Liter sized ion clock with 10/sup -15/ stability

We have recently completed a breadboard ion-clock physics package based on Hg ions shuttled between a quadrupole and a 16-pole rf trap. With this architecture we have demonstrated short-term stability ~2-3times10-13 at 1 second, averaging to 10-15 at 1 day. This development shows that H-maser quality stabilities can be produced in a small clock package, comparable in size to an ultra-stable quartz oscillator required for holding 1-2times10-13 at 1 second. This performance was obtained in a sealed vacuum configuration where only a getter pump was used to maintain vacuum. We have selected materials for the vacuum tube, ion trap and UV windows that will allow a 450 C tube bake-out to prepare for tube seal-off. This approach to the vacuum follows the methods used in flight vacuum tube electronics, such as flight TWTA's where tube operation lifetime and shelf life of up to 15 years is achieved. We have made a thorough study of residual gas shifts of the ion-clock frequency and a study of alternate noble gasses as a buffer gas within the sealed tube. We find that neon is more suitable than the traditional use of helium, with 2-3 times less pressure induced frequency pulling. Since neon is heavier than helium, negligible diffusion losses will occur over the operation lifetime. We have developed a modular optical system that integrates lens, mirrors, 202Hg lamp and exciter, photomultiplier tube and pulse generation electronics, all into a small package that attaches to the vacuum tube, aligned with its optical ports and ion trap inside. Similarly, the reference magnetic field coil, an inner layer magnetic shield and a 40.5 GHz microwave feed with window have been incorporated into this breadboard