Long life cathode structure for electric propulsion

Abstract

The application discloses a long-life cathode structure for electric propulsion, which can extend the service life of the cathode by several times by splicing the cathode into a multi-section structure through materials with different melting points. The multi-section structure is composed of a first cathode material assembly and a second cathode connecting assembly, the first cathode material assembly is composed of cathode materials in sections, and the second cathode connecting assembly is composed of different materials. The application can extend the service life of the cathode by several times under the condition that the original material and the original propulsion system are used.

Description

Technical Field

[0001] This invention belongs to the field of space electric propulsion, and specifically relates to a long-life cathode structure for electric propulsion. Background Technology

[0002] With the development of aerospace technology and space exploration, traditional chemical thrusters can no longer meet the needs of deep space exploration, and the demand for electric propulsion technology in various high-performance platforms is becoming increasingly urgent. Electric propulsion, compared to chemical thrusters, has advantages such as lower mass, higher specific impulse, and reusability, leading to its widespread application. Among these, ion thrusters have an even higher specific impulse than other types of electric thrusters and are a key area of ​​research and development for many countries. The performance, lifespan, and reliability of ion thrusters are crucial aspects of high-quality spacecraft and their payload design.

[0003] Traditional ion thrusters have high specific impulse but low thrust, which still cannot meet the requirements. Magnetoplasma thrusters work by using plasma generated from the ionization of the working fluid by a high-temperature electric arc. This plasma is accelerated under the combined action of magnetic and electric fields, thus generating a reverse thrust on the thruster. The acceleration mechanism involves four coupled acceleration modes: self-field acceleration, vortex acceleration, Hall acceleration, and aerodynamic acceleration. NASA has hailed it as the most powerful electric propulsion technology. It has numerous advantages in large spacecraft orbit transfers, manned lunar landings, and deep space exploration.

[0004] The commonly used ion propulsion method accelerates and ejects ions generated by the ionization of the working fluid under the influence of an electrostatic field, thus generating thrust. The additional magnetic field is provided by a superconducting magnet instead of a conventional copper coil, which not only achieves a higher magnetic field strength and significantly reduces the overall size of the component, but also ensures a more uniform cathode plasma discharge due to the uniform magnetic field of the superconducting magnet.

[0005] In electric propulsion systems, a long-standing problem for researchers is their service life, and the service life is directly affected by the lifespan of the cathode. When the thruster is working, high-temperature plasma accumulates at the front of the cathode, causing severe burning of the cathode material. After a long period of operation, it is almost melted. Currently, the only way to improve the service life is to develop new materials.

[0006] Current cathodes are all single-use structures, and considering performance requirements such as airtightness, components are difficult to replace during space operations. Therefore, their lifespan directly depends on the properties of the materials. To solve the cathode lifespan problem, researchers are constantly developing new materials. However, the development cycle for new materials is long, and their cost is high.

[0007] In order to further extend the lifespan while maximizing the material properties, a new type of cathode structure needs to be designed from a structural perspective. Summary of the Invention

[0008] To address the problem that the lifespan of existing cathodes is difficult to further improve, this invention provides a long-life cathode structure for electric propulsion, which further extends the service life of the cathode by changing the structure without changing the cathode material.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A long-life cathode structure for electric propulsion includes a heating wire, a cathode material assembly, and a cathode connection assembly. The cathode material assembly comprises a first cathode material segment, a second cathode material segment, a third cathode material segment, and a cathode nozzle body coaxially connected. The first, second, and third cathode material segments and the cathode nozzle body are made of the same material and are separated by the cathode connection assembly. The cathode connection assembly is composed of materials A1, A2, and A3. The first cathode material segment is connected to the second cathode material segment via material A1, the second cathode material segment is connected to the third cathode material segment via material A2, and the third cathode material segment is connected to the cathode nozzle body via material A3. The heating wire heats the cathode nozzle body to the thermionic emission temperature and causes the first, second, and third cathode material segments to reach their respective melting points.

[0011] Furthermore, it also includes a cathode inlet pipe, a fixing ring, an inner cavity, an outer cavity, and a nozzle mounting base. The cathode inlet pipe is fixedly connected to the front end of the inner cavity, and the rear end of the inner cavity is threadedly connected to the nozzle mounting base. The nozzle mounting base is fixedly connected to the cathode nozzle body. The inner cavity, nozzle mounting base, and cathode nozzle body are all hollow structures, together forming the cathode inlet channel. The fixing ring and outer cavity are fixedly nested on the outside of the inner cavity. Before the thruster starts, i.e., during the preheating stage, the heating wire is energized. The current in the heating wire generates Joule heat, heating the cathode nozzle body to the thermionic emission temperature. At this time, the cathode begins to emit thermionic electrons, which react with the propellant gas. When the body collides, it generates partial ionization, and the electron density continues to rise to a steady state. At this point, it enters a self-sustaining discharge state. The power supply to the heating wire is removed, and the anode power supply is turned on. The electric field is used to maintain plasma generation. After the first stage of cathode material reaches its service life, the heating wire is heated to the melting point T1 of material A1. Material A1 dissolves, and the consumption of the second stage of cathode material begins. The cathode life is then recalculated. Similarly, when the second stage of cathode material reaches its service life, the heater is heated to the melting point T2 of material A2. Material A2 dissolves, and the consumption of the third stage of cathode material begins. The cathode life is extended without changing the cathode material or adding mechanical structure.

[0012] Further, the melting points of the material A1, the material A2 and the material A3 respectively satisfy: cathode operating temperature < T1 < T2 < T3 < cathode melting point, wherein T1 is the melting point of the material A1, T2 is the melting point of the material A2, and T3 is the melting point of the material A3; meanwhile, the electron emissivity of the material A1, the material A2 and the material A3 is lower than that of the material of the cathode material assembly, the materials have good electrical conductivity and certain ablation resistance.

[0013] Further, the difference between the melting point values of materials of adjacent cathode connection assemblies is above 50°C. In consideration of the precision range of temperature control of the heating wire, the situation that the next section of cathode material is melted in advance is avoided by increasing the differences among T1, T2 and T3.

[0014] Further, the length of each section of cathode material satisfies that the next section of cathode material is not damaged before the service life of the previous section of cathode material ends, so as to prevent the next section of cathode material from participating in discharge in advance and thus shortening the service life of the next section of cathode material in advance. The length of each section of cathode material is determined according to the radius, material, pore diameter of the cathode and experimental results.

[0015] Further, the melting point of the heating wire is 500°C higher than the melting points T1, T2 and T3 of the material A1, the material A2 and the material A3, so as to prevent the heating wire from fusing in advance or reaching the end of its service life before the rear-section cathode material starts to be used.

[0016] Further, the cathode further comprises a ceramic housing, which is used for ensuring insulation between the heating wire and the cathode material.

[0017] Further, the ceramic housing is used for preventing the heating wire from heating the thruster.

[0018] The beneficial effects of the present invention are:

[0019] When the thruster works, the cathode nozzle is in an extreme high-temperature environment and is bombarded by a large number of high-energy particles, so corrosion loss is very prone to occur, and the corrosion loss usually occurs in the front end part of the cathode. Through the multi-section structure, the cathode is divided into multiple sections for use, and the using effect equivalent to replacing a plurality of cathodes is achieved without replacing the cathode.

[0020] The novel cathode structure proposed by the present invention can further greatly prolong the effective working life of the cathode under the condition that the original materials and the overall system are not changed, and prolong the original life of the cathode to several times of that of the existing cathode with extremely low manufacturing cost, so as to ensure the long-term effective operation of equipment. The present invention is of great significance for the wider application of electric propulsion technology. Description of Drawings

[0021] Figure 1 is a schematic diagram of a monomer structure of the segmented cathode of the present invention;

[0022] Figure 2 This is a schematic diagram of the overall cathode system including the segmented cathode of the present invention;

[0023] Figure 3 This is a schematic diagram of the propulsion device of the present invention;

[0024] Figure 4 This is a top view of the thruster;

[0025] Figure 1 Explanation of reference numerals in the attached figures:

[0026] 1. Material A1, 2. Material A2, 3. Material A3, 4. First section cathode material, 5. Second section cathode material, 6. Third section cathode material, 7. Cathode nozzle body.

[0027] Figure 2 Explanation of reference numerals in the attached figures:

[0028] 8. Nozzle mounting base; 9. Inner cavity; 10. Outer cavity; 11. Fixing ring; 12. Liquid inlet; 13. Liquid outlet; 14. Cathode air inlet pipe.

[0029] Other figure labels explanations:

[0030] 15. Heating wire; 16. Ceramic shell; 21. Insulating pipe; 22. Anode body; 23. Spiral heat exchange unit; 24. Multi-channel heat exchange unit. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] The present invention provides a long-life cathode structure for electric propulsion, comprising a cathode material assembly and a cathode connection assembly, which are coaxially connected.

[0033] like Figure 1As shown, the cathode material assembly consists of a first cathode material 4, a second cathode material 5, a third cathode material 6, and a cathode nozzle body 7. All these materials have the same composition. The material segments are separated by cathode connecting components. The first cathode material 4, the second cathode material 5, the third cathode material 6, and the cathode nozzle body 7 are connected by friction welding using the cathode connecting components. The material composition is LaB6. The cathode connecting components consist of materials A11, A22, and A33, which are different metals or alloys with melting points higher than the cathode's operating temperature. The first cathode material 4 is connected to the second cathode material 5 via material A11, the second cathode material 5 is connected to the third cathode material 6 via material A22, and the third cathode material 6 is connected to the cathode nozzle body 7 via material A33.

[0034] like Figure 2 As shown, the overall structure of the long-life cathode for electric propulsion includes a cathode inlet pipe 14, a fixing ring 11, an inner cavity 9, an outer cavity 10, a nozzle fixing seat 8, and a cathode nozzle body 7. The cathode inlet pipe 14 is fixedly connected to the front end of the inner cavity 9, and the rear end of the inner cavity 9 is threadedly connected to the nozzle fixing seat 8. The nozzle fixing seat 8 is fixedly connected to the cathode nozzle body 7. The inner cavity 9, the nozzle fixing seat 8, and the cathode nozzle body 7 are all hollow structures, forming a cathode inlet channel. The fixing ring 11 and the outer cavity 10 are fixedly nested on the outside of the inner cavity 9. In this invention, the cathode nozzle body 7 and the first cathode material 4, the second cathode material 5, the third cathode material 6, material A11, material A22, and material A33 are all porous cathode nozzles.

[0035] Specifically, the inner cavity 9 is fixed to the cathode inlet pipe 14 by welding, and connected to the nozzle mounting base 8 by threads. The nozzle mounting base 8 is fixed to the cathode nozzle body 7 by high-temperature welding. Together, they constitute the air inlet channel of the porous cathode nozzle of the magnetic plasma thruster. When the thruster is working, the propellant is introduced from the air inlet channel of the cathode nozzle, ionized into plasma at the cathode tip, and finally accelerated by electric and magnetic field coupling.

[0036] like Figure 3 As shown, the ceramic shell 16 has an annular groove, and the heating wire 15 is arranged inside the annular groove to prevent the heating wire 15 from heating components other than the cathode. Before the thruster is started, i.e., during the preheating stage, the heating wire 15 is energized. The current in the heating wire 15 generates Joule heat, heating the cathode nozzle body 7 to the thermionic emission temperature. At this time, the cathode begins to emit thermionic electrons. The thermionic electrons collide with the propellant gas to produce partial ionization, and the electron density continues to rise to a steady state. At this time, it enters a self-sustaining discharge state, and the power supply of the heating wire 15 can be removed, and the anode power supply can be turned on to maintain plasma generation using an electric field.

[0037] After the propeller has operated for a certain period of time, the electron emissivity of the first-section cathode material 4 decreases significantly, making reignition difficult. At this time, the first-section cathode material 4 is considered invalid. The heating wire 15 is used to heat the cathode temperature to T1, at which point the material A1 11 dissolves, and consumption of the second-section cathode material 5 starts. Since the second-section cathode material 5 has not emitted electrons yet, its performance in all aspects is close to that of a new material, so it can almost be considered that its service life starts to be counted again.

[0038] Similarly, after the second-section cathode material 5 operates until it fails, the heating wire 15 is used to heat the cathode temperature to T2, at which point the material A2 2 dissolves, and consumption of the third-section cathode material 6 starts.

[0039] After the third-section cathode material 6 operates until it fails, the heating wire 15 is used to heat the cathode temperature to T3, at which point the material A3 3 dissolves, and consumption of the cathode nozzle main body 7 starts.

[0040] So far, the cathode is consumed to the last section, and without upgrading its material, the service life is almost increased by 4 times.

[0041] The propeller cathode ensures that the temperature does not become excessively high during operation through the cooling liquid channel reserved inside it, which would otherwise affect the reliability of the overall system. Two liquid inlet 12 and liquid outlet 13 connected to the cooling liquid channel are uniformly distributed on the upper and lower sides of the end portion of the outer cavity 10 away from the porous cathode nozzle. During operation, the cooling liquid enters from the liquid inlet 12, flows through the inner cavity wall to the liquid outlet 13 at the upper part of the outer cavity 10, and flows out from the liquid outlet. Through heat exchange with the outer surface of the inner cavity 9, the cooling liquid takes away the excessive heat generated by the cathode during operation of the propeller, thereby ensuring stable operation of the propeller system.

[0042] The melting points of said material A1, material A2 and material A3 respectively satisfy: cathode operating temperature < T1 < T2 < T3 < cathode melting point, wherein T1 is the melting point of material A1, T2 is the melting point of material A2, and T3 is the melting point of material A3; meanwhile, the electron emissivity of material A1, material A2 and material A3 is lower than that of the materials of the cathode material assembly, they have good electrical conductivity and certain ablation resistance. Any metal material whose melting point, electron emissivity, ablation resistance and electrical conductivity meet the above description can be used as the material of the cathode connection assembly. Since the number of sections of the long-life structure described in the present invention can be changed according to the service life requirements of the propeller, if a cathode structure with more than 4 sections is required, more materials for the cathode connection assembly are needed, therefore no specific requirements are imposed on the above three materials.

[0043] As Figure 4 shown, an insulating layer is provided between the insulating pipe member 21 and the propeller anode and the propeller cathode. The propeller anode comprises an anode body 22, a spiral heat exchange unit 23 and a multi-channel heat exchange unit 24.

[0044] The spiral heat exchange unit 23 has a spiral channel, which significantly increases the flow path of cooling water, provides good heat conduction capacity, and improves the anode heat exchange capability.

[0045] Specifically, the front section of the cathode is divided into several sections of materials, and a material whose melting point is between the cathode operating temperature and the melting point of the cathode itself is used between each section. Starting from the front end, each intermediate material is sequentially named material A11, material A22, and material A33, with melting points T1, T2, and T3 respectively.

[0046] The melting points of the materials satisfy the following relationship:

[0047] Cathode operating temperature < T1 < T2 < T3 < Cathode melting point.

[0048] The working mode of the novel cathode is as follows:

[0049] When the first section of cathode material approaches the end of its service life, the operating voltage is increased to raise the temperature of the cathode itself to T1. At this time, material A1 melts when reaching its melting point, and the second section of cathode material starts to be consumed.

[0050] When the second section of cathode material approaches the end of its service life, the operating voltage is further increased to raise the temperature of the cathode itself to T2. At this time, material A2 melts when reaching its melting point, and the third section of cathode material starts to be consumed.

[0051] When the third section of cathode material approaches the end of its service life, the operating voltage is further increased to raise the temperature of the cathode itself to T3. At this time, material A3 melts when reaching its melting point, and the cathode nozzle main body 7 starts to be consumed.

[0052] Due to the working characteristics of the cathode, the burned部位 is all located at the front end of the cathode. Therefore, before material A11, material A22, and material A33 melt, the cathode materials behind them are almost in a brand-new state, so the service life of the cathode can be almost recalculated, and the service life is increased to several times that of the original cathode.

[0053] Further, since a metal material is used to connect the sections of the cathode, the air tightness problem caused by using a mechanical structure to segment the cathode is avoided.

[0054] Further, since no mechanical structure is added at all, the original system can be directly used to realize the separation of scrapped cathodes, which reduces the later R&D cost.

[0055] Further, because the structure is simple and no mechanical hydraulic structure is added, the problem of liquid leakage does not need to be considered in the extreme space environment.

[0056] Further, the heating wire is made of tungsten, which has a melting point of 3410°C.

[0057] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above. For example, the number of cathode segments can be increased or decreased according to the required cathode lifespan, as well as the length of each cathode segment. All such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A long-life cathode structure for electric propulsion, characterized in that, It comprises a heating wire, a cathode material assembly and a cathode connection assembly; the cathode material assembly consists of a coaxially connected first-section cathode material, a second-section cathode material, a third-section cathode material and a cathode nozzle main body; the first-section cathode material, the second-section cathode material, the third-section cathode material and the cathode nozzle main body have the same material composition and are separated by the cathode connection assembly; the cathode connection assembly consists of material A1, material A2 and material A3; the first-section cathode material is connected to the second-section cathode material via material A1, the second-section cathode material is connected to the third-section cathode material via material A2, and the third-section cathode material is connected to the cathode nozzle main body via material A3; the heating wire is configured to heat the cathode nozzle main body to a thermionic emission temperature, and enable the first-section cathode material, the second-section cathode material and the third-section cathode material to reach their respective melting points; The melting points of the material A1, the material A2 and the material A3 satisfy the following condition: cathode operating temperature < T1 < T2 < T3 < cathode melting point, wherein T1 is the melting point of the material A1, T2 is the melting point of the material A2, and T3 is the melting point of the material A3; meanwhile, the electron emissivity of the material A1, the material A2 and the material A3 is lower than that of the material of the cathode material assembly; The difference between the melting point values of materials of adjacent cathode connection assemblies is more than 50°C; The melting point of the heating wire is 500°C higher than the melting point T3 of the material A3.

2. The long-life cathode structure for electric propulsion according to claim 1, characterized in that, The invention further comprises a cathode air inlet pipe, a fixing ring member, an inner cavity body, an outer cavity body and a nozzle fixing seat; the cathode air inlet pipe is fixedly connected to the front end of the inner cavity body, the rear end of the inner cavity body is connected with the nozzle fixing seat through threads, and the nozzle fixing seat is fixedly connected with the cathode nozzle main body; the inner cavity body, the nozzle fixing seat and the cathode nozzle main body are all hollow structures, and together form a cathode air inlet channel; the fixing ring member and the outer cavity body are fixedly nested outside the inner cavity body; before the thruster is started, that is, in the preheating stage, the heating wire is energized, and current in the heating wire generates Joule heat to heat the cathode nozzle main body to the thermionic emission temperature. At this time, the cathode starts to emit thermoelectrons, and the thermoelectrons collide with propellant gas to generate weak ionization, and the electron density continuously rises to a steady state, then the device enters a self-sustaining discharge state, the power supply of the heating wire is removed, the anode power supply is turned on, and an electric field is used to maintain plasma generation; after the service life of the first-section cathode material is exhausted, the heating wire is heated to the melting point T1 of the material A1, the material A1 melts, and the second-section cathode material starts to be consumed, and the cathode life is recalculated. Similarly, after the service life of the second-section cathode material is exhausted, the heater is heated to the melting point T2 of the material A2, the material A2 melts, and the third-section cathode material starts to be consumed. The cathode life is prolonged without changing the cathode material and adding a mechanical structure.

3. The long-life cathode structure for electric propulsion according to claim 1, characterized in that, The lengths of the cathode materials of each section satisfy that the next-section cathode material is not damaged before the service life of the previous-section cathode material ends, so as to prevent the next-section cathode material from participating in discharge in advance, which would shorten the service life of the next-section cathode material in advance. The length of each section of cathode material is determined according to the radius, material, pore diameter of the cathode and experimental results.

4. The long-life cathode structure for electric propulsion according to claim 1, characterized in that, The invention further comprises a ceramic outer shell, which is configured to ensure insulation between the heating wire and the cathode material.

5. A long-life cathode structure for electric propulsion according to claim 1, characterized in that, The ceramic housing is used to prevent the heating wire from heating the propeller.

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