| CPC H01J 35/065 (2013.01) [H01J 35/112 (2019.05); H01J 35/147 (2019.05)] | 20 Claims |

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1. An x-ray tube, comprising:
a field emitter including an emission surface;
an anode; and
a focus electrode disposed between the field emitter and the anode;
wherein:
the focus electrode includes:
a first surface that is substantially perpendicular to the field emitter emission surface and nearest to the field emitter;
a second surface that is axially nearest to the anode, wherein the field emitter and the anode form an axis; and
a third surface that extends between the first surface and the second surface;
a first location on the focus electrode between the first surface and the third surface is further from the anode than a second location on the focus electrode between the third surface and the second surface; and
the focus electrode further comprises a protrusion extending towards the anode.
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