X-RAY SOURCE WITH MULTIPLE GRIDS
Some embodiments include an x-ray source, comprising: an anode; a field emitter configured to generate an electron beam; a first grid configured to control field emission from the field emitter; a second grid disposed between the first grid and the anode; a third grid disposed between the first grid and the anode; and a middle electrode disposed between the first grid and the anode wherein the second grid is either disposed between the first grid and middle electrode or between the middle electrode and the anode; wherein the third grid is a mesh grid.
1 . An x-ray source comprising:
an anode;
a field emitter configured to generate an electron beam;
a first grid configured to control field emission from the field emitter; and
a second grid disposed between the first grid and the anode.
2 . The x-ray source of claim 1 , further comprising a voltage source configured to apply a first voltage to the first grid and a second voltage to the second grid.
3 . The x-ray source of claim 2 , wherein the first voltage and the second voltage are the same.
4 . The x-ray source of claim 2 , wherein the voltage source is a variable voltage source configured to vary at least one of the first voltage or the second voltage.
5 . The x-ray source of claim 2 , further comprising a third grid disposed between the first grid and the anode, wherein the voltage source is configured to apply a third voltage to the third grid.
6 . The x-ray source of claim 5 , wherein:
the third grid is disposed at a same distance from the field emitter as the second grid; and
the voltage source is configured to independently apply the third voltage and the second voltage.
7 . The x-ray source of claim 5 , wherein the third grid comprises a mesh grid.
8 . An x-ray source comprising:
a vacuum enclosure;
an anode disposed in the vacuum enclosure;
a plurality of field emitters disposed in the vacuum enclosure, each field emitter configured to generate an electron beam;
a plurality of first grids, each first grid associated with a corresponding one of the field emitters and configured to control field emission from the corresponding field emitter; and
a second grid disposed between the plurality of first grids and the anode.
9 . The x-ray source of claim 8 , further comprising a spacer disposed between the first grids and the anode, wherein the second grid is disposed on the spacer.
10 . The x-ray source of claim 9 , wherein:
the spacer comprises a plurality of openings; and
each field emitter is aligned to a corresponding one of the openings.
11 . The x-ray source of claim 10 , further comprising a third grid disposed between the first grids and the anode, wherein for each of the openings, the second grid is disposed along a first edge of the opening and the third grid is disposed along a second edge of the opening opposite the first edge.
12 . The x-ray source of claim 8 , further comprising a third grid disposed between the first grids and the anode, wherein the third grid is laterally offset from the second grid.
13 . The x-ray source of claim 8 , wherein each of the first grids includes a single row of openings.
14 . The x-ray source of claim 8 , wherein the second grid comprises a mesh grid.
15 . A method of operating an x-ray source, comprising:
applying a voltage to a first grid to control field emission from a field emitter to generate an electron beam;
directing the electron beam toward an anode to generate x-rays; and
applying voltages to a second grid and a third grid disposed between the first grid and the anode to alter an electric field between the first grid and the anode.
16 . The method of claim 15 , further comprising applying different voltages to the second grid and the third grid to steer the electron beam.
17 . The method of claim 15 , further comprising adjusting a focal spot position on the anode by varying the voltages applied to the second grid and the third grid.
18 . The method of claim 15 , wherein applying the voltages to the second grid and the third grid protects the field emitter from at least one of arcing and ion bombardment.
19 . The method of claim 15 , wherein the second grid and the third grid are disposed at a same distance from the field emitter.
20 . The method of claim 15 , further comprising scanning a focal spot along a track on the anode by varying the voltages applied to the second grid and the third grid.