尘埃颗粒在射频等离子体鞘层中的非线性共振现象的理论研究

一种自洽的理论模型用于研究尘埃颗粒在射频鞘层中垂直方向的非线性共振现象.利用射频鞘层动力学模型，研究了鞘层电场和尘埃颗粒的充电过程.考虑作用在尘埃颗粒上的各种作用力(如重力、电场力、离子拖拽力、中性气体摩擦力及探针的扰动力)，并通过数值求解颗粒运动方程，模拟了该尘埃颗粒在探针扰动下的非线性振荡过程.所得结果不仅很好地再现了最近的实验观察，同时还发现这种非线性振动过程与等离子体参数、施加的射频偏压的功率、探针的扰动电位和位置等有着密切的联系. 关键词： 射频鞘层 尘埃颗粒 尘埃充电 非线性共振 迟滞     

对含有非热力学平衡离子的尘埃等离子体中孤波特性的理论研究

得到了描述由尘埃颗粒电荷变化、非热力学平衡分布的离子和Boltzmann分布的电子组成的未磁化的热尘埃等离子体中的尘埃声波的修正的KdV (mKdV) 方程. 并对诸多的尘埃等离子体参数对尘埃声孤波结构的影响进行了理论研究，结果表明，尘埃等离子体参数决定着尘埃声孤波结构，且只在这些参数特别选定的一些区域，才会出现稳定的孤波. 关键词： 非热力学平衡离子 尘埃颗粒电荷变化 尘埃声孤波     

尘埃等离子体物理

尘埃等离子体物理是近年来发展起来的新的研究领域。本文介绍了尘埃等离子体物理的研究内容，特点及研究近况。     

等离子体鞘层中尘埃粒子的分布特性

采用柱槽状电极的流体模型，数值模拟了等离子体鞘层及鞘层中尘埃粒子的分布结构. 研究了尘埃粒子数、粒子大小、电极尺寸等因素对尘埃分布结构的影响. 研究表明：当等离子体密度较高时，鞘层较薄，反之鞘层较厚；当尘埃粒子数少时，尘埃分布形成一层结构，反之则形成多层结构；随电极尺寸的不同，尘埃粒子形成一些复杂而又有趣的结构. 关键词： 尘埃粒子 等离子体鞘层 电极     

尘埃粒子充放电过程对尘埃等离子体电导率的影响

在只受弱电磁场作用且忽略空间色散的情况下，通过求解含碰撞项的电子的Boltzmann方程及尘埃粒子充放电的Shukla方程，导出了弱电离尘埃等离子体的电导率和介电常数计算公式. 将固体火箭喷焰的有关参数代入公式对电导率进行定量分析，结果表明，尘埃粒子的大小及其浓度对弱电离尘埃等离子体的电导率有明显的影响. 关键词： 尘埃等离子体 Boltzmann方程 Shukla方程 电导率     

量子尘埃等离子体中尘埃充电对尘埃声波的影响

采用流体动力学方程组和尘埃充电方程组成的自洽模型系统,对量子尘埃等离子体中的尘埃声波波动性质进行了研究。通过线性理论分析方法得到系统的尘埃声波波动方程及其色散关系,并对色散关系进行了数值分析。研究表明:充电效应定性地修正了尘埃声波的色散特性,引起尘埃声波的耗散,其耗散强度主要与尘埃等离子体的参数有关。最后,分析了引起尘埃声波耗散的物理原因。     

空间尘埃等离子体结构的模拟

尘埃等离子体是一种高温带电气体，它们通常存在于星际空间，在地球上空，在闪电区，一般也会产生这种气体．由于在等离子体中的尘埃都是带电的，因此它们之间存在着静电相互作用．但尘埃等离子体空间内有着各种不同的间隔区，有的间隔区内尘埃间是相互吸引的，而在另一些间隔区内，尘埃间是相互排斥的．因此近年来德国马普研究所的地球外物理研究中心和悉尼大学的科学家们一直在探寻在等离子体内混合有多少尘埃时就会产生相互作用．他们的研究方法主要是计算机模拟．     

尘埃等离子体

尘埃等离子体物理是近十年里等离子体学科中一个活跃的分支领域之一，带电尘埃广泛存在于空间等离子体、实验室聚变装置、低温等离子体工业应用等众多小同的环境中，并且呈现出相同或相似的性质．这是一种部分或完全电离的等离子体，其基本成分除了电子和离子外，还有（通常）带负电的、且电荷不是常数的微粒．带电颗粒有着与电予和离子完全不同的动力学行为，其与等离子体的相互作用呈现出许多新的物理现象．文章介绍了尘埃等离子体物理的简要发展历史、基本性质和主要研究方向以及最近一些热点问题．     

弱电离尘埃等离子体层反射与透射的SO-FDTD方法分析

将弱电离尘埃等离子体复介电常数表示以jω 为自变量的分式多项式形式, 利用移位算子时域有限差分(SO-FDTD)方法, 给出了弱电离尘埃等离子体频域本构关系的时域形式. 推导了弱电离尘埃等离子体电磁特性的时域递推关系式. 用SO-FDTD方法计算了弱电离尘埃等离子体层的反射和透射系数, 分析了尘埃粒子浓度和尘埃粒子半径的变化对反射系数和透射系数的影响. 结果表明: 有尘埃粒子时的反射系数比没有尘埃粒子时反射系数小, 而透射系数要比没有尘埃粒子时的透射系数大; 当尘埃粒子浓度或尘埃粒子半径增大时, 其反射系数均减小.     

等离子体增强化学气相沉积中对尘埃颗粒诊断

采用SiH4,C2H4和Ar在射频容性耦合柱状放电室中产生了尘埃颗粒,利用发射光谱测得射频尘埃等离子体放电室中的一些基本碎片的发射光谱,并给出了这些碎片的光发射强度随着实验条件变化的曲线。随着功率和气压的增加,碎片的光发射强度逐步增加,尤其是随功率增加得更快,这说明功率对硅烷和乙烯的离解作用明显。随着硅烷和乙烯流量的增加,碎片的光发射强度随之下降。利用朗缪尔探针的实验结果得出尘埃密度的变化趋势,给出了尘埃密度随射频功率变化的曲线,其结果与硅烷和乙烯的离解变化趋势基本吻合。     

Pattern phenomena in an rf discharge dusty plasma system

Various dust patterns are observed in an rf discharge dusty plasma system. According to the dust growth process from small to large in size, the formation of different dust patterns can be divided into two stages: the small-particle stage (or dust cloud stage), and the large-particle stage (or dust crystal stage). The evolution relations between different dust patterns with gas pressure changing are investigated. Dust voids, dust acoustic waves and strong turbulence modes are presented at the small-particle stage. The self-organized dust lattices and dust clusters are investigated at the large-particle stage. The static structure of a dust lattice is characterized by means of the pair correlation function. Dust clusters formed by particles with different numbers and the regular evolution of the clusters with gas pressure are also investigated. The packing sequences of dust clusters are verified through two-dimensional confined molecular dynamics simulations.     

Experimental study on parameters of dust plasma in SiH4/C2H4/Ar discharges

Measurements of dust plasma parameters were carried out in the discharges of （SiH4/C2H4/Ar） mixtures. Dust particles were formed in the capacitively coupled radio-frequency discharge of these reactive mixtures in a cylindrical chamber. Langmuir probe was employed for diagnosing and measuring the important plasma parameters such as electron density and electron temperature. The results showed that the electron density dropped, and in contrast the electron temperature rose when the dust particles formed. The curves of the electron density and temperature versus the RF power and pressure were presented and analysed. Further, it was found that the wriations of electron temperature and the size of dust void with the RF power followed the similar trends. These trends might be useful for understanding more about the characteristics of dusty voids.     

Influence of gas pressure on the pattern evolutions of dust clusters and fractals in a dusty plasma system

Dusty plasma has been produced through chemical reaction in a capacitively coupled radio frequency (rf) discharge system. Dust clusters with a few particles and dust fractals are observed. As gas pressure is increased, the suspended height of dust particles descends and the average interparticle distance decreases accordingly. The influence of gas pressure on the pattern evolutions is investigated. Dust clusters or fractals not only can evolve regularly on a horizontal plane, but also can evolve from a horizontal plane to a vertical line array. Under appropriate conditions, the evolutions are reversible. When the evolution is from a symmetrical pattern with a centre particle to another pattern, the centre particle will first show its unsteadiness.     

Dust particles in collisionless plasma sheath with arbitrary electron energy distribution function

Dust particles often appear in industrial plasmas as undesirable product of the plasma-wall interactions. Large particles of several micrometers in diameter are concentrated in a thin layer (the sheath) above the lower electrode of the rf driven parallel plate device, where the electric force is strong enough to compensate particle’s gravity. Experimental and theoretical uncertainties are significantly increased in the plasma sheath. Common models of dust charging in the plasma sheath suppose the Maxwellian electron energy distribution function (EEDF) in conjunction with a flux of cold ions satisfying classical Bohm criterion at the sheath edge. In this paper we generalize this model to arbitrary EEDF with adapted Bohm criterion. We limit our considerations to collisionless or slightly collisional plasma, where the EEDF inside the sheath is expressed through the EEDF in the plasma bulk. Derived theoretical formulas are incorporated into numerical model, describing collisionless radio frequency (rf) plasma sheath together with the electrical charge, various kinds of forces, balancing radius and oscillation frequency of particles.     

CE/SE方法数值模拟炸药粉尘爆轰

采用CE/SE方法数值模拟悬浮在空气中的RDX炸药粉尘的两相爆轰过程.炸药颗粒在爆轰波阵面后的高温高速气流中加速并升温,释放能量支持爆轰波传播.数值模拟爆轰波管中的粉尘爆轰,得到爆轰波流场中的物理量分布,确定爆轰参数,数值结果与文献符合较好.数值模拟复杂通道中的炸药粉尘爆轰,预测了爆轰波的发展和传播过程以及爆轰波后的流场演化.数值结果表明CE/SE方法能成功模拟气体-固体两相爆轰,为粉尘爆轰的研究提供了新的数值预测手段.     

Evolution of a dust void in a radio-frequency plasma sheath

The onset and growth of a dust void are investigated in a radio-frequency (rf) sheath of a capacitively coupled argon plasma. A circularly symmetric void emerges and grows with increasing rf power and pressure in the central region of the dust cloud levitating in the sheath. Experimental measurements of the void diameter are compared with the predictions of a simple phenomenological theory, based on a balance of forces on dust grains.     

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.     

Analysis of Optical Disk Readout Signal Deterioration Caused by Dust on the Substrate

A noise power spectrum estimation method is presented for optical disk readout signal influenced by dust on the substrate. The noise due to dust has been modeled using geometrical optics and assuming the Poisson distribution for the dust particles. The noise power spectrum consists of two components: one comes from the effect of individual dust particles passing across the light beam, and the other comes from the effect of overlapping area of a particle and the inverted image of another particle. The feasibility of a thin-substrate optical disk was studied using this model. Dust will not have a serious effect on the readout signal when a 0.6 mm-thick substrate is used in place of the conventional 1.2 mm-thick substrate.     

Formation and dissociation of dust molecules in dusty plasma

Dust molecules are observed in a dusty plasma experiment.By using measurements with high spatial resolution,the formation and dissociation of the dust molecules are studied.The ion cloud in the wake of an upper dust grain attracts the lower dust grain nearby.When the interparticle distance between the upper dust grain and the lower one is less than a critical value,the two dust grains would form a dust molecule.The upper dust grain always leads the lower one as they travel.When the interparticle distance between them is larger than the critical value,the dust molecule would dissociate.     

悬浮RDX炸药粉尘爆轰的数值模拟

用两相流模型对悬浮RDX炸药粉尘爆轰波进行了数值模拟。RDX炸药颗粒在爆轰波阵面后的高温高速气流中加速并升温,颗粒表面发生熔化。参考液滴在高速气流作用下剥离的效应,假设炸药熔化部分在高速气流的作用下发生剥离,破碎成极小的颗粒,瞬时发生分解反应,释放出能量支持爆轰波传播。数值模拟了在不同粒径和浓度的悬浮RDX炸药粉尘中爆轰波的发展与传播过程,得到了爆轰波流场中气-固两相的物理量分布,并确定了爆轰波参数。在较低的RDX粉尘浓度条件下,爆轰波阵面压力的峰值曲线出现振荡。当RDX粉尘浓度在80~150 g/m3时,数值模拟得到的爆轰波阵面压力峰值曲线的振荡是规则的;当RDX粉尘浓度为70 g/m3时,爆轰波阵面压力峰值曲线出现不规则振荡。