The dynamics of macroparticles in a direct current glow discharge plasma under microgravitation conditions

The dynamics of large-sized (70-180 μm) spherical bronze particles in a direct current glow discharge plasma was studied experimentally under microgravitation conditions. The temperatures, velocities, pair correlation functions, and self-diffusion coefficients of macroparticles were measured at various discharge currents. The charges of dust particles (on the order of 10⁶ e) corresponded to high surface potentials of about 30–40 V. The experimental data were in close agreement with the simulation data on Yukawa systems with weak screening of dust charges. The influence of macroparticles on equilibrium ionization in a dense dust cloud was considered.     

Interaction between glow discharge plasma and dust particles

The effect of dust particle concentration on gas discharge plasma parameters was studied through development of a self-consistent kinetic model which is based on solving the Boltzmann equation for the electron distribution function. It was shown that an increase in the Havnes parameter causes an increase in the average electric field and ion density, as well as a decrease in the charge of dust particles and electron density in a dust particle cloud. Self-consistent simulations for a wide range of plasma and dust particle parameters produced several scaling laws: these are laws for dust particle potential and electric field as a function of dust particle concentration and radius, and the discharge current density. The simulation results demonstrate that the process of self-consistent accommodation of parameters of dust particles and plasma in condition of particle concentration growth causes a growth in the number of high-energy electrons in plasma, but not to depletion of electron distribution function.     

Levitation of charged macroparticles in the anode region of a glow discharge

Levitation of dust particles in the anode region of a dc glow discharge was observed for the first time. A dust cloud of several tens of particles formed at a distance of several millimeters above the central part of the anode. When the discharge parameters were varied, the shape of the cloud and its position above the anode varied. An analysis of the experimental conditions revealed that these particles are positively charged in contrast to other experiments on the levitation of dust particles in a gas-discharge plasma. An estimate of the particle charge taking into account processes of electron emission from their surface is consistent with results of measurements of the electric field strength.     

Ordered dust structures in glow discharge plasmas

Ordering of dust grains suspended in glow discharge plasmas into quasi-steady liquid-or crystallike structures in an external field is considered. The self-consistent electric field generated by free electrons, ions, and dust grains is found. An estimate is obtained for the confining potential required to hold dust grains in the direction perpendicular to the discharge axis. It is shown that the potential energy of interaction between ordered dust particles has the form characteristic of ionic crystals. Critical parameters are estimated for a liquidlike dust structure. The correlation function calculated for a dusty plasma by using this approach is compared with a measured one.     

Ordered dust structures in a glow discharge

Highly ordered three-dimensional dust structures are created in a striated glow discharge, and their horizontal cross-sectional images are analyzed. Calculated correlation functions, local correlation parameters, and corresponding approximations are used to classify the state of a structure according to the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) two-dimensional melting theory and a phenomenological approach. An orientational map based on an orientational parameter is proposed to expose domains in a cross section of a structure. It is shown that a plasma crystal is a polycrystal consisting of hexagonal domains (crystallites). Thermophoretic forces are used to create corners of various angles in the perimeter of the structure. Transition between hexagonal and square cell shapes is observed.     

Transport properties of macroparticles in dust plasma induced by solar radiation

The paper deals with the results of experimental investigation of the dynamic behavior of macroparticles charged by way of photoemission, under conditions of microgravity. The experimental data have been obtained for bronze particles subjected to solar radiation in a buffer gas at a pressure of 40 Torr (Mir space station). Different procedures for determining the transport properties of macroparticles by analyzing video records of experiments are treated. The velocity distribution, the temperature, the charge, the friction coefficient, and the dust particle diffusion coefficients are found. The results of comparing the experimental and theoretical estimates demonstrate that the dynamic behavior of macroparticles under the conditions of investigations are defined by the process of their ambipolar diffusion.     

Analysis of the size and shape of polydisperse dust particles in a complex glow discharge plasma

The size and shape factor distribution of levitating particles is studied by the method of extraction of dust particles from the discharge chamber. Two dust traps existing in a glow discharge in the strata and above the lower wall of the tube near the bend in the current channel are investigated separately. It is found that the size distribution of polydisperse particles of an arbitrary shape is of the bimodal type due to simultaneous levitation of particles with two shape factors. Polydisperse spherical particles of any size exhibit levitation due to the separation of particles over the wall thickness. For identical parameters of the discharge, the size of the particle in neon is slightly larger than in krypton; the particle size in the trap located in a stratum is substantially larger than the particle size in the trap above the wall of the discharge tube. Precision determination of the shape and size of particles makes it possible to estimate the electric field strength for dust traps. It is shown that the glow discharge can be used as a tool for separation of dust particles in a wide range of their sizes.     

Influence of inhomogeneous conditions on the kinetic energy of dust macroparticles in plasma

A brief review of the mechanisms leading to the “anomalous heating” of charged dust particles (macroparticles) in a plasma is presented. Their comparative characteristics are given. An analytical model to estimate the influence of spatial inhomogeneities on the anomalous heating of macroparticles in plasma–dust systems is proposed.     

Dusty plasma structures in He-Kr DC glow discharge

Ion drift in gas mixtures has certain properties that can be used to generate ion flows with desired characteristics. For example, when the field is strong, ion heating is significant, and there is a large difference in atomic weight between ions and atoms, the ion velocity distribution can be highly anisotropic. Ion distribution anisotropy, in turn, can cause a substantial change in properties of dust structures in plasmas. Experiments on dusty plasma structures in glow discharge in mixtures of light and heavy gases (helium and krypton) are performed, and results of numerical simulations of ion and electron drift in the mixture are presented.     

磁控直流辉光等离子体放电特性

本文利用单探针诊断等离子体参数来研究自行设计的磁控直流辉光等离子体实验装置的放电特性, 从而得出电子密度与气体压强、电子密度分布与磁场位型以及磁场强度等的关系. 另外, 用有限元的方法对线圈通电产生的磁场进行数值计算, 模拟出不同接线方式的两种磁场位型分布. 通过实验得出这两种不同的位型的磁场均对等离子体的状态有一定的“控制”作用, 而且这种“控制”作用与现有理论相符合.     

Generation of homogeneous plasma in a low-pressure glow discharge

The possibility of producing homogeneous plasma in a low-pressure discharge with the use of a hollow anode or hollow cathode is analyzed. It is shown that, in contrast to the high-pressure discharge, where uniform ionization is needed to produce homogeneous plasma, in the low-pressure discharge, nearly uniform radial distribution of the plasma parameters can be achieved under nonuniform ionization conditions by increasing the ionization probability at the system periphery and reducing it near the system axis. It is shown that the magnetic field can facilitate generation of the homogeneous plasma instead of interfering with it.     

一种简单的辉光放电等离子体诊断方法

以碰撞为能量交换机制,按局部热力学平衡近似处理低气压等离子体,并考虑辉光放电二极之间的电位分布,得到了电子密度与气体压力的关系和电子温度与电场强度的关系。提出了一种利用压强、电压和电流就获得电子温度和密度的诊断方法。用Langmuir探针方法验证了获得的结果。     

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以碰撞为能量交换机制,按局部热力学平衡近似处理低气压等离子体,并考虑辉光放电二极之间的电位分布,得到了电子密度与气体压力的关系和电子温度与电场强度的关系。提出了一种利用压强、电压和电流就获得电子温度和密度的诊断方法。用Langmuir探针方法验证了获得的结果。     

Dusty plasma in the stratified glow discharge in moderate magnetic field

This article presents the experimental study of dust structures formed in striations of glow discharge in an external magnetic field of up to 10⁴ G, which was created using a cryomagnet. A magnetic field classification based on probe theory is described. In moderate magnetic field, we obtained stable dust structures. The corresponding experimental setup and the experiment itself are described in detail. Special attention was paid to the influence of magnetic field on the change of the diameter and inter‐particle distance of dusty cloud. And, we also determined the dependence of angular velocity of dust rotation on magnetic induction.     

Experimental investigation of discharge characteristics in enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation (EGD-PIII) that involves a small pointed anode and large area tabular cathode, the high negative substrate bias not only acts as the plasma producer but also supplies the implantation voltage. Consequently, an electric field is created to focus the electrons and the electron focusing field in turn enhances the glow discharge process. In this work, the discharge characteristics of EGD-PIII are investigated experimentally. The discharge initiation and extinction characteristics during pulsed biasing are discussed. The duration of the post pulse-off plasma is explained from the viewpoint of particle motion and experimentally verified by employing an auxiliary disk. Our experiments show that a dual-pulse method may be utilized to determine the remnant plasma.     

Realization of SOC behavior in a dc glow discharge plasma

Experimental observations consistent with Self Organized Criticality (SOC) have been obtained in the electrostatic floating potential fluctuations of a dc glow discharge plasma. Power spectrum exhibits a power law which is compatible with the requirement for SOC systems. Also the estimated value of the Hurst exponent (self similarity parameter), H being greater than 0.5, along with an algebraic decay of the autocorrelation function, indicate the presence of temporal long-range correlations, as may be expected from SOC dynamics. This type of observations in our opinion has been reported for the first time in a glow discharge system.     

Mass spectrometry of molecules and radicals in glow discharge plasma

The article represents a method and equipment developed for mass spectrometric analysis of plasma, that is, for measurement of concentration of atoms and molecules, and their fragments, including free radicals. A compact and inexpensive mass spectrometer is based on a quadrupole residual gas analyzer (RGA-200, Stanford Research Systems). The design of the two-section differential pumping chamber makes it possible to bring the mass-spectrometer analyzer to the entrance diaphragm to a distance of 40 mm in order to measure quick reacting and easily condensed particles. The equipment was used for analyzing the composition of spherical glow discharge plasma in methanol vapor and acetone-nitrogen mixture. A procedure for mass spectrum processing is proposed. Time-varying concentrations of all observed neutral particles are measured. Presently available data on sections of complete and dissociative ionization of molecules and their fragments, which are necessary for reconstructing concentrations of particles in plasma from measured mass spectra, are presented.     

Sizing of particles levitating in a glow discharge dusty plasma

The dust particle size distribution in a volume glow discharge dusty plasma is studied. Polydisperse quartz particles are used as a dust component. It is found that a dusty plasma forms in a glow discharge not only in a dust trap but also near the wall at the bottom of the discharge chamber. Dust objects in the latter region are large: they contain up to 30000 particles. The size of particles levitating in discharge striations is three times larger than that of particles levitating near the wall. The idea of using the glow discharge dusty plasma for particle-size fractionation of polydisperse powder is put forward.