Thermal emission cathode based on microwave enhancement regulation

Abstract

The invention discloses a thermal emission cathode based on microwave enhanced regulation and control, belongs to the field of space electric propulsion and the field of electric vacuum devices, and aims to solve the problems that a conventional thermal emission cathode is poor in electron emission current regulation and control capability and large in interference to a plasma environment. The device comprises a thermionic emission unit, a microwave feed-in connector and a resonant cavity, wherein the thermionic emission unit is coaxially arranged in the resonant cavity; the microwave feed-in connector is inserted into the resonant cavity from the side face vertical cavity and is in conduction connection with the waveguide of the thermionic emission unit. The hot electron emission unit is used for emitting hot electrons in a direct-current electric field; the microwave feed-in connector is used for feeding microwaves into the resonant cavity chamber, the microwaves are repeatedly reflected at the open-circuit end and the short-circuit end of the resonant cavity chamber, standing waves are formed on the waveguide surface of the electron emission unit, a strong standing wave electric field is formed on an emitter of the electron emission unit, and then regulation and control of increasing electron emission current are achieved.

Description

Technical Field

[0001] The invention relates to a thermal emission cathode based on microwave enhanced control, belonging to the field of space electric propulsion and electric vacuum devices. Background Art

[0002] Thermionic cathode is an electron emission device based on thermionic emission effect. Its principle is that when the material is heated to a certain temperature, the surface electrons gain enough energy to overcome the work function and escape from the surface of the material. It often uses low work function materials such as tungsten, lanthanum hexaboride, barium tungsten-barium oxide as emitters.

[0003] In the field of space electric propulsion, thermal emission cathodes are often used as neutralizers and electron sources for high-precision, low-power electric propulsion systems to avoid vector eccentricity and working fluid consumption caused by traditional hollow cathodes (high-current cathodes that rely on the hollow cathode effect to generate plasma). In addition, thermal emission cathodes are also widely used in vacuum devices such as electron tubes, traveling wave tubes, and electron microscopes.

[0004] There are usually two ways to control the electron emission current of the thermal emission cathode, namely, regulating the emitter heating power and regulating the extraction electrode voltage. Since there is usually a narrow range between the critical emission temperature of the emitter and the tolerance temperature of the material, regulating the emitter heating power has higher risks, lower precision and lower response speed. Regulating the extraction electrode voltage is currently the most commonly used control method, but increasing the extraction electrode voltage usually leads to a large amount of interception of the electron current. At the same time, it will also increase the interference with the plasma in the plasma environment, raise the local plasma space potential, and cause unexpected effects on the entire system. Summary of the invention

[0005] In order to solve the problems that conventional thermal emission cathodes have poor electron emission current control capability and great interference to the plasma environment, the present invention provides a thermal emission cathode based on microwave enhanced control.

[0006] The thermal emission cathode based on microwave enhanced control described in the present invention comprises a thermal electron emission unit, a microwave feeding connector 2 and a resonant cavity 3, wherein the thermal electron emission unit is coaxially arranged in the resonant cavity 3; the microwave feeding connector 2 is inserted into the resonant cavity 3 from the side perpendicular to the cavity and is connected to the waveguide of the thermal electron emission unit;

[0007] The thermal electron emission unit is used to emit thermal electrons under a DC electric field;

[0008] The microwave feeding connector 2 is used to feed microwaves into the resonance chamber 3. The microwaves are repeatedly reflected at the open-circuit end and the short-circuit end of the resonance chamber 3, forming standing waves on the waveguide surface of the electron emission unit and forming a strong standing wave electric field on the emitter of the electron emission unit, thereby achieving the regulation of increasing the electron emission current.

[0009] Preferably, the thermal electron emission unit includes a heating electrode 5, an insulating ceramic tube 6, an emitter 7 and a central waveguide 8, the tail end of the central waveguide 8 is fixedly mounted on the insulating mounting plate 4; the central waveguide 8 is provided with an axial central through hole, the insulating ceramic tube 6 is coaxially mounted in the central through hole, the two heating electrodes 5 axially pass through the insulating ceramic tube 6 in parallel and are insulated from each other, the head and tail ends of the two heating electrodes 5 extend from the two ends of the central waveguide 8, the emitter 7 is mounted at the head ends of the two heating electrodes 5 by welding or clamping, and the heating power supply is loaded at the tail ends of the two heating electrodes 5.

[0010] Preferably, it also includes an output pole housing 1, which is coaxially installed outside the central waveguide 8, and the front halves of the two do not contact to form an annular cavity as a resonance chamber 3, and the output pole housing 1 contacts the tail end of the central waveguide 8 to form a short-circuit end at the tail end of the resonance chamber 3, and the head end of the resonance chamber 3 is closed and serves as an open end;

[0011] The side opening of the lead-out pole housing 1 is used to install the microwave feed-in connector 2;

[0012] The tail end of the lead-out pole housing 1 is mounted on an insulating mounting plate 4 .

[0013] Preferably, the microwave feeding connector 2 includes a microwave interface insulation 2-1, a microwave interface shielding electrode 2-2 and a microwave transmission signal electrode 2-3. The microwave transmission signal electrode 2-3 in the center extends into the resonance cavity 3 and contacts and conducts with the outer surface of the central waveguide 8.

[0014] Preferably, the length of the resonance chamber 3 is an odd number of times the 1 / 4 wavelength of the microwave.

[0015] Preferably, the lead-out pole housing 1 is made of aluminum or copper.

[0016] Preferably, the inner surface of the lead-out pole housing 1 is smoothed.

[0017] Preferably, the insulating ceramic tube 6 is made of alumina.

[0018] Preferably, the microwave feeding connector 2 is an SMA connector or an N-type connector.

[0019] Preferably, the structures can be fixedly installed by means of bolts or the like.

[0020] Beneficial effects of the present invention: The present invention uses a coaxial resonator structure and a strong standing wave electric field formed by microwaves to enhance the electron emission process of the thermal emission cathode, thereby increasing the probability of electrons breaking through the surface potential, thereby achieving the purpose of rapidly increasing the electron emission current. While increasing the electron emission current of the emitter, it achieves fast and effective emission current regulation without causing voltage rise. This greatly improves the adjustable and controllable capabilities of the thermal emission cathode and maintains its low interference with other equipment in the working environment. The above working characteristics greatly improve the cathode accuracy-related performance of the present invention, and have a wider range of applications in the fields of high-precision space electric propulsion, high-precision electric vacuum devices, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a front schematic diagram of the thermal emission cathode of the present invention.

[0022] Figure 2 It is a schematic diagram of the back side of the thermal emission cathode of the present invention.

[0023] Figure 3 It is a side schematic diagram of the thermal emission cathode of the present invention.

[0024] Figure 4 It is a schematic diagram of the cross-sectional structure of the thermal emission cathode of the present invention.

[0025] Figure 5 It is a schematic diagram of the overall working principle of the thermal emission cathode of the present invention.

[0026] Figure 6 It is a schematic diagram of the local electric field intensity formed by the direct current voltage of the thermal emission cathode of the present invention during operation.

[0027] Figure 7 It is a schematic diagram of the local electric field intensity formed by microwaves during operation of the thermal emission cathode of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0031] Specific implementation method 1: The following is combined Figures 1 to 7 This embodiment is described. A thermal emission cathode based on microwave enhanced control described in this embodiment includes a thermal electron emission unit, a microwave feeding connector 2 and a resonant cavity 3. The thermal electron emission unit is coaxially arranged in the resonant cavity 3; the microwave feeding connector 2 is inserted into the resonant cavity 3 from the side perpendicular to the cavity and is connected to the waveguide of the thermal electron emission unit;

[0032] The thermal electron emission unit is used to emit thermal electrons under a DC electric field;

[0033] The microwave feeding connector 2 is used to feed microwaves into the resonance chamber 3. The microwaves are repeatedly reflected at the open-circuit end and the short-circuit end of the resonance chamber 3, forming standing waves on the waveguide surface of the electron emission unit and forming a strong standing wave electric field on the emitter of the electron emission unit, thereby achieving the regulation of increasing the electron emission current.

[0034] Combination Figures 1 to 4 A specific example is given. The thermal emission cathode includes a thermal electron emission unit, an extraction pole shell 1, a microwave feed connector 2 and a resonant cavity 3. The thermal electron emission unit includes a heating electrode 5, an insulating ceramic tube 6, an emitter 7 and a central waveguide 8. The tail end of the central waveguide 8 is fixedly mounted on the insulating mounting plate 4; the central waveguide 8 is provided with an axial central through hole, and the insulating ceramic tube 6 is coaxially mounted in the central through hole. The insulating ceramic tube 6 and the central waveguide 8 are matched in a coaxial manner and fixedly connected by a tight fit or brazing; two heating electrodes 5 axially pass through the insulating ceramic tube 6 in parallel and are insulated from each other. The two heating electrodes 5 are connected to the insulating ceramic tube 6 by brazing. The head and tail ends of the two heating electrodes 5 extend from the two ends of the central waveguide 8. The emitter 7 is mounted at the head ends of the two heating electrodes 5 by welding or clamping, and the heating power is loaded on the tail ends of the two heating electrodes 5.

[0035] The lead-out housing 1 is coaxially mounted outside the central waveguide 8, and the front halves of the two do not contact each other to form an annular cavity as a resonance chamber 3. The lead-out housing 1 contacts the tail end of the central waveguide 8 to form a short-circuit end at the tail end of the resonance chamber 3, and the head end of the resonance chamber 3 is closed and serves as an open-circuit end.

[0036] The lead-out pole housing 1 and the heating electrode 5 and the emitter 7 should be insulated from each other; except for the head ends of the two heating electrodes 5 being connected to each other through the emitter 7, the other parts should be insulated from each other.

[0037] The side opening of the lead-out pole housing 1 is used to install the microwave feeding connector 2, which is fixed by bolts or threads.

[0038] The tail ends of the lead-out pole housing 1 and the central waveguide 8 are mounted on the insulating mounting plate 4 by bolts or other means.

[0039] The microwave feed connector 2 uses a standard connector such as an SMA connector or an N-type connector. The microwave feed connector 2 includes a microwave interface insulation 2-1, a microwave interface shielding electrode 2-2, and a microwave transmission signal electrode 2-3. The microwave transmission signal electrode 2-3 in the center extends into the resonant cavity 3 and contacts and conducts with the outer surface of the central waveguide 8.

[0040] The length of the resonant cavity 3 is an odd multiple of 1 / 4 wavelength of the microwave. For example, under 2.45 GHz microwave, the cavity length can be selected to be 3.06 mm.

[0041] The lead-out pole housing 1 is made of a metal material with high electrical conductivity, such as aluminum, copper, etc. The inner surface of the lead-out pole housing 1 is smoothed. The lead-out pole housing 1 is a three-section structure, with a small-diameter section 1-1 at the head end and a large-diameter section 1-2 at the tail end, and a mounting base 1-3 is provided at the tail end, wherein the microwave feeding connector 2 is mounted on the large-diameter section 1-2 at the tail end.

[0042] The insulating ceramic tube 6 is made of alumina.

[0043] The central waveguide 8 is made of a metal material with strong temperature resistance and high conductivity, such as molybdenum. The central waveguide 8 is a three-section structure, the small-diameter section is used to form a resonant cavity 3 with the lead-out pole housing 1, and the large-diameter section is used to be engaged with the large-diameter section 1-2 at the tail end of the lead-out pole housing 1, and the two are in contact to form an electrically conductive structure.

[0044] The structures can be fixed and installed by means of bolts or the like.

[0045] The thermal emission cathode in this embodiment is connected to other facilities of the system through the insulating mounting plate 4 during operation. The microwave feed connector composed of the microwave interface insulation 2-2, the microwave interface shielding electrode 2-2, and the microwave transmission signal electrode 2-3 is a standard connector, which can be connected to a microwave coaxial transmission line or a microwave standard waveguide. Before connecting to the microwave source in the parallel system, a microwave isolator should be installed to avoid damage to the microwave source by the lead-out electrode voltage. The lead-out electrode housing 1 is connected to the positive electrode of the lead-out electrode power supply, one of the two heating electrodes 5 is connected to the positive electrode of the heating power supply, and the other end is connected to the negative electrode of the heating power supply, wherein the lead-out electrode power supply and the heating power supply share a negative electrode.

[0046] In this embodiment, a thermal emission cathode based on microwave enhanced control needs to work under high vacuum conditions. During operation, first turn on the heating power supply to preheat the emitter 7 to remove residual gas on the surface of the emitter 7. The preheating power should be less than one-third of the heating power of the emitter 7 in the electron emission mode. After the preheating is completed, gradually increase the heating power until the emitter 7 enters the electron emission mode. At the same time, turn on the extraction pole power supply, and apply an extraction voltage of about 30-70V to the extraction pole shell 1. At this time, a DC electric field will be generated between the emitter 7 and the extraction pole shell 1, such as Figure 6As shown, the lead-out electrode receives a portion of the electron emission current of the emitter 7. When the electron emission current needs to be regulated, the microwave power supply is turned on and the microwave power is fed into the resonant cavity 3 through the microwave feeding connector 2. Since microwaves are reflected at both the short-circuited end and the open-circuited end, microwaves form standing waves on the surface of the central conductor 8, such as Figure 5 As shown. Since the cavity length is 1 / 4 wavelength, the maximum value of the standing wave electric field intensity is at the front end of the central conductor 8, that is, the surrounding area of ​​the emitter 7, as shown Figure 7 As shown. At this time, the standing wave electric field will strengthen the thermal emission process of the emitter 7 and increase the electron emission current. When the microwave power fed in is adjusted, the electron emission current of the thermal emission cathode of the present invention will change at a faster response speed, and the increase in the electron current is positively correlated with the magnitude of the microwave power fed in. The specific implementation method shall be subject to the actual operation.

[0047] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A thermal emission cathode based on microwave enhanced control, characterized in that: It comprises a thermal electron emission unit, a microwave feeding connector (2) and a resonant chamber (3), wherein the thermal electron emission unit is coaxially arranged in the resonant chamber (3); the microwave feeding connector (2) is inserted into the resonant chamber (3) from the side perpendicular to the cavity and is connected to the waveguide of the thermal electron emission unit; The thermal electron emission unit is used to emit thermal electrons under a DC electric field; The microwave feeding connector (2) is used to feed microwaves into the resonance chamber (3); the microwaves are repeatedly reflected at the open circuit end and the short circuit end of the resonance chamber (3), forming standing waves on the waveguide surface of the electron emission unit and forming a strong standing wave electric field on the emitter of the electron emission unit, thereby achieving regulation to increase the electron emission current.

2. According to claim 1, a thermal emission cathode based on microwave enhanced control is characterized in that: The thermal electron emission unit comprises a heating electrode (5), an insulating ceramic tube (6), an emitter (7) and a central waveguide (8), wherein the tail end of the central waveguide (8) is fixedly mounted on an insulating mounting plate (4); the central waveguide (8) is provided with an axial central through hole, the insulating ceramic tube (6) is coaxially mounted in the central through hole, two heating electrodes (5) axially pass through the insulating ceramic tube (6) in parallel and are insulated from each other, the head and tail ends of the two heating electrodes (5) extend from the two ends of the central waveguide (8), the emitter (7) is mounted on the head ends of the two heating electrodes (5) by welding or clamping, and a heating power source is loaded on the tail ends of the two heating electrodes (5).

3. According to claim 2, a thermal emission cathode based on microwave enhanced control, characterized in that: It also includes an output pole housing (1), which is coaxially mounted on the outside of the central waveguide (8), and the front halves of the two do not contact each other to form an annular cavity as a resonance chamber (3), and the output pole housing (1) contacts the tail end of the central waveguide (8) to form a short-circuit end at the tail end of the resonance chamber (3), and the head end of the resonance chamber (3) is closed and serves as an open-circuit end; The side opening of the lead-out pole housing (1) is used for installing a microwave feed-in connector (2); The tail end of the lead-out pole housing (1) is mounted on an insulating mounting plate (4).

4. The thermal emission cathode based on microwave enhanced control according to claim 3, characterized in that: The microwave feed-in connector (2) comprises a microwave interface insulation (2-1), a microwave interface shielding electrode (2-2) and a microwave transmission signal electrode (2-3). The microwave transmission signal electrode (2-3) at the center extends into the resonant cavity (3) and contacts and conducts with the outer surface of the central waveguide (8).

5. The thermal emission cathode based on microwave enhanced control according to claim 1, characterized in that: The length of the resonant cavity (3) is an odd number of times the 1 / 4 wavelength of the microwave.

6. The thermal emission cathode based on microwave enhanced control according to claim 3, characterized in that: The lead-out pole housing (1) is made of aluminum or copper.

7. The thermal emission cathode based on microwave enhanced control according to claim 3, characterized in that: The inner surface of the lead-out pole housing (1) is smoothed.

8. The thermal emission cathode based on microwave enhanced control according to claim 2, characterized in that: The insulating ceramic tube (6) is made of alumina.

9. A thermal emission cathode based on microwave enhanced control according to claim 1 or 4, characterized in that: The microwave feed connector (2) is an SMA connector or an N-type connector.

10. The thermal emission cathode based on microwave enhanced control according to claim 3, characterized in that: The structures can be fixed and installed by means of bolts or the like.

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