John D. Prestage

New Ion Trap for Frequency Standard Applications

We have designed a novel linear ion trap which permits storage of a large number of ions with reduced susceptibility to the second‐order Doppler effect caused by the rf confining fields. This new trap should store about 20 times the number of ions as a conventional rf trap with no corresponding increase in second‐order Doppler shift from the confining field. In addition the sensitivity of this shift to trapping parameters, i.e., rf voltage, rf frequency, and trap size, is greatly reduced.

Atomic Clocks and Oscillators for Deep-Space Navigation and Radio Science

This paper describes new oscillator and atomic clock technologies that, when combined, create a master oscillator for use in deep-space navigation and science measurements. This atomic clock promises to execute spacecraft navigation using a one-way downlink only method, saving many millions of dollars per year. We will describe the complementary technology developments by the Jet Propulsion Laboratory toward a space-ready mercury atomic-ion clock and by the Applied Physics Laboratory, Johns Hopkins University, in reducing the size, mass, and operating power of its quartz, ultrastable oscillator.

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 NASAs 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.

Simple analytic potentials for linear ion traps

We have developed a simple analytical model for the electric and ponderomotive (trapping) potentials in linear ion traps. We have used this model to calculate the required voltage drive to our mercury trap, and the result compares well with our experiments. The model gives a detailed picture of the geometric shape of the trapping potential and allows an accurate calculation of the well depth. The simplicity of the model allowed us to investigate related, more exotic trap designs which may have advantages in light‐collection efficiency.

Higher pole linear traps for atomic clock applications

We investigate experimentally and theoretically higher pole linear ion traps for frequency standard use. We have built a 12-pole trap and have successfully loaded ions into it from a linear quadrupole trap. By solving the Boltzmann equation describing large ion clouds where space charge interactions are important we show that clock frequency changes due to ion number fluctuations are much smaller in ion clocks based multipole traps than comparable clocks based on quadrupole linear traps.

Long term stability of Hg/sup +/ trapped ion frequency standards

The standards report the development of a second /sup 199/Hg/sup +/ linear ion trap (LIT) based frequency standard to provide a capability for measuring stability beyond all existing frequency standards. Increased signal using a second light collection system together with a previously demonstrated atomic line Q /spl ap/ 2 /spl times/ 10/sup 12/ yields a performance better than /spl sigma//sub y/ (/spl tau/ = 7 /spl times/ 10/sup -14///spl tau//sup 1/2/). Sensitivity to the leading perturbations are measured to identify regulation requirements to obtain a stability of 10/sup -16/.<<ETX>>

Ultra-stable Hg+

Abstract We report the development of a fieldable frequency standard based on 199Hg+ ions confined in a hybrid r.f./dc linear ion trap. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the r.f. confining fields. A 160 mHz wide atomic resonance line for the 40·5 GHz clock transition is used to steer the output of a 5 MHz crystal oscillator to obtain a stability of 2 × 10−15 for 24 000 s averaging times. For longer averaging intervals, measurements are limited by instabilities in available hydrogen maser frequency standards. Measurements with 37 mHz linewidth for the Hg+ clock transition demonstrate that the inherent stability for this frequency standard is at least as good as 1 × 10−15.

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/spl times/10/sup -16//day.

SpaceTime Mission: Clock Test of Relativityat Four Solar Radii

SpaceTime is a mission concept developed to test the Equivalence Principle. The mission is based on a clock experiment that will search for a violation of the Equivalence Principle through the observation of a variation of the fine structure constant, α. A spatio-temporal variation of α is expected in some string theories aimed at unifying gravity with other forces in nature. SpaceTime uses a special tri- clock instrument on a spacecraft which approaches the sun to within four solar radii. The instrument consists of three trapped ion clocks based on mercury, cadmium, and ytterbium ions, in the same environment. This configuration allows for a differential measurement of the frequency of the clocks and the cancellation of perturbations common to the three. The observation of any frequency drift between each of the clocks, as the tri-clock instrument approaches the sun, signals the existence of a scalar partner to the tensor gravity. Some relevant details of the mission design are discussed in the paper.

Linear ion trap for second-order Doppler shift reduction in frequency standard applications

The authors have designed and are presently testing a novel linear ion trap that permits storage of a large number of ions with reduced susceptibility to the second-order Doppler effect caused by the RF confining fields. This new trap should store about 20 times the number of ions as a conventional RF trap with no corresponding increase in second-order Doppler shift from the confining field. In addition, the sensitivity of this shift to trapping parameters, i.e., RF voltage, RF frequency, and trap size, is greatly reduced. The authors have succeeded in trapping mercury ions and xenon ions in the presence of helium buffer gas. Trap times as long as 2* 10/sup 3/ s have been measured. >