Barium tungsten lanthanum hexaboride composite hollow cathode

Abstract

The application discloses a barium tungsten lanthanum hexaboride composite hollow cathode, which comprises a cathode tube, a gas inlet is arranged at a first end of the cathode tube, a cathode top is arranged at a second end of the cathode tube, and a cathode top through hole is arranged in the cathode top; a touch electrode is arranged outside the cathode tube, an end of the touch electrode is provided with a touch electrode top, a touch electrode through hole is arranged in the touch electrode top, and the touch electrode is coaxial with the cathode tube; an emitter comprises a first emitter and a second emitter, the first emitter and the second emitter are sequentially arranged on an inner wall of the second end of the cathode tube in a direction from the gas inlet to the cathode top; a heater is arranged around an outer wall of the cathode tube; wherein the first emitter is a barium tungsten emitter, the second emitter is a lanthanum hexaboride emitter, and the lanthanum hexaboride emitter is heated by heat generated by self-sustaining work of the barium tungsten emitter, so that the starting power consumption is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of space electric propulsion technology, and relates to a hollow cathode for electric thrusters, specifically a barium-tungsten-lanthanum hexaboride composite hollow cathode. Background Technology

[0002] Electric thrusters, with their advantages of high specific impulse and long lifespan, will be mainly used for tasks such as position maintenance, attitude adjustment, and orbit transfer on high-orbit satellite platforms. Ion thrusters and Hall thrusters are two commonly used electric propulsion devices. Hollow cathodes primarily provide high-energy electrons for propellant ionization and neutralize the ion plume, making them a core component of both ion and Hall propulsion systems. Hollow electrodes are the components in the thruster with the highest plasma density, current density, and temperature; their performance, reliability, and lifespan are all important indicators limiting thruster performance.

[0003] However, the traditional hollow cathode has high heating power consumption, high activation temperature, long start-up time, and short lifespan to reach the temperature required by the transmitter, which seriously affects the application of electric thrusters. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of traditional hollow cathodes, such as high heating power consumption, high activation temperature, long start-up time, and short lifespan, and to provide a hollow cathode with low power consumption, which can make full use of the heat it generates and start up quickly.

[0005] To achieve the above objectives, the present invention provides a barium-tungsten-lanthanum hexaboride composite hollow cathode, comprising: a cathode tube, the first end of which is an air inlet, and the second end of which is provided with a cathode top, wherein the cathode top is provided with a cathode top through hole;

[0006] A contact electrode is sleeved outside the cathode tube. The end of the contact electrode is provided with a contact electrode top, which is close to the cathode top. A contact electrode through hole is opened on the contact electrode top. The contact electrode is coaxial with the cathode tube.

[0007] The emitter includes a first emitter and a second emitter, which are sequentially disposed on the inner wall of the second end of the cathode tube along the direction from the air inlet to the top of the cathode, for the purpose of exciting electrons;

[0008] A heater is provided around the outer wall of the cathode tube. After generating heat, the heat is conducted to the inner wall of the cathode tube to heat the emitter.

[0009] The first emitter is a barium tungsten emitter, and the second emitter is a lanthanum hexaboride emitter.

[0010] Preferably, a ceramic layer is provided between the cathode tube and the contact electrode to insulate the cathode tube and the contact electrode.

[0011] Preferably, the ceramic layer is brazed with the cathode tube using ceramic-metal brazing, and the ceramic layer is brazed with the contact electrode using ceramic-metal brazing.

[0012] Preferably, a heat-conducting layer is provided between the outer wall of the cathode tube and the heater.

[0013] Preferably, the heater is surrounded by a heat shield layer to prevent heat loss from the emitter.

[0014] Preferably, the coaxiality between the cathode tube and the contact electrode is ≤0.02μm.

[0015] Preferably, the cathode top and the contact electrode top are coaxial, with a coaxiality of ≤0.02μm.

[0016] Preferably, the size of the cathode top through hole is 0.4 to 1.2 mm, and the size of the contact electrode top through hole is 0.5 to 2.5 mm.

[0017] Preferably, the cathode tube is made of molybdenum, and the contact electrode is made of pure tungsten.

[0018] Preferably, the emitter, cathode tube, contact electrode, and heat shield layer are all cylindrical structures.

[0019] The beneficial effects of this invention are:

[0020] (1) The emission temperature of the barium tungsten emitter is 800℃ and the emission temperature of the lanthanum hexaboride emitter is 1500℃. In this application, both barium tungsten emitters and lanthanum hexaboride emitters are provided in the cathode tube. Since the emission temperature of the barium tungsten emitter is relatively low, after the heater is turned on, the heat is transferred to the cathode tube and can first reach the emission temperature of the barium tungsten emitter. The heat generated by the self-sustaining operation of the barium tungsten emitter can be used to heat the lanthanum hexaboride emitter, thereby reducing the heating power required for the self-sustaining operation of the lanthanum hexaboride emitter. This reduces the heating power and heating time of the barium tungsten and lanthanum hexaboride composite hollow cathode, and improves the emission current and service life of the barium tungsten and lanthanum hexaboride composite hollow cathode.

[0021] (2) The composite hollow cathode of barium tungsten and lanthanum hexaboride can reduce the start-up power consumption and start-up time of the electric propulsion system and improve the life of the electric propulsion system. It can be used on a large scale in subsequent electric propulsion products. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the barium-tungsten-lanthanum hexaboride composite hollow cathode structure of the present invention.

[0023] Among them, 1-ceramic layer, 2-contact electrode, 21-contact electrode top, 211-contact electrode top through hole, 3-cathode tube, 31-cathode top, 32-air inlet, 311-cathode top through hole, 4-thermal shielding layer, 5-heating wire, 6-thermal conductive layer, 8-lanthanum hexaboride emitter, 9-barium tungsten emitter. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] like Figure 1 As shown, this invention provides a barium-tungsten lanthanum hexaboride composite hollow cathode, comprising a cathode tube 3, the first end of which is an inlet 32 ​​for the entry of working gas, and the second end of which is provided with a cathode top 31, the center of which has a cathode top through hole 311; a contact electrode 2, which is sleeved on the outside of the cathode tube 3, the end of which is provided with a contact electrode top 21, and the contact electrode 2 is coaxial with the cathode tube 3; an emitter, comprising a first emitter and a second emitter, which are sequentially disposed on the inner wall of the other end of the cathode tube 3 for exciting electrons; a heater, which surrounds the outer wall of the cathode tube 3 for heating the emitter, the heater being a heating wire 5; and a heat shield layer 4, which surrounds the heater for preventing heat loss from the emitter; wherein the first emitter is a barium-tungsten emitter 9, and the second emitter is a lanthanum hexaboride emitter 8. The lanthanum hexaboride emitter 8, barium tungsten emitter 9, cathode tube 3, contact electrode 2, and heat shielding layer 4 are all cylindrical structures.

[0026] In some embodiments, to provide voltage, a contact electrode 2 is sleeved outside the cathode tube 3. The contact electrode 2 includes a contact electrode shell, and a contact electrode top 21 is provided at the bottom of the contact electrode. The material of the contact electrode top 21 is high-density pure tungsten, and the material of the cathode tube 3 is molybdenum. Applying a high voltage of 250V to the contact electrode 2 can provide the starting voltage for the barium tungsten hexaboride lanthanum composite hollow cathode and maintain the stable operation of the hollow cathode. The contact electrode 2 is coaxial with the cathode tube 3, and the contact electrode top 21 is coaxial with the cathode top 31. The coaxiality between the cathode tube 3 and the contact electrode 2 is ≤0.02μm, and the coaxiality between the cathode top 31 and the contact electrode top 21 is ≤0.02μm. A contact electrode top through hole 211 is also provided in the middle of the contact electrode top 21. The contact electrode top through hole 211 has a pointed shape. The pointed design facilitates discharge and reduces the difficulty of ignition. The cathode top 31 has a throttling effect, which makes the pressure inside the cathode tube 3 reach thousands of kilometres, ensuring sufficient neutral particle density and improving ionization efficiency. The cathode top 31 is provided with a cathode top through hole 311 in the middle for the escape of working gas.

[0027] In some embodiments, in order to reduce heating power consumption and heating time, a first emitter and a second emitter are arranged side by side on the inner wall of the end of the cathode tube 3 away from the air inlet 32. A first limiting groove and a second limiting groove are provided on the inner wall of the cathode tube 3 to lock the first emitter and the second emitter to ensure that they do not shift. The first emitter is a barium-tungsten emitter 9, and the second emitter is a lanthanum hexaboride emitter 8, both with hollow structures. The emission temperature of the barium-tungsten emitter 9 is 800℃, and the emission temperature of the lanthanum hexaboride emitter 8 is 1500℃. The barium-tungsten emitter 9 and the lanthanum hexaboride emitter 8 are combined to form a barium-tungsten-lanthanum hexaboride composite hollow cathode. This allows the barium-tungsten-lanthanum hexaboride composite hollow cathode to ignite and start up by heating only to 800℃. After starting operation, through the self-sustaining operation of the barium-tungsten emitter 9 and the bombardment of plasma, the lanthanum hexaboride emitter 8 reaches its emission temperature of 1500℃, increasing the maximum emission current of the barium-tungsten-lanthanum hexaboride composite hollow cathode and meeting the needs of electric thrusters with different power consumptions. The lanthanum hexaboride emitter 8 and the barium-tungsten emitter 9 are the core components; after reaching their respective emission temperatures, they emit primordial electrons, ionizing neutral gas. Therefore, the barium-tungsten lanthanum hexaboride composite hollow cathode can heat the lanthanum hexaboride emitter through the self-sustaining working heat of the barium-tungsten emitter 9, reducing the heating power required for the lanthanum hexaboride emitter to sustain its operation, thereby further reducing the heating power and heating time of the barium-tungsten lanthanum hexaboride composite hollow cathode, and improving the emission current and service life of the barium-tungsten lanthanum hexaboride composite hollow cathode.

[0028] In some embodiments, in order to heat the emitter, a heating wire 5 is provided around the outer wall of the cavity to heat the first emitter, lanthanum hexaboride emitter 8, and the second emitter, barium tungsten emitter 9. The heating wire 5 is made of high-temperature resistant materials such as tungsten wire or tungsten rhenium wire, so that the lanthanum hexaboride emitter 8 and the barium tungsten emitter 9 can reach the lowest emission temperature.

[0029] In some embodiments, to prevent short circuits in the heating wire 5, a heat-conducting layer 6 is provided between the outer wall of the cathode tube 3 and the heating wire 5. The heat-conducting layer 6 can effectively prevent short circuits caused by direct contact between the heating wire 5 and the cathode tube 3, and can extend the lifespan of the heating wire 5. When the heating wire 5 is turned on, heat is generated. The heat is transferred through the heat-conducting layer 6 and the cathode tube 3 to the inner wall of the cathode tube 3, thereby heating the lanthanum hexaboride emitter 8 and the second emitter, the barium tungsten emitter 9. To block the heat radiation of the heating wire 5, ensure the heating temperature of the lanthanum hexaboride emitter 8 and the barium tungsten emitter 9, and improve heating efficiency, a heat shielding layer 4 is provided around the heating wire 5 to prevent heat loss from the lanthanum hexaboride emitter 8 and the barium tungsten emitter 9.

[0030] In some embodiments, to ensure sealing, a ceramic layer 1 is provided between the cathode tube 3 and the contact electrode 2 to insulate them. The ceramic layer 1 is bonded to the cathode tube 3 using ceramic-metal brazing, which ensures the sealing of the weld between the ceramic layer 1 and the cathode tube 3 and prevents weld failure at a high temperature of 1000°C. Similarly, the ceramic layer 1 is bonded to the outer shell of the contact electrode 2 using ceramic-metal brazing, which also ensures the sealing of the weld between the ceramic layer 1 and the contact electrode 2 and prevents weld failure at a high temperature of 1000°C.

[0031] Working principle:

[0032] The heating power supply is turned on, providing heating current to the heating wire to heat the barium tungsten emitter and the lanthanum hexaboride emitter. Xenon gas enters through the inlet of the cathode tube and flows through the cathode tube at the rated flow rate. A high voltage of 250V is applied to the outer shell of the contact electrode, which breaks down the xenon gas. After the barium tungsten emitter reaches its emission temperature, it emits primordial electrons. These primordial electrons collide with and ionize the neutral gas to generate plasma. When the electron concentration reaches a certain level, the electrons in the cathode tube achieve an avalanche effect. A large number of electrons are accelerated and extracted under the electric field generated by the high voltage of the contact electrode. The barium tungsten lanthanum hexaboride composite hollow cathode is successfully ignited. At this time, the heating power supply of the heating wire is turned off. Under the self-sustaining operation of the barium tungsten emitter and the effect of ion bombardment of the lanthanum hexaboride emitter surface in the cathode tube, the emission temperature of the lanthanum hexaboride emitter is gradually reached. A large number of primordial electrons escape from the surface of the lanthanum hexaboride emitter, increasing the emission current of the barium tungsten lanthanum hexaboride composite hollow cathode.

[0033] In summary, this invention simultaneously incorporates a barium-tungsten emitter and a lanthanum hexaboride emitter within the cathode tube. The self-sustaining operation of the barium-tungsten emitter heats the lanthanum hexaboride emitter, achieving its emission temperature and reducing the heating power required for its self-sustaining operation. This, in turn, reduces the heating power and heating time of the barium-tungsten-lanthanum hexaboride composite hollow cathode, thereby reducing the start-up power and start-up time of the electric propulsion system and improving its lifespan. Furthermore, the composite hollow cathode has a simple structure, reducing cost and overall weight, making it convenient for practical use.

[0034] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A barium-tungsten-lanthanum hexaboride composite hollow cathode, characterized in that, The barium-tungsten-lanthanum hexaboride composite hollow cathode comprises: A cathode tube, wherein the first end of the cathode tube is an air inlet, the second end of the cathode tube is provided with a cathode top, and the cathode top is provided with a cathode top through hole; A contact electrode is sleeved outside the cathode tube. The end of the contact electrode is provided with a contact electrode top, which is close to the cathode top. The contact electrode top has a contact electrode top through hole, and the contact electrode is coaxial with the cathode tube. The emitter includes a first emitter and a second emitter, which are sequentially disposed on the inner wall of the second end of the cathode tube along the direction from the air inlet to the top of the cathode, for exciting electrons; A heater is provided around the outer wall of the cathode tube. After generating heat, the heat is conducted to the inner wall of the cathode tube to heat the emitter. The first emitter is a barium tungsten emitter, and the second emitter is a lanthanum hexaboride emitter.

2. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, A ceramic layer is provided between the cathode tube and the contact electrode to insulate the cathode tube and the contact electrode.

3. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 2, characterized in that, The ceramic layer is brazed with the cathode tube using ceramic-metal brazing, and the ceramic layer is brazed with the contact electrode using ceramic-metal brazing.

4. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, A heat-conducting layer is provided between the outer wall of the cathode tube and the heater.

5. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, The heater is surrounded by a heat shield layer to prevent the emitter from losing heat.

6. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, The coaxiality of the cathode tube and the contact electrode is ≤0.02μm.

7. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, The cathode top and the contact electrode top are coaxial, with a coaxiality of ≤0.02μm.

8. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, The size of the cathode top through hole is 0.4~1.2mm, and the size of the contact electrode top through hole is 0.5~2.5mm.

9. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, The cathode tube is made of molybdenum, and the contact electrode is made of pure tungsten.

10. The barium-tungsten-lanthanum hexaboride composite hollow cathode as described in claim 1, characterized in that, The emitter, cathode tube, contact electrode, and heat shield layer are all cylindrical structures.

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