CN109441746B - A self-triggering method applied to a vacuum arc thruster - Google Patents

Abstract

The embodiment of the present invention provides a self-triggering method applied to a vacuum arc thruster. The method includes: selecting a carbon-based material as a trigger electrode; setting a self-triggering electrode structure, the self-triggering electrode structure includes: a cathode, an anode, a trigger electrode and an insulating medium; the cathode is a cylindrical structure with one end of a cone, and the anode is a horn-shaped nozzle Structure, the insulating medium is a cylindrical structure, the cathode is wrapped inside the insulating medium, and the anode is fixed at one end of the insulating medium; a plurality of trigger electrodes are evenly arranged to penetrate the insulating medium, and the tips protrude on the inner surface of the insulating medium; A low voltage is applied between (and the cathode) and the anode, and the creeping discharge is generated between the trigger electrode and the anode, thereby generating plasma that conducts the cathode and the anode, realizing low-voltage self-triggering, and establishing a vacuum arc between the cathode and the anode. The self-triggering method proposed by the present invention can realize reliable low-voltage triggering without an external triggering power supply.

Description

A self-triggering method applied to a vacuum arc thruster

technical field

The invention relates to the technical field of vacuum arc thrusters, in particular to a self-triggering method applied to vacuum arc thrusters.

Background technique

Low-voltage vacuum arc starting is of great significance to the optimization of VATs (vacuum arc thrusters).

Triggering of vacuum arcs often requires special methods, such as fuses, trailing arcs, and sparking arcs. The purpose of all triggering methods used to initiate a cold cathode arc is to establish one or more stable cathode points, thereby generating a large amount of plasma to connect the electrodes. The easiest way to start a vacuum arc is to apply a high voltage to break down the vacuum gap and use the same power source to sustain the arc. This is a reliable method for most cathode materials and does not require any additional triggering components. However, the downside of this method is that it requires a high voltage, which is prone to insulation problems.

Vacuum arc thrusters have been widely developed and used in recent years. It is a thruster that uses vacuum metal plasma to generate thrust. Among all the triggering methods, the most widely used vacuum arc thruster is the triggering method using spark plugs. The spark plug generates a tiny amount of plasma near the cathode and causes the breakdown of the vacuum gap, which can discharge at a few hundred volts between the electrodes. In this case, the initiation of the discharge and the maintenance of the arc current come from different power sources. However, the defects of this triggering method are: due to the design of the trigger circuit and the power circuit and the interaction between them, the design becomes more complicated; in addition, the spark plug is easily affected by deposition and corrosion.

Therefore, low voltage triggering without a trigger circuit is of great significance. A "no trigger" concept has been proposed by A.Anders and I.G.Brown. They placed a conductive layer on the surface of the insulating medium connecting the cathode and anode. Due to the low electrical resistance between the cathode and the anode, the explosive effect between the conductive layer and the cathode due to Joule heating can generate plasma. Although this method is feasible in most cases, it still has some disadvantages due to deposition and corrosion problems. The conductive layer is usually made of the same material as the cathode (not graphite) to avoid carbon contamination issues in some applications. However, some materials with low melting point (such as lead) may make the resistance between cathode and anode too low, and some easily oxidized materials (such as Li, Mg, Ba) are easily corroded resulting in very high resistance between cathode and anode. Impedance (>100kΩ); both conditions will cause trigger failure. Also, the special requirement of 10 μm between cathode and insulator is a potential disadvantage for vacuum arc thrusters, since it is almost impossible to maintain in outer space.

Therefore, it is necessary to devise a method for triggering the vacuum arc using a special creeping discharge-generated plasma. The carbon fiber material with efficient field emission characteristics is used as the trigger electrode to achieve a lower trigger voltage without an external trigger circuit.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a self-triggering method applied to a vacuum arc thruster to solve the above-mentioned problems in the background art.

In order to achieve the above object, the present invention has adopted the following technical solutions:

An embodiment of the present invention provides a self-triggering method applied to a vacuum arc thruster, characterized in that the method includes:

A carbon-based material with a micron-scale structure with field electron emission characteristics is selected as the trigger electrode;

A self-triggering electrode structure is provided, and the self-triggering electrode structure includes: a cathode, an anode, a triggering electrode and an insulating medium; wherein,

The cathode is set as a cylindrical structure with one end of a cone, the anode is set as a horn-shaped nozzle structure, the insulating medium is set as a cylindrical structure, and the cathode is wrapped inside the insulating medium, so the the anode is fixed to one end of the insulating medium; and,

A plurality of the trigger electrodes are evenly arranged, and the trigger electrodes penetrate the insulating medium, so that the tips of the trigger electrodes protrude on the inner surface of the insulating medium;

A low voltage is applied between the trigger electrode, the cathode and the anode, and creeping discharge is generated between the trigger electrode and the anode, thereby generating plasma that conducts the cathode and the anode, so as to realize Low voltage self-triggering creates a vacuum arc between the cathode and the anode.

Preferably, the carbon-based material with micron-scale structure size with field electron emission characteristics is selected as the trigger electrode, including:

According to the Fowler-Nordheim law expressing the relationship between the field emission current density and the electric field strength:

where the field-induced current density j _FE of the cathode is a function of the electric field strength E in V/m, φ is the work function of the field emission point, and t(y) and v(y) are table functions with respect to φ and E , take the unit value;

In formula (1), the field-induced current density j _FE and the electric field strength E are exponential functions, and a slight increase in the electric field strength will lead to a sharp increase in the current density;

According to the above formula, to enhance the electric field strength on the surface of the tip of the trigger electrode, the carbon-based material as the trigger electrode is arranged at a predetermined distance from the anode, and the carbon-based material with a filamentary structure is used.

Preferably, the carbon-based material as the trigger electrode is arranged at a predetermined distance from the anode, including:

The preset distance between the tip of the trigger electrode and the anode is set as: 0-5mm.

Preferably, the cathode is arranged in a cylindrical structure with a tapered end, the anode is arranged in a horn-shaped nozzle structure, the insulating medium is arranged in a cylindrical structure, the cathode is covered inside the insulating medium, and the anode is fixed on the insulating medium end, including:

Materials for making the cathode include, but are not limited to: lead, copper and aluminum;

The material made of the anode is stainless steel;

The cylindrical diameter of the cathode is set as: 1-20mm, the cone angle of the conical structure is set as: 0°-120°, and the distance between the tip of the cone and the outlet of the insulating medium is set as: 0-20mm;

A solid polytetrafluoroethylene tube is selected as the insulating medium, the inner diameter of the insulating medium is set equal to the cylindrical diameter of the cathode, and the difference between the outer diameter and the inner diameter of the insulating medium is 2-4 mm.

Preferably, a plurality of trigger electrodes are evenly arranged, and the trigger electrodes are penetrated through the insulating medium, so that the tips of the trigger electrodes protrude on the inner surface of the insulating medium, including:

The plurality of trigger electrodes are independent of each other, are connected in parallel with each other, and are connected in series with a current limiting resistor R ₂ of a specific resistance value after being connected outside the cylindrical portion of the insulating medium;

The tip of the trigger electrode is protruded on the inner surface of the insulating medium, and under the action of the field enhancement coefficient β, the electric field intensity at the emission point on the tip surface of the trigger electrode is increased to reach the critical field of field electron emission. powerful;

The critical field strength is: 10 ⁸ V/m.

Preferably, the current limiting resistor R ₂ is used to limit the current flowing through the trigger electrode before the vacuum arc is formed;

The current limiting resistor R ₂ is also used to increase the resistance of the trigger electrode branch after the vacuum arc between the cathode and the anode is formed, so as to protect the trigger electrode from being damaged during the discharge process;

The resistance range of the current limiting resistor R ₂ is set as: 0-100kΩ.

Preferably, a low voltage is applied between the trigger electrode, the cathode and the anode, and creeping discharge is generated between the trigger electrode and the anode, thereby generating plasma that conducts the cathode and the anode, so as to realize low-voltage self-triggering. A vacuum arc is established between the anodes, including:

After a plurality of the trigger electrodes are connected in series with a current limiting resistor R ₂ , they are then connected to the negative high voltage terminal of the power supply;

connecting the cathode with the negative high-voltage terminal of the power supply, and connecting the branch of the trigger electrode to the negative high-voltage terminal of the power supply in parallel with the branch of the cathode connected to the negative high-voltage terminal of the power supply;

The anode is connected to the ground terminal of the external circuit through a wire.

Preferably, a low voltage is applied between the trigger electrode, the cathode and the anode, and creeping discharge is generated between the trigger electrode and the anode, thereby generating plasma that conducts the cathode and the anode, so as to realize low-voltage self-triggering. A vacuum arc is established between the anodes, which also includes:

After a low voltage is applied between the trigger electrode and the anode, creeping flashover occurs between the trigger electrode and the anode, and creeping flashover plasma is generated;

The surface flashover plasma propagates to the region between the cathode and the anode and diffuses to the cathode, thereby establishing electrical conduction between the cathode and the anode, inducing the cathode field By emission, a metal plasma is generated at the conical tip of the cathode, traversing the vacuum gap between the cathode and the anode, forming a vacuum arc.

It can be seen from the technical solutions provided by the above embodiments of the present invention that the embodiments of the present invention provide a self-triggering method applied to a vacuum arc thruster. A carbon-based material of a size is used as a trigger electrode; a self-trigger electrode structure is provided, and the self-trigger electrode structure includes: a cathode, an anode, a trigger electrode and an insulating medium; wherein, the cathode is set as a cylindrical structure with a tapered end, The anode is arranged in a horn-shaped nozzle structure, the insulating medium is arranged in a cylindrical structure, the cathode is wrapped inside the insulating medium, and the anode is fixed at one end of the insulating medium; and, uniformly arranged A plurality of the trigger electrodes, and penetrate the trigger electrodes through the insulating medium, so that the tips of the trigger electrodes protrude on the inner surface of the insulating medium; apply a low voltage between the trigger electrodes, the cathode and the anode. Voltage, by triggering the creepage discharge between the electrode and the anode, and then generating the plasma that conducts the cathode and the anode, realizing low-voltage self-triggering, and establishing a vacuum arc between the cathode and the anode. The self-triggering method proposed by the present invention can realize reliable low-voltage triggering without an external triggering power source, and on the basis of reducing the electrode triggering voltage, it does not affect the propulsion effect of the vacuum arc thruster, and further reduces the vacuum arc thruster. The mass and volume of the device provide conditions for simplifying the structure.

Additional aspects and advantages of the present invention will be set forth in part in the following description, which will be apparent from the following description, or may be learned by practice of the present invention.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a process flow diagram of a self-triggering method applied to a vacuum arc thruster according to an embodiment of the present invention;

2 is a schematic diagram of the results of electric field simulation performed on a self-triggered electrode structure by using ANSYS Maxwell 3D software according to an embodiment of the present invention;

3 is a schematic diagram of a plasma generated along a surface flashover by a self-triggering electrode structure provided in an embodiment of the present invention;

4 is a schematic structural diagram of an experimental system for a self-triggering method applied to a vacuum arc thruster according to an embodiment of the present invention;

Fig. 5 is the voltage waveform diagram between electrodes of the traditional high-voltage vacuum breakdown method provided by the embodiment of the present invention;

6 is a waveform diagram of the voltage between electrodes of a self-triggering method applied to a vacuum arc thruster according to an embodiment of the present invention;

7 is a schematic diagram of a discharge phenomenon of a conventional high-voltage vacuum breakdown method under the same discharge conditions provided by an embodiment of the present invention;

8 is a schematic diagram of a discharge phenomenon of a self-triggering method applied to a vacuum arc thruster under the same discharge conditions provided in an embodiment of the present invention;

9 is a schematic diagram of an experimental result of the effect of changing the resistance of the current limiting resistor on breakdown characteristics provided by an embodiment of the present invention;

FIG. 10 is a schematic diagram of an experimental result of the effect of changing the distance between the cathode and the trigger electrode on the breakdown characteristic according to an embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, but not to be construed as a limitation of the present invention.

It will be understood by those skilled in the art that the singular forms "a", "an", "the" and "the" as used herein can include the plural forms as well, unless expressly stated otherwise. It should be further understood that the word "comprising" used in the description of the present invention refers to the presence of stated features, integers, steps, operations, elements and/or components, but does not exclude the presence or addition of one or more other features, Integers, steps, operations, elements, components and/or groups thereof. It will be understood that when we refer to an element as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Furthermore, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as herein, are not to be taken in an idealized or overly formal sense. explain.

In order to facilitate the understanding of the embodiments of the present invention, the following will take several specific embodiments as examples for further explanation and description in conjunction with the accompanying drawings, and each embodiment does not constitute a limitation to the embodiments of the present invention.

Example 1

The embodiment of the present invention provides a self-triggering method applied to a vacuum arc thruster, which uses a special carbon-based material as a triggering electrode to realize reliable low-voltage triggering without an external triggering power supply.

A process flow diagram of a self-triggering method applied to a vacuum arc thruster provided by an embodiment of the present invention is shown in FIG. 1 , and specifically includes the following steps:

Step S110 : selecting a carbon-based material with a micron-scale structure with field electron emission characteristics as the trigger electrode.

Carbon-based materials such as diamond, graphite, and carbon nanotubes can be used as electron sources because their field emission properties, especially under poor vacuum conditions, are superior to conventional metal field emission. Therefore, low voltage triggering can be accomplished using carbon fibers as trigger electrodes.

Carbon fibers possess many unique properties under high vacuum conditions, such as low electronic work function and cathode sputtering coefficient, high mechanical strength values, and good electrical and thermal conductivity. The surface atoms at the carbon fiber tips constitute the structure of an ideal graphite lattice, interacting through mostly weak σ bonds, and thus have rather weak surface activity. Due to its huge anisotropy, the most pronounced field emission of carbon fibers occurs at this tip surface.

In addition to the field emission properties of the cathode, the electric field strength is also a key factor in determining the emission current. The Fowler-Nordheim law is used to express the relationship between the field emission current density and the electric field strength as follows:

where the field-induced current density j _FE of the cathode is a function of the electric field strength E in V/m, φ is the work function of the field emission point, and t(y) and v(y) are table functions with respect to φ and E , take the unit value.

It can be seen from equation (1) that the field-induced current density j _FE has an exponential function relationship with the electric field strength E. Therefore, a slight increase in the electric field strength will lead to a sharp increase in the current density. The carbon-based material as the trigger electrode is arranged at a predetermined distance from the anode, and the carbon-based material with a filamentary structure is used. Due to the specific filamentary structure of the carbon fiber and its short distance from the anode, the electric field strength on its tip surface is significantly enhanced.

Wherein, the preset distance between the tip of the trigger electrode and the anode can be set as: 0-5mm.

Step S120: Setting up a self-triggering electrode structure, the self-triggering electrode structure includes: a cathode, an anode, a triggering electrode and an insulating medium; wherein,

The cathode is arranged as a cylindrical structure with one end of a cone, the anode is arranged as a horn-shaped nozzle structure, the insulating medium is arranged as a cylindrical structure, the cathode is covered inside the insulating medium, and the anode is fixed at one end of the insulating medium; and,

A plurality of trigger electrodes are evenly arranged, and the trigger electrodes are penetrated through the insulating medium, so that the tips of the trigger electrodes protrude on the inner surface of the insulating medium.

In the embodiment of the present invention, the material for making the cathode includes but not limited to: lead, copper and aluminum; the material for making the anode can be stainless steel; and the cylindrical diameter of the cathode is set to: 1-20mm, The cone angle of the cone-shaped structure of the cathode is set as: 0°-120°, and the distance between the tip of the cone and the outlet of the insulating medium can be set as: 0-20mm.

A solid polytetrafluoroethylene tube is selected as the insulating medium, the inner diameter of the insulating medium is set equal to the cylindrical diameter of the cathode, and the difference between the outer diameter and the inner diameter of the insulating medium is 2-4 mm.

The setting of the plurality of trigger electrodes is as follows: the plurality of trigger electrodes are independent of each other, are connected in parallel with each other, and are connected in series with a current limiting resistor R ₂ with a specific resistance value after being connected outside the cylindrical portion of the insulating medium. Among them, the resistance value range of the current limiting resistor R ₂ is set as: 0-100kΩ.

The current limiting resistor R ₂ is used to limit the current flowing through the trigger electrode before the vacuum arc is formed; it is also used to increase the trigger electrode branch after the vacuum arc between the cathode and the anode is formed. The resistance of the circuit protects the trigger electrode from being damaged during the discharge process.

The schematic diagram of the electric field simulation result of the self-triggering electrode structure using ANSYS Maxwell 3D software provided by the embodiment of the present invention is shown in Figure 2. A low voltage (1kV) is applied between the cathode, the triggering electrode and the anode, and the triggering electrode passes through the insulating medium , and the tip protrudes from the inner surface of the insulating medium, the maximum electric field strength of the tip of the trigger electrode reaches 3.5312×10 ⁷ V/m, which is 40 times that of the tip of the cathode. Due to the existence of the field enhancement coefficient β, the emission points (usually some protrusions) on the tip surface of the trigger electrode usually show a much larger electric field strength than the surface of the trigger electrode. The field enhancement coefficient β can increase the electric field intensity by dozens of times, so that the emission point on the surface of the trigger electrode tip reaches the critical field intensity of field electron emission, and the critical field intensity is: 10 ⁸ V/m.

The electric field vector distribution is also an important factor affecting the creepage flashover. As shown in Figure 3, the electric field vector has a component perpendicular to the inner surface of the hole and a component parallel to the inner surface of the hole. A schematic diagram of the resulting plasma is marked in FIG. 3 . As described by shao, Harris and Anderson on the mechanism of fast creeping flashover in vacuum, the initial electrons emitted from the carbon fiber will bombard the insulating medium and generate a flashover along the inner surface between the carbon fiber and the anode. The distribution of the electric field vector also provides conditions for ions in the plasma to diffuse to the cathode and initiate a vacuum arc. Since the field emission current amplitude of a single carbon fiber is usually μA, in order to increase the trigger current and improve the trigger reliability, carbon fiber bundles can be used as trigger electrodes and uniformly arranged in the insulating medium of the self-trigger electrode structure.

Step S130 : applying a low voltage between the trigger electrode, the cathode and the anode, and generating creeping discharge between the trigger electrode and the anode, thereby generating plasma that conducts the cathode and the anode to realize low-voltage self-triggering, between the cathode and the anode Create a vacuum arc.

After a plurality of the trigger electrodes are connected in series with a current limiting resistor R ₂ , they are then connected to the negative high voltage terminal of the power supply.

The cathode is directly connected to the negative high-voltage terminal of the power supply, and the branch of the trigger electrode connected to the negative high-voltage terminal of the power supply is connected in parallel with the branch of the cathode connected to the negative high-voltage terminal of the power supply.

The anode is connected to the ground terminal of the external circuit through a wire.

After a low voltage is applied between the trigger electrode and the anode, creeping flashover occurs between the trigger electrode and the anode, and creeping flashover plasma is generated.

The surface flashover plasma propagates to the region between the cathode and the anode and diffuses to the cathode, thereby establishing electrical conduction between the cathode and the anode, inducing the cathode field By emission, a metal plasma is generated at the conical tip of the cathode, traversing the vacuum gap between the cathode and the anode, forming a vacuum arc.

Embodiment 2

This embodiment provides an experimental system applied to a self-triggering method of a vacuum arc thruster, the specific implementation structure of which is shown in Figure 4, and may specifically include the following content:

Pulse power supplies use energy storage capacitors as the energy source for discharge. Before discharging, the storage capacitor C is charged to a specific voltage. When the switch SG is closed, the voltage of the capacitor C begins to be applied across the electrodes through the current limiting resistor R1 and the inductor L. A diode D in series with the circuit is used to prevent the reverse flow of the circuit current to avoid oscillation of the current. In the experiment, the discharge was carried out under high vacuum, and the gas pressure was maintained at 10 ^-4 Pa. During the discharge process, the voltage between point A and the ground is defined as the inter-pole voltage, which can be obtained through a high-voltage probe (TEK-P6015A); the current flowing through the anode is the arc current, which can be obtained through a Rogowski coil.

The specific structural schematic diagram of the self-triggering electrode structure is shown in Figure 4. The solid polytetrafluoroethylene tube is used as the insulating medium, and its inner diameter and outer diameter are 5 mm and 7 mm, respectively. The cathode is made of lead, and the anode is made of stainless steel; the cathode is a cylindrical structure with a cone shape, the diameter of the cylindrical shape is 5mm, one end is cone-shaped, and the cone angle is 60°. internal. The anode is a horn-shaped nozzle structure, which is fixed on the same end of the solid polytetrafluoroethylene cylinder and the cone angle. The distance between the cone tip of the cathode and the outlet of the solid Teflon tube is 5 mm.

The trigger electrode branch is connected in parallel with the cathode branch, and 8 independent trigger electrodes are included in this experiment. The trigger electrodes are connected in parallel with each other, and are connected in series with the current limiting resistor R ₂ after being connected outside the solid PTFE cylinder. Each trigger electrode is 0.16mm in diameter and consists of a bundle of carbon fibers. The carbon fiber bundles are passed through the solid teflon tube with the tips protruding from the inner wall surface of the solid teflon tube. The front and side views of the trigger electrodes are shown in Figures 4c and 4d, respectively.

Using this experimental system, a series of experiments are carried out to test the effect of the self-triggering method proposed in the embodiment of the present invention.

In order to distinguish this self-triggering method from the traditional high-voltage breakdown method, the typical voltage and current waveforms of the two vacuum breakdown methods were recorded, as shown in Figure 5 and Figure 6. For the convenience of comparison, the X-axis and Y-axis of the main coordinate system in the two figures are set as the same scale. At the same time, the voltage waveform during triggering is enlarged to show its details.

As shown in Figure 5, after the switch SG is closed, the inter-electrode voltage waveform of the traditional high-voltage vacuum breakdown method shows a changing trend of increasing rapidly and then decreasing rapidly. Under the coaxial electrode structure, the vacuum breakdown voltage reaches more than 10kV. It can be speculated that the cathode metal plasma is induced by field emission and propagates to the anode, causing rapid breakdown of the vacuum gap. When the vacuum breaks down, the arc current starts to increase. At this time, the inter-electrode voltage is maintained at the arc voltage (not shown in the figure because it is less than 200V).

In the self-triggering method proposed by the embodiment of the present invention, the vacuum arc has different establishment mechanisms. As shown in Fig. 6, when the switch SG is closed, a surface flashover can occur between the trigger electrode and the anode at a relatively small voltage. At this time, the cone tip of the cathode cannot form an effective field emission due to the small field strength. . When the surface flashover occurs, a sustain voltage of 200-400V appears in the voltage waveform. After a period of time, the arc is triggered and the voltage is reduced to the arc voltage. It can be inferred that there is a creeping flashover between the trigger electrode and the anode during this time, and the plasma generated by the creeping flashover propagates to the area between the cathode and the anode during this time. The time from when the inter-electrode voltage starts to rise until it drops to the arc voltage is called the delay time. After the plasma diffuses to the cathode, the vacuum arc is finally established and the arc current begins to increase. This self-triggering method reduces the electrode breakdown voltage by several hundred volts, which is less than 8% of the vacuum breakdown voltage.

In order to verify the authenticity of the self-triggering process analysis, the discharge phenomena of the two triggering methods under the same discharge conditions were recorded, as shown in Figure 7 and Figure 8, respectively, in which the light intensity is represented by a color bar. It can be seen from the figure that the region with the largest light intensity in both discharge modes appears near the tip of the cathode. It is generally believed that the area with high light intensity indicates the most intense discharge. Usually the area with the highest light intensity indicates the most intense discharge process. Therefore, the discharge phenomenon proves that the vacuum arcs of the two discharge modes are both initiated by the cathode tip and are vacuum metal arcs.

When the vacuum arc is established, the current amplitude is determined by the energy of the storage capacitor and can exceed tens of amps. In the self _- triggering electrode structure, a current limiting resistor R2 is set in series with the triggering electrode to protect it from being damaged during the discharge process. The specific principle is as follows:

Before the vacuum arc is formed, there is no electrical connection between the cathode and the anode, and creeping discharge occurs between the trigger electrode and the anode. Resistor _R2 can limit the current flowing through the trigger electrode to avoid excessive current. After the vacuum arc is formed, the cathode and the anode are electrically connected through the plasma, and the cathode-anode branch and the trigger electrode branch become in a parallel relationship. The trigger electrode itself is a semiconductor, which has a higher impedance than the metal cathode. The current limiting resistor R ₂ is connected in series with the trigger electrode to further increase the resistance of the trigger electrode branch. According to the fundamental laws of circuits, the current in a parallel circuit is inversely proportional to its resistance. Therefore, the current flowing through the trigger electrode branch is much smaller than the current in the cathode-anode branch, which avoids damage to the trigger electrode caused by the high current.

According to the above analysis, it can be found that the triggering key of this "self-triggering" method lies in the creeping discharge process. In order to further explore the influence of electrode parameters on the triggering process, the changes of breakdown characteristics were studied by changing the resistance of the current limiting resistor and changing the distance between the cathode and the triggering electrode.

In the experiment, every 80 discharges were taken as a set of data, and the average value of trigger voltage and delay time was calculated. The results are shown in Figure 9 and Figure 10.

It can be seen from Figure 9 that the resistance value of the current limiting resistor R ₂ has an influence on the trigger voltage. When the current-limiting resistor is increased, the average trigger voltage increases. When the current limiting resistor was increased to an extreme value of 100kΩ, the trigger voltage rose to around 3kV, but the "self-trigger" method still worked. It can be inferred that before triggering, the field-induced current flows through the current-limiting resistor, and the trigger voltage increases due to the voltage dividing effect of the resistor.

It can be seen from Fig. 10 that as the distance between the cathode and the trigger electrode gradually increases, the delay time is significantly prolonged, and there is an approximately proportional relationship with it. It can be inferred that the greater the distance between the cathode and the trigger electrode, the more time it takes for the plasma to diffuse to the cathode. During the experiment, it was found that the increase of the distance between the cathode and the trigger electrode did not affect the trigger voltage.

In the course of this experiment, the relevant experiments of the self-triggering method were mainly carried out using lead with low melting point as the cathode material, and the reliable triggering times of more than 10 ⁴ level have been achieved under this material. The high melting point cathode material has higher trigger reliability because it is not easy to generate metal particles during the discharge process. In addition, after conducting self-triggering tests on several common cathode materials (such as copper and aluminum), it is found that the number of reliable triggering times can reach ¹⁰⁵ levels.

Due to its small mass and simple structure, the vacuum arc thruster has higher requirements on triggering. This "self-triggering" method can meet the requirements of vacuum arc thrusters in terms of voltage reduction effect, reliability and applicability. In order to explore the discharge characteristics of the method proposed in the present invention after being applied to a vacuum arc thruster, it was compared with the traditional high-voltage breakdown method, and plasma density measurement and thrust specific impulse measurement were carried out at a distance of 100 mm from the anode nozzle. , the results are shown in Table 1.

Table 1

As can be seen from Table 1, under the same energy storage conditions, the "self-triggering" method proposed in this paper reduces the voltage required for arc generation to less than 8% of that in the high-voltage breakdown mode. At the same time, the plasma generation characteristics and propulsion characteristics of the vacuum arc thruster remain unchanged. Therefore, it can be seen that the "self-triggering" method proposed by the present invention will not affect the propulsion effect of the vacuum arc thruster on the basis of reducing the electrode triggering voltage. Since this self-triggering method does not require a specially designed triggering circuit, it provides conditions for further reducing the mass and volume of the vacuum arc thruster and simplifying the structure compared with the triggering method of the spark plug.

To sum up, the embodiments of the present invention provide a self-triggering method applied to a vacuum arc thruster. The method includes: selecting a carbon-based material as a triggering electrode; setting a self-triggering electrode structure, and the self-triggering electrode structure includes: a cathode , anode, trigger electrode and insulating medium; the cathode is a cylindrical structure with a cone at one end, the anode is a horn-shaped nozzle structure, the insulating medium is a cylindrical structure, the cathode is wrapped inside the insulating medium, and the anode is fixed on the insulating medium. One end; a plurality of trigger electrodes are evenly arranged to penetrate the insulating medium, and the tips protrude on the inner surface of the insulating medium; a low voltage is applied between the trigger electrode (and the cathode) and the anode, and creeping discharge is generated between the trigger electrode and the anode, thereby generating The plasma of the cathode and the anode is turned on to achieve low-voltage self-triggering, and a vacuum arc is established between the cathode and the anode. The self-triggering method proposed by the present invention can realize reliable low-voltage triggering without an external triggering power source, and on the basis of reducing the electrode triggering voltage, it does not affect the propulsion effect of the vacuum arc thruster, and further reduces the vacuum arc thruster. The mass and volume of the thruster provide conditions for simplifying the structure.

Those of ordinary skill in the art can understand that the accompanying drawing is only a schematic diagram of an embodiment, and the modules or processes in the accompanying drawing are not necessarily necessary to implement the present invention.

Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the various embodiments may be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the apparatus or system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and reference may be made to some descriptions of the method embodiments for related parts. The apparatus and system embodiments described above are only illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, It can be located in one place, or it can be distributed over multiple network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution in this embodiment. Those of ordinary skill in the art can understand and implement it without creative effort.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (8)

1. a self-triggering method applied to a vacuum arc thruster, is characterized in that, the method comprises: A carbon-based material with a micron-scale structure with field electron emission characteristics is selected as the trigger electrode; A self-triggering electrode structure is provided, and the self-triggering electrode structure includes: a cathode, an anode, a triggering electrode and an insulating medium; wherein, The cathode is set as a cylindrical structure with one end of a cone, the anode is set as a horn-shaped nozzle structure, the insulating medium is set as a cylindrical structure, and the cathode is wrapped inside the insulating medium, so the the anode is fixed to one end of the insulating medium; and, A plurality of the trigger electrodes are evenly arranged, and the trigger electrodes penetrate the insulating medium, so that the tips of the trigger electrodes protrude on the inner surface of the insulating medium; A low voltage is applied between the trigger electrode, the cathode and the anode, and creeping discharge is generated between the trigger electrode and the anode, thereby generating plasma that conducts the cathode and the anode, so as to realize Low voltage self-triggering creates a vacuum arc between the cathode and the anode. 2. the self-triggering method that is applied to vacuum arc thruster according to claim 1, is characterized in that, described selecting has the carbon-based material of the micron-scale structure size of field electron emission characteristic as trigger electrode, comprising: According to the Fowler-Nordheim law expressing the relationship between the field emission current density and the electric field strength:

where the field-induced current density j _FE of the cathode is a function of the electric field strength E in V/m, φ is the work function of the field emission point, and t(y) and v(y) are table functions with respect to φ and E , take the unit value; In formula (1), the field-induced current density j _FE and the electric field strength E are exponential functions, and a slight increase in the electric field strength will lead to a sharp increase in the current density; According to the above formula, to enhance the electric field strength on the surface of the tip of the trigger electrode, the carbon-based material as the trigger electrode is arranged at a predetermined distance from the anode, and the carbon-based material with a filamentary structure is used. 3. The self-triggering method applied to a vacuum arc thruster according to claim 2, wherein the carbon-based material used as the trigger electrode is arranged at a position at a preset distance from the anode, comprising: The preset distance between the tip of the trigger electrode and the anode is set as: 0-5mm. 4. The self-triggering method applied to a vacuum arc thruster according to claim 1, wherein the cathode is set to a cylindrical structure with one end of a cone, the anode is set to a horn-shaped nozzle structure, and an insulating medium It is arranged in a cylindrical structure, the cathode is wrapped inside the insulating medium, and the anode is fixed at one end of the insulating medium, including: Materials for making the cathode include, but are not limited to: lead, copper and aluminum; The material for making the anode is stainless steel; The cylindrical diameter of the cathode is set as: 1-20mm, the cone angle of the conical structure is set as: 0°-120°, and the distance between the tip of the cone and the outlet of the insulating medium is set as: 0-20mm; A solid polytetrafluoroethylene tube is selected as the insulating medium, the inner diameter of the insulating medium is set equal to the cylindrical diameter of the cathode, and the difference between the outer diameter and the inner diameter of the insulating medium is 2-4 mm. 5. The self-triggering method applied to a vacuum arc thruster according to claim 1, wherein the plurality of trigger electrodes are evenly arranged, and the trigger electrodes are penetrated through an insulating medium, so that the tips of the trigger electrodes are in an insulating state. The inner surface of the media protrudes, including: The plurality of trigger electrodes are independent of each other, are connected in parallel with each other, and are connected in series with a current limiting resistor R ₂ of a specific resistance value after being connected outside the cylindrical portion of the insulating medium; The tip of the trigger electrode is protruded on the inner surface of the insulating medium, and under the action of the field enhancement coefficient β, the electric field intensity at the emission point on the tip surface of the trigger electrode is increased to reach the critical field of field electron emission. powerful; The critical field strength is: 10 ⁸ V/m. 6. The self-triggering method applied to a vacuum arc thruster according to claim 5, wherein the current limiting resistor R ₂ is used to limit the current flowing through the trigger electrode before the vacuum arc is formed; The current limiting resistor R ₂ is also used to increase the resistance of the trigger electrode branch after the vacuum arc between the cathode and the anode is formed, so as to protect the trigger electrode from being damaged during the discharge process; The resistance range of the current limiting resistor R ₂ is set as: 0-100kΩ. 7. The self-triggering method applied to a vacuum arc thruster according to claim 1, wherein the described low voltage is applied between the trigger electrode, the cathode and the anode, and creeping discharge is generated between the trigger electrode and the anode , and then generate the plasma that conducts the cathode and the anode, realizes low-voltage self-triggering, and establishes a vacuum arc between the cathode and the anode, including: After a plurality of the trigger electrodes are connected in series with a current limiting resistor R ₂ , they are then connected to the negative high voltage terminal of the power supply; connecting the cathode with the negative high-voltage terminal of the power supply, and connecting the branch of the trigger electrode to the negative high-voltage terminal of the power supply in parallel with the branch of the cathode connected to the negative high-voltage terminal of the power supply; The anode is connected to the ground terminal of the external circuit through a wire. 8 . The self-triggering method applied to a vacuum arc thruster according to claim 7 , wherein a low voltage is applied between the trigger electrode, the cathode and the anode, and creeping discharge is generated between the trigger electrode and the anode. 9 . , and then generate the plasma that conducts the cathode and the anode, realizes low-voltage self-triggering, and establishes a vacuum arc between the cathode and the anode, and also includes: After a low voltage is applied between the trigger electrode and the anode, creeping flashover occurs between the trigger electrode and the anode, and creeping flashover plasma is generated; The surface flashover plasma propagates to the region between the cathode and the anode and diffuses to the cathode, thereby establishing electrical conduction between the cathode and the anode, inducing the cathode field By emission, a metal plasma is generated at the conical tip of the cathode, traversing the vacuum gap between the cathode and the anode, forming a vacuum arc.

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