Composite cathode, cathode focusing electrode structure and preparation method of composite cathode

Abstract

The invention relates to the technical field of vacuum electronic devices, and provides a composite cathode, a cathode focusing electrode structure and a preparation method of the composite cathode. The composite cathode comprises a cathode body and a composite ring, a spherical groove is formed in one end of the cathode body, the composite ring is arranged on the peripheral wall of the cathode body in a sleeving mode and is arranged on the inner side of the focusing electrode in an inserted mode, the composite ring is provided with an annular face extending in the circumferential direction of the composite ring, and at least part of the composite ring is exposed out of a notch of the spherical groove. The annular surface is positioned between the inner wall surface of the spherical groove and the inner wall surface of the focusing electrode; and the annular surface and the inner wall surface of the spherical groove form a smooth curved surface. According to the composite cathode disclosed by the invention, the turning quality of the cathode curved surface corresponding to the composite cathode can be ensured, the laminar flow property of the electron beam at the outer edge of the cathode is greatly improved, and the transmission state of the electron beam is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum electronic devices, and in particular to a composite cathode, a cathode focusing electrode structure and a method for preparing the composite cathode. Background Art

[0002] A klystron is a high-power microwave vacuum electronic device primarily used to amplify or generate high-frequency electromagnetic wave signals. It is widely used in radar, particle accelerators, satellite communications, and other fields. Its core principle is based on velocity modulation and density modulation of an electron beam, achieving energy exchange and signal amplification through the interaction between electrons and high-frequency electromagnetic fields.

[0003] In microwave vacuum electronic devices, the electron gun is one of the most important components of the klystron. The electron gun consists of a cathode, a heating assembly, and a focusing electrode. The heating assembly provides the cathode with the temperature required to emit electrons in the form of thermal energy. The focusing electrode and the cathode are usually at the same potential. Through the design of appropriate electrical boundaries, they can jointly form the electrostatic field distribution required for electron forming.

[0004] However, in actual applications, it is found that due to the material properties of the cathode, the cathode usually shrinks and deforms during the cathode preparation process, which requires fine turning of the cathode surface. During the turning process of the cathode surface, the cathode will experience edge collapse. The defects of the cathode surface edge will affect the uniformity of electron beam emission, the laminarity of the trajectory and the magnitude of the cathode emission current. In addition, the trajectory laminarity of the outer edge of the cathode is poor, which affects the transmission state of the electron beam. Summary of the Invention

[0005] The present invention provides a composite cathode, a cathode focusing electrode structure and a method for preparing the composite cathode, which can ensure the turning quality of the cathode curved surface, greatly improve the laminar flow of the electron beam at the outer edge of the cathode, and ensure the transmission state of the electron beam.

[0006] In a first aspect, the present invention provides a composite cathode comprising: a cathode body, wherein a spherical groove is formed at one end of the cathode body; a composite ring, the composite ring being sleeved on the circumferential wall of the cathode body and being configured to be inserted into the inner side of the focusing electrode, the composite ring having an annular surface extending along its circumference, at least a portion of the composite ring being exposed from the notch of the spherical groove, such that the annular surface is located between the inner wall surface of the spherical groove and the inner wall surface of the focusing electrode; The annular surface and the inner wall surface of the spherical groove form a smooth curved surface.

[0007] According to a composite cathode provided by the present invention, a stopper is provided on the peripheral wall of the cathode body, and the stopper is arranged close to the notch of the spherical groove; The composite ring is sleeved on the peripheral wall of the stop, the first end of the composite ring contacts the side wall of the stop, the second end of the composite ring is exposed from the notch of the spherical groove, and the annular surface is formed at the second end of the composite ring.

[0008] According to a composite cathode provided by the present invention, an annular groove is provided on the inner wall of the composite ring, and the annular groove extends along the circumference of the composite ring; The annular groove is embedded with solder, and the solder is used to weld the cathode body and the composite ring into one. The solder includes any one of nickel-based solder, palladium-based solder and platinum-based alloy solder.

[0009] According to a composite cathode provided by the present invention, the melting point of the material of the composite ring is greater than 1200°C, and the thermal expansion coefficient is not higher than 6.0×10 -6 1 / ℃.

[0010] According to a composite cathode provided by the present invention, the material of the composite ring includes any one of tungsten, tungsten alloy, molybdenum and molybdenum alloy.

[0011] According to a composite cathode provided by the present invention, the cathode body comprises: A tungsten sponge matrix, wherein porous voids are formed in the tungsten sponge matrix; An emitting material is contained in the porous voids.

[0012] In a second aspect, the present invention further provides a cathode focusing electrode structure, comprising: A composite cathode as described above; a heating assembly connected to a cathode body corresponding to the composite cathode; The focusing electrode is coaxially arranged with the composite cathode, and the focusing electrode is sleeved on the outside of the composite ring corresponding to the composite cathode.

[0013] In a third aspect, the present invention further provides a method for preparing the composite cathode as described above, comprising: preparing the cathode body and the composite ring; The composite ring is sleeved on the peripheral wall of the cathode body, and the cathode body and the composite ring are welded into one body by brazing; The cathode body and the composite ring are turned to form an annular surface on the composite ring, and the inner wall surface of the spherical groove and the annular surface of the composite ring form a smooth curved surface.

[0014] According to a preparation method provided by the present invention, the steps of preparing the cathode body include: The copper metal in the tungsten-copper alloy is removed by chemical etching and / or high-temperature smelting to obtain a tungsten sponge matrix with porous voids; The emission material is melted into a liquid state under a hydrogen atmosphere, and the tungsten sponge matrix is immersed in the liquid emission material to prepare the cathode body.

[0015] According to a preparation method provided by the present invention, the step of sleeve-arranging the composite ring on the peripheral wall of the cathode body and welding the cathode body and the composite ring into one body by brazing comprises: Turning the peripheral wall of the stopper corresponding to the cathode body until the diameter of the peripheral wall of the stopper matches the inner diameter of the composite ring; Solder is embedded in the annular groove of the composite ring, the composite ring is sleeved on the peripheral wall of the stop, and the cathode body and the composite ring are welded into one body based on the solder.

[0016] The composite cathode, cathode focusing electrode structure and preparation method of the composite cathode provided by the present invention are as follows: by configuring a composite ring on the cathode body, the composite ring is sleeved on the peripheral wall of the cathode body and is located near the notch of the spherical groove, so that the annular surface of the composite ring and the inner wall surface of the spherical groove can be simultaneously turned; during the processing, the composite ring not only bears part of the stress of the turning tool, but also protects the area where the notch of the spherical groove is located, effectively ensuring the integrity of the edge of the cathode body during the turning process, and while ensuring the turning quality of the cathode curved surface corresponding to the composite cathode, it also ensures the smoothness and continuity of the curved surface formed by the annular surface and the inner wall surface of the spherical groove; this design can also ensure, based on the transition effect of the composite ring, that the outer edge of the cathode curved surface is not directly exposed to the transition zone between the cathode body and the focusing electrode, so that the electron trajectory of the outer edge of the cathode can be emitted more strictly along the outer edge of the cathode curved surface, greatly improving the laminar flow of the electron beam flow at the outer edge of the cathode, and ensuring the transmission state of the electron beam flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a schematic diagram of the cross-sectional structure of the composite cathode provided by the present invention.

[0019] Figure 2 It is a schematic diagram of the three-dimensional structure of the cathode body provided by the present invention.

[0020] Figure 3 It is a schematic diagram of the cross-sectional structure of the cathode body provided by the present invention.

[0021] Figure 4 It is a partially enlarged schematic diagram of the cooperation between the cathode body and the composite ring provided by the present invention.

[0022] Figure 5 It is a schematic cross-sectional structural diagram of the cathode focusing electrode structure provided by the present invention.

[0023] Figure 6 It is a schematic flow chart of the preparation method of the composite cathode provided by the present invention.

[0024] Figure 7 It is a schematic diagram of the three-dimensional structure of the composite ring provided by the present invention (without the annular surface).

[0025] Figure 8 It is a schematic diagram of the cross-sectional structure of the composite ring provided by the present invention (without the annular surface).

[0026] Figure 9 The present invention provides Figure 7 The cross-sectional structural diagram shown is a composite ring sleeved on the peripheral wall of the cathode body.

[0027] Figure 10 The present invention provides Figure 7 The diagram shows a three-dimensional structure in which the composite ring is sleeved on the peripheral wall of the cathode body.

[0028] Figure 11 The present invention provides Figure 10 The cathode body and the composite ring are turned simultaneously, and a schematic diagram of the three-dimensional structure of the composite cathode is obtained.

[0029] Figure 12 It is a simulation schematic diagram of the potential line distribution of the electron gun based on the cathode focusing electrode structure provided by the present invention.

[0030] Figure 13 It is a simulation schematic diagram of the electron trajectory distribution of the electron gun based on the cathode focusing electrode structure provided by the present invention.

[0031] Figure 14 It is a simulation schematic diagram of the electron trajectory cross section of an electron gun based on a cathode focusing electrode structure in the prior art.

[0032] Figure 15 It is a simulation schematic diagram of the electron trajectory cross section of the electron gun based on the cathode focusing electrode structure provided by the present invention.

[0033] Reference numerals: 1. cathode body; 101. spherical groove; 102. stopper; 2. Composite ring; 201. Annular surface; 202. Annular groove; 3. Heating assembly; 4. Focusing electrode; 5. First supporting tube; 6. Second supporting tube; 7. Third supporting tube. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] The following combination Figures 1-15 , the composite cathode, cathode focusing electrode structure and composite cathode preparation method provided by the embodiments of the invention are described in detail through specific embodiments and their application scenarios.

[0036] In the first aspect, Figure 1 As shown, an embodiment of the present invention provides a composite cathode, comprising: a cathode body 1 and a composite ring 2; A spherical groove 101 is formed at one end of the cathode body 1, and the composite ring 2 is sleeved on the peripheral wall of the cathode body 1 and is configured to be inserted on the inner side of the focusing electrode 4. The composite ring 2 has an annular surface 201 extending along its circumference, and at least part of the composite ring 2 is exposed at the notch of the spherical groove 101, so that the annular surface 201 is located between the inner wall surface of the spherical groove 101 and the inner wall surface of the focusing electrode 4; wherein the annular surface 201 and the inner wall surface of the spherical groove 101 form a smooth curved surface.

[0037] It is understandable that since the operating temperature of the cathode body 1 is usually above 900°C, in order to meet the working requirements of the cathode body 1, the composite ring 2 is made of a material with a high melting point and a low thermal expansion coefficient, so that when the temperature changes, the size of the composite ring 2 changes less, which helps to reduce thermal stress and avoid deformation, cracking and other problems due to thermal expansion and contraction, and is also beneficial to reduce the impact of the deformation of the composite ring 2 on the cathode body 1.

[0038] In practical applications, the inner wall surface of the spherical groove 101 is spherical, and the inner wall surface of the spherical groove 101 serves as the cathode curved surface of the composite cathode, which is used to realize the emission of the electron beam; the annular surface 201 of the composite ring 2 can be prepared by turning, and the annular surface 201 and the inner wall surface of the spherical groove 101 can be turned at the same time to ensure that the curvature radius of the annular surface 201 is equal to the curvature radius of the inner wall surface of the spherical groove 101, and the tangent direction of the side edge of the spherical groove 101 close to the annular surface 201 is the same as the tangent direction of the side edge of the annular surface 201 close to the spherical groove 101, thereby forming a smooth curved surface between the annular surface 201 and the inner wall surface of the spherical groove 101.

[0039] Since the composite ring 2 is arranged close to the notch of the spherical groove 101, when the annular surface 201 and the inner wall surface of the spherical groove 101 are turned at the same time, the composite ring 2 not only bears part of the stress of the turning tool, but also protects the edge of the cathode body 1 (the area where the notch of the spherical groove 101 is located), effectively ensuring the integrity of the edge of the cathode body 1 during the turning process. While ensuring the turning quality of the cathode curved surface, it also ensures the smoothness and continuity of the curved surface formed by the annular surface 201 and the inner wall surface of the spherical groove 101.

[0040] At the same time, if Figure 1 and Figure 5 As shown, by arranging the composite ring 2 outside the cathode body 1, the outer edge of the cathode curved surface corresponding to the composite cathode is not directly exposed to the transition area between the cathode body 1 and the focusing electrode 4. Figure 12 and Figure 13 As shown, in Figure 12 Under the electric field constraint corresponding to the potential line shown, the composite cathode can emit Figure 13 As shown in the electron beam flow, the present application arranges a composite ring 2 on the outside of the cathode body 1. Based on the transition effect of the composite ring 2, it is ensured that the outer edge of the cathode curved surface is not directly exposed to the transition zone between the cathode body 1 and the focusing electrode 4, so that the electron trajectory of the outer edge of the cathode is strictly emitted along the outer edge of the cathode curved surface, which greatly improves the laminar flow of the electron beam flow at the outer edge of the cathode.

[0041] Further, if Figure 14 As shown, for an electron gun without the composite ring 2 of the present invention, it can be seen from the electron trajectory cross-section that the electron layer boundary has more discrete electrons. Figure 15 As shown, for the electron gun provided with the composite ring 2 shown in the present invention, it can be seen from the electron trajectory cross-sectional diagram that the electron layer boundary is clearer and the discrete electrons are basically removed, which also shows that by providing the composite ring 2, the laminar flow of the electron beam at the outer edge of the cathode can be greatly improved.

[0042] In some embodiments, as Figure 1 、 Figure 2 and Figure 3 As shown, the peripheral wall of the cathode body 1 is provided with a stopper 102, and the stopper 102 is arranged close to the notch of the spherical groove 101; The composite ring 2 is sleeved on the peripheral wall of the stopper 102 , with the first end of the composite ring 2 contacting the side wall of the stopper 102 , the second end of the composite ring 2 being exposed from the notch of the spherical groove 101 , and the annular surface 201 being formed at the second end of the composite ring 2 .

[0043] It can be understood that by providing the stopper 102 on the peripheral wall of the cathode body 1 , it is convenient to position the composite ring 2 on the cathode body 1 based on the stopper 102 .

[0044] In actual application, the peripheral wall of the stop 102 fits against the inner wall of the composite ring 2, and the wall surface corresponding to the first end of the composite ring 2 abuts against the side wall of the stop 102. The edge between the inner wall of the composite ring 2 and the end surface corresponding to the second end of the composite ring 2 can be turned to form an annular surface 201 at the second end of the composite ring 2.

[0045] In some embodiments, as Figure 1 and Figure 4 As shown, the inner wall of the composite ring 2 is provided with an annular groove 202, and the annular groove 202 extends along the circumference of the composite ring 2; Solder is embedded in the annular groove 202 . The solder is used to weld the cathode body 1 and the composite ring 2 into one. The solder includes any one of nickel-based solder, palladium-based solder and platinum-based alloy solder.

[0046] It can be understood that since the annular groove 202 is opened on the inner wall of the composite ring 2, when the composite ring 2 is sleeved on the peripheral wall of the stop 102, the peripheral wall of the stop 102 forms a seal on the notch of the annular groove 202, ensuring that the solder in the annular groove 202 is in a sealed environment.

[0047] When the composite ring 2 is sleeved on the peripheral wall of the stop 102 , the composite ring 2 can be heated to melt the solder in the annular groove 202 . After the solder cools and solidifies, the cathode body 1 and the composite ring 2 are welded together.

[0048] Among them, the nickel-based solder can be nickel-chromium-borosilicate (Ni-Cr-B-Si) solder, and the melting point range of the nickel-based solder is 970°C-1000°C; the palladium-based solder can be palladium-silver-copper (Pd-Ag-Cu) solder, and the melting point range of the palladium-based solder is 700°C-1237°C; the platinum-based alloy solder can be platinum-iridium (Pt-Ir) alloy solder, platinum-rhodium (Pt-Rh) alloy solder, platinum-nickel (Pt-Ni) alloy solder or platinum-tungsten (Pt-W) alloy solder, and the melting point range of the platinum-based alloy solder is 1200°C-1500°C.

[0049] In some embodiments, the melting point of the material of the composite ring 2 is greater than 1200°C, and the thermal expansion coefficient is not higher than 6.0×10 - 6 1 / ℃.

[0050] It can be understood that, considering that the operating temperature of the cathode body 1 is usually above 900°C, by limiting the melting point and thermal expansion coefficient of the material of the composite ring 2, it is ensured that the composite ring 2 can adapt to the working environment of the cathode body 1, and the size of the composite ring 2 changes little in the environment where the cathode body 1 is located. When the composite ring 2 is mounted on the peripheral wall of the cathode body 1, the deformation of the composite ring 2 will not cause adverse effects on the cathode body 1.

[0051] In practical applications, the melting point is greater than 1200℃ and the thermal expansion coefficient is not higher than 6.0*10 -6 The materials of 1 / ℃ can be shown in Table 1, as shown below: Table 1: Melting point and thermal expansion coefficient of materials

[0052] In order to facilitate turning of the composite ring 2, the composite ring 2 is preferably made of any one of tungsten, tungsten alloy, molybdenum, and molybdenum alloy. The specific selection of tungsten alloy can be referred to in Table 2 below, and the specific selection of molybdenum alloy can be referred to in Table 3 below.

[0053] Table 2: Melting point and thermal expansion coefficient of tungsten alloy

[0054] Table 3: Melting point and thermal expansion coefficient of molybdenum alloys

[0055] In some embodiments, the cathode body 1 includes: a tungsten sponge matrix and an emission material. Porous voids are formed in the tungsten sponge matrix, and the emission material is accommodated in the porous voids.

[0056] In practical applications, the tungsten sponge matrix can be prepared by mixing tungsten powder with a pore-forming agent (such as carbonate, organic powder), pressing it into a green body, and then sintering the green body at a high temperature (for example, 1600-2000°C) in a reducing atmosphere (such as hydrogen) to volatilize the pore-forming agent in the green body to prepare a tungsten sponge matrix with a porosity of 15%-30%.

[0057] The emitting material can be barium calcium aluminate (such as 411 salt, 612 salt, etc.) or rare earth oxide (yttrium oxide, lanthanum oxide, etc.). After the emitting material is heated to a molten state, the tungsten sponge matrix is placed in the molten emitting material. The capillary action can ensure that the emitting material enters the porous gaps of the tungsten sponge matrix.

[0058] In the second aspect, Figure 5 As shown, an embodiment of the present invention further provides a cathode focusing electrode structure, comprising: the composite cathode as described above; A heating component 3, the heating component 3 is connected to the cathode body 1 corresponding to the composite cathode; The focusing electrode 4 is coaxially arranged with the composite cathode and is sleeved on the outside of the composite ring 2 corresponding to the composite cathode. The inner wall surface of the spherical groove 101 corresponding to the cathode body 1 and the annular surface 201 on the composite ring 2 form a smooth curved surface.

[0059] Since the cathode focusing electrode structure includes a composite cathode, the specific structure of the composite cathode refers to the above embodiment, and the cathode focusing electrode structure of this embodiment includes all the technical solutions of the above embodiment, and therefore has at least all the beneficial effects achieved by all the technical solutions of the above embodiment, which will not be repeated here.

[0060] Furthermore, the cathode focusing electrode structure also includes a first supporting tube 5 and a second supporting tube 6. The cathode body 1 corresponding to the composite cathode is coaxially installed at the port of the first supporting tube 5. The second supporting tube 6 is sleeved on the outside of the first supporting tube 5, and the focusing electrode 4 is coaxially installed at the port of the second supporting tube 6.

[0061] Furthermore, the cathode focusing electrode structure also includes a third support tube 7, which is inserted into the inner side of the first support tube 5. The cathode body 1 corresponding to the composite cathode is also coaxially installed at the port of the third support tube 7. An accommodating space is formed between the first support tube 5 and the third support tube 7. The heating component 3 is arranged in the accommodating space and is connected to the cathode body 1. The heating component 3 can be configured to include components such as a hot wire ring and porcelain beads. The hot wire ring can be a plurality of concentrically arranged rings, which are wound by a spring-shaped hot wire, and the porcelain beads are used to insulate and fix the hot wire ring.

[0062] In the third aspect, Figure 6 As shown, an embodiment of the present invention further provides a method for preparing the composite cathode as described above, comprising the following steps: Step 610: Prepare the cathode body and the composite ring.

[0063] Specifically, the steps of preparing the cathode body include but are not limited to the following steps: The copper metal in the tungsten-copper alloy is removed by chemical etching and / or high-temperature smelting to obtain a tungsten sponge matrix with porous voids; The cathode body is prepared by melting the emission material into a liquid state under a hydrogen atmosphere, and then placing the tungsten sponge matrix into the liquid emission material. The melting temperature of the emission material is 1400-2000°C.

[0064] like Figure 7 and Figure 8 As shown, the steps for preparing the composite ring 2 include but are not limited to the following steps: Select parts made of tungsten or molybdenum and perform CNC machining on the parts to prepare metal rings; The inner wall of the metal ring is turned to form an annular groove 202 on the inner wall of the metal ring.

[0065] Step 620: sleeve the composite ring onto the peripheral wall of the cathode body, and weld the cathode body and the composite ring into one body by brazing.

[0066] Specifically, if Figure 9 and Figure 10 As shown, in actual application, the peripheral wall of the stopper 102 corresponding to the cathode body 1 can be turned until the diameter of the peripheral wall of the stopper 102 matches the inner diameter of the composite ring 2; Solder is embedded in the annular groove of the composite ring 2. The composite ring 2 is sleeved on the peripheral wall of the stop 102, so that the cathode body 1 and the composite ring 2 can be welded together using high-temperature brazing. The solder can be any one of nickel-based solder, palladium-based solder, and platinum-based alloy solder.

[0067] Step 630 , lathe the cathode body and the composite ring to form an annular surface on the composite ring, and the inner wall surface of the spherical groove and the annular surface of the composite ring form a smooth curved surface.

[0068] Specifically, if Figure 1 and Figure 11 As shown, in actual application, the edge of the composite ring 2 close to the spherical groove can be turned by a tool first to preliminarily form an annular surface 201 on the composite ring 2, and then the inner wall surface of the spherical groove 101 and the annular surface of the composite ring 2 are turned at the same time until the inner wall surface of the spherical groove 101 and the annular surface of the composite ring 2 are precision turned as a whole to the designed curvature radius, ensuring that the inner wall surface of the spherical groove and the annular surface of the composite ring form a smooth curved surface.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A composite cathode, characterized in that: include: a cathode body, wherein a spherical groove is formed at one end of the cathode body; a composite ring, the composite ring being sleeved on the circumferential wall of the cathode body and being configured to be inserted into the inner side of the focusing electrode, the composite ring having an annular surface extending along its circumference, at least a portion of the composite ring being exposed from the notch of the spherical groove, such that the annular surface is located between the inner wall surface of the spherical groove and the inner wall surface of the focusing electrode; The annular surface and the inner wall surface of the spherical groove form a smooth curved surface.

2. The composite cathode according to claim 1, wherein The peripheral wall of the cathode body is provided with a stopper, and the stopper is arranged close to the notch of the spherical groove; The composite ring is sleeved on the peripheral wall of the stop, the first end of the composite ring contacts the side wall of the stop, the second end of the composite ring is exposed from the notch of the spherical groove, and the annular surface is formed at the second end of the composite ring.

3. The composite cathode according to claim 2, characterized in that An annular groove is provided on the inner wall of the composite ring, and the annular groove extends along the circumference of the composite ring; The annular groove is embedded with solder, and the solder is used to weld the cathode body and the composite ring into one. The solder includes any one of nickel-based solder, palladium-based solder and platinum-based alloy solder.

4. The composite cathode according to claim 1, wherein The melting point of the composite ring material is greater than 1200 ° C, and the thermal expansion coefficient is not higher than 6.0×10 -6 1 / ℃.

5. The composite cathode according to claim 4, characterized in that The material of the composite ring includes any one of tungsten, tungsten alloy, molybdenum and molybdenum alloy.

6. The composite cathode according to any one of claims 1 to 5, characterized in that The cathode body comprises: A tungsten sponge matrix, wherein porous voids are formed in the tungsten sponge matrix; An emitting material is contained in the porous voids.

7. A cathode focusing electrode structure, characterized in that: include: The composite cathode according to any one of claims 1 to 6; a heating assembly connected to a cathode body corresponding to the composite cathode; The focusing electrode is coaxially arranged with the composite cathode, and the focusing electrode is sleeved on the outside of the composite ring corresponding to the composite cathode.

8. A method for preparing a composite cathode according to any one of claims 1 to 6, characterized in that: include: preparing the cathode body and the composite ring; The composite ring is sleeved on the peripheral wall of the cathode body, and the cathode body and the composite ring are welded into one body by brazing; The cathode body and the composite ring are turned to form an annular surface on the composite ring, and the inner wall surface of the spherical groove and the annular surface of the composite ring form a smooth curved surface.

9. The preparation method according to claim 8, characterized in that The steps of preparing the cathode body include: The copper metal in the tungsten-copper alloy is removed by chemical etching and / or high-temperature smelting to obtain a tungsten sponge matrix with porous voids; The emission material is melted into a liquid state under a hydrogen atmosphere, and the tungsten sponge matrix is immersed in the liquid emission material to prepare the cathode body.

10. The preparation method according to claim 8, characterized in that The step of sleeve-arranging the composite ring on the peripheral wall of the cathode body and welding the cathode body and the composite ring into one body by brazing comprises: Turning the peripheral wall of the stopper corresponding to the cathode body until the diameter of the peripheral wall of the stopper matches the inner diameter of the composite ring; Solder is embedded in the annular groove of the composite ring, the composite ring is sleeved on the peripheral wall of the stop, and the cathode body and the composite ring are welded into one body based on the solder.

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