Thermionic cathode based on microwave-enhanced control

Abstract

The application discloses a kind of hot emission cathode based on microwave enhancement control, belongs to space electric propulsion field and electric vacuum device field, the present application is to solve the problem of conventional hot emission cathode electron emission current regulation and control ability, the big interference of plasma environment.For solving the problem of conventional hot emission cathode electron emission current regulation and control ability, the big interference of plasma environment.The present application includes hot electron emission unit, microwave feed-in joint and resonant chamber, hot electron emission unit is coaxially arranged in resonant chamber;Microwave feed-in joint is inserted into resonant chamber from side vertical cavity and is connected with the waveguide of hot electron emission unit;Hot electron emission unit is used to emit hot electron under direct current electric field;Microwave feed-in joint is used to feed microwave into resonant chamber, and microwave is repeatedly reflected at open end and short end of resonant chamber, to form standing wave on the waveguide surface of electron emission unit, and to form strong standing wave electric field on the emitter of electron emission unit, to realize the regulation and control of increasing electron emission current.

Description

Technical Field

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

[0002] A thermionic cathode is an electron-emitting device based on the thermionic emission effect. The principle is that when a material is heated to a certain temperature, surface electrons gain enough energy to overcome the work function and escape from the material's surface. Low-work function materials such as tungsten, lanthanum hexaboride, and barium tungsten-barium oxide are commonly used as emitters.

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

[0004] There are two common methods for controlling the electron emission current from a thermal emission cathode: regulating the emitter heating power and regulating the extraction electrode voltage. Because the critical emission temperature of the emitter and the material's tolerance temperature are typically within a narrow range, regulating the emitter heating power carries a high risk, low precision, and slow response speed. Regulating the extraction electrode voltage is currently the most commonly used control method, but increasing the extraction electrode voltage typically results in significant interception of the electron current. Furthermore, in a plasma environment, this can increase interference with the plasma, raising the local plasma potential and causing unintended effects on the entire system. Summary of the Invention

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

[0006] The present invention discloses a thermal emission cathode based on microwave enhanced control, comprising a thermal electron emission unit, a microwave feed connector 2, and a resonant cavity 3. The thermal electron emission unit is coaxially arranged in the resonant cavity 3. The microwave feed 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 thermionic 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 resonant cavity 3. The microwaves are repeatedly reflected at the open-circuit end and the short-circuit end of the resonant cavity 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 control 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 further 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 touch each other to form an annular cavity as the 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;

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

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

[0013] Preferably, 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.

[0014] Preferably, the length of the resonant cavity 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 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 fixed and 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 barrier, 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 precision-related performance of the present invention, and its application range in the fields of high-precision space electric propulsion, high-precision electric vacuum devices, etc. is more extensive. 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 DC 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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making any creative efforts shall fall 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 with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0031] Specific implementation method 1: Figures 1 to 7 This embodiment describes a thermal emission cathode based on microwave enhanced control, comprising a thermal electron emission unit, a microwave feed connector 2, and a resonant cavity 3. The thermal electron emission unit is coaxially arranged in the resonant cavity 3. The microwave feed connector 2 is inserted into the resonant cavity 3 from the side perpendicular to the cavity and is conductively connected to the waveguide of the thermal electron emission unit.

[0032] The thermionic 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 resonant cavity 3. The microwaves are repeatedly reflected at the open-circuit end and the short-circuit end of the resonant cavity 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 control of increasing the electron emission current.

[0034] Combine Figures 1 to 4 To give a specific example, the thermal emission cathode includes a thermal electron emission unit, an extraction pole shell 1, a microwave feeding joint 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 coaxially matched and fixedly connected by 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 end of the two heating electrodes 5 by welding or clamping. The heating power supply is loaded on the tail end of the two heating electrodes 5.

[0035] The lead-out housing 1 is coaxially mounted on the outside of the central waveguide 8. The front halves of the two do not touch each other to form a ring cavity as the resonant cavity 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 resonant cavity 3. The head end of the resonant cavity 3 is closed and serves as an open-circuit end.

[0036] The lead-out electrode 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 for installing the microwave feed-in 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. It includes a microwave interface insulator 2-1, a microwave interface shielding electrode 2-2, and a microwave transmission signal electrode 2-3. The microwave transmission signal electrode 2-3, located in the center, extends into the resonant cavity 3 and contacts and conducts electricity 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 housing 1 is made of a high-conductivity metal material, such as aluminum or copper. The inner surface of the lead-out housing 1 is smooth. The lead-out housing 1 has a three-section structure: a small-diameter section 1-1 at the front end and a large-diameter section 1-2 at the rear end. A mounting base 1-3 is provided at the rear end, where the microwave feed connector 2 is mounted.

[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 electrical conductivity, such as molybdenum. The central waveguide 8 has a three-segment structure. The small-diameter segment forms a resonant cavity 3 with the lead-out housing 1, and the large-diameter segment engages with the large-diameter segment 1-2 at the tail end of the lead-out housing 1, forming an electrically conductive structure.

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

[0045] During operation, the thermal emission cathode in this embodiment is connected to the rest of the system via an insulating mounting plate 4. The microwave feed connector, consisting of a microwave interface insulator 2-2, a microwave interface shielding electrode 2-2, and a microwave transmission signal electrode 2-3, is a standard connector capable of connecting to a microwave coaxial transmission line or a standard microwave waveguide. Before connecting to the microwave source in the parallel system, a microwave DC blocker should be installed to prevent damage to the microwave source from the voltage at the lead electrode. The lead electrode housing 1 is connected to the positive electrode of the lead electrode power supply. One of the two heating electrodes 5 is connected to the positive electrode of the heating power supply, while the other end is connected to the negative electrode of the heating power supply. The lead electrode power supply and the heating power supply share a common negative pole.

[0046] In this embodiment, a thermal emission cathode based on microwave enhanced control needs to work under high vacuum conditions. During operation, the heating power is first turned on to preheat the emitter 7 to remove the 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, the heating power is gradually increased until the emitter 7 enters the electron emission mode. At the same time, the extraction power supply is turned on, and an extraction voltage of about 30-70V is applied to the extraction pole shell 1. At this time, a DC electric field is 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 feed 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, as shown in FIG. 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 area around the emitter 7, as shown Figure 7 As shown. At this point, the standing wave electric field intensifies the thermal emission process of emitter 7, increasing the electron emission current. When the microwave power is adjusted, the electron emission current of the thermal emission cathode of the present invention changes at a relatively fast response rate, with the magnitude of the increase in electron current positively correlated with the microwave power. The specific implementation is subject to actual operation.

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

Claims

1. A thermal emission cathode based on microwave enhanced control, characterized in that: The invention comprises a thermal electron emission unit, a microwave feed connector (2), an extraction pole shell (1) and a resonant cavity (3); the thermal electron emission unit comprises an emitter (7) and a central waveguide (8); the thermal electron emission unit is coaxially arranged in the resonant cavity (3); the microwave feed connector (2) is inserted into the resonant cavity (3) from the side perpendicular to the cavity and is conductively connected to the central waveguide of the thermal electron emission unit; The thermal electron emission unit is used to emit thermal electrons under a direct current electric field; the extraction pole shell (1) is coaxially installed outside the central waveguide (8); the extraction pole shell (1) and the central waveguide (8) do not contact each other at their front halves to form a ring cavity as a resonance chamber (3); the extraction pole shell (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); the head end of the resonance chamber (3) is closed and serves as an open-circuit end; The microwave feeding connector (2) is used to feed microwaves into the resonant cavity (3). The microwaves are repeatedly reflected at the open-circuit end and the short-circuit end of the resonant cavity (3), forming a standing wave on the surface of the central waveguide (8) 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. The thermal emission cathode based on microwave enhanced control according to claim 1, characterized in that: The thermal electron emission unit also includes a heating electrode (5) and an insulating ceramic tube (6). 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 on the head ends of the two heating electrodes (5) by welding or clamping. The heating power supply is loaded on the tail ends of the two heating electrodes (5).

3. The thermal emission cathode based on microwave enhanced control according to claim 2, characterized in that: 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 installed 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 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) in 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. The 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 lead-out pole housing (1) and the microwave feed connector (2) can be fixedly installed by means of bolts; the lead-out pole housing (1) and the tail end of the central waveguide (8) can be installed on the insulating mounting plate (4) by means of bolts.

Images