Field emitter based electron source with minimized beam emittance growth

A cathode assembly for an x-ray source comprising:

• a substrate;
• an extraction element positioned adjacent to the substrate and having an opening with a meshed grid positioned therein;
• an insulating layer between the substrate and the extraction element, the insulating layer having a cavity generally aligned with the opening in the extraction element;
• a field emitter element disposed in the cavity of the insulating layer and configured to emit an electron beam when an emission voltage is applied across the extraction element;
• 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
• a controller configured to:
• control the emission voltage applied across the extraction element;
• 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 element;
• and,
• control the compression voltage
• applied across the ECE to vary compression of the electron beam, the compression voltage applied across the ECE being associated with the emission voltage applied across the extraction electrode and being controlled by the controller to compress the electron beam in space and momentum phase space so as to minimize emittance growth thereof.

A multiple spot x-ray source comprising:

• a plurality of field emitter units configured to generate at least one electron beam;
• a target anode positioned in a path of the at least one electron beam and configured to emit a beam of high-frequency electromagnetic energy conditioned for use in a CT imaging process when the electron beam impinges thereon;
• and
• wherein each of the plurality of field emitter units further comprises:
• a carbon nanotube (CNT) emitter element including a plurality of CNT groups;
• a gate electrode to extract the electron beam from the CNT emitter element, the gate electrode including a meshed grid positioned in the electron beam path and relative to the CNT emitter element such that each of the plurality of CNT groups is aligned with a respective opening in the meshed grid;
• a focusing element positioned to receive the electron beam from the emitter element and focus the electron beam to form a focal spot on the target anode;
• an emittance compensation electrode (ECE) positioned between the meshed grid and the focusing element and configured to control electron beam emittance growth;
• and,
• wherein the field emitter unit further comprises a controller configured to apply a variable voltage to at least one of the gate electrode and the ECE to modulate current density in the electron beam and control electron beam emittance growth, respectively and wherein the voltage applied to the ECE by the controller is determined such that the voltage to be applied to the gate electrode is chosen so as to control emittance growth of the electron beam.