Interactions of charged dust particles in clouds of charges

Two charged dust particles inside a cloud of charges are considered as Debye atoms forming a Debye molecule. Cassini coordinates are used for the numerical solution of the Poisson-Boltzmann equation for the charged cloud. The electric force acting on a dust particle by the other dust particle was determined by integrating the electrostatic pressure on the surface of the dust particle. It is shown that attractive forces appear when the following two conditions are satisfied. First, the average distance between dust particles should be approximately equal to two Debye radii. Second, attraction takes place when similar charges are concentrated predominantly on the dust particles. If the particles carry a small fraction of total charge of the same polarity, repulsion between the particles takes place at all distances. We apply our results to the experiments with thermoemission plasma and to the experiments with nuclear-pumped plasma.     

Interaction of charged dust particles in clouds of thermodynamically equilibrium charges

The solution of the Poisson-Boltzmann equation for a cloud of charges surrounding two charged dust particles treated as Debye atoms forming a Debye molecule is investigated numerically using Cassini coordinates. The electric force exerted on a dust particle by the other dust particle was determined by integrating the electrostatic pressure on the surface of the dust particle. It is shown that attractive forces appear when the following two conditions are satisfied. First, the Debye radius (corresponding to the electron density at half the mean distance between the dust particles) must be approximately equal to half the mean distance between the dust particles. Attraction between the dust particles emerges at a distance equal approximately to half the mean distance between the dust particles. Second, attraction takes place when like charges are concentrated predominantly on the dust particles. If the particles carry a small fraction of charge of the same polarity, repulsion between the particles takes place at all distances.     

A study of methods for moving particles in RF processing plasmas

Methods for moving charged particles in RF processing plasmas are investigated. These methods include varying RF power, varying chamber pressure, attraction and repulsion by an electrostatic probe, and movement with magnetic fields. Varying RF power changes the depth of the potential wells where particles are trapped. The RF power affects shape and location of the traps and the bulk plasma potential. Increasing the chamber pressure moves the sheath edge closer to the wafer being processed. Since particle traps are found at the plasma sheath edge increasing the chamber pressure will move the particle traps (and any trapped particles) closer to the wafer being processed. The Langmuir probe can repel particles when under negative bias and attract them when positively biased. This probe can also distort the sheath edge when the tip resides within the sheath. Applying a magnetic field can change the characteristics of the particle traps and produce a force on the charged dust particles     

Levitation and dynamics of a collection of dust particles in afully ionized plasma sheath

Examines the dynamics of a collection of charged dust particles in the plasma sheath above a large body in a fully ionized space plasma when the radius of the large body is much larger than the sheath thickness. The dust particles are charged by the plasma, and the forces on the dust particles are assumed to be from the electric field in the sheath and from gravitation only. These forces will often act in opposite directions and may balance, making dust suspension and collection possible. The dust particles are supplied by injection or by electrostatic levitation. The ability of the sheath to collect dust particles, will be optimal for a certain combination of gravitation and plasma and dust particle parameters. In a dense dust sheath, the charges on the dust particles contribute significantly to the total space charge, and collective effects become important. These effects will reduce the magnitude of the sheath electric field strength and the charge on the dust particles. As dust particles are collected, the dust sheath is stretched and the largest dust particles may drop out, because the sheath is no longer able to suspend them. In a tenuous dust sheath, the inner layer, from the surface and about one Debye length thick, will be unstable for dust particle motion, and dust will not collect there. In a dense dust sheath, collective effects will decrease the thickness of this inner dust-free layer, making dust collection closer to the surface possible. By linearization of the force and current equations, the necessary and sufficient conditions for a stable dust sheath are found. The authors consider conditions which resemble those of planetary system bodies, but the results may also be of relevance to some laboratory plasmas     

Studies of the dynamic behaviour of charged dust particles in high electric fields using laser Doppler velocimetry

As a preliminary study for the collection of dust particles in an electrostatic precipitator, laser Doppler velocimetry has been used to measure the velocity of small dust particles charged in the high electric field of a model electrostatic precipitator. A differential optical system is adopted for the velocimeter. The period-measuring system is used to analyse Doppler beat signals and to obtain velocity data from them. By means of the laser Doppler velocimeter, the dynamic behaviour of the velocity and direction of moving dust particles is fully revealed as a function of the applied electric voltage in the entire collecting space of the model electrostatic precipitator, and is shown in vectorial flow diagrams of particle velocity.     

Predicting particle trajectories on an electrodynamic screen – Theory and experiment

The electrodynamic screen, or EDS, was first introduced to the electrostatics community in the early 1970's. Since that time, it has been studied by several research groups who have investigated its use as a means to remove unwanted particles from insulator surfaces. In the typical EDS, interdigitated electrodes are embedded or deposited on the surface, then energized by three-phase square or sinusoidal voltages of magnitude 500–1200 V at frequencies between 5 and 200 Hz. The resulting electric field entrains previously deposited particles and moves them laterally across the surface. Electrodynamic screens have been proposed for use on solar cells in Mars and Moon space missions, as well as the removal of dust from renewable-energy solar collectors such as photovoltaic panels, solar reflectors, and mirrors. Though often considered merely a nuisance, dust has the potential to partially or totally obscure the solar flux incident on any solar collector.Development of EDS technology has evolved mostly from a “trial and error” approach to choosing such parameters as electrode spacing, depth, and width, as well as voltage magnitude and frequency. Though some theoretical studies may be found in the literature, a more detailed understanding would be valuable in optimizing EDS performance for a particular application and composition of ambient dust, which may vary with geographical location with respect to size, permittivity, and conductivity. A theoretical understanding of how particles are entrained and made to move on an EDS will facilitate proper choice of relevant parameters in future EDS systems. Our work thus attempts to analyze the motion of dust particles subject to all the forces encountered at the surface of an EDS, including the coulomb and dielectrophoretic forces, as well as aerodynamic drag, gravity, and friction. Previous work has shown that particles entrained in the traveling-wave electrostatic field of an EDS exhibit one of two behaviors: ordered, lateral motion; and semi-chaotic motion. These two behaviors have been found both experimentally and in theoretical simulations. This paper attempts to correlate trajectory computations with video observations of these behaviors as recorded in a laboratory setting.     

Electrostatic force distribution on an electrodynamic screen

The enormous potential of solar energy harvesting plants to provide clean energy is severely limited by dust accumulation on their optical surfaces. In lieu of the most commonly-practiced manual cleaning method of using high-pressure water jets, electrodynamic screen (EDS) technology offers an attractive solution for removing dust particles from optical surfaces using electrostatic forces. In this paper, the impacts of different EDS design parameters in the electric field distribution on an EDS have been studied. Furthermore, based on electric field expressions, closed-form solutions for multipolar dielectrophoretic (DEP) forces in the EDS application are provided. Detailed evaluation of the EDS performance necessitates investigation of different forces involved in the dust removal process. Different comparisons are made between repelling and attracting forces exerted on dust particles deposited on an EDS surface. These comparisons elucidate EDS performance in the removal of a given size range of dust particles. The significant detrimental impact of relative humidity upon the dust removal process is quantitatively addressed. It is shown how just a 10 percent increase in relative humidity can make the repelling force ineffective in the dust removal process.     

A particle-in-cell simulation of dust charging and shielding in lowpressure glow discharges

The transport of particles (“dust”) in low pressure electrical glow discharges is being studied in regard to its role in contaminating silicon wafers during plasma etching and deposition. Particles (10 s nm-μm) negatively charge in glow discharges and, to first order, appear to be massively large negative ions around which sheaths develop. The forces on particles in plasmas include electrostatic (drift of charged particles in electric fields) and viscous ion drag. The latter force is momentum transfer from ions to particles by either collisions or orbital motion. This force critically depends on the charge on the particle and the shape of the sheath surrounding the particle. In this work, we report on a pseudoparticle-in-cell (PIC) simulation of the transport of electrons and ions in the vicinity of dust particles in low pressure glow discharges. The simulation produces the electrical charge on the dust particle, the sheath structure around the dust particle and the orbital dynamics of the ions. A companion molecular dynamics simulation uses these parameters to produce ion-dust and electron-dust particle cross sections for momentum transfer and collection. Results will be discussed for charge, sheath thickness, cross sections and viscous ion drag forces on dust particles as a function of radius and plasma parameters     

Electric field and Lorentz force contribution to atmospheric vortex phenomena

The physics that initiate and sustain tornados and dust devils is still under investigation. Forces that operate throughout a wide range of scales and could contribute to atmospheric vortex phenomena are the Lorentz force and the force of electric fields. The Lorentz force results in a circular motion of charged particles in a magnetic field. An electric field will pull or repel a charged particle in the direction of the field. This paper will demonstrate that the Lorentz force and the force of electric fields, acting on charged particles that exist in atmospheric vortex phenomena, plausibly contribute to the set of physics that will explain tornados and other atmospheric vortex phenomena.     

Interaction of a dielectric macroparticle with a point charge in plasma

The electrostatic interaction of a charged spherical dielectric macroparticle with a point charge in a plasma in the presence of an external uniform electric field is considered. The electrostatic force and the torque acting on the macroparticle have been determined, and the form of the interaction potential has been established for a nonuniform distribution of free charge on the macroparticle surface. A simple (for calculations) expression for the interaction potential that describes well the exact potential at all interparticle distances is proposed. The angular velocity of the spinning of dust particles caused by a nonuniform distribution of free charge over their surface has been estimated.     

Manipulation of single particles by utilizing electrostatic force

Because manipulation of single particles is of great importance in the fields of electronics and biology, the author has been investigating an electrostatic manipulation system. The manipulation probe consisted of dipole pin electrodes. When voltage was applied between the electrodes, the dielectrophoresis and coulombic force generated in the non-uniform electrostatic field was applied to the particle near the tip of the electrode. The particle was captured by the application of voltage and then it is released from the probe by turning off the voltage application. It was possible to manipulate not only insulative but also conductive particles. However, if a particle was charged, the Coulomb adhesion force prevented the release of the particle even when the voltage application was turned off. This condition was generally observed for small particles. Asymmetric and coaxial electrode systems were developed so that the release of the attached particle was independent of the position of the probe. Instead of turning off the voltage application, high voltage was applied to the electrodes to blow off the particle by the ionic wind generated in a corona discharge field, and the applicability of this system was demonstrated. Further, a vibration separator was developed. A three-dimensional field calculation was conducted to calculate the dielectrophoretic force by using the finite difference method and the calculated force was compared to the measured force. It was deduced that the predominant force for the particle adhesion was not dielectrophoresis but Coulomb force generated due to triboelectrification.     

Formation of plasma dust structures at atmospheric pressure

The formation of strongly coupled stable dust structures in the plasma produced by an electron beam at atmospheric pressure was detected experimentally. Analytical expressions were derived for the ionization rate of a gas by an electron beam in an axially symmetric geometry by comparing experimental data with Monte Carlo calculations. Self-consistent one-dimensional simulations of the beam plasma were performed in the diffusion drift approximation of charged plasma particle transport with electron diffusion to determine the dust particle levitation conditions. Since almost all of the applied voltage drops on the cathode layer in the Thomson glow regime of a non-self-sustained gas discharge, a distribution of the electric field that grows toward the cathode is produced in it; this field together with the gravity produces a potential well in which the dust particles levitate to form a stable disk-shaped structure. The nonideality parameters of the dust component in the formation region of a highly ordered quasi-crystalline structure calculated using computational data for the dust particle charging problem were found to be higher than the critical value after exceeding which an ensemble of particles with a Yukawa interaction should pass to the crystalline state.     

Impacts of neutral shadowing force on dust particle dynamics in cryogenic plasma

Recently, it was shown that the neutral shadowing force can have a strong impact on the structural properties of the charged dust particles in cryogenic dusty plasmas. Therefore, in this work, we have investigated the impact of the neutral shadowing force on the dynamical properties by means of molecular dynamics simulations. By computing the velocity auto‐correlation function of particles and their spectrum, we found that the neutral shadowing force has a strong impact on the dust particle dynamics if the mean free path of neutrals exceeds the mean inter‐dust particle distance.     

The influence of dust particle geometry on its charge and plasma potential

In this paper, a self‐consistent numerical model describing the behaviour of plasma around isolated highly charged dust particles with different shapes of rotation figures is presented. Dust particles in the form of a sphere, oblate ellipsoids (disk‐like particles), and elongated ellipsoids (rod‐like particles) are considered in the presence of an external electric field. Using the developed model, self‐consistent distributions of a space charge and plasma potential are obtained around non‐spherical dust particles. These distributions are carefully analysed by decomposing them in a series of Legendre polynomials. Decompositions of these distributions are compared with particles of different geometry. In addition, for different geometries of dust particles, the dependencies of the charge of a dust particle on geometry in the absence of an external field are investigated.     

Formation of dust-acoustic shock waves in a strongly coupled cryogenic dusty plasma

The nonlinear propagation of ultra-low-frequency dust-acoustic (DA) waves in a strongly coupled cryogenic dusty plasma has been investigated, by using the Boltzmann distributed electrons and ions, as well as modified hydrodynamic equations for strongly coupled charged dust grains. The reductive perturbation technique is used to derive the Burger equation. It is shown that strong correlations among negatively charged dust particles acts like a dissipation, which is responsible for the formation of the DA shock waves. The latter are associated with the negative potential, i.e. with the compression of negatively charged cryogenic dust particle density. It is also found that the effective dust-temperature, which arises from electrostatic interactions among negatively charged dust particles, significantly affects the height of the DA shock structures. New laboratory experiments at cryogenic temperature should be conducted to verify our theoretical prediction.     

高压电场内细颗粒堆积机理研究

细颗粒的堆积既是电厂尾部除尘系统的核心问题,也是航天领域空间环境内限制动力或光学元件性能的关键问题。电场力因具有长程有效性和强可操作性成为控制细颗粒堆积的主要手段。本文通过微观实验研究了高压平行板电场间细颗粒堆积的机理,观察到颗粒在预极化、预荷电、变外电场电压等工况下的堆积形貌,并发展了图像处理的方法统计堆积颗粒数。研究表明,偶极力是外电场下颗粒成链的主因,而颗粒的倒伏则是来自曳力的作用,颗粒链的极限高度主要受外电场场强和颗粒堆积结构的影响。     

Closed-form solution of mid-potential between two parallel charged plates with more extensive application

Efficient calculation of the electrostatic interactions including repulsive force between charged molecules in a biomolecule system or charged particles in a colloidal system is necessary for the molecular scale or particle scale mechanical analyses of these systems. The electrostatic repulsive force depends on the mid-plane potential between two charged particles. Previous analytical solutions of the mid-plane potential, including those based on simplified assumptions and modern mathematic methods, are reviewed. It is shown that none of these solutions applies to wide ranges of interparticle distance from 0 to 10 and surface potential from 1 to 10. Three previous analytical solutions are chosen to develop a semi-analytical solution which is proven to have more extensive applications. Furthermore, an empirical closed-form expression of mid-plane potential is proposed based on plenty of numerical solutions. This empirical solution has extensive applications, as well as high computational efficiency.     

Electrostatic adhesion of ion and triboelectric-charged particles

The adhesion of ∼10 μm charged toner particles is of considerable importance in the electrophotographic process for copying or printing documents. If the non-electrostatic short-range adhesion force is reduced with nanoparticle surface additives, the toner adhesion is dominated by an electrostatic force. However, the measured adhesion of triboelectrically charged toner is greater than the prediction of an electrostatic image force model that assumes a uniform surface charge distribution. The enhanced electrostatic adhesion of triboelectrically charged toner is attributed to a non-uniform surface charge distribution. To provide support for this interpretation, the adhesion of ion-charged toner is of interest since a more uniform surface charge distribution is expected. Electric field detachment measurements on ion-charged toner for different charge levels show that the adhesion of ion-charged toner is indeed less than that of triboelectrically charged toner.     

考虑电离作用的淤泥异向絮凝三维数值模拟

鉴于试验观察淤泥絮凝结构的技术难度,本文尝试以布朗动力学为基础,采用蒙特卡洛方法动态模拟电离作用下颗粒成长为絮团的过程.为结合实际情况,泥沙颗粒初始位置由颗粒粒径和淤泥密度决定,颗粒初始速度按照相应条件下高斯随机分布给定.边界条件用和实际符合较好的循环边界.在模拟数据分析的基础上,讨论并比较了颗粒粒径和淤泥密度对絮凝时间以及絮团开放程度的影响.另一方面,讨论了电离作用后颗粒电荷量对絮团生长的影响.解释了泥沙颗粒表面电荷密度变化对絮凝过程和絮团结构的影响,模拟结果和实际情况较为一致.     

空间尘埃等离子体对量子卫星通信性能的影响

为了研究尘埃等离子体中带电尘埃的粒子半径、粒子浓度和带电荷数对量子通信性能的影响,首先根据Mie散射理论得到单个带电尘埃粒子的光散射截面;然后通过粒子浓度求出总的消光截面,得出链路衰减的数学模型,提出了带电粒子特性与量子纠缠度的关系;针对退极化信道,当单个尘埃粒子所吸附带电粒子的个数为50时,给出了尘埃粒子半径、粒子浓度与信道容量和量子误码率的定量关系.仿真结果表明,当量子信号的传输距离为10km时,尘埃粒子浓度从1×10~(10) m~(-3)增加到10×10~(10) m~(-3),信道容量从0.6726降低到0.1075;尘埃粒子半径从0.1μm增加到10μm时,量子误码率由1.334×10~(-3)增加到5.309×10~(-3).由此可见,尘埃等离子体中带电尘埃粒子的半径和浓度对量子卫星通信性能有显著的影响.因此,为确保量子通信的可靠性,应根据所探测到的等离子体环境的状况,调整卫星通信系统的各项指标参数.