A cold cathode microfocus X-ray tube based on dual electrostatic lenses

Abstract

The application discloses a cold cathode micro-focus X-ray tube based on double electrostatic lenses, and belongs to the technical field of X-ray tubes.The cold cathode micro-focus X-ray tube 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, a cathode, a grid, a first focusing electrode, a second focusing electrode, a third focusing electrode, an electrode core column, an electrode lead and field emission material in the cathode cylinder.The field emission material generates electrons under the action of field emission, the formed electron beam is converged for the first time under the action of the first electrostatic lens, a first focus is formed, the electron beam is converged for the second time under the action of the second electrostatic lens, a second focus is formed, and finally the anode target is bombarded to generate X-rays.The cold cathode micro-focus X-ray tube improves the converging compression capacity of the electron beam by forming double electrostatic lenses, the size of the converging focus is reduced without affecting the emission area, and the resolution of the X-ray tube is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of X-ray tubes, and particularly relates to a cold cathode micro-focus X-ray tube based on double electrostatic lenses. BACKGROUND

[0002] With the increasing demand of modern industrial nondestructive testing, in order to adapt to various detection requirements, X-ray tube technology also needs to develop continuously, and the most core point is to improve the resolution of the X-ray tube. The cathode electron gun of the X-ray tube is equivalent to the engine of the automobile, 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] The traditional X-ray tube generally adopts a hot cathode electron gun, which needs to be heated to a high temperature of thousands of degrees through direct or indirect heating. Electrons are emitted from the surface of the cathode due to thermal motion. The existing hot cathode has defects such as high working temperature, low service life, large energy loss, slow switching response, small current density, large focal point size, low resolution and blurred image, and the detection accuracy is difficult to meet the requirements. In view of this, people have proposed a cold cathode electron gun which is completely different from the working principle of the hot cathode electron gun. The working principle is as follows: under the condition of a certain intensity of electric field, electrons escape from the surface of the cathode through tunneling effect to realize electron emission. The unique working principle of the cold cathode X-ray tube makes it have advantages that the hot cathode X-ray tube cannot achieve. The cold cathode X-ray tube does not need high temperature heating, has the characteristics of low cathode temperature, more stable working, low power consumption, long service life and large current density, and is also easy to realize smaller focal point size and ultra-high resolution.

[0004] The existing cold cathode X-ray tube adopts an electron gun structure of a single electrostatic focusing lens, and the convergence and compression capability of the electron beam is limited. In order to realize a smaller focal point, it is usually necessary to reduce the electron emission area of the cathode, but this will make the cathode load too high, the working current of the X-ray tube is greatly reduced, and the service life and stability are also affected. Therefore, the existing cold cathode X-ray tube is difficult to realize a smaller focal point size while maintaining the emission area. Although in large electron microscopes, an electron optical system is formed by multiple electron lenses to enable the electron beam to achieve extremely high resolution, the main lens usually adopts a magnetic lens. The structure of the magnetic lens part is complex and bulky, and it is difficult to miniaturize. The price is also very high, and it is difficult to apply to the existing micro-focus X-ray tube. SUMMARY

[0005] In view of the problems existing in the hot cathode X-ray tube and the existing micro-focus X-ray tube electron gun, the application provides a cold cathode micro-focus X-ray tube based on double electrostatic lenses, a plurality of focusing electrodes are compactly arranged, two electrostatic focusing lenses are sequentially formed in the electron beam running track, the electron beam running track sequentially forms two focus points corresponding to the electrostatic focusing lenses by controlling the electric field, so that the focus point size with smaller compression ratio is obtained, and the resolution of the cold cathode micro-focus X-ray tube is significantly improved.

[0006] The technical scheme adopted by the application is as follows:

[0007] A cold cathode micro-focus X-ray tube based on double electrostatic lenses comprises a shell, a window located at the top of the shell, an anode assembly located below the window, and a cathode electron gun assembly connected with the shell.

[0008] The anode assembly comprises an anode target.

[0009] The cathode electron gun assembly comprises a cathode cylinder, and a cathode, 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 wire located in the cathode cylinder.

[0010] The cathode cylinder is in communication with the shell, and the shell, the window and the cathode cylinder jointly form a sealed environment.

[0011] The third focusing electrode is integrally arranged with the cathode cylinder; the electrode core column is located at one end of the cathode cylinder 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 wire; the cathode, the grid, the first focusing electrode and the second focusing electrode are sequentially arranged, the second focusing electrode is located on one side of the third focusing electrode, and the cathode is connected with the cathode cylinder; the cathode and the third focusing electrode have the same electric potential, and form a potential difference with the grid, the first focusing electrode and the second focusing electrode; the field emission material is arranged on a side of the cathode adjacent to the grid and is located in an electron emission area; the grid, the first focusing electrode, the second focusing electrode and the third focusing electrode are all provided with a through hole in the center, and the centers of the through holes are coaxial with the center of the anode target.

[0012] Further, the cathode electron gun assembly further comprises a first insulating ring, a second insulating ring and a third insulating ring; 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.

[0013] Further, 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 rod and an insulating column.

[0014] The cathode, the grid, the first focusing electrode and the second focusing electrode are all provided with through holes matched with electrode screws, and the electrode screws penetrating through the through holes realize the electrical connection and fixation of the cathode, the grid, the first focusing electrode and the second focusing electrode; the insulating column is sleeved on the electrode screw, so that the electrode screw is isolated from the cathode.

[0015] The electrode core column is connected to the corresponding grid, the first focusing electrode and the second focusing electrode through the electrode lead and the electrode screw in sequence.

[0016] Further, the cathode, the grid and the first focusing electrode jointly 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.

[0017] Further, the cathode comprises a disc base and a boss located at the center of the disc 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.

[0018] Further, the through hole of the cathode has a sunken step inside, which is used for limiting the insulating column.

[0019] Further, the structure of the grid is a disc with a sunken platform in the middle, the first through hole is opened in the center of the sunken platform, and the thickness of the sunken platform is set to 100-350 μm.

[0020] Further, the distance between the boss and the sunken platform is 200-500 μm.

[0021] Further, the structure of the first focusing electrode is a disc with a through hole opened in the center, and the through hole is a round hole with a diameter of 0.5-2 mm.

[0022] Further, the first focusing electrode comprises a hollow disc, a trapezoidal ring and a cylindrical bowl connected in sequence from top to bottom, and jointly forms a horn-shaped structure with an upward opening; the second through hole is opened in the center of the bottom surface of the cylindrical bowl; the trapezoidal ring is provided with a step at the joint with the cylindrical bowl, which is used for placing the aperture electrode; the third through hole is opened in the center of the aperture electrode; the cylindrical bowl is sunken into the sunken platform of the grid, and the distance between the cylindrical bowl and the sunken platform is 0.5-2 mm.

[0023] Further, the structure of the second focusing electrode is a disc with a fourth through hole opened in the middle, and the fourth through hole is circular or a first rectangle with a circular arc-shaped wide side, and the long straight side of the first rectangle is perpendicular to the concentric shaft of the anode assembly.

[0024] Further, the structure of the third focusing electrode is a disc with a fifth through hole opened in the middle.

[0025] Further, 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.

[0026] Further, 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.

[0027] Further, the anode target is close to the lower surface of the window, the center of the through hole of the grid, the first focusing electrode, the second focusing electrode and the third focusing electrode is coaxial with the center of the anode target and the center of the window, and the shape of the fifth through hole is preferably circular.

[0028] Further, the anode assembly further comprises an anode rod, an anode cover, an anode head, an anode cap and a Kovar cylinder coaxial with the center of the window, and the axis vertically passes through the window; wherein the bottom of the anode rod is connected with the shell, the anode cover is sleeved below the anode rod, the Kovar cylinder 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 arranged on the top surface of the anode head; the side surface of the anode cap is provided with a first opening, and the top is provided with a second opening coaxial with the axis of the anode assembly.

[0029] The center of the through hole of the grid, the first focusing electrode, the second focusing electrode and the third focusing electrode is coaxial with the center of the first opening and the center of the anode target, and the axis is perpendicular to the axis of the anode assembly.

[0030] At this time, the shape of the fifth through hole is preferably a second rectangle.

[0031] Further, the cold cathode micro-focus X-ray tube based on the double electrostatic lens further comprises an exhaust pipe arranged on the side wall of the shell, and after exhausting by using the exhaust pipe, the sealed environment is in high vacuum.

[0032] The working principle of the cold cathode micro-focus X-ray tube based on the double electrostatic lens is as follows:

[0033] 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 the electrode stem is used to apply a voltage to the grid, the first focusing electrode and the second focusing electrode; the field emission material arranged above the cathode generates electrons under the action of field emission; the electrons pass through the through hole at the center of the grid under the grid electric field to form an electron beam moving towards the anode assembly; the electron beam is first converged to form a first focusing point under the first electrostatic focusing lens formed by the cathode, the grid, the first focusing electrode electric field, and then diverges; the electron beam is secondly converged 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, 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.

[0034] By adjusting the spacing between the cathode, the grid, the first focusing electrode, the second focusing electrode, the third focusing electrode, and the voltage applied on the first focusing electrode and the second focusing electrode, the focusing characteristics of the two electrostatic focusing lenses can be controlled respectively to control the position and size of the electron beam focus point converging on the anode target.

[0035] Compared with the prior art, the application has the following advantages:

[0036] The application provides a cold cathode micro-focus X-ray tube based on double electrostatic lenses, adopts multiple focusing electrodes, and is connected and fixed through electrode screws. The cathode, the grid and the first focusing electrode jointly form a first electrostatic focusing lens, and the second focusing electrode, the third focusing electrode and an anode assembly form a second electrostatic focusing lens. A compact cold cathode electron gun assembly with two electrostatic focusing lenses is formed. After being accelerated by the grid electric field, the electrons emitted by the cold cathode form a first focus point 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 focus point is much smaller than that of the cathode surface, and the divergence angle of the electron beam after the electron beam is emitted from the first focus point is greatly reduced, so that the electron beam can enter the second electrostatic focusing lens at a smaller angle. The image point of the first electrostatic focusing lens serves as the object point of the second electrostatic focusing lens, and then a second focus point is formed under the action of the second electrostatic focusing lens. 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 focus point is located on the anode target. By adjusting the voltage applied to the multiple focusing electrodes and the spacing between the cathode, the grid and the multiple focusing electrodes, the electron beam is sequentially focused to form corresponding two focus points in the movement process, and a smaller converging focus point is realized on the anode target. Compared with the existing electron gun structure, the application can improve the converging compression capability of the electron beam, reduce the high requirement for the cathode emission current density, further reduce the size of the converging focus point without increasing the size of the electron gun and affecting the emission area, enable the X-ray tube to achieve higher resolution, and reduce the precision requirement for the electron gun parts, thereby greatly reducing the processing and assembly difficulty. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 FIG. 1 is a schematic diagram of the overall structure of a cold cathode micro-focus X-ray tube based on double electrostatic lenses according to Embodiment 1 of the application;

[0038] Figure 2 FIG. 2 is a schematic diagram of the structure of an anode assembly in Embodiment 1 of the application;

[0039] Figure 3 FIG. 3 is a schematic diagram of the structure of an anode cap in Embodiment 1 of the application;

[0040] Figure 4The combined structure schematic diagram of the cathode electron gun assembly in the embodiment 1 of the present application;

[0041] Figure 5 The exploded structure schematic diagram of the cathode electron gun assembly in the embodiment 1 of the present application; wherein, (a) is an appearance view; (b) is an exploded view;

[0042] Figure 6 The cathode structure schematic diagram in the embodiment 1 of the present application;

[0043] Figure 7 The structure schematic diagram of the grid in the embodiment 1 of the present application; wherein, (a) is a top view; (b) is a front view;

[0044] Figure 8 The structure schematic diagram of the horn-shaped first focusing electrode in the embodiment 1 of the present application; wherein, (a) is a top view; (b) is a front view;

[0045] Figure 9 The structure schematic diagram of the second focusing electrode in the embodiment 1 of the present application; wherein, (a) is a top view; (b) is a front view;

[0046] Figure 10 The structure schematic diagram of the third focusing electrode in the embodiment 1 of the present application; wherein, (a) is a front view; (b) is a top view;

[0047] Figure 11 The double focusing electron beam simulation trajectory schematic diagram of the embodiment 1 of the present application; wherein, (a) is an electron beam trajectory schematic diagram; (b) is an electron beam trajectory simulation result diagram;

[0048] Figure 12 The double focusing electron beam focal spot schematic diagram of the embodiment 1 of the present application;

[0049] Figure 13 The single focus electron beam simulation trajectory schematic diagram of the comparative example 1;

[0050] Figure 14 The overall structure schematic diagram of the cold cathode microfocus X-ray tube based on the double electrostatic lens proposed in the embodiment 2 of the present application;

[0051] Figure 15 The structure schematic diagram of the second focusing electrode in the embodiment 2 of the present application; wherein, (a) is a top view; (b) is a front view;

[0052] Figure 16 The structure schematic diagram of the third focusing electrode in the embodiment 2 of the present application; wherein, (a) is a top view; (b) is a front view;

[0053] The explanations of the marks in the drawings are as follows:

[0054] 1 - housing; 11 - metal shell; 12 - insulating shell; 13 - large Kovar ring; 14 - small Kovar 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 - Kovar cylinder; 341 - first opening; 342 - second opening; 343 - cap body; 344 - cap brim; 4 - cathode electron gun assembly; 40 - cathode cylinder; 41 - cathode; 42 - field emission material; 43 - grid; 44 - first focusing electrode; 45 - second focusing electrode; 46 - third focusing electrode; 47 - electrode stem; 48 - electrode lead; 49 - electrode screw; 410 - insulating post; 411 - first insulating ring; 412 - second insulating ring; 413 - third insulating ring; 4101 - disc base; 4102 - boss; 4103 - cathode screw through hole; 4104 - sunken step; 4105 cathode edge step; 4301 - sunken deck; 4302 - first through hole; 4303 - grid screw through hole; 4304 - grid screw thread hole; 4401 - second through hole; 4402 - hollow disc; 4403 - trapezoidal ring; 4404 - open hole electrode; 4405 - third through hole; 4406 - cylindrical bowl; 4407 - first focusing electrode screw through hole; 4408 - first focusing electrode screw thread hole; 4501 - fourth through hole; 4502 - circular arc wide edge; 4503 - second focusing electrode screw thread hole; 4601 - fifth through hole; 4111 - first focus point; 4112 - second focus point; 4113 - electron beam waist. DETAILED DESCRIPTION

[0055] In order to make the objectives, technical solutions and beneficial effects of the present application clearer, the specific embodiments of the present application are described in detail below with reference to the drawings.

[0056] It should be understood that the following specific examples are only used to enable those of ordinary skill in the art to more fully understand the present application, but in no way limit the present application.

[0057] Example 1

[0058] This embodiment proposes a cold cathode microfocus X-ray tube based on double electrostatic lens, the overall structure as shown in Figure 1 It includes a housing 1, a window 2 located at 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.

[0059] The outer shell 1 includes an upper metal shell 11, a lower insulating shell 12, a large Kovar ring 13, and a small Kovar ring 14; wherein, the small Kovar ring 14 is located at the lower end of the insulating shell 12, and the large Kovar ring 13 is located at the upper end of the insulating shell 12; the insulating shell 12, the large Kovar ring 13, and the small Kovar ring 14 are fired together as a whole using a glass lathe; the metal shell 11 is connected to the insulating shell 12 through the large Kovar ring 13; the cathode electron gun assembly 4 is located on the side wall of the metal shell 11; the internal shape of the metal shell 11 is cylindrical.

[0060] The metal shell 11 is made of stainless steel, oxygen-free copper, or Monel alloy pure iron, etc.; the insulating shell 12 is made of glass or ceramic, etc.

[0061] The window 2 is made of beryllium, diamond, etc., and its size is smaller than the cylindrical size of the metal shell 11. It is connected to the top of the metal shell 11 by laser, brazing or argon arc welding.

[0062] 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. It is welded to the metal shell 11 as a whole through processes such as brazing.

[0063] 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 Kovar tube 36; wherein, the anode head 33, anode cap 34, and anode target 35 are located inside the metal shell 11; the anode rod 31 is located inside the insulating shell 12, with its top extending into the metal shell 11; the anode rod 31 has a multi-segment cylindrical structure, and the thicker the cylinder, the better for heat dissipation; the Kovar tube 36 is brazed to the bottom of the anode rod 31 and connected to the insulating shell 12 through a small Kovar ring 14 welded together; the anode cover 32 is sleeved on the anode rod 31. Below rod 31, a step is set in the sleeve area of ​​anode rod 31 for fixation. Anode cover 32 covers the upper part of small Kovar ring 14 and Kovar cylinder 36. Anode head 33 is a cylindrical structure located at the top of anode rod 31. Anode head 33 and anode rod 31 can be integrated into a single structure, or the anode head 33 can be fixed to the top of anode rod 31 by means of threading, riveting, brazing, etc. The top of anode head 33 is cylindrical with a sloping top surface. The angle of the sloping surface is called the target angle. Anode target 35 is placed on the top surface of anode head 33. Anode cap 34 is sleeved on the top of anode head 33, such as... Figure 3As shown, it comprises a cap body 343 and a brim 344 on top of the cap body 343; the cap body 343 is shaped as a first circular cylindrical column matching the anode head 33, and the side surface of the cap body 343 is provided with a first opening hole 341; the brim 344 is shaped as a second circular cylindrical column with a ring width larger than that of the first circular cylindrical column, and the middle hollow area of the second circular cylindrical column is a second opening hole 342, the center of the second opening hole 342 is collinear with the axis of the anode assembly 3; the central axis of the first opening hole 341 intersects with the central axis of the second opening hole 342 at the anode target 35.

[0064] The through hole centers of the grid 43, the first focusing pole 44, the second focusing pole 45 and the third focusing pole 46 are coaxial with the center of the first opening hole 341 and the center of the anode target 35, and the axis is perpendicular to the axis of the anode assembly 3.

[0065] The housing 1, the window 2 and the anode assembly 3 are coaxial.

[0066] As shown in Figure 4 and Figure 5 The cathode electron gun assembly 4 comprises a cathode cylinder 40, and a cathode 41, a field emission material 42, a grid 43, a first focusing pole 44, a second focusing pole 45, a third focusing pole 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 pole 44 and the second focusing pole 45 inside the cathode cylinder 40; each electrode assembly comprises an electrode screw 49 and an insulating column 410.

[0067] The cathode cylinder 40 can be connected with the metal shell 11 by any one of laser, argon arc welding, brazing and the like, the housing 1, the window 2, the anode assembly 3 and the cathode electron gun assembly 4 together form a sealed environment, and after exhaust by the exhaust pipe 15, the sealed environment is in an ultrahigh vacuum state; the third focusing pole 46 is located at the connection between the metal shell 11 and the cathode cylinder 40; the third focusing pole is integrally processed with the cathode cylinder 40; the cathode 41 is connected with the cathode cylinder 40; the electrode core column 47 is specifically a ceramic electrode core column and is located at the end of the cathode cylinder 40 opposite to the third focusing pole 46; the cathode 41, the grid 43, the first focusing pole 44 and the second focusing pole 45 are sequentially and superimposedly arranged, and the second focusing pole 45 is located on one side of the third focusing pole 46; the cathode 41 and the third focusing pole 46 are grounded.

[0068] 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 pole 44; and the third insulating ring 413 is located between the first focusing pole 44 and the second focusing pole 45.

[0069] Figure 5 (a) in the figure is an appearance view of the cathode electron gun assembly 4, Figure 5(b) is an exploded view of the cathode electron gun assembly 4, as shown in Figure 5 As shown in (b) of the figure, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 each have two sets of electrode assemblies in this embodiment, the cathode 41, the grid 43, the first focusing electrode 44 and the second focusing electrode 45 are provided with through holes matched with the electrode screw rod 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 rod 49 penetrating through; in the electrode assembly, the insulating column 410 is sleeved on the electrode screw rod 49, so that the electrode screw rod 49 is isolated from the cathode 41; the electrode core column 47 is connected to the corresponding grid 43, first focusing electrode 44 and second focusing electrode 45 through the electrode lead 48 and electrode screw rod 49 in turn. 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.

[0070] As shown in Figure 6 In order to reduce the gap between the cathode 41 and the grid 43 and form a region with a strong electric field to make the field emission material 42 produce field emission, the cathode 41 used in this embodiment includes a disc base 4101 and a boss 4102 located at the center of the disc 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 requirements; the field emission material 42 is specifically carbon nanotubes, diamond film, metal tips or semiconductor tips, etc., and is a rotationally symmetric figure, specifically a circle, a ring or a hub, etc., located at the center of the top surface of the boss 4102 and in the electron emission region; the through hole of the cathode 41 is provided on the disc base 4101, and the through hole of the cathode 41 is specifically a cathode screw rod through hole 4103 with a hole diameter larger than the diameter of the electrode screw rod 49 and a sufficient voltage withstand spacing, so that the electrode screw rod 49 can pass through the cathode screw rod through hole 4103 to avoid spark breakdown; a sunken step 4104 is arranged inside the cathode screw rod through hole 4103 for limiting the insulating column 410; a cathode edge step 4105 is arranged at the edge of the disc base 4101 for limiting the first insulating ring 411.

[0071] As shown in Figure 7 In order to reduce the size of the grid 43 and reduce the interception of electrons by the grid 43, the structure of the grid 43 is designed as a disc with a sunken platform 4301 in the middle in this embodiment, Figure 7 (a) is a top view of the grid 43, Figure 7(b) is a front view of the grid 43; wherein the first through hole 4302 is opened in the center of the sunken platform 4301, and the aperture of the first through hole 4302 is 300 μm; the thickness of the sunken platform 4301 is 300 μm, the bottom surface of the sunken platform 4301 is adjacent to the cathode 41, the distance between the top surface of the convex platform 4102 and the bottom surface of the sunken platform 4301 is controlled to make the grid 43 work at a suitable voltage, and the distance is preferably 200-300 μm, and the voltage applied to the grid 43 is 2000-3000 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 grid screw through hole 4303 is straight, and the aperture is larger than the diameter of the electrode screw 49, and there is enough voltage resistance distance so that the electrode screw 49 passes through the grid screw through hole 4303 to avoid spark breakdown; the grid threaded hole 4304 is matched and connected with the corresponding electrode screw 49 connected in an electric way, thereby realizing the fastening connection of the cathode 41, the first insulating ring 411 and the grid 43.

[0072] As shown in Figure 8 , in order to enhance the convergence ability of the first focusing electrode 44 and reduce the diameter of the electron beam, the embodiment adopts the mode of not thickening the first focusing electrode 44, and specifically designs the structure of the first focusing electrode 44 as a horn-shaped first focusing electrode, which includes the hollow disc 4402, the trapezoidal ring 4403 and the cylindrical bowl 4406 connected in sequence from top to bottom, and together forms a horn-shaped structure with an upward opening, 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 the second through hole 4401 is opened in the center of the bottom surface of the cylindrical bowl 4406; the trapezoidal ring 4403 is provided with a step at the joint with the cylindrical bowl 4406 for placing the aperture electrode 4404, and the aperture electrode 4404 is provided with the third through hole 4405 in the center, which can intercept the edge electrons with a larger divergence angle, effectively reducing the size of the electron beam focus; the cylindrical bowl 4406 is sunken into the sunken platform 4301 of the grid 43, and the distance between the cylindrical bowl 4406 and the sunken platform 4301 is 0.5-1 mm; the horn-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 at the same time obtaining a stronger electron beam convergence effect.

[0073] The through hole of the first focusing electrode 44 is opened on the hollow disc 4402, including the first focusing electrode screw through hole 4407 and the 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, the size of the first focusing electrode threaded hole 4408 is the same as that of the grid threaded hole 4304, and the first focusing electrode threaded hole 4408 is matched and connected with the corresponding electrode screw 49 connected in an electric way; thereby realizing the fastening connection of the cathode 41, the first insulating ring 411, the grid 43, the second insulating ring 412 and the first focusing electrode 44.

[0074] As shown in Figure 9 , the structure of the second focusing electrode 45 is a disc with a fourth through hole 4501 in the middle. In order to facilitate the adjustment of the focusing of the electron beam parallel and perpendicular to the axis direction of the anode assembly 3, the shape of the fourth through hole 4501 is designed as a first rectangle with a circular arc wide side 4502, which is concentric with the disc, and the long straight side of the first rectangle is perpendicular to the axis of the anode assembly 3, Figure 9 (a) is a top view of the second focusing electrode 45, Figure 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 disc, specifically the second focusing electrode threaded hole 4503, which is matched and connected with the corresponding electrode screw rod 49 for electrical connection, thereby realizing the fastening connection of 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. As shown in Figure 10 , the third focusing electrode 46 is grounded and located at the connection between the metal shell 11 and the cathode cylinder 40. The structure is a disc 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-width ratio of the fifth through hole 4601, the best focusing effect of the electron beam in different directions can be achieved synchronously. Figure 10 (a) is a front view of the third focusing electrode 46, Figure 10 (b) is a top view of the third focusing electrode 46.

[0075] 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, the fifth through hole 4601 of the third focusing electrode 46 and the first opening 341 are coaxial, with the axis passing through the center of the anode target 35 and the center of the field emission material 42, and perpendicular to the axis of the anode assembly 3.

[0076] The cathode 41, the grid 43 and the first focusing electrode 44 jointly 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.

[0077] In the 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, a voltage of 2-3 KV is applied to the grid electrode 43 and the first focusing electrode 44 and the second focusing electrode 45 by the electrode stem 47; 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 in the center of the grid electrode 43 under the grid electric field to form an electron beam moving towards the anode assembly 3; the electron beam is subjected to the first convergence under the action of the first electrostatic focusing lens to form the first focusing point 4111; the electron beam is subjected to the second convergence under the action of the second electrostatic focusing lens to pass through the third focusing electrode 46 to form the second focusing point 4112, and the electron beam strikes 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 is emitted through the second opening 342 and the window 2.

[0078] In the embodiment, the cathode electron gun assembly 4 of the double electrostatic focusing lens is used to realize the double focusing electron beam, and the simulation trajectory of the double focusing electron beam is as shown in Figure 11 , wherein, Figure 11 (a) in the figure is a schematic diagram of the electron beam trajectory, Figure 11 (b) in the figure is a simulation result diagram of the electron beam trajectory, wherein the Y coordinate represents the size perpendicular to the axis direction of the anode assembly 3, and the Z coordinate represents the size along the forward direction of the electron beam; it can be seen that the electrons emitted by the cold cathode are accelerated by the grid electric field, and form the first focusing point 4111 under the action of the first electrostatic lens, which is located between the first focusing electrode 44 and the opening electrode 4404. At the same time, the electron beam divergence angle is greatly reduced, the electron beam can enter the second electrostatic focusing lens at a smaller angle, and the waist 4113 of the electron beam has a smaller diameter. The image point of the first lens is used as the object point of the second lens, and then a smaller second focusing point 4112 is formed under the action of the second electrostatic lens, which is located on the anode target 35. By adjusting the distance between the cathode 41, the grid electrode 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 converging on the anode target 35 can be controlled, and the focal spot of the double focusing electron beam on the anode target is as shown in Figure 12 , wherein the X coordinate represents the size parallel to the axis direction of the anode assembly 3, and the Y coordinate represents the size perpendicular to the axis direction of the anode assembly 3.

[0079] Comparative Example 1

[0080] The comparative example provides a cold cathode microfocus X-ray tube, which is structurally identical to that of Example 1, except that the structure of the cathode electron gun assembly is adjusted, specifically: the cathode electron gun assembly comprises a cathode cylinder, and a cathode, a grid, a focusing electrode, an electrode core column, an electrode lead wire and a field emission material located inside the cathode cylinder, and the focusing electrode faces the anode assembly. The other structures of the comparative example are identical to those of Example 1.

[0081] The comparative example only comprises one electrostatic focusing lens, and realizes a single focus electron beam. The simulated trajectory of the electron beam is shown in Figure 13 The Y coordinate in the figure represents the size perpendicular to the axis direction of the anode assembly 3, and the Z coordinate represents the size along the direction of the electron beam. Compared with the simulated trajectory of the double electrostatic focusing lens electron beam of Example 1, it can be seen that: by setting multiple focusing electrodes to form a double electrostatic focusing lens, the convergence compression capability of the electron beam can be improved, the electron beam waist 4113 has a smaller diameter, and the obtained electron beam can obtain a smaller converged focus on the anode target 35.

[0082] Example 2

[0083] The present embodiment provides a cold cathode microfocus X-ray tube based on a double electrostatic lens, which has a structure as shown in Figure 14 The structure of the cold cathode microfocus X-ray tube based on a double electrostatic lens is shown in

[0084] The structures and materials of the housing 1, the window 2 and the exhaust pipe 15 are identical to those of Example 1.

[0085] The anode assembly 3 comprises an anode target 35 closely attached to the lower surface of the window 2.

[0086] In order to make the overall structure of the cold cathode microfocus X-ray tube more symmetrical, the cathode electron gun assembly 4 is designed as a rotationally symmetrical structure, which is structurally identical to that of Example 1, except that: the cathode electron gun assembly 4 is arranged at the bottom end of the housing 1, the third focusing electrode 46 is arranged towards the window 2, and 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 pass through the centers of the anode target 35 and the window 2 perpendicularly; the cathode cylinder 40 is connected to the insulating shell 12 through the small Kovar ring 14; the housing 1, the window 2 and the cathode electron gun assembly 4 together form a sealed environment; as shown in Figure 15 The structure of the second focusing electrode 45 is a disc with a fourth through hole 4501 in the middle, and the fourth through hole 4501 is circular in shape, Figure 15 (a) in FIG. 4 is a top view of the second focusing electrode 45, Figure 15(b) is a front view of the second focusing pole 45; as Figure 16 As shown in the figure, the third focusing pole 46 is a disc with a fifth through hole 4601 in the middle, and the fifth through hole 4601 is circular in shape, Figure 16 (a) is a top view of the third focusing pole 46, Figure 16 (b) is a front view of the third focusing pole 46; the other structures are the same.

[0087] In this embodiment, the transmission target structure is adopted, 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 selected to be diamond which has good heat dissipation, high strength and less X-ray absorption, the material of the anode target 35 is selected to be tungsten, and a uniform tungsten film is formed on the window 2 by magnetic control sputtering and other methods.

[0088] In this embodiment, the anode assembly 3 is grounded with the metal shell 11, and a negative high voltage is applied to the grid 43, the first focusing pole 44 and the second focusing pole 45 by the electrode stem 47, so that the anode assembly 3 is still at a high potential relative to the grid 43, the first focusing pole 44 and the second focusing pole 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 grid 43 under the grid electric field to form an electron beam moving towards the anode assembly 3; the electron beam is first converged under the action of the first electrostatic focusing lens to form a first focusing point 4111; the electron beam is secondly converged under the action of the second electrostatic focusing lens to pass through the third focusing pole 46 to form a second focusing point 4112, and the electron beam is accelerated under the anode electric field to bombard the center of the anode target 35; the anode target 35 generates X-rays under the bombardment of the electron beam, which is emitted through the window 2.

[0089] The above embodiments only illustrate the principles and advantages of the present application, and are not used to limit the present application, and are only used to help understand the principles of the present application, and the protection scope of the present application is not limited to the above configurations and embodiments, and those skilled in the art can make other various specific modifications and combinations without departing from the essence of the present application according to the disclosed technology, but still within the protection scope of the present application.

Claims

1. A cold cathode microfocus X-ray tube based on a double electrostatic lens, characterized in that The application relates to a cathode electron gun assembly and an anode assembly. The anode assembly (3) comprises an anode target (35). The cathode electron gun assembly (4) comprises a cathode cylinder (40), a cathode (41), 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 stem (47) and an electrode lead (48) arranged in the cathode cylinder (40). The cathode cylinder (40) is in communication with the shell (1), and the shell (1), the window (2) and the cathode cylinder (40) jointly form a sealed environment. The third focusing electrode (46) is integrally arranged with the cathode cylinder (40); the electrode stem (47) is arranged at one end of the cathode cylinder (40) opposite to the third focusing electrode (46) and is connected to the grid (43), the first focusing electrode (44) and the second focusing electrode (45) through the electrode lead (48); the cathode (41), the grid (43), the first focusing electrode (44) and the second focusing electrode (45) are arranged in sequence, the second focusing electrode (45) is arranged on one side of the third focusing electrode (46), and the cathode (41) is connected with the cathode cylinder (40); the cathode (41) and the third focusing electrode (46) have the same potential, and a potential difference is formed between the cathode (41) and the third focusing electrode (46) and the grid (43), the first focusing electrode (44) and the second focusing electrode (45); the field emission material (42) is arranged on a side of the cathode (41) adjacent to the grid (43) and is located in an electron emission area; the grid (43), the first focusing electrode (44), the second focusing electrode (45) and the third focusing electrode (46) are provided with through holes in the centers thereof, and the centers of the through holes are coaxial with the center of the anode target (35). The cathode (41) comprises a disc base (4101) and a boss (4102) located in the center of the disc base (4101), and the field emission material (42) is located in the center of the boss (4102); the first focusing electrode (44) comprises a hollow disc (4402), a trapezoidal ring (4403) and a cylindrical bowl (4406) connected in sequence from top to bottom and jointly forming a horn-shaped structure with an upward opening; a second through hole (4401) is formed in the center of the bottom surface of the cylindrical bowl (4406); a step is arranged at the joint of the trapezoidal ring (4403) and the cylindrical bowl (4406) and used for placing a perforated electrode (4404); a third through hole (4405) is formed in the center of the perforated electrode (4404); the cylindrical bowl (4406) is sunk into a sunken platform (4301), and the distance between the cylindrical bowl (4406) and the sunken platform (4301) is 0.5-2 mm. The second focusing electrode (45) is a disc with a fourth through hole (4501) in the middle, the fourth through hole (4501) is shaped as a first rectangle with a circular arc wide side (4502), the long straight side of the first rectangle is perpendicular to the concentric axis of the anode assembly (3); the third focusing electrode (46) is a disc with a fifth through hole (4601) in the middle, the fifth through hole (4601) is shaped as a second rectangle; the size of the fourth through hole (4501) and the fifth through hole (4601) is 10-20mm; The distance from the first focusing electrode (44) to the third focusing electrode (46) is the same as the distance from the third focusing electrode (46) to the anode target (35); The anode assembly (3) further comprises an anode rod (31), an anode cover (32), an anode head (33), an anode cap (34) and a Kovar cylinder (36) coaxial with the center of the window (2), the axis vertically passes through the window (2); wherein the bottom of the anode rod (31) is connected with the shell (1), the anode cover (32) is sleeved below the anode rod (31), the Kovar cylinder (36) is sleeved at 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 at the top of the anode head (33); the top surface of the anode head (33) is beveled, and the anode target (35) is placed on the top surface of the anode head (33); the side surface of the anode cap (34) is provided with a first opening (341), and the top is provided with a second opening (342) with a center coaxial with the axis of the anode assembly (3); The through hole centers 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 center of the first opening (341) and the center of the anode target (35), and the axis is perpendicular to the axis of the anode assembly (3); A voltage is applied to the anode assembly (3) to form an anode high-voltage electric field; the cathode (41) and the third focusing electrode (46) are grounded, and the electrode stem (47) is used to apply a voltage to the grid electrode (43), the first focusing electrode (44) and the second focusing electrode (45); the field emission material (42) placed above the cathode (41) generates electrons under the action of field emission; the electrons pass through the through hole in the center of the grid electrode (43) under the electric field of the grid electrode (43) to form an electron beam moving towards the anode assembly (3); the electron beam is first converged to form a first focusing point under the first electrostatic focusing lens formed by the electric field of the cathode (41), the grid electrode (43) and the first focusing electrode (44), and then diverges; the electron beam continues to converge for the second time under the second electrostatic focusing lens formed by the electric field of the second focusing electrode (45), the third focusing electrode (46) and the anode, and forms a second focusing point on the anode target (35); the electron beam bombards the anode target (35) under the acceleration of the anode electric field, and the anode target (35) generates X-rays under the bombardment of the electron beam, and the X-rays are emitted through the second opening (342) and the window (2).

2. The cold cathode microfocus X-ray tube based on dual electrostatic lenses according to claim 1, characterized in that The structure of the gate (43) is a disc with a sunken platform (4301) in the middle, the sunken platform (4301) is provided with a first through hole (4302) in the center, and the thickness of the sunken platform (4301) is 100-300 μm; the distance between the boss (4102) and the sunken platform (4301) is 200-500 μm.

3. The cold cathode microfocus X-ray tube based on dual electrostatic lenses according to claim 2, characterized in that The double-electrostatic-lens-based cold cathode microfocus X-ray tube further comprises an exhaust pipe (15) arranged on the side wall of the shell (1), and the sealed environment is vacuumized after exhaust by the exhaust pipe (15).

4. The cold cathode microfocus X-ray tube based on dual 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 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).

5. The cold cathode microfocus X-ray tube based on dual electrostatic lenses according to claim 2, characterized in that, The cathode electron gun assembly (4) further comprises electrode assemblies corresponding to the gate (43), the first focusing electrode (44) and the second focusing electrode (45) respectively, and each electrode assembly comprises an electrode screw (49) and an insulating column (410). The cathode (41), the gate (43), the first focusing electrode (44) and the second focusing electrode (45) are all provided with through holes matched with the electrode screw (49), the electrical connection and fixation of the cathode (41), the gate (43), the first focusing electrode (44) and the second focusing electrode (45) are realized by the electrode screw (49) penetrating through, and the insulating column (410) is sleeved on the electrode screw (49), so that the electrode screw (49) is isolated from the cathode (41). The electrode core column (47) is connected to the corresponding gate (43), first focusing electrode (44) and second focusing electrode (45) through the electrode lead (48) and the electrode screw (49) in sequence respectively.

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