The USNO Rubidium Fountain

We present initial evaluations of our rubidium atomic fountain - the first of six that are designed for continuous operation and for inclusion into the USNO timescale. We have demonstrated short-term performance in weak-gradient, MOT-loaded operation of 1.3 times 10^-13/tau^frac12. We have made a comparison between our rubidium fountain (NRF1) and cesium fountain (NCF), demonstrating a relative stability characterized by white-frequency noise down to an Allan deviation of 1.5 times 10^-15. Assuming that each fountain exhibits the same noise type, the data are consistent with an Allan deviation for our rubidium fountain of 7 times 10^-16 at 11 hours. Further upgrades to our cesium fountain should enable more precise comparisons