Electron Beam Focusing and Centering

A method and device for control of an electron beam flux, electron spot size, and/or electron spot location. Electromagnetic radiation from an anode of the x-ray tube can be focused on a detector. The detector can send a signal to a control module based on the electromagnetic radiation focused on the detector. The control module can control the electron beam with a beam control device and/or a current control device. The signal can also indicate anode temperature at the electron spot.

DEFINITIONS

“Spot size” as used herein in reference to an x-ray spot size or an electron spot size on a target means the full width half max measurement (FWHM) of the spot. In other words, on a plot of the spot intensity, the spot size is the width (diameter) at half of full (maximum) intensity.

REFERENCE NUMBERS SHOWN IN THE FIGURES

1x-ray tube2camera3lens4detector5substantially evacuated enclosure6gap between anode and beam control device7gap between beam control device and flux control device8gap between electron emitter and beam control device and/or flux control device11anode12cathode13electron emitter14axis between the electron emitter and the anode, or approximate center of an electron beam15control module16beam control device(s)17flux control device18electromagnetic radiation emitted from the anode to the detector19x-rays21wires24window for transmission of x-rays out of the enclosure (“x-ray window)25electron spot26electron beam27window for transmission of electromagnetic radiation emitted from the anode to the detector (“detector window”)28temperature level output61electron spot location setpoint62electron spot size setpoint63voltage provided by the control module to the beam control device64Input to electron spot size setpoint65Input to electron spot location setpoint66control of electron beam trajectory and/or diameter67control of electron spot location and/or size on the anode target68control of x-ray spot location and/or size69signal from the detector to the control module, indicated electron spot size, electron spot location, and or anode temperature71flux setpoint72measured flux73voltage provided by the control module to the flux control device74operator input to flux setpoint76control of electron beam flux78control of x-ray fluxd pinhole diameterD electron beam diameter

DETAILED DESCRIPTION

As illustrated inFIGS. 1 and 2, x-ray sources10and20are shown comprising an x-ray tube1and a control module15. The x-ray tube1can include an anode11and a cathode12attached to a substantially evacuated enclosure5. The cathode12can include an electron emitter13configured to emit electrons towards the anode11. The anode11can include a target material for production of x-rays19in response to electron bombardment. An electron spot25can be formed on the anode11where the electrons impinge upon or bombard the anode11. The electron spot25has a size and location on the anode11.

The x-ray sources10and20can include control devices comprising a beam control device16and a flux control device17. The control devices16and17can be disposed between the electron emitter13and the anode11. The beam control device16can be used to control electron beam26trajectory and/or width (and thus also electron spot25location and/or size on the anode11). Normally, the flux control device17will be disposed between the beam control device16and the electron emitter13, but the opposite configuration is within the scope of this invention. The flux control device17can be used for control of electron beam26flux within the x-ray tube1. The flux control device17and/or the beam control device16can be made of electrically conducting materials such as metal, a semiconductor material doped to achieve a desired level of conductivity, or other types of conductors such as carbon. The electron emitter13can be configured to emit electrons through the control devices towards the anode11.

There can be a gap8between one of the control devices (beam control device16and/or flux control device17) and the electron emitter13. There can be a gap6between one of the control devices (beam control device16and/or flux control device17) and the anode11. There can be a gap7between the flux control device17and the beam control device16(if both a beam control device16and a flux control device17are used). The gaps6,7, and8can allow each of the electron emitter13, the beam control device16, the flux control device17, and the anode11, to be operated at different voltages relative to each other.

A detector4and a lens3can be disposed in a position to receive electromagnetic radiation18from the anode11. The electromagnetic radiation18can pass in a single straight-line path from the anode11to the detector4. The electromagnetic radiation18from the anode11can be emitted from an x-ray window24portion of the anode, as shown inFIG. 1. The detector4can face the anode11and the lens can be disposed between the detector and the anode. The detector4and the lens3can comprise components of a camera2. The anode11can emit electromagnetic radiation18through the lens3towards the detector4. The lens3can focus the electromagnetic radiation18onto the detector4, and the detector4can detect the electromagnetic radiation18. In one embodiment, the lens3can be a pinhole type of lens. In one embodiment, the pinhole can have a diameter d of between3to30micrometers. In another embodiment, the lens can be a focusing optic, such as a glass lens.

In one embodiment, the detector4and the lens3can be disposed at least partly within the substantially evacuated enclosure5of the x-ray tube1, and thus at least part of the detector4and the lens3can be subjected to vacuum, and can be subjected to substantially the same vacuum as the electron emitter13. In another embodiment, a detector window27can separate the lens3and detector4from the vacuum of the evacuated enclosure5. The detector window27can be designed to pass the type of electromagnetic radiation18detected by the detector4. Thus, the detector window27is optional. For clarity, shown inFIG. 11is x-ray source110, which is similar to x-ray source10inFIG. 1, but without the detector window27. Similarly, the detector window27may be removed from the side window x-ray source20shown inFIG. 2.

As shown inFIG. 10on x-ray source100, the detector4and lens3need not be attached to the enclosure5nor be part of the x-ray tube, but rather the camera2, detector4, and lens3can be a physically separate unit. In this embodiment, the electromagnetic radiation18focused by the lens3on the detector4can be the x-rays19emitted from the x-ray tube. AlthoughFIG. 10shows an end window transmission anode design, this type of design, in which the detector4and lens3are not part of the x-ray tube1, can also be used with a side window x-ray tube. In contrast, as shown inFIGS. 1-2, the detector4and lens3can be attached to the enclosure5and can be part of the x-ray tube.

Whether the detector4and the lens3are disposed at least partly within the substantially evacuated enclosure5and subjected to vacuum, or separated from the substantially evacuated enclosure5by a detector window27, or whether the detector4and the lens3are or are not part of the x-ray tube1, may depend on manufacturing considerations, product size constraints, material cost, and the effect of the substantially evacuated enclosure5vacuum on the detector4.

The electromagnetic radiation18emitted by the anode11, received by the detector4, and focused on the detector4by the lens3can be used to show electron spot25size and/or location on the anode11. The electromagnetic radiation18emitted through and focused by the lens3and received by the detector4can be various types of electromagnetic radiation18, including infrared light, visible light, ultraviolet light, and x-rays. The lens3can be configured to focus, and the detector4can be configured to detect, any of these types of electromagnetic radiation18.

The beam control device16can be electrically coupled to a control module15. The control module15can be electrically coupled to the detector4and can receive a signal69(FIG. 6) from the detector4. The signal69can be based on the electromagnetic radiation18emitted from the anode11onto the detector4and can indicate the electron spot25size and/or location where the electron beam26impinges on the anode11.

The signal69from the detector4can further indicate a temperature of the anode11. Typically the detector4would detect infrared radiation for determination of anode11temperature. The control module can then provide a temperature level output28. This temperature level output28can be displayed for an operator to see. The temperature level output28can also be used as an alert or alarm. If the anode11temperature at the electron spot25is too high, and thus the anode11is in danger of being damaged, then the electron spot25size can be increased, the electron spot location25can be changed, and/or the electron beam26flux can be reduced. The previous mentioned changes can be done automatically based on anode11temperature at the electron spot, or can be done with operator intervention.

The beam control device16can be a single electrically conductive plate, or multiple electrically conductive plates. The plate(s) can be disposed with a face thereof facing an axis14between the electron emitter13and the anode11, or approximate center of the electron beam26. Alternatively, a single plate with a hole for passage of the electron beam26may be used, with a face of the plate perpendicular to the axis14between the electron emitter13and the anode11, or approximate center of the electron beam26(typically used if electron spot25size control, but not electron spot25location control, is desired). Alternatively, the beam control device16can be separate metal wire segments. The beam control device16can be a coil of wire, or multiple separate coils of wire, instead of, or in conjunction with, the plate(s). An electric current through the wires can produce an electromagnetic field, which can be used for control of the electron beam26.

FIGS. 3-6, and the following description, further provide details of electron beam26control (and thus electron spot25size and/or location control) through use of the beam control device16. The control module15can provide a voltage63(FIG. 6) to the beam control device16, and can modify this voltage63to change a trajectory of the electron beam26based on the signal69from the detector4and an electron spot location setpoint61. There can be a single electron spot location setpoint61for the life of the x-ray source, for maintaining a constant electron spot location in spite of changes in environment or rough handling of the x-ray source. Alternatively, the electron spot location setpoint61can be changed based on x-ray source time of operation (e.g. total time of operation at that electron spot location), amount of x-ray19flux (e.g. sum total x-ray flux at that electron spot location), operator input, and/or anode11temperature (see65inFIG. 6). Changing the electron spot location setpoint61can allow for optimum use of the anode11, by allowing a change of electron spot25from one location to another as the anode11target material wears out in the prior location. Changing the electron spot location setpoint61can allow for diversity of use of the x-ray source, such as if one region of the anode11has one thickness and/or material, and another region has a different thickness and/or material.

A beam control device16made of a single segment may be used, such as a plate with a hole in the center, but such a device might not provide the desired control of electron beam26trajectory. A beam control device16made of a single segment, disposed on one side of the electron beam26may provide some control of electron beam26trajectory, but multiple segments may provide better control. Multiple beam control segments16a-d,with the ability of the control module15to send a different voltage to each, used for controlling electron beam26trajectory, are shown inFIGS. 3-5. The individual segments can be electrically isolated from each other, and thus each segment can have a different voltage from other segments.

As shown inFIG. 3, the beam control device16can include two separate segments16a-b.The two separate segments16a-bcan be disposed on opposite sides of an axis14between the electron emitter13and the anode11, or approximate center of the electron beam26. The control module15can send a different voltage to each segment16a-b(through wires21) to cause the electron beam26to shift one direction or another for control of electron beam26trajectory, and thus of electron spot25location, and ultimately x-ray19spot location.

As shown inFIG. 4, the beam control device16can include three separate segments16a-c,which can be disposed substantially uniformly around the axis14or approximate center of the electron beam26. The control module15can send a different voltage to at least one segment16a-c(through wires21) relative to at least one of the other segments to cause the electron beam26to shift one direction or another for control of electron beam26trajectory, and thus for control of electron spot25location, and ultimately for control of x-ray19spot location. Three beam control devices16a-ccan provide control in more directions, and thus achieve better overall control, than two beam control devices16a-b.

As shown inFIG. 5, the beam control device16can include four separate segments16a-dwhich can be disposed substantially uniformly around the axis14or approximate center of the electron beam26. The control module15can send a different voltage to at least one segment16a-d(through wires21) relative to at least one other of the segments16a-dto cause the electron beam26to shift one direction or another for control of electron beam26trajectory, and thus for control of electron spot25location, and ultimately for control of x-ray19spot location. Four beam control segments16a-dcan provide control in more directions, and thus achieve better overall control, than three beam control segments16a-b.

More than four beam control segments can be used for improved beam control, but circuitry can be more complicated, in order have the ability to provide a separate voltage to the various segments of the beam control device16. Also, manufacturing may be more complicated with more segments of the beam control device16. These issues may be considered in determining the number of segments of the beam control device16for a particular design. The control module15can provide a voltage63to the beam control device16, and can modify this voltage63to change a diameter D of the electron beam26based on the signal69from the detector4and an electron spot size setpoint62. The electron spot size setpoint62can be modified by various ways such as by operator input64and/or anode temperature. Thus, if the detector4and the control module15show that the electron spot25size out of the range of the electron spot size setpoint62, the electron spot25size can be modified by the control module15making the beam control device16voltage63relatively more negative or relatively more positive. If the voltage change causes the spot size to go in the wrong direction, as indicated the by signal69from the detector4, then the control module15can cause the voltage63to change in the opposite direction (relatively more positive or relatively more negative). Thus, the electron spot25size can be controlled by the signal69from the detector4to the control module15and by the control module15modifying the voltage63to the beam control device16.

Unlike changing voltage for electron beam26trajectory control, in which control can be performed by a relative difference of voltage of one beam control device16with respect to another, all beam control devices16can have a uniform increase or decrease in voltage for electron spot25size control. If only a single beam control device16is used, such as a hole in a plate for example, then the voltage of this plate can be increased or decreased for electron spot25size control.

Control of electron beam26trajectory and of electron spot25size may be accomplished simultaneously, by raising or lowering the voltage63of one or some segment(s) of the beam control device16with respect to other segment(s) of the beam control device16for trajectory control, and also raising or lowering the voltage63of all segments of the beam control device16uniformly for electron spot25size control. Thus, the control module15can control voltage63to the beam control device16, which can control electron beam26trajectory and/or diameter (see66inFIG. 6), which can control electron spot location and/or size on the anode target (see67inFIG. 6), which can control x-ray spot location and/or size (see68inFIG. 6).

The x-ray sources described herein, with feedback of electron spot25size, can be used to produce very small, and tightly controlled, electron spot25sizes on the anode11, and thus very small x-ray19spot sizes. This can be accomplished by use of feedback from the detector4indicating actual electron spot25size, which can be used to control the electron spot25size within relatively tight tolerances. The x-ray sources described herein can produce and tightly control an x-ray19spot size of between 20 to 80 micrometers in one embodiment or between 5 and 100 micrometers in another embodiment. The x-ray sources described herein can also produce and tightly control other x-ray spot sizes.

As illustrated inFIGS. 1,2,7,10, and11, the flux control device17can be electrically coupled to the control module15. The control module15can provide a voltage73to the flux control device17based on a flux setpoint71. The flux setpoint71can be an electron beam26flux setpoint or an x-ray19flux setpoint. The control module15can receive a measurement of present electron beam26flux (measured flux72) such as by, for example, measuring electrical current through a high voltage multiplier used for providing high negative voltage to the electron emitter13or by measuring electrical current between the anode11and ground. Such measurements can show the electrical current between the electron emitter13and the anode11through the x-ray tube1, and can be defined as measured electron beam26flux. Alternatively, the control module15can receive a measurement of present x-ray19flux (measured x-ray19flux), by measuring x-ray19flux output from the x-ray source, such as with an x-ray detector, for example. The measured electron beam26flux and/or the measured x-ray19flux is referred to as “measured flux”72inFIG. 72. The control module15can then modify the voltage73to the flux control device17based on the measured flux72and the flux setpoint71. In one embodiment, the flux setpoint71can be modified or set based on input from operator and/or anode temperature (see74inFIG. 7).

If the measured flux72is too high relative to the flux setpoint71(measured flux72>flux setpoint71), the control module15can cause the voltage73on the flux control device17to become relatively more negative, which can reduce electron beam26flux and consequently also reduce x-ray19flux. If the measured flux72is too low relative to the flux setpoint71(measured flux72<flux setpoint71), the control module15can cause the voltage73on the flux control device17to become relatively more positive, which can increase electron beam26flux and consequently also increase x-ray19flux. Thus, the control module15can control voltage73to the flux control device17, which can control electron beam flux (see76inFIG. 7), which can control x-ray flux (see78inFIG. 7).

In one embodiment in which the x-ray source includes both a beam control device16and a flux control device17, the control module15can provide a voltage to the flux control device17that is more negative than a voltage at the electron emitter13and a voltage to the beam control device16that may be more positive than, or less positive than, a voltage at the electron emitter13.

In one embodiment, the control module15can be capable of, or configured for, some or all of the following:1. providing a voltage63to the beam control device16;2. receiving a signal69from the detector4based on the electromagnetic radiation18emitted from the anode11onto the detector4, the signal69indicating an electron spot25size and/or an electron spot25location where the electron beam26impinges on the anode11;3. modifying the voltage63to the beam control device16to change a trajectory of the electron beam26based on the signal69from the detector4and an electron spot location setpoint61;4. modifying the voltage63to the beam control device16to change a diameter D of the electron beam26based on the signal69from the detector4and an electron spot size setpoint62;5. providing a voltage73to the flux control device17;6. receiving a measurement of present electron beam flux or x-ray flux (“measured flux”)72; and7. modifying the voltage73to the flux control device17based on the measured flux72and a flux setpoint71.

The various embodiments described herein can be used with a transmission window x-ray tube, as shown inFIGS. 1,10, and11, in which x-rays19are emitted from the x-ray tube1through the an x-ray window24portion of the anode11in substantially the same direction as electrons travel in the electron beam26within the x-ray tube1. The various embodiments described herein can also be used with a reflection/side window x-ray tube, as shown inFIG. 2, in which in which x-rays19are emitted from the anode11through a portion of the substantially evacuated enclosure5and then out through an x-ray window24. The emitted x-rays19can be emitted primarily in a direction different from the direction electrons travel in the electron beam26within the x-ray tube1.

Method

A method80for control of an electron beam26within an x-ray tube1can be used for control of electron spot25size and/or location on the anode11, by controlling the electron beam26. As shown inFIG. 8, the method80can comprise some or all of the following:81. Sending an electron beam26within the x-ray tube1from an electron emitter13to an anode11, the electron beam26forming an electron spot25on the anode11.82. Emitting electromagnetic radiation18from the anode11, the electromagnetic radiation18caused by the electron beam26impinging on the anode11. The electromagnetic radiation18can emit from an x-ray window24portion of the anode11.83. Focusing the electromagnetic radiation18emitted from the anode11onto a detector4. The electromagnetic radiation18can transmit solely within the evacuated enclosure from the anode to the detector.84. Sending a signal69, based on the electromagnetic radiation18focused on the detector4, from the detector4to a control module15, the signal69indicating an electron spot25size and/or location and/or anode11temperature at the electron spot25location.85. Changing a diameter of the electron beam26within the x-ray tube1based on the signal69and an electron spot size setpoint62and/or changing a trajectory of the electron beam26based on the signal69and an electron spot location setpoint61and/or providing a temperature level output28based on the signal69.86. Modifying the trajectory of the electron beam26can further include individually changing voltages of multiple, separate segments of a beam control device16, the multiple, separate segments being disposed substantially uniformly around an axis14between the electron emitter13and the anode11.

As shown inFIG. 9, a method90for control of an electron beam26flux within an x-ray tube1can comprise some or all of the following:91. Sending an electron beam26within the x-ray tube1from an electron emitter13to an anode11, the electron beam26forming an electron spot25on the anode11.92. Emitting electromagnetic radiation18from the anode11, the electromagnetic radiation18caused by the electron beam26impinging on the anode11. The electromagnetic radiation18can emit from an x-ray window24portion of the anode11.93. Receiving a flux setpoint71(x-ray19flux setpoint or electron beam26flux setpoint);94. Measuring actual flux (“measured flux”72, which can be x-ray19flux or electron beam26flux).95. Comparing the flux setpoint71to the measured flux72.96. Increasing or decreasing a voltage73to a flux control device17based on the comparison of the flux setpoint71to the measured flux72.