A microcavity charging model for mixed-size lunar dust

Abstract

This invention discloses a microcavity charging model for mixed-size lunar dust and a method for evaluating the electrostatic lift probability of lunar dust based on this model, belonging to the field of planetary dust dynamics and spacecraft surface environment control technology. Addressing the problem that existing uniform-size models cannot explain the particle size selectivity of electrostatic lift of lunar dust with a wide particle size distribution, a non-uniform microcavity geometric model is constructed, considering the diameter of the target large particle and the diameter of neighboring small particles. The relationship between the total Coulomb force on the target particle and the particle size parameter is derived, which can be simplified under certain conditions. Combined with the van der Waals adhesion model, a lift criterion factor is established, revealing that the lift probability decreases exponentially with increasing particle size. This method can predict the electrostatic migration ability of lunar dust with different particle sizes, providing a theoretical basis for lunar dust protection, resource classification and collection, and optimization of dust removal parameters.

Description

Technical Field

[0001] This invention relates to the fields of planetary dust dynamics, electrostatic transport theory, and spacecraft surface contamination control technology. Specifically, it relates to a non-uniform microcavity charging model that considers the wide particle size distribution of real lunar dust, and a method and system for predicting the probability of electrostatic lifting of lunar dust based on this model. Background Technology

[0002] The lunar surface is covered by a regolith layer several meters thick, with particles ranging in size from submicron to hundreds of micrometers. Due to the lack of an atmosphere and the high vacuum environment of the moon, solar ultraviolet radiation and space plasma charge lunar dust, leading to electrostatic lift and dust migration. This poses a serious threat to the optical lenses, solar panels, sealing mechanisms, and the health of astronauts. During the Apollo program, the "horizon glow" and large particle migration were observed; however, traditional electrostatic lift models (such as the monodisperse patched charge model) assume all particles are the same size, failing to explain why particles tens of micrometers in size can also be lifted. In reality, the microcavity structure formed by the mixture of particles of different sizes in natural lunar dust produces significant charge and force amplification effects. Therefore, establishing a non-uniform microcavity charging model that reflects the actual particle size coupling is crucial for accurately predicting the electrostatic migration behavior of lunar dust and guiding the development of dust removal technologies. Based on these needs, this invention proposes a novel particle size-dependent lift probability assessment method through rigorous geometric and electrodynamic derivations, filling a gap in existing theories. Summary of the Invention

[0003] To address the problem of prediction bias caused by neglecting particle size non-uniformity in existing models, this invention provides a method for evaluating the electrostatic lifting probability of lunar dust based on a microcavity charging model with non-uniform particle size. By analyzing the particle size-dependent competition mechanism between Coulomb repulsion and adhesion, the universal law of the lifting probability decaying exponentially with particle size is obtained, and dust removal strategies can be optimized accordingly.

[0004] Consider a typical non-uniform microcavity structure in real lunar dust: a target large particle (diameter) ) is composed of multiple smaller neighboring particles (diameter) ,satisfy The particles are surrounded by electron beams, forming closed or semi-closed cavities. Under electron beam or photoelectron irradiation, secondary electrons are reabsorbed within the microcavities, resulting in negatively charged patches on the particle surface. (Particle spherical capacitance) Therefore, the accumulated charge ,Right now , ,in Where is the particle radius, The particle diameter is denoted as .

[0005] The center-to-center distance between the target large particle and a single neighboring small particle is:

[0006]

[0007] Surface area of ​​target large particles The projected area occupied by a single small particle on the surface of a target large particle. Therefore, the number of small particles forming microcavities around the target large particle is:

[0008]

[0009] The Coulomb repulsion between a single pair of particles is:

[0010]

[0011] The total Coulomb repulsive force on the target large particle is the sum of the contributions from all neighboring small particles:

[0012]

[0013] exist Under typical conditions, we can approximate the following:

[0014]

[0015] This simplified formula clearly shows that the larger the target particle and the smaller the surrounding particles, the stronger the Coulomb repulsion. This is the key amplification effect of non-uniform microcavities.

[0016] Van der Waals adhesion exhibits a superlinear increase with particle size due to multi-point contact and surface roughness:

[0017]

[0018] in (Experimental calibration: α≈1.5~1.8).

[0019] Define the lifting criterion factor:

[0020]

[0021] because , It is a negative number, therefore With the target large particle diameter The increase in [something] leads to a sharp decrease, resulting in a significant reduction in the probability of large particles being lifted; at the same time... and The inverse relationship indicates that when the surrounding small particles are sufficiently small, even large particles may satisfy the lifting condition. Based on this mechanical competition model, statistical analysis of a large number of microcavity configurations reveals that the lifting probability follows an exponentially decaying distribution.

[0022]

[0023] in It is determined by the dielectric properties and surface morphology of the material.

[0024] Beneficial effects

[0025] This study is the first to theoretically reveal the amplification mechanism of the Coulomb repulsion force in non-uniform particle-size microcavities, correcting the deficiency of traditional uniform models in underestimating the uplift probability of large particles; it provides an exponential function form of the uplift probability that can be directly used for engineering prediction, and specific parameters can be calibrated experimentally; based on criterion factors... It can quantitatively provide the lifting threshold of particles of different sizes, providing a basis for adaptive control of dust removal systems; it can be extended to the dust migration analysis of other celestial bodies without atmosphere (such as asteroids and Martian satellites).

[0026] In summary, this invention, through the synergy of active electron injection and Lorentz force rotation, breaks through the bottleneck of existing lunar dust removal technology and has significant engineering application value and scientific significance. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a microcavity charging model with mixed particle sizes.

[0028] Figure 2 This is a magnified view of a mixed-particle-size microcavity charging model.

[0029] Figure 3 Flowchart of the method for assessing the probability of static lift of lunar dust

[0030] Figure 4 This is a schematic diagram of a ground-based experimental setup used to verify the model of this invention, including a vacuum chamber, a reflector, a lunar dust simulator electron beam emission source, a sample stage, and a high-speed camera observation system.

[0031] Figure 5 This is a high-speed camera projection image of lunar dust simulants under electron beam bombardment.

[0032] Figure 6 It is an optical microscope mosaic image of the distribution of sedimentary particles of lunar dust simulants along four directions, covering a radial distance range of 2.45–7.25 mm. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0034] Example 1: Model Validation Experiment

[0035] To verify the correctness of the non-uniform particle size microcavity charging model proposed in this invention, an electron beam bombardment experiment was conducted in a lunar surface simulation environment. The experimental setup is as follows:

[0036] Vacuum environment: Cylindrical stainless steel vacuum chamber, 1.0 m in diameter and 1.5 m in length, with an internal pressure below 10... -2 Pa, simulating the high vacuum conditions on the moon;

[0037] Electron beam source: A tungsten filament is used as the hot cathode, located 110 mm directly above the sample, with a negative bias voltage of -200 V applied; the filament heating current is adjustable to generate a continuous electron beam;

[0038] Electron beam current density: 1.6 × 10⁻⁶ 9 cm -2 ·s -1 This is comparable to the typical photoelectron flux produced by solar irradiation on the lunar surface.

[0039] Incident electron energy: approximately 98 eV at the surface of the lunar dust sample;

[0040] Test samples: CLDS-i lunar dust simulants (developed by the Institute of Geochemistry, Chinese Academy of Sciences) were used, with the main components being volcanic ash, plagioclase, pyroxene, etc., and the particle size distribution ranging from submicron to 100 μm; spherical silica microspheres (median particle size 20 μm) were also used as controls.

[0041] Sample preparation method: Simulated lunar dust is densely filled into a cylindrical pit processed on a quartz glass substrate. The pit has a diameter of 4 mm and a depth of 1 mm to simulate the localized accumulation of lunar dust on the surface of an optical instrument.

[0042] Observation equipment: High-speed camera with a frame rate of 2000 fps, which can clearly capture the rising trajectory of micron-sized dust particles; the camera is set outside the observation window of the vacuum chamber and focuses on the vertical cross section of the dust pile and the surface of the substrate respectively;

[0043] Experimental procedure: After evacuating to the set pressure, slowly turn on the heating power supply to raise the temperature of the tungsten filament and apply a bias voltage to generate an electron beam; continuously record the motion images of lunar dust particles within 0 to 6 seconds after the electron beam is turned on; after the experiment, turn off the power supply and wait for the pressure inside the chamber to return to normal before taking out the sample for microscopic observation.

[0044] Experimental phenomena: Within approximately 1-3 seconds after the electron beam is applied, simulated lunar dust particles were clearly observed jumping off the substrate surface (lifting phenomenon) using a high-speed camera. After jumping, the particles then exhibited a noticeable rotational motion around the central region of the electron beam, with some particles being transported to areas several millimeters away for deposition. The lifting behavior of particles of different sizes showed significant differences: smaller dust particles (those with smaller bright spots observed by the naked eye) were more easily excited to jump, while larger particles required longer electron beam exposure times or higher electron fluxes to lift. This particle size-selective lifting phenomenon is completely consistent with the qualitative trend predicted by the model of this invention: "the lifting probability decreases with increasing particle size." By repeating the experiment with varying electron beam current densities, it was observed that larger particles were relatively easier to lift in areas with densely packed small particles, which confirms the model's core conclusion that "the smaller the diameter ds of the surrounding small particles, the greater the Coulomb repulsion." These experimental phenomena provide direct support for the non-uniform microcavity charging model proposed in this invention.

[0045] Example 2: Model-based optimization of electron beam dust removal parameters

[0046] The aforementioned evaluation method was integrated into the dust removal system of a lunar rover's robotic arm. First, the particle size distribution of lunar dust on the surface to be cleaned was acquired using an onboard microscope. Then, the theoretical lifting criterion factor for particles of different sizes was calculated using the model of this invention. The controller, according to The electron beam heating current (10~20A) and negative bias voltage (-100~-300V) are automatically adjusted to match the electron flux with the optimal microcavity charging conditions. For areas dominated by fine dust, lower electron energy is used to avoid overcharging and redeposition; for mixed particle size areas, the electron flux is automatically increased to enhance the Coulomb repulsion force of the microcavity around large particles.

[0047] Example 3: Application of Lunar Dust Classification and Collection

[0048] Based on the monotonically negative correlation between the predicted uplift probability and particle size, a multi-stage electrostatic deflection collection device was designed. Deflection electrodes with different voltage gradients were placed downstream of the electron beam uplift region, preferentially deflecting small-diameter dust particles (with high predicted uplift probability) to the first-stage collection chamber, while larger-diameter dust particles (with low predicted uplift probability) entered further-stage collection chambers. Simulated lunar soil grading experiments showed that this method can effectively grade lunar dust particles, providing technical support for in-situ oxygen production from lunar soil and particle size control of 3D printing raw materials.

[0049] The above description is merely a specific embodiment of the present invention, intended to exemplify the solution and advantages of the present invention, and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, combinations of implementation methods, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A microcavity charging model for lunar dust with mixed particle sizes, characterized in that, The steps involved in calculating the probability of electrostatic lift of lunar dust using the applied model are as follows: Step S1: Obtain the particle size distribution data of the lunar dust sample to be evaluated, including at least the equivalent diameter of the target large particles. And the equivalent diameter of the surrounding small particles adjacent to the target large particle. And satisfy ; Step S2: Construct a geometric model of a non-uniform particle size microcavity and determine the center distance between the target large particle and a single adjacent small particle. And the number of small particles forming microcavities around the target large particles. ; Step S3: Based on spherical particle capacitor Under electron irradiation or photoelectron emission conditions, the accumulated charge of the target large particles is established. The accumulated charge of adjacent small particles ; Step S4: Calculate the Coulomb repulsion between a single pair of particles Thus, the total Coulomb repulsive force experienced by the target large particle is obtained. And derive the parsing expression; Step S5: Establish a van der Waals adhesion force model ,in It is a superlinear exponent and satisfies ; Step S6: Define the lifting criterion factor By comparison With preset threshold The size of the target particles is used to determine the probability of electrostatic lifting and to construct the particle size distribution. With the probability of rising The exponential decay function between them.

2. The method according to claim 1, characterized in that, The analytical expression for the total Coulomb repulsion force in step S4 is: and in Simplified under the condition to .

3. The method according to claim 1, characterized in that, The lifting probability mentioned in step S6 It conforms to the exponential decay model: ,in For amplitude coefficient, The attenuation coefficient is determined experimentally or based on the force ratio. Obtained from particle size statistics.

4. The method according to claim 1, characterized in that, The Van der Waals adhesion index The range of values ​​is It was measured by atomic force microscopy or calibrated using standard simulated lunar dust samples.

5. A system for assessing the probability of electrostatic lift of lunar dust based on the method of any one of claims 1 to 4, characterized in that, include: The particle size analysis module is used to acquire microscopic images of lunar dust and extract the diameter of large target particles. and the diameter of adjacent small particles Statistical distribution; The microcavity charging calculation module calculates the theoretical total Coulomb repulsion force distribution according to steps S2 to S4 in claim 1; Adhesion assessment module, based on particle size and preset index Calculate van der Waals adhesion forces; The probability output module is based on the lifting criterion factor. Generate particle size-lift probability curves or numerical tables.

6. The application of the method according to claim 1 in optimizing electron beam dust removal parameters, characterized in that: The evaluation method is used to predict the lifting probability of particles of different sizes in the lunar dust to be treated, and the energy density or flux of the electron beam is adjusted accordingly to make the electron injection conditions meet the optimal efficiency of microcavity charging, thereby achieving selective lifting of lunar dust.

7. The application of the method according to claim 1 in the graded collection of lunar dust, characterized in that: Based on the monotonic relationship between the predicted uplift probability and particle size, multi-level electric or magnetic field separation thresholds are set to guide lunar dust of different particle size ranges to different collection chambers, thereby achieving particle size classification collection.

8. The method according to claim 1, characterized in that, The term "neighboring small particles" refers to a group of surrounding particles that are in direct contact with the target large particle or whose distance from it is smaller than the radius of the target large particle, and whose diameter... The median or weighted average is obtained from the statistical analysis of the microscopic images.

9. The method according to claim 3, characterized in that, The attenuation coefficient The dielectric constant and surface morphology of lunar dust materials were determined through a series of electron beam bombardment experiments and microscopic post-processing calibrations.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, it implements the steps of the evaluation method according to any one of claims 1 to 4.

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