^-13 for 1000 s averaging time. The limit of error, estimated from two complete accuracy evaluations, one performed in late 1979 and the second early in 1981, is about 1.5 × 10^-13. The frequencies of the three clocks, CsVIA, CsVIB, and CsVIC, remained within 2 × 10^-13 of that of CsV during their first year and a half of operation as primary clocks, and within 5 × 10^-14 during the final part of this period subsequent to a number of improvements made to certain of the electronics systems.