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

An engineering prototype linear ion trap frequency standard (LITS-4) using ¹⁹⁹Hg⁺ 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 ²⁰²Hg⁺ 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 σ_y(τ)=2.0×10^-14/τ^1/2 can be achieved when operated with a sufficiently stable local oscillator