Cs Fountain Clocks for Commercial Realisations - an Improved and Robust Design.

We report on the design, assembly, testing and delivery of a series of new caesium fountain primary frequency standards built through commercial and scientific collaboration with international users. The new design, based on proven NPL solutions, improves reliability, simplicity of operation and transportability. The complete system consists of a novel physics package, a specially developed optical package and dedicated electronics for system control. We present results showing that despite their simplified and more compact design, the new fountains have state-of-the-art performance in terms of signal-to-noise ratio and robust long-term operation. With a sufficiently low noise local oscillator they are capable of reaching a short-term stability below 3×10-14 (1 s) and have potential accuracy in the low 10-16 range, similar to the best caesium fountains currently in operation. This cost-effective solution could be used to increase the availability of accurate frequency references and timescales and provide redundancy in critical locations.