Stability measurements of a JPL multi-pole mercury trapped ion frequency standard at the USNO

Two 12-pole mercury trapped ion frequency standards were recently developed and compared at JPL. In July 2002 one of these standards was installed at the United States Naval Observatory (USNO) where it has since been continuously operating. The standard is configured with a hydrogen maser as the local oscillator and is continuously compared to approximately 10 other cavity-tuned hydrogen masers, 50 cesium standards, and the USNO master clock UTC(USNO). Stability measurements between the trapped ion standard and several USNO formulated clock ensembles over the entire 9 month operating period to date show very stable operation with a worst case differential frequency drift between any 60 day averaging period measured to be <2×10^-16/day.