Electron-beam spot optimization

This application claims priority to U.S. Provisional Patent Application No. 62/325,007, filed on Apr. 20, 2016, which is incorporated herein by reference in its entirety.

The present application is related to x-ray sources.

Customers of x-ray tubes often desire consistency of shape, size, and location of x-ray emission for all x-ray tubes of a given model. This is especially important if the customer is replacing an x-ray tube on an instrument that is already optimized for emitting x-rays to a specific location. The shape, size, and location of x-ray emission is determined by an electron-beam spot on a target material inside of the x-ray tube. Due to variation in the manufacturing process, each x-ray tube of a given model can have a different electron-beam spot shape, size, and location. It would be beneficial to the customer to reduce this variation between x-ray tubes of a given model.

It has been recognized that it would be advantageous to reduce variation between x-ray tubes of a given model. The present invention is directed to methods of tuning an electron-beam spot on a target material in an x-ray tube, and various embodiments of x-ray sources, that satisfy these needs. Each embodiment may satisfy one, some, or all of these needs.

The method can comprise (1) energizing the x-ray tube to cause: (a) emission of electrons from an electron-emitter to the target material; (b) creating an electron-beam spot where the electrons impinge on the target material; and (c) emission of x-rays from the target material; (2) evaluating the electron-beam spot with respect to a predetermined characteristic; and (3) moving a focusing-ring along a longitudinal-axis of the x-ray tube to tune the electron-beam spot to the predetermined characteristic, the longitudinal-axis extending from the electron-emitter inside the x-ray tube to the target material.

The x-ray source can include an x-ray tube and a focusing-ring. The focusing-ring can at least partially encircle portions of the x-ray tube, such as for example all or part of the electron-emitter, the cathode, the evacuated-enclosure, or combinations thereof. The focusing-ring can be located outside of a vacuum of the evacuated enclosure. The focusing-ring can adjust an electron-beam spot, on a target material on an anode of the x-ray tube, when moved along a longitudinal-axis extending linearly from the electron-emitter to the target material.

FIG. 1 is a schematic, cross-sectional side-view of an x-ray source including a transmission-target x-ray tube 10 , a focusing-ring 13 , and a power supply 37 , in accordance with an embodiment of the present invention.

FIG. 2 is a schematic side-view of the x-ray tube 10 and focusing-ring 13 of FIG. 1 , in accordance with an embodiment of the present invention.

FIG. 3 is a schematic, cross-sectional side-view of an x-ray source including a side-window x-ray tube 30 , a focusing-ring 13 , and a power supply 37 , in accordance with an embodiment of the present invention.

As illustrated in FIGS. 1-3 , x-ray sources are shown including x-ray tubes 10 and 30 , a focusing-ring 13 , and a power supply 37 . The x-ray tubes 10 and 30 can include an anode 18 and a cathode 12 . The anode 18 can be electrically-conductive and can include a target material 38 configured for production and emission of x-rays 34 in response to impinging electrons. The cathode 12 can be electrically-conductive and can include an electron-emitter 14 capable of emitting electrons to the target material 38 on or in the anode 18 , forming an electron-beam spot 33 on the anode 18 . An evacuated-enclosure 11 can be attached to the cathode 12 and the anode 18 and can electrically-insulate the cathode 12 from the anode 18 . Examples of materials of the evacuated-enclosure 11 include ceramic and glass.

As shown in FIG. 1 , the target material can be on or in an x-ray window 16 part of the anode 18 of a transmission-target x-ray tube 10 ; and x-rays 34 , formed in the target material 38 in response to impinging electrons, can transmit through the x-ray window 16 and out of the x-ray tube 10 . As shown in FIG. 3 , the target material 38 can be on or in the anode 18 , but separate from the x-ray window 16 , of a side-window x-ray tube 30 ; and x-rays 34 , formed in the target material 38 in response to impinging electrons, can transmit through a hollow core 19 inside of the evacuated enclosure 11 to and through the x-ray window 16 and out of the x-ray tube 10 . The x-ray window 16 of x-ray tubes 10 and 30 can include some or all of the properties (e.g. low deflection, high x-ray transmissivity, low visible and infrared light transmissivity) of the x-ray windows described in U.S. patent application Ser. No. 14/597,955, filed on Jan. 15, 2015, which is incorporated herein by reference in its entirety.

The x-ray sources can each include a focusing-ring 13 , for tuning the electron-beam spot 33 to a predetermined characteristic (e.g. electron-beam spot 33 size, electron-beam spot 33 shape, electron-beam spot 33 location, or combinations thereof). The focusing-ring 13 can partially or completely encircle the electron-emitter 14 , the cathode 12 , the evacuated-enclosure 11 , or combinations thereof, and can encircle such along a longitudinal-axis 15 of the x-ray tube 10 or 30 . The longitudinal-axis 15 can extend linearly from the electron-emitter 14 to the target material 38 . The focusing-ring 13 can tune the electron-beam spot 33 by moving 36 the focusing-ring 13 along the longitudinal-axis 15 .

A relative-motion means can control motion of the focusing-ring 13 with respect to the electron-emitter 14 . For example, the relative-motion means can be mating threads 22 between an interior of the focusing-ring 13 and an exterior of the x-ray tube 10 or 30 ; and the mating threads 22 on the exterior of the x-ray tube 10 or 30 can be on an exterior of the cathode 12 , the evacuated-enclosure 11 , or both. The mating threads 22 at an interior of the focusing-ring 13 can extend for various distances, depending on how much adjustment is needed. For example, the inner-threads of the focusing-ring 13 can extend for a distance d of between 5 millimeters and 40 millimeters in a direction parallel to the longitudinal-axis 15 . Other examples of relative-motion means include rack and pinion 23 , a piston, and human-pressure (e.g. changing the position of the focusing-ring 13 by hand-pressure).

Once the focusing-ring 13 is optimally located for desired electron-beam spot 33 size, shape, and location, it can be immovably fastened onto the x-ray tube 10 or 30 . For example, the focusing-ring 13 can be immovably fastened by an adhesive, a set screw 24 , a weld or solder 26 , a clamp 28 , press-fit, a connector 29 , or combinations thereof.

The focusing-ring 13 can be located outside of a vacuum of the evacuated enclosure 11 , which can result in one or more of the following benefits: (a) easier selection of materials for the focusing-ring 13 (some materials may be incompatible with the vacuum, due to outgassing or other issues); (b) the position of the focusing-ring 13 can be adjusted after forming the vacuum and without affecting the vacuum, thus allowing tuning the electron-beam spot 33 after sealing the x-ray tube 10 or 30 ; and (c) the evacuated-enclosure 11 can be smaller, allowing the x-ray tubes 10 or 30 to be inserted into smaller locations and reducing the cost of the evacuated-enclosure 11 . The vacuum can be located at a hollow core 19 inside of the evacuated enclosure 11 .

The focusing-ring 13 can have various sizes, for optimal tuning the electron-beam spot 33 . For example, an inner-diameter D of the focusing-ring 13 can be at least 4 millimeters in one aspect, at least 8 millimeters in another aspect, or at least 16 millimeters in another aspect; and less than 30 millimeters in one aspect, less than 60 millimeters in another aspect, or less than 150 millimeters in another aspect. The focusing-ring 13 can be electrically-conductive and can be metallic, for optimal tuning the electron-beam spot 33 .

The x-ray source can further comprise a power supply 37 . The power supply 37 can provide a voltage differential (e.g. many kilovolts) between the electron-emitter 14 and the anode 18 and can provide electrical current to heat a filament if a filament is used as the electron-emitter 14 .

The focusing-ring 13 can be electrically-coupled to the cathode 12 (see FIG. 1 ), and thus have the same voltage as the cathode 12 . For example, electrical connector 37 c1 can be electrically-coupled to the cathode 12 , electrical connector 37 c2 can be electrically-insulated from the cathode 12 , thus allowing electrical current to flow through the electron-emitter 14 (if a filament is used), and the focusing-ring 13 can have the same voltage as electrical connector 37 c1 . Electrical connector 37 a can provide electrical voltage to the anode 18 .

Alternatively, the focusing-ring 13 can be electrically-insulated from the cathode 12 (see FIG. 3 ), such as for example by the evacuated-enclosure 11 , and the power supply 37 can provide a separate voltage to the focusing-ring 13 (e.g. via electrical connector 37 fr ). For example, the power supply 37 can be configured to maintain a voltage between the focusing-ring 13 and the cathode 12 of between 10 volts and 500 volts. Each of these two options ( FIG. 1 or FIG. 2 ) has its advantages and disadvantages, and each may be preferable for specific x-ray source designs.

Method

A method of tuning an electron-beam spot 33 on a target material 38 in an x-ray tube 10 or 30 can comprise some or all of the following steps, which can be performed in the order specified. The x-ray tube 10 or 30 can include characteristics as described above.

1. Energizing the x-ray tube 10 or 30 to cause:

a. emission of electrons from an electron-emitter 14 to the target material 38 ; b. creation of an electron-beam spot 33 where the electrons impinge on the target material 38 ; and c. emission of x-rays 34 from the target material 38 .

2. Evaluating the electron-beam spot 33 with respect to predetermined characteristic(s). Examples of the predetermined characteristic(s) include one or more of the following: electron-beam spot 33 size, electron-beam spot 33 shape, and electron-beam spot 33 location. The evaluation can be accomplished by receiving the x-rays 34 into a detector 35 (e.g. CCD image sensor), the detector 35 determining actual characteristic(s) of the electron-beam spot 33 , then the detector 35 comparing actual characteristic(s) to the predetermined characteristic(s). Alternatively, the comparison of actual characteristic(s) to the predetermined characteristic(s) can be performed manually. 3. Moving a focusing-ring 13 along a longitudinal-axis 15 of the x-ray tube 10 or 30 to tune the electron-beam spot 33 to the predetermined characteristic(s). The longitudinal-axis 15 can extend from the electron-emitter 14 inside the x-ray tube to the target material 38 on/in the anode 18 . The movement can be done manually, or automatically by a computer. Moving can include threading the focusing-ring 13 on inner-threads of the focusing-ring 13 that mate with outer-threads on the x-ray tube, or other relative-motion means (see description above). 4. Repeat steps 2 and 3 until the actual characteristic(s) are sufficiently close to the predetermined characteristic(s). 5. Immovably fastening the focusing-ring 13 with respect to the electron-emitter 14 . This can include one or more of the following:

a. Inserting an adhesive into a gap 25 between the focusing-ring 13 and the x-ray tube 10 or 30 . b. Tightening a set screw 24 in the focusing-ring 13 against the x-ray tube 10 or 30 . c. Welding and/or soldering 26 the focusing-ring 13 onto the x-ray tube 10 or 30 . d. Clamping the focusing-ring 13 onto the x-ray tube 10 or 30 (see clamp 28 in FIG. 2 ). e. Pinching the focusing-ring 13 shut against the x-ray tube 10 or 30 . This can be accomplished by starting with a focusing-ring 13 that is a tube with a slotted opening or gap 27 along its length. Pressure can be applied to the focusing-ring 13 to partially or totally close the opening or gap 27 and thus press the focusing-ring 13 against the x-ray tube 10 or 30 . f. Using a connector 29 to fasten the focusing-ring 13 to the x-ray tube 10 or 30 . g. Press fit/friction fit/interference fit 31 between an interior of the focusing-ring 13 and an exterior of the x-ray tube 10 or 30 .

Repeating this procedure with each x-ray tube of a given model, and using the same predetermined characteristic(s) for each (e.g. electron-beam spot 33 size, shape, and/or location), can reduce variation between x-ray tubes of that model.