A dual frequency extracted self-neutralizing radio frequency ion thruster

Abstract

The application discloses a double-frequency self-neutralizing radio frequency ion thruster, and belongs to the technical field of radio frequency ion thrusters. The double-frequency self-neutralizing radio frequency ion thruster comprises a gas distributor, a discharge chamber, a coil, a double-frequency grid assembly and a ceramic ring. The double-frequency grid assembly comprises an inner concave screen grid and an outer convex acceleration grid. The discharge chamber is arranged on the outer sidewall of the gas distributor. The coil is arranged outside the discharge chamber. The inner concave screen grid is arranged on the side of the discharge chamber far from the gas distributor. The ceramic ring is arranged on the other side of the inner concave screen grid. The outer convex acceleration grid is arranged on the other side of the ceramic ring. The double-frequency self-neutralizing radio frequency ion thruster can significantly improve the self-bias voltage lifting capacity, ion acceleration efficiency and overall operation stability of the self-neutralizing radio frequency ion thruster by introducing a double-frequency bias mechanism and combining gas homogenization and grid structure optimization measures.

Description

Technical Field

[0001] This invention relates to the field of radio frequency ion thruster technology, and in particular to a dual-frequency self-neutralizing radio frequency ion thruster. Background Technology

[0002] The space-based gravitational wave detection mission constructs a large-scale equilateral triangle constellation using three spacecraft to precisely measure the extremely subtle length changes caused by gravitational waves using a laser interferometer. To ensure the ultra-high accuracy of the ranging system, the spacecraft must operate in a stable microgravity environment. However, non-conservative external disturbances such as solar radiation pressure can affect the stability of the test mass; therefore, drag-free control technology must be employed to suppress interference. This technology compensates for external disturbances in real time through the propulsion system, ensuring that the spacecraft's orbit always follows the internal test mass, thus significantly reducing the impact of non-conservative acceleration on measurement accuracy. The drag-free control system relies on capacitive sensors to monitor the relative displacement between the test mass and the spacecraft in real time. Based on this, the controller calculates the required compensation thrust, and a micro-thruster executes precise thrust commands to eliminate relative displacement errors. As the core actuator of this system, the performance of the micro-thruster directly determines the accuracy and stability of the drag-free control.

[0003] Among numerous micro-thrusters, electric propulsion, characterized by long lifespan, high specific impulse, and high efficiency, plays a crucial role in the development of gravitational wave detection. Radio frequency (RF) ion propulsion technology, as one of the world's most advanced space propulsion technologies, has been practically applied in many spacecraft missions. RF ion thrusters possess high specific impulse, fast response, long lifespan, and stable thrust output capabilities, fully meeting the stringent requirements of space gravitational wave detection for micro-thrust control precision and stability, thus becoming a vital technological support for constructing high-performance drag-free control systems.

[0004] Traditional radio frequency (RF) ion thrusters rely on external neutralizers to neutralize the ion beam, while self-neutralizing RF ion thrusters eliminate the need for a separate neutralizer. They achieve self-neutralization by utilizing the difference in response time between ions and electrons in an oscillating electric field, requiring no additional working fluid or power supply. This significantly reduces system size and weight, facilitating miniaturization and integration of the thruster. Its basic principle is as follows: Figure 4As shown, plasma is generated in the discharge chamber due to inductive coupling, and the thruster's grid is powered by an RF power supply. Due to the mass difference between ions and electrons, their response times to the oscillating field differ, and they are extracted at different time points. This process generates a self-biasing effect, dynamically adjusting the sheath voltage. After extraction, ions are focused and accelerated by the grid and ejected from the tail, generating thrust. Simultaneously, when the plasma potential approaches zero, the sheath before the grid collapses, allowing a large number of electrons to be extracted from the discharge region. Throughout the process, a DC blocking capacitor is installed in the thruster to prevent the generation of DC current in the system. During the entire operation, the number of extracted ions and electrons remains balanced in a time-averaged sense, thus achieving self-neutralization of the ion beam without the need for an additional neutralization device, improving the system's reliability and integration efficiency.

[0005] However, under actual operating conditions, the formation of self-bias voltage is highly dependent on the effective coupling between the radio frequency electric field and the plasma. When the discharge power is limited or the effective contact area between the grid and the plasma is insufficient, even increasing the amplitude of the radio frequency voltage applied to the grid is insufficient to improve the self-bias voltage, resulting in limited ion acceleration capability and consequently affecting the overall thrust output performance of the thruster. Furthermore, since the radio frequency voltage is directly applied to the grid, its structure is exposed to high-frequency, strong electric fields and thermal loads for extended periods, easily leading to structural fatigue and thermal deformation, which in turn affects the extraction performance and lifetime of the grid system. Compared to traditional DC-type radio frequency ion thrusters, the self-bias voltage that a self-neutralizing grid system can generate is typically lower, making it difficult to provide sufficient acceleration potential for ions. To suppress sputtering corrosion of the accelerating grid by high-energy ions, the grid spacing often needs to be reduced in the system design, which not only increases the processing complexity but also further limits the effective extraction rate and lifetime of the ion beam.

[0006] Furthermore, traditional self-neutralizing radio frequency (RF) ion thrusters typically employ a single-frequency RF voltage applied to the grid. A time-averaged self-bias voltage is established through the asymmetric response between the plasma and the RF sheath, resulting in continuous ion extraction and intermittent electron extraction, ultimately achieving self-neutralization. While this structure is simple, requires no neutralizer, and possesses strong integration potential, it still has significant limitations in self-bias voltage control, ion acceleration efficiency, and structural stability. Particularly under conditions of limited discharge power or grid coupling area, achieving high-amplitude self-bias voltage is difficult, limiting further improvements in thruster performance.

[0007] In summary, current self-neutralizing radio frequency ion thrusters still face significant technical bottlenecks in areas such as self-bias enhancement, gate structure durability, and overall system energy efficiency. System optimization is urgently needed in key areas such as gate structure design and radio frequency bias mechanism to meet their engineering application requirements in future long-lifetime, high-precision gravitational wave detection missions. Summary of the Invention

[0008] The purpose of this invention is to provide a dual-frequency self-neutralizing radio frequency ion thruster to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides a dual-frequency self-neutralizing radio frequency ion thruster, comprising a gas distributor, a discharge chamber, a coil, a dual-frequency gate assembly, and a ceramic ring. The dual-frequency gate assembly includes a concave screen gate and a convex acceleration gate. The discharge chamber is sleeved on the outer wall of the gas distributor, and the coil is sleeved outside the discharge chamber. The concave screen gate is disposed on the side of the discharge chamber away from the gas distributor, and the ceramic ring is disposed on the other side of the concave screen gate and the convex acceleration gate is disposed on the other side of the ceramic ring.

[0010] Preferably, the gas distributor includes a cylindrical block and a truncated conical block. The cylindrical block is fixedly installed above the truncated conical block. The cylindrical block and the truncated conical block are smoothly connected by a transition arc. The outer side of the cylindrical block is provided with threads, and its top is provided with an air inlet. The inclined surface of the truncated conical block is provided with a plurality of evenly arranged openings. The gas distributor is made of ceramic material.

[0011] Preferably, the discharge chamber includes a cylindrical block and a connecting flange, the connecting flange being disposed below the cylindrical block, and the discharge chamber being made of quartz glass.

[0012] Preferably, the coil is a spiral electromagnetic induction coil made of copper, and the coil is connected to a radio frequency power supply.

[0013] Preferably, the concave screen gate is a thin-walled cylindrical structure with concave features, and a cylindrical concave region is provided at the center of the concave screen gate.

[0014] Preferably, the recessed screen gate is connected to a dual-frequency radio frequency power supply, which consists of a high-frequency signal and a low-frequency signal.

[0015] Preferably, the low-frequency signal has a frequency range of 2-4MHz, and the high-frequency signal has a frequency higher than or equal to 13.56MHz.

[0016] Preferably, the ceramic ring has a cylindrical annular structure, and six through holes are evenly distributed on the ceramic ring. The ceramic ring is made of ceramic material.

[0017] Preferably, the convex accelerating gate is a thin-walled cylindrical structure with convex features, and a cylindrical convex region is provided at the center of the convex accelerating gate.

[0018] Preferably, both the concave region and the convex region have multiple small holes evenly distributed in a hexagonal shape on their planes, and both the concave screen gate and the convex acceleration gate are made of molybdenum.

[0019] Therefore, the present invention employs the above-mentioned dual-frequency self-neutralizing radio frequency ion thruster, which has the following beneficial effects:

[0020] (1) By using a gas distributor, the working gas entering the discharge chamber becomes more uniform, thereby improving the uniformity and stability of the plasma in the discharge chamber.

[0021] (2) The structure of the gate is a thin cylindrical shape with concave features. When connected to an RF source and working for a long time, it can effectively maintain the flatness of the gate, avoid deformation, and improve the system reliability and lifespan.

[0022] (3) Two radio frequency signals of high and low frequencies are loaded on the grid. By adjusting the voltage amplitude and phase angle of the dual-frequency signals, the energy and flux of the extracted ions can be independently controlled, which significantly improves the performance and working efficiency of the thruster.

[0023] (4) The accelerated gate structure is designed as a thin-walled cylinder with convex features and is used in conjunction with a ceramic ring structure. This enables precise control of the gate pitch, with a minimum pitch of 0.4 mm. It also has good structural stability, ensuring stable operation of the thruster system.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a dual-frequency self-neutralizing radio frequency ion thruster according to an embodiment of the present invention;

[0026] Figure 2 This is a cross-sectional view of a dual-frequency self-neutralizing radio frequency ion thruster according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram illustrating the working principle of a dual-frequency self-neutralizing radio frequency ion thruster according to an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram illustrating the working principle of a traditional radio frequency ion thruster in the background technology.

[0029] Figure Labels

[0030] 1. Gas distributor; 2. Discharge chamber; 3. Coil; 4. Concave screen grid; 5. Ceramic ring; 6. Protruding acceleration grid. Detailed Implementation

[0031] 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 only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0033] Example

[0034] like Figure 1-3 As shown, this invention provides a dual-frequency self-neutralizing radio frequency ion thruster, comprising a gas distributor 1, a discharge chamber 2, a coil 3, a dual-frequency gate assembly, and a ceramic ring 5. The dual-frequency gate assembly includes a concave screen gate 4 and a convex accelerating gate 6. The discharge chamber 2 is sleeved on the outer wall of the gas distributor 1, the coil 3 is sleeved outside the discharge chamber 2, the concave screen gate 4 is located on the side of the discharge chamber 2 away from the gas distributor 1, the ceramic ring 5 is located on the other side of the concave screen gate 4, and the convex accelerating gate 6 is located on the other side of the ceramic ring 5.

[0035] The gas distributor 1 adopts a one-piece molded structure with a complex geometry, comprising a cylindrical block and a truncated conical block. The cylindrical block is fixedly mounted on top of the truncated conical block, and the two blocks are smoothly connected by a transition arc. The outer surface of the cylindrical block is threaded for easy assembly, and its top has an air inlet. The inclined surface of the truncated conical block has several evenly arranged openings. The gas distributor 1 is made of ceramic material and is used to introduce the working gas into the discharge chamber 2 in a relatively uniform manner.

[0036] The discharge chamber 2 includes a cylindrical block and a connecting flange, which is located below the cylindrical block. The discharge chamber 2 is made of quartz glass and is used to excite and maintain inductively coupled plasma.

[0037] Coil 3 is a spiral-shaped electromagnetic induction coil made of copper, and is fitted outside the discharge chamber 2. Coil 3 is connected to a radio frequency power supply, which generates an alternating electromagnetic field inside the discharge chamber 2, causing gas ionization and thus forming a stable inductively coupled plasma inside the discharge chamber 2.

[0038] The concave gate 4 is a thin-walled cylindrical structure with a concave feature, featuring a central cylindrical concave region. Multiple hexagonally distributed small holes, made of molybdenum, are formed on the plane of the concave region. This structure helps maintain the flatness of the gate and prevents structural deformation under long-term operating conditions. The concave gate 4 is connected to a dual-frequency RF power supply, which consists of a high-frequency signal and a low-frequency signal. The low-frequency signal has a frequency range of 2-4MHz, and the high-frequency signal should be higher than or equal to 13.56MHz. By adjusting the voltage amplitude and phase angle of the high and low frequency signals, the energy and flux of the ions can be controlled separately, improving the overall performance of the thruster. The concave gate 4 is used to extract ions close to the gate surface and minimize the bombardment effect of ions on the concave gate 4, extending device lifespan.

[0039] The ceramic ring 5 is a cylindrical annular structure with six through holes evenly distributed on it, and is made of ceramic material. This component is used to precisely adjust the spacing between the screen grid and the accelerating grid, thereby affecting the extraction performance of the ion beam. At the same time, the small holes can also serve as positioning structures for the grid assembly.

[0040] The convex accelerating gate 6 is a thin-walled cylindrical structure with a convex feature. A cylindrical convex region is located at the center, and multiple hexagonally distributed small holes are also formed on the plane of this region. The material is molybdenum. This convex region structure, in conjunction with the ceramic ring 5, allows for precise control of the gate pitch, down to a minimum of 0.4 mm. The convex accelerating gate 6 is grounded and, together with the concave screen gate 4, forms a gate system used to accelerate and extract ions from the plasma, generating thrust.

[0041] The working gas is first introduced into the discharge chamber 2 by the gas distributor 1. A spiral-shaped electromagnetic induction coil 3, powered by a radio frequency (RF) power supply, is wound around the outside of the discharge chamber 2. Under the excitation of the coil 3, an inductively coupled plasma is formed inside the discharge chamber 2. Subsequently, the plasma is extracted through a dual-frequency grid assembly located at the outlet. Two RF signals, one high-frequency and one low-frequency, are simultaneously loaded on the concave grid, constituting a dual-frequency drive. By adjusting the voltage amplitude and phase difference of the high-frequency and low-frequency RF signals, the ion flux and energy can be controlled separately during extraction, flexibly responding to different thrust and specific impulse requirements.

[0042] Working Principle: A high-frequency signal and a low-frequency signal are superimposed to form a composite radio frequency waveform, which is applied to the grid, thereby generating a more complex potential change process in the sheath region. Compared with single-frequency excitation, dual-frequency drive can effectively enhance the average potential difference between the grid and the plasma, thus improving the self-bias level. The low-frequency component, with its longer period, allows the sheath region to fully respond, establishing a stronger bias potential in a time-averaged sense to enhance ion acceleration energy. The high-frequency component contributes to sheath stability, improves electronic control precision, and suppresses ineffective electron loss. The asymmetry of the composite waveform also makes the extraction process of ions and electrons time-controllable, achieving more precise and efficient self-neutralization. To ensure that dual-frequency excitation maintains the stability of the accelerating electric field while improving self-bias capability, the frequency and amplitude of the high and low frequency signals need to be optimized. The low-frequency signal frequency is selected in the range of 2 to 4 MHz, which can effectively improve the average potential bias in front of the grid and avoid fluctuations in the accelerating electric field caused by ions directly responding to low-frequency changes, thus ensuring the stability of the thrust output. The low-frequency voltage amplitude needs to be controlled within a reasonable range to prevent drastic fluctuations in the acceleration region potential, which could cause problems such as ion spectrum broadening or thrust instability. The high-frequency signal should be higher than or equal to 13.56MHz to dominate electron behavior and maintain the stability of the sheath potential structure. Its amplitude should be set slightly higher or comparable to the low-frequency signal to enhance the self-bias voltage while considering the grid's operating state. By rationally matching the amplitude, frequency, and phase relationship of the high and low frequency signals, the thruster can effectively shape the grid front electric field structure, averaging the potential during the ion's main response time to achieve stable acceleration. Simultaneously, it optimizes the extraction timing and energy distribution of ions and electrons, achieving refined control of the thruster's output performance. Furthermore, to further improve thruster performance, this device incorporates a gas distributor 1 structure to achieve uniform distribution of the working gas within the discharge chamber 2, improving the uniformity of plasma density distribution from the source. In terms of structural design, the grid adopts a concave structure, reducing the thickness of the central region to facilitate ion extraction, while the periphery is reinforced to withstand thermal stress, effectively preventing structural deformation during operation. The accelerating gate is designed with a convex structure, which, together with a ceramic ring, is used for positioning and spacing adjustment. This allows for a stable gate spacing of less than 0.4 mm, ensuring the quality of the ion beam while effectively suppressing ion corrosion of the accelerating gate and extending gate life.

[0043] Therefore, the present invention employs a dual-frequency self-neutralizing radio frequency ion thruster as described above. By introducing a dual-frequency bias mechanism and combining gas homogenization and gate structure optimization measures, the self-neutralizing radio frequency ion thruster can significantly improve its self-bias voltage enhancement capability, ion acceleration efficiency, and overall operational stability.

[0044] 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 them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A dual-frequency self-neutralizing radio frequency ion thruster, characterized in that: The device includes a gas distributor, a discharge chamber, a coil, a dual-frequency gate assembly, and a ceramic ring. The dual-frequency gate assembly includes a concave screen gate and a convex acceleration gate. The discharge chamber is sleeved on the outer wall of the gas distributor, and the coil is sleeved outside the discharge chamber. The concave screen gate is located on the side of the discharge chamber away from the gas distributor, and the ceramic ring is located on the other side of the concave screen gate. The convex acceleration gate is located on the other side of the ceramic ring. The gas distributor includes a cylindrical block and a truncated conical block. The cylindrical block is fixedly installed above the truncated conical block. The cylindrical block and the truncated conical block are smoothly connected by a transition arc. The outer side of the cylindrical block is provided with threads, and its top is provided with an air inlet. The inclined surface of the truncated conical block is provided with several evenly arranged openings. The gas distributor is made of ceramic material.

2. The dual-frequency self-neutralizing radio frequency ion thruster according to claim 1, characterized in that: The discharge chamber includes a cylindrical block and a connecting flange, the connecting flange being located below the cylindrical block, and the discharge chamber being made of quartz glass.

3. The dual-frequency self-neutralizing radio frequency ion thruster according to claim 1, characterized in that: The coil is a spiral electromagnetic induction coil made of copper, and the coil is connected to a radio frequency power supply.

4. The dual-frequency self-neutralizing radio frequency ion thruster according to claim 1, characterized in that: The concave screen gate is a thin-walled cylindrical structure with concave features, and a cylindrical concave region is provided at the center of the concave screen gate.

5. A dual-frequency self-neutralizing radio frequency ion thruster according to claim 4, characterized in that: The recessed screen gate is connected to a dual-frequency radio frequency power supply, which consists of a high-frequency signal and a low-frequency signal.

6. A dual-frequency self-neutralizing radio frequency ion thruster according to claim 5, characterized in that: The low-frequency signal has a frequency range of 2-4MHz, and the high-frequency signal has a frequency higher than or equal to 13.56MHz.

7. A dual-frequency self-neutralizing radio frequency ion thruster according to claim 1, characterized in that: The ceramic ring has a cylindrical annular structure with six through holes evenly distributed on it, and is made of ceramic material.

8. A dual-frequency self-neutralizing radio frequency ion thruster according to claim 4, characterized in that: The convex accelerating gate is a thin-walled cylindrical structure with convex features, and a cylindrical convex region is provided at the center of the convex accelerating gate.

9. A dual-frequency self-neutralizing radio frequency ion thruster according to claim 8, characterized in that: Both the concave region and the convex region have multiple small holes evenly distributed in a hexagonal shape on their planes. Both the concave screen gate and the convex acceleration gate are made of molybdenum.

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