Space-Charge Effects in the Field-Assisted Thermionic Emission from Nonuniform Cathodes

Abstract

Thermionic cathodes are important in many electronic devices, due to their low cost and robust nature. Their transition from thermionic to space-charge-limited emission remains poorly understood, even though it is the regime in which they are normally operated. This study uses simulations of electron emission and propagation from a cathode of varying work function to illustrate how space charge affects current characteristics. It is confirmed that initially current comes primarily from areas of low work function, but then saturates. There is an optimal temperature for electron-beam brightness, and cathodes with a fine-grained work-function structure yield a higher-quality beam.

Topics & Concepts