Cathode heater assembly for traveling wave tube and preparation method

Abstract

The invention provides a cathode heater assembly for a traveling wave tube and a preparation method, and belongs to the technical field of electric vacuum devices. Comprising a cathode cake which is a solid spherical cathode and is used as a traveling wave tube electron source to emit electrons; the heater is of a composite structure composed of a boron nitride insulating layer, a graphite electrode layer and a boron nitride covering layer, the graphite electrode layer is located between the boron nitride insulating layer and the boron nitride covering layer, the graphite electrode layer is of a single-spiral structure, the boron nitride insulating layer is brazed to the bottom of the cathode cake, and the heater is used for heating the cathode cake; the heater lead comprises a first heater lead and a second heater lead, the first heater lead is brazed at the first end of the single spiral structure of the graphite electrode layer through the boron nitride covering layer, and the second heater lead is brazed at the second end of the single spiral structure of the graphite electrode layer through the boron nitride covering layer; the first end is far away from the center of the single-spiral structure of the graphite electrode layer, and the second end is close to the center of the single-spiral structure of the graphite electrode layer.

Description

Technical Field

[0001] The invention relates to the technical field of electric vacuum devices, and in particular to a cathode thermal subassembly for a traveling wave tube and a preparation method thereof. Background Art

[0002] The traveling wave tube is a key component of the satellite. In the traveling wave tube, the cathode reaches a specific working temperature to generate and emit electrons. The thermal subassembly provides heat to the cathode. The cathode thermal subassembly maintains the cathode at the working temperature by heating, and continuously generates and emits electrons. In the traditional cathode thermal subassembly, the thermal subassembly is wound into a double helix structure with tungsten-rhenium wire, electrophoresis and sintering are performed, and the lead leg is covered with a tungsten spring, and then loaded into the cathode tube together with alumina powder and sintered together. The cathode is prepared through salt immersion, spherical surface turning, film coating and other processes to form a cathode thermal subassembly.

[0003] However, the traditional cathode thermal sub-assembly is operated in a high-temperature environment of 1200℃ for a long time. The alumina is slowly reduced by tungsten at high temperature, causing the thermal sub-circuit of the cathode thermal sub-assembly and the aging of the traveling wave tube. In addition, the interior of the sintered alumina is loose and easy to absorb and release air, and the double helix structure is large in volume, resulting in a large volume and pores, resulting in a long heat transfer path and excessive power consumption of the thermal sub-assembly, which leads to problems such as excessive operating temperature of the cathode thermal sub-assembly. Summary of the invention

[0004] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present invention provides a cathode thermal subassembly for a traveling wave tube and a preparation method thereof.

[0005] According to an embodiment of one aspect of the present invention, there is provided a cathode thermal subassembly for a traveling wave tube, comprising:

[0006] Cathode cake, the cathode cake is a solid spherical cathode, used to emit electrons as a traveling wave tube electron source; heater, the heater is a composite structure composed of a boron nitride insulating layer, a graphite electrode layer and a boron nitride covering layer, the graphite electrode layer is located between the boron nitride insulating layer and the boron nitride covering layer, the graphite electrode layer is a single spiral structure, the boron nitride insulating layer is brazed to the bottom of the cathode cake, and the heater is used to heat the cathode cake; heater lead, the heater lead includes a first heater lead and a second heater lead, the first heater lead is brazed to the first end of the single spiral structure on the graphite electrode layer through the boron nitride covering layer, the second heater lead is brazed to the second end of the single spiral structure on the graphite electrode layer through the boron nitride covering layer, the first end is a position far away from the center of the single spiral structure of the graphite electrode layer, and the second end is a position close to the center of the single spiral structure of the graphite electrode layer.

[0007] According to an embodiment of the present invention, the thickness of the boron nitride insulating layer is 1 mm; the thickness of the boron nitride covering layer is 1 mm±0.05 mm.

[0008] According to an embodiment of the present invention, the boron nitride covering layer has a first hole and a second hole, the first hole corresponds to the first end of the single spiral structure on the graphite electrode layer, and the second hole corresponds to the second end of the single spiral structure on the graphite electrode layer, and the diameters of the first hole and the second hole are both 0.5mm-0.8mm.

[0009] According to an embodiment of the present invention, the first heater lead is brazed to the first end of the single spiral structure on the graphite electrode layer through the first hole, and the second heater lead is brazed to the second end of the single spiral structure on the graphite electrode layer through the second hole.

[0010] According to an embodiment of the present invention, the graphite electrode layer has a length of 15 mm, a width of 0.2 mm, and a thickness of 0.2 mm; and the thermal conductivity of the graphite electrode layer is greater than or equal to 2000 W / (m·K).

[0011] According to an embodiment of the present invention, the material of the heater lead includes molybdenum-rhenium alloy and nickel wire, and is prepared by wrapping the nickel wire with a molybdenum-rhenium alloy strip.

[0012] According to another embodiment of the present invention, a method for preparing a cathode thermal subassembly is provided, the method comprising:

[0013] Boron chloride and ammonia are used to deposit a boron nitride insulating layer on an isostatic graphite mold by chemical vapor deposition; a graphite electrode layer is prepared on the boron nitride insulating layer; the graphite electrode layer is laser processed to obtain a graphite electrode layer with a single helix structure, wherein the first end of the graphite electrode layer with the single helix structure is located away from the center of the single helix structure of the graphite electrode layer, and the second end of the graphite electrode layer with the single helix structure is located close to the center of the single helix structure of the graphite electrode layer; a boron nitride covering layer is prepared on the graphite electrode layer with the single helix structure, and a heater lead hole is processed on the boron nitride covering layer to obtain a heater; the graphite electrode layer with the single helix structure of the heater and the heater lead are vacuum brazed through the heater lead hole, and the boron nitride insulating layer of the heater is brazed to the bottom of the cathode cake to obtain a cathode heater assembly.

[0014] According to an embodiment of the present invention, after the boron nitride insulating layer of the heater is brazed with the bottom of the cathode cake, the method further includes: coating the surface of the cathode cake.

[0015] According to an embodiment of the present invention, the boron nitride insulating layer of the heater is brazed with the bottom of the cathode cake, comprising:

[0016] Solder is added between the heater and the bottom of the cathode cake, and the boron nitride insulating layer of the heater is connected to the bottom of the cathode cake by using the solder.

[0017] According to an embodiment of the present invention, the heater lead includes a first heater lead and a second heater lead, both of which are composed of molybdenum-rhenium alloy and nickel wire, and the heater lead holes include a first hole and a second hole, the first hole corresponds to the first end of the single spiral structure on the graphite electrode layer, and the second hole corresponds to the second end of the single spiral structure on the graphite electrode layer.

[0018] According to an embodiment of the present invention, vacuum brazing of a graphite electrode layer having a single helical structure of a heater and a heater lead wire is performed through a heater lead wire hole, comprising:

[0019] Through the first hole of the heater lead hole, vacuum brazing is performed with the molybdenum-rhenium alloy strip at the first end of the single spiral structure on the graphite electrode layer, and the molybdenum-rhenium alloy strip is used to wrap the nickel wire and then vacuum brazing is performed to obtain the first heater lead;

[0020] The second end of the single spiral structure on the graphite electrode layer is vacuum brazed with the molybdenum-rhenium alloy strip through the second hole of the heater lead hole, and the nickel wire is wrapped with the molybdenum-rhenium alloy strip and then vacuum brazed to obtain the second heater lead.

[0021] According to an embodiment of the present invention, a cathode heater assembly is formed by adopting a heater, a heater lead and a cathode cake of a composite structure composed of a boron nitride insulating layer, a graphite electrode layer and a boron nitride covering layer. Since the heater insulating layer adopts boron nitride with high thermal conductivity and the electrode layer adopts pyrolytic graphite with high density and low degassing rate, the technical problems of traditional alumina ceramics having low thermal conductivity and being reduced to cause heater short circuit, and traditional alumina ceramics being loose inside after sintering and being easy to absorb and degas, resulting in large volume and excessive power consumption of the heater are solved, thereby achieving a cathode heater assembly with lightweight, low degassing rate and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0023] Figure 1 A schematic diagram of a cathode thermal subassembly for a traveling wave tube according to an embodiment of the present invention;

[0024] FIG2( a ) is a schematic diagram of a boron nitride insulating layer and a graphite electrode layer in a heater according to an embodiment of the present invention;

[0025] FIG2( b ) is a schematic diagram of a heater according to an embodiment of the present invention;

[0026] Figure 3 Schematic diagram of holes on the boron nitride cover layer;

[0027] Figure 4 (a) is a schematic diagram showing the soldering of the heater lead to the graphite electrode layer;

[0028] Figure 4 (b) Schematic diagram of the heater lead being brazed to the graphite electrode layer through the boron nitride covering layer;

[0029] Figure 5 The figure is a flow chart of a method for preparing a cathode thermal subassembly according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0031] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0032] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0033] Figure 1 Schematic diagram of a cathode thermal subassembly for a traveling wave tube according to an embodiment of the present invention.

[0034] like Figure 1 As shown, the cathode heater assembly includes a cathode cake 1, a heater 2 and a heater lead 3, wherein the heater lead 3 includes a first heater lead 3-1 and a second heater lead 3-2.

[0035] According to an embodiment of the present invention, the cathode cake 1 may be a solid spherical cathode used as a traveling wave tube electron source to emit electrons. The cathode 1 may be a salt-impregnated cathode, which is prepared by impregnating aluminate into a porous tungsten sponge structure and then machining it into a spherical surface. The salt-impregnated cathode cake has the characteristics of high emission current density, long life, nano-electron bombardment, etc., and is widely used in electric vacuum devices.

[0036] According to an embodiment of the present invention, the heater 2 is used to heat the cathode cake and is arranged at the bottom of the cathode cake 1. 20 Mn7Ni3 high temperature active solder is used to braze the heater 2 and the cathode cake 1 together. For example, FIG2(a) is a schematic diagram of a boron nitride insulating layer and a graphite electrode layer in a heater according to an embodiment of the present invention; FIG2(b) is a schematic diagram of a heater according to an embodiment of the present invention.

[0037] According to an embodiment of the present invention, in conjunction with Figures 2 (a) and 2 (b), the heater 2 is a composite structure consisting of a boron nitride insulating layer 2-1, a graphite electrode layer 2-2 and a boron nitride covering layer 2-3. The heater 2 is prepared by sequentially depositing the boron nitride insulating layer 2-1, the graphite electrode layer 2-2 and the boron nitride covering layer 2-3 on a deposition mold (not shown in the figure).

[0038] According to an embodiment of the present invention, the graphite electrode layer 2-3 is located between the boron nitride insulating layer 2-1 and the boron nitride covering layer 2-3. After the graphite electrode layer 2-3 is deposited, the graphite electrode layer can be processed to form a single spiral structure, and a planar structure.

[0039] According to the embodiment of the present invention, since the graphite electrode layer is a planar single helical structure, compared with the heater made of the traditional axially wound double helical tungsten-rhenium wire, the cathode heater component can be smaller and lighter.

[0040] According to an embodiment of the present invention, the boron nitride covering layer 2-3 is located on the graphite electrode layer 2-2. Since the thickness of the boron nitride covering layer 2-3 is 1 mm ± 0.05 mm, the single helical structure of the graphite electrode layer 2-2 can be observed through the boron nitride covering layer 2-3, so that holes corresponding to the two ends of the single helical structure can be processed on the boron nitride covering layer later. In the present invention, in order to better reflect the boron nitride covering layer 2-3, the graphite electrode layer 2-2 under the boron nitride covering layer 2-3 is not visualized in FIG. 2 (b).

[0041] According to an embodiment of the present invention, the single helical structure of the graphite electrode layer 2-3 includes a first end a and a second end b. The boron nitride cover layer 2-3 includes a first hole 2-31 and a second hole 2-32. The first hole 2-31 may correspond to the first end a of the single helical structure of the graphite electrode layer 2-2, and the second hole 2-32 may correspond to the second end b of the single helical structure of the graphite electrode layer 2-2. Figure 3 Schematic diagram of the holes in the boron nitride capping layer.

[0042] According to an embodiment of the present invention, the first hole 2-31 on the boron nitride covering layer 2-3 corresponds to the first end a of the single spiral structure of the graphite electrode layer 2-2, and the second hole 2-32 corresponds to the second end b of the single spiral structure of the graphite electrode layer 2-2. The purpose is to braze the heater lead through the holes in the boron nitride covering layer to the corresponding positions of the first end and the second end of the graphite electrode layer.

[0043] For example, FIG4(a) is a schematic diagram of the heater lead being brazed to the graphite electrode layer; FIG4(b) is a schematic diagram of the heater lead being brazed to the graphite electrode layer through the boron nitride covering layer.

[0044] As shown in Figures 4 (a) and 4 (b), the first heater lead 3-1 is brazed to the first end a of the single spiral structure on the graphite electrode layer 2-2 through the first hole 2-31 on the boron nitride covering layer 2-3; the second heater lead 3-2 is brazed to the second end b of the single spiral structure on the graphite electrode layer 2-2 through the second hole 2-32 on the boron nitride covering layer 2-3.

[0045] According to an embodiment of the present invention, in combination with FIG. 2( a ), the first end a may be located away from the center of the single helical structure of the graphite electrode layer, and the second end b may be located close to the center of the single helical structure of the graphite electrode layer.

[0046] According to an embodiment of the present invention, Figure 1 As shown, the boron nitride covering layer 2-3 in the heater 2 is brazed to the bottom of the cathode cake to form a cathode heater assembly.

[0047] According to an embodiment of the present invention, the thickness of the boron nitride insulating layer may be 1 mm, and the thickness of the boron nitride covering layer may be 1 mm±0.05 mm.

[0048] According to the embodiment of the present invention, the thermal conductivity of the boron nitride insulating layer is 3 times higher than that of the traditional aluminum oxide, and the material is dense and has a low outgassing rate.

[0049] According to an embodiment of the present invention, the graphite electrode layer 2-2 deposited on the boron nitride insulating layer 2-1 has a length of 15 mm, a width of 0.2 mm, and a thickness of 0.2 mm. It can be processed into an electrode layer with a single spiral planar structure, and its thermal conductivity is greater than or equal to 2000 W / (m·K), and it has the characteristics of dense material and low outgassing rate.

[0050] According to an embodiment of the present invention, the sizes of the first hole 2-31 and the second hole 2-32 on the boron nitride covering layer 2-3 can be 0.5mm-0.8mm, so that the heater lead can be brazed to the graphite electrode layer.

[0051] According to an embodiment of the present invention, the material of the heater lead wire is molybdenum-rhenium alloy and nickel wire. 20 The molybdenum-rhenium alloy strip is brazed to the first end a and the second end b of the graphite electrode layer by Mn7Ni3 high temperature active solder, and the molybdenum-rhenium alloy strip is wrapped with nickel wire for clamp welding.

[0052] According to an embodiment of the present invention, brazing the molybdenum-rhenium alloy to the first end a of the graphite electrode layer may include: 20 Mn7Ni3 high temperature active solder is used to vacuum braze the first end a of the graphite electrode layer with the molybdenum-rhenium alloy.

[0053] According to an embodiment of the present invention, a cathode heater assembly is formed by adopting a heater, a heater lead and a cathode cake of a composite structure composed of a boron nitride insulating layer, a graphite electrode layer and a boron nitride covering layer. Since the heater insulating layer adopts boron nitride with high thermal conductivity and the electrode layer adopts pyrolytic graphite with high density and low degassing rate, the technical problems of traditional alumina ceramics having low thermal conductivity and being reduced to cause heater short circuit, and traditional alumina ceramics being loose inside after sintering and being easy to absorb and degas, resulting in large volume and excessive power consumption of the heater are solved, thereby achieving a cathode heater assembly with lightweight, low degassing rate and high reliability.

[0054] Figure 5 The figure is a flow chart of a method for preparing a cathode thermal subassembly according to an embodiment of the present invention.

[0055] like Figure 5 As shown, the method includes: operation S510 to operation S550.

[0056] At operation 510, boron chloride and ammonia are used to deposit a boron nitride insulating layer on an isostatically pressed graphite mold using chemical vapor deposition.

[0057] In operation 520, a graphite electrode layer is formed on the boron nitride insulating layer.

[0058] In operation 530, the graphite electrode layer is laser processed to obtain a graphite electrode layer having a single spiral structure, wherein the first end of the graphite electrode layer having the single spiral structure is far away from the center of the single spiral structure of the graphite electrode layer, and the second end of the graphite electrode layer having the single spiral structure is close to the center of the single spiral structure of the graphite electrode layer.

[0059] In operation 540, a boron nitride covering layer is prepared on the graphite electrode layer having a single helical structure, and two heater lead holes are processed on the boron nitride covering layer to obtain a heater, wherein the two heater lead holes correspond to the first end and the second end respectively.

[0060] In operation 550, the graphite electrode layer with a single spiral structure of the heater is vacuum brazed with the heater lead through the heater lead hole, and the boron nitride insulating layer of the heater is brazed with the bottom of the cathode cake to obtain a cathode heater assembly.

[0061] According to an embodiment of the present invention, high-purity boron chloride (BCl3) and ammonia (NH3) can be used at a certain furnace pressure and a high temperature of 2100°C to deposit high-purity and high-density hexagonal pyrolytic boron nitride h-BN on an isostatically pressed graphite grinding tool using a chemical vapor deposition method to form a boron nitride insulating layer with a thickness of 1 mm.

[0062] According to the embodiment of the present invention, the thermal conductivity of the deposited boron nitride insulation layer is 3 times higher than that of the traditional aluminum oxide, and has better density and lower outgassing rate.

[0063] According to an embodiment of the present invention, high-purity and high-density pyrolytic graphite can be deposited on a boron nitride insulating layer by chemical vapor deposition at a high temperature of 2000°C±20°C in an atmosphere of high-purity CH4 to form a graphite electrode layer, and the deposited graphite electrode layer can be structurally processed by high-speed milling or laser processing to form a planar single spiral structure, thereby completing the composite structure of the boron nitride insulating layer and the graphite electrode layer.

[0064] According to an embodiment of the present invention, the graphite length of the graphite electrode layer is 15 mm, the width is 0.2 mm, the thickness is 0.2 mm, the cold resistance is 15.3Ω±0.5Ω, the resistance in the hot state is 7.5Ω±0.3Ω, and the power consumption is about 3.1W.

[0065] According to an embodiment of the present invention, the thermal conductivity of the deposited graphite electrode layer can be greater than or equal to 2000 W / (m·K), which is ten times that of isostatic graphite. The material is dense and has a low degassing rate.

[0066] According to an embodiment of the present invention, the first end of the single helical graphite electrode layer is far away from the center of the single helical structure of the graphite electrode layer, and the second end of the single helical graphite electrode layer is close to the center of the single helical structure of the graphite electrode layer.

[0067] According to an embodiment of the present invention, high-purity and high-density pyrolytic boron nitride can be deposited on the graphite electrode layer of the composite structure of the boron nitride insulating layer and the graphite electrode layer by chemical vapor deposition in an atmosphere of high-purity CH4 at a high temperature of 2000°C±20°C to form a boron nitride covering layer with a thickness of 1mm±0.05mm.

[0068] According to an embodiment of the present invention, a boron nitride insulating layer, a graphite electrode layer and a boron nitride covering layer form a heater with a composite structure, and two heater lead holes are processed on the boron nitride covering layer, i.e., a first hole and a second hole, wherein the position of the first hole corresponds to the position of the first end of the single spiral structure of the graphite electrode layer, and the position of the second hole corresponds to the position of the second end of the single spiral structure of the graphite electrode layer.

[0069] According to an embodiment of the present invention, the first heater lead can be vacuum brazed to the first end of the graphite electrode layer through the first hole, and the second heater lead can be vacuum brazed to the second end of the graphite electrode layer through the second hole to form a heater with heater leads.

[0070] According to an embodiment of the present invention, the boron nitride insulating layer of the heater with the heater lead and the cathode cake can be connected at a temperature of 1350° C. using TiCr 20 Mn7Ni3 high temperature active solder is used for brazing to form the cathode thermal sub-assembly.

[0071] According to an embodiment of the present invention, the boron nitride insulating layer of the heater with the heater lead is brazed with the cathode cake, which can be brazed in a vacuum protection furnace, specifically: the temperature is raised to 1250°C±10°C at a heating rate not exceeding 15°C / min, and the temperature is kept for 25-35min; then the temperature is raised to 1350°C±10°C at a heating rate not exceeding 20°C / min, and the temperature is kept for 3-5min, TiCr 20 The Mn7Ni3 high temperature active solder begins to dissolve; it is cooled to 800℃±10℃ within 30 minutes; it is cooled to 400℃±10℃ within 30 minutes, and then cooled to room temperature with the furnace. The cooling process solidifies the solder, so brazing is carried out. After brazing is completed, the cathode thermal sub-assembly is obtained.

[0072] According to an embodiment of the present invention, a cathode heater assembly is formed by adopting a heater, a heater lead and a cathode cake of a composite structure composed of a boron nitride insulating layer, a graphite electrode layer and a boron nitride covering layer. Since the heater insulating layer adopts boron nitride with high thermal conductivity and the electrode layer adopts pyrolytic graphite with high density and low degassing rate, the technical problems of traditional alumina ceramics having low thermal conductivity and being reduced to cause heater short circuit, and traditional alumina ceramics being loose inside after sintering and being easy to absorb and degas, resulting in large volume and excessive power consumption of the heater are solved, thereby achieving a cathode heater assembly with lightweight, low degassing rate and high reliability.

[0073] According to an embodiment of the present invention, after the boron nitride insulating layer of the heater is brazed to the bottom of the cathode cake, the surface of the cathode cake needs to be coated.

[0074] According to an embodiment of the present invention, brazing the boron nitride insulating layer of the heater to the bottom of the cathode cake includes: adding solder between the heater and the bottom of the cathode cake, and connecting the boron nitride insulating layer of the heater to the bottom of the cathode cake using the solder.

[0075] According to an embodiment of the present invention, the heater and the cathode cake may be welded by solder, and the cathode cake and the heater with heater leads may form a cathode heater assembly.

[0076] According to an embodiment of the present invention, the heater lead includes a first heater lead and a second heater lead, both of which are composed of molybdenum-rhenium alloy and nickel wire, and the heater lead holes include a first hole and a second hole, the first hole corresponds to the first end of the single spiral structure on the graphite electrode layer, and the second hole corresponds to the second end of the single spiral structure on the graphite electrode layer.

[0077] According to an embodiment of the present invention, the single helix structure of the graphite electrode layer can be observed through the boron nitride covering layer, and a first hole can be processed at a position of the boron nitride covering layer corresponding to the first end of the single helix structure until the first end of the single helix structure is exposed; and a second hole can be processed at a position of the boron nitride covering layer corresponding to the second end of the single helix structure until the second end of the single helix structure is exposed.

[0078] According to an embodiment of the present invention, the first end of the single spiral structure of the graphite electrode layer can be vacuum brazed with the molybdenum-rhenium alloy strip through the first hole. After the welding is completed, the nickel wire is wrapped with the molybdenum-rhenium alloy strip and then brazed to obtain the first heater lead, thereby achieving the brazing of the first heater lead to the graphite electrode layer.

[0079] According to an embodiment of the present invention, the second end of the single spiral structure of the graphite electrode layer can be vacuum brazed with the molybdenum-rhenium alloy strip through the second hole. After the welding is completed, the nickel wire is wrapped with the molybdenum-rhenium alloy strip and then brazed to obtain the second heater lead, thereby achieving the brazing of the second heater lead to the graphite electrode layer.

[0080] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A cathode thermal subassembly for a traveling wave tube, characterized in that: include: A cathode cake (1), wherein the cathode cake (1) is a solid spherical cathode and is used as a traveling wave tube electron source to emit electrons; A heater (2), the heater (2) being a composite structure consisting of a boron nitride insulating layer (2-1), a graphite electrode layer (2-2) and a boron nitride covering layer (2-3), the graphite electrode layer (2-2) being located between the boron nitride insulating layer (2-1) and the boron nitride covering layer (2-3), the graphite electrode layer (2-2) being a single helical structure, the boron nitride insulating layer (2-1) being brazed to the bottom of the cathode cake (1), and the heater (2) being used to heat the cathode cake (1); A heater lead (3), the heater lead (3) comprising a first heater lead (3-1) and a second heater lead (3-2), the first heater lead (3-1) being brazed to a first end (a) of a single helical structure on the graphite electrode layer (2-2) through the boron nitride covering layer (2-3), the second heater lead (3-2) being brazed to a second end (b) of the single helical structure on the graphite electrode layer (2-2) through the boron nitride covering layer (2-3), the first end (a) being located away from a center of the single helical structure of the graphite electrode layer (2-2), and the second end (b) being located close to a center of the single helical structure of the graphite electrode layer (2-2).

2. The cathode thermal subassembly according to claim 1, characterized in that: The thickness of the boron nitride insulating layer (2-1) is 1 mm; the thickness of the boron nitride covering layer (2-3) is 1 mm±0.05 mm.

3. The cathode thermal subassembly according to claim 2, characterized in that: The boron nitride covering layer (2-3) has a first hole (2-31) and a second hole (2-32), the first hole (2-31) corresponds to the first end (a) of the single helical structure on the graphite electrode layer (2-2), the second hole (2-32) corresponds to the second end (b) of the single helical structure on the graphite electrode layer (2-2), and the diameters of the first hole (2-31) and the second hole (2-32) are both 0.5 mm to 0.8 mm.

4. The cathode thermal subassembly according to claim 3, characterized in that: The first heater lead (3-1) is brazed to the first end (a) of the single helix structure on the graphite electrode layer (2-2) through the first hole (2-31), and the second heater lead (3-2) is brazed to the second end (b) of the single helix structure on the graphite electrode layer (2-2) through the second hole (2-32).

5. The cathode thermal subassembly according to claim 1, characterized in that: The graphite electrode layer (2-2) has a length of 15 mm, a width of 0.2 mm, and a thickness of 0.2 mm; the thermal conductivity of the graphite electrode layer (2-2) is greater than or equal to 3000 W / (m·K).

6. The cathode thermal subassembly according to claim 1, characterized in that: The material of the heater lead (3) includes a molybdenum-rhenium alloy and a nickel wire, and is prepared by wrapping the nickel wire with a molybdenum-rhenium alloy strip.

7. A method for preparing a cathode thermal subassembly according to any one of claims 1 to 6, characterized in that: The method comprises: Depositing a boron nitride insulating layer (2-1) on an isostatic graphite mold using boron chloride and ammonia by chemical vapor deposition; Preparing a graphite electrode layer (2-2) on the boron nitride insulating layer (2-1); Laser processing is performed on the graphite electrode layer (2-2) to obtain a graphite electrode layer (2-2) having a single helical structure, wherein the first end (a) of the graphite electrode layer (2-2) having the single helical structure is located away from the center of the single helical structure of the graphite electrode layer (2-2), and the second end (b) of the graphite electrode layer (2-2) having the single helical structure is located close to the center of the single helical structure of the graphite electrode layer (2-2); A boron nitride covering layer (2-3) is prepared on a graphite electrode layer (2-2) having a single helical structure, and two heater lead holes are processed on the boron nitride covering layer (2-3) to obtain a heater, wherein the two heater lead holes correspond to the first end (a) and the second end (b) respectively; The graphite electrode layer (2-2) with a single helical structure of the heater (2) and the heater lead (3) are vacuum brazed through the heater lead hole, and the boron nitride insulating layer (2-1) of the heater and the bottom of the cathode cake (1) are brazed to obtain a cathode heater assembly.

8. The method according to claim 7, characterized in that After the boron nitride insulating layer (2-1) of the heater (2) is brazed with the bottom of the cathode cake (1), the method further comprises: coating the surface of the cathode cake (1).

9. The method according to claim 7, characterized in that: The brazing of the boron nitride insulating layer (2-1) of the heater (2) and the bottom of the cathode cake (1) comprises: Solder is added between the heater (2) and the bottom of the cathode cake (1), and the boron nitride insulating layer (2-1) of the heater (2) is connected to the bottom of the cathode cake (1) using the solder.

10. The method according to claim 7, characterized in that The heater lead (3) comprises a first heater lead (3-1) and a second heater lead (3-2), the first heater lead (3-1) and the second heater lead (3-2) both being composed of a molybdenum-rhenium alloy and a nickel wire, the heater lead holes comprising a first hole (2-31) and a second hole (2-32), the first hole (2-31) corresponding to a first end (a) of a single helical structure on the graphite electrode layer (2-2), and the second hole (2-32) corresponding to a second end (b) of the single helical structure on the graphite electrode layer (2-2); The method of vacuum brazing the graphite electrode layer (2-2) having a single helical structure of the heater (2) and the heater lead (3) through the heater lead hole comprises: Through the first hole (2-31) of the heater lead hole, vacuum brazing is performed with a molybdenum-rhenium alloy strip at the first end (a) of the single spiral structure on the graphite electrode layer (2-2), and the molybdenum-rhenium alloy strip is used to wrap the nickel wire and then vacuum brazing is performed to obtain a first heater lead (3-1); The second end (b) of the single helix structure on the graphite electrode layer (2-2) is vacuum brazed with the molybdenum-rhenium alloy strip through the second hole (2-32) of the heater lead hole, and the molybdenum-rhenium alloy strip is used to wrap the nickel wire. Then vacuum brazing is performed to obtain the second heater lead (3-2).

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