Apparatus for modifying electron beam aspect ratio for X-ray generation

An x-ray tube comprising:

• a housing enclosing a vacuum chamber;
• an electron generator unit positioned within the housing, the electron generator unit comprising:
• an emitter element configured to generate an electron beam having a first aspect ratio;
• 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;
• an emittance compensation electrode (ECE) positioned downstream from the extraction element and configured to compress the electron beam in space and momentum phase space;
• and
• at least one shaping electrode positioned to receive the electron beam after passing through the extraction electrode, the shaping electrode defining a non-circular opening therein and being configured to shape the electron beam to have a second aspect ratio different from the first aspect ratio;
• and
• a target anode positioned in a path of the shaped electron beam and configured to emit high-frequency electromagnetic energy when the shaped electron beam impinges thereon;
• 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.

An x-ray tube comprising:

• a circular emitter element configured to generate an electron beam having a circular cross-section;
• an extraction electrode positioned adjacent to the emitter element to extract the electron beam out therefrom, the extraction electrode including an opening therethrough that includes a meshed grid positioned therein to reduce a voltage needed to extract the electron beam from the emitter element, with the meshed grid having a plurality of openings therein;
• a shaping electrode positioned to receive the electron beam from the circular emitter element and having a non-circular aperture formed therethrough, the non-circular aperture of the shaping electrode configured to focus and shape the electron beam as it passes through the shaping electrode such that a shape of the electron beam is modified to have a non-circular cross-section;
• an emittance compensation electrode (ECE) positioned between the circular emitter element and the shaping electrode and configured to control electron beam emittance growth by compressing electrons in the beam along the direction of travel of the electron beam;
• a target anode positioned in a path of the non-circular electron beam and being configured to emit high-frequency electromagnetic energy when the non-circular electron beam impinges thereon;
• and
• a controller configured to apply a variable voltage to the shaping electrode to generate an electrostatic force to control focusing and shaping of the electron beam;
• wherein the controller is further 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
• wherein the shaping electrode comprises a plurality of electrode pieces arranged to define the non-circular aperture, and wherein each of the plurality of electrode pieces receives an individually variable voltage from the controller in order to focus and shape the electron beam as it passes through the non-circular aperture.