A shield structure is provided that is suitable for use in connection with an x-ray device that includes an anode and cathode disposed in a vacuum enclosure in a spaced apart arrangement so that a target surface of the anode is positioned to receive electrons emitted by the cathode. The shield structure is configured to be interposed between the anode and the cathode and includes an interior surface that defines an aperture through which the electrons are passed from the cathode to the target surface of the anode. Additionally, the aperture includes an inlet and an outlet sized so that the area of the inlet is relatively smaller than the area of the outlet. Finally, the shield structure is situated in the x-ray device such that the inlet of the aperture is positioned near the cathode and the outlet of the aperture is positioned near the anode target surface.