A magnetic array structure suitable for micro microwave ion thrusters

Abstract

The present invention belongs to the field of space electric propulsion in aerospace propulsion technology, and relates to a magnetic array structure suitable for a micro-microwave ion thruster, which is composed of multiple Halbach-type permanent magnet strips; the multiple Halbach-type permanent magnet strips are arranged in a circular ring shape, and the magnetic field enhancement of each Halbach magnetic strip points to the center of the distribution circle where the ring is located. Under the condition of the same magnet volume, the magnetic field intensity of the magnetic mirror area can be enhanced, and efficient ionization can be maintained while ensuring electron confinement, thereby improving energy utilization efficiency; the present invention forms a magnetic field gradient through a specific arrangement of Halbach permanent magnet strips, and can use the magnetic field gradient drift to induce plasma migration toward the gate, increase the plasma density in front of the gate, and thus increase the current density of the thruster. The present invention maintains efficient confinement of electrons and maintains a high electron energy acquisition efficiency by rationally designing the magnetic field structure; guides the plasma to migrate toward the gate, and increases the extracted ion current.

Description

Technical Field

[0001] The present invention belongs to the field of space electric propulsion in aerospace propulsion technology, and in particular relates to a magnetic array structure suitable for a miniature microwave ion thruster. Background Art

[0002] In a microwave ion thruster, microwaves are fed into the discharge chamber via an antenna. Permanent magnets form magnetic mirrors to confine electrons, which are heated by electron cyclotron resonance. High-energy electrons ionize neutral gas to produce plasma, and a grid system accelerates and ejects the ions, generating thrust. The magnetic mirrors created by permanent magnets are the core of the microwave ion thruster's design and are essential for efficiently confining electrons and obtaining energy.

[0003] At present, there are two main magnetic field structure designs for microwave ion thrusters. One is the common built-in permanent magnet design ( Figure 1 ), generating magnetic mirror confinement from inside the discharge chamber; the other is the cusp permanent magnet design ( Figure 2 ), a cusped magnetic field is generated outside the discharge chamber. Figure 1 As for the magnetic field structure design shown, the internal placement of the permanent magnets increases the risk of plasma erosion or thermal demagnetization. As microwave power increases or plasma density rises, the permanent magnets are the first to fail due to demagnetization. Therefore, this magnetic field structure layout limits the maximum power of the micro-microwave ion thruster. Figure 2 This is the 1cm miniature microwave ion thruster of Harbin Institute of Technology. It uses three independent circular magnets to form a cusp magnetic field structure to generate a thrust of 1 to 100μN. The set power does not exceed 2W. This magnetic field structure forms a weak magnetic field area in the middle of the discharge chamber. The plasma will converge to the weak magnetic field area and cannot be well drawn out. Therefore, the discharge loss of this magnetic field structure is relatively large.

[0004] In summary, existing built-in permanent magnets are at risk of being eroded by plasma or demagnetized by heat, while the magnetic field structure of external permanent magnets causes electron confinement inside the discharge chamber, resulting in low current density and large discharge losses. Summary of the Invention

[0005] The purpose of the present invention is to provide a magnetic array structure suitable for a small-caliber miniature microwave ion thruster, which solves the problem of electron confinement and energy acquisition inside the discharge chamber by an external permanent magnet and solves the problem of low current density caused by the magnetic field structure of the external permanent magnet.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention discloses a magnetic array structure suitable for a micro microwave ion thruster, wherein the magnetic array structure is composed of a plurality of Halbach type permanent magnet strips;

[0008] Multiple Halbach permanent magnet strips are arranged in a circular ring shape, and the magnetic field enhancement of each Halbach magnet strip points to the center of the distribution circle where the ring is located.

[0009] Furthermore, each Halbach permanent magnet strip is made up of three-level magnets, with the same length and width but different heights.

[0010] Furthermore, the three-level magnet is divided into a first-level magnet, a second-level magnet, and a third-level magnet;

[0011] Arranged from the first pole to the third pole, the height of the three-pole magnets increases successively and the coercive force decreases successively.

[0012] Furthermore, the direction in which the first-stage magnet points toward the third-stage magnet is defined as the positive direction of the X-axis, and the direction in which the first-stage magnet moves away from the discharge chamber is defined as the positive direction of the Z-axis. Then, in the magnetic pole direction, the N-stages of the first-stage magnet are magnetized along the positive direction of the Z-axis, the N-stages of the second-stage magnet are magnetized along the positive direction of the X-axis, and the N-stages of the third-stage magnet are magnetized along the negative direction of the Z-axis.

[0013] Furthermore, the magnetic field distribution formed by a single Halbach permanent magnet strip is specifically as follows: the distribution of electron cyclotron resonance lines is higher in the middle area than that of ordinary bar magnets, which can help electrons in microwave ion thrusters better obtain microwave energy.

[0014] Furthermore, the coercive force of the tertiary magnet is in the range of 500 to 600 kA / m.

[0015] Furthermore, as the diameter of the microwave ion thruster increases, the number of Halbach permanent magnet strips required increases, and the coercive force of the magnet increases accordingly.

[0016] Furthermore, the magnetic array structure includes six Halbach type permanent magnet strips;

[0017] Six Halbach permanent magnetic strips are evenly distributed on the circumference at intervals of 60 degrees, and are named Halbach magnetic stripe No. 1, Halbach magnetic stripe No. 2, Halbach magnetic stripe No. 3, Halbach magnetic stripe No. 4, Halbach magnetic stripe No. 5, and Halbach magnetic stripe No. 6;

[0018] Among them, the magnetic field enhancement direction of Halbach stripe No. 1 points to the center of the distribution circle; Halbach stripe No. 2 rotates 60°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 3 rotates 120°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 4 rotates 180°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 5 rotates 240°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 6 rotates 300°, and the magnetic field enhancement direction points to the center of the distribution circle.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The present invention discloses a magnetic array structure suitable for a small-caliber miniature microwave ion thruster, which is composed of multiple Halbach-type permanent magnet strips; the multiple Halbach-type permanent magnet strips are arranged in a circular ring shape, and the magnetic field enhancement of each Halbach magnetic strip is directed toward the center of the distribution circle where the ring is located. Compared with the existing technology, under the condition of the same magnet volume, the magnetic field intensity of the magnetic mirror area can be enhanced, and efficient ionization can be maintained while ensuring electron confinement, thereby improving energy utilization efficiency; the present invention forms a magnetic field gradient through a specific circular Halbach permanent magnet strip arrangement method, and can use the magnetic field gradient drift to induce plasma migration toward the gate, increase the plasma density in front of the gate, and thus improve the current density of the thruster. The present invention maintains efficient confinement of electrons and maintains a high electron energy acquisition efficiency by rationally designing the magnetic field structure; guides the plasma to migrate toward the gate, and improves the extracted ion current.

[0021] Furthermore, the magnetic array structure consists of six specially designed Halbach magnetic strips, which can enhance the magnetic field in a specified direction, increase the height of the electron cyclotron resonance zone, and assist electrons in the microwave ion thruster to better obtain microwave energy.

[0022] Furthermore, the magnetic field structure in the discharge chamber forms a magnetic field gradient pointing to the gate, which promotes the plasma to drift toward the gate and can increase the thruster-induced current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the magnetic field topology of a 2 cm microwave ion thruster;

[0024] Figure 2 Schematic diagram of the magnetic field topology of a 1 cm tangential microwave ion thruster;

[0025] Figure 3 Schematic diagram of the structure of the magnetic array structure of the present invention;

[0026] Figure 4 Schematic diagram of the Halbach magnetic stripe structure, where the white arrow indicates the magnetization direction of the magnet;

[0027] Figure 5 The magnetic field distribution formed by the Halbach magnetic stripe, where the white solid line is the 0.15T contour line, the so-called electron cyclotron resonance region;

[0028] Figure 61 are three views of the magnetic array structure in the embodiment, wherein the direction indicated by the black arrow is the direction of magnetic field enhancement; FIG. a is a left view of the magnetic array structure, FIG. b is a front view of the magnetic array structure, and FIG. c is a top view of the magnetic array structure;

[0029] Figure 7 : The magnetic field distribution formed by the magnetic array structure in the embodiment, wherein the white solid line is the electron cyclotron resonance region, and the white arrow is the magnetic field gradient direction;

[0030] Figure 8 The ignition simulation results of the micro microwave ion thruster using the magnetic array structure in the embodiment are shown;

[0031] Figure 9 The simulation results are derived for the micro microwave ion thruster using the magnetic array structure in the embodiment. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following is a further detailed description with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0033] The components described and illustrated in the drawings and embodiments of the present invention may be arranged and designed in a variety of different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely represents a selected embodiment of the present invention. All other embodiments derived by those skilled in the art based on the drawings and embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to its process, element, method, article or apparatus.

[0035] In response to the technical problems faced in the miniaturization process of existing micro microwave ion thrusters, the present invention mainly aims to provide a magnetic array structure for a small-caliber micro microwave ion thruster using external permanent magnets. The magnetic array structure is suitable for microwave ion thrusters with a diameter not greater than 2.5 cm.

[0036] The present invention discloses a magnetic array structure suitable for a micro microwave ion thruster, which is composed of six Halbach magnetic strips. Figure 4As shown, it includes a first-level magnet, a second-level magnet and a third-level magnet. In terms of size, the length and width of the three-level magnets are the same, but the height is different, showing an increasing relationship. In terms of coercive force distribution, the coercive force of the first-level magnet is greater than the coercive force of the second-level magnet and the coercive force of the third-level magnet, and the coercive force range is between 500 and 600 KA / m. The direction of the first-level magnet pointing to the third-level magnet is defined as the positive direction of the X-axis, and the direction of the first-level magnet away from the discharge chamber (the same direction as the third-level magnet pointing to the discharge chamber) is defined as the positive direction of the Z-axis. In the direction of the magnetic pole, if Figure 4 As shown, the first level N magnets are magnetized along the positive direction of the Z axis, the second level N magnets are magnetized along the positive direction of the X axis, and the third level N magnets are magnetized along the negative direction of the Z axis. The magnetic field distribution formed by a single Halbach magnetic strip is as follows: Figure 5 As shown, the electron cyclotron resonance line distribution is higher in the middle than that of ordinary bar magnets, which can help electrons in microwave ion thrusters better obtain microwave energy.

[0037] The magnetic array structure includes six Halbach type permanent magnet strips arranged as follows Figure 6 As shown. Six Halbach magnets are evenly distributed on the circumference at intervals of 60 degrees. Among them, the magnetic field enhancement direction of Halbach stripe No. 1 points to the center of the distribution circle; Halbach stripe No. 2 rotates 60°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 3 rotates 120°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 4 rotates 180°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 5 rotates 240°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 6 rotates 300°, and the magnetic field enhancement direction points to the center of the distribution circle. The magnetic field distribution of the magnetic array composed of six Halbach stripes is shown as follows. Figure 7 As shown, the magnetic field distribution of the 0-180° section is as follows Figure 7 As shown in (a), the magnetic field distribution of the 30-210° section is as follows Figure 7 (b) is shown. Figure 7 It can be seen that the magnetic array composed of six specific Halbach magnetic strips forms a specifically oriented magnetic field gradient. This specifically oriented magnetic field gradient can regulate the drift direction of the plasma along the magnetic field gradient, causing the plasma to move according to the set magnetic field gradient.

[0038] The magnetic field structure of the present invention was used to simulate and verify a 1cm micro microwave ion thruster. The simulation example of the present invention was carried out according to the experimental process, with a gas flow rate of 0.3sccm and an input microwave power of 1W. Figure 8 This is the plasma distribution formed during the ignition stage. Figure 9The plasma distribution during the extraction phase with gate voltage applied (screen voltage 300V, acceleration gate voltage -50V). The change in plasma distribution shows that the plasma density upstream of the gate increases significantly after the gate voltage is applied, indicating that this magnetic field configuration can induce plasma migration and effectively increase the plasma density upstream of the gate. Simulation results show that under the same operating conditions, the thruster's extracted ion current is 0.47 mA and the current density is 0.60 mA / cm 3 , the current density is increased by 57.9% compared with the 2 cm aperture microwave ion thruster.

[0039] The magnetic array structure disclosed in the present invention utilizes the local magnetic field enhancement characteristics of the Halbach permanent magnet strip to enhance the magnetic field strength inside the discharge chamber. Under the same volume conditions, the electron cyclotron resonance region is larger than that of ordinary magnetic strips, thereby improving the electron energy acquisition efficiency.

[0040] The magnetic array structure designed in the present invention can enhance the magnetic field strength in the magnetic mirror area under the condition of equal magnet volume, maintain efficient ionization while ensuring electron confinement, and improve energy utilization efficiency; further, when the magnet is placed outside the magnet, the magnet will not face the problem of plasma erosion and the risk of thermal demagnetization is reduced; furthermore, the Halbach magnetic array structure of the present invention forms a specific magnetic field gradient direction, which can utilize the magnetic field gradient drift to induce plasma migration toward the gate, increase the plasma density in front of the gate, and thus increase the current density.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A magnetic array structure suitable for a micro microwave ion thruster, characterized in that: The magnetic array structure is composed of multiple Halbach type permanent magnet strips; Multiple Halbach permanent magnet strips are arranged in a circular ring shape, and the magnetic field enhancement of each Halbach magnetic strip points to the center of the distribution circle where the ring is located; Each Halbach permanent magnet strip is made up of three-level magnets, with the same length and width but different heights; The three-level magnet is divided into the first-level magnet, the second-level magnet, and the third-level magnet; Arranged from the first to the third pole, the height of the three-pole magnet increases successively, and the coercive force decreases successively; The direction of the primary magnet pointing to the third magnet is defined as the positive direction of the X axis, and the direction of the first magnet away from the discharge chamber is defined as the positive direction of the Z axis. Then, in the magnetic pole direction, the N-level of the first magnet is magnetized along the positive direction of the Z axis, the N-level of the second magnet is magnetized along the positive direction of the X axis, and the N-level of the third magnet is magnetized along the negative direction of the Z axis.

2. The magnetic array structure suitable for a micro microwave ion thruster according to claim 1, characterized in that: The magnetic field distribution formed by a single Halbach permanent magnet strip is specifically as follows: the electron cyclotron resonance line distribution is higher in the middle area than that of ordinary bar magnets, which can help electrons in microwave ion thrusters better obtain microwave energy.

3. The magnetic array structure suitable for a micro microwave ion thruster according to claim 1, characterized in that: The coercive force of the tertiary magnet ranges from 500 to 600 kA / m.

4. The magnetic array structure suitable for a micro microwave ion thruster according to claim 1, characterized in that: As the diameter of the microwave ion thruster increases, the number of Halbach permanent magnet strips required increases, and the coercive force of the magnet increases accordingly.

5. The magnetic array structure suitable for a micro microwave ion thruster according to claim 1, characterized in that: The magnetic array structure includes six Halbach type permanent magnet strips; Six Halbach permanent magnetic strips are evenly distributed on the circumference at intervals of 60 degrees, and are named Halbach magnetic stripe No. 1, Halbach magnetic stripe No. 2, Halbach magnetic stripe No. 3, Halbach magnetic stripe No. 4, Halbach magnetic stripe No. 5, and Halbach magnetic stripe No. 6; Among them, the magnetic field enhancement direction of Halbach stripe No. 1 points to the center of the distribution circle; Halbach stripe No. 2 rotates 60°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 3 rotates 120°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 4 rotates 180°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 5 rotates 240°, and the magnetic field enhancement direction points to the center of the distribution circle; Halbach stripe No. 6 rotates 300°, and the magnetic field enhancement direction points to the center of the distribution circle.

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