Method and apparatus for controlling electron beam current
First Claim
1. An x-ray generating device comprising:
- a. a chamber;
b. a field emission cathode, comprising a film comprising carbon nanotube-containing materials on a conducting substrate;
c. an anode target;
d. a gate electrode comprising a metal grid, wherein the grid is placed between the cathode and the anode; and
e. a power supply structure to place the gate electrode at a higher electrical potential than the cathode for extracting the electrons from cathode, and to establish a large electrical potential difference between the cathode and the anode for generating the x-ray radiations.
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Abstract
An x-ray generating device includes a field emission cathode formed at least partially from a nanostructure-containing material having an emitted electron current density of at least 4 A/cm2. High energy conversion efficiency and compact design are achieved due to easy focusing of cold cathode emitted electrons and dramatic reduction of heating at the anode. In addition, by pulsing the field between the cathode and the gate or anode and focusing the electron beams at different anode materials, pulsed x-ray radiation with varying energy can be generated from a single device. Methods and apparatus for independent control of electron emission current and x-ray energy in x-ray tubes are also provided. The independent control can be accomplished by adjusting the distance between the cathode and anode. The independent control can also be accomplished by adjusting the temperature of the cathode. The independent control can also be accomplished by optical excitation of the cathode. The cathode can include field emissive materials such as carbon nanotubes.
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Citations
29 Claims
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1. An x-ray generating device comprising:
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a. a chamber;
b. a field emission cathode, comprising a film comprising carbon nanotube-containing materials on a conducting substrate;
c. an anode target;
d. a gate electrode comprising a metal grid, wherein the grid is placed between the cathode and the anode; and
e. a power supply structure to place the gate electrode at a higher electrical potential than the cathode for extracting the electrons from cathode, and to establish a large electrical potential difference between the cathode and the anode for generating the x-ray radiations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An x-ray generating device comprising:
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a. a chamber;
b. a group of field emission cathodes, wherein each cathode comprises a carbon nanotube-containing film on a conducting substrate;
c. an anode target;
d. a gate electrode placed between the cathode and the anode; and
e. a power supple structure to place the gate electrode at a higher electrical potential than the cathode for extracting the electrons from cathode; and
to establish a large electrical potential difference between the cathode and the anode for generating the x-ray radiations. - View Dependent Claims (12, 13, 14)
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15. An x-ray generating device comprising:
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a. a chamber;
b. a field emission cathode, comprising a carbon nanotube-containing film on a conducting substrate;
c. an anode target;
d. a gate electrode comprising a metal grid, wherein the grid is placed between the cathode and the anode;
e. an electron beam focusing structure placed between the gate electrode and the anode; and
f. a power supply structure to place the gate electrode at a higher electrical potential then the cathode for extracting the electrons from cathode, and to place the focusing structure at a lower electrical potential than the gate electrode for focusing the electron beam, and to establish a large electrical potential difference between the cathode and anode target for generating the x-ray radiations. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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24. An x-ray generating device comprising:
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a. a chamber;
b. a field emission cathode, the cathode comprising a carbon nanotube-containing film having an emitted electron current density of at least 1 mA/cm2 when subjected to an applied electrical field of more than 2 V/micron;
c. an anode target;
d. a gate electrode; and
e. a power supply structure to place the gate electrode at a higher electrical potential than the cathode for extracting the electrons from cathode, and to establish a large electrical potential difference between the cathode and the anode for generating the x-ray radiations. - View Dependent Claims (25, 26)
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27. An x-ray generating device comprising:
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a. a chamber;
b. a field emission cathode, comprising a carbon nanotube-containing film electrophoretically deposited on a conducting substrate;
c. an anode target;
d. a gate electrode comprising a metal grid;
e. an insulating spacer between the gate electrode and the cathode;
and f. a power supply that enables automatic adjustment of the electrical field between the gate electrode and cathode to maintain a constant x-ray intensity.
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28. A self-focusing x-ray source comprising:
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a. a chamber;
b. a field emission cathode, comprising a carbon nanotube-containing film deposited on a conducting substrate with a concave surface;
c. a gate electrode with the same curvature as the cathode surface;
d. an anode target;
e. an insulating spacer between the gate electrode and the cathode;
and f. a power supply that enables automatic adjustment of the electrical field between the gate electrode and the cathode such that a constant x-ray intensity is maintained.
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29. An x-ray generating device comprising:
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a. a chamber;
b. a field emission cathode, comprising a film comprising carbon nanotube-containing materials on a conducting substrate;
c. an anode target;
d. a gate electrode comprising a metal grid, wherein the grid is placed between the cathode and the anode;
e. a power supply structure to place the gate electrode at a higher electrical potential than the cathode for extracting the electrons from cathode, and to establish a large electrical potential difference between the cathode and the anode for generating the x-ray radiations;
f. wherein the field emission cathode comprises carbon nanotubes; and
g. wherein the field emitted electrons are self focused to a small area on the anode.
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Specification