Patent ID: 7801277

Claim:
An electron gun comprising: an emitter element configured to generate an electron beam; an extraction electrode positioned adjacent to the emitter element to extract the electron beam out therefrom, the extraction electrode including an opening therethrough; a meshed grid disposed in the opening of the extraction electrode to enhance intensity and uniformity of an electric field at a surface of the emitter element; an emittance compensation electrode (ECE) positioned adjacent to the meshed grid on the side of the meshed grid opposite that of the emitter element and configured to control emittance growth of the electron beam; and a controller configured to: cause a voltage to be applied to the extraction electrode to generate a desired current density in the electron beam; determine a voltage to be applied to the ECE, said voltage chosen so as to minimize emittance growth of the electron beam based on the voltage applied to the extraction electrode; and cause the determined voltage to be applied to the ECE such that electric fields present at opposing sides of the meshed grid are equal.