  Heated metal filaments under electric fields and low pressures of alkali
metal gaseject electrons by thermionic emission as a function of the pressure
of the gas and thetemperature of the filament. To explore this process in a
program to develop large-area alkali metal photocathodes, we have designed and
built a gauge following thestudies of Taylor and Langmuir. We present
proof-of-principle measurements ofthe thermionic emission of a tungsten
filament in cesium vapor. We describe a secondgeneration design that corrects
flaws in the first gauge.
