X-ray tube with stabilized electron beam
By introducing field forming cups and low Z layers into the x-ray tube, the electron beam instability problem is solved, the stability of x-ray flux is achieved, and the equipment weight and cost are reduced.
Patent Information
- Application Number
- CN202411100498.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-08-16
- Filing Date
- 2024-08-12
- Publication Date
- 2025-02-21
AI Technical Summary
The electron beam instability in the x-ray tube causes the x-ray flux to be unstable, the size and shape of the electron spot at the target change, and the electron beam current is variable, which in turn causes problems to the user.
The field-forming cup and a low Z layer are introduced in the x-ray tube, located inside the second shell, and the low Z layer is made of a relatively low atomic number material covering the side of the barrier disc facing the cathode.
Through the combination of the field forming cup and low Z layer, the electron beam is effectively stabilized, electron rebound and backscattering are reduced, the weight and cost of the x-ray tube are reduced, and the performance of the x-ray tube is improved.
Smart Images
Figure CN119495540A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to x-ray sources. Background Art
[0002] X-rays have many uses, including imaging, X-ray fluorescence analysis, X-ray diffraction analysis, and static dissipation.
[0003] A high voltage between the cathode and anode of an x-ray tube, and sometimes a heated filament, causes electrons to be emitted from the cathode to the anode. The anode may include a target material. The target material may generate x-rays in response to electrons striking the cathode.
[0004] BRIEF DESCRIPTION OF THE DRAWINGS (Drawings may not be drawn to scale)
[0005] Figure 1 is a cross-sectional side view of an x-ray tube 10 having a cathode 15 and an anode 16 insulated from each other by a first housing 11 and a second housing 12. A blocking disk 13 may be located at a joint 14 between the first housing 11 and the second housing 12.
[0006] Figure 2 is a cross-sectional side view of an x-ray tube 20 having the features of the x-ray tube 10 , with the addition of a field shaping cup 22 at least partially located within the second housing 12 .
[0007] Figure 3 is a cross-sectional side view of an x-ray tube 30 having the features of the x-ray tube 10 , with the addition of a low-Z layer 21 on the side of the baffle disk 13 facing the cathode 15 .
[0008] Figure 4 is a cross-sectional side view of an x-ray tube 40 having features of x-ray tubes 20 and 30 combined.
[0009] Definitions The following definitions, including their pluralities, apply throughout this patent application.
[0010] As used herein, the terms "on," "on," "at," and "over" mean directly on or above (with some other solid material in between). The terms "directly on," "adjacent," "adjacent," and "adjoining" mean in direct and immediate contact, or with only an adhesive or braze between these structures.
[0011] As used herein, the term "parallel" means perfectly parallel; parallel within normal manufacturing tolerances; or nearly perfectly parallel such that any deviation from perfectly parallel has a negligible effect on everyday use of the device.
[0012] The term "x-ray tube" as used herein is not limited to tubular / cylindrical devices. The term "tube" is used because this is the standard term for x-ray emitting devices. DETAILED DESCRIPTION
[0013] In an x-ray tube, a high voltage between the cathode and anode, and sometimes a heated filament, causes electrons to be emitted from the cathode to the anode. These electrons can strike a target at the anode, producing x-rays.
[0014] If the electron beam is unstable, then the x-ray flux will also be unstable. Electron beam instability can cause the size and shape of the electron spot at the target to shift or change. Electron beam instability can also cause variable electron beam current. Variable electron spot size or shape and variable electron beam current can cause problems for x-ray tube users. A stable electron beam, and the resulting stable x-ray beam, are useful features of an x-ray tube.
[0015] Some electrons may hit the target but fail to produce x-rays and then bounce back or backscatter. These backscattered electrons may collect on electrically insulating surfaces inside the x-ray tube. For example, these backscattered electrons may collect on the inner surface of the ceramic cylinder that insulates the cathode from the anode. This electron accumulation can cause electron beam instability and / or early arc failure of the x-ray tube. It would be beneficial to reduce such electrons on electrically insulating surfaces.
[0016] Some x-ray tubes are portable. The greater weight of the x-ray tube can cause stress to the user and is an ergonomic disadvantage. The x-ray tube needs to be shielded from x-rays emitted in undesired directions. High-density material is often used for this shielding, and therefore it can be heavy. Reducing the mass of this shielding material would be useful.
[0017] An x-ray tube may have (a) a negatively charged cathode and a grounded anode; (b) a positively charged anode and a grounded cathode; or (c) a negatively charged cathode, a positively charged anode, and a grounded center region. X-ray tube type (c) is known as a bipolar x-ray tube and is used with very high voltages between the cathode and anode. Bipolar x-ray tubes are particularly susceptible to electron beam and x-ray beam instabilities. The present invention is particularly useful for bipolar x-ray tubes.
[0018] Figure 1 1 shows a bipolar x-ray tube 10 having a cathode 15 and an anode 16. The cathode 15 may include an electron emitter 15e (e.g., a filament) configured to emit electrons toward the anode 16. The anode 16 may include a target 17 configured to emit x-rays out of the x-ray tube 10 in response to striking electrons from the cathode 15.
[0019] The first housing 11 and the second housing 12 may be located between the cathode 15 and the anode 16. The first housing 11 may be closer to the cathode 15 than the second housing 12. The first housing 11 may abut the cathode 15. The second housing 12 may be closer to the anode 16 than the first housing 11. The second housing 12 may abut the anode 16. The first housing 11 and the second housing 12 may be electrically insulated and may electrically insulate the cathode 15 from the anode 16. Example materials for the first housing 11 and the second housing 12 include ceramics and glass.
[0020] The blocking disk 13 may be located between the cathode 11 and the anode 16. The blocking disk 13 may be separated from and electrically insulated from the cathode 11 and the anode 16. The blocking disk 13 may be located at a joint 14 between the first housing 11 and the second housing 12. The blocking disk 13 may be located between the first housing 11 and the second housing 12. The blocking disk 13 may be surrounded by the first housing 11. The blocking disk 13 may be conductive. The blocking disk 13 may have a hole 13a.
[0021] The cathode 15 may receive a large negative voltage from a power supply. The anode 16 may receive a large positive voltage from a power supply. The blocking disk 13 may be grounded. The X-ray tube 10 may be a bipolar X-ray tube.
[0022] A vacuum may be contained in the hollow area 11h of the first housing 11, the hole 13a of the blocking disk 13, and the hollow area 12h of the second housing 12. These hollow areas 11h, 13a, and 12h may be connected and continuous. Therefore, they may be combined to form a single hollow area.
[0023] The hollow area 11h of the first housing 11, the hole 13a of the blocking disk 13, and the hollow area 12h of the second housing 12 may provide a path 19 for the electron beam to go from the electron emitter 15e to the target 17. The path 19 may be a straight line from the electron emitter 15e to the target 17. The path 19 may pass completely through the hollow area without intersecting any solid material.
[0024] The blocking disk 13 may close off substantially all of the hollow region 11h of the first housing 11, except for the hole 13a passing through the blocking disk 13. The blocking disk 13 may be configured to substantially block and prevent x-rays generated at the target 17 from being transmitted or backscattered into the hollow region 11h in the first housing 11, except for passing through the hole 13a. The blocking disk 13 may be made of a material having a high atomic number and may have a sufficient thickness to block such x-rays. For example, the blocking disk 13 may be 4 mm thick and may be made of tungsten (e.g., tungsten with a weight percentage of ≥90%).
[0025] Although the above described x-ray tube 10 is useful, it is subject to electron beam and x-ray beam instabilities. Some electrons may bounce or backscatter from the target 17 without losing all of their energy. Some of these bounced electrons may gather at the triple junction 12c on the second housing 12, near the junction of the second housing 12, the internal vacuum of the x-ray tube 10, and the baffle disk 13. Due to the low electric field strength at the triple junction 12c, these electrons gather at the triple junction 12c. . These gathered electrons can cause the electron beam to fluctuate and become unstable.
[0026] As described below and in Figure 2 The additional features in the x-ray tube 20 shown in Figure 1 help overcome this electron beam instability. The x-ray tube 20 can include all of the features of the x-ray tube 10. The x-ray tube 20 can also include a field shaping cup 22 at least partially located inside the second housing 12. The path 19 of the electron beam can pass through a hole 22h in the bottom 22b of the field shaping cup 22.
[0027] The field shaping cup 22 may be electrically conductive. Thus, the field shaping cup 22 may provide an electrically conductive material and path for removing electrons that strike the triple junction 12c, thereby stabilizing the electron beam.
[0028] The field shaping cup 22 may include a cup wall 22w extending from the cup bottom 22b. The cup wall 22w may extend into the hollow region 12h of the second housing 12. All or nearly all of the cup wall 22w may extend into the hollow region 12h of the second housing 12 to facilitate the manufacture of the x-ray tube. For example, ≥80%, ≥90%, or ≥95% of the cup wall 22w may extend into the hollow region 12h of the second housing 12.
[0029] The cup wall 22w may cover or extend into less than half of the second housing 12. For example, 0.1≤L1 / L2≤0.25, where L1 is the length of the cup wall 22w and L2 is the length from the hole 22h in the cup bottom 22b to the target 17, and both lengths L1 and L2 are measured parallel to the path 19. This range balances the competing needs of providing sufficient distance for high voltage isolation and providing sufficient protection for the triple junction 12c.
[0030] The cup bottom 22b may abut the blocking disk 13, the second housing 12, or both. The cup wall 22w may be spaced from the inner surface 12i of the second housing 12 to facilitate evacuation of air from that area and allow easier insertion of the field shaping cup 22 into the second housing 12.
[0031] The field shaping cup 22 may be electrically coupled to the blocking disk 13. The field shaping cup 22 may be integral or monolithic with the blocking disk 13. However, it is preferred that the field shaping cup 22 is manufactured separately from the blocking disk 13 and is made of a material different from that of the blocking disk 13. Although the blocking disk 13 is typically made of a very dense, high atomic number material, such as tungsten, for substantially blocking x-rays, the field shaping cup 22 may also be made of a less dense material to reduce the weight and cost of the x-ray tube. Exemplary materials for the construction of the field shaping cup 22 include iron, nickel, cobalt, or a combination thereof. Thus, the density of the field shaping cup 22 may be less than that of the blocking disk 13. Furthermore, the element with the highest atomic number of the field shaping cup 22 may be less than the element with the highest atomic number of the blocking disk 13.
[0032] There may be a small space around the circumference of the blocking disc 13 between the blocking disc 13 and the first housing 11 to allow the blocking disc 13 to be inserted into the inside of the first housing 11. Therefore, the blocking disc 13 may be surrounded by the first housing 11.
[0033] Another source of x-ray beam instability in the x-ray tube 10 is electrons bouncing back into the hollow region 11h of the first housing 11. These electrons can then be repelled by the negative voltage at the cathode 15. These repelled electrons are not focused but are scattered. Many of these electrons can strike the blocking disk 13, where they either generate x-rays or bounce back toward the first housing 11.
[0034] Most of these x-rays generated in the hollow region 11h of the first housing 11 are emitted in undesired directions. These x-rays generated in the blocking disk 13 will generally be high energy x-rays because the blocking disk 13 will generally include a high atomic number material, such as tungsten (Z=74). Dense material can be added around the first housing 11 to block these x-rays, but this material needs to be thick and dense to block these high energy x-rays. This will add considerable weight and cost to the x-ray tube.
[0035] The electrons that hit the blocking disk 13 and then bounce or backscatter to the first housing 11 may be accumulated on the inner surface 11i of the first housing 11. These electrons may cause the electron beam to vary and become unstable.
[0036] An additional feature in the x-ray tube 30 is described below and is Figure 3 As shown in FIG. 1 , this electron beam instability can be overcome. The problem of high-energy x-rays generated in the hollow region 11h of the first housing 11 and electrons gathered at the inner surface 11i of the first housing 11 can be minimized by adding a low-Z layer 21 on the side of the blocking disk 13 facing the electron emitter 15e. The low-Z layer 21 can be sputtered, welded or brazed on the blocking disk 13.
[0037] The low-Z layer 21 may have a material composition different from that of the blocking disk 13. The low-Z layer 21 may be made of a material that generates x-rays with relatively low energy, which are more easily blocked. The low-Z layer 21 may be made of a material that backscatters a smaller percentage of electrons.
[0038] For the low-Z layer 21, it may be helpful to select a material with a relatively low atomic number. For example, Z21 < Z13, where Z21 is the atomic number of the highest atomic number element in the low-Z layer 21, and Z13 is the atomic number of the highest atomic number element in the blocking disk 13. The following are example values of Z21 and Z13: Z13 ≥ 74, Z21 ≤ 29, Z21 < 42.
[0039] For example, the low-Z layer 21 may include titanium (Z = 22), carbon (Z = 6), chromium (Z = 24), or a combination thereof. Titanium backscatters approximately 35% of the incident electrons, while tungsten backscatters approximately 50%. In addition, the x-rays generated by titanium (Z = 22) have a lower energy than those generated by tungsten (Z = 74). The low-Z layer 21 may include iron (Z = 26), cobalt (Z = 27), nickel (Z = 28), or a combination thereof.
[0040] The low-Z layer 21 can achieve its intended benefits with a relatively thin layer. For example, the following is an example relationship between the thickness T13 of the blocking disk 13 and the thickness T21 of the low-Z layer 21: 10 ≤ T13 / T21, 100 ≤ T13 / T21, or 500 ≤ T13 / T21; and T13 / T21 ≤ 5000, T13 / T21 ≤ 10,000, or T13 / T21 ≤ 100,000. Both thicknesses T13 and T21 are measured parallel to the path 19.
[0041] The hole 21h passing through the low-Z layer 21 can be aligned with the path 19 of the electron beam and can be hollow. The low-Z layer 21 can be conductive. The low-Z layer 21 can completely cover the side of the blocking disk 13 facing the electron emitter 15e.
[0042] Figure 1-4 A transmission target x-ray tube is shown, where the target 17 is mounted on the x-ray window 18. The present invention is equally applicable to a reflection target / side window x-ray tube.
[0043] As Figure 2 shown, the field shaping cup 22 can be used without the low-Z layer 21. As Figure 3 shown, the low-Z layer 21 can be used without the field shaping cup 22. As Figure 4 shown, the field shaping cup 22 can be combined with the low-Z layer 21.
Claims
1. An X-ray tube, comprising: a cathode and an anode; the cathode includes an electron emitter configured to emit electrons toward the anode; the anode includes a target configured to emit X-rays out of the X-ray tube in response to electrons impinging from the cathode; electrically insulating first and second outer casings located between the cathode and the anode and electrically insulating the cathode from the anode; the first outer casing is closer to the cathode than the second outer casing, and the second outer casing is closer to the anode than the first outer casing; a conduction blocking disc having a hole located between the cathode and the anode and separated from and electrically insulated from the cathode and the anode; a hollow region within the first outer casing, the hole in the blocking disc, and a hollow region within the second outer casing provide a path for the electron beam from the electron emitter to the target; the blocking disc is configured to prevent X-rays generated at the target from penetrating into the hollow region within the first outer casing; a conductive field shaping cup extending into the hollow region of the second outer casing, the path of the electron beam passing through a hole in the bottom of the cup of the field shaping cup; a low-Z layer on a side of the blocking disc facing the electron emitter; a hole through the low-Z layer is aligned with the path of the electron beam; the material composition of the low-Z layer is different from the material composition of the blocking disc; and Z21 < Z13, where Z21 is the atomic number of the highest atomic number element in the low-Z layer, and Z13 is the atomic number of the highest atomic number element in the blocking disc.
2. The x-ray tube according to claim 1, characterized in that the field shaping cup includes a cup wall extending from the bottom of the cup, and 0.1 ≤ L1 / L2 ≤ 0.25, where L1 is the length of the cup wall, and L2 is the length from the hole in the bottom of the cup to the target, and the lengths L1 and L2 are both measured parallel to the path.
3. The x-ray tube according to claim 1, characterized in that the field shaping cup includes iron, nickel, and cobalt.
4. The x-ray tube according to claim 1, characterized in that the field shaping cup is electrically coupled to the blocking disc.
5. The x-ray tube according to claim 1, characterized in that the field shaping cup includes a cup wall extending from the bottom of the cup, and the bottom of the cup abuts the blocking disc and the second outer casing.
6. The x-ray tube according to claim 1, characterized in that the field shaping cup includes a cup wall extending from the bottom of the cup, and ≥ 80% of the cup wall extends into the hollow region of the second outer casing.
7. The x-ray tube according to claim 1, characterized in that the field shaping cup includes a cup wall extending from the bottom of the cup, and the cup wall is spaced apart from the inner surface of the second outer casing.
8. The x-ray tube according to claim 1, characterized in that 100 ≤ T13 / T21 ≤ 10000, where T13 is the thickness of the blocking disc, and T21 is the thickness of the low-Z layer, and the thicknesses T13 and T21 are both measured parallel to the path.
9. The x-ray tube according to claim 1, characterized in that the low-Z layer completely covers the side of the blocking disc facing the electron emitter.
10. The x-ray tube according to claim 1, characterized in that the low-Z layer includes iron, nickel, and cobalt.