Operation of NIM5 fountain with 1.5x10-15 uncertainty and design of new NIM6 in NIM

8th Symposium on Frequency Standards and Metrology 2015

Fang, F.^1 ; Liu, N.^1 ; Liu, K.^1 ; Chen, W.^1 ; Suo, R.^1 ; Li, Tianchu^1

Time and Frequency Division, National Institute of Metrology, Beijing, China^1

关键词: Background signals;    Cesium fountain primary frequency standard;    Cryogenic sapphire oscillators;    Density distributions;    Microwave synthesizers;    Optical molasses;    Vacuum system;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/723/1/012009/pdf
DOI  :  10.1088/1742-6596/723/1/012009

来源: IOP

【 摘 要 】

The cesium fountain primary frequency standard NIM5 started to operate since 2008 and started to report to BIPM since 2014. The major constrains of NIM5 is a relatively large background signal at the detection and microwave leakages due to the Ramsey cavity. A new fountain clock NIM6 is under construction. Besides some improvements on the vacuum system, a new Ramsey cavity and a microwave synthesizer are made to reduce the Type B uncertainty. Another feature of NIM6 is collecting atoms from a MOT loading optical molasses to get more atoms with a more uniform density distribution. With a new frequency synthesizer based on cryogenic sapphire oscillator (CSO), NIM6 is aiming to reach the quantum projection noise, thus leading to a reduced Type A uncertainty compared with NIM5.