CN105736272A - Variable cross-section channel structure of low-power cusped magnetic field plasma thruster - Google Patents

Abstract

The invention relates to a variable cross-section channel structure of a low-power cusp magnetic field plasma thruster, which relates to the field of cusp magnetic field plasma thrusters. The present invention aims to solve the problem that under the low power working condition of the existing tangential magnetic field plasma thruster, the insufficient ionization leads to performance degradation when the current density is low, and the performance degradation is also caused by the intensified interaction between the plasma and the wall surface when the current density is high. The problem. The channel is constructed by a ceramic channel and a permanent magnet. The ceramic channel is a one-piece structure, which is divided into two sections: the upstream part of the channel and the downstream part of the channel. The channel structure gradually expands from the upstream part of the channel to the downstream part of the channel. The outer wall of the ceramic channel is used for To achieve clearance fit with the inner wall of the permanent magnet. This structure increases the atomic density and ionization rate in the upstream ionization area, and at the same time reduces the interaction with the channel wall during the accelerated ejection of ions generated by ionization, prolonging the life of the thruster. It is used in the low power working condition of the tangent magnetic field plasma thruster.

Description

A variable cross-section channel structure of a low-power tangent magnetic field plasma thruster

technical field

The invention relates to a variable-section channel structure of a low-power cusp magnetic field plasma thruster. It belongs to the field of tangential magnetic field plasma thrusters.

Background technique

Electric propulsion is gradually favored by the aerospace industry due to its advantages such as high specific impulse, long life, compact structure, small size and light pollution. have an important role. The cusped magnetic field plasma thruster is a new type of electric propulsion concept emerging internationally. Different from the traditional Hall thruster, the cusped magnetic field plasma thruster relies on multi-stage permanent magnets to form a cusped magnetic field. Among them, the adjacent The polarities of the two permanent magnets are opposite. The anode is placed upstream of the ceramic discharge channel, and the hollow cathode is placed at the outlet. After the working fluid enters the channel through the upstream gas distributor, it collides with the electrons released by the cathode and ionizes. The ejection is accelerated downward to form a thrust, and the electrons finally reach the anode through collision conduction. This design feature makes the tangential magnetic field thruster have the advantages of simple structure, wide thrust range, high specific impulse and long life, and thus has gained more and more research institutions at home and abroad.

With the rapid development of small satellite technology, various small satellite propulsion equipment is emerging in an endless stream. Both experiments and theory have confirmed that the tangential magnetic field thruster can realize the stepless adjustment of thrust from micronewtons to newtons, which makes it have great application value in the field of small satellite propulsion, such as microgravity compensation, atmospheric drag compensation, Attitude adjustment, etc., which requires the tangent magnetic field thruster to be able to realize the real-time change of thrust under low power. An effective measure for the tangential magnetic field thruster to adjust the thrust is to adjust the anode flow rate. However, when the flow rate of the working fluid changes, The change of flux density makes the change of thruster performance more significant. At low flow rate or low flux density, the sufficient ionization criterion is not satisfied, the ionization in the channel is insufficient, and the performance of the thruster is low; while at high flow rate and high flux density, the degree of interaction between the plasma and the wall surface is intensified, which also causes performance Decline.

Contents of the invention

The present invention aims to solve the problem that under the low power working condition of the existing tangential magnetic field plasma thruster, the insufficient ionization leads to performance degradation when the current density is low, and the performance degradation is also caused by the intensified interaction between the plasma and the wall surface when the current density is high. The problem. A variable-section channel structure of a low-power tangent magnetic field plasma thruster is now provided.

A variable-section channel structure of a low-power tangent magnetic field plasma thruster, which is constructed of ceramic channels and permanent magnets,

The ceramic channel is a one-piece structure, which is divided into two sections: the upstream part of the channel and the downstream part of the channel.

The one-piece structure is a channel structure gradually expanding from the upstream part of the channel to the downstream part of the channel. The outer wall of the ceramic channel is used to achieve clearance fit with the inner wall of the permanent magnet.

The expansion angle range of the upstream part of the channel is 0° to 20°, and the expansion angle range of the downstream part of the channel is 10° to 30°.

The beneficial effects of the present invention are as follows: the channel structure constructed by the ceramic channel and the permanent magnet is designed with a variable cross-section, so that the ceramic channel matches the configuration of the magnetic field, wherein the gap between the outer wall surface of the ceramic channel and the inner wall surface of the permanent magnet is always kept at 0.5 mm, to ensure the effective confinement of the electrons by the magnetic mirror effect, and the existence of the gap can reduce the heat transfer coefficient between the channel wall and the permanent magnet, and prevent the high-temperature ceramic channel from transferring heat to the permanent magnet through heat conduction. Both the ceramic channel and the magnetic field adopt a gradually expanding shape, that is, the cross-sectional area of the ceramic gradually increases from upstream to downstream. Among them, the expansion angle of the upstream part of the channel is small, while the expansion angle of the downstream part of the channel is slightly larger. The magnetic field configuration and ceramic channel structure formed by the permanent magnet are as follows: First, in terms of the magnetic field configuration design, it is composed of a three-stage shirt-cobalt 2:17 permanent magnet. The maximum temperature resistance of this permanent magnet is 350 degrees Celsius, which can ensure that the thruster works There will be no demagnetization due to excessive temperature. The permanent magnets are axially magnetized, and the polarities are opposite between the two. The export-grade permanent magnets have the longest length. The length ratio of the three-stage permanent magnets that can be referred to is 16:16:56. Through this magnetic field configuration design, the magnetic interface at the exit of the channel can be approximately perpendicular to the axis of the channel, which can reduce the divergence angle of the plume according to the thermalization potential theory. Through this gradually expanding variable cross-section design, the magnetic field intensity can be distributed reasonably. A strong upstream magnetic field can increase the ionization rate and restrain the plasma from contacting the wall. A weak magnetic field at the channel exit and plume area can reduce the ignition voltage and reduce the Small plume divergence angle. Secondly, in terms of ceramic channel design, the axial length of the small expansion angle part upstream of the channel is the same as the total length of the two upstream stages of the permanent magnet, which ensures that the upstream ionization space is long enough, and the large expansion angle part of the downstream channel corresponds to a section of the permanent magnet outlet. Therefore, the interface between the two different expansion angle parts of the channel corresponds to the second magnetic tip position of the magnetic field configuration, which can reduce the intersection of the inner wall surface of the channel and the magnetic field lines.

The cross-sectional area of the upstream part of the channel is small, which can increase the density of neutral gas, and the permanent magnet here is thicker and the magnetic field strength is higher, which can effectively restrain electrons to achieve sufficient ionization of neutral gas, so the overall ionization rate of the thruster can be improved . In the downstream of the channel, the cross-sectional area is larger, and the ions generated after the electrons ionize the neutral gas are accelerated and ejected under the action of the axial electric field, which can reduce the possibility of collision with the wall of the channel, thereby reducing the ion pair. Corrosion of the wall surface prolongs the life of the thruster and reduces the temperature of the wall surface to ensure a reliable working temperature of the permanent magnet. In addition, the gradual decrease of the magnetic field intensity inside the channel from the upstream to the exit can also gradually reduce the degree of ion magnetization, further reducing the ion radial velocity component caused by the magnetic field. After the exit magnetic field is weakened, the magnetic field intensity in the plume area can also be reduced. The weaker the magnetic field in the plume area, the smaller the divergence angle of the plume, which can reduce the impact of the thruster on the solar panels. At the same time, the weakened magnetic field in the plume region is more conducive to the smooth entry of electrons into the channel, which can reduce the ignition voltage, prevent the formation of additional ionization regions at the exit, effectively guide the ionization region to move to the upstream high neutral gas density region, and realize the effective separation of the ionization region and the acceleration region. Improve the overall acceleration efficiency of thrusters.

Description of drawings

Fig. 1 is the overall structural diagram of a channel structure of a low-power tangential magnetic field plasma thruster;

Fig. 2 is a schematic structural view of the variable cross-section ceramic channel described in Embodiment 1;

Fig. 3 is the configuration diagram of the variable cross-section magnetic field formed by the permanent magnet described in Embodiment 1;

Fig. 4 is an assembly diagram of a variable cross-section channel tangent magnetic field plasma thruster;

Fig. 5 is a schematic diagram of the working principle of the tangent magnetic field plasma thruster.

detailed description

Specific Embodiment 1: Referring to Fig. 1 to Fig. 3, this embodiment will be described in detail. A variable cross-section channel structure of a low-power tangent magnetic field plasma thruster described in this embodiment, the channel is constructed by a ceramic channel and a permanent magnet.

The ceramic channel is a one-piece structure, which is divided into two sections: the upstream part of the channel and the downstream part of the channel.

The one-piece structure is a channel structure gradually expanding from the upstream part of the channel to the downstream part of the channel. The outer wall of the ceramic channel is used to achieve clearance fit with the inner wall of the permanent magnet.

The expansion angle range of the upstream part of the channel is 0° to 20°, and the expansion angle range of the downstream part of the channel is 10° to 30°.

In this embodiment, as shown in Figure 1 and Figure 2, both the ceramic channel and the permanent magnet have a gradually expanding shape. D expansion angle is larger.

Specific embodiment 2: This embodiment is described in detail with reference to Fig. 4. This embodiment is a further description of the variable cross-section channel structure of a low-power tangent magnetic field plasma thruster described in Embodiment 1. In this embodiment , the permanent magnets include a first-level permanent magnet 1, a second-level permanent magnet 2 and a third-level permanent magnet 3, and the first-level permanent magnet 1, the second-level permanent magnet 2 and the third-level permanent magnet 3 are sequentially arranged from the downstream to the upstream of the channel; the three permanent magnets The magnets are all magnetized along the axial direction, and the magnetization directions of two adjacent permanent magnets are opposite;

The inner wall surface of the first-stage permanent magnet 1 and the outer wall surface of the downstream part of the channel realize clearance fit, and the length of the first-stage permanent magnet 1 is the same as the axial length of the downstream part of the channel,

The inner wall surface of the second-stage permanent magnet 2 and the inner wall surface of the third-stage permanent magnet 3 realize clearance fit with the outer wall surface of the upstream part of the passage, and the sum of the lengths of the second-stage permanent magnet 2 and the third-stage permanent magnet 3 is equal to the axial length of the upstream part of the passage same,

The first-level permanent magnet 1 and the second-level permanent magnet 2 are connected through the first magnetizer 7-1, and the second-level permanent magnet 2 and the third-level permanent magnet 3 are connected through the second magnetizer 7-2.

In this embodiment, the variable cross-section magnetic field configuration is composed of three-stage rare earth permanent magnet cobalt 2:17 permanent magnets, 2:17 is the type of rare earth permanent magnet cobalt, and the polarities of the two adjacent permanent magnets are opposite. Among the three-stage permanent magnets, the export-grade permanent magnet 1 is the longest, and the magnet guide 7 is between the two permanent magnets to increase the tip area and reduce the repulsive force between the permanent magnets, which is convenient for installation.

Embodiment 3: This embodiment is a further description of the variable cross-section channel structure of a low-power tangent magnetic field plasma thruster described in Embodiment 1. In this embodiment, the material of the ceramic channel is boron nitride Ceramic, the wall thickness is 2mm, the minimum inner diameter of the upstream part of the channel is 15mm, the inner diameter of the outlet is 47mm, the expansion angle of the upstream part of the channel is 13°, and the expansion angle of the downstream part of the channel is 22°.

In this embodiment, the axial length of the upstream part U of the channel is the same as the total length of the second-stage permanent magnet 2 and the third-stage permanent magnet 3, and the axial length of the downstream part D of the channel is the same as the length of the first-stage permanent magnet 1, that is, the two expansion angles of the channel The interface corresponds to the second magnetic tip of the magnetic field configuration. The wall thickness of the ceramic channel is uniform, both 2mm. If the wall thickness is too thin, the life of the thruster will be reduced, and if the wall thickness is too thick, the effect of the magnetic mirror effect will also be reduced, and the interaction between the plasma and the wall will be aggravated.

Embodiment 4: This embodiment is a further description of the variable-section channel structure of a low-power tangent magnetic field plasma thruster described in Embodiment 1. In this embodiment, the permanent magnet is made of rare earth permanent magnet cobalt 2:17 structure, the minimum inner diameter of the permanent magnet is 20mm, the maximum inner diameter is 52mm, the maximum outer diameter of the permanent magnet is 62mm, and the strongest magnetic induction intensity generated by the permanent magnet in the ceramic channel is 0.5T.

In this embodiment, the radial size of the permanent magnet is determined according to the actual rated operating conditions of the thruster. For a 500W low-power cusp thruster, the minimum inner diameter of the upstream of the permanent magnet is 20mm, and the minimum inner diameter of the outlet is 52mm. The outer diameter of the permanent magnet can be specifically designed, and it is not necessarily the same. It should try to make the outlet magnetic interface AB perpendicular to the channel axis, and the strongest magnetic field strength at the tip can reach 0.5T. The maximum outer diameter of the permanent magnet in Fig. 3 is 62mm.

Embodiment 5: This embodiment is a further description of the variable cross-section channel structure of a low-power tangent magnetic field plasma thruster described in Embodiment 1. In this embodiment, the magnetic interface at the outlet of the channel is perpendicular to channel axis.

In this embodiment, the axial length of the upstream small expansion angle part of the channel is the same as the total length of the upstream two-stage permanent magnets, and the axial length of the downstream large expansion angle part is the same as the downstream one-stage permanent magnet length, that is, the intersection of the two expansion angles of the ceramic channel The interface is located at the second magnetic tip of the magnetic field potential.

Embodiment 6: This embodiment is a further description of the variable cross-section channel structure of a low-power tangent magnetic field plasma thruster described in Embodiment 1. In this embodiment, the outer wall surface of the ceramic channel and the permanent magnet The gap formed after the inner wall surface is matched is 0.5mm.

Referring to Fig. 4, the assembly process of the variable cross-section channel cusp magnetic field plasma thruster is explained. When assembling the thruster, firstly, the first-level permanent magnet 1, the second-level permanent magnet 2 and the third-level permanent magnet are sequentially loaded into the casing 4 3 and the corresponding guide magnet. Since the polarities of adjacent permanent magnets in the three-stage permanent magnets are opposite, there is a great repulsive force between the permanent magnets, so it is necessary to use M4 bolts to tighten the thruster end cover 5 and the housing 4 immediately after the permanent magnets are installed. Connect to hold permanent magnets. Then the variable cross-section ceramic channel 8 is installed inside the permanent magnet, and the bottom part of the ceramic channel 8 is embedded in the end cover 5 to fix the ceramic channel. Finally, the anode 6 is inserted into the interior of the ceramic channel 8, the conduit of the anode 6 is tapped with threads, and the anode 6 is fixed with the ceramic channel 8 and the thruster end cover 5 through nuts, thereby completing the assembly of the entire variable-section channel reciprocating magnetic field thruster .

As shown in Figure 5, the working process and principle of the variable cross-section channel tangential magnetic field plasma thruster:

The hollow cathode 9 is arranged above the outlet of the thruster channel, and the hollow cathode 9 is provided with a xenon gas flow of 3 sccm. After being heated by an 8A current for 5 minutes, it starts to work normally and releases electrons. At the same time, a 5-10 sccm xenon gas flow is provided to the anode 6. After the magnetic field lines in the plume area are captured, they move spirally along the magnetic field lines and enter into the channel. After entering the channel, the electrons are constrained by the magnetic mirror effect, and it is difficult to reach the wall. The electrons will continue to reciprocate and spiral along the magnetic force lines until they collide with neutral gas atoms. After destroying the original balance, the electrons conduct to the anode. Finally, it reaches the anode to realize the whole discharge process. The ions produced by ionization are much larger than electrons in mass, so they are almost not magnetized, and will not be bound by magnetic force lines, so they can be ejected under the acceleration of the axial electric field to form thrust.

Design principle of variable cross-section channel:

The ionization process of the tangential magnetic field plasma thruster mainly occurs in the upstream part of the channel, as shown in the ellipse area in Figure 5, but the main potential drop is concentrated near the magnetic interface AB at the channel exit, which makes the ions generated by upstream ionization mainly in the channel Export completion accelerated. The separation of the ionization region and the acceleration region makes the ions have a high acceleration efficiency, and the energy of the electric field is almost completely used to accelerate the ions. However, when the ions are produced in the upstream part of the channel and move towards the channel outlet, due to the weak electric field inside the channel, it is difficult for the ions to be completely ejected in the axial direction, which makes the ions likely to collide with the wall surface during the movement towards the exit, resulting in energy loss. In addition, a prominent problem of low-power cutting magnetic field plasma thrusters is insufficient ionization rate. Neutral gas density is a major factor affecting the ionization rate. In order to increase the ionization rate, it is necessary to increase the neutral gas density near the ionization region. Therefore, the present invention proposes a gradually expanding channel with variable cross-section. This variable cross-section channel reduces the cross-sectional area of the channel in the upstream part of the channel, increasing the neutral gas density in the upstream ionization zone, and at the same time increases the cross-sectional area in the downstream, reducing the probability of collision with the wall during the ion ejection process , so as to achieve the beneficial effect of killing two birds with one stone.

Claims (6)

1. A variable cross-section channel structure of a low-power reciprocated magnetic field plasma thruster, characterized in that the channel is constructed of ceramic channels and permanent magnets, The ceramic channel is a one-piece structure, which is divided into two sections: the upstream part of the channel and the downstream part of the channel. The one-piece structure is a channel structure gradually expanding from the upstream part of the channel to the downstream part of the channel. The outer wall of the ceramic channel is used to achieve clearance fit with the inner wall of the permanent magnet. The expansion angle range of the upstream part of the channel is 0° to 20°, and the expansion angle range of the downstream part of the channel is 10° to 30°. 2. The variable cross-section channel structure of a low-power cusp magnetic field plasma thruster according to claim 1, wherein the permanent magnets include a primary permanent magnet (1), a secondary permanent magnet (2) and three The first-level permanent magnet (3), the first-level permanent magnet (1), the second-level permanent magnet (2) and the third-level permanent magnet (3) are arranged sequentially from the downstream to the upstream of the channel; the three permanent magnets are all magnetized along the axial direction, and The magnetization directions of two adjacent permanent magnets are opposite; The inner wall surface of the first-stage permanent magnet (1) and the outer wall surface of the downstream part of the channel realize clearance fit, and the length of the first-stage permanent magnet (1) is the same as the axial length of the downstream part of the channel, The inner wall surface of the second-stage permanent magnet (2) and the inner wall surface of the third-stage permanent magnet (3) realize clearance fit with the outer wall surface of the upstream part of the channel, and the sum of the lengths of the second-stage permanent magnet (2) and the third-stage permanent magnet (3) is the same as the axial length of the upstream part of the channel, The first-level permanent magnet (1) and the second-level permanent magnet (2) are connected through the first magnetizer (7-1), and the second-level permanent magnet (2) and the third-level permanent magnet (3) are connected through the second magnetizer (7-1). 2) connect. 3. the variable cross-section channel structure of a kind of low-power tangential magnetic field plasma thruster according to claim 1, is characterized in that, the material of ceramic channel is boron nitride ceramics, and wall thickness is 2mm, and the channel upstream part The minimum inner diameter is 15mm, the outlet inner diameter is 47mm, the expansion angle of the upstream part of the channel is 13°, and the expansion angle of the downstream part of the channel is 22°. 4. The variable cross-section channel structure of a low-power tangential magnetic field plasma thruster according to claim 1, wherein the permanent magnet is made of rare earth permanent magnet cobalt 2:17, and the minimum inner diameter of the permanent magnet is 20mm. The maximum inner diameter is 52mm, the maximum outer diameter of the permanent magnet is 62mm, and the strongest magnetic induction intensity generated by the permanent magnet in the ceramic channel is 0.5T. 5 . The variable cross-section channel structure of a low-power tangent magnetic field plasma thruster according to claim 1 , wherein the magnetic interface at the channel outlet is perpendicular to the axis of the channel. 6. The variable cross-section channel structure of a low-power tangent magnetic field plasma thruster according to claim 1, wherein the gap formed after the outer wall of the ceramic channel cooperates with the inner wall of the permanent magnet is 0.5 mm.