Advances in the NIM Cs fountain clocks

• Main Authors: Fang, Fang, Chen, Weiliang, Liu, Kun, Dai, Shaoyang, Liu, Nianfeng, Han, Lei, Zheng, Fasong, Li, Tianchu
• Format: Conference Proceeding
• Language: English
• Subjects: Atomic fountain clocks; frequency comparison; primary frequency standards
• ISSN: 2327-1949
• DOI: 10.1109/FCS.2019.8856067

Two Cs fountains clocks have been built in NIM. NIM5 fountain clock has been reported to BIPM since 2014. The microwave synthesizer and computer control system of NIM5 had been modified recently. The Type-B uncertainty is 9×10 -16 , limited by the interferometric switch in the microwave chain. The new NIM6 fountain clock has been built and evaluated, the preliminary results are presented in the paper. With an ultra-stable microwave signal generated from an optical comb which locked to an ultra-stable laser, the frequency instability of NIM6 fountain clock reached 5 \times 10^-14/\tau^1/2 at high density. The direct comparison of two fountain clocks has also been done, a relative frequency difference of 4.4 \times 10^{16} was obtained for 20 days averaging time, consistent with the total uncertainties of the two clocks.