Design of a Cesium Vapour Pressure Gauge Based on Electronic Thermionic Emission

We describe the design and underlying principles of a tungsten-filament gauge for the partial vapor pressure of cesium. Operation is based on the temperature dependence of electronic thermionic emission from a tungsten filament with a thermally equilibrated partial coverage of cesium, which increases with vapor pressure and decreases with filament temperature. Due to the reduction of the work function of thermionic emission, the current from the filament is a measure of the coverage. By fitting the curve of emission versus filament temperature to a theoretical model, the cesium vapor pressure is obtained. We explain the physical principles behind the device, and describe the construction, operation, and calibration of a prototype built to test the performance of this concept. We document the construction, operation, and calibration of the gauge and analyse the differences between the predicted and experimentally measured data. Based on the analysis, we elaborate on how to design this gauge to obtain better data on desired thermionic emission.