Cold cathode microfocus X-ray tube based on double electrostatic lenses

Abstract

The invention discloses a cold cathode microfocus X-ray tube based on double electrostatic lenses, which belongs to the technical field of X-ray tubes, and comprises a shell, a window, an anode assembly and a cathode electron gun assembly, the anode assembly comprises an anode target; the cathode electron gun assembly comprises a cathode cylinder, and a cathode, a grid electrode, a first focusing electrode, a second focusing electrode, a third focusing electrode, an electrode core column, an electrode lead and a field emission material which are positioned in the cathode cylinder; the field emission material generates electrons under the action of field emission, the formed electron beams are converged for the first time under the action of the first electrostatic lens to form a first focus, are converged for the second time under the action of the second electrostatic lens to form a second focus, and finally bombard the anode target to generate X-rays. According to the X-ray tube, the convergence and compression capacity of electron beams is improved by forming the double electrostatic lenses, the size of a convergence focus is reduced under the condition that the emission area is not affected, and the resolution ratio of the X-ray tube is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of X-ray tubes, and in particular relates to a cold cathode micro-focus X-ray tube based on double electrostatic lenses. Background Art

[0002] With the increasing demand for non-destructive testing in modern industry, in order to meet various testing needs, X-ray tube technology also needs to continue to develop and progress, and the most important point is to improve the resolution of X-ray tubes. The cathode electron gun of the X-ray tube is equivalent to the engine of a car and is the core component of the X-ray tube. Its performance directly affects the resolution, working stability and service life of the X-ray tube.

[0003] Traditional X-ray tubes generally use hot cathode electron guns, which require direct or indirect heating to make the cathode reach a high temperature of thousands of degrees, and electrons are emitted from the cathode surface due to thermal motion. Existing hot cathodes have the defects of high operating temperature, low life, large energy loss, slow switching response, small current density, large focal spot size, low resolution and blurred images, and the detection accuracy is difficult to meet the requirements. In response to this, people have proposed a cold cathode electron gun with a completely different working principle from the hot cathode electron gun. Its working principle is specifically as follows: under the condition of a certain intensity of electric field, electrons escape from the cathode surface through the tunneling effect to achieve electron emission. The unique working principle of the cold cathode X-ray tube gives it advantages that hot cathode X-rays cannot achieve. Cold cathode X-ray tubes do not require high-temperature heating, and have the characteristics of low cathode temperature, more stable operation, low power consumption, long life, and higher current density. At the same time, it is also easy to achieve a smaller focal spot size and ultra-high resolution.

[0004] Existing cold cathode X-ray tubes use an electron gun structure with a single electrostatic focusing lens, which has limited ability to converge and compress the electron beam. In order to achieve a smaller focus, it is usually necessary to reduce the cathode electron emission area, but this will make the cathode load too high, significantly reduce the operating current of the X-ray tube, and also affect the service life and stability. Therefore, it is difficult for existing cold cathode X-ray tubes to achieve a smaller focus size while maintaining the emission area. Although large electron microscopes also use multiple electron lenses to form an electron optical system to enable the electron beam to achieve extremely high resolution, their main lenses usually use magnetic lenses, which have complex parts and large volumes, are difficult to miniaturize, and are very expensive, making them difficult to apply to existing micro-focus X-ray tubes. Summary of the invention

[0005] In view of the problems existing in the above-mentioned hot cathode X-ray tube and the existing microfocus X-ray tube electron gun, the present invention provides a cold cathode microfocus X-ray tube based on double electrostatic lenses, by compactly arranging a plurality of focusing electrodes, two electrostatic focusing lenses are sequentially formed in the electron beam running trajectory, and by controlling the electric field, two focal points corresponding to the electrostatic focusing lenses are sequentially formed in the electron beam running trajectory, so as to obtain a focal point size with a smaller compression ratio, thereby significantly improving the resolution of the cold cathode microfocus X-ray tube.

[0006] The technical solution adopted by the present invention is as follows: A cold cathode micro-focus X-ray tube based on a double electrostatic lens comprises a housing, a window located at the top of the housing, an anode assembly located below the window, and a cathode electron gun assembly connected to the housing; The anode assembly includes an anode target; The cathode electron gun assembly comprises a cathode tube, and a cathode located inside the cathode tube, a field emission material, a grid, a first focusing electrode, a second focusing electrode, a third focusing electrode, an electrode core column and an electrode lead; The cathode cylinder is connected to the outer shell, and the outer shell, the window and the cathode cylinder together form a sealed environment; The third focusing electrode is integrally arranged with the cathode tube; the electrode core column is located at the end of the cathode tube opposite to the third focusing electrode, and is connected to the grid, the first focusing electrode and the second focusing electrode through the electrode lead; the cathode, the grid, the first focusing electrode and the second focusing electrode are stacked in sequence, the second focusing electrode is located on one side of the third focusing electrode, and the cathode is connected to the cathode tube; the cathode and the third focusing electrode have the same potential, and a potential difference is formed between the grid, the first focusing electrode and the second focusing electrode; the field emission material is placed on a side of the cathode adjacent to the grid, and is in the electron emission region; the grid, the first focusing electrode, the second focusing electrode and the third focusing electrode are all provided with through holes in their centers, and the center of the through hole is coaxial with the center of the anode target.

[0007] Furthermore, the cathode electron gun assembly also includes a first insulating ring, a second insulating ring and a third insulating ring; wherein the first insulating ring is located between the cathode and the grid; the second insulating ring is located between the grid and the first focusing electrode; and the third insulating ring is located between the first focusing electrode and the second focusing electrode.

[0008] Furthermore, the cathode electron gun assembly further comprises electrode assemblies corresponding to the grid, the first focusing electrode and the second focusing electrode respectively, and each electrode assembly comprises an electrode screw and an insulating column; The cathode, the grid, the first focusing electrode and the second focusing electrode are all provided with through holes matching the electrode screws, and the cathode, the grid, the first focusing electrode and the second focusing electrode are electrically connected and fixed through the electrode screws passing through; the insulating column is sleeved on the electrode screws to isolate the electrode screws from the cathode; The electrode core column is connected to the corresponding grid, the first focusing electrode and the second focusing electrode through the electrode lead wire and the electrode screw in sequence.

[0009] Furthermore, the cathode, the grid, and the first focusing electrode together constitute a first electrostatic focusing lens, and the second focusing electrode, the third focusing electrode, and the anode assembly constitute a second electrostatic focusing lens.

[0010] Furthermore, the cathode includes a disk base and a boss located at the center of the disk base, the diameter and height of the boss are adjusted according to requirements, and the field emission material is located at the center of the boss.

[0011] Furthermore, a sunken step is provided inside the through hole of the cathode for limiting the position of the insulating column.

[0012] Furthermore, the structure of the grid is a disk with a sunken table in the middle, a first through hole is opened in the center of the sunken table, and the thickness of the sunken table is set to 100-350 μm.

[0013] Furthermore, the distance between the boss and the sunken table is 200-500 μm.

[0014] Furthermore, the structure of the first focusing electrode is a disk with a through hole in the center, and the through hole is specifically a circular hole with a diameter of 0.5-2 mm.

[0015] Furthermore, the first focusing electrode includes a hollow disc, a trapezoidal ring and a cylindrical bowl connected in sequence from top to bottom, together forming a trumpet-shaped structure opening upward; wherein a second through hole is opened at the center of the bottom surface of the cylindrical bowl; a step is provided at the junction of the trapezoidal ring and the cylindrical bowl for placing the open hole electrode; a third through hole is opened at the center of the open hole electrode; the cylindrical bowl is sunken into the sunken table of the grid, and the distance between the cylindrical bowl and the sunken table is 0.5~2 mm.

[0016] Furthermore, the structure of the second focusing electrode is a disk with a fourth through hole in the middle, the shape of the fourth through hole is circular or a first rectangle with an arc-shaped wide side, and the long straight side of the first rectangle is perpendicular to the concentric axis of the anode assembly.

[0017] Furthermore, the structure of the third focusing electrode is a disk with a fifth through hole in the middle.

[0018] Furthermore, the size of the fourth through hole of the second focusing electrode and the fifth through hole of the third focusing electrode is 10-20 mm.

[0019] Furthermore, the distance from the first focusing electrode to the third focusing electrode is the same as the distance from the third focusing electrode to the anode target, so as to form a more symmetrical lens structure.

[0020] Furthermore, the anode target is closely attached to the lower surface of the window, and the through-hole centers of the gate, the first focusing electrode, the second focusing electrode and the third focusing electrode are coaxial with the anode target center and the window center. At this time, the shape of the fifth through-hole is preferably circular.

[0021] Furthermore, the anode assembly further comprises an anode rod, an anode cover, an anode head, an anode cap and a calender tube coaxial with the center of the window, and the axis passes vertically through the window; wherein the bottom of the anode rod is connected to the shell, the anode cover is sleeved under the anode rod, the calender tube is sleeved at the bottom of the anode rod, the anode head is located at the top of the anode rod, and the anode cap is sleeved at the top of the anode head; the top surface of the anode head is an inclined surface, and the anode target is placed on the top surface of the anode head; a first opening is provided on the side of the anode cap, and a second opening is provided on the top, the center of which is colinear with the axis of the anode assembly; The centers of the through holes of the grid, the first focusing electrode, the second focusing electrode and the third focusing electrode are coaxial with the center of the first opening and the center of the anode target, and the axes are perpendicular to the axis of the anode assembly; At this time, the shape of the fifth through hole is preferably the second rectangle.

[0022] Furthermore, the cold cathode micro-focus X-ray tube based on dual electrostatic lenses also includes an exhaust pipe arranged on the side wall of the shell, and after exhausting through the exhaust pipe, the sealed environment is made into a high vacuum.

[0023] The working principle of the cold cathode micro-focus X-ray tube based on double electrostatic lenses proposed in the present invention is: A voltage is applied to the anode assembly to form an anode high-voltage electric field; the cathode and the third focusing electrode are grounded, and a voltage is applied to the grid, the first focusing electrode, and the second focusing electrode by using an electrode core column; the field emission material placed above the cathode generates electrons under the action of field emission; the electrons pass through the through hole in the center of the grid under the grid electric field to form an electron beam moving toward the anode assembly; the electron beam converges for the first time under the first electrostatic focusing lens formed by the cathode, the grid, and the first focusing electrode electric field to form a first focusing point, and then diverges; the electron beam continues to converge for the second time under the second electrostatic focusing lens formed by the second focusing electrode, the third focusing electrode, and the anode electric field, and forms a second focusing point on the anode target; the electron beam bombards the anode target under the acceleration of the anode electric field, and the anode target generates X-rays under the bombardment of the electron beam, and the X-rays are emitted through the second opening and the window.

[0024] By adjusting the spacing between the cathode, the grid, the first focusing electrode, the second focusing electrode, and the third focusing electrode, as well as the voltage applied to the first focusing electrode and the second focusing electrode, the focusing characteristics of the two electrostatic focusing lenses can be controlled and changed respectively, thereby controlling the focal position and size of the electron beam converged on the anode target.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a cold cathode micro-focus X-ray tube based on a double electrostatic lens, which adopts a plurality of focusing electrodes and is connected and fixed by an electrode screw. The cathode, the grid and the first focusing electrode together constitute the first electrostatic focusing lens, and the second focusing electrode, the third focusing electrode and the anode assembly constitute the second electrostatic focusing lens. A compact cold cathode electron gun assembly with two electrostatic focusing lenses is formed; after the electrons emitted by the cold cathode are accelerated by the grid electric field, a first focusing focus is formed under the action of the first electrostatic lens, which is located between the first focusing electrode and the aperture electrode. The cross-sectional area of ​​the first focusing point is much smaller than that of the cathode surface, and the divergence angle of the electron beam after being emitted from the first focusing point is greatly reduced, and the electron beam can enter the second electrostatic focusing lens at a smaller angle. The image point of the first electrostatic focusing lens is used as the object point of the second electrostatic focusing lens, and then a smaller second focusing point is formed under the action of the second electrostatic focusing lens, and the focusing effect of the second electrostatic focusing lens is greatly improved, so that an electron beam spot much smaller than that of the existing single electrostatic focusing lens micro-focus X-ray tube can be obtained, and the second focusing point is located on the anode target. The present invention adjusts the voltage applied to multiple focusing electrodes and the spacing between the cathode, the grid and the multiple focusing electrodes, so that the electron beam is focused in sequence during the movement to form two corresponding focal points, and a smaller convergence focus is achieved on the anode target; compared with the existing electron gun structure, the present invention can improve the convergence and compression capability of the electron beam, reduce the high requirements for the cathode emission current density, and further reduce the convergence focus size without increasing the size of the electron gun or affecting the emission area, so that the X-ray tube can achieve a higher resolution, and at the same time, the precision requirements for the electron gun parts are also reduced, and the difficulty of processing and assembly is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the overall structure of a cold cathode micro-focus X-ray tube based on double electrostatic lenses proposed in Example 1 of the present invention; Figure 2 is a schematic structural diagram of the anode assembly in Example 1 of the present invention; Figure 3 Schematic diagram of the structure of the anode cap in Example 1 of the present invention; Figure 4 This is a schematic diagram of the combined structure of the cathode electron gun assembly in Example 1 of the present invention; Figure 5 Schematic diagram of the disassembled structure of the cathode electron gun assembly in Example 1 of the present invention; wherein (a) is an appearance diagram; (b) is an exploded diagram; Figure 6 Schematic diagram of the cathode structure in Example 1 of the present invention; Figure 7 Schematic diagram of the structure of the gate in Embodiment 1 of the present invention; wherein (a) is a top view; (b) is a front view; Figure 8Schematic diagram of the structure of the horn-shaped first focusing electrode in Embodiment 1 of the present invention; wherein (a) is a top view; (b) is a front view; Fig. 9 Schematic diagram of the structure of the second focusing electrode in Embodiment 1 of the present invention; wherein (a) is a top view; (b) is a front view; Fig.10 Schematic diagram of the structure of the third focusing electrode in Embodiment 1 of the present invention; wherein (a) is a front view; (b) is a top view; Fig.11 Schematic diagram of the simulation trajectory of the dual-focusing electron beam of Example 1 of the present invention; wherein (a) is a schematic diagram of the electron beam trajectory; (b) is a diagram of the simulation result of the electron beam trajectory; Fig.12 Schematic diagram of the focal spot of the double-focusing electron beam according to Example 1 of the present invention; Fig.13 It is a schematic diagram of the single-focus electron beam simulation trajectory of Comparative Example 1; Fig.14 This is a schematic diagram of the overall structure of a cold cathode micro-focus X-ray tube based on a double electrostatic lens proposed in Example 2 of the present invention; Fig.15 Schematic diagram of the structure of the second focusing electrode in Embodiment 2 of the present invention; wherein (a) is a top view; (b) is a front view; Fig.16 Schematic diagram of the structure of the third focusing electrode in Embodiment 2 of the present invention; wherein (a) is a top view; (b) is a front view; The descriptions of the symbols in the accompanying drawings are as follows: 1-shell; 11-metal shell; 12-insulating shell; 13-large cutting ring; 14-small cutting ring; 15-exhaust pipe; 2-window; 3-anode assembly; 31-anode rod; 32-anode cover; 33-anode head; 34-anode cap; 35-anode target; 36-cutting tube; 341-first opening; 342-second opening; 343-cap body; 344-cap brim; 4-cathode electron gun assembly; 40-cathode tube; 41-cathode; 42-field emission material; 43-grid; 44-first focusing electrode; 45-second focusing electrode; 46-third focusing electrode; 47-electrode core column; 48-electrode lead; 49-electrode screw; 410-insulating column; 411-first insulating ring; 412-second insulating ring; 413-third insulating ring; 410 1-disc base; 4102-boss; 4103-cathode screw through hole; 4104-sunken step; 4105 cathode edge step; 4301-sunken table; 4302-first through hole; 4303-grid screw through hole; 4304-grid threaded hole; 4401-second through hole; 4402-hollow disk; 4403-trapezoidal ring; 4404-opening electrode; 4405-third through hole; 4406-cylindrical bowl; 4407-first focusing pole screw through hole; 4408-first focusing pole threaded hole; 4501-fourth through hole; 4502-arc-shaped wide edge; 4503-second focusing pole threaded hole; 4601-fifth through hole; 4111-first focusing point; 4112-second focusing point; 4113-electron beam waist. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and beneficial effects of the present invention more clear, the specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings.

[0028] It should be understood that the following specific embodiments are only used to enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0029] Example 1

[0030] This embodiment proposes a cold cathode micro-focus X-ray tube based on a double electrostatic lens, the overall structure of which is as follows: Figure 1 As shown, it includes a housing 1 , a window 2 located on the top of the housing 1 , an anode assembly 3 located inside the housing 1 , and a cathode electron gun assembly 4 and an exhaust pipe 15 located on the side wall of the housing 1 .

[0031] The shell 1 includes an upper metal shell 11, a lower insulating shell 12, a large felling ring 13 and a small felling ring 14; wherein the small felling ring 14 is located at the lower end of the insulating shell 12, and the large felling ring 13 is located at the upper end of the insulating shell 12; the insulating shell 12, the large felling ring 13 and the small felling ring 14 are fired into a whole through a glass lathe; the metal shell 11 is connected to the insulating shell 12 through the large felling ring 13; the cathode electron gun assembly 4 is located on the side wall of the metal shell 11; and the internal shape of the metal shell 11 is cylindrical.

[0032] The material of the metal shell 11 is stainless steel, oxygen-free copper or monel alloy pure iron, etc.; the material of the insulating shell 12 is glass or ceramic, etc.

[0033] The window 2 is made of beryllium, diamond, etc. The size of the window 2 is smaller than the cylindrical size of the metal shell 11, and is connected to the top of the metal shell 11 by laser, brazing or argon arc welding.

[0034] The exhaust pipe 15 is located on the side wall of the metal shell 11, and is not located on the same side wall as the cathode electron gun assembly 4. The exhaust pipe 15 is welded to the metal shell 11 as a whole through brazing or other processes.

[0035] like Figure 2 As shown, the anode assembly 3 includes a coaxial anode rod 31, an anode cover 32, an anode head 33, an anode cap 34, an anode target 35 and a calender tube 36; wherein the anode head 33, the anode cap 34 and the anode target 35 are located inside the metal shell 11; the anode rod 31 is located inside the insulating shell 12, and the top thereof extends into the metal shell 11; the anode rod 31 is a multi-section cylindrical structure, and the thicker the cylinder, the more conducive to heat dissipation; the calender tube 36 is sleeved on the bottom of the anode rod 31 through a brazing process, and is connected to the insulating shell 12 through a welded small calender ring 14; the anode cover 32 is sleeved on the anode The anode rod 31 is fixed by setting a step in the sleeve area of ​​the anode rod 31. The anode cover 32 covers the small cuttable ring 14 and the upper part of the cuttable cylinder 36. The anode head 33 is a cylindrical structure, located at the top of the anode rod 31. The anode head 33 and the anode rod 31 can be made into an integrated structure, and the anode head 33 can also be fixed to the top of the anode rod 31 by means of threading, riveting, brazing, etc. The top of the anode head 33 is cylindrical, and the top surface is an inclined surface. The angle of the inclined surface is called the target angle, and the anode target 35 is placed on the top surface of the anode head 33; the anode cap 34 is sleeved on the top of the anode head 33, as shown in FIG. Figure 3As shown, it includes a cap body 343 and a brim 344 located on the top of the cap body 343; the cap body 343 is shaped like a first circular cylinder that is sleeved and matched with the anode head 33, and a first opening 341 is provided on the side of the cap body 343; the brim 344 is shaped like a second circular cylinder whose ring width is greater than the ring width of the first circular cylinder, and the middle hollow area of ​​the second circular cylinder is the second opening 342, and the center of the second opening 342 is colinear with the axis of the anode assembly 3; the central axis of the first opening 341 and the central axis of the second opening 342 intersect at the anode target 35.

[0036] The centers of the through holes of the grid electrode 43, the first focusing electrode 44, the second focusing electrode 45 and the third focusing electrode 46 are coaxial with the centers of the first opening 341 and the anode target 35, and the axes are perpendicular to the axis of the anode assembly 3; The housing 1, the window 2 and the anode assembly 3 are coaxial.

[0037] like Figure 4 and Figure 5 As shown, the cathode electron gun assembly 4 includes a cathode tube 40, and a cathode 41 located inside the cathode tube 40, a field emission material 42, a grid 43, a first focusing electrode 44, a second focusing electrode 45, a third focusing electrode 46, an electrode core column 47, an electrode lead 48, a first insulating ring 411, a second insulating ring 412, a third insulating ring 413, and electrode assemblies corresponding to the grid 43, the first focusing electrode 44, and the second focusing electrode 45; each electrode assembly includes an electrode screw 49 and an insulating column 410.

[0038] The cathode tube 40 can be connected to the metal shell 11 by any method such as laser, argon arc welding, brazing, etc. The shell 1 and the window 2, the anode assembly 3, and the cathode electron gun assembly 4 together form a sealed environment. After exhausting by the exhaust pipe 15, the sealed environment is ultra-high vacuum. The third focusing electrode 46 is located at the connection between the metal shell 11 and the cathode tube 40; the third focusing electrode and the cathode tube 40 are processed into an integrated structure; the cathode 41 is connected to the cathode tube 40; the electrode core column 47 is specifically a ceramic electrode core column, which is located at the end of the cathode tube 40 opposite to the third focusing electrode 46; the cathode 41, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 are arranged in sequence, and the second focusing electrode 45 is located on one side of the third focusing electrode 46; the cathode 41 and the third focusing electrode 46 are grounded.

[0039] The first insulating ring 411 is located between the cathode 41 and the gate 43 ; the second insulating ring 412 is located between the gate 43 and the first focusing electrode 44 ; and the third insulating ring 413 is located between the first focusing electrode 44 and the second focusing electrode 45 .

[0040] Figure 5 (a) is an appearance diagram of the cathode electron gun assembly 4. Figure 5(b) is an exploded view of the cathode electron gun assembly 4, as shown in FIG. Figure 5 As shown in (b) in the figure, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 in this embodiment each have two sets of electrode assemblies, and the cathode 41, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 are all provided with through holes matching the electrode screw 49, and the cathode 41, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 are fixed by the electrode screw 49 that penetrates through; in the electrode assembly, the insulating column 410 is sleeved on the electrode screw 49 to isolate the electrode screw 49 from the cathode 41; the electrode core column 47 is connected to the corresponding grid 43, the first focusing electrode 44 and the second focusing electrode 45 through the electrode lead 48 and the electrode screw 49 in sequence. Preferably, when used for electrical connection, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 can only use one set of electrode assemblies.

[0041] like Figure 6 As shown, in order to reduce the gap between the cathode 41 and the grid 43 and form a region with a strong electric field, so that the field emission material 42 generates field-induced electron emission, the cathode 41 used in this embodiment includes a disk base 4101 and a boss 4102 located at the center of the disk base 4101; wherein the top surface of the boss 4102 faces the grid 43; the diameter and height of the boss 4102 are adjusted according to demand; the field emission material 42 is specifically a carbon nanotube, a diamond film, a metal tip or a semiconductor tip, etc., and has a rotationally symmetrical shape, specifically a circular, annular or hub shape, etc., located The center of the top surface of the boss 4102 is in the electron emission area; the through hole of the cathode 41 is opened on the disc base 4101, and the through hole of the cathode 41 is specifically a cathode screw through hole 4103, the aperture is larger than the diameter of the electrode screw 49, and there is enough voltage-resistant spacing so that the electrode screw 49 can pass through the cathode screw through hole 4103 to avoid sparking and breakdown; a sunken step 4104 is provided inside the cathode screw through hole 4103 to limit the insulating column 410; a cathode edge step 4105 is provided on the edge of the disc base 4101 to limit the first insulating ring 411.

[0042] like Figure 7 As shown, in order to reduce the size of the gate 43 and reduce the interception of electrons by the gate 43, the structure of the gate 43 is designed as a disk with a sunken table 4301 in the middle in this embodiment. Figure 7 (a) is a top view of the gate 43. Figure 7(b) is a front view of the gate 43; wherein a first through hole 4302 is opened at the center of the sunken table 4301, and the aperture of the first through hole 4302 is 300 μm; the thickness of the sunken table 4301 is 300 μm, and the bottom surface of the sunken table 4301 is adjacent to the cathode 41. By controlling the distance between the top surface of the boss 4102 and the bottom surface of the sunken table 4301, the gate 43 works at a suitable voltage, and the distance is preferably 200-300 μm. The voltage applied to the gate 43 is 2000-3000 μm. V; the through hole of the grid 43 is opened on the disc, including the grid screw through hole 4303 and the grid threaded hole 4304; the straight hole diameter of the grid screw through hole 4303 is larger than the diameter of the electrode screw 49, and a sufficient voltage-resistant spacing is left so that the electrode screw 49 can pass through the grid screw through hole 4303 to avoid sparking and breakdown; the grid threaded hole 4304 is matched and connected with the corresponding electrically connected electrode screw 49, thereby realizing the fastening connection between the cathode 41, the first insulating ring 411 and the grid 43.

[0043] like Figure 8 As shown, in order to enhance the convergence capability of the first focusing electrode 44 and reduce the electron beam diameter, the present embodiment adopts a method of not thickening the first focusing electrode 44. Specifically, the structure of the first focusing electrode 44 is designed to be a trumpet-shaped first focusing electrode, including a hollow disk 4402, a trapezoidal ring 4403, and a cylindrical bowl 4406 connected in sequence from top to bottom, together forming a trumpet-shaped structure opening upward. Figure 8 (a) is a top view of the first focusing electrode 44. Figure 8 (b) is a front view of the first focusing electrode 44; wherein, a second through hole 4401 is opened at the center of the bottom surface of the cylindrical bowl 4406; a step is provided at the junction of the trapezoidal ring 4403 and the cylindrical bowl 4406 for placing the aperture electrode 4404, and a third through hole 4405 is opened at the center of the aperture electrode 4404, which can intercept edge electrons with a large divergence angle and effectively reduce the focal size of the electron beam; the cylindrical bowl 4406 is sunken into the sunken table 4301 of the grid 43, and the distance between the cylindrical bowl 4406 and the sunken table 4301 is 0.5~1 mm; the trumpet-shaped first focusing electrode helps to reduce the distance between the first focusing electrode 44 and the grid 43, making the structure more compact and obtaining a stronger electron beam convergence effect.

[0044] The through hole of the first focusing electrode 44 is opened on the hollow disk 4402, including a first focusing electrode screw through hole 4407 and a first focusing electrode threaded hole 4408. The size of the first focusing electrode screw through hole 4407 is the same as that of the grid screw through hole 4303, and the size of the first focusing electrode threaded hole 4408 is the same as that of the grid threaded hole 4304. The first focusing electrode threaded hole 4408 is matched and connected with the corresponding electrically connected electrode screw 49, thereby realizing the fastening connection between the cathode 41, the first insulating ring 411, the grid 43, the second insulating ring 412 and the first focusing electrode 44.

[0045] like Fig. 9 As shown, the structure of the second focusing electrode 45 is a disk with a fourth through hole 4501 in the middle. In order to facilitate the focusing adjustment of the electron beam parallel to and perpendicular to the axis direction of the anode assembly 3, the shape of the fourth through hole 4501 is designed to be a first rectangle with an arc-shaped wide side 4502. The arc-shaped wide side 4502 is concentric with the disk, and the long straight side of the first rectangle is perpendicular to the axis of the anode assembly 3. Fig. 9 (a) is a top view of the second focusing electrode 45. Fig. 9 (b) is a front view of the second focusing electrode 45; the through hole of the second focusing electrode 45 is provided on the disk, specifically, the second focusing electrode threaded hole 4503, which is matched and connected with the corresponding electrode screw 49 for electrical connection; thereby realizing the fastening connection between the cathode 41, the first insulating ring 411, the grid 43, the second insulating ring 412, the first focusing electrode 44, the third insulating ring 413 and the second focusing electrode 45. Fig.10 As shown, the third focusing electrode 46 is grounded and is located at the connection between the metal shell 11 and the cathode cylinder 40. The structure is specifically a disk with a fifth through hole 4601 in the middle, and the shape of the fifth through hole 4601 is a second rectangle; by adjusting the length-to-width ratio of the fifth through hole 4601, the electron beams can achieve the best focusing effect in different directions synchronously; Fig.10 (a) is a front view of the third focusing electrode 46. Fig.10 (b) is a top view of the third focusing electrode 46 .

[0046] The first through hole 4302 of the gate 43, the second through hole 4401 of the first focusing electrode 44, the fourth through hole 4501 of the second focusing electrode 45, the fifth through hole 4601 of the third focusing electrode 46 and the first opening 341 are coaxial, and the axis passes through the center of the anode target 35 and the center of the field emission material 42, and is perpendicular to the axis of the anode assembly 3.

[0047] The cathode 41, the grid 43 and the first focusing electrode 44 together constitute a first electrostatic focusing lens, and the second focusing electrode 45, the third focusing electrode 46 and the anode assembly 3 constitute a second electrostatic focusing lens.

[0048] In this embodiment, a voltage of 130-180 KV is applied to the anode assembly 3 to form an anode electric field; the cathode 41 and the third focusing electrode 46 are grounded, and a voltage of 2-3 KV is applied to the grid electrode 43 by means of the electrode core 47, and voltages are applied to the first focusing electrode 44 and the second focusing electrode 45; the field emission material 42 in the electron emission region generates electrons under the action of field emission; the electrons pass through the through hole at the center of the grid electrode 43 under the grid electric field to form an electron beam moving toward the anode assembly 3; the electron beam converges for the first time under the action of the first electrostatic focusing lens to form a first focusing point 4111; the electron beam continues to converge for the second time under the second electrostatic focusing lens, passes through the third focusing electrode 46 to form a second focusing point 4112, and the electron beam bombards the center of the anode target 35 under the acceleration of the anode electric field; the anode target 35 generates X-rays under the bombardment of the electron beam, which are emitted through the second opening 342 and the window 2.

[0049] This embodiment uses a cathode electron gun assembly 4 with a double electrostatic focusing lens to realize a double-focused electron beam. The simulation trajectory of the double-focused electron beam is as follows: Fig.11 As shown, Fig.11 (a) is a schematic diagram of the electron beam trajectory. Fig.11 (b) in the figure is the result of the electron beam trajectory simulation. In the figure, the Y coordinate represents the dimension perpendicular to the axis of the anode assembly 3, and the Z coordinate represents the dimension along the direction of the electron beam. It can be seen that after the electrons emitted by the cold cathode are accelerated by the grid electric field, they form a first focusing point 4111 under the action of the first electrostatic lens, which is located between the first focusing electrode 44 and the aperture electrode 4404. While obtaining a smaller focus, the electron beam divergence angle is greatly reduced, and the electron beam can enter the second electrostatic focusing lens at a smaller angle, and the electron beam waist 4113 has a smaller diameter. The image point of the first lens serves as the object point of the second lens, and then forms a smaller second focusing point 4112 under the action of the second electrostatic lens. The second focusing point is located on the anode target 35. By adjusting the spacing between the cathode 41, the grid 43, the first focusing electrode 44, the second focusing electrode 45, and the third focusing electrode 46, and the voltage applied to the first focusing electrode 44 and the second focusing electrode 45, the position and size of the second focusing point 4112 of the electron beam converged on the anode target 35 can be controlled. The focal spot of the double-focused electron beam on the anode target is shown in FIG. Fig.12 As shown in the figure, the X coordinate represents the dimension parallel to the axis direction of the anode assembly 3, and the Y coordinate represents the dimension perpendicular to the axis direction of the anode assembly 3.

[0050] Comparative Example 1 This comparative example provides a cold cathode micro-focus X-ray tube, which is different from Example 1 in structure only in the structural adjustment of the cathode electron gun assembly, specifically: the cathode electron gun assembly includes a cathode cylinder, and a cathode, a grid, a focusing electrode, an electrode core column, an electrode lead and a field emission material located inside the cathode cylinder, and the focusing electrode faces the anode assembly. The other structures of this comparative example are the same as those of Example 1.

[0051] This comparative example only includes one electrostatic focusing lens to realize a single-focus electron beam. The electron beam simulation trajectory is as follows: Fig.13 As shown in the figure, the Y coordinate represents the dimension perpendicular to the axial direction of the anode assembly 3, and the Z coordinate represents the dimension along the direction of the electron beam. Compared with the simulation trajectory of the double electrostatic focusing lens electron beam in Example 1, it can be seen that: by setting a plurality of focusing electrodes to cooperate to form a double electrostatic focusing lens, the ability to converge and compress the electron beam can be improved, the diameter of the electron beam waist 4113 is smaller, and the resulting electron beam can obtain a smaller-sized convergence focus on the anode target 35.

[0052] Example 2

[0053] This embodiment provides a cold cathode micro-focus X-ray tube based on a double electrostatic lens, the structure of which is as follows: Fig.14 As shown, a transmission target structure is adopted, which specifically includes a shell 1, a window 2 located at the top of the shell 1, an anode assembly 3 located inside the shell 1, a cathode electron gun assembly 4 located at the bottom of the shell 1, and an exhaust pipe 15 located on the side wall of the shell 1.

[0054] The structures and materials of the housing 1 , the window 2 and the exhaust pipe 15 are the same as those of the first embodiment.

[0055] The anode assembly 3 includes an anode target 35 which is closely attached to the lower surface of the window 2 .

[0056] In order to make the overall structure of the cold cathode micro-focus X-ray tube more symmetrical, the cathode electron gun assembly 4 is designed as a rotationally symmetrical structure in this embodiment. Compared with the structure of embodiment 1, the only difference is that: the cathode electron gun assembly 4 is arranged at the bottom end of the shell 1, and the third focusing electrode 46 is arranged toward the window 2, so that the axes of the first through hole 4302 of the grid 43, the second through hole 4401 of the first focusing electrode 44, the fourth through hole 4501 of the second focusing electrode 45 and the fifth through hole 4601 of the third focusing electrode 46 vertically pass through the center of the anode target 35 and the center of the window 2; the cathode cylinder 40 is connected to the insulating shell 12 through a small welded var ring 14; the shell 1, the window 2 and the cathode electron gun assembly 4 together form a sealed environment; Fig.15 As shown, the structure of the second focusing electrode 45 is a disk with a fourth through hole 4501 in the middle, and the shape of the fourth through hole 4501 is circular. Fig.15 (a) is a top view of the second focusing electrode 45. Fig.15(b) is a front view of the second focusing electrode 45; Fig.16 As shown, the structure of the third focusing electrode 46 is a disk with a fifth through hole 4601 in the middle, and the shape of the fifth through hole 4601 is circular. Fig.16 (a) is a top view of the third focusing electrode 46. Fig.16 (b) is a front view of the third focusing electrode 46; other structures are the same.

[0057] This embodiment adopts a transmission target structure, in which the anode target 35 is combined with the window 2. The anode target 35 is located below the window 2. The material of the window 2 is diamond, which has good heat dissipation, high strength and low X-ray absorption. The material of the anode target 35 is tungsten, and a uniform metal tungsten film is formed on the window 2 by magnetron sputtering or the like.

[0058] In this embodiment, the anode assembly 3 is grounded to the metal shell 11, and a negative high voltage is applied to the gate 43, the first focusing electrode 44 and the second focusing electrode 45 by using the electrode core column 47, so the anode assembly 3 is still at a high potential relative to the gate 43, the first focusing electrode 44 and the second focusing electrode 45; the field emission material 42 in the electron emission area generates electrons under the action of field emission; the electrons pass through the through hole in the center of the gate 43 under the gate electric field to form an electron beam moving toward the anode assembly 3; the electron beam converges for the first time under the action of the first electrostatic focusing lens to form a first focusing point 4111; the electron beam continues to converge for the second time under the second electrostatic focusing lens, passes through the third focusing electrode 46 to form a second focusing point 4112, and the electron beam bombards the center of the anode target 35 under the acceleration of the anode electric field; the anode target 35 generates X-rays under the bombardment of the electron beam and emits them through the window 2.

[0059] The above embodiments only illustrate the principles and advantages of the present invention, and are not intended to limit the present invention. They are only intended to help understand the principles of the present invention. The protection scope of the present invention is not limited to the above configurations and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the disclosed technology without departing from the essence of the present invention, but they are still within the protection scope of the present invention.

Claims

1. A cold cathode micro-focus X-ray tube based on double electrostatic lenses, characterized in that: It comprises a housing (1), a window (2) located at the top of the housing (1), an anode assembly (3) located below the window (2), and a cathode electron gun assembly (4) connected to the housing (1); The anode assembly (3) comprises an anode target (35); The cathode electron gun assembly (4) comprises a cathode cylinder (40), and a cathode (41) located inside the cathode cylinder (40), a field emission material (42), a grid (43), a first focusing electrode (44), a second focusing electrode (45), a third focusing electrode (46), an electrode core column (47), and an electrode lead (48); The cathode cylinder (40) is in communication with the outer shell (1), and the outer shell (1), the window (2) and the cathode cylinder (40) together form a sealed environment; The third focusing electrode (46) is integrally arranged with the cathode tube (40); the electrode core column (47) is located at an end of the cathode tube (40) opposite to the third focusing electrode (46), and is connected to the grid electrode (43), the first focusing electrode (44) and the second focusing electrode (45) through an electrode lead wire (48); the cathode (41), the grid electrode (43), the first focusing electrode (44) and the second focusing electrode (45) are sequentially stacked, the second focusing electrode (45) is located on one side of the third focusing electrode (46), and the cathode (41) and the cathode (43) are connected to each other. The cathode (41) and the third focusing electrode (46) have the same potential, forming a potential difference with the grid electrode (43), the first focusing electrode (44) and the second focusing electrode (45); the field emission material (42) is placed on a surface of the cathode (41) adjacent to the grid electrode (43) and is located in the electron emission region; the grid electrode (43), the first focusing electrode (44), the second focusing electrode (45) and the third focusing electrode (46) are all provided with through holes at their centers, and the center of the through hole is coaxial with the center of the anode target (35).

2. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 1, characterized in that: The cathode (41) comprises a disk base (4101) and a boss (4102) located at the center of the disk base (4101), and the field emission material (42) is located at the center of the boss (4102); the grid (43) has a structure of a disk with a sunken table (4301) in the middle, a first through hole (4302) is opened at the center of the sunken table (4301), and the thickness of the sunken table (4301) is 100-300 μm; the distance between the boss (4102) and the sunken table (4301) is 200-500 μm.

3. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 2, characterized in that: The structure of the first focusing electrode (44) is a disk with a through hole in the center, and the through hole is specifically a circular hole with a diameter of 0.5-2 mm.

4. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 2, characterized in that: The first focusing electrode (44) comprises a hollow disk (4402), a trapezoidal ring (4403) and a cylindrical bowl (4406) which are connected in sequence from top to bottom, and together form a trumpet-shaped structure which opens upward; wherein a second through hole (4401) is provided at the center of the bottom surface of the cylindrical bowl (4406); a step is provided at the junction of the trapezoidal ring (4403) and the cylindrical bowl (4406) for placing the hole-opening electrode (4404); a third through hole (4405) is provided at the center of the hole-opening electrode (4404); and the cylindrical bowl (4406) is sunken into the sinking table (4301), and the distance between the cylindrical bowl (4406) and the sinking table (4301) is 0.5-2 mm.

5. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to any one of claims 3 or 4, characterized in that: The structure of the second focusing electrode (45) is a disk with a fourth through hole (4501) in the middle, the shape of the fourth through hole (4501) is circular or a first rectangle with an arc-shaped wide side (4502), and the long straight side of the first rectangle is perpendicular to the concentric axis of the anode assembly (3); the structure of the third focusing electrode (46) is a disk with a fifth through hole (4601) in the middle; the size of the fourth through hole (4501) and the fifth through hole (4601) is 10-20 mm.

6. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 5, characterized in that: The anode target (35) is closely attached to the lower surface of the window (2); the centers of the through holes of the grid (43), the first focusing electrode (44), the second focusing electrode (45) and the third focusing electrode (46) are coaxial with the centers of the anode target (35) and the window (2); and the shape of the fifth through hole (4601) is circular.

7. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 5, characterized in that: The anode assembly (3) further comprises an anode rod (31), an anode cover (32), an anode head (33), an anode cap (34) and a cuttable cylinder (36) coaxial with the center of the window (2), and the axis thereof passes vertically through the window (2); wherein the bottom of the anode rod (31) is connected to the housing (1), the anode cover (32) is sleeved under the anode rod (31), the cuttable cylinder (36) is sleeved on the bottom of the anode rod (31), the anode head (33) is located at the top of the anode rod (31), and the anode cap (34) is sleeved on the top of the anode head (33); the top surface of the anode head (33) is an inclined surface, and the anode target (35) is placed on the top surface of the anode head (33); a first opening (341) is provided on the side of the anode cap (34), and a second opening (342) is provided on the top, the center of which is colinear with the axis of the anode assembly (3); The centers of the through holes of the grid (43), the first focusing electrode (44), the second focusing electrode (45) and the third focusing electrode (46) are coaxial with the centers of the first opening (341) and the anode target (35), and the axes are perpendicular to the axis of the anode assembly (3); The shape of the fifth through hole (4601) is a second rectangle.

8. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 2, characterized in that: The cold cathode micro-focus X-ray tube based on dual electrostatic lenses further comprises an exhaust pipe (15) arranged on the side wall of the housing (1); after exhausting the air through the exhaust pipe (15), the sealed environment becomes a vacuum.

9. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 2, characterized in that: The cathode electron gun assembly (4) further comprises a first insulating ring (411), a second insulating ring (412) and a third insulating ring (413); wherein the first insulating ring (411) is located between the cathode (41) and the grid (43); the second insulating ring (412) is located between the grid (43) and the first focusing electrode (44); and the third insulating ring (413) is located between the first focusing electrode (44) and the second focusing electrode (45).

10. The cold cathode micro-focus X-ray tube based on double electrostatic lenses according to claim 2, characterized in that: The cathode electron gun assembly (4) further comprises electrode assemblies corresponding to the grid electrode (43), the first focusing electrode (44) and the second focusing electrode (45), respectively, each electrode assembly comprising an electrode screw (49) and an insulating column (410); The cathode (41), the grid (43), the first focusing electrode (44) and the second focusing electrode (45) are all provided with through holes matching the electrode screw (49), and the cathode (41), the grid (43), the first focusing electrode (44) and the second focusing electrode (45) are electrically connected and fixed by the electrode screw (49) passing through; the insulating column (410) is sleeved on the electrode screw (49) to isolate the electrode screw (49) from the cathode (41); The electrode core column (47) is connected to the corresponding grid electrode (43), the first focusing electrode (44) and the second focusing electrode (45) respectively through the electrode lead wire (48) and the electrode screw (49) in sequence.

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