Working medium-free cathode neutralization circuit for microwave ion thruster

Abstract

The invention belongs to the field of space electric propulsion, and particularly relates to a working medium-free cathode neutralization circuit for a microwave ion thruster. The circuit comprises an ion thruster, a bias power supply and a cathode power supply circuit, the ion thruster is used for coupling discharge to generate ion plume, and the cathode power supply circuit is used for releasing electrons to neutralize the ion plume generated by the ion thruster; the bias power supply is used for adjusting the potential difference between the cathode and the ion thruster; the positive electrode of the bias power supply is connected with the ion thruster, and the negative electrode of the bias power supply is connected with the cathode power supply circuit, so that high-precision neutralization of ion plume of the thruster is realized, the problem of thrust eccentricity of a reasoning system caused by insufficient neutralization precision of the ion plume of the thruster is solved, and meanwhile, the service life of the cathode is prolonged.

Description

Technical Field

[0001] The present application belongs to the field of space electric propulsion, and specifically relates to a fluid-free cathode neutralization circuit for a microwave ion thruster. Background Art

[0002] In the space gravitational wave detection mission, if the propulsion system uses a traditional hollow cathode, there will be a problem of thrust eccentricity, that is, even if the hollow cathode is miniaturized, the plasma ejected from its working fluid plume will cause the thruster plume to change in the direction of the cathode side, thereby causing a change in the thrust direction. Therefore, a cathode that does not use working fluid gas must be used, relying on the surface electric field and the thermal electron emission of the material to directly release electrons to the thruster ion plume for neutralization. In a miniaturized propulsion system, a working fluid-free thermal emission cathode needs to meet the needs of thruster ion plume neutralization, and in the project indicators, a neutralization effect that meets high precision needs to be achieved. Summary of the invention

[0003] In order to solve the problem of thrust eccentricity of the inference system caused by insufficient neutralization accuracy of the thruster ion plume in the prior art, a propellant-free cathode neutralization circuit for microwave ion thrusters is proposed.

[0004] A propellant-free cathode neutralization circuit for a microwave ion thruster, comprising an ion thruster, a bias power supply and a cathode power supply circuit;

[0005] The ion thruster is used for coupled discharge to generate ion plume, and the cathode power supply circuit is used for releasing electrons to neutralize the ion plume generated by the ion thruster; the bias power supply is used for adjusting the potential difference between the cathode and the ion thruster; the positive pole of the bias power supply is connected to the ion thruster, and the negative pole of the bias power supply is connected to the cathode power supply circuit.

[0006] Preferably, the cathode power supply circuit comprises a contact holding electrode power supply, a first resistor, a second resistor, a cathode and a heating power supply;

[0007] The holding electrode power supply is used to apply high voltage to the cathode holding electrode, the heating power supply is used to heat the cathode, and the cathode is used to emit an electron beam under the high voltage and heating applied by the holding electrode;

[0008] The heating power supply is connected in parallel with the cathode; the positive pole of the touch-holding electrode power supply is connected to one end of the first resistor, the other end of the first resistor is connected to the cathode touch-holding electrode, and the negative pole of the touch-holding electrode power supply is connected to the negative pole of the heating power supply; the cathode touch-holding electrode is also connected to one end of the second resistor, and the other end of the second resistor is connected to the negative pole of the bias power supply.

[0009] Preferably, the cathode includes a hot wire, filling ceramic and a cathode tube shell; the filling ceramic is filled inside the cathode tube shell, and the hot wire is arranged inside the filling ceramic; one end of the hot wire is connected to the negative pole of the heating power supply, and the other end of the hot wire is welded to the cathode tube shell, and the other end of the hot wire is also connected to the positive pole of the heating power supply.

[0010] Preferably, the ion thruster comprises a thruster ionization chamber, a gas input unit, a microwave source input unit, a screen grid power supply, a third resistor, an acceleration grid power supply and a fourth resistor;

[0011] The gas input unit is used to input the set gas into the thruster ionization chamber; the microwave source input unit is used to generate a microwave signal and input the microwave signal into the thruster ionization chamber; the microwave signal is used to ionize the input set gas in the thruster ionization chamber to generate set gas ions;

[0012] The ion thruster screen grid is connected to one end of the third resistor, the other end of the third resistor is connected to the positive electrode of the screen grid power supply, and the negative electrode of the screen grid power supply is connected to the positive electrode of the bias power supply; the ion thruster acceleration grid is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to the negative electrode of the acceleration grid power supply, and the acceleration grid power supply is connected to the positive electrode of the bias power supply;

[0013] The screen grid power supply is used to apply voltage to the ion thruster screen grid, and the acceleration grid is used to apply voltage to the ion thruster acceleration grid. The thruster ionization chamber is provided with a small hole. The voltage difference between the ion thruster screen grid and the ion thruster acceleration grid accelerates the set gas ions passing through the small hole to generate an ion plume.

[0014] Beneficial Effects

[0015] The present application discloses a propellant-free cathode neutralization circuit for a microwave ion thruster, which connects the ion thruster and the cathode neutralization circuit through a bias power supply to achieve high-precision neutralization of the thruster ion plume. The advantages include the following:

[0016] (1) Improve the neutralization accuracy of the thruster ion plume; the bias power supply is connected to the cathode contact electrode to ensure the stability of the cathode contact electrode shell with respect to the plume potential;

[0017] (2) Extending the life of the cathode; setting one end of the hot wire of the integrated emitter component to negative and one end of the shell to positive, and using the "thermophoresis" effect to suppress the ceramic insulation failure caused by evaporation of the hot wire during use, thereby extending the life of the cathode. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of a fluid-free cathode neutralization circuit for a microwave ion thruster according to a specific embodiment of the present application;

[0019] Figure 2 A cathode structure diagram of a specific implementation method of the present application;

[0020] In the figure, 1 is a hot wire, 2 is a cathode tube shell, 3 is a filling ceramic, 4 is a cathode, 5 is a heating power supply, 6 is a first resistor, 7 is a contact holding electrode power supply, 8 is a second resistor, 9 is a bias power supply, 10 is a screen grid power supply, 11 is a third resistor, 12 is a fourth resistor, 13 is an accelerating grid power supply, 14 is a thruster ionization chamber, 15 is a setting gas bottle, 16 is a pressure reducing valve, 17 is a flow meter, 18 is a gas path insulator, 19 is a microwave source, and 20 is a DC isolator. DETAILED DESCRIPTION

[0021] Specific implementation method 1: The following will be combined with the attached embodiment of the present invention Figure 1 To Attachment Figure 2 , illustrate this implementation mode, and clearly and completely describe the technical solutions in the embodiments of the present invention:

[0022] A propellant-free cathode neutralization circuit for a microwave ion thruster, comprising an ion thruster, a bias power supply and a cathode power supply circuit;

[0023] The ion thruster is used for coupled discharge to generate ion plume, and the cathode power supply circuit is used for releasing electrons to neutralize the ion plume generated by the ion thruster; the bias power supply is used for adjusting the potential difference between the cathode and the ion thruster; the positive pole of the bias power supply is connected to the ion thruster, and the negative pole of the bias power supply is connected to the cathode power supply circuit.

[0024] Specifically, as attached Figure 2 As shown in the figure, for the cathode, the key component for emitting electrons is the emitter. The emitter is a material with a low surface electron work function (work function), which can make electrons more easily leave the material surface. However, the emitter material will have the corresponding electron emission ability only after reaching a certain working temperature. By using the Schottky effect, an electric field can be applied to the surface of the emitter to increase the electron emission ability. This is different from the traditional hollow cathode emitter, in which the touch-holding electrode only serves as an ignition starter during operation. The touch-holding electrode of the working fluid-free cathode needs to apply voltage all the time during operation, so a power supply with adjustable voltage is required to work continuously. As the main component exposed to the external plasma, the potential of the touch-holding electrode relative to the plasma plume area will significantly affect the neutralization effect of the charge because the plasma is highly sensitive to the electric field and magnetic field. Therefore, for the neutralization circuit, the relative potential adjustment power supply between the cathode and the thruster is connected to the touch-holding electrode (gate), so that the cathode has less influence on the external electric field during the process of adjusting the potential of the internal touch-holding electrode grid and the emitter by the cathode.

[0025] In traditional electric propulsion systems, when the thruster and cathode work in combination, the adjustment and active control of the relative potential between the cathode and the thruster are optional, that is, it is not necessary to actively apply the potential control of the cathode relative to the thruster. However, for the entire electric propulsion system for gravitational wave detection, when using ion thrusters for coupled discharge, in order to achieve the high-precision neutralization, low thrust noise, and precise regulation requirements of multiple control means in the project indicators, active control is applied to the bias power supply of the cathode relative to the thruster. This means that when you want to adjust the potential of the cathode relative to the thruster, you need to connect one end of a bias power supply to the thruster and the other end to the cathode. When the voltage at both ends of the power supply is adjusted, the part where the cathode is connected to the bias power supply will be stable and controllable with respect to the potential of the thruster, which is very beneficial to the electron emission of the cathode and the external plasma The environment can add a means to continue to control, which is beneficial for high-precision neutralization and reducing thrust noise. The role of the bias power supply is to adjust the potential difference between the cathode and the plume. This is because when the impedance of the cathode increases, the cathode becomes insensitive to the potential change of the plume relative to the ground, and it is easy to under-neutralize. It can be understood that the impedance between the cathode and the plume is similar to the role of a resistor in a circuit. When the impedance becomes higher, the resistance value becomes larger. Even if the voltage at the plume end has the same fluctuation, the increase or decrease in the lead-out current between the cathode and the plume through this resistor will not be as sensitive as when the impedance is small, and it will also cause the lead-out current value to be very small. This is the so-called insufficient neutralization. Therefore, an external power supply is required to apply an additional voltage to adjust the voltage difference between the cathode and the plume to be sufficient so that the neutralization current is sufficient.

[0026] In order to solve the problem that when the cathode is working without a working fluid, the touch-holding electrode needs to apply a potential all the time, causing the outer shell of the touch-holding electrode exposed to the plasma environment to become an electrode plate, the bias power supply of the cathode is connected to the end of the touch-holding electrode, so that the touch-holding electrode and the end of the bias power supply connected to the cathode have the same potential, ensuring the stability of the outer shell of the cathode touch-holding electrode with respect to the plume potential.

[0027] Further, the cathode power supply circuit includes a contact holding electrode power supply 7, a first resistor 6, a second resistor 8, a cathode 4 and a heating power supply 5;

[0028] The holding electrode power supply 7 is used to apply high voltage to the cathode holding electrode, the heating power supply 5 is used to heat the cathode, and the cathode is used to emit an electron beam under the high voltage and heating applied by the holding electrode;

[0029] The heating power supply 5 is connected in parallel with the cathode 4; the positive pole of the touch-holding electrode power supply 7 is connected to one end of the first resistor 6, the other end of the first resistor 6 is connected to the cathode touch-holding electrode, and the negative pole of the touch-holding electrode power supply 7 is connected to the negative pole of the heating power supply 5; the cathode touch-holding electrode is also connected to one end of the second resistor 8, and the other end of the second resistor 8 is connected to the negative pole of the bias power supply 9.

[0030] Specifically, for a traditional hollow cathode, the touch-holding electrode only needs to apply a high voltage at the beginning of the ignition process, so that a gas breakdown discharge is formed between the touch-holding electrode and the cathode top plate connected to the armored hot wire to form a plasma. The plasma spreads to the emitter area heated by the heater, causing the gas inside the emitter to be ionized, thereby achieving ignition of the hollow cathode. After successful ignition, the touch-holding electrode does not need to continue to apply a high voltage, and the formation of plasma can be maintained by relying on the collision heating effect of the plasma ions and the emitter and the resistance effect of the plasma and the external electric field discharge. Therefore, the voltage applied by the touch-holding electrode mainly plays an ignition role in the hollow cathode. After the cathode is successfully ignited, the touch-holding electrode is generally disconnected from the power supply, and its potential is suspended relative to other components. It is in a state of passive exposure to the plasma environment, and therefore will not actively affect the plasma environment.

[0031] However, in the fluidless cathode, the structure of the touch-holding electrode includes an extraction grid that maintains the electric field on the surface of the emitter, which requires the touch-holding electrode to actively apply potential all the time during the operation and regulation of the cathode. For the overall circuit of the entire thruster and cathode, if the touch-holding electrode of the cathode shell exposed to the external plasma environment is not directly connected to the cathode bias power supply that adjusts the cathode relative to the thruster circuit, then when the fluidless cathode works directly, the touch-holding electrode power supply will cause most of the cathode shell (touch-holding electrode shell) exposed to the outside to form a large electrode relative to the plasma environment. As the potential increases and decreases, it will absorb and repel the ions and electrons in the plasma, which will seriously affect the neutralization effect of the electron beam emitted by the cathode and the ion beam emitted by the thruster. In miniaturized thrusters that require high-precision neutralization, this effect cannot be ignored and needs to be suppressed.

[0032] Furthermore, the cathode includes a hot wire 1, a filling ceramic 3 and a cathode tube shell 2; the filling ceramic 3 is filled inside the cathode tube shell 2, and the hot wire 1 is arranged inside the filling ceramic 3; one end of the hot wire 1 is connected to the negative pole of the heating power supply 5, and the other end of the hot wire 1 is welded to the cathode tube shell 2, and the other end of the hot wire 1 is also connected to the positive pole of the heating power supply 5.

[0033] Specifically, as attached Figure 1 As shown, for the cathode hot wire heating circuit, the potential of the hot wire heater of the integrated emitter component and the cathode cylindrical shell on its surface are swapped, so that one end of the hot wire is negative and one end of the shell is positive, and the "thermophoresis" effect is used to suppress two special ceramic insulation failure problems caused by evaporation of the hot wire during use, reduce the evaporation and penetration of the hot wire of the heater in the ceramic sintered package, alleviate insulation failure and hot wire necking, and increase the working life of the hot wire of the fluid-free cathode.

[0034] The cathode substrate is the so-called barium tungsten emitter material, and the heater is a multi-turn hot wire. One end of the hot wire extends from the middle at the bottom, and the other end is welded to the outer wall of the cathode tube shell. In the previous hollow cathode, the hot wire used an armored heater, also known as a mineral insulated heating cable.

[0035] The hot wire inside the armored heater is insulated by filling magnesium oxide ceramic powder, and wrapped with a metal protective tube on the outside and wound as a whole. The external protective tube is not connected to the electricity or has the same potential as the hot wire. During the internal hot wire heating process, the life of the hot wire is reduced mainly because the hot wire metal evaporates due to heat and gradually penetrates into the mineral insulation layer, causing local hot wire necking. The resistance per unit length of the necked part is larger, and more heating power will be allocated here, further accelerating the thermal evaporation of the metal and causing the hot wire to burn out. For the traditional hollow cathode, its working life is required to be several thousand hours, while for the fluidless cathode used in gravitational wave detection, the cathode life is required to be 20,000 hours. The hot filament is a single-point failure component. Once damaged, it will cause the cathode failure, and then the propulsion system will not work. Therefore, the influence of the "thermophoresis" effect between the traditional hollow cathode hot filament and the protection tube on the cathode life may not be a major problem, and this effect does not have a significant impact on the cathode hot filament life. However, for the fluidless hot cathode used, since the diameter of the hot filament has become very thin in the process of miniaturization and integration, only 0.15mm, the influence of the thermophoresis effect on the hot filament life cannot be ignored, and direct measures other than simply thickening the hot filament must be taken to increase the hot filament life.

[0036] Thermophoresis is essentially a phenomenon in which particles that are not charged themselves drift toward electrodes under the action of an electric field. The thermophoresis effect is that at higher temperatures, in materials that do not have fluidity (which can be solids), the charge between solid molecules will show semiconductor-like characteristics due to the increase in temperature, that is, electrons or holes can generate charge movement under the application of an electric field. Similarly, metal vapor particles that gradually penetrate into insulating ceramics due to evaporation will also be affected by the electric field, and will move toward the electrodes due to the different positive and negative directions of the applied electrodes. The penetration of metal vapor in sponge-like pores will lead to a consequence, namely a short circuit between metals, that is, the metal vapor that penetrates into the sponge-like ceramic will be deposited with repeated heating and cooling, eventually leading to insulation failure of the ceramic.

[0037] For the fluid-free cathode, due to its different structure compared to the traditional hollow cathode armored hot wire, this feature causes two main problems for the long-term life stability of the hot wire:

[0038] First of all, unlike the hollow cathode armored heater, there is usually only one hot wire between the ceramic packages of the armored heater, which means that the armored heater will not have the problem of short circuit between the hot wires due to metal penetrating the ceramic.

[0039] Secondly, unlike the insulation problem between hot wires, in the fluid-free cathode structure, the cathode tube is part of the heating positive and negative electrodes. In fact, the cathode tube and the hot wire wrapped inside can also be regarded as two main electrodes. There will also be insulation problems between the cathode hot wire and the ceramic tube.

[0040] Both of these problems will cause a partial short circuit in the heating wire, resulting in a change in resistance, which in turn leads to unstable heating or even burning of the heating wire.

[0041] Further, the ion thruster includes a thruster ionization chamber 14, a gas input unit, a microwave source input unit, a screen grid power supply 10, a third resistor 11, an acceleration grid power supply 13 and a fourth resistor 12;

[0042] The gas input unit is used to input the set gas into the thruster ionization chamber 14; the microwave source input unit is used to generate a microwave signal and input the microwave signal into the thruster ionization chamber 14; the microwave signal is used to ionize the input set gas in the thruster ionization chamber 14 to generate set gas ions;

[0043] The ion thruster screen grid is connected to one end of the third resistor 11, the other end of the third resistor 11 is connected to the positive electrode of the screen grid power supply 10, and the negative electrode of the screen grid power supply 10 is connected to the positive electrode of the bias power supply 9; the ion thruster acceleration grid is connected to one end of the fourth resistor 12, the other end of the fourth resistor 12 is connected to the negative electrode of the acceleration grid power supply 13, and the acceleration grid power supply 13 is connected to the positive electrode of the bias power supply 9;

[0044] The screen grid power supply 10 is used to apply voltage to the ion thruster screen grid, and the acceleration grid is used to apply voltage to the ion thruster acceleration grid. The thruster ionization chamber is provided with a small hole. The voltage difference between the ion thruster screen grid and the ion thruster acceleration grid accelerates the set gas ions passing through the small hole to generate an ion plume.

[0045] Further, the gas input unit includes a set gas bottle 15, a pressure reducing valve 16, a flow meter 17 and a gas path insulator 18;

[0046] It is assumed that the gas outlet of the gas bottle 15 is connected to the gas inlet of the pressure reducing valve 16, the gas outlet of the pressure reducing valve 16 is connected to the gas inlet of the flow meter, the gas outlet of the flow meter 17 is connected to the gas inlet of the gas path insulator 18, and the gas outlet of the gas path insulator 18 is connected to the gas inlet of the thruster ionization chamber 14;

[0047] The setting gas bottle is used to transmit the setting gas to the pressure reducing valve 16; the pressure reducing valve is used to reduce the pressure of the input setting gas, and input the reduced-pressure setting gas to the flow meter 17, the flow meter 17 is used to obtain the flow signal of the setting gas after reduction, the flow meter 17 inputs the reduced-pressure setting gas to the gas path insulator 18, and the gas path insulator 18 inputs the reduced-pressure setting gas to the thruster ionization chamber 14; the gas path insulator 18 is used to insulate the setting gas bottle 15, the pressure reducing valve 16 and the flow meter 17 from the ion thruster.

[0048] Specifically, the gas circuit is isolated to prevent the gas supply line from being electrified, so that the control circuit in the gas supply of the upstream gas circuit is insulated from the thruster.

[0049] Further, the microwave source input unit includes a microwave source 19 and a DC block 20;

[0050] The microwave source 19 is used to generate a microwave signal and transmit the microwave signal to the DC isolator 20 ; the DC isolator 20 is used to isolate the DC component in the microwave signal and send the microwave signal with the DC component isolated to the thruster ionization chamber 14 .

[0051] Furthermore, the filling ceramic is alumina filling ceramic.

[0052] Furthermore, the gas is assumed to be xenon.

[0053] Furthermore, the bias power supply is an adjustable bias power supply.

[0054] Furthermore, the touch-holding electrode power supply is an adjustable power supply; the heating power supply is an adjustable power supply.

[0055] Specifically, the electrode power supply and the bias power supply can be feedback-controlled by a program, and are required to be turned on and working all the time during the entire working process, so that the electron energy and the amount of extraction current can be adjusted.

[0056] For the circuit connected between the cathode and the thruster, when the thruster needs to adjust the potential of the cathode relative to the thruster or the plume, it mainly depends on the voltage of the bias power supply. The end of the bias power supply connected to the cathode is ensured to be directly connected to the holding electrode, so that from the perspective of the external plasma, the potential of the main part of the cathode exposed to the plume, i.e., the outer shell of the holding electrode, is relatively stable, which has little effect on the neutralization process of the plume charge.

[0057] For the connection part between the cathode and the thruster, since regulation is required and the potential of the cathode relative to the thruster needs to be controlled and adjusted, an adjustable bias power supply must be applied for control feedback.

[0058] By reversing the cathode heating power supply, the central hot wire of the micro-integrated thermal sub-part is changed from the traditional positive pole to the negative pole, and the thermophoresis phenomenon is utilized to change the original cathode tube from the negative pole to the positive pole, that is, the positive and negative poles of the hot wire are reversed, so that the electric field of the two surrounding electrodes formed between the cathode tube and the hot wire outside the hot wire ceramic changes in the opposite direction for the metal vapor particles, thereby changing the electrophoresis direction of the metal particles in the ceramic, so that the original electric field for the metal vapor particles that are heated and evaporated changes from accelerating the evaporation to inhibiting the evaporation, so that the insulation performance between the hot wire and the cathode tube is enhanced. In addition, it also plays another role, that is, the insulation failure between the hot wires caused by metal vapor is also suppressed, thereby solving the special problem caused by the structure of this fluid-free cathode that is different from that of the armored hot wire heater.

[0059] In order to solve the problem that the need to continuously apply an electric field to the holding electrode will affect the external plasma environment, the position where the bias power supply that adjusts the cathode potential relative to the thruster is connected to the cathode circuit is set to the position where the positive electrode of the holding electrode power supply is located, so that when the bias power supply adjusts the cathode voltage unchanged, the potential of the entire cathode holding electrode shell, which is the main contact part from the perspective of the plume area, relative to the external plasma environment is unchanged, thereby making the potential of the main exposed contact part of the fluid-free cathode relatively stable during the process of emitting electrons and neutralizing the external excess plasma positively charged ions, rather than acting as a large-area electrode plate that absorbs or repels positive and negative charges to affect the neutralization process of cathode electrons and thruster ions.

[0060] 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 features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A fluid-free cathode neutralization circuit for a microwave ion thruster, characterized in that: including an ion thruster, a bias power supply, and a cathode power supply circuit; The ion thruster is used for generating ion plume by coupled discharge, and the cathode power supply circuit is used for releasing electrons to neutralize the ion plume generated by the ion thruster; The bias power supply is used to adjust the potential difference between the cathode and the ion thruster; the positive electrode of the bias power supply is connected to the ion thruster, and the negative electrode of the bias power supply is connected to the cathode power supply circuit.

2. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 1, characterized in that: The cathode power supply circuit includes a contact holding electrode power supply, a first resistor, a second resistor, a cathode and a heating power supply; The holding electrode power supply is used to apply high voltage to the cathode holding electrode, the heating power supply is used to heat the cathode, and the cathode is used to emit an electron beam under the high voltage and heating applied by the holding electrode; The heating power supply is connected in parallel with the cathode; the positive pole of the touch-holding electrode power supply is connected to one end of the first resistor, the other end of the first resistor is connected to the cathode touch-holding electrode, and the negative pole of the touch-holding electrode power supply is connected to the negative pole of the heating power supply; the cathode touch-holding electrode is also connected to one end of the second resistor, and the other end of the second resistor is connected to the negative pole of the bias power supply.

3. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 2, characterized in that: The cathode includes a hot wire, a filling ceramic and a cathode tube shell; the filling ceramic is filled inside the cathode tube shell, and the hot wire is arranged inside the filling ceramic; one end of the hot wire is connected to the negative pole of the heating power supply, and the other end of the hot wire is welded to the cathode tube shell, and the other end of the hot wire is also connected to the positive pole of the heating power supply.

4. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 1, characterized in that: The ion thruster includes a thruster ionization chamber, a gas input unit, a microwave source input unit, a screen grid power supply, a third resistor, an acceleration grid power supply and a fourth resistor; The gas input unit is used to input the set gas into the thruster ionization chamber; the microwave source input unit is used to generate a microwave signal and input the microwave signal into the thruster ionization chamber; the microwave signal is used to ionize the input set gas in the thruster ionization chamber to generate set gas ions; The ion thruster screen grid is connected to one end of the third resistor, the other end of the third resistor is connected to the positive electrode of the screen grid power supply, and the negative electrode of the screen grid power supply is connected to the positive electrode of the bias power supply; the ion thruster acceleration grid is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to the negative electrode of the acceleration grid power supply, and the acceleration grid power supply is connected to the positive electrode of the bias power supply; The screen grid power supply is used to apply voltage to the ion thruster screen grid, and the acceleration grid is used to apply voltage to the ion thruster acceleration grid. The thruster ionization chamber is provided with a small hole. The voltage difference between the ion thruster screen grid and the ion thruster acceleration grid accelerates the set gas ions passing through the small hole to generate an ion plume.

5. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 4, characterized in that: The gas input unit includes a set gas bottle, a pressure reducing valve, a flow meter and a gas path insulator; The gas outlet of the gas bottle is connected to the gas inlet of the pressure reducing valve, the gas outlet of the pressure reducing valve is connected to the gas inlet of the flow meter, the gas outlet of the flow meter is connected to the gas inlet of the gas path insulator, and the gas outlet of the gas path insulator is connected to the gas inlet of the thruster ionization chamber; The setting gas bottle is used to transmit the setting gas to the pressure reducing valve; the pressure reducing valve is used to reduce the pressure of the input setting gas, and input the reduced-pressure setting gas to the flow meter, the flow meter is used to obtain the flow signal of the set gas after reduction, the flow meter inputs the reduced-pressure setting gas to the gas path insulator, and the gas path insulator inputs the reduced-pressure setting gas to the thruster ionization chamber; the gas path insulator is used to insulate the setting gas bottle, the pressure reducing valve and the flow meter from the ion thruster.

6. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 4, characterized in that: The microwave source input unit includes a microwave source and a DC block; The microwave source is used to generate microwave signals and transmit the microwave signals to the DC isolator; the DC isolator is used to isolate the DC components in the microwave signals and send the microwave signals with the DC components isolated to the thruster ionization chamber.

7. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 3, characterized in that: The filler ceramic is alumina filled ceramic.

8. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 4, characterized in that: Set the gas to Xenon.

9. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 1, characterized in that: The bias power supply is an adjustable bias power supply.

10. The fluid-free cathode neutralization circuit for a microwave ion thruster according to claim 2, characterized in that: The contact holding electrode power supply is an adjustable power supply; the heating power supply is an adjustable power supply.

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