Grid voltage generation for x-ray tube

[0001] This claims priority to U.S. Provisional Patent Application No. 61/740,944, filed on Dec. 21, 2012, which is hereby incorporated herein by reference in its entirety.

[0002] The present application is related generally to x-ray sources.

[0003] At least one grid can be disposed between an anode and a cathode of an x-ray tube for improved electron beam control and for a smaller electron beam spot size, and a resulting smaller x-ray spot size. The grid can have a voltage that is different from a voltage of an electron emitter on the cathode. If two grids are used, one grid can have a voltage that is more positive than the voltage of the electron emitter and the other grid can have a voltage that is less positive than the voltage of the electron emitter. The electron emitter can have a very large absolute value of voltage, such as negative tens of kilovolts for example. Voltage for the electron emitter can be provided by a primary high voltage multiplier (“primary HVM”) and a grid high voltage multiplier (“grid HVM”).

[0004] One method to provide voltage to the grid(s) is to use an alternating current source, which can be connected to ground at one end. The alternating current source can provide alternating current to the grid HVM. An input to the grid HVM can be electrically connected to the primary HVM. The grid HVM can then generate a voltage for the grid that is more positive or less positive than the voltage provided by the HVM. For example, the primary HVM might provide negative 40 kV, a grid may generate a negative 500 volts, thus providing negative 40.5 kV to a grid. If there is a second grid HVM, it may be configured to generate a positive voltage, such as positive 500 volts for example, thus providing negative 39.5 kV to a second grid. Typically, voltage to each grid may be controlled. Typically only one grid at a time would be used.

[0005] A problem of the previous design is a very large voltage differential between the alternating current source and the grid HVM. The alternating current source might provide an alternating current having an average value of zero or near zero volts. The alternating current source can transfer this alternating current signal, through a transformer, to the grid HVM, which has a very large DC bias, such as negative 40 kilovolts for example.

[0006] In order to prevent arcing between the alternating current source and the grid HVM, special precautions may be needed, such as a large amount of insulation on transformer primary and secondary wires, or other voltage standoff methods. This added insulation or other voltage standoff methods can result in an increased power supply size and weight, which can be undesirable. Also, the increased insulation or other voltage standoff methods can result in power transfer inefficiencies, thus resulting in wasted electrical power. Power supply size, weight, and power loss are especially significant for portable x-ray sources. Furthermore, the large voltage difference between the grid HVM and the alternating current source (e.g. tens of kilovolts), can result in failures due to arcing, in spite of added insulation, because it is difficult to standoff such large voltages without an occasional failure.

[0007] It has been recognized that it would be advantageous to improve electron beam control, have a smaller electron beam spot size, and have a smaller x-ray spot size. It has been recognized that it would be advantageous to reduce the size and weight of x-ray sources, to reduce power loss, and to avoid arcing. The present invention is directed to an x-ray source and a method for controlling an electron beam of an x-ray tube that satisfies these needs.

[0008] The x-ray source can comprise an x-ray tube and a power supply. The x-ray tube can comprise an anode attached to an evacuated enclosure, the anode configured to emit x-rays; a cathode including an electron emitter attached to the evacuated enclosure, the electron emitter configured to emit electrons towards the anode; and an electrically conducting grid disposed between the electron emitter and the anode, with a gap between the grid and the anode, and a gap between the grid and the electron emitter.

[0009] The power supply can comprise an internal grid control configured to provide alternating current and a grid high voltage multiplier electrically coupled between the internal grid control and the grid. The grid high voltage multiplier can be configured to receive alternating current from the internal grid control and generate a direct current (“DC”) voltage based on the alternating current, and to provide the DC voltage to the grid. A primary high voltage multiplier can be configured to provide a DC bias voltage at a high voltage connection to the electron emitter and the grid high voltage multiplier. Electrically insulating potting can substantially surround a cathode end of an exterior of the x-ray tube, a high voltage connection end of an exterior of the primary high voltage multiplier, the grid high voltage multiplier, and the internal grid control.

[0010] A method for controlling an electron beam of an x-ray tube can comprise obtaining an x-ray tube and control electronics and sending a light control signal. Obtaining an x-ray tube and control electronics can include obtaining (1) an anode attached to an evacuated enclosure, the anode configured to emit x-rays; (2) an electron emitter attached to the evacuated enclosure and configured to emit electrons towards the anode; (3) an electrically conducting grid disposed between the electron emitter and the anode, with a gap between the grid and the anode, and a gap between the grid and the electron emitter; (4) an internal grid control configured to provide alternating current; (5) a grid high voltage multiplier electrically coupled between the internal grid control and the grid, configured to receive alternating current from the internal grid control and generate a direct current (“DC”) voltage based on the alternating current; and configured to provide the DC voltage to the grid; (6) a primary high voltage multiplier electrically coupled to and configured to provide a DC bias voltage to the electron emitter and to the grid high voltage multiplier; and (7) electrically insulating potting substantially surrounding a cathode end of an exterior of the x-ray tube, at least part of the primary high voltage multiplier, the grid high voltage multiplier, and the internal grid control. Sending a light control signal can comprise sending a light control signal to the internal grid control, the internal grid control modifying the alternating current to the grid high voltage multiplier based on the light control signal, and the grid high voltage multiplier modifying the grid voltage based on the modified alternating current.

• • [0017] 1 primary high voltage multiplier (“primary HVM”)
  • [0018] is high voltage connection for the primary HVM
  • [0019] 1b high voltage connection end of an exterior of the primary HVM
  • [0020] 2 x-ray tube
  • [0021] 3 anode
  • [0022] 4 ground
  • [0023] 5a first electrically conducting grid
  • [0024] 5b second electrically conducting grid
  • [0025] 6 evacuated enclosure
  • [0026] 7 electron emitter
  • [0027] 8 first transformer
  • [0028] 9 second transformer
  • [0029] 10 x-ray source
  • [0030] 11a first grid high voltage multiplier (“first grid HVM”)
  • [0031] 11b second grid high voltage multiplier (“second grid HVM”)
  • [0032] 12a first internal grid control
  • [0033] 12b second internal grid control
  • [0034] 13 alternating current source for the electron emitter
  • [0035] 14 electrically insulating potting
  • [0036] 15a external light source
  • [0037] 15b light beam transmitting through transparent potting
  • [0038] 15c power fiber optic cable
  • [0039] 16 solar cell
  • [0040] 17a first external grid control
  • [0041] 17b first control signal as a light beam
  • [0042] 17c first control fiber optic cable
  • [0043] 18a second external grid control
  • [0044] 18b second control signal as a light beam
  • [0045] 18c second control fiber optic cable
  • [0046] 19 cathode
  • [0047] 19b cathode end of an exterior of the x-ray tube
  • [0048] 21 gap between grid and electron emitter
  • [0049] 22 gap between the two grids
  • [0050] 23 gap between grid and anode
  • [0051] 25a first light sensor of the first internal grid control
  • [0052] 25b second light sensor of the second internal grid control
  • [0053] 27 power supply
  • [0054] 31 battery

[0055] As illustrated in FIGS. 1-6, x-ray sources 10, 20, 30, 40, 50, and 60 are shown comprising, an x-ray tube 2 and a power supply 27. The x-ray tube 2 can include an anode 3 attached to an evacuated enclosure 6, the anode 3 configured to emit x-rays; a cathode including an electron emitter 7 attached to the evacuated enclosure 6, the electron emitter 7 configured to emit electrons towards the anode 3; and an electrically conducting grid 5a disposed between the electron emitter 7 and the anode 3, with a gap 23 between the grid 5a and the anode 3, and a gap 21 between the grid 5a and the electron emitter 7.

[0056] The power supply 27 for the x-ray tube 2 can comprise an internal grid control 12a configured to provide alternating current; a grid high voltage multiplier (“grid HVM”) 11a electrically coupled between the internal grid control 12a and the grid 5a; a primary high voltage multiplier (“primary HVM) 1; and electrically insulating potting 14.

[0057] The grid HVM 11a can be configured to receive alternating current from the internal grid control 12a, generate a direct current (“DC”) voltage based on the alternating current, and provide the DC voltage to the grid 5a. The primary HVM 1 can be configured to provide a DC bias voltage at a high voltage connection la to the electron emitter 7. The primary HVM 1 can be configured to provide a DC bias voltage at a high voltage connection la to the grid HVM 11a. The primary HVM 1 can be configured to provide a DC bias voltage at a high voltage connection 1a to the internal grid control 12a. The grid HVM 11a might provide a DC voltage for the grid 5a that is anywhere from less than a volt to a few volts to over a hundred volts greater than or less than the DC bias voltage provided by the primary HVM 1. The grid HVM 11a can provide a DC voltage for the grid 5a that is at least 10 volts greater than or less than the DC bias voltage provided by the primary HVM 1 in one aspect, at least 100 volts greater than or less than the DC bias voltage provided by the primary HVM 1 in another aspect, or at least 1000 volts greater than or less than the DC bias voltage provided by the primary HVM 1 in another aspect.

[0058] As shown in FIGS. 1-4 and 6, a transformer 8 can electrically couple the internal grid control 12a and the grid HVM 11a and can be configured to transfer electrical power from the internal grid control 12a to the grid HVM 11a. A transformer is typically used for conversion of direct current to alternating current, and may also be used to step up voltage from the internal grid control 12a to the grid HVM 11a. As shown in FIG. 5, the internal grid control 12a can be electrically connected to the grid HVM 11a without a transformer.

[0059] As shown in FIGS. 1-6, the electrically insulating potting 14 can substantially surround a cathode end 19b of an exterior of the x-ray tube 2, a high voltage connection end 1b of an exterior of the primary HVM 1, the grid HVM 11a, and the internal grid control 12a.

[0060] The internal grid control 12a can have a light sensor 25a configured to receive a light control signal 17b emitted by an external grid control 17a. The internal grid control 12a can be configured to modify the alternating current to the grid HVM 11a based on the light control signal 17b and the grid HVM 11a can be configured to modify the grid 5a voltage based on the modified alternating current.

[0061] As shown in FIGS. 1, 3, and 5-6, the potting 14 can be substantially transparent to light (the wavelength(s) of light emitted by the external grid control 17a), and the light control signal 17b can be emitted from the external grid control 17a directly through the potting 14 to the internal grid control 12a. As shown in FIGS. 2 & 4, a control fiber optic cable 17c can extend through the potting 14 and can couple the light sensor 25a of the internal grid control 12a to the external grid control 17a, and the light control signal 17b can be emitted from the external grid control 17a through the control fiber optic cable 17c to the light sensor 25a.

[0062] The x-ray sources 10, 20, 30, 40, 50, and 60 can further comprise a solar cell 16 electrically coupled to the internal grid control 12a and disposed in the potting 14. The solar cell 16 can be configured to receive light 15b emitted by an external light source 15a and convert energy from the light 15b into electrical energy for the internal grid control 12a. Various types of light sources may be used, such as an LED or a laser for example. It can be important to select a light source with sufficient power output.

[0063] As shown in FIGS. 1, 3, and 5-6, the potting 14 can be substantially transparent to light (the wavelength(s) of light emitted by the external light source 15a), and the light 15b from the external light source 15a can be emitted from the external light source 15a directly through the potting 14 to the solar cell 16. As shown in FIGS. 2 & 4, a power fiber optic cable 15c can extend through the potting 14 and can couple the solar cell 16 to the external light source 15a, and the light 15b from the external light source 15a can be emitted from the external light source 15a through the power fiber optic cable 15c to the solar cell 16.

[0064] As shown in FIGS. 3 & 4, the x-ray sources 30 and 40 can comprise a battery 31 electrically coupled to the internal grid control 12a and to the solar cell 16 and disposed in the potting 14. The solar cell 16 can be configured to provide electrical power to the battery 31 to recharge the battery 31. The battery 31 can be configured to provide electrical power to the internal grid control 12a. The battery can be recharged when the x-ray source 30 or 40 is not in use, then the x-ray source can be used without the external light source 15a for the life of the battery. A battery recharger can be associated with the solar cell 16 or with the battery 31. It can be important to select an external light source 15a, such as a laser for example, with sufficient power to recharge the battery in a reasonable amount of time. Alternatively, if no battery 31 is used, as shown in FIGS. 1, 2, 5, and 6, then the external light source 15 can attached to the x-ray source 10, 20, or 50 and can be in use to provide light to the solar cell 16 while the x-ray source is in operation.

[0065] Although a single grid 5a may be used, typically two grids 5a-b will be used, with one grid having a more positive voltage and the other grid having a less positive voltage than the voltage provided by the primary HVM 1. This design can allow for improved electron beam control. X-ray sources 10, 20, 30, 40, and 50 in FIGS. 1-5 show two grids 5a-b and associated controls, but x-ray source 60 in FIG. 6 includes only a single grid 5a with associated controls. A design with a single grid can be simpler, easier, and cheaper to make.

[0066] Thus, as shown in FIGS. 1-5, the grid 5a can be called a first grid 5a, and the x-ray sources 10, 20, 30, 40, and 50 can further comprise a second electrically conducting grid 5b disposed between the first grid 5a and the anode 3, with a gap 23 between the second grid 5b and the anode 3, and a gap 22 between the first grid 5a and the second grid 5b. The internal grid control 12a can be called a first internal grid control 12a, and the x-ray sources 10, 20, 30, 40, and 50 can further comprise a second internal grid control 12b configured to provide alternating current. The DC voltage can be called a first DC voltage. The grid HVM 11a can be called a first grid HVM 11a, and the x-ray sources 10, 20, 30, 40, and 50 can further comprise a second grid high voltage multiplier (“second grid HVM”) 11b electrically coupled between the second internal grid control 12a and the second grid 5b. The second grid HVM 11b can be configured to: (1) receive alternating current from the second internal grid control 12b, (2) generate a second DC voltage based on the alternating current from the second internal grid control 12b, and (3) provide the second DC voltage to the second grid 5b.

[0067] Either the first grid HVM 11a or the second grid HVM 11b can be configured to provide a DC voltage to the first grid 5a or to the second grid 5b, that is more positive than the DC bias voltage provided by the primary HVM 1, and the other of the first grid HVM 11a or the second grid HVM 11b can be configured to provide a DC voltage to the other of the first grid 5a or second grid 5b that is less positive than the DC bias voltage provided by the primary HVM 1.

[0068] A Cockcroft-Walton multiplier can be used for the grid HVMs 11a-b. A schematic of a Cockcroft-Walton multiplier is shown on FIG. 6 of U.S. Pat. No. 7,839,254, incorporated herein by reference. Diodes in a Cockcroft-Walton multiplier can be disposed in one direction to generate a more positive voltage, or in an opposite direction, to generate a less positive voltage.

[0069] The high voltage connection 1a of the primary HVM 1 can be electrically coupled to the second grid HVM 11b. The high voltage connection 1a of the primary HVM 1 can be electrically coupled to the second internal grid control 12b. Electrically insulating potting 14 can substantially surround the second grid HVM 11b and the second internal grid control 12b.

[0070] The transformer 8 can define a first transformer. A second transformer 9 can be disposed in the potting 14 and electrically coupled between the second internal grid control 12b and the second grid HVM 11b. The second transformer 9 can be configured to transfer electrical power from the second internal grid control 12b to the second grid HVM 11b.

[0071] The external grid control 17a can be a first external grid control 17a. The light control signal 17b from the first external grid control 17a can be a first light control signal 17b. A second external grid control 18a can emit a second light control signal 18b for control of the second internal grid control 12b. The second internal grid control 12b can have a second light sensor 25b and can be configured to receive the second light control signal 18b emitted by the second external grid control 18a. The second internal grid control 12b can be configured to modify the alternating current to the second grid HVM 11b based on the second light control signal 18b. The second grid HVM 11b can be configured to modify the second grid 5b voltage based on the modified alternating current.

[0072] As shown in FIGS. 1, 3, and 5, the potting 14 can be substantially transparent to light (the wavelength(s) of light emitted by the external grid control 18b), and the second light control signal 18b can be emitted from the second external grid control 18a directly through the potting 14 to the second internal grid control 12b. As shown in FIGS. 2 and 4, the control fiber optic cable 17c can define a first control fiber optic cable 17c and a second control fiber optic cable 18c can extend through the potting 14 and can couple the light sensor 25b of the second internal grid control 12b to the second external grid control 18a. The second light control signal 18b can be emitted from the external grid control 18a through the control second fiber optic cable 18c to the second light sensor 25b.

[0073] As shown in FIGS. 3-4, a solar cell 16 and a battery 31 can be electrically coupled to each other and to the first internal grid control 12a and to the second internal grid control 12b and can be disposed in the potting 14. The solar cell 16 can be configured to receive light emitted by an external light source 15a and convert energy from the light into electrical energy. The solar cell 16 can be configured to charge the battery 31 with electrical power. The battery 31 can be configured to provide electrical power to the first internal grid control 12a and to the second internal grid control 12b. Although shown in FIGS. 3-4 is a solar cell 16 providing electrical power for a single battery 31, the single battery providing electrical power for both internal grid controls 12a-b, a separate solar cell and a separate battery may be used for each internal grid control.

[0074] Alternatively, as shown in FIGS. 1-2 and 5, the solar cell 16 can be directly electrically coupled to the first internal grid control 12a and to the second internal grid control 12b and can be disposed in the potting 14. The solar cell 16 can be configured to receive light emitted by an external light source 15a and convert energy from the light into electrical energy. The solar cell 16 can be configured to directly provide the first internal grid control 12a and to the second internal grid control 12b with electrical power. Although shown in FIGS. 1-2 and 5 is a solar cell 16 providing electrical power to both internal grid controls 12a-b, a separate solar cell may be used for each internal grid control.

[0075] The grid(s) 5a-b can allow for improved electron beam control, a smaller electron beam spot size, and a smaller x-ray spot size. Encasing the internal grid control(s) 12a-b in potting 14, and controlling them via external grid control(s) 17a and/or 18a allows the internal grid control to be maintained at approximately the same voltage as an input to the grid HVM(s) 11a-b, which can avoid a need for a large amount of insulation on transformer wires between the internal grid control(s) 12a-b and the grid HVM(s) 11a-b. This can result in reduced size and weight of the x-ray sources 10, 20, 30, 40, 50, and 60 and reduced power loss due to transformer inefficiencies and help to avoid arcing.

Method

[0076] A method for controlling an electron beam of an x-ray tube 2 can comprise obtaining an x-ray tube 2 and control electronics with:

• [0077] 1. an anode 3 attached to an evacuated enclosure 6, the anode 3 configured to emit x-rays;
• [0078] 2. an electron emitter 7 attached to the evacuated enclosure 6 and configured to emit electrons towards the anode 3;
• [0079] 3. an electrically conducting grid 5a disposed between the electron emitter 7 and the anode 3, with a gap 23 between the grid 5a and the anode 3, and a gap 21 between the grid 5a and the electron emitter 7;
• [0080] 4. an internal grid control 12a configured to provide alternating current;
• [0081] 5. a grid HVM 11a:
  • [0082] a. electrically coupled between the internal grid control 12a and the grid 5a;
  • [0083] b. configured to receive alternating current from the internal grid control 12a and generate a direct current (“DC”) voltage based on the alternating current; and
  • [0084] c. configured to provide the DC voltage to the grid 5a;
• [0085] 6. a primary HVM 1 electrically coupled to and configured to provide a DC bias voltage to the electron emitter 7;
• [0086] 7. the primary HVM 1 electrically coupled to and configured to provide a DC bias voltage to the internal grid control 12a and/or to the grid HVM 11a; and
• [0087] 8. electrically insulating potting 14 substantially surrounding a cathode end 19b of an exterior of the x-ray tube 2, at least part of the primary HVM 1, the grid HVM 11a, and the internal grid control 12a.

[0088] The method can further comprise sending a light control signal 17b to the internal grid control 12a, the internal grid control 12a modifying the alternating current to the grid HVM 11a based on the light control signal 17b, and the grid HVM 11a modifying the grid voltage based on the modified alternating current.

[0089] The method can further comprise sending light energy 15b to a solar cell 16, the solar cell 16 receiving the light and converting energy from the light into electrical energy. The electrical energy can be used to charge a battery 31 with electrical power and the battery 31 can provide electrical power to the internal grid control 12a. Alternatively, the electrical energy can be used to provide electrical power to the internal grid control 12a directly.

[0090] The potting 14 in the method can be substantially transparent to light (transparent to the wavelength(s) of light emitted by the external grid controls 17a and 18a and/or light emitted by the external light source 15a). Sending the light control signal 17b can include sending the light control signal 17b through the potting 14. Sending light energy 15b to a solar cell 16 can include sending the light energy 15b through the potting.

[0091] The control electronics in the method can further comprise a control fiber optic cable 17c extending through the potting 14 and coupling the internal grid control 12a to the external grid control 17a. The method step of sending a light control signal can include sending the light control signal 17b through the control fiber optic cable 17c.

[0092] The control electronics in the method can further comprise a power fiber optic cable 15c extending through the potting 14 and coupling the solar cell 16 to the external light source 15a. The method step of sending a sending light energy 15b to a solar cell 16 can include sending the light energy 15b through the power fiber optic cable 15c.

[0093] The method step of obtaining an x-ray tube 2 and control electronics can further include:

• [0094] 1. the grid 5a is a first grid 5a, and further comprising a second electrically conducting grid 5b disposed between the first grid 5a and the anode 3, with a gap 23 between the second grid 5b and the anode 3, and a gap 22 between the first grid 5a and the second grid 5b;
• [0095] 2. the internal grid control 12a is a first internal grid control 12a, and further comprising a second internal grid control 12b configured to provide alternating current;
• [0096] 3. the DC voltage is a first DC voltage;
• [0097] 4. the grid HVM 11a is a first grid HVM 11a, and further comprising a second grid HVM 11b:
  • [0098] a. electrically coupled between the second internal grid control 12b and the second grid 5b;
  • [0099] b. configured to receive alternating current from the second internal grid control 12b and generate a second direct current (“DC”) voltage based on the alternating current; and
  • [0100] c. configured to provide the second DC voltage to the second grid 5b;
• [0101] 5. one of the first grid HVM 11a or the second grid HVM 11b is configured to provide a DC voltage to the first grid 5a or second grid 5b that is more positive than the DC bias voltage provided by the primary HVM 1, and the other of the first grid HVM 11a or the second grid HVM 11b is configured to provide a DC voltage to the other of the first grid 5a or the second grid 5b that is less positive than the DC bias voltage provided by the primary HVM 1;
• [0102] 6. the primary HVM 1 electrically coupled to the second grid HVM 11b and/or to the second internal grid control 12b; and
• [0103] 7. the electrically insulating potting 14 substantially surrounding the second grid HVM 11b and the second internal grid control 12b.

[0104] The method step of obtaining an x-ray tube 2 and control electronics can further include a solar cell 16 and a battery 31 electrically coupled to each other. The battery 31 can be electrically coupled to the first internal grid control 12a and to the second internal grid control 12b. The battery 31 can be disposed in the potting 14. The solar cell 16 can be configured to receive light emitted by an external light source 15a and convert energy from the light into electrical energy. The solar cell 16 can be configured to charge the battery 31 with electrical power. The battery 31 can be configured to provide electrical power to the first internal grid control 12a and to the second internal grid control 12b.

[0105] The method step of obtaining an x-ray tube 2 and control electronics can further include a solar cell 16 electrically coupled to the first internal grid control 12a and to the second internal grid control 12b and disposed in the potting 14. The solar cell 16 can be configured to receive light emitted by an external light source 15a and convert energy from the light into electrical energy. The solar cell 16 can be configured to directly provide electrical power to the first internal grid control 12a and to the second internal grid control 12b.

[0106] Sending the light control signal 17b in the method can be a first light control signal 17b, and the method may further comprise sending a second light control signal 18b to the second internal grid control 12b, the second internal grid control 12b modifying the alternating current to the second grid HVM 11b based on the second light control signal 18b, and the second grid HVM 11b modifying the second grid voltage based on the modified alternating current to the second grid HVM 11b.