Radio frequency ion thruster based on composite coil

Abstract

The invention discloses a radio frequency ion thruster based on a composite coil, and belongs to the field of space electric propulsion. The thruster comprises a radio frequency coil, a direct current magnetic field coil, an insulating layer, an ionization chamber, a screen grid, an acceleration grid and a neutralizer, and the radio frequency coil and the direct current magnetic field coil are wound around the ionization chamber to form a composite constraint environment of an alternating electromagnetic field and a steady magnetic field; the radio frequency coil and the DC magnetic field coil are wrapped by the insulating layers. And the screen grid, the acceleration grid and the neutralizer are sequentially arranged at the outlet end of the ionization chamber. The problem that an existing radio frequency ion thruster is difficult to ignite and start can be solved, meanwhile, the in-orbit operation stability of the thruster is improved, and the service life of the thruster is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of space electric propulsion, in particular to a radio frequency ion thruster based on a composite coil. BACKGROUND

[0002] Among numerous micro-propulsion technologies, radio frequency electric propulsion technology stands out as an ideal candidate for gravitational wave detection missions due to its unique technical advantages and outstanding performance. This technology achieves ionization and acceleration of gas through high-frequency electromagnetic fields, enabling efficient ionization over a wide range of gas flow, while also featuring compact system structure, light weight, small volume, and high specific impulse (i.e., impulse generated per unit mass of propellant), providing strong support for long-term on-orbit operation and high-precision attitude control of gravitational wave detection spacecraft.

[0003] In related technologies, the gas flow supplied to the thruster is extremely small, and the gas pressure is extremely low. This extremely rarefied gas environment makes the ignition process of the thruster extremely difficult, and the traditional overshoot ignition method commonly used in radio frequency thrusters consumes a large amount of working gas, resulting in waste of propellant resources and reduced long-term on-orbit operation stability of the thruster.

[0004] Therefore, there is an urgent need for a radio frequency ion thruster based on a composite coil to solve the above technical problems. SUMMARY

[0005] The present application provides a radio frequency ion thruster based on a composite coil, which can effectively improve the on-orbit operation stability of the thruster. The technical solution is as follows: On the one hand, a radio frequency ion thruster based on a composite coil is provided, which includes a radio frequency coil, a direct current magnetic field coil, an insulating layer, an ionization chamber, a screen grid, an acceleration grid, and a neutralizer, wherein: The radio frequency coil and the direct current magnetic field coil are wound around the circumference of the ionization chamber to form a composite confinement environment of alternating electromagnetic field and steady magnetic field; The radio frequency coil and the direct current magnetic field coil are both wrapped with the insulating layer on the outside; The screen grid, the acceleration grid, and the neutralizer are sequentially arranged at the outlet end of the ionization chamber.

[0006] On the other hand, a method for using a radio frequency ion thruster based on a composite coil is provided, which includes: The radio frequency coil passing through the radio frequency current generates an alternating magnetic field in the ionization chamber, and forms a vortex electric field through electromagnetic induction to accelerate free electrons in the ionization chamber; The direct current magnetic field coil generates a steady magnetic field in the ionization chamber when energized, so that the free electrons perform cyclotron motion under the action of the magnetic field, ensuring efficient collision and ionization of the free electrons and the working medium. The screen grid and the acceleration grid form an electric field to extract and accelerate ions to form an ion beam. The neutralizer is used to neutralize the ion beam to form a stable thrust.

[0007] The technical scheme provided by the present application can bring at least the following beneficial effects: through the composite design of the radio frequency coil and the direct current magnetic field coil, the radio frequency ion thruster can be quickly ignited at very low pressure, the ionization efficiency and specific impulse of the working medium are significantly improved, and the service life of the radio frequency electric propulsion system is prolonged; the problems of difficult ignition and start of the existing radio frequency ion thruster, the need for higher gas pressure in the ionization chamber, and the consumption of a large amount of working gas at the moment of ignition are solved. BRIEF DESCRIPTION OF DRAWINGS

[0008] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0009] Figure 1 is a structure schematic diagram of a radio frequency ion thruster based on a composite coil provided by an embodiment of the present application; Figure 2 is a cross-sectional structure schematic diagram of a radio frequency ion thruster based on a composite coil provided by an embodiment of the present application; Figure 3 is a radio frequency ion thruster ignition schematic diagram of a composite coil configuration provided by an embodiment of the present application.

[0010] Reference signs: 1-radio frequency coil; 2-direct current magnetic field coil; 3-insulating layer; 4-ionization chamber; 5-screen grid; 6-acceleration grid; 7-neutralizer. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme 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 some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0012] As mentioned above, due to the extremely small gas flow supplied to the thruster and the extremely low air pressure, the extremely rarefied gas environment makes the ignition process of the thruster extremely difficult, and the traditional overshoot ignition method inevitably consumes a large amount of working gas, resulting in waste of propellant resources.

[0013] Based on this, the concept of the present application is to realize the rapid ignition of the thruster under extremely low air pressure through the composite design of the radio frequency coil and the direct current magnetic field coil.

[0014] The specific implementation of the above concept is described below.

[0015] Please refer to Figure 1 The radio frequency ion thruster based on the composite coil provided by the embodiment of the present application comprises a radio frequency coil 1, a direct current magnetic field coil 2, an insulation layer 3, an ionization chamber 4, a screen grid 5, an acceleration grid 6 and a neutralizer 7, wherein: the radio frequency coil 1 and the direct current magnetic field coil 2 are wound around the periphery of the ionization chamber 4 to form a composite constraint environment of alternating electromagnetic field and steady magnetic field; the radio frequency coil 1 and the direct current magnetic field coil 2 are both wrapped with the insulation layer 3; the screen grid 5, the acceleration grid 6 and the neutralizer 7 are sequentially arranged at the outlet end of the ionization chamber 4.

[0016] As shown in Figure 1 and Figure 2 , the radio frequency coil 1 and the direct current magnetic field coil 2 are compactly arranged and wound around the periphery of the ionization chamber 4 to reduce the volume of the thruster.

[0017] The radio frequency coil 1 adopts copper or silver Litz wire, which can effectively reduce the skin effect of high-frequency current and improve the coupling efficiency of electromagnetic energy, thereby reducing the volume and weight of the power supply system.

[0018] The direct current magnetic field coil 2 adopts nickel-iron alloy material, which has high magnetic permeability and can generate a strong magnetic field under limited current conditions, effectively enhancing the discharge process, restraining electron movement and reducing electron loss to the wall.

[0019] The ionization chamber 4 adopts a cylindrical high-purity quartz glass tube, which has good high-temperature resistance, low-pressure resistance and insulation performance to provide a stable reaction chamber for ionization of the working medium.

[0020] The radio frequency coil 1 and the direct current magnetic field coil 2 are both externally covered with the insulation layer 3 made of polytetrafluoroethylene material, which is used to prevent electromagnetic interference between the two coils and ensure the stability of the discharge.

[0021] The ionization chamber 4 is sequentially provided with a screen grid 5, an acceleration grid 6 and a neutralizer 7 at one end, and the plasma ions generated by the ionization chamber 4 are introduced and accelerated to form an ion beam under the action of the electric field formed by the screen grid 5 and the acceleration grid 6, and since the ion beam is positively charged, the neutralizer 7 is arranged to spray an electron stream to achieve neutralization with the ion beam, and finally a stable thrust is formed.

[0022] On this basis, the embodiment further provides a use method of the radio frequency ion thruster based on the composite coil, which is applied to the thruster in any one of the above-mentioned embodiments, and the method comprises the following steps of: An alternating magnetic field is generated in the ionization chamber 4 by the radio frequency coil 1 connected with a radio frequency current, and a vortex electric field is formed by electromagnetic induction to accelerate free electrons in the ionization chamber; A steady magnetic field is generated in the ionization chamber 4 by the direct-current magnetic field coil 2 after being connected with electricity, so that the free electrons perform cyclotron motion under the action of the magnetic field, and efficient collision and ionization of the free electrons and the working medium are ensured; An electric field is formed by the screen grid 5 and the acceleration grid 6 to introduce and accelerate ions to form an ion beam; The ion beam is neutralized by the neutralizer 7 to form a stable thrust.

[0023] Specifically, when the radio frequency coil 1 is connected with a radio frequency current, an alternating magnetic field is generated in the ionization chamber 4, and a vortex electric field is formed by electromagnetic induction. The electric field can accelerate the free electrons in the chamber to obtain sufficient energy to collide with neutral working medium atoms or molecules in an inelastic manner, thereby realizing ionization of the working medium. Since the average free path of the electrons is long when the working medium flow is extremely low, the collision probability of the electrons and the working medium is significantly reduced, so that the traditional radio frequency discharge is difficult to maintain a stable ionization process at low pressure.

[0024] Therefore, the direct-current magnetic field coil 2 is added outside the radio frequency coil 1 in the embodiment, and a steady magnetic field is generated in the ionization chamber 4 after the direct-current magnetic field coil 2 is connected with electricity, so that the electrons move along a cyclotron trajectory under the action of the magnetic field. Since the cyclotron radius of the electrons is much smaller than the inner diameter of the ionization chamber 4, the electrons can go back and forth in the chamber many times, thereby significantly increasing the effective path length thereof. In this way, the collision probability of the electrons and the neutral working medium atoms is improved, and efficient collision and ionization of the electrons and the working medium can still be ensured even under the condition of extremely low pressure below 1 millitorr.

[0025] Further, the synergy of the radio frequency electric field and the direct current magnetic field also changes the electron energy distribution function (EEDF). Without the direct current magnetic field, the electron energy distribution is concentrated in the low-energy region, and it is difficult to effectively excite ionization; under the action of the composite magnetic field, the proportion of high-energy electrons increases, and the EEDF has a trend of high-energy tail enhancement, which is beneficial to the sustainability and stability of the ionization process. Through this composite principle, the thruster designed in the embodiment can realize rapid ignition at extremely low pressure and ultra-low flow, and the ignition power demand is lower than that of the traditional thruster. At the same time, the electron confinement effect reduces the loss of electrons to the cavity wall, thereby reducing the wall sputtering and cavity loss, and prolonging the service life of the thruster.

[0026] The following embodiment verifies the working focus on the ignition performance optimization and ionization efficiency improvement under the ultra-low flow condition.

[0027] First, the ignition characteristics are compared and verified. The ignition processes of the traditional radio frequency thruster without adding a direct current magnetic field and the composite coil configuration thruster are tested respectively under the same vacuum environment conditions, wherein the ignition of the composite coil configuration thruster is as shown in FIG. 1, and it is observed that the latter has a significantly stable discharge establishment capability in the extremely low pressure range, and the test results are shown in Table 1. Figure 3

[0028] Table 1 Among them, the ignition working medium is Ar, and the radio frequency coils of the traditional and composite coil radio frequency ion thrusters are both 60W input power, wherein the direct current coil magnetic field of the composite coil radio frequency ion thruster is input with a current of 10A.

[0029] From the above experimental results, it can be seen that when the flow rate is 0.4sccm and 0.6sccm, the traditional radio frequency thruster and the composite coil radio frequency ion thruster both use the overshoot ignition mode, but as the flow rate increases to 0.6sccm and above, the composite coil radio frequency ion thruster gradually changes to the natural ignition mode, while the traditional radio frequency thruster still maintains the overshoot ignition. Overshoot ignition usually requires additional energy input to overcome the initial ionization resistance, so that the working medium quickly reaches the ionization state. Under low flow conditions, the number of working medium molecules is small, and the ionization process is relatively difficult. The traditional radio frequency thruster may be difficult to achieve natural ignition under normal conditions due to the lack of effective magnetic field assistance, and therefore relies on the additional energy provided by the overshoot ignition.

[0030] ​The composite coil RF ion thruster can achieve natural ignition at a lower flow rate (0.6 sccm and above), which is due to the unique composite coil configuration. The magnetic field generated by the composite coil can produce a restraining effect on the charged particles, change the particle motion trajectory, and increase the collision probability between particles, thereby reducing the energy threshold required for ionization. When the flow rate increases, the number of working substance molecules increases, and the magnetic field assistance of the composite coil becomes more significant, so that the ionization process can occur naturally under more moderate conditions without the need for additional energy impact provided by the overshoot ignition.

[0031] The embodiment breaks through the ignition pressure threshold limit of the existing RF thruster, and still guarantees reliable start and efficient ionization in an extremely rare working substance environment, while the composite coil configuration meets the stringent requirements of compactness, lightweight and long life for space payloads, providing new power support for ultra-long period tasks such as space gravitational wave detection.

[0032] In view of the problems of difficult ignition of rare working substance at a small flow rate and low ionization efficiency, the embodiment adds a direct current coil to generate a magnetic field to enhance RF discharge, which can realize fast ignition of the RF ion thruster, reduce the response time of the electric propulsion system, improve the ionization efficiency of the working substance, thereby improving the specific impulse of the thruster and the utilization rate of the working substance, and prolonging the on-orbit service life of the RF electric propulsion system and even the satellite platform.

[0033] The RF ion thruster based on the composite coil provided by the embodiment adds a direct current magnetic field coil 2 and a composite RF coil 1 to generate a magnetic field, which can solve the problem of difficult ignition of rare working substance at a small flow rate, improve the ionization efficiency and utilization rate of the working substance, and prolong the on-orbit service life of the RF electric propulsion system and even the satellite platform. Compared with the conventional RF ion thruster, it has the advantages of easy ignition at extremely low pressure, high specific impulse, high ionization rate and utilization rate of the working substance, etc., which can improve the key indicators such as pressure application range, service life, and working substance application of the entire RF electric propulsion system. It is expected to be applied in gravitational wave detection tasks (which require ultra-long on-orbit service). In addition, it is also suitable for gas-fed RF electric thrusters.

[0034] In summary, the embodiment uses the RF coil to provide energy to excite electrons, and uses the direct current magnetic field coil to prolong the residence time of electrons and improve the collision probability, and the combined effect of the two realizes efficient ionization. This principle not only guarantees stable ignition at low pressure, but also significantly improves the utilization efficiency of the working substance and the specific impulse performance, providing reliable support for long-term on-orbit electric propulsion tasks.

[0035] Finally, it needs to be pointed out that, in this document, relational terms such as first, second, third, and fourth and the like can only be used to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual relationship or order between or among such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0036] The above description is only the preferred embodiment of the present application, and it should be pointed out that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A radio frequency ion thruster based on a compound coil, characterized in that, The thruster comprises a radio frequency coil, a direct current magnetic field coil, an insulation layer, an ionization chamber, a screen grid, an acceleration grid and a neutralizer, wherein: The radio frequency coil and the direct current magnetic field coil are wound around the periphery of the ionization chamber to form a combined constraint environment of alternating electromagnetic field and steady magnetic field. The radio frequency coil and the direct current magnetic field coil are both wrapped with the insulation layer. The screen grid, the acceleration grid and the neutralizer are sequentially arranged at the outlet end of the ionization chamber.

2. The thruster of claim 1, wherein The radio frequency coil and the direct current magnetic field coil are compactly arranged and wound around the periphery of the ionization chamber to reduce the volume of the thruster.

3. The thruster of claim 1 wherein, The ionization chamber adopts a cylindrical high-purity quartz glass tube to provide a stable reaction chamber for ionization of the working medium.

4. The thruster of claim 1 wherein, The radio frequency coil adopts copper or silver Litz wire to reduce the skin effect of high-frequency current and improve the coupling efficiency of electromagnetic energy.

5. The thruster of claim 1 wherein, The direct current magnetic field coil adopts nickel-iron alloy material to generate a strong magnetic field under limited current conditions, enhance the discharge process and reduce the loss of electrons to the wall surface.

6. The thruster of claim 1 wherein, The insulation layer adopts polytetrafluoroethylene material to prevent electromagnetic interference between the radio frequency coil and the direct current magnetic field coil and ensure the stability of the discharge.

7. The thruster of claim 1 wherein, The screen grid and the acceleration grid are used together to form an electric field to extract and accelerate the plasma in the ionization chamber to form an ion beam.

8. The thruster of claim 1 wherein, The neutralizer is used to generate an electron stream and neutralize the ion beam to generate stable thrust for the thruster.

9. A method of using a radio frequency ion thruster based on a compound coil, characterized by, The method is applied to the thruster of any one of claims 1-8, and the method comprises: The radio frequency coil passing through radio frequency current generates an alternating magnetic field in the ionization chamber and forms a vortex electric field through electromagnetic induction to accelerate free electrons in the ionization chamber; The direct current magnetic field coil passing through current generates a steady magnetic field in the ionization chamber to make the free electrons perform cyclotron motion under the action of the magnetic field, ensuring efficient collision and ionization of the free electrons and the working medium; The screen grid and the acceleration grid form an electric field to extract and accelerate ions to form an ion beam; The neutralizer is used to neutralize the ion beam to form stable thrust.

10. The thruster of claim 1 wherein, The cyclotron radius of the cyclotron motion is much smaller than the inner diameter of the ionization chamber.

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