Capacitively coupled high self-bias self-neutralizing radio frequency ion thruster with micro-cavity structure

Abstract

The application discloses a micro-cavity structure capacitive coupling high self-bias self-neutralization radio frequency ion thruster, and belongs to the field of space electric propulsion. The method comprises the following steps: the thruster comprises a radio frequency matcher, a radio frequency power supply and an axisymmetric cylindrical discharge cavity, wherein the first bottom surface and the side surface of the discharge cavity are provided with current collecting electrodes, the second bottom surface of the discharge cavity is provided with an acceleration bias electrode and an insulator; the acceleration bias electrode is a circular flat plate and is provided with a plurality of lead-out holes with the same inner diameter, the insulator is arranged around the circumference of the acceleration bias electrode and is connected with the current collecting electrode of the side surface of the cavity; the inner surface of the first bottom surface is provided with uniformly distributed micro-cavities, the micro-cavities are arrayed cylindrical grooves; and the radio frequency power supply is electrically connected with the first bottom surface through the radio frequency matcher. The application can make the radio frequency ion thruster no longer need an external neutralizer, and improve the application reliability of the thruster.

Description

Technical Field

[0001] This invention relates to the field of space electric propulsion technology, and in particular to a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure. Background Technology

[0002] Space-based gravitational wave detection has become a key strategic frontier. Its core challenges lie in achieving stringent objectives such as ultra-high precision drag-free control, sub-micro Newton thrust adjustment, and disturbance-free attitude stabilization. To achieve these objectives, the probe must be equipped with a high-performance micro-propulsion system, which must possess key capabilities such as ultra-low thrust noise, high specific impulse, and long-term stable operation.

[0003] In related technologies, traditional radio frequency ion thrusters are usually equipped with a separate electron neutralizer to neutralize space charge. However, the neutralizer requires an additional working fluid supply, heating power supply and complex control circuitry, which not only increases the complexity of the system, but also introduces the potential risk of single point of failure. Once the neutralizer fails, it will directly affect the reliability of the entire mission and cause huge losses to space exploration.

[0004] Therefore, there is an urgent need for a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention provides a capacitively coupled, high-self-biased, self-neutralizing radio frequency ion thruster with a microcavity structure, which eliminates the need for an external neutralizer, thus improving the thruster's application reliability. The technical solution is as follows: On one hand, a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure is provided. The thruster includes a radio frequency matching unit, a radio frequency power supply, and an axisymmetric cylindrical discharge cavity, wherein: The first bottom surface and the side surface of the discharge cavity are both configured as electrodes, and the second bottom surface of the discharge cavity is configured as an accelerating bias electrode and an insulator; The accelerating bias electrode is a circular plate with multiple lead-out holes of the same inner diameter. The insulator is disposed around the circumference of the accelerating bias electrode and connected to the power-connecting electrode on the side of the cavity. The inner surface of the first bottom surface is provided with uniformly distributed microcavities, which are arrayed cylindrical grooves. The radio frequency power supply is electrically connected to the first bottom surface through the radio frequency matching unit.

[0006] On the other hand, a method for using a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure is provided, the method comprising: when the radio frequency ion thruster enters the working state, injecting working fluid into the discharge cavity and turning on the radio frequency power supply; The radio frequency matching device is used to couple the single-frequency continuous wave signal output by the radio frequency power supply to the electrode to establish a high-frequency electric field in the microcavity. By utilizing the electrode with a high area asymmetry and the accelerating bias electrode, the electron migration speed is faster than that of ions during the radio frequency cycle, so as to form a stable negative DC self-bias. The discharge cavity is periodically extracted using the extraction port to allow the radio frequency ion thruster to complete the plume neutralization.

[0007] The technical solution provided by this invention offers at least the following beneficial effects: By utilizing the capacitive coupling discharge principle combined with a microcavity structure, a stable generation of high-amplitude DC self-bias voltage is achieved. This self-bias voltage can reach hundreds or even thousands of volts, far exceeding that of traditional inductive coupling schemes, thereby effectively accelerating ions and periodically extracting electrons, achieving self-neutralization. Simultaneously, through the effect of the high-amplitude self-bias voltage, ions and electrons are periodically extracted from the extraction holes, achieving electrical neutrality. The thruster can complete plume neutralization without an independent neutralizer. Furthermore, the microcavity structure creates a localized electric field enhancement effect, reducing the gas breakdown voltage and enabling reliable ignition of the thruster even under extremely low propellant flow conditions. This thruster employs a single-RF source drive design, avoiding multi-source interference problems and simplifying the power supply system and control logic. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a simplified cross-sectional schematic diagram of a microcavity structure capacitively coupled self-neutralizing radio frequency ion thruster provided in an embodiment of the present invention; Figure 2 This is a partially enlarged schematic diagram of a microcavity structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the simulation results of the instantaneous voltage and current distribution on the surface of the electrode under the conditions of 13.56MHz and 1W input power, provided by an embodiment of the present invention. Figure 4This is a cloud map of electron density distribution in a radial plane (z = constant) provided by an embodiment of the present invention; Figure 5 This is a schematic diagram of the electron density distribution curve along the thruster's axis of symmetry (z-axis) provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the radial electron density distribution curve with the midpoint of the axis of symmetry as the origin, provided by an embodiment of the present invention; Figure 7 This is a cloud map of the internal potential distribution of a thruster provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the deposition distribution of radio frequency power inside the thruster according to an embodiment of the present invention.

[0010] Figure label: 1-Electrical electrode; 2-Accelerating bias electrode; 3-Insulator; 4-RF matching unit; 5-RF power supply. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0012] As mentioned earlier, traditional radio frequency ion thrusters are typically equipped with a separate electron neutralizer, which increases system complexity and introduces a potential single point of failure risk, reducing reliability in use.

[0013] Based on this, the concept of this invention lies in overcoming the problems existing in existing radio frequency ion thrusters by designing a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure. The specific implementation of the above concept is described below.

[0014] Please refer to Figure 1This invention provides a capacitively coupled self-biased self-neutralizing radio frequency ion thruster with a microcavity structure. The thruster includes a radio frequency matching unit, a radio frequency power supply, and an axisymmetric cylindrical discharge cavity. The first bottom surface and side surface of the discharge cavity are configured as electrodes, and the second bottom surface is configured as an accelerating bias electrode and an insulator. The accelerating bias electrode is a circular flat plate with multiple lead-out holes of the same inner diameter. The insulator is disposed around the circumference of the accelerating bias electrode and connected to the electrodes on the side surface of the cavity. The inner surface of the first bottom surface is provided with uniformly distributed microcavities, which are arrayed cylindrical grooves. The radio frequency power supply is electrically connected to the first bottom surface through the radio frequency matching unit.

[0015] Specifically, the discharge cavity uses the receiving electrode 1 as the upper electrode and the accelerating bias electrode 2 as the lower electrode. The overall structure of the discharge cavity is an axisymmetric cylindrical shape. The working fluid is injected from the top, forming plasma in the microcavity region. Ions and electrons are periodically extracted through the lower electrode aperture array. The accelerating bias electrode 2 is located on the second bottom surface of the discharge cavity, i.e., the outlet end. An insulating component 3 is provided between the receiving electrode 1 and the accelerating bias electrode 2. An RF power supply 5 is provided at one end of the thruster. One end of the RF power supply 5 is coupled to the receiving electrode 1 through an RF matching device 4 containing a DC blocking capacitor. A microcavity is provided on the inner surface of the first bottom surface of the receiving electrode 1. The microcavities are small cylindrical grooves distributed in an array and are uniformly distributed on the inner surface of the receiving electrode 1.

[0016] The electrode 1 is made of stainless steel, and the microcavity consists of uniformly distributed small cylindrical grooves with a depth of L2 and a diameter of D2, evenly distributed on the inner surface of the first bottom surface of the electrode 1. The entire discharge cavity has a height of L1 and a diameter of D3. The accelerating bias electrode 2 is made of molybdenum and is located at the outlet end of the discharge cavity. It has a diameter of D1 and multiple lead-out holes with an inner diameter of D4. During operation, it can be grounded or a modulated bias voltage can be applied to control the energy of the extracted particles. Among these parameters, D3>D1, L1>L2, and D1>D4. The two electrodes are electrically isolated by high-performance insulating material to ensure stable capacitive coupling discharge. The RF power supply 5 operates in the MHz band and outputs a single-frequency continuous wave signal, which is coupled to the electrode 1 via an RF matching circuit 4 containing a DC blocking capacitor. The DC blocking capacitor blocks the DC component, ensuring the dynamic formation of a negative DC self-bias voltage.

[0017] During capacitive coupling discharge, due to the significant asymmetry of the upper and lower electrode areas, electrons and ions exhibit different migration behaviors under the influence of the radio frequency electric field. Negative charges accumulate on the surface of electrode 1, forming a stable negative DC self-bias voltage. This self-bias voltage can reach hundreds or even thousands of volts, far exceeding that of traditional inductive coupling schemes. It can effectively accelerate ions and periodically extract electrons, achieving self-neutralization.

[0018] For example, the discharge cavity has an inner diameter D3 = 20.32 cm and a height L1 = 6 cm. The receiving electrode 1 is made of 304 stainless steel, and each microcavity is a small cylindrical pit with a diameter D2 = 1 cm and a depth L2 = 1 cm, arranged in a concentric ring array. The accelerating bias electrode 2 has a molybdenum gate with an inner diameter D1 = 18 cm and multiple lead-out holes with a diameter D4 = 2 mm. The gate is grounded as a reference potential. The two electrodes are separated by a PTFE insulating ring with a spacing of 2 cm. The RF power supply uses a 13.56 MHz industrial band solid-state source, coupled to the upper electrode through an RF matching network containing a DC blocking capacitor.

[0019] During operation, argon gas is injected into the discharge cavity as the working fluid at a flow rate of 5–50 μm / s. After the RF power supply 5 is turned on, a high-frequency electric field is established in the microcavity region through capacitive coupling. Due to the high asymmetry of the upper and lower electrode areas (the upper electrode has a large area with a microcavity, while the lower electrode has a small area with a gate), the electron migration speed is faster than that of ions during the RF cycle, resulting in the accumulation of net negative charge on the upper electrode, forming a stable negative DC self-bias voltage.

[0020] Experimental simulation results show that the voltage and current distributions are as follows: Figure 3 As shown in the figure, under the conditions of 13.56MHz and 1W input power, the voltage amplitude on the surface of the electrode is close to 100V and the current amplitude is about 0.2A, exhibiting typical capacitive discharge characteristics.

[0021] electron density distribution such as Figures 4-6 As shown in the figure, the electron density is highest in the ring-shaped region with a radius of approximately 6 cm, reaching 2.17 × 10¹. 5 m -3 This indicates that the plasma is mainly concentrated in the peripheral region of the microcavity; in the central region of the discharge cavity, the electron density reaches a peak of 1.8 × 10¹. 5 m -3 This indicates that the plasma is uniformly distributed and the central region is actively ionized; the density in the central region is approximately 1.8 × 10¹ 5 m -3 The distribution is relatively uniform, and it rapidly decays to zero when it approaches the sidewall of electrode 1, which is consistent with the boundary characteristics of capacitive discharge.

[0022] Electric potential distribution as Figure 7 As shown in the figure, the potential of the plasma main region is about 57V, which drops to about 30V near the grounding electrode 1. Since the accelerating bias electrode 2 is grounded, the potential near it is 0V, forming an effective extraction electric field.

[0023] Power deposition such as Figure 8As shown in the figure, the maximum power density occurs near the accelerating bias electrode 2, reaching 1600 W / m³, while it remains between 100 and 400 W / m³ in most of the discharge cavity. This indicates that the energy is mainly deposited in the extraction region, which is beneficial for efficient ionization and particle acceleration.

[0024] Simulation results show that the electron density reaches 1.8–2.17 × 10¹ in the discharge region. 5 m -3 The degree of ionization is higher than that of traditional planar electrode structures. Power deposition analysis shows that energy is mainly concentrated in the extraction region, which is beneficial to improving acceleration efficiency. The localized enhancement effect of the electric field brought about by the microcavity structure is significant at 10... -3 Stable ignition is possible at pressures in the Pa range.

[0025] Therefore, this invention employs a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure as described above. By optimizing the electrode design (the electrode with an array-type microcavity structure, which is highly asymmetrical with the area of ​​the accelerating bias electrode), and combining the capacitive coupling discharge principle with single radio frequency source drive, it achieves stable generation of high-amplitude DC self-bias (up to hundreds to thousands of volts), effectively improving ionization efficiency and solving the problem of difficult low-flow ignition. At the same time, it achieves self-neutralization by periodically extracting ions and electrons, eliminating the need for a separate neutralizer, simplifying the system architecture and improving reliability.

[0026] Furthermore, this embodiment also provides a method for using a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure, applicable to the thruster described in any embodiment. The method includes: when the radio frequency ion thruster enters the working state, injecting working fluid into the discharge cavity and turning on the radio frequency power supply; using the radio frequency matching device to couple the single-frequency continuous wave signal output by the radio frequency power supply to the charging electrode to establish a high-frequency electric field in the microcavity; using the charging electrode and the accelerating bias electrode, which have a high area asymmetry, to make the electron migration speed faster than that of ions during the radio frequency cycle to form a stable negative DC self-bias; and using the extraction hole to periodically extract the power and ions in the discharge cavity so that the radio frequency ion thruster can complete the plume neutralization.

[0027] Finally, it should be noted that in this document, relational terms such as first, second, third, and fourth are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A capacitively coupled self-biased self-neutralizing radio frequency ion thruster with a microcavity structure, characterized in that, The thruster includes an RF matching unit, an RF power supply, and an axisymmetric cylindrical discharge cavity, wherein: The first bottom surface and the side surface of the discharge cavity are both configured as electrodes, and the second bottom surface of the discharge cavity is configured as an accelerating bias electrode and an insulator; The accelerating bias electrode is a circular plate with multiple lead-out holes of the same inner diameter. The insulator is disposed around the circumference of the accelerating bias electrode and connected to the power-connecting electrode on the side of the cavity. The inner surface of the first bottom surface is provided with uniformly distributed microcavities, which are arrayed cylindrical grooves. The radio frequency power supply is electrically connected to the first bottom surface through the radio frequency matching unit; The area and height of the first bottom surface are asymmetrical with respect to the accelerating bias electrode, and the inner diameter of the first bottom surface is larger than the diameter of the accelerating bias electrode to form a stable negative DC self-bias. The inner diameter of the lead-out hole is smaller than the diameter of the accelerating bias electrode. The lead-out hole is used to periodically draw out electrons and ions from the discharge cavity to achieve self-neutralization of the thruster. The radio frequency matching unit is equipped with a DC blocking capacitor, which is used to block the DC component to prevent the electrode from generating a static DC potential.

2. The thruster as described in claim 1, characterized in that, The depth of the microcavity is less than the inner height of the discharge cavity.

3. The thruster as described in claim 1, characterized in that, The radio frequency power supply operates in the MHz band and is used to output a single-frequency continuous wave signal.

4. The thruster as described in claim 1, characterized in that, The electrode is made of stainless steel.

5. The thruster as described in claim 1, characterized in that, The accelerating bias electrode is made of molybdenum.

6. The thruster as claimed in claim 1, characterized in that, The insulator is an insulating material that meets performance requirements. The insulator is used to electrically isolate the electrode and the accelerating bias electrode so that the capacitive coupling discharge is in a stable state.

7. A method of using a capacitively coupled high self-biased self-neutralizing radio frequency ion thruster with a microcavity structure, characterized in that, Applied to the thruster as described in any one of claims 1-6, the method comprises: When the radio frequency ion thruster enters the working state, working medium is injected into the discharge cavity and the radio frequency power supply is turned on; The radio frequency matching device is used to couple the single-frequency continuous wave signal output by the radio frequency power supply to the electrode to establish a high-frequency electric field in the microcavity. By utilizing the electrode with a high area asymmetry and the accelerating bias electrode, the electron migration speed is faster than that of ions during the radio frequency cycle, so as to form a stable negative DC self-bias. The discharge cavity is periodically extracted using the extraction port to allow the radio frequency ion thruster to complete the plume neutralization.

Images