Patent ID: 8588372

Claim:
An electron generator unit comprising: an emitter element configured to generate an electron beam having a first aspect ratio shape; an extraction electrode positioned adjacent to the emitter element to extract the electron beam out therefrom, the extraction electrode including an opening therethrough in which a meshed grid is positioned; at least one shaping electrode positioned to receive the electron beam after passing through the extraction electrode, the shaping electrode defining a non-circular aperture therein and being configured to provide at least one of shaping and focusing of the electron beam to have a second aspect ratio shape different from the first aspect ratio shape so as to form a focal spot having a desired size and aspect ratio on a target anode; an emittance compensation electrode (ECE) positioned between the extraction electrode and the shaping electrode and configured to control emittance growth of the electron beam, such that electrons in the electron beam are compressed along a direction of travel of the electron beam and caused to have nearly the same momentum; 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 that minimizes 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; wherein, in applying the determined voltage to the ECE, the spread of electrons in the electron beam along the direction of travel of the electron beam is controlled so as to minimize emittance growth.