Accuracy Evaluation of NIM5 Cesium Fountain Clock

Tie NIM5 fountain clock is the second fountain clock built at NIM（National Institute of Metrology,China）,and has been operating stably and sub-continually since 2008.The fountain operates with a simple one-stage optical molasses to collect cold atoms,which reduces the collisional frequency shift dramatically.The fractional frequency uncertainty is estimated to be 2×10-15.The typical frequency instability of 2.5×10-14 is obtained at10 s.Comparisons with other fountain frequency standards worldwide demonstrate agreement within the stated uncertainties.