Discharge channel for suppressing low frequency discharge oscillation in a hall thruster

Abstract

The application relates to the technical field of Hall thrusters, in particular to a discharge channel for inhibiting low-frequency discharge oscillation of a Hall thruster, which comprises a first discharge channel and a second discharge channel, wherein: the first discharge channel is close to the anode of the Hall thruster, one end of the first discharge channel is in a flat structure, and the other end of the first discharge channel is in a sawtooth structure; the second discharge channel is close to the outlet of the Hall thruster, one end of the second discharge channel is in a flat structure, and the other end of the second discharge channel is in a sawtooth structure; the sawtooth structure end of the first discharge channel and the sawtooth structure end of the second discharge channel correspond to each other, and the first discharge channel is assembled and connected with the second discharge channel through the sawtooth structure end; the material characteristics of the first discharge channel and the material characteristics of the second discharge channel are different. The application can simultaneously realize the discharge oscillation inhibition and life increase of the Hall thruster without additional feedback circuits and components, and is helpful to the release of stress caused by temperature change of the Hall thruster.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of Hall thruster, in particular to a discharge channel for suppressing low-frequency discharge oscillation of Hall thruster. BACKGROUND

[0002] As an electrostatic electric propulsion technology, Hall thruster has the characteristics of large thrust density, moderate specific impulse and simple structure, and has been widely used in commercial spaceflight and low-orbit Internet constellation in recent years.

[0003] During the operation of Hall thruster, due to the collision between particles and the gradient drift and other factors, there is discharge oscillation in Hall thruster with a frequency ranging from kHz to GHz. Among them, the low-frequency and large-amplitude oscillation with a frequency ranging from 1 kHz to 30 kHz is often observed during the operation of the thruster, which is macroscopically manifested as periodic oscillation of discharge current. The low-frequency and large-amplitude discharge oscillation in Hall thruster can increase the divergence angle of the thruster plume, increase the load of the power processing unit, induce abnormal arc extinction of the thruster, shorten the service life of the thruster, and reduce the efficiency of the thruster. Therefore, suppressing or weakening the low-frequency discharge oscillation of Hall thruster is of great significance to the performance improvement of the thruster.

[0004] The methods for suppressing oscillation in plasma can be divided into two types: active control and passive control. Active control refers to using a feedback control system such as a feedback coil or a filter circuit to compensate for the oscillation by external energy or to apply a signal opposite in phase to the oscillation, so as to suppress or weaken the oscillation. Passive control refers to using the energy dissipation mechanism inside the plasma to consume the energy that induces the oscillation of the plasma by regulating the motion behavior and confinement state of the plasma, so as to suppress the discharge oscillation. Both active control and passive control can achieve suppression or weakening of the discharge oscillation in plasma, but active control requires additional feedback system and control circuit, which increases the complexity and design cost of the device. Passive control achieves suppression of discharge oscillation according to the intrinsic characteristics of the plasma. SUMMARY

[0005] The present application provides a discharge channel for suppressing low-frequency discharge oscillation of Hall thruster, which is based on the principle of passive control and utilizes the energy dissipation caused by the collision between primary electrons and the wall of the discharge channel in the process of generating secondary electrons to achieve suppression of discharge oscillation.

[0006] In order to achieve the above-mentioned purpose, the application provides a discharge channel for inhibiting low-frequency discharge oscillation of a Hall thruster, comprising a first discharge channel and a second discharge channel, wherein: the first discharge channel is close to an anode of the Hall thruster, one end is flat, and the other end is sawtooth-shaped; the second discharge channel is close to an outlet of the Hall thruster, one end is flat, and the other end is sawtooth-shaped; the sawtooth-shaped end of the first discharge channel corresponds to the sawtooth-shaped end of the second discharge channel, and the first discharge channel is assembled and connected with the second discharge channel through the sawtooth-shaped end; the material properties of the first discharge channel are different from those of the second discharge channel.

[0007] Further, the first discharge channel adopts insulating material with large secondary electron emission coefficient.

[0008] Further, the second discharge channel adopts ceramic material with sputtering resistance and corrosion resistance.

[0009] Further, the sawteeth at the connection of the first discharge channel and the second discharge channel are uniformly distributed in the circumferential direction.

[0010] Further, the number of sawtooth tips is 6-9, which are uniformly distributed in the angular direction, and the angular distance between adjacent two sawtooth tips is 40°-60°.

[0011] Further, the angle of the sawtooth tip is 60°.

[0012] Further, the concave area between adjacent two sawteeth of the first discharge channel is trapezoidal, and the concave area between adjacent two sawteeth of the second discharge channel is triangular.

[0013] Further, the length of the first discharge channel is 2 times the length of the second discharge channel.

[0014] The application provides a discharge channel for inhibiting low-frequency discharge oscillation of a Hall thruster, which has the following beneficial effects:

[0015] The application has simple structure, adopts two materials with different properties to form the discharge channel of the thruster, realizes inhibition of low-frequency discharge oscillation by using energy consumption caused by electron collision with the wall, does not need additional feedback circuit and components, can realize discharge oscillation inhibition and life increase of the Hall thruster at the same time, and the connection between the discharge channels is sawtooth-shaped, which increases the sealing property of the discharge channel and helps the Hall thruster release stress caused by temperature change. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application. In the drawings:

[0017] Fig. 1 is a structural schematic diagram of a discharge channel for suppressing low-frequency discharge oscillation of a Hall thruster according to an embodiment of the present application;

[0018] Fig. 2 is a schematic diagram of a first discharge channel of a discharge channel for suppressing low-frequency discharge oscillation of a Hall thruster according to an embodiment of the present application;

[0019] Fig. 3 is a schematic diagram of a second discharge channel of a discharge channel for suppressing low-frequency discharge oscillation of a Hall thruster according to an embodiment of the present application;

[0020] In the figure: 1 - first discharge channel, 2 - second discharge channel, 3 - sawtooth structure, 4 - flat structure, 5 - sawtooth tip, 6 - sawtooth tip angle, 7 - concave area. DETAILED DESCRIPTION

[0021] In order to make the personnel in the technical field better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0022] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0023] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", and the like indicate the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0024] And, the above-mentioned partial terms can be used to represent other meanings in addition to the orientation or positional relationship, for example, the term "upper" can also be used to represent a certain dependent relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to the specific circumstances.

[0025] In addition, the meaning of the term "a plurality of" should be two and more than two.

[0026] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0027] As Figs. 1-3 shown, the present application provides a discharge channel for inhibiting low-frequency discharge oscillation of a Hall thruster, comprising a first discharge channel 1 and a second discharge channel 2, wherein: the first discharge channel 1 is close to the anode of the Hall thruster, one end is a flat structure 4, and the other end is a sawtooth structure 3; the second discharge channel 2 is close to the outlet of the Hall thruster, one end is a flat structure 4, and the other end is a sawtooth structure 3; the sawtooth structure 3 port of the first discharge channel 1 corresponds to the sawtooth structure 3 port of the second discharge channel 2, and the first discharge channel 1 is assembled and connected with the second discharge channel 2 through the sawtooth structure 3 port; the material properties of the first discharge channel 1 and the second discharge channel 2 are different.

[0028] Specifically, the principle of the discharge channel for inhibiting low-frequency discharge oscillation of the Hall thruster provided by the embodiments of the present application is as follows: in the discharge channel of the Hall thruster, the electron energy density located in the ionization region and the acceleration region satisfies the following equation:

[0029]

[0030]

[0031] In the above formula, the superscript "A" represents a physical quantity located in the ionization region, "cat" represents a physical quantity related to the hollow cathode; u = 3n e T e / 2 is the energy density of the electron, n e is the electron density, which satisfies n i = n e = n (n represents the plasma density, and n i represents the ion density) under the quasi-neutral assumption, T e is the electron temperature; υ e represents the speed of the electron entering the ionization region from the acceleration region of the thruster, represents the speed of the electron absorbed by the anode, and N represents the neutral atom density, L Arepresents the length of the ionization region, L represents the length of the acceleration region, E represents the electric field strength; K(T e ) represents the energy change due to the non-elastic collision such as ionization, excitation, etc. between the electron and the neutral atom; S wall represents the energy change due to the collision between the electron and the wall; the "+" on the right side of the equal sign in the above formula represents the energy gain, and the "-" represents the energy loss.

[0032] It can be seen from the above that the energy gained by the electron is related to the characteristics of the hollow cathode and the distribution of the electric field, and this part of the energy is related to the inherent physical characteristics of the thruster, and thus is difficult to control. The energy lost by the electron is related to the non-elastic collision of the electron and the collision between the electron and the wall. The non-elastic collision of the electron belongs to the microscopic behavior between particles, and it is difficult to control. However, the energy loss due to the collision between the electron and the wall satisfies the following relationship:

[0033] S wall = n e ε w (T e )ν w (T e )

[0034] The energy lost by a single electron due to the collision with the wall is:

[0035] ε w = 2T e +(1-σ)φ w

[0036] σ is the secondary electron emission coefficient, which is related to the characteristics of the material, and φ w is the wall sheath potential:

[0037]

[0038] m e and m i represent the densities of the electron and the ion, respectively, and ν w represents the frequency of the collision between the electron and the wall:

[0039]

[0040] R Δ is the width of the discharge channel of the Hall thruster.

[0041] It can be seen from the above several formulas that the geometric parameters (R Δ) and material properties (σ) can achieve the change of wall energy consumption. In the case of ensuring the structure size of the thruster unchanged, the adjustment of the energy consumption of the wall can only be achieved by changing the material properties. As can be seen from the above formula, increasing the secondary electron emission coefficient of the material can increase the energy consumption of the wall, thereby realizing the suppression of the low-frequency oscillation in the discharge process of the thruster. Therefore, in the embodiment of the present application, the principle of passive control is used to set two discharge channels with different material properties, and the energy dissipation caused by the secondary electron emission on the wall of the ionization zone discharge channel is used to realize the suppression of the low-frequency discharge oscillation of the Hall thruster. Compared with a single complete discharge channel, the discharge channel with two sections of different material properties is more likely to release the stress generated by the temperature change during the operation of the Hall thruster at the interface, and the sputtering resistance of the material can also prolong the service life of the Hall thruster.

[0042] Further, the first discharge channel 1 adopts an insulating material with a large secondary electron emission coefficient. The first discharge channel 1 adopts an insulating material with a large secondary electron emission coefficient, preferably Al2O3 ceramic, or a nano-diamond film plated on the surface of the material, mainly to increase the secondary electron emission coefficient of the material, increase the energy consumption in the process of electron collision with the wall of the discharge channel to produce secondary electrons, thereby achieving the effect of suppressing the low-frequency discharge oscillation of the Hall thruster, and because the energy of the secondary electrons emitted by the wall is reduced, the temperature of the anode of the Hall thruster will not be too high to cause the excitation conductor of the thruster to be damaged, which helps to reduce the temperature of the anode of the Hall thruster.

[0043] Further, the second discharge channel 2 adopts a sputtering-resistant and corrosion-resistant ceramic material. The second discharge channel 2 adopts a sputtering-resistant and corrosion-resistant ceramic material, generally pure NB ceramic or graphite, which mainly plays a protective role and can prolong the service life of the thruster.

[0044] Further, the sawteeth at the connection of the first discharge channel 1 and the second discharge channel 2 are uniformly distributed in the circumferential direction. The first discharge channel 1 and the second discharge channel 2 are composed of two cylindrical insulating non-magnetic materials with different material properties, each of which has a horizontal flat structure 4 port at one end and a sawtooth structure 3 port at the other end. The sawtooth structure 3 port of the first discharge channel 1 corresponds to the sawtooth structure 3 port of the second discharge channel 2, and the two are connected together through the sawtooth structure 3 port. The sawteeth at the connection are uniformly distributed in the circumferential direction of the cylinder. During the operation of the thruster, heat will cause thermal expansion of the structure, and the thermal stress generated by thermal expansion may cause the discharge channel to break. In order to avoid the breakage of the channel caused by the different thermal expansion coefficients of the two materials during the operation of the thruster, the sawtooth structure 3 connection method is adopted, and the connection of the two channels is welded by ceramic glue or other welding methods, so that the thermal stress is uniformly released at the connection port as much as possible, and the sealing of the whole channel is enhanced.

[0045] Further, the number of sawteeth 5 is 6-9, which are uniformly distributed in the angular direction, and the angular distance between adjacent two sawteeth 5 is 40°-60°. If n sawteeth are uniformly distributed in the angular direction, then the angular distance between adjacent two sawteeth 5 is 360° / n. In the embodiment of the present application, the number of sawteeth 5 is preferably 6-9, which are uniformly distributed in the circumferential direction, and the angular distance between adjacent two sawteeth 5 is 40°-60°. The number of sawteeth and the angular distance can be selected according to actual conditions.

[0046] Further, the angle of the sawtooth angle 6 is 60°. The sawteeth generally present an equilateral triangle, so the angle of the sawtooth angle 6, i.e. the vertex angle, is 60°, so that the stress released along each side of the sawtooth is as uniform as possible.

[0047] Further, the concave area 7 between adjacent two sawteeth of the first discharge channel 1 is a trapezoid, and the concave area 7 between adjacent two sawteeth of the second discharge channel 2 is a triangle, and the sawtooth structure 3 end face of the first discharge channel 1 and the second discharge channel 2 can completely match. The concave area 7 on one side is set as a trapezoid, and the concave area 7 on the other side is set as a triangle, mainly to increase the contact length of the sawtooth boundary, thereby reducing the thermal stress released per unit length.

[0048] Further, the length of the first discharge channel 1 is twice the length of the second discharge channel 2. The physical process mainly occurring in the first discharge channel 1 is the generation of ions, and the distribution area thereof in the axial direction is relatively large, while the physical process mainly occurring in the second discharge channel 2 is the acceleration of ions under the action of the axial electric field, and the area thereof is relatively small. The shorter the acceleration area in the discharge channel, the more conducive to reducing the sputtering corrosion of the radial diffusion of ions on the discharge channel at the outlet of the thruster, so as to increase the service life of the thruster. Therefore, in the embodiment of the present application, the length of the first discharge channel 1 is longer than the length of the second discharge channel 2, preferably twice the length of the second discharge channel 2.

[0049] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A discharge channel for suppressing low frequency discharge oscillations in a Hall Thruster, characterized by, The first discharge channel and the second discharge channel are arranged in the Hall thruster, wherein: The first discharge channel is arranged close to the anode of the Hall thruster, and has a flat structure at one end and a sawtooth structure at the other end; The second discharge channel is arranged close to the outlet of the Hall thruster, and has a flat structure at one end and a sawtooth structure at the other end; The sawtooth structure end of the first discharge channel corresponds to the sawtooth structure end of the second discharge channel, and the first discharge channel is assembled and connected with the second discharge channel through the sawtooth structure ends; The material properties of the first discharge channel are different from those of the second discharge channel; The first discharge channel adopts an insulating material with a large secondary electron emission coefficient; The second discharge channel adopts a ceramic material resistant to sputtering and corrosion; The length of the first discharge channel is 2 times the length of the second discharge channel.

2. The discharge channel to suppress low frequency discharge oscillation of a Hall Thruster according to claim 1, wherein, The sawteeth at the connection of the first discharge channel and the second discharge channel are uniformly distributed in the circumferential direction.

3. The discharge channel to suppress low frequency discharge oscillation of a Hall Thruster according to claim 2, wherein, The number of sawtooth tips is 6-9, and the sawtooth tips are uniformly distributed in the angular direction, and the angular distance between adjacent two sawtooth tips is 40°-60°.

4. The discharge channel to suppress low frequency discharge oscillation of a Hall Thruster according to claim 3, wherein, The angle of the sawtooth tip is 60°.

5. The discharge channel to suppress low frequency discharge oscillation of a Hall Thruster according to claim 4, wherein, The concave area between adjacent two sawteeth of the first discharge channel is a trapezoid, and the concave area between adjacent two sawteeth of the second discharge channel is a triangle.

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