Analysis of Anode Current From a Thermionic Cathode With a 2-D Work Function Distribution
Abhijit Jassem, D. Chernin, John Petillo, Y. Y. Lau, Aaron Jensen, Serguei Ovtchinnikov
Abstract
A model of a thermionic cathode in a planar diode in which the Poisson and Vlasov equations are solved in 3-D assuming an infinite magnetic field is presented. We explore how 2-D work function variations across the cathode surface may affect the transition between temperature-limited and space-charge-limited flow, commonly known as the “knee” of the Miram curve. We study a variety of work function distributions, both realistic and idealized, and demonstrate how emission from the lowest work function regions dominates the total anode current even when such regions make up a relatively small fraction of cathode area. Our model also illustrates the ability of cathodes to reach the full Child-Langmuir current despite the presence of a sizeable nonemitting region. We find that as the length scale of these work function variations decreases, the Miram knee grows sharper, indicating improved cathode performance.