A mercury ion frequency standard engineering prototype for the NASA deep space network

An engineering prototype linear ion trap frequency standard (LITS-4) using /sup 199/Hg/sup +/ is operational and currently under test for NASA's Deep Space Network (DSN). The DSN requires high stability and reliability with continuous operation. For practical considerations optical pumping and atomic state selection are accomplished with a /sup 202/Hg/sup +/ RF discharge lamp, and the trapped ions are cooled to near room temperature using a helium buffer gas. The standard is closely modeled from earlier research standards LITS-1 and LITS-2 which have demonstrated excellent frequency stability for uninterrupted comparison intervals up to 5 months. During an initial 135 day test in the DSN, LITS-4 operated continuously using a quartz crystal as the local oscillator. Recent signal to noise measurements indicate that a short term stability of /spl sigma//sub y/(/spl tau/)=2.0/spl times/10/sup -14///spl tau//sup 1/2/ can be achieved when operated with a sufficiently stable local oscillator.