Simulation study for the characterization of anode shape effect on the electron beam emittance of thermionic electron gun

Abstract

A systematic method had been used to develop the anode electrode shape of the thermionic electron gun by studying its effect on the emittance value, where the emittance parameter has been considered an important criterion for determining the fineness of the beam propagation. In this study, it has been found that the extended field outside the electron gun has a negative effect on the electron beam emittance parameter. A new shape of the anode has been developed and introduced in this research work to eliminate the unwanted field at the electron beam side. The cylindrical shape of the anode, which encapsulates the Wehnelt cylinder, has the effect of eliminating the adverse stray field, hence the enhancement of the beam emittance values. The new design is developed to be used in the illumination system of the electron microscopes where the highest laminar flow of the electron beam is needed.