Cathode assembly for pulse grid-control microwave tube and preparation method of cathode assembly

Abstract

The invention provides a cathode assembly for a pulse grid control microwave tube and a preparation method of the cathode assembly. The cathode assembly comprises a cathode and a shadow grid, the emitting surface of the cathode comprises a grid groove which is arranged in a shape-modeling manner with the shadow grid; the shadow gate is located in the gate groove and is not in contact with the cathode; the surface, back to the bottom wall of the grid groove, of the shadow grid is flush with the emitting surface of the cathode, so that the shadow grid and the cathode keep the same electric field equipotential surface. The cathode assembly can solve the problems that after an existing non-interception grid-controlled electron gun works for a period of time, cathode emission is reduced due to the fact that the temperature of a shadow grid is too high, the service life of a microwave tube is finally shortened, and the reliability of the microwave tube is finally improved.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and more specifically, to a cathode assembly for a pulse-gated microwave tube and a preparation method thereof. Background Art

[0002] With the development of electronic countermeasure technology, military radars such as airborne, shipborne, satellite and spacecraft require longer and longer range, stronger maneuverability and higher reliability. Therefore, the radar system also puts forward high power, small size and light weight requirements for microwave tubes. The octave-band grid-controlled traveling wave tube is increasingly widely used in radar transmitters due to its stable operation, low adjustment voltage, wide frequency band, high power, relatively simple ventilation and heat dissipation structure design, small size and light weight.

[0003] At present, high-conductivity non-intercepted grid-controlled electron guns are widely used in pulse traveling wave tubes and are the most important components of pulse traveling wave tubes. Non-intercepted grid refers to the structure of the electron gun, which is formed by setting a specific grid structure such as Figure 1 As shown in , the electron beam will not be intercepted by the grid when passing through the grid, thereby improving the utilization efficiency of the electron beam. The non-intercepted grid-controlled electron gun is actually based on the grid-free gun, adding a shadow grid and a control grid with the same potential as the cathode to form the structure of the grid-controlled electron gun. The shadow grid unit and the control grid unit are arranged in the center, and the grid wires are aligned. When working, the shadow grid blocks electrons for the control grid, so that the electrons are not intercepted by the control grid. Other electrons close to the shadow grid are forced to pass through the unblocked small units due to the shadow grid potential, so that the control grid is blocked and the intercepted current is greatly reduced, from 10% of the original intercepted total current to 0.1%, which can reduce the temperature rise caused by current interception. The use of shadow grids is easier to achieve in terms of processing and assembly. Therefore, the current non-intercepted grid-controlled guns basically use a double-grid structure. However, after the electron gun has been working for a period of time, the cathode emission is reduced due to the continuous heating of the shadow grid, which will eventually shorten the life of the microwave tube and reduce its reliability. Summary of the invention

[0004] In view of the above problems, the present invention provides a cathode assembly for a pulsed gate-controlled microwave tube to solve the problem that after the existing non-intercepted gate-controlled electron gun has worked for a period of time, the cathode emission is reduced due to the excessively high temperature of the shadow grid, thereby improving the life and reliability of the microwave tube.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a cathode assembly for a pulse-gated microwave tube, comprising:

[0007] cathode and shadow grid;

[0008] The emitting surface of the cathode includes a grid groove arranged in the same shape as the shadow grid;

[0009] The shadow grid is located in the grid groove and has no contact with the cathode;

[0010] The surface of the shadow grid facing away from the bottom wall of the grid groove is flush with the emission surface of the cathode, so that the shadow grid and the cathode maintain consistent electric field equipotential surfaces.

[0011] A preferred solution is that the cathode assembly also includes a support tube for accommodating the cathode; the shadow grid includes an inner ring, an outer ring and a connecting structure connecting the inner ring and the outer ring; the inner ring and the connecting structure are located in the grid groove, and the outer ring is fixed to the support tube.

[0012] A preferred solution is that the cathode is a tungsten substrate formed with a gate groove, and the porosity of the tungsten substrate is in the range of 20-35%; the shadow grid is a molybdenum shadow grid with a surface coated with a thin film that suppresses grid electron emission.

[0013] A preferred solution is that the distance between the portion of the shadow grid located in the grid groove and the corresponding wall surface of the grid groove is 0.01-0.02 mm.

[0014] The present invention also provides a method for preparing a cathode assembly for a pulse-gated microwave tube as described above, characterized in that it comprises the following steps:

[0015] S1. Provide a cathode substrate and a shadow grid;

[0016] S2, impregnating the active emission material on the cathode substrate, and melting the active emission material so that it is immersed in the pores of the cathode substrate, so that the pores of the cathode substrate are filled with the active emission material;

[0017] S3, performing surface treatment on the cathode substrate filled with active emission material to remove the active emission material remaining on the surface of the cathode substrate;

[0018] S4, processing a grid groove that is arranged in the same shape as the shadow grid on the emission surface of the cathode substrate, and performing ion cleaning and coating on the emission surface of the cathode substrate with the grid groove by cathode plasma sputtering to obtain a cathode;

[0019] S5. Assemble the shadow grid into the grid groove to form a cathode assembly, and ensure that the shadow grid has no contact with the cathode and the upper surface of the shadow grid is flush with the cathode emission surface.

[0020] The preferred solution is that step S1 further includes pressing the loose tungsten powder with a particle size of 1-10 μm into a porous tungsten blank with a certain shape and strength by isostatic pressing, and then sintering the pressed porous tungsten blank at a high temperature through hydrogen heat treatment to form a cathode matrix, and making the porosity of the cathode matrix reach 20-35%.

[0021] The preferred solution is that step S2 further includes coating the active emission material and a binder on the surface of the cathode substrate, then melting the active emission material by hydrogen heat treatment, and infiltrating and filling the pores of the cathode substrate by capillary action, wherein the immersion temperature is 1500-1800°C and the temperature is kept for 1 to 5 minutes.

[0022] The preferred solution is that step S3 further includes first using a carbide scraper or a single-sided razor blade to remove the blocky active emission material remaining on the surface of the cathode substrate, then using a file or a carbide scraper to remove the residual active emission material outside the emission surface of the cathode substrate, and then using a carbide knife to scrape off the active emission material on the emission surface of the cathode substrate, and finally using sandpaper to clean the residual active emission material on the emission surface, and using a microscope to observe that there is no active emission material on the emission surface of the cathode substrate, and it presents a smooth and uniform emission surface.

[0023] A preferred solution is that step S4 further includes etching the emission surface of the cathode substrate first and then coating it with a film, and the thickness of the film is 0.1-0.9 μm.

[0024] Preferably, step S5 further includes providing a support tube, fixing the cathode in the support tube, assembling the shadow grid into the grid groove and keeping the upper surface of the shadow grid flush with the cathode emission surface, and connecting the shadow grid to the support tube so that there is no contact between the shadow grid and the cathode.

[0025] The beneficial effects of the present invention are:

[0026] The present invention adopts a cathode with a grid groove and an embedded shadow grid, adopts a precision milling machine process to prepare the cathode and precisely assembles the shadow grid into the grid groove, so that the emission surface of the cathode is flush with the upper surface of the shadow grid, ensuring that the shadow grid and the cathode are non-contacting, reducing the temperature of the shadow grid and ensuring that the electric field equipotential surfaces of the two are consistent, and completely eliminating the electric field distortion caused by the bending of the shadow grid equipotential surface. The cathode assembly of the novel embedded shadow grid provided by the present invention can not only make the shadow grid and the cathode non-contacting, so that the heat conduction mode of the prior art is replaced by the heat radiation mode, greatly reducing the temperature of the shadow grid, reducing the evaporation rate of the shadow grid surface suppressing the emission film layer, and effectively reducing the possibility of grid emission, but also can use the flushness of the shadow grid and the cathode emission surface to ensure the consistency of the electric field equipotential surfaces of the two, thereby solving the problem of electric field shielding effect and electron trajectory distortion caused by the inconsistency between the shadow grid equipotential surface and the cathode equipotential surface, increasing the cathode current, improving the laminar flow of electron injection, and improving the life and reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0028] Figure 1 A schematic diagram of the existing cathode structure close to the shadow grid is shown.

[0029] Figure 2-Figure 3 A schematic diagram of the structure of the cathode assembly provided by the present invention is shown.

[0030] Figure 4 A micrograph of a cathode substrate of the present invention is shown.

[0031] Figure 5 A micrograph of a grooved cathode substrate of the present invention is shown.

[0032] Figure 6 A micrograph of a cathode assembly of the present invention is shown.

[0033] Figure 7 A comparison diagram of emission characteristics of the cathode assembly of the present invention and the existing close-fitting shadow grid cathode structure in a diode is shown. DETAILED DESCRIPTION

[0034] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0035] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0036] Techniques and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the techniques and equipment should be considered part of the specification.

[0037] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0038] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0039] Since the existing double-grid structure is that the shadow grid and the cathode are closely attached, its structure is as follows Figure 1As shown, the close-fitting shadow grid 102 is in close contact with the cathode body 101, and the suppression elements of the shadow grid film layer will diffuse to the surface of the cathode at high temperature, resulting in a reduction in cathode emission, and ultimately shortening the life and reliability of the microwave tube. According to research, theoretically, the cathode and the shadow grid are separated by a certain distance, which can effectively change the heat transfer between the cathode and the shadow grid from heat conduction to heat radiation, greatly reduce the temperature of the shadow grid, and reduce the adverse effects of the shadow grid suppression elements on the cathode. However, this design will cause serious distortion of the electron trajectory, form electric field shielding, and lead to a reduction in cathode current. In the standard shadow grid electron gun, the shadow grid is very close to the cathode and is at the cathode potential. At this time, the electric field equipotential surface close to the shadow grid will bend, resulting in serious distortion of the electron trajectory. When the shadow grid is in close contact with the cathode emission surface, the distortion of the electron trajectory is significantly reduced but cannot be completely eliminated. At this time, the shadow grid and the cathode temperature are consistent, and long-term high-temperature operation will lead to greater distortion of the grid emission and the electric field after the grid is deformed. In order to solve the above problems, the present invention provides a cathode assembly for a pulse-gated microwave tube, which can ensure the normal emission of the cathode while reducing the temperature of the shadow grid, effectively improving the life and reliability of the pulse-gated microwave tube. Figures 1 to 7 As shown, the cathode assembly for the pulse-gated microwave tube specifically includes: a cathode 2 and a shadow grid 1; the emitting surface of the cathode 2 includes a grid groove 21 that is arranged in the same shape as the shadow grid 1; the shadow grid 1 is located in the grid groove 21 and has no contact with the cathode 2, so that the temperature of the shadow grid 1 is reduced; the surface of the shadow grid 1 that faces away from the bottom wall of the grid groove 21 is flush with the emitting surface of the cathode 2, so that the shadow grid 1 and the cathode 2 maintain the same electric field equipotential surface. Figure 2 It can be seen that the emission surface of the cathode 2 is an inwardly concave arc surface, and the surface of the shadow grid 1 facing away from the bottom wall of the grid groove 21 is flush with the emission surface of the cathode 2, which means that the upper surface of the shadow grid 1 is coplanar with the emission surface of the cathode 2, and the two together form an arc surface, and the upper surface of the shadow grid 1 neither protrudes from the emission surface of the cathode 2 nor is lower than the emission surface of the cathode 2. The present invention can solve a series of problems of the existing non-intercepted grid-controlled electron gun, such as the grid emission caused by the excessively high temperature of the shadow grid after continuous operation for a period of time; the reduction of the electron beam quality and the deterioration of the laminar flow caused by the deformation of the grid; the gradual evaporation of the emission film layer inhibited by the shadow grid surface to the cathode surface, resulting in a reduction in the emission current, etc., thereby extending the life of the microwave tube and improving its reliability.

[0040] In the above embodiment, the cathode assembly also includes a support tube 3 for accommodating the cathode 2; the shadow grid 1 includes an inner ring 13, an outer ring 11 and a connecting structure 12 connecting the inner ring 13 and the outer ring 11; the inner ring 13 and the connecting structure 12 are located in the grid groove 21, the outer ring 11 is fixed to the support tube 3, and a downward extending extension portion 111 is formed on the outer ring 11, and the shadow grid 1 is connected to the outer wall of the support tube 3 through the extension portion 111.

[0041] Furthermore, the cathode 2 is a tungsten substrate with a gate groove 21 formed on one side, and the porosity of the tungsten substrate is in the range of 20-35%; the shadow grid 1 is a molybdenum shadow grid with a surface coated with a gate electron emission suppression film.

[0042] More specifically, the distance between the portion of the shadow grid 1 located in the grid groove 21 and the corresponding wall of the grid groove 21 is 0.01-0.02 mm. Within this distance range, it can be ensured that the shadow grid 1 and the cathode 2 have no contact, and the heat therebetween is converted from conduction to radiation, which greatly reduces the temperature of the shadow grid 1. At the same time, within the above-mentioned accuracy range, the impact of the electric field shielding effect can be minimized.

[0043] It can be understood that the purpose of the present invention is to reduce the shadow grid temperature of the non-intercepted gate-controlled electron gun in the pulse-gated microwave tube in response to the demand for high power, long life and high reliability, reduce the distortion of the electric field distribution in the tube caused by high-temperature deformation of the shadow grid and the adverse effects of the shadow grid film layer suppression elements on the cathode; solve the problem of reduced cathode current due to electric field shielding generated by the shadow grid; effectively increase the cathode current of the pulse-gated microwave tube, and increase reliability and life.

[0044] The present invention provides a method for preparing a cathode assembly for a pulse-gated microwave tube as described above, the method comprising the following steps: S1, providing a cathode substrate and a shadow grid 1;

[0045] S2, impregnating the active emission material on the cathode substrate, and melting the active emission material so that it is immersed in the pores of the cathode substrate, so that the pores of the cathode substrate are filled with the active emission material;

[0046] S3, performing surface treatment on the cathode substrate filled with active emission material to remove the active emission material remaining on the surface of the cathode substrate;

[0047] S4, processing a grid groove 21 that is arranged in the same shape as the shadow grid 1 on the emission surface of the cathode substrate, and performing ion cleaning and coating on the emission surface of the cathode substrate with the grid groove 21 by cathode plasma sputtering to obtain a cathode 2;

[0048] S5, assembling the shadow grid 1 into the grid groove 21 to form a cathode assembly, and ensuring that the shadow grid 1 has no contact with the cathode 2 and the upper surface of the shadow grid 1 is flush with the emission surface of the cathode 2.

[0049] Compared with the use of ordinary gate-controlled cathodes, the present invention prepares a cathode substrate with uniform pore size and impregnates the emitting material aluminate therein, thereby improving the diffusion of active materials, and increasing the cathode emission, uniformity and life; in addition, a cathode 2 with a gate groove is prepared by precision machining, and then assembled with a shadow grid 1 coated with an inhibition film. Compared with the ordinary structure close to the shadow grid cathode, this structure reduces the shadow grid temperature, reduces the shadow grid film layer to inhibit the diffusion and evaporation of elements to the cathode, improves the cathode's anti-poisoning ability and life, and improves the reliability of the gate-controlled cathode; at the same time, the electric field equipotential surfaces of the cathode 2 and the shadow grid 1 are consistent, which can also solve the problem of electric field shielding of the existing structure, so that the emission current of the cathode is improved.

[0050] Specifically, the cathode 2 with the gate groove 21 is prepared, including providing a cathode substrate, processing the gate groove 21 on the surface of the cathode substrate, and preparing and assembling the thermal subassembly. In a further embodiment of the present invention, a tungsten substrate with uniform porosity is prepared, and the tungsten substrate with uniform porosity is made of tungsten powder with a particle size of 1-10 μm, and the loose tungsten powder is pressed into a porous tungsten blank with a certain shape and strength by isostatic pressing, and then the pressed porous tungsten blank is sintered at high temperature by a hydrogen heat treatment method, so that the tungsten blank finally reaches a porosity of 20-35%.

[0051] In a further embodiment of the present invention, the preparation of cathode 2 includes impregnation of active emission material and treatment of surface residual salt, wherein the active emission material is aluminate, specifically BaO, CaO and Al in a molar ratio of 6:1:2. 2 O 3 , and then use hydrogen heat treatment to melt the aluminate, which is then infiltrated into the pores of the tungsten matrix by capillary action, so that the porous tungsten matrix is ​​filled with aluminate. The tungsten matrix impregnated with aluminate is cleaned on the surface, and a carbide scraper or a single-sided razor blade is used to remove the blocky emission material remaining on the surface; then the lathe is started, and the lathe speed is adjusted to 1000-2000 rpm. The residual salt outside the emission surface is removed with a file or a carbide scraper, and then the emission material on the emission surface is carefully scraped off with a carbide knife, and then the residual salt on the emission surface is removed with sandpaper, and the emission surface is observed under a microscope until there is no residual salt on the emission surface and the emission surface is smooth and uniform.

[0052] In a further embodiment of the present invention, when preparing the gate groove 21 on the emitting surface of the cathode 2, first, a processing plan and process route are formulated, including analyzing the requirements of the cathode surface gate groove drawing; then the processing procedures are designed, such as part positioning reference, determination of the fixture plan, division of work steps, tool selection and determination of cutting amount, etc.; then the CNC machining program is adjusted, such as selecting tool setting points and tool change points, determining tool compensation and machining routes, etc. Finally, the prepared impregnated aluminate tungsten matrix is ​​fixed on the machine tool, and then the gate groove processing program is input, and the spindle speed is set to 30000-40000r / min, the cutting feed rate is 1-10mm / min, the down-cutting feed rate is 2-5mm / min, and the down-cutting feed amount is 0.001-0.01μm; the fixture is aligned according to the process regulations, and then the workpiece coordinate system is input into the offset page, and the coordinates, coordinate values, positive and negative signs, decimal points and syntax are checked; the tool size is 0.1-0.5mm, and the actual tool size is guaranteed to be consistent with the tool compensation value; when the tool moves to a distance of 30-50mm from the workpiece, the Z-axis remaining coordinate value and the X- and Y-axis coordinate values ​​are guaranteed to be consistent with the drawing; after the gate groove 21 is processed, the processed gate groove 21 is measured and inspected to ensure that the gate groove accuracy reaches ±0.01-0.02mm. The hot wire is placed in the cathode tube 3, and then alumina powder and a binder are filled into the cathode tube 3 and dried after centrifugation. The hot wire assembly and the cathode tube 3 are fixed after high-temperature sintering.

[0053] In a further embodiment of the present invention, the cathode plasma sputtering method is used to perform ion cleaning and coating on the emitting surface of the cathode 2 with the gate groove 21, which specifically includes first selecting a suitable mold according to the cathode 2 to be coated; then preheating the working room, degassing for 5±0.5 minutes, and etching the cathode 2; finally, coating the cathode 2, adjusting the coating voltage, current and time according to the specific film thickness requirements, so that the film thickness reaches 0.1-0.9μm.

[0054] In a further embodiment of the present invention, the preparation of the shadow grid 1 includes the preparation of the shadow grid and the suppression film layer. The processing and preparation of the shadow grid 1 requires a series of processes, including stamping the shadow grid blank, shaping the shadow grid, processing the shadow grid blank, ultrasonic cleaning, electrochemical polishing, and high-frequency degassing. Finally, the shadow grid 1 is plated with a suppression film and then subjected to high-frequency degassing to complete the preparation of the shadow grid 1.

[0055] In a further embodiment of the present invention, in the step of preparing the hot wire assembly, the hot wire and the alumina powder are sintered at high temperature by a hydrogen heat treatment method so that they are fixed in the cathode tube 3, the sintering temperature is 1600-1800°C, and the heat preservation is carried out for 5-20 minutes.

[0056] In a further embodiment of the present invention, a support cylinder 3 is provided, the cathode 2 is fixed in the support cylinder 3, the shadow grid 1 is assembled into the grid groove 21 and the upper surface of the shadow grid 1 is kept flush with the emission surface of the cathode 2, and the shadow grid 1 is connected to the support cylinder 3 so that there is no contact between the shadow grid 1 and the cathode 2. More specifically, the cathode 2 is first welded and fixed to the cathode cylinder 3, and then the prepared shadow grid 1 is assembled with the cathode 2 with the film-coated grid groove 21, specifically, the shadow grid 1 is installed into the grid groove 21 and the shadow grid 1 and the cathode cylinder 3 are positioned and welded by laser welding so that there is no contact between the shadow grid 1 and the cathode 2, and finally it is ensured that the upper surface of the shadow grid 1 and the surface where the notch of the grid groove 21 is located completely overlap.

[0057] More specifically, in this embodiment, the cathode substrate is prepared, which specifically includes the following steps: a certain amount of 1-10μm tungsten powder is deoxidized and loaded into a forming mold bag, and the tungsten powder is pressed into a porous tungsten blank by an isostatic pressing process, and the pressure is increased to 50MPa-300MPa, and the pressure is maintained for 5 to 10 minutes. After the pressed porous tungsten blank is demolded, the pressed porous tungsten blank is subjected to high-temperature sintering by a hydrogen heat treatment method, so that the theoretical porosity of the tungsten blank finally reaches the required value of the cathode tungsten base, wherein the sintering specification is a sintering temperature of 1800-2000℃, and the heat preservation is carried out for 10 to 30 minutes; the porosity range of the sintered tungsten base is 20 to 35%.

[0058] In a further embodiment of the present invention, the aluminate emitting material is impregnated into the prepared porous tungsten substrate. The specific steps include coating the aluminate emitting material and a binder on the surface of the tungsten substrate, and then using a hydrogen heat treatment method to melt the aluminate, and use capillary action to infiltrate and fill the cathode tungsten base channels, wherein the salt immersion temperature is 1500-1800°C, and the heat preservation is 1 to 5 minutes.

[0059] In a specific embodiment, a certain amount of tungsten powder is loaded into a mold and isostatically pressed. After the pressed porous tungsten blank is demolded, it is sintered at high temperature by a hydrogen heat treatment method, wherein the sintering specification is a sintering temperature of 1850±20°C and a heat preservation time of 20 minutes; the porosity range of the sintered tungsten base is 27%; Figure 5 1 is a microscopic observation image of a cathode substrate prepared in an embodiment of the present invention; an aluminate-containing emission material is impregnated in a tungsten substrate.

[0060] Use sandpaper to clean the residual salt on the cathode emission surface; install the surface-treated tungsten substrate on the machine tool, then enter the gate groove processing program, set the spindle speed to 36000 / min, cutting feed rate to 2mm / min, down-cut feed rate to 3mm / min, and down-cut feed amount to 0.008μm; use a tool size of 0.2mm to complete the gate groove processing. Figure 5 This is a microscope observation image of a cathode with a gate groove prepared in an embodiment of the present invention.

[0061] Then, the shadow grid 1 is installed into the grid groove 21 and the shadow grid 1 is welded to the cathode tube 3 to complete the preparation of the cathode assembly. Figure 6 The image shown is a microscope observation image of the cathode assembly prepared in the embodiment of the present invention. The embedded shadow grid cathode assembly prepared in this embodiment was subjected to temperature test and pulse emission characteristic test in the diode. The emission performance curve is shown in FIG. Figure 7 As shown, the temperature test data is shown in Table 1.

[0062] Table 1 Comparison of temperature tests between embedded shadow grid cathode assembly and close-fitting shadow grid cathode structure

[0063]

[0064] From the temperature test in Table 1, it can be seen that the grid temperature of the embedded shadow grid cathode assembly of the present invention is 100-150°C lower than the cathode temperature, which can effectively reduce the grid temperature; Figure 7 It can be seen that the slope of the new cathode assembly of the present invention is 1.44 and the inflection point current density is 15A / cm when the working temperature is 1050°C, the pulse width of the pulse voltage is 10us, and the frequency is 200Hz. 2 , which are better than the structure close to the shadow grid cathode.

[0065] In an optional embodiment, tungsten powder is loaded into a mold and isostatically pressed; after the pressed porous tungsten blank is demolded, it is subjected to high-temperature sintering using a hydrogen heat treatment method, wherein the sintering specification is a sintering temperature of 1880±20°C and a heat preservation time of 20 minutes; the porosity of the sintered tungsten matrix is ​​23%; the surface-treated tungsten matrix is ​​mounted on a machine tool, and then the gate groove processing program is input, setting the spindle speed to 32000 / min, the cutting feed rate to 1.5 / min, the down-cutting feed rate to 2mm / min, and the down-cutting feed amount to 0.006μm; a tool size of 0.15mm is used to complete the gate groove 21 processing.

[0066] In another optional embodiment, tungsten powder is loaded into a mold and isostatically pressed; after the pressed porous tungsten blank is demolded, it is sintered at high temperature by hydrogen heat treatment method, wherein the sintering specification is sintering temperature of 1800±20℃, and heat preservation for 20 minutes; the porosity of the sintered tungsten base is 30%; the surface treated tungsten base is installed on the machine tool, and then the gate groove processing program is input, and the spindle speed is set to 40000 / min, cutting feed rate 4 / min, down-cutting feed rate 4mm / min, and down-cutting feed amount 0.009μm; the tool size is 0.1mm to complete the processing of the gate groove 21. Tests show that the emission performance of the cathode assembly prepared above fully meets the design requirements. Through the above description, the present invention discloses a method for preparing an embedded shadow grid cathode assembly, in which tungsten powder is used to prepare a cathode substrate with uniform pore size, thereby improving the uniformity and life of the cathode emission current; a cathode 2 with a gate groove 21 is prepared by a precision machining method, and a shadow grid 1 is assembled to the gate groove 21 without contact between the shadow grid 1 and the cathode 2, thereby reducing the temperature of the shadow grid 1, reducing the shadow grid film layer to inhibit the diffusion and evaporation of elements to the cathode 2, improving the anti-poisoning ability and life of the cathode 2, and improving the reliability of the gate-controlled cathode; at the same time, the electric field equipotential surfaces of the cathode 2 and the shadow grid 1 are consistent, which can also solve the problem of electric field shielding of the original structure, and the emission current of the cathode is improved.

[0067] In summary, the present invention adopts a cathode with a grid groove and an embedded shadow grid, adopts a precision milling machine process to prepare the cathode and precisely assembles the shadow grid into the grid groove, so that the emission surface of the cathode is flush with the upper surface of the shadow grid, ensuring that the shadow grid and the cathode are non-contacting, reducing the temperature of the shadow grid and ensuring that the electric field equipotential surfaces of the two are consistent, and completely eliminating the electric field distortion caused by the bending of the shadow grid equipotential surface. The cathode assembly of the novel embedded shadow grid provided by the present invention can not only make the shadow grid and the cathode non-contacting, so that the heat conduction method of the prior art is replaced by the heat radiation method, greatly reducing the temperature of the shadow grid, reducing the evaporation rate of the emission-inhibiting film layer on the surface of the shadow grid, and effectively reducing the possibility of grid emission, but also can use the flushness of the shadow grid and the cathode emission surface to ensure the consistency of the electric field equipotential surfaces of the two, thereby solving the problem of electric field shielding effect and electron trajectory distortion caused by the inconsistency between the shadow grid equipotential surface and the cathode equipotential surface, increasing the cathode current, improving the laminar flow of electron injection, and improving the life and reliability of the device.

[0068] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A cathode assembly for a pulse-gated microwave tube, characterized in that: include: cathode and shadow grid; The emitting surface of the cathode includes a grid groove arranged in the same shape as the shadow grid; The shadow grid is located in the grid groove and has no contact with the cathode; The surface of the shadow grid facing away from the bottom wall of the grid groove is flush with the emission surface of the cathode, so that the shadow grid and the cathode maintain consistent electric field equipotential surfaces.

2. The cathode assembly for a pulse-gated microwave tube according to claim 1, characterized in that: The cathode assembly also includes a support tube for accommodating the cathode; the shadow grid includes an inner ring, an outer ring and a connecting structure connecting the inner ring and the outer ring; the inner ring and the connecting structure are located in the grid groove, and the outer ring is fixed to the support tube.

3. The cathode assembly for a pulse-gated microwave tube according to claim 1, characterized in that: The cathode is a tungsten substrate with a gate groove formed therein, and the porosity of the tungsten substrate is in the range of 20-35%; the shadow grid is a molybdenum shadow grid with a thin film coated on the surface to suppress the gate electron emission.

4. The cathode assembly for a pulse-gated microwave tube according to claim 1, characterized in that: The distance between the part of the shadow grid located in the grid groove and the corresponding wall surface of the grid groove is 0.01-0.02mm.

5. A method for preparing a cathode assembly for a pulse-gated microwave tube according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Provide a cathode substrate and a shadow grid; S2, impregnating the active emission material on the cathode substrate, and melting the active emission material so that it is immersed in the pores of the cathode substrate, so that the pores of the cathode substrate are filled with the active emission material; S3, performing surface treatment on the cathode substrate filled with active emission material to remove the active emission material remaining on the surface of the cathode substrate; S4, processing a grid groove that is arranged in the same shape as the shadow grid on the emission surface of the cathode substrate, and performing ion cleaning and coating on the emission surface of the cathode substrate with the grid groove by cathode plasma sputtering to obtain a cathode; S5. Assemble the shadow grid into the grid groove to form a cathode assembly, and ensure that the shadow grid has no contact with the cathode and the upper surface of the shadow grid is flush with the cathode emission surface.

6. The preparation method according to claim 5, characterized in that: Step S1 further includes pressing the bulk tungsten powder into a porous tungsten blank by isostatic pressing, and sintering the porous tungsten blank at high temperature by hydrogen heat treatment to form a cathode substrate.

7. The preparation method according to claim 5, characterized in that: Step S2 further includes coating the active emission material on the surface of the cathode substrate, melting the active emission material by hydrogen heat treatment, and infiltrating the active emission material into the pores of the cathode substrate.

8. The preparation method according to claim 5, characterized in that: Step S3 further includes removing the active emission material remaining on the cathode substrate, and observing that there is no active emission material on the emission surface of the cathode substrate, and the emission surface is smooth and uniform.

9. The preparation method according to claim 5, characterized in that: Step S4 further includes etching and coating the emission surface of the cathode substrate.

10. The preparation method according to claim 5, characterized in that: Step S5 further includes providing a support tube, fixing the cathode in the support tube, assembling the shadow grid into the grid groove and fixing it to the support tube so that there is no contact between the shadow grid and the cathode.

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