Patent ID: 9224572
Filing Date: 2015-12-29
Classification: H01J

Abstract:
1. An X-ray tube assembly comprising: an emitter configured to emit an electron beam defining a downstream direction toward a target, the emitter disposed proximate an upstream end of the X-ray tube assembly, the emitter defining a maximum emission area from which the electron beam may be emitted from the emitter; an emitter focusing electrode disposed proximate the emitter and outward of the emitter in an axial direction; an extraction electrode disposed proximate the emitter focusing electrode, the extraction electrode disposed downstream of the emitter and the emitter focusing electrode, the extraction electrode configured to surround the electron beam in the axial direction, the extraction electrode having a negative bias voltage setting wherein the extraction electrode has a negative bias voltage with respect to the emitter at the negative bias voltage setting; and a downstream focusing electrode disposed proximate the extraction electrode and downstream of the extraction electrode, the downstream focusing electrode configured to surround the electron beam in the axial direction, the downstream focusing electrode having a positive bias voltage with respect to the emitter; wherein, when the extraction electrode is at the negative bias voltage setting, the electron beam is emitted from an emission area that is smaller than the maximum emission area.