Arc-shaped plasma thruster

Abstract

The invention belongs to the technical field of plasma thrusters, and particularly relates to an arc-shaped plasma thruster which is composed of a plasma generator and a plasma accelerator. The plasma generator comprises a discharge chamber with a linear tubular structure, and an inductive coupling coil and an external coil for generating a magnetic field are wound outside the discharge chamber; the plasma accelerator comprises an accelerating chamber of an arc-shaped tubular structure, one end of a discharge chamber is fixedly connected with the middle of the accelerating chamber to form an epsilon-shaped through cavity, the other end of the discharge chamber is a working medium gas inlet, and the two ends of the accelerating chamber are two plasma outlets. Accelerating magnetic field coils and annular permanent magnets are sequentially and symmetrically arranged on the outer side of the accelerating chamber from the middle to the two ends, and the polarities of the annular permanent magnets located at the two ends of the accelerating chamber are opposite. Ablation between the plasma and the chamber wall can be effectively reduced, the energy loss of the plasma and the wall surface loss of the plasma are reduced, the ionization efficiency is remarkably improved, and the density of the generated plasma is higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of plasma thrusters, and particularly relates to an arc-shaped plasma thruster. Background Art

[0002] With the continuous development of space technology, the requirements for spacecraft propulsion systems are also increasing day by day. Although traditional chemical thrusters have played an important role in past space missions, they have limitations such as relatively low specific impulse. Specific impulse is an important indicator to measure the efficiency of a propulsion system. The higher the specific impulse, the greater the velocity increment that can be generated with the same propellant mass. Plasma thrusters utilize electrical energy to increase the jet velocity to a higher magnitude, can save a large amount of propellant, thereby effectively increasing the payload of the satellite and reducing the launch mass, and the electric propulsion system also has characteristics such as high control accuracy and high safety.

[0003] However, existing plasma thrusters still have some problems. For example, the ionization efficiency of existing plasma thrusters is not high enough, resulting in a relatively low density of the generated plasma, thus affecting the magnitude of the thrust; and some thrusters have technical problems in the acceleration and focusing of the plasma, making the energy of the plasma beam unable to be effectively converted into thrust; moreover, some existing plasma thrusters have complex structures, poor reliability and maintainability, increasing the usage cost and risk of the spacecraft.

[0004] Most existing electrodeless plasma thrusters are a cylindrical discharge chamber with an electromagnetic nozzle opened at one end, lacking magnetic confinement. Therefore, a large amount of plasma loss will occur in the side wall area of the thruster chamber, and wall ablation will also occur. Therefore, further improvement and perfection are urgently needed. Summary of the Invention

[0005] In view of the above situation, the present invention provides an arc-shaped plasma thruster, which can generate high-density and uniform plasma under low pressure, and can reduce plasma wall loss, effectively improving the efficiency of the thruster.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An arc-shaped plasma thruster is composed of two parts: a plasma generator and a plasma accelerator. The plasma generator is an inductively coupled plasma source (ICP), including a discharge chamber with a linear tubular structure. An inductively coupled coil is wound around the outer wall of the discharge chamber, and a coil with a rectangular cross-section for generating a magnetic field is wound outside the inductively coupled coil.

[0008] The plasma accelerator includes an acceleration chamber in the shape of an arc-shaped tubular structure. One end of the discharge chamber is fixedly connected to the middle of the acceleration chamber to form a through cavity in the shape of "∈". The other end of the discharge chamber is the working gas inlet, and both ends of the acceleration chamber are two plasma outlets.

[0009] On the outer side of the tube wall of the acceleration chamber, acceleration magnetic field coils and at least one set of annular permanent magnets are symmetrically arranged in sequence from the middle to both ends. The polarities of the annular permanent magnets arranged on the two arms of the acceleration chamber are opposite.

[0010] Further, both the discharge chamber and the acceleration chamber are high-temperature resistant glass tubes with a circular diameter, and the discharge chamber and the acceleration chamber are integrally formed and fixedly connected.

[0011] Further, the inductive coupling coil outside the discharge chamber, the coil for generating an external magnetic field, and the acceleration magnetic field coil outside the acceleration chamber all adopt multi-turn coils with a rectangular cross-section of the wire.

[0012] Further, the working gas introduced into the working gas inlet of the discharge chamber is argon. The microwave power is injected from the working gas inlet through a coaxial cable and enters the lumen of the discharge chamber through a needle antenna. The inductive coupling coil outside the discharge chamber is used to introduce an alternating radio frequency current, generate a time-varying magnetic field in the discharge chamber, and then be able to induce an alternating electric field, which can heat electrons, enable electrons to obtain energy, cause electrons to collide with the working gas in the discharge chamber, and ionize the working gas to generate plasma.

[0013] Further, two sets of annular permanent magnets are respectively arranged at both ends of the acceleration chamber. One set of annular permanent magnets at one end of the acceleration chamber are all N poles, and one set of annular permanent magnets at the other end of the acceleration chamber are all S poles, which can form closed magnetic force lines basically parallel to the arc-shaped tube wall of the acceleration chamber inside and outside the tube wall of the acceleration chamber.

[0014] The present invention also includes other components that enable its normal use, which are all conventional means in the art. In addition, the devices or components not defined in the present invention, such as the discharge chamber, the needle antenna, the inductive coupling coil, etc., all adopt the existing technologies in the art.

[0015] The beneficial effects of the present invention are as follows:

[0016] The structure of the arc-shaped plasma thruster is relatively simple, and its reliability and maintainability are good. Compared with most existing cylindrical plasma thrusters, due to the addition of magnetic force lines parallel to the wall of the acceleration chamber for restriction, it can effectively reduce the ablation between the plasma and the chamber wall, reduce the energy loss of the plasma and the wall loss of the plasma, significantly improve the ionization efficiency, generate a higher plasma density, and the efficiency of converting the plasma energy into thrust is also higher, capable of generating a stronger thrust and improving the thrust efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. 1 is a schematic structural diagram of the arc-shaped plasma thruster in the present invention.

[0018] Figure 2 FIG. 2 is a magnetic field line distribution diagram of the arc-shaped plasma thruster in the present invention.

[0019] In the figures: 1. Discharge chamber; 2. Inductive coupling coil; 3. Coil for generating external magnetic field; 4. Acceleration chamber; 5. Working gas inlet; 6. Plasma outlet; 7. Acceleration magnetic field coil; 8. Permanent magnet I; 9. Permanent magnet II. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all embodiments.

[0021] Embodiment

[0022] As shown in Figure 1-2 FIG. 1, an arc-shaped plasma thruster is composed of two parts: a plasma generator and a plasma accelerator.

[0023] The plasma generator is an inductively coupled plasma source (ICP), including a discharge chamber 1 with a linear tubular structure, and an inductive coupling coil 2 and a coil 3 for generating an external magnetic field are wound around the outer wall of the discharge chamber.

[0024] The plasma accelerator includes an acceleration chamber 4 with an arc-shaped tubular structure. One end of the discharge chamber is fixedly connected to the middle of the acceleration chamber to form a through cavity in the shape of "∈". The other end of the discharge chamber is a working gas inlet 5, and both ends of the acceleration chamber are two plasma outlets 6.

[0025] On the outer wall of the acceleration chamber, an acceleration magnetic field coil 7 and at least one group of annular permanent magnets are symmetrically arranged in sequence from the middle to both ends. The polarities of the annular permanent magnets arranged on the two arms of the acceleration chamber are opposite.

[0026] Two groups of annular permanent magnets are respectively arranged at both ends of the acceleration chamber, namely permanent magnet I 8 and permanent magnet II 9. The permanent magnet II near the plasma outlet is larger than the permanent magnet I near the middle part of the acceleration chamber, which can generate a stronger magnetic field. And a group of annular permanent magnets at one end of the acceleration chamber are all N poles, and a group of annular permanent magnets at the other end of the acceleration chamber are all S poles, which can form closed magnetic field lines that are basically parallel to the arc-shaped tube wall of the acceleration chamber inside and outside the tube wall of the acceleration chamber, effectively reducing plasma ablation between the plasma and the chamber wall, reducing the energy loss of the plasma and reducing the wall loss of the plasma.

[0027] Both the discharge chamber and the acceleration chamber are high-temperature resistant glass tubes with a circular diameter, a radian of 120°, and are integrally formed and fixedly connected between the discharge chamber and the acceleration chamber. The inductively coupled coil outside the discharge chamber, the coil for generating an external magnetic field, and the acceleration magnetic field coil outside the acceleration chamber all use multi-turn coils with a rectangular cross-section of the wire. The rectangular coil can pass a larger current, and the generated magnetic field is more uniform, capable of generating a higher density of plasma. Three coils with a rectangular cross-section are arranged outside the discharge chamber and a direct current is passed through them to generate a constant magnetic field, and its overall structure is a magnetically enhanced inductively coupled plasma source (ICP).

[0028] The working gas introduced through the working gas inlet of the discharge chamber is argon; the microwave power of 2.45 GHz is injected from the working gas inlet through a coaxial cable and enters the inner cavity of the discharge chamber through a needle antenna; the coils outside the discharge chamber are divided into two groups. The inductively coupled coil outside the discharge chamber is used to pass an alternating radio frequency current to generate a time-varying magnetic field in the discharge chamber. According to Faraday's law, this magnetic field will induce an alternating electric field, which will heat the electrons, enable the electrons to obtain energy, cause the electrons to collide with the working gas in the discharge chamber, ionize the working gas to generate plasma, and the magnetic field intensity is matched with the microwave frequency, aiming to effectively couple power to the plasma.

[0029] The coil for generating an external magnetic field is used to generate a uniform magnetic field in the middle of the ionization chamber, form closed magnetic force lines between the two arms of the arc-shaped acceleration chamber, and the annular permanent magnet at the plasma outlet strengthens the magnetic field at the outlet, which is beneficial to the confinement of the plasma near the outlet. The thruster electrons are completely magnetized, and the ions will also pass through the closed magnetic force lines of the magnetic field to generate a net magnetic thrust, thereby generating a greater thrust. At the same time, the inductively coupled plasma source with an external magnetic field used in this thruster will generate a right-handed polarized wave in the plasma, which can increase the plasma density by an order of magnitude under low pressure and effectively improve the uniformity and heating efficiency of the plasma.

[0030] The fluid model of this arc-shaped plasma thruster is as follows:

[0031] At the place where two magnetic force lines are connected, the plasma flux passes through the applied field approximately perpendicularly. Introduce Cartesian vector coordinates {1 x ,1 y ,1 z}, define 1 b =B / B and 1 ⊥ =1 y ×1 b , and define the magnetic vector reference {1 b ,1 ⊥ ,1 y}.

[0032] The stream function ψ of the planar magnetic field B = ψ Ba (z, x), satisfying

[0033]

[0034] The magnetic field lines are represented by ψ B Under the assumption of full electron magnetization, the electron stream function lines coincide with the magnetic field lines, and the ion stream function lines may not coincide with the magnetic field lines. Note:

[0035]

[0036] The magnetic field B a is in the 1 y direction and lies in the z = 0 plane. The magnetic field intensity and stream function for a single current-carrying wire with current I are respectively:

[0037]

[0038] where ρ and θ are polar coordinates, and 1 θ is the polar coordinate direction.

[0039] The fluid equations for electrons and ions are:

[0040]

[0041]

[0042]

[0043]

[0044] At the same time, the quasi-neutrality condition is supplemented:

[0045] n = n e = n i (8)

[0046] The electron fluid velocity can be written as:

[0047]

[0048] The condition satisfied by electrons is T e = n γ-1 , under this condition, equation (5) can be written as:

[0049]

[0050] The electron energy H e is conserved along the magnetic field lines,

[0051]

[0052] where u ye can be obtained from calculation as follows:

[0053]

[0054] In the steady state, the equations are fewer as:

[0055]

[0056] The electric potential is a function of the electron density and the magnetic current function:

[0057]

[0058] Substituting Equation (14) into Equations (7) and (12) gives:

[0059]

[0060]

[0061] The hydrodynamic equations describing the thruster model are obtained.

[0062] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Without departing from the scope and spirit of the illustrated embodiments, many modifications and changes are obvious to those of ordinary skill in the art. Any technical deformation made within the spirit and principle of the present invention falls within the protection scope of the present invention.

Claims

1. An arc plasma thruster, characterized in that: The invention consists of two parts: a plasma generator and a plasma accelerator; the plasma generator is an inductively coupled plasma source, comprising a discharge chamber of a straight tubular structure, the outer side of the tube wall of the discharge chamber is wound with an inductively coupled coil and an external coil for generating a magnetic field; the plasma accelerator comprises an acceleration chamber of an arc-shaped tubular structure, one end of the discharge chamber is fixedly connected to the middle of the acceleration chamber to form a through cavity in the shape of "∈", the other end of the discharge chamber is a working gas inlet, the two ends of the acceleration chamber are two plasma outlets, the outer side of the tube wall of the acceleration chamber is symmetrically arranged with an accelerating magnetic field coil and an annular permanent magnet in sequence from the middle to the two ends, and the polarities of the annular permanent magnets located at the two ends of the acceleration chamber are opposite.

2. An arc plasma thruster according to claim 1, characterized in that: The discharge chamber and the acceleration chamber are both high-temperature resistant glass tubes with circular diameters, and the discharge chamber and the acceleration chamber are integrally formed and fixedly connected.

3. An arc plasma thruster according to claim 1, characterized in that: The inductive coupling coil and the external magnetic field generating coil outside the discharge chamber, as well as the accelerating magnetic field coil outside the accelerating chamber are all multi-turn coils with rectangular conductor cross-sections, and the external magnetic field generating coil and the inductive coupling coil are placed at intervals.

4. An arc plasma thruster according to claim 1, characterized in that: The working gas introduced into the working gas inlet of the discharge chamber is argon gas; the inductive coupling coil outside the discharge chamber is used to pass an alternating radio frequency current to ionize the working gas and generate plasma.

5. The arc plasma thruster according to claim 1, characterized in that: Two groups of annular permanent magnets are respectively arranged at the two ends of the acceleration chamber, and a group of annular permanent magnets located at one end of the acceleration chamber are all N poles, and a group of annular permanent magnets located at the other end of the acceleration chamber are all S poles, which can form closed magnetic lines of force basically parallel to the arc-shaped tube wall of the acceleration chamber inside and outside the tube wall of the acceleration chamber.

6. An arc plasma thruster according to any one of claims 1 to 5, characterized in that: For arc plasma thrusters, a magnetohydrodynamic equation model including magnetic field is established. Due to the change in the topology of the magnetic field, the internal magnetic lines of force of the thruster and the magnetic lines of force of the thruster are connected closed magnetic lines of force. The electrons are magnetized, but the ions are not magnetized. By establishing a collisionless, quasi-neutral, two-fluid model, the plasma density, ion velocity, electrostatic potential, plasma current, and magnetic thrust can be calculated.

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