Issues with the Explosive Field Emission Model in PIC Code-Unlimited Current Density

Fowler-Nordheim equation was originally developed to describe field emission from small tip, but now its form is widely used in describing various kinds of field emission macroscopic applications including high power microwave scenarios. In this article we test explosive field emission model in a particle-in-cell (PIC) code simulation of Vircator, and found as the externally applied voltage increases, the field emission current density also keep on increasing, to an extent that it exceeds experimentally possible value. The reason for this is that in the theoretical derivation of Fowler-Nordheim equation, an ideal current source capable of supplying infinite current was assumed, therefore there is no limitation of field emission current density.