An inductively coupled two-stage plasma thruster

Abstract

The present invention relates to the field of spacecraft propulsion technology, and discloses an inductively coupled two-stage plasma thruster, comprising an inner wall and an alumina outer wall, wherein the inner wall is a cylindrical Pyrex heat-resistant glass tube with one end closed, and a radio frequency source is arranged inside the inner wall, and the radio frequency source comprises a bare copper wire coil, a ferrite column, two ferrite disks and two permanent magnet rings; the front part of the outer wall is a cylindrical channel, and the rear part is a conical tube with a small front and a large rear; an anode is arranged inside the rear part of the outer wall, and two axially symmetrical permanent magnet blocks are arranged on the outer side of the front part of the outer wall and the tail of the outer side of the rear part of the outer wall respectively; a cathode is arranged on the front side of the outer wall; and the frequency of the radio frequency source is 4MHZ. The beneficial effects of the present application are: high thrust or high specific impulse operation can be achieved according to demand.

Description

Technical Field

[0001] The invention relates to the field of spacecraft propulsion technology, and in particular to an inductively coupled two-stage plasma thruster. Background Art

[0002] With the development of aerospace technology, the demand for spacecraft propulsion systems in space missions has become more diversified. Deep space exploration, orbit transfer and position keeping of communication satellites and other tasks have high specific impulse, high efficiency and long life requirements for space propulsion technology. Traditional chemical propulsion is limited by chemical energy and wall temperature, and has a low specific impulse. Electric propulsion uses electric energy to increase the jet speed to a higher level, which can save a lot of propellant, thereby effectively increasing the payload of the satellite, reducing the launch mass, and achieving the purpose of extending life and reducing costs. In addition, the electric propulsion system also has the characteristics of high control accuracy and high safety. It can meet the requirements of different tasks such as spacecraft attitude control, position keeping, drag compensation, orbit transfer, deep space exploration, etc., so it has a wide range of applications.

[0003] In a traditional steady-state plasma thruster, an axial electric field is formed between the anode and cathode, and a radial magnetic field is formed between the inner and outer magnetic poles. The electrons emitted by the cathode drift toward the discharge chamber under the joint action of the orthogonal axial electric field and radial magnetic field. The neutral propellant atoms coming out of the anode collide with it and are ionized. They are ejected at high speed under the action of the axial electric field to generate thrust. The electric field of this thruster is used for the ionization and acceleration of the working fluid, so the thrust and specific impulse are not separated from each other. For specific space flight missions and specific power, this type of plasma thruster can only achieve high thrust or high specific impulse. It cannot meet the aerospace needs of multi-attitude adjustment missions. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an inductively coupled two-stage plasma thruster.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] An inductively coupled two-stage plasma thruster, comprising an inner wall, an outer wall and a propellant delivery pipe, wherein the inner wall is a cylindrical Pyrex heat-resistant glass tube with one end closed, a radio frequency source is arranged in the inner cavity of the inner wall, and the radio frequency source comprises a coil, a cylindrical hollow insulating carrier, a ferrite cylinder, two ferrite disks and two permanent magnet rings, wherein the coil is wound on the insulating carrier, the ferrite cylinder is coaxially arranged at the center of the insulating carrier, the two ferrite disks are respectively fixedly arranged at the two ends of the ferrite cylinder, and the two permanent magnet rings are respectively fixedly arranged on the circumferential edge of one ferrite disk, and the magnetic poles of the two permanent magnet rings are both distributed transversely and the magnetic fields of the two permanent magnet rings are in opposite directions;

[0007] The outer wall is arranged on the outside of the inner wall and is coaxial with the inner wall. The front part of the outer wall is a cylindrical channel, and the rear part is a conical cylinder with a smaller front and a larger rear. The rear end face of the outer wall is fixedly connected to the rear end of the inner wall through a closed end face; an anode is arranged inside the rear part of the outer wall, and two axially symmetrical permanent magnet blocks are respectively arranged on the outside of the front part of the outer wall and the tail of the outside of the rear part of the outer wall, and the two permanent magnet blocks on the same side are fixed by an L-shaped soft iron sheet; the two permanent magnet blocks located at the front have the same magnetic field direction as the samarium cobalt magnet ring located at the front end of the ferrite cylinder, and the two permanent magnet blocks located at the front and rear have the same magnetic field direction as the samarium cobalt magnet ring located at the rear end of the ferrite cylinder. A cathode is arranged on the front side of the outer wall, and the anode and cathode are respectively connected to the propellant delivery pipe.

[0008] Preferably, the frequency of the radio frequency source is 4 MHz. Compared with 13.56 MHz in the prior art, this frequency can reduce capacitive coupling and central ferrite loss, and the coupling efficiency of the radio frequency source is improved overall.

[0009] Preferably, the coil is a bare copper wire coil, the insulating carrier material is an epoxy polymer, and the permanent magnet ring is a samarium cobalt magnet ring.

[0010] It should be noted that the anode and cathode of the present application are prior art, such as the anode disclosed in Chinese Patent No. 201610599709.7 or 201910243684.0, and the hollow cathode structure disclosed in "A Hollow Cathode for Electric Propulsion without Heater" (Author: Zhang Yan, Kang Xiaolu, Qiao Caixia) published in "Rocket Propulsion" (Volume 40, Issue 2, April 2014), which can be used in the technical solution of the present application.

[0011] The working principle of the present application is: the positions of the outer wall and the four permanent magnet blocks are combined to form an ionization chamber with four magnetic tips and magnetic field lines parallel to the outer wall surface, which can reduce the wall loss of ions and increase the plasma density.

[0012] The bare copper wire coil and the ferrite column in its center can generate high-density plasma and can be distributed around the coil in the form of a ring. The electrons can move back and forth along the axial magnetic field and be heated by the angular electric field induced by the coil. The magnetic flux lines of the two permanent magnet rings pass through the ferrite column and the ferrite disk, so that the magnetic field has a component parallel to the inner wall. There is a magnetic tangent in the ionization chamber, which can constrain the plasma and limit the wall loss of charged particles. In addition, the ferrite column and ferrite disk can prevent eddy currents from appearing in the magnetic circuit, thereby reducing the power loss of the RF source, and have a better coupling with the inductive power of the RF source on the other hand.

[0013] The beneficial effects of the present application are as follows: the radio frequency source is used as an ionization source, which is located inside the thruster and can generate plasma by ionization alone. Voltages are applied to the anode and cathode separately to accelerate the ions in the plasma. Therefore, the generation and acceleration of the plasma are independent of each other; thereby achieving independent thrust and specific impulse control of the thruster. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] Figure 1 This is a schematic diagram of the structure of an inductively coupled two-stage plasma thruster according to Example 1 of the present invention.

[0016] Figure 2 for Figure 1 Magnetic field distribution diagram of the permanent magnet ring and permanent magnet block. DETAILED DESCRIPTION

[0017] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0018] Example 1

[0019] like Figure 1-Figure 2 An inductively coupled two-stage plasma thruster shown includes an inner wall 1, an alumina outer wall 2 and a propellant delivery pipe 3, wherein the inner wall is a cylindrical Pyrex heat-resistant glass tube with one end closed, the inner diameter of the Pyrex heat-resistant glass tube is 26 mm, a radio frequency source is arranged in the inner cavity of the inner wall, and the radio frequency source includes a bare copper wire coil 4 with a length of 25 mm and an inner diameter of 20 mm, a cylindrical hollow epoxy polymer insulating carrier 5, a ferrite cylinder 6, two ferrite disks 7 with an outer diameter of 22 mm and two permanent magnet rings 8 with an inner diameter of 22 mm and a wall thickness of 1 mm, the coil is wound on the insulating carrier, the ferrite cylinder is coaxially arranged at the center of the insulating carrier, the two ferrite disks are respectively fixedly arranged at the two ends of the ferrite cylinder, the two permanent magnet rings are respectively fixedly arranged on the circumferential edge of one ferrite disk, the magnetic poles of the two permanent magnet rings are both distributed laterally and the magnetic fields of the two are in opposite directions;

[0020] The outer wall 2 is arranged outside the inner wall and coaxial with the inner wall. The front part 201 of the outer wall is a cylindrical channel with an inner diameter of 46mm and a length of 10mm. The rear part 202 of the outer wall is a conical cylinder with a small front and a large rear. The inner diameter of the large end of the rear part of the outer wall is 92mm. The rear end face 203 of the outer wall is fixedly connected to the rear end of the inner wall through a closed end face. An anode 9 is arranged inside the rear part of the outer wall. Two axially symmetrical permanent magnet blocks 10 are respectively arranged on the outer side of the front part of the outer wall and the tail of the outer side of the rear part of the outer wall. The two permanent magnet blocks on the same side are fixed by an L-shaped soft iron sheet 11. Figure 2As shown, the two permanent magnet blocks located at the front of the outer wall have the same magnetic field direction as the samarium cobalt magnet ring located at the front end of the ferrite cylinder, and the two permanent magnet blocks located at the front and rear have the same magnetic field direction as the samarium cobalt magnet ring located at the rear end of the ferrite cylinder. A cathode 12 is provided on the front side of the outer wall, and the anode and cathode are respectively connected to the propellant delivery pipe.

[0021] The frequency of the radio frequency source is 4 MHz. Compared with 13.56 MHz in the prior art, this frequency can reduce capacitive coupling and central ferrite loss, and the coupling efficiency of the radio frequency source is improved overall.

[0022] The RF source of the thruster of the present application is used as an ionization source. It is located inside the thruster and ionizes the plasma alone. Voltages are applied to the anode and cathode separately to accelerate the ions in the plasma. Therefore, the generation and acceleration of the plasma are independent of each other, and the thrust and specific impulse are independent of each other. The thruster can also be used for alternative working fluids that are more difficult to ionize than xenon. In the acceleration stage, the thrust is a function of the DC voltage, and in the ionization stage, it is a function of the RF voltage.

[0023] The thrust calculation formula of the thruster is as follows:

[0024]

[0025] here, is the ion current density, is the azimuth, To measure the distance from the probe to the thruster, is the ion current.

[0026] The total thrust of the thruster is

[0027]

[0028] in represents the average ion velocity, which can be obtained from the electron distribution function.

[0029] The mean cosine is given by:

[0030]

[0031] The mass flow rate can be calculated by the following formula:

[0032]

[0033] here is the basic elementary charge, is the ion mass.

[0034] It should be understood by those skilled in the art that the present invention is not limited by the above-described embodiments. The above-described embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An inductively coupled two-stage plasma thruster, characterized in that: It comprises an inner wall, an outer wall and a propellant delivery pipe, wherein the inner wall is a cylindrical Pyrex heat-resistant glass tube with one end closed, a radio frequency source is arranged in the inner cavity of the inner wall, and the radio frequency source comprises a coil, a cylindrical hollow insulating carrier, a ferrite cylinder, two ferrite disks and two permanent magnet rings, wherein the coil is wound on the insulating carrier, the ferrite cylinder is coaxially arranged at the center of the insulating carrier, the two ferrite disks are respectively fixedly arranged at the two ends of the ferrite cylinder, the two permanent magnet rings are respectively fixedly arranged on the circumferential edge of one ferrite disk, the magnetic poles of the two permanent magnet rings are both horizontally distributed and the magnetic fields of the two are in opposite directions; The outer wall is arranged on the outside of the inner wall and is coaxial with the inner wall. The front part of the outer wall is a cylindrical channel, and the rear part is a conical cylinder with a small front and a large rear. The rear end face of the outer wall is fixedly connected to the rear end of the inner wall through a closed end face; an anode is arranged inside the rear part of the outer wall, and two axially symmetrically arranged permanent magnet blocks are respectively arranged on the outside of the front part of the outer wall and the tail of the outside of the rear part of the outer wall, and the two permanent magnet blocks on the same side are fixed by an L-shaped soft iron sheet; the two permanent magnet blocks located at the front part have the same magnetic field direction as the samarium cobalt magnet ring located at the front end of the ferrite cylinder, and the two permanent magnet blocks located at the front and rear parts have the same magnetic field direction as the samarium cobalt magnet ring located at the rear end of the ferrite cylinder. A cathode is arranged on the front side of the outer wall, and the anode and cathode are respectively connected to the propellant delivery pipe; The frequency of the radio frequency source is 4 MHZ; the coil is a bare copper wire coil, the insulating carrier material is epoxy polymer, the permanent magnet ring is a samarium cobalt magnet ring, and the outer wall material is alumina.

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