Comparisons between 3 fountain clocks at LNE-SYRTE

Comparisons between three Cs fountains are described. All three LNE-SYRTE fountain clocks are now using a cryogenic sapphire oscillator as a starting point to generate the microwave probe signal. As a result, all three fountains have a fractional frequency instability in the 10-14 range at 1 s. All three fountains are also using a recently developed generation of microwave synthesizers allowing to switch the microwave probe signal without introducing detrimental phase transient. Several series of measurements have been made totalizing more than 80 days of simultaneous operation under optimized conditions of a pair of either fountains. Results of these measurements are presented. Finally, modifications of the FO2 fountain has been completed to allow simultaneous operation with Rb and Cs. Operation with Rb leads to a fractional frequency instability of 6.3 × 10-14τ-1/2.

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