Space Charge vs. Image Force in Thermionic Emission

Abstract

This paper is a joint report on work by the two authors, preliminary to further and more detailed publication on different phases of the problems here discussed. Attention is called to certain deficiencies in the Schottky image force as an explanation of the thermionic work function, both on theoretical and experimental grounds. Evidence is advanced to show that space charge is more important than image force over most of the region in which the image force is thought to be valid. It is further shown that space charge with Fermi-Dirac statistics is able to account for observed phenomena of thermionic emission, including the effect of external fields. Numerical examples indicate some of the consequences of this point of view.