Microwave DC cathode suitable for oxidizing working medium and working method thereof

Abstract

This invention belongs to the field of space electric propulsion in aerospace propulsion technology, and relates to a microwave DC cathode suitable for oxidizing working fluids and its operating method. The microwave DC cathode includes a discharge cavity body, a microwave antenna, leads, an insulating medium, contact electrodes, a microwave connector, and a high-temperature resistant component. The microwave antenna is horizontally mounted inside the discharge cavity body; the microwave connector is vertically fixed to the discharge cavity body; the high-temperature resistant component is installed between the discharge cavity and the microwave connector; the leads, insulating medium, and contact electrodes are sequentially stacked and fixed at the outlet end of the discharge cavity body from the inside out; lead-out holes are pre-machined at the center of the leads and contact electrodes, and a center hole is pre-machined at the center of the contact electrode; the discharge cavity is formed by the discharge cavity body, leads, and high-temperature resistant component forming an outer envelope, and the microwave antenna is the inner envelope; the head of the microwave antenna is pointed, with the pointed end facing the lead-out hole. This invention addresses the cathode requirements of electric propulsion systems in ultra-low Earth orbit environments.

Description

Technical Field

[0001] This invention belongs to the field of space electric propulsion in aerospace propulsion technology, specifically relating to a microwave DC cathode suitable for oxidizing working fluids and its working method. Background Technology

[0002] In recent years, ultra-low Earth orbit (ULE) spacecraft (100-350 km orbit range) have demonstrated high operational safety and low cost, facilitating multi-satellite launches and showing great promise in the field of low-Earth orbit satellite internet construction. However, the severe atmospheric drag in ULE significantly limits the on-orbit operational lifespan of spacecraft. Satellites require propulsion systems for orbit maintenance, and electric propulsion technology is ideal for this purpose. However, the high levels of atomic oxygen in the ULE environment pose a severe challenge to the on-orbit operational capabilities of existing electric propulsion technologies.

[0003] Hall thrusters and ion thrusters, as the most commonly used electric thrusters, are extremely dependent on the electron emission capability and operational life of the cathode. Existing hollow cathode technology typically uses materials with extremely high electron emission capabilities, such as barium tungsten or lanthanum hexaboride, as the emitter. However, these common emitter materials are highly susceptible to cathode poisoning in the highly oxidizing environment of ultra-low orbit, losing their electron emission capability and directly leading to the failure of the entire propulsion system.

[0004] There are some academic papers on providing electrons using microwave plasma neutralizers; however, due to their operating principle, these plasma neutralizers struggle to provide large electron currents at low power. Hall thrusters and ion thrusters typically require an electron current of over 1.5 A from the cathode, while microwave plasma neutralizers usually only provide electron currents in the hundreds of milliamperes, which is insufficient. Furthermore, existing microwave plasma neutralizer technologies all use permanent magnets, but strong permanent magnets can interfere with the magnetic fields of Hall thrusters and ion thrusters, making them unsuitable for use.

[0005] In summary, there is an urgent need to develop novel cathodes with large emission currents that can operate for extended periods in highly oxidizing environments such as ultra-low orbit. Summary of the Invention

[0006] The purpose of this invention is to provide a microwave DC cathode suitable for oxidizing working fluids and its operating method, which can generate a large electron current without the use of permanent magnets or electromagnets and without an emitter, thus solving the cathode requirements of electric propulsion systems in ultra-low orbit environments.

[0007] This invention is achieved through the following technical solution:

[0008] This invention discloses a microwave DC cathode suitable for oxidizing working fluids, comprising a discharge cavity body, a microwave antenna, a lead electrode, an insulating medium, a contact electrode, a microwave connector, and a high-temperature resistant component;

[0009] An air inlet is pre-machined at one end of the main body of the discharge cavity, and the other end serves as the air outlet.

[0010] The microwave antenna is installed horizontally inside the discharge cavity body.

[0011] The microwave connector is fixed vertically to the discharge cavity body, and the axis of the microwave connector is perpendicular to the axis of the microwave antenna.

[0012] A high-temperature resistant component is installed between the discharge chamber and the microwave connector to isolate the discharge chamber from the microwave connector;

[0013] The lead electrode, insulating medium, and contact electrode are stacked and fixed at the outlet end of the discharge cavity body from the inside to the outside.

[0014] The center position of the lead electrode is pre-machined with a lead hole, and the center position of the contact electrode is pre-machined with a center hole. The lead hole and the center hole are used to emit electron current.

[0015] The discharge cavity body is a hollow cavity, which serves as the discharge chamber. The discharge chamber consists of the discharge cavity body, the lead-out electrode, and the high-temperature resistant component forming the outer envelope, while the microwave antenna forms the inner envelope.

[0016] The head of the microwave antenna is pointed, with the pointed end facing the lead-out hole.

[0017] Furthermore, heat dissipation fins are installed on the side of the discharge cavity body.

[0018] Furthermore, the length of the discharge chamber is designed to be 1 / 4 wavelength of the operating frequency, which is used to achieve microwave discharge with 1 / 4 wavelength short-circuit coupling.

[0019] Furthermore, the microwave connector has an inner conductor at its center, and the end of the inner conductor is pre-machined with an external thread;

[0020] The end of the inner conductor passes through the high-temperature resistant component vertically and is then threaded into the microwave antenna.

[0021] Furthermore, both the lead-out electrode and the contact electrode are single-sided sealed cylindrical structures.

[0022] Furthermore, both the lead-out electrode and the contact electrode are made of oxygen-resistant metal materials; the insulating medium is annular and made of insulating material.

[0023] Furthermore, a toroidal permanent magnet or an electromagnetic coil is used for magnetic confinement outside the contact pole.

[0024] Furthermore, the lead-out hole includes a cylindrical hole and a conical hole that are connected. The cylindrical hole is close to the discharge chamber, and the large-diameter end of the conical hole is close to the contact electrode. The maximum diameter of the conical hole is consistent with the diameter of the central hole of the contact electrode.

[0025] Furthermore, a circular groove along the horizontal direction is pre-machined on the inner wall of the discharge cavity body and located at the air inlet end, and the microwave antenna is installed in the circular groove of the discharge cavity body along the horizontal direction.

[0026] This invention also discloses a method for operating a microwave DC cathode suitable for oxidizing working fluids, comprising the following steps:

[0027] The oxidizing working gas flows evenly into the discharge chamber through the inlet end;

[0028] Microwave power is fed into the discharge chamber along the path of microwave connector, high-temperature resistant component, and microwave antenna. A strong microwave electric field is then generated at the tip of the microwave antenna. Under the action of the microwave electric field, the working gas undergoes an ionization reaction, generating a high-density plasma between the tip of the microwave antenna and the lead-out electrode, thus completing the first step of microwave discharge.

[0029] Electrons in high-density plasma enter the space between the lead-out electrode and the contact electrode through the lead-out hole of the lead-out electrode, and become seed electrons for DC discharge;

[0030] A negative voltage is applied to the lead-out electrode, and the contact electrode is grounded. As the negative voltage gradually increases, with the help of seed electrons, a DC glow discharge is formed between the lead-out electrode and the contact electrode, completing the second step of DC discharge.

[0031] Subsequently, the electrons generated by the DC discharge flow out from the lead-in hole under the action of the electric field, completing the emission of a large electron current.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] This invention discloses a microwave DC cathode suitable for oxidizing working fluids, comprising a discharge cavity body, a microwave antenna, leads, an insulating medium, contact electrodes, a microwave connector, and a high-temperature resistant component. The microwave antenna is installed inside the discharge cavity body. The leads, insulating medium, and contact electrodes are sequentially stacked and fixed on the outlet end of the discharge cavity body from the inside out. The microwave connector is fixed to the discharge cavity body. The discharge cavity is a coaxial space, with the discharge cavity body, leads, and high-temperature resistant component forming the outer envelope, and the microwave antenna forming the inner envelope. The high-temperature resistant component is installed between the discharge cavity body and the microwave connector, isolating the discharge cavity from the microwave connector and fundamentally eliminating the risk of microwave connector failure due to plasma erosion. This significantly improves the thermal withstand capability of the microwave DC cathode without affecting microwave power transmission.

[0034] It can generate a large electron current in a working environment without using permanent magnets or electromagnets, without an emitter, with an oxidizing working fluid, and with low power. First, it avoids the problem of oxidation poisoning of the emitter; second, it avoids the magnetic field from interfering with or affecting the thruster working with it; and third, it realizes a large electron current under low power and low working fluid flow.

[0035] Furthermore, heat dissipation fins are installed on the side of the discharge cavity body to improve heat dissipation capacity.

[0036] Furthermore, seed electrons can be generated by short-circuit coupling with a 1 / 4 wavelength, which can form plasma in the absence of emitters, permanent magnets, or electromagnets, serving as a seed electron source.

[0037] Furthermore, a two-section design was adopted for the lead-out hole, specifically including a connected cylindrical hole and a conical hole. The cylindrical hole is close to the discharge chamber, and the large-diameter end of the conical hole is close to the contact electrode. The maximum diameter of the conical hole is consistent with the diameter of the central hole of the contact electrode. On the one hand, this can increase the local electric field strength on the surface of the lead-out electrode, increase the probability of generating secondary electrons when ions bombard the lead-out plate, and thus reduce the discharge voltage and discharge power. On the other hand, as the high-pressure gas in the discharge chamber flows out of the lead-out hole, it is dispersed along the conical surface and then intercepted by the contact electrode. Combined with the airtight effect of the insulating medium, this can increase the local gas pressure between the electrodes, thereby reducing the working fluid flow rate requirement under the same discharge current and further improving efficiency. This design can effectively reduce the operating power and working fluid flow rate of the microwave DC cathode.

[0038] Furthermore, the design of high-temperature resistant components and heat dissipation fins effectively improves the thermal resistance of the microwave DC cathode, allowing it to operate for extended periods in a vacuum environment and meeting the requirements of electric propulsion systems. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a microwave DC cathode structure suitable for oxidizing working fluids disclosed in this invention.

[0040] Figure 2 This is a schematic diagram showing the installation location of the heat sink fins;

[0041] Figure 3 for Figure 1 A magnified view of a section at point A in the middle;

[0042] Figure 4 The electric field distribution of the two-stage design for the lead-out hole;

[0043] Figure 5 The electric field distribution when the lead-out hole is not designed in a two-stage manner;

[0044] Figure 6 The image shows a microwave DC cathode discharge as an example.

[0045] The components are: 1. Discharge cavity body; 2. Microwave antenna; 3. Lead-out electrode; 4. Insulating medium; 5. Contact electrode; 6. Microwave connector; 7. Discharge cavity; 8. Air inlet; 9. High temperature resistant component; 10. Heat dissipation fins; 61. Inner conductor. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0047] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0048] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0049] Figure 1 This is a schematic diagram of a microwave DC cathode suitable for oxidizing working fluids disclosed in this invention, including a discharge cavity body 1, a microwave antenna 2, a lead electrode 3, an insulating medium 4, a contact electrode 5, a microwave connector 6, an air intake structure 8, a high-temperature resistant component 9, and heat dissipation fins 10. The interior of the discharge cavity body 1 is a hollow cavity, referred to as the discharge chamber 7.

[0050] The discharge cavity body 1 serves as the main structural element, with screw holes in multiple directions. All other structures are fixed to the discharge cavity body 1, specifically:

[0051] like Figure 1 As shown, a circular groove along the horizontal direction is pre-machined on the inner wall of the discharge cavity body 1 and located at the air inlet end. The microwave antenna 2 is installed in the circular groove of the discharge cavity body 1 along the horizontal direction.

[0052] The lead-out electrode 3, the insulating medium 4, and the contact electrode 5 are stacked sequentially from the inside to the outside and fixed to the outlet end of the discharge cavity body 1 by the same batch of insulating bolts; the front end of the microwave antenna 2 faces the lead-out electrode 3.

[0053] Mounting holes are pre-drilled on the housing of the discharge cavity body 1. The microwave connector 6 is fixed in the mounting holes of the discharge cavity body 1 by bolts using its own flange structure. The axis of the microwave connector 6 is perpendicular to the axis of the microwave antenna 2.

[0054] like Figure 1As shown, a stepped hole is pre-formed on the lower inner wall of the microwave connector 6. The high-temperature resistant component 9 is installed in the stepped hole, and the lower surface of the high-temperature resistant component 9 is placed on the stepped surface of the mounting hole. The high-temperature resistant component 9 is limited by the step of the stepped hole and the step of the mounting hole.

[0055] High-temperature resistant component 9 can be made of quartz medium or BN ceramic.

[0056] The leftmost part of the discharge chamber 7 is the air inlet 8. A circumferential hole is made in the air inlet 8 to serve as an air inlet and achieve uniform air intake.

[0057] The discharge chamber 7 is a coaxial space, with the discharge chamber body 1, the lead electrode 3 and the high-temperature resistant component 9 forming an outer envelope, and the microwave antenna 2 forming an inner envelope.

[0058] The length of the coaxial discharge chamber 7 is designed to be 1 / 4 wavelength of the operating frequency, thereby realizing microwave discharge with 1 / 4 wavelength short-circuit coupling. A pointed design is adopted at the head of the microwave antenna 2 to ensure that the strongest microwave electric field in the discharge chamber 7 is at the front of the pointed tip of the microwave antenna 2, and to control the position of microwave discharge to be close to the lead-out hole of the lead electrode 3 and far away from the microwave connector 6.

[0059] like Figure 1 As shown, the microwave connector 6 has an inner conductor 61 at its center. The end of the inner conductor 61 is designed with an external thread. The end of the inner conductor 61 passes through the high-temperature resistant component 9 in the vertical direction and is threadedly connected to the microwave antenna 2 to ensure smooth microwave transmission and fix the axial position of the microwave antenna 2.

[0060] Both lead-out electrode 3 and contact electrode 5 are single-sided cylindrical structures with a convex shape. The convex side of the convex structure is far away from the discharge cavity body 1. Lead-out holes are opened at the center of the top end cap of lead-out electrode 3, and central holes are opened at the center of the top end cap of contact electrode 5. Lead-out holes and central holes are used to emit electron current. Both lead-out electrodes 3 and contact electrodes 5 are made of oxygen corrosion resistant metal materials.

[0061] The insulating medium 4 is annular and made of mica or ceramic high-temperature resistant insulating medium. It is used for potential isolation between the lead electrode 3 and the contact electrode 5, and also serves as an airtight seal.

[0062] like Figure 3 As shown, the lead-out hole of the lead electrode 3 adopts a two-section design. The section near the discharge chamber 7 is a cylindrical hole, and the section near the contact electrode 5 is a tapered hole. The large-diameter end of the tapered hole is close to the contact electrode 5, and the maximum diameter of the tapered hole is consistent with the diameter of the central hole of the contact electrode 5. This design can increase the local electric field strength on the surface of the lead electrode 3, reduce the discharge voltage, maintain the gas pressure between the electrodes, and reduce the working fluid flow requirement.

[0063] A high-temperature resistant component 9 is used to isolate the discharge chamber 7 from the microwave connector 6, eliminating the risk of microwave connector 6 failure due to plasma erosion at the source, and greatly improving the heat resistance of the microwave DC cathode without affecting microwave power transmission.

[0064] Even better, such as Figure 2 As shown, heat dissipation fins 10 are installed on both sides of the discharge cavity body 1 to improve heat dissipation capacity.

[0065] The above-mentioned method for operating a microwave DC cathode suitable for oxidizing working fluids includes the following steps:

[0066] During operation, the oxidizing working gas flows evenly into the discharge chamber 7 through the inlet 8;

[0067] Microwave power is fed into the discharge chamber 7 along the path of microwave connector 6, high-temperature resistant component 9, and microwave antenna 2. Then, a strong microwave electric field is generated at the tip of microwave antenna 2 through 1 / 4 wavelength short-circuit coupling. Under the action of microwave electric field, the working gas undergoes an ionization reaction, thereby generating high-density plasma between the tip of microwave antenna 2 and the top end cap of lead electrode 3, completing the first step of microwave discharge.

[0068] Since the location where the discharge occurs is close to the lead-out hole of lead-out electrode 3, electrons in the plasma can easily enter the space between lead-out electrode 3 and contact electrode 5 through the lead-out hole of lead-out electrode 3, becoming seed electrons for the second DC discharge.

[0069] A negative voltage is applied to lead 3 and contact 5 is grounded. As the negative voltage gradually increases, with the help of seed electrons, a DC glow discharge will be formed between lead 3 and contact 5. The discharge is quiet and stable, completing the second step of DC discharge.

[0070] Subsequently, the electrons generated by the DC discharge will flow out from the lead-in hole under the action of the electric field, completing the emission of a large electron current.

[0071] The lead electrode 3, the discharge cavity body 1, and the microwave antenna 2 are short-circuited through direct contact on the metal surface and are at the same potential, thus avoiding unnecessary DC discharge inside the discharge cavity 7 during operation.

[0072] In another specific embodiment, a ring-shaped permanent magnet or an electromagnetic coil is used outside the contact pole 5 for magnetic confinement, guiding more electrons to move outward from the central hole along the magnetic field lines, slightly increasing the electron extraction current, but also increasing the DC power.

[0073] Figure 4 The electric field distribution of the two-stage design for the lead-out hole is shown below. Figure 4In the diagram, the solid black lines represent electric field lines, and the color cloud represents the electric field intensity distribution; the darker the color, the stronger the electric field. For comparison, when the lead-out hole does not use a two-stage design, the result is as follows: Figure 5 The electric field distribution shown; compare Figure 4 and Figure 5 It can be observed that there is a significant electric field enhancement effect at the boundary of the three-conical surface of the pole in the two-stage design.

[0074] Figure 6 For the present invention Figure 1 The image shown is a real shot of the actual working process of the microwave DC cathode. Figure 6 The central region that emits light is the large electron current emitted. The right side is the microwave DC cathode of this invention, and the left side is the current target for measurement.

[0075] Compared with existing technologies, the microwave DC cathode of the present invention can generate a large electron current in a working environment without the use of permanent magnets or electromagnets, without an emitter, with an oxidizing working medium, and with low power. It can not only avoid the problem of oxidation poisoning of the emitter, but also avoid the magnetic field from interfering with or affecting the thruster working in conjunction with it. It can also achieve a large electron current under low power and low working medium flow rate, which is a great help to the development of ultra-low orbit electric propulsion technology.

[0076] Furthermore, in scenarios without power limitations, permanent magnets or electromagnets can be used for magnetic confinement to further enhance the electron extraction current.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A microwave DC cathode suitable for oxidizing working fluids, characterized in that, It includes a discharge cavity body (1), a microwave antenna (2), a lead-out electrode (3), an insulating medium (4), a contact electrode (5), a microwave connector (6), and a high-temperature resistant component (9); An air inlet (8) is pre-machined at one end of the discharge cavity body (1), and the other end serves as an air outlet; The microwave antenna (2) is installed horizontally inside the discharge cavity body (1); The microwave connector (6) is fixed vertically on the discharge cavity body (1), and the axis of the microwave connector (6) is perpendicular to the axis of the microwave antenna (2); A high-temperature resistant component (9) is installed between the discharge chamber (7) and the microwave connector (6) to isolate the discharge chamber (7) from the microwave connector (6); The lead electrode (3), insulating medium (4) and contact electrode (5) are stacked and fixed on the outlet end of the discharge cavity body (1) from the inside to the outside; The center position of the lead electrode (3) is pre-machined with a lead hole, and the center position of the contact electrode (5) is pre-machined with a center hole. The lead hole and the center hole are used to emit electron current. The discharge cavity body (1) has a hollow cavity inside, which serves as the discharge chamber (7). The discharge chamber (7) consists of the discharge cavity body (1), the lead electrode (3), and the high-temperature resistant component (9) forming an outer envelope, while the microwave antenna (2) forms an inner envelope. The head of the microwave antenna (2) is pointed, with the pointed end facing the lead-out hole; The lead-out hole includes a cylindrical hole and a conical hole that are connected. The cylindrical hole is close to the discharge chamber (7), and the large-diameter end of the conical hole is close to the contact electrode (5). The maximum diameter of the conical hole is consistent with the diameter of the central hole of the contact electrode (5). A circular groove along the horizontal direction is pre-machined on the inner wall of the discharge cavity body (1) and located at the air inlet end (8). The microwave antenna (2) is installed in the circular groove of the discharge cavity body (1) along the horizontal direction.

2. The microwave DC cathode suitable for oxidizing working fluids according to claim 1, characterized in that, Heat dissipation fins (10) are installed on the side of the discharge cavity body (1).

3. The microwave DC cathode suitable for oxidizing working fluids according to claim 1, characterized in that, The length of the discharge chamber (7) is designed to be 1 / 4 wavelength of the operating frequency, which is used to realize microwave discharge with 1 / 4 wavelength short-circuit coupling.

4. A microwave DC cathode suitable for oxidizing working fluids according to claim 1, characterized in that, The microwave connector (6) has an inner conductor (61) at its center, and the end of the inner conductor (61) is pre-machined with an external thread; After the end of the inner conductor (61) passes through the high-temperature resistant component (9) in the vertical direction, it is threadedly connected to the microwave antenna (2).

5. A microwave DC cathode suitable for oxidizing working fluids according to claim 1, characterized in that, Both the lead-out electrode (3) and the contact electrode (5) are single-sided sealed cylindrical structures.

6. A microwave DC cathode suitable for oxidizing working fluids according to claim 1, characterized in that, Both the lead-out electrode (3) and the contact electrode (5) are made of oxygen-resistant metal materials; the insulating medium (4) is annular and made of insulating material.

7. A microwave DC cathode suitable for oxidizing working fluids according to claim 1, characterized in that, A toroidal permanent magnet or an electromagnetic coil is used for magnetic confinement outside the contact pole (5).

8. A method for operating a microwave DC cathode suitable for oxidizing working fluids according to any one of claims 1-7, characterized in that, Includes the following processes: Oxidizing working gas flows evenly into the discharge chamber (7) through the inlet (8); Microwave power is fed into the discharge chamber (7) along the path of microwave connector (6), high-temperature resistant component (9), and microwave antenna (2). Then, a strong microwave electric field is generated at the tip of microwave antenna (2). Under the action of the microwave electric field, the working gas ionization reaction occurs, and a high-density plasma is generated between the tip of microwave antenna (2) and the lead-out electrode (3), thus completing the first step of microwave discharge. Electrons in the high-density plasma enter the space between the lead-out electrode (3) and the contact electrode (5) through the lead-out hole of the lead-out electrode (3) and become seed electrons for DC discharge; A negative voltage is applied to the lead-out electrode (3), and the contact electrode (5) is grounded. As the negative voltage gradually increases, with the help of seed electrons, a DC glow discharge is formed between the lead-out electrode (3) and the contact electrode (5), completing the second step of DC discharge. Subsequently, the electrons generated by the DC discharge flow out from the lead-in hole under the action of the electric field, completing the emission of a large electron current.

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