Hollow cathode assembly

Abstract

The invention discloses a hollow cathode assembly, which comprises an emitter, a top pore plate, a heater, a gas-guide tube, an auxiliary electrode and a contact electrode, the touch pole is of a cylindrical structure, one end of the touch pole is combined and fixed with a plate body, the center of the plate body is provided with a through hole, and the emitter, the top hole plate, the heater, the auxiliary pole and the gas-guide tube are coaxially arranged with the touch pole; the gas-guide tube is of a hollow tube body structure and is arranged in the touch holding electrode in a penetrating manner; the top hole plate is combined and fixed at one end, close to the plate body, of the gas-guide tube; a small hole is formed in the center of the top hole plate; the heater wraps the peripheral surface of the gas guide pipe; the emitter is located in the air guide pipe and abuts against the top hole plate, a cavity penetrating through the emitter is formed in the center of the emitter, and the cavity is communicated with the small hole; the auxiliary electrode penetrates through the gas guide tube, one end of the auxiliary electrode is located in the cavity, the cavity is of a conical structure, the inner diameter of an opening in the side close to the top pore plate is smaller than that of an opening in the side away from the top pore plate, discharge current oscillation can be reduced, and the stability of the hollow cathode assembly is improved.

Description

Technical Field

[0001] The present invention relates to the field of plasma materials and thermal materials, and more particularly to a hollow cathode assembly. Background Art

[0002] With the development of low-orbit constellation technology, electric propulsion technology for satellite attitude control and orbit maintenance has also made great progress. Among the many thrusters, Hall thrusters and ion thrusters have the characteristics of total impulse and high efficiency, becoming the most promising propulsion components in low-orbit constellations. The hollow cathode is the igniter and neutralizer of the Hall thruster and ion thruster, which directly determines the ignition efficiency, working state and efficiency of the thruster. The emitter in the hollow cathode assembly has a relatively low work function, which provides initial electrons for the hollow cathode or thruster. However, due to the high surface activity of the emitter material, it is easy to react chemically with gases such as oxygen and water vapor when exposed to the atmospheric environment, causing emitter poisoning, increasing the ignition time of the hollow cathode assembly or failing to ignite. In addition, during the operation of the hollow cathode assembly, discharge current oscillation will occur, resulting in unstable discharge of the hollow cathode assembly. For this reason, the main problem in the development of the hollow cathode assembly is how to reduce the ignition time of the hollow cathode assembly and improve the stability of the hollow cathode assembly. Summary of the invention

[0003] In view of the above problems, an object of the present invention is to provide a hollow cathode assembly which reduces the ignition time of the hollow cathode assembly and improves the stability of the hollow cathode assembly.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A hollow cathode assembly, comprising:

[0006] Emitter, top hole plate, heater, air guide tube, auxiliary electrode and touch-holding electrode;

[0007] The touch-holding electrode is a cylindrical structure, one end of which is fixedly connected to a plate body, the center of which is provided with a through hole, and the emitter, top hole plate, heater, auxiliary electrode and air guide tube are all coaxially arranged with the touch-holding electrode;

[0008] The air guide tube is a hollow tube structure and is inserted into the touch-holding electrode;

[0009] The top hole plate is fixed to one end of the air guide tube close to the plate body, and a small hole is opened in the center of the top hole plate;

[0010] The heater is wrapped around the outer peripheral surface of the air guide tube;

[0011] The emitter is located in the air guide tube and abuts against the top hole plate. A cavity penetrating the emitter is provided at the center of the emitter, and the cavity is connected to the small hole.

[0012] The cavity is a conical structure, and the inner diameter of the opening on the side close to the top hole plate is smaller than the inner diameter of the opening on the side away from the top hole plate;

[0013] The auxiliary pole is arranged through the air guide tube and one end of the auxiliary pole is located in the cavity.

[0014] In addition, an optional solution is that the cone angle α of the cavity has a value range of 0°<α<180°.

[0015] In addition, an optional solution is that the cone angle α of the cavity is 30°.

[0016] In addition, an optional solution is that the material of the contact electrode is one of tantalum, molybdenum or graphite.

[0017] In addition, an optional solution is that the inner diameter of the air duct is larger than the outer diameter of the projectile, and the outer diameter of the air duct is smaller than the inner diameter of the heater.

[0018] In addition, an optional solution is that the hollow cathode assembly further comprises a heat shield tube, the heat shield tube is arranged on a side of the heater away from the air guide tube, and a gap is provided between the heat shield tube and the heater in the radial direction of the air guide tube.

[0019] In addition, an optional solution is that the inner diameter of the contact holding electrode is larger than the outer diameter of the heat shield tube, and the inner diameter of the through hole is larger than the inner diameter of the small hole.

[0020] In addition, an optional solution is that the heater is a tungsten wire or a rhenium tungsten wire, which is spirally wound on the outer circumference of the air guide tube at a position corresponding to the emitter.

[0021] In addition, an optional solution is that the inner diameter of the small hole is much smaller than the inner diameter of the opening of the cavity on one side close to the top hole plate.

[0022] In addition, optionally, the emitter is a barium tungsten cathode or a lanthanum hexaboride cathode.

[0023] The beneficial effects of the present invention are as follows:

[0024] In view of the technical problems existing in the prior art, the present invention provides a hollow cathode assembly, which adds an auxiliary electrode on the basis of the traditional hollow cathode assembly, realizes plasma cleaning of the emitter surface through secondary discharge, can remove the deteriorated substances on the emitter surface in a short time, quickly restore the emitter performance, ensure the consistency of the ignition time of the hollow cathode assembly and the controllability of the electric propulsion equipment. Designing the cavity of the emitter to be a conical structure can effectively increase the inner surface area of ​​the emitter, which is conducive to the diffusion of plasma toward the top hole plate during the ignition process, and effectively control the discharge area of ​​the plasma, reduce the discharge current oscillation, and improve the stability of the hollow cathode assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0026] Figure 1 A cross-sectional view of a hollow cathode assembly provided by an embodiment of the present invention is shown.

[0027] Figure 2 A cross-sectional view of an emitter provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0029] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] In the present invention, unless otherwise clearly stipulated and limited, a first feature being “on” or “under” a second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them.

[0031] In the description of this embodiment, the terms "upper", "lower", "left", "right" and other directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0032] In a traditional hollow cathode assembly, the emitter is located inside the gas duct, and a top hole plate is installed at the top of the gas duct to reduce the flow conductance of the working gas. Since the aperture of the small hole on the top hole plate is much smaller than the inner diameter of the emitter and the gas duct, the pressure inside the emitter is more than three orders of magnitude higher than the external vacuum environment pressure, which ensures the stability of the plasma discharge state of the hollow cathode assembly. The ignition process of the hollow cathode assembly is as follows: First, the working gas is introduced into the gas duct, and the heater heats the emitter to the working temperature. Then, the emitter generates electron emission under the action of the high voltage of the touch electrode. The electrons are accelerated under the action of the electric field and collide with the working gas atoms to ionize the gas. As the density of ions and electrons increases, a discharge channel is formed; finally, the heater stops heating, and a stable discharge phenomenon occurs between the emitter and the touch electrode.

[0033] Traditional hollow cathode assemblies are prone to discharge current oscillation during operation. Research has found that this problem occurs because the discharge area is concentrated near the top hole plate when the hollow cathode assembly is working. As the discharge current increases, the plasma distribution area gradually expands from the top hole plate position to the inside of the emitter, resulting in unstable discharge area, which in turn causes the self-sustaining voltage of the hollow cathode assembly to oscillate, resulting in unstable discharge of the hollow cathode assembly.

[0034] In view of the defects of the prior art, the present invention provides a hollow cathode assembly, combined with Figure 1-2 As shown, the hollow cathode assembly includes an emitter 1, a top hole plate 2, a heater 3, an air guide tube 4, an auxiliary electrode 5 and a touch-holding electrode 6. The touch-holding electrode is a thin-walled cylindrical structure, one end of which is fixedly connected to a plate body 61, and a through hole 62 is formed at the center of the plate body 61. The main function of the through hole 62 is to trigger the discharge of the emitter 1 and protect the internal high-temperature components, reduce the heat radiation loss, and prevent the internal high-temperature components from being corroded by external high-energy ions.

[0035] The emitter 1, the top hole plate 2, the heater 3, the air guide tube 4 and the auxiliary pole 5 are all coaxially arranged with the touch-holding pole 6.

[0036] The heater 3 is wrapped around the outer peripheral surface of the air guide tube 4 .

[0037] The air guide tube 4 is a hollow tube structure, which is inserted into the touch-holding electrode 6. The top hole plate 2 is fixed to one end of the air guide tube 4 close to the plate body 61, and a small hole 21 is opened in the center of the top hole plate 2. The small hole 21 and the through hole 62 are coaxially arranged. During operation, a high voltage is applied to the touch-holding electrode 6, and the electric field will achieve breakdown between the top hole plate 2 and the plate body 61. This breakdown phenomenon causes some ions to diffuse into the air guide tube 4.

[0038] The projectile 1 is located in the air guide tube 4 and is connected to the top hole plate 2. A cavity 11 is provided in the center of the projectile 1 and passes through the projectile 1. The cavity 11 is connected to the small hole 21. The cavity 11 is a conical structure, and the inner diameter of the opening on the side close to the top hole plate 2 is smaller than the inner diameter of the opening on the side away from the top hole plate 2.

[0039] The auxiliary pole 5 is disposed in the air guide tube 4 and one end of the auxiliary pole 5 is located in the cavity 11 .

[0040] The gas guide tube 4 and the top hole plate 2 are both made of metal materials. The electric field generated by the high voltage of the contact electrode 6 can only act on the inner surface of the emitter 1 through the small hole 21 of the top hole plate 2. At this time, the electric field intensity on the inner surface of the emitter 1 is relatively small. Only when the activity of the inner surface of the emitter 1 is high can electron emission occur, so that the hollow cathode assembly can be successfully ignited.

[0041] In order to improve the phenomenon that the electric field strength on the surface of the emitter 1 is weak and the electron emission ability of the emitter 1 is greatly affected by the activity of the material, the auxiliary electrode 5 is inserted into the gas guide tube 4. Specifically, during the ignition process of the hollow cathode assembly, the voltage applied to the auxiliary electrode 5 and the touch-holding electrode 6 is the same, and the electric field generated by the voltage of the auxiliary electrode 5 directly acts on the surface of the cavity 11. Even if the surface activity of the emitter 1 is poor, the current emitted by it under the action of the electric field of the auxiliary electrode 5 can still generate a stable gas discharge between the auxiliary electrode 5 and the emitter 1. At this time, the plasma bombards the surface of the cavity 11 of the emitter 1, which can ion purify the emitter 1, etch away the substances on the surface of the cavity 11 that are not conducive to electron emission, and restore the activity of the inner surface of the emitter 1, and finally generate a stable gas discharge between the emitter 1 and the touch-holding electrode 5, so as to achieve the successful ignition of the hollow cathode assembly in the poisoned state. After successful ignition, the auxiliary electrode 5 is powered off, and the touch-holding electrode 6 continues to supply power to ensure the stable progress of the gas ionization process, so that the emitter 1 continues to emit electrons to the touch-holding electrode 1. Since the hollow cathode assembly provided by the embodiment of the present invention has a discharge phenomenon on the auxiliary electrode 5 and the holding electrode 6 respectively during the ignition process, and there is a sequence, the ignition mode of the hollow cathode assembly is called a two-stage ignition mode, which is different from the one-time discharge phenomenon during the ignition process of the traditional hollow cathode assembly. In other embodiments, the voltages applied to the auxiliary electrode 5 and the holding electrode 6 may also be different, and can be set according to specific circumstances.

[0042] In a specific embodiment, the cavity 11 is a conical structure, and the cone angle is α, and the value range of α is 0°<α<180°. The current emitted by the emitter 1 is proportional to the surface area of ​​the cavity 11. The conical cavity 11 can effectively expand the inner surface area of ​​the emitter 1, increase the discharge area of ​​the plasma, and thus expand the working current range of the hollow cathode assembly.

[0043] Under the same voltage, the distance between the inner surface of the cavity 11 and the auxiliary pole 5 gradually decreases along the direction close to the top hole plate 2, and the electric field tends to gradually increase. Compared with the traditional cylindrical emitter, the peak position of the electric field intensity will move toward the top hole plate 2, which is conducive to the diffusion of plasma toward the top hole plate 2 during the ignition process. For the traditional cylindrical emitter, its cavity is a cylindrical surface (i.e., the cone angle α=0°). During the ignition process, the plasma is concentrated in the section where the auxiliary pole 5 is located in the cavity, and the efficiency of the plasma diffusion toward the top hole plate 2 is greatly reduced.

[0044] When the traditional hollow cathode assembly is working normally, the discharge area is concentrated near the top hole plate 2. As the discharge current increases, the distribution area of ​​the plasma gradually expands from the top hole plate 2 to the inside of the emitter 1, resulting in an unstable discharge area, causing the self-sustaining voltage of the hollow cathode assembly to oscillate, resulting in the problem of unstable discharge of the hollow cathode assembly. In the embodiment of the present invention, the cavity 11 is designed as a conical structure. Since the current emitted by the emitter 1 is proportional to the area of ​​the inner surface of the cavity 11, under the same emission current, the emitter 1 with a conical cavity 11 is Figure 2 The length in the X direction is smaller than that of the cylindrical emitter, that is, compared with the traditional hollow cathode assembly, the range of plasma expansion into the emitter 1 is smaller, which is beneficial to improving the discharge stability of the hollow cathode assembly.

[0045] In an optional example, the cone angle α of the cavity 11 is 30°.

[0046] In one embodiment, the material of the air guide tube 4 may be, but is not limited to, metal materials such as tantalum and molybdenum, and should have properties such as high temperature resistance, corrosion resistance, and strong electrical conductivity. The inner diameter of the air guide tube 4 is larger than the inner diameter of the projectile 1, so that the projectile 1 can be installed in the air guide tube 4. The outer diameter of the air guide tube 4 is smaller than the inner diameter of the heater 3, so that the heater 3 can be tightly wrapped around the outer peripheral surface of the air guide tube 4 to heat the projectile during the ignition stage.

[0047] In one embodiment, the hollow cathode assembly further includes a heat shield tube 7, which is disposed on a side of the heater away from the air duct 4, and the heat shield tube 7 and the heater 3 are not in contact, and the heat shield tube 7 and the heater 3 include a gap in the radial direction of the air duct 4. In this embodiment, the heat shield tube 7 may be, but is not limited to, a metal material such as tantalum or molybdenum. In actual production, whether to set the heat shield tube 7 may be selected according to demand.

[0048] In one embodiment, the inner diameter of the electrode 6 is larger than the outer diameter of the heat shield tube 7, and the inner diameter of the through hole 62 is larger than the inner diameter of the small hole 21. The electrode 6 can be made of, but not limited to, metal materials such as stainless steel and molybdenum, or non-metallic conductive materials such as graphite.

[0049] In one embodiment, the heater 3 is a high melting point metal such as tungsten wire or rhenium tungsten wire, and is spirally wound on the outer peripheral surface of the air guide tube 4 at a position corresponding to the emitter 1. It should be noted that the material of the heater 3 is not limited to tungsten wire or rhenium tungsten wire. This embodiment is only used as an example. Other high melting point metals can also be selected according to needs in specific production.

[0050] In one embodiment, the inner diameter of the small hole 21 is much smaller than the inner diameter of the opening of the cavity 11 close to the top hole plate 2, which is beneficial to increase the pressure difference between the inner and outer vacuum environments of the emitter 1 and ensure a stable plasma discharge state of the hollow cathode assembly.

[0051] In one embodiment, the emitter 1 may be, but is not limited to, a barium tungsten cathode, an oxide cathode, or a lanthanum hexaboride cathode.

[0052] In one embodiment, the material of the auxiliary electrode 5 may be, but is not limited to, high melting point metals such as tungsten and molybdenum.

[0053] The advantages of the hollow cathode assembly provided by the embodiment of the present invention will be described below with reference to examples:

[0054] Comparative Example

[0055] The emitter is a barium tungsten cathode with a cone angle of 0°. The top hole plate material is the same as the emitter material and is integrated. The heater material is rhenium tungsten wire, the heat shield tube material is tantalum, the contact electrode material is graphite, and the auxiliary electrode material is tungsten wire. The hollow cathode assembly is assembled and placed in a vacuum system. The experimental results show that the ignition time is 240s, the current oscillation amplitude is 0.5A, and the working current range is 1.0-2.5A.

[0056] Example

[0057] The emitter is a barium tungsten cathode with a cone angle of 30°. The top hole plate material is the same as the emitter material and is integrated. The heater material is rhenium tungsten wire, the heat shield tube material is tantalum, the contact electrode material is graphite, and the auxiliary electrode material is tungsten wire. The hollow cathode assembly is assembled and placed in a vacuum system. The experimental results show that the ignition time is 140s, the current oscillation amplitude is ≤0.1A, and the working current range is 0.8-4.0A.

[0058] By comparing the experimental results of the embodiment and the comparative example, the hollow cathode assembly provided by the embodiment of the present invention has a shorter ignition time, a smaller current oscillation amplitude, and a wider operating current range than the traditional hollow cathode assembly.

[0059] After the hollow cathode assemblies of the comparative example and the embodiment were exposed to the laboratory atmosphere for 3 months, it was found that the ignition time of the embodiment was 150s, and the ignition time of the comparative example was 400s. The ignition time of the embodiment was greatly shortened.

[0060] The hollow cathode assembly provided in the embodiment of the present invention adds an auxiliary electrode to the traditional hollow cathode assembly, realizes plasma cleaning of the emitter surface through secondary discharge, can remove the deteriorated material on the emitter surface in a short time, quickly restore the emitter performance, ensure the consistency of the ignition time of the hollow cathode assembly and the controllability of the electric propulsion equipment. Designing the cavity of the emitter to be a conical structure can effectively increase the inner surface area of ​​the emitter, which is conducive to the diffusion of plasma toward the top hole plate during the ignition process, and effectively control the discharge area of ​​the plasma, reduce the discharge current oscillation, and improve the stability of the hollow cathode assembly.

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A hollow cathode assembly, characterized in that: include: Emitter, top hole plate, heater, air guide tube, auxiliary electrode and touch-holding electrode; The touch-holding electrode is a cylindrical structure, one end of which is fixedly connected to a plate body, the center of which is provided with a through hole, and the emitter, top hole plate, heater, auxiliary electrode and air guide tube are all coaxially arranged with the touch-holding electrode; The air guide tube is a hollow tube structure and is inserted into the touch-holding electrode; The top hole plate is fixed to one end of the air guide tube close to the plate body, and a small hole is opened in the center of the top hole plate; The heater is wrapped around the outer peripheral surface of the air guide tube; The emitter is located in the air guide tube and abuts against the top hole plate. A cavity penetrating the emitter is provided at the center of the emitter, and the cavity is connected to the small hole. The cavity is a conical structure, and the inner diameter of the opening on the side close to the top hole plate is smaller than the inner diameter of the opening on the side away from the top hole plate; The auxiliary pole is disposed through the air guide tube and one end thereof is located in the cavity.

2. The hollow cathode assembly according to claim 1, characterized in that The cone angle α of the cavity has a value range of 0°<α<180°.

3. The hollow cathode assembly according to claim 1, characterized in that The cone angle α of the cavity is 30°.

4. The hollow cathode assembly according to claim 1, characterized in that: The material of the contact electrode is one of tantalum, molybdenum or graphite.

5. The hollow cathode assembly according to claim 1, characterized in that: The inner diameter of the air guide tube is larger than the outer diameter of the projectile, and the outer diameter of the air guide tube is smaller than the inner diameter of the heater.

6. The hollow cathode assembly according to claim 1, characterized in that: The hollow cathode assembly further comprises a heat shield tube, which is arranged on a side of the heater away from the air guide tube, and a gap is provided between the heat shield tube and the heater in the radial direction of the air guide tube.

7. The hollow cathode assembly according to claim 1, characterized in that: The inner diameter of the contact holding electrode is larger than the outer diameter of the heat shield tube, and the inner diameter of the through hole is larger than the inner diameter of the small hole.

8. The hollow cathode assembly according to claim 1, characterized in that The heater is a tungsten wire or a rhenium-tungsten wire, which is spirally wound on the outer circumference of the air guide tube at a position corresponding to the emitter.

9. The hollow cathode assembly according to claim 1, characterized in that: The inner diameter of the small hole is much smaller than the inner diameter of the opening of the cavity close to the top hole plate.

10. The hollow cathode assembly according to claim 1, characterized in that The emitters shown are either barium tungsten cathodes or lanthanum hexaboride cathodes.

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