On Contact Ionization in Thermionic Converters

Instances in which the work function M does not exceed the ionization potential I, and the cesium pressure is too low to permit envocation of volume ionization as a result of substantial temperature rise in plasma due to Joule losses, are discussed. Methods of circumventing these difficulties by postulating the presence of regions of sufficiently high work function on the otherwise low workfunction emitter surface or by generalizing the concept of contact ionization by using the Saha-Langmuir theory are compared. The latter approach is shown to be more desirable. (L.N.N.)