A new cesium beam frequency standard performance data

Abstract

IntroductionRecent papers have discussed the principles of a new architecture for cesium beam frequency standards.14 The design goal of the new architecture was to develop an atomic frequency standard that is essentially independent of emironmental effects. Reduction in Ram-pulling due to cesium beam tube design effects was discussed in 1991 la2. With the addition of electronics that address power shift, C-field effects, and Rabi pulling, the new cesium standard shows the expected reduction in overall instabilities due to environmental factors and electronics errors. T h s paper reports actual performance data obtained from a number of standards designed incorporating the new architecture as measured by various measurement laboratories. The data substantiates the design theories, plans, and goals to produce a frequency standard whose sensitivity to emironmental factors is greatly reduced when compared to existing standards. BackgroundPrevious cesium beam frequency standards generally eAbit a substantial response to environmental influences, such as tem rature, pressure, humidity, and external magnetic fieldsr9. An example of this is shown in Figure 1 where data collected Over a year shows that frequency changes measured in several frequency standards maintained in a constant temperature environment, show a strong correlation with measured humidity.Responses to environmental effects have become the major limitation on overall ixmmcy and on long-term stability in atomic frequency standards. This in turn requires metrology laboratories using these devices to design elaborate physical facilities to house the instruments in an attempt to minimize the environmental effects.In addition, warm-up of a cesium frequency standard requires 24-36 hours of stabilization time to achieve final stability. This is a consequence of the typical cesium beam tube design, which conventionally consists of a copper Rrtmsey cavity weighmg more than 1 kg. with a cesium oven at one end operating at 90-13OoC, and a hotwire ionizer at the other end operating in excess of 900OC.Typical thermal response times of a cesium tube are on the order of 6-10 hours, resulting in overall thermal equilibrium times of at least 24 hours.Primarily through an expanded understanding of the underlying causes of the cesium standard's sensitivity to outside enirironmental factors, and extensive computer modeling of the atomic physics and of the electronic architecture, we became convinced that with the proper design, en\ironmental factors cwld be greatly reduced.At the same time this should result in a more useful instrument that requires no special operating environment, and that should be fully operational meeting all specifications w i t h 30 minutes of power-up. The latter condition is especially desirable for field transportable, fast set-up metrology and calibration facilities.Consequently, a multi-facility, multi-year program was undertaken to develop a cesium standard based on the new architecture. Environmental TestingAs a part of the investigation of the...