Preliminary Research and Development of the Cesium Tube Accuracy Evaluation System

Abstract

A method has been developed which measures the velocity distribution of the atoms in a beam tube using the Ramsey dual interaction region principle. The method involves pulsing the R F excitation signal at a period related to the atoms' t ime-of-fl ight between the interactioL regions. The pulse method, with its abil i ty to measure velocity distribution enables calculations of cavity phase shift and secondorder Doppler effect. This research has motivated the development of a system, complete unto itself, for determining the accuracy of cesium beam tubes. Design goals for the system are outlined. The system development to date is discussed. Frequency synthesis is accomplished at 5 .00688MHz. This avoids frequency synthesis at X-band and thereby eliminates packaging and weight problems. A novel synthesizer design is used which incorporates a digital frequency lock of the 5.00688MHz VCXO. A resolution of 1. 4 mill ihertz/second is realizable; lock is within 2. 8 X lo-' ' at one second of a 5.0000 MHz reference with potential to better than 1 x IO-'* at one second. This synthesizer and its application to the accuracy evaluation system are discussed. Some results on the evaluationof commercial cesiumbeam tubes are given.