Plasma-dust Structures Research Articles

Formation of Dusty Structures in Spherical Glow Discharge

We study, for the first time, plasma-dust structures in the spherical geometry of a discharge, which are formed either spontaneously or specially. High molecular gases, such as acetone and ethyl alcohol, are used for the generation of strata. Strata are required for the formation of structures of injected grains. The generation of grains in air plasma occurs spontaneously, and a structure is formed around the anode, when strata are not observed. Experiments were carried out in the range of pressures 30–100 Pa at a discharge current of 20–30 mA. To control the chemical composition of the gas environment, mass-spectrometry is used.

Термоядролық реакторда қабырға маңындағы плазмалы-тозаңды құрылымдардың қасиеттерiн зерттеу

Термоядролық реакторда қабырға маңындағы плазмалы-тозаңды құрылымдардың қасиеттерiн зерттеу

PREPARATION OF THE COSMIC EXPERIMENT "COULOMB-PLASMA"

Studies of dusty plasma have been actively carried out for about a quarter of a century in many laboratories on Earth, and on board the International Space Station under microgravity conditions. At present, a new experiment is being prepared. We describe the goals and objectives of the experiment, its features and differences from previous experiments, explain the need for it in microgravity. The objective of the experiment is to study the evolution of the open dissipative systems of strongly interacting macroparticles in a gas-discharge plasma, to obtain data on phase transitions and dynamics of active Brownian particles and dynamics of defects and dislocations in plasma-dust structures. Key words: dusty plasma, microgravity, cosmic experiment, open thermodynamic systems, active Brownian particles

On the thermophoresis in dense dust structures in neon plasma

Numerical study of the effect of dust particle concentration on the thermophoretic force acting on a dust particle inside a dust structure in plasma has been carried out. The experimental data on the formation of voids in dust structures formed by 2.55 μm dust particles in a glow dc discharge in neon have been used. The simulation has been performed using the diffusion-drift model with taking into account joule heating of discharge. The dependence of the thermophoretic force acting on a dust particle in a dust structure on the ratio of atom mean free path to the distance between the adjacent particles in the dust structure has been obtained.

Coulomb Dust Spheres in a Glow Discharge in Neon at Cryogenic Temperatures

The discharge parameters for the formation of charged spherical dust structures (Coulomb dust spheres) in neon plasma at a discharge tube wall temperature of 77 K are determined. The dust spheres were experimentally observed at fixed neon pressures of 0.15, 0.9, and 1.2 Torr. They were also obtained by extrapolation at pressures of 0.42 and 0.65 Torr. The dust spheres form at the discharge current corresponding to the intersection points of the dependences of the radial and axial dimensions of the dust structures on the discharge current. The correlation between the plasma parameters at which the dust spheres are formed and their composition, phase and dynamic states of their components, and dimensions of the dust spheres is analyzed. The variations in the parameters of the discharge plasma and dust spheres caused by a change in the gas pressure are numerically simulated. A continuous second-order phase transition is discovered in dust spheres at pressures of 0.15–0.65 Torr. An increase in the “chemical potential” of dust spheres is found near the liquidus line and the line separating the dust mixture components on the P–I phase diagram.

Surface Modification of Melamine-Formaldehyde (MF-R) Macroparticles in Complex Plasma

The surface modification of melamine-formaldehyde (MF-R) macroparticles (4.12 ± 0.09 μm in diameter) in dc glow discharges in neon, argon, and an argon–oxygen mixture (90% Ar, 10% O2) was studied experimentally. The macroparticles were treated in the discharge plasma for 10, 20, 40, and 60 min. The macroparticles were placed in ordered plasma–dust structures and then extracted from them. The results of atomic force microscopy of the surface profile are presented. Quantitative data on destruction of the surface layer and aspects of its modification are discussed. The amount of substance removed from the particle surface for the exposure time was calculated using the fractal analysis method.

Dusty plasma in a glow discharge in helium in temperature range of 5–300 K

Dusty plasma structures in glow discharge in helium in the temperature range of 5–300 K are investigated experimentally. We have described the experimental setup that makes it possible to continuously vary the temperature regime. The method for experimental data processing has been described. We have measured interparticle distances in the temperature range of 9–295 K and compared them with the Debye radius. We indicate the ranges of variations in experimental parameters in which plasma–dust structures are formed and various types of their behavior are manifested (rotation, vibrations of structures, formation of vertical linear chains, etc.). The applicability of the Yukawa potential to the description of the structural properties of a dusty plasma in the experimental conditions is discussed.

Study of the modification of spherical melamine-formaldehyde particles levitating in complex plasma

The surface modification of spherical melamine-formaldehyde particles during their levitation in a dusty plasma as a part of plasma–dust structures in a trap formed in strata in a neon glow discharge has been investigated using scanning electron microscopy. The dependence of the particle size on the time of plasma exposure has been found and measured, and the modification of the surface structure has been studied. The source of the observed modification has been interpreted.

Theory of hysteresis during electron heating of electromagnetic wave scattering by self-organized dust structures in complex plasmas

Dust structuring is a natural and universal process in complex plasmas. The scattering of electromagnetic waves by dust structures is governed by the factor of coherency, i.e., the total number of coherent electrons in a single structure. In the present paper, we consider how the factor of coherency changes due to additional pulse electron heating and show that it obeys a hysteresis. After the end of the pulse heating, the scattering intensity differs substantially from that before heating. There are three necessary conditions for scattering hysteresis: first, the radiation wavelength should be larger than the pattern (structure) size; second, the total number of coherent electrons confined by the structure should be large; and third, the heating pulse duration should be shorter than the characteristic time of dust structure formation. We present the results of numerical calculations using existing models of self-consistent dust structures with either positively or negatively charged dust grains. It is shown that, depending on the grain charge and the ionization rate, two types of hysteresis are possible: one with a final increase of the scattering and the other with a final decrease of the scattering. It is suggested that the hysteresis of coherent scattering can be used as a tool in laboratory experiments and that it can be a basic mechanism explaining the observed hysteresis in radar scattering by noctilucent clouds during active experiments on electron heating in mesosphere.

Gas rotation in discharges in a longitudinal magnetic field

This paper reviews theoretical and experimental work on gas rotation in discharges ignited in a longitudinal magnetic field. There is abundant evidence that such a field causes plasma-dust structures to rotate in the plane perpendicular to itself. This rotation cannot be explained solely by the dragging action of azimuthally moving ions. Drag is also exerted by the gas rotating under the moment produced by the Ampere force that arises in discharge regions with a nonuniform magnetic field near solenoid end faces and due to the narrowing of the discharge channel cross section. In a stratified discharge in a uniform magnetic field, an eddy electric current due to the noncollinearity of the plasma-density and temperature gradients brings the gas to rotation.

The role of gas composition in plasma-dust structures in RF discharge

The influence of a mixture of light and heavy gases, i.e., helium and argon, on plasma-dust structures in the radiofrequency discharge has been studied. The dust chains in the sheath of the radiofrequency discharge, the average distance between the dust particles and their chains, have been analyzed. A significant effect of small amounts of argon on the correlation characteristics of dust particles has been observed. The results of numerical simulation of ion and electron drift in the mixture of helium and argon are presented. It is shown that even 1% of argon admixture to helium produces such an effect that argon ions become the main components of the discharge, as they drift with lightweight helium forming a strongly anisotropic velocity distribution function.

Dense dust structures in cryogenic complex plasma

In the previous researches of cryogenic complex (dusty) plasma [1] we observed experimentally complex plasma systems formed in cryogenic environments. Particularly it was revealed from the experiments that dust structures with high concentration of macroparticles can be formed. So-called super dense dusty plasma structures in which interparticle distance is comparable with particle size were also observed. Thus concentration of particles was close to concentration of background plasma. Similar formations had unusual properties (sphere-like form, free boundaries, etc.) and represent new object in dusty plasma researches. In the present work new results on experimental investigations of dense dust structures at cryogenic temperatures were presented. The experiments were made by means of recently developed techniques and cryogenic facilities (optical cryostat). Possible nature of the unusual properties of super dense dusty plasma structures was discussed.

Non-self-maintained discharge supported by a proton beam for studying stretched dust structures

The main parameters of non-self-maintained discharge supported by a proton beam in inert gas are obtained. The discharge is used to study dust structures in nuclear excited plasma. Its main features include low gas pressure (∼133 Pa) and low proton beam current density (∼10−6 A/cm2). It is shown that a trap for negatively charged dust particles is formed in the discharge near-collector area at a sufficiently large negative voltage on the collector (−100 V), which is caused by a large negative potential jump in the Langmuir electrode layer whose width increases with distance from the center of the discharge. The possibility of generating stretched dust structures in non-self-maintained discharge is considered.

An alternative neuronal method for non-analytic pseudo-potentials in a charge-varying dusty plasma with trapped dust grains

AbstractSolitary waves are investigated in a charge-varying dusty plasma involving dust trapping. A potentially useful neuronal method that may handle a wide variety of non-analytic pseudo-potentials is used. This method could be advantageously exploited in rendering a cumbersome pseudo-potential analytically more tractable. Making use of the approximate Sagdeev pseudo-potential, our results show the possibility of development of localized dust structures in a dusty plasma with variable charge trapped dust grains.

Consequences of an attractive force on collective modes and dust structures in a strongly coupled dusty plasma

We present investigations of the combined effects of Debye–Hückel repulsive and overlapping Debye spheres attractive interaction potentials around charged dust particles on collective modes, phase separation and ordered structures in a strongly coupled dusty plasma. We obtain static and dynamical information via Molecular Dynamics simulations in the liquid and crystallized phases and identify the onset of an instability in the transverse mode, by using lattice summation method. The results are useful for understanding the origin of coagulation/agglomeration of charged dust particles and the formation of ordered dust structures in low-temperature laboratory and space plasmas.

Characteristics of electron drift in the low-pressure gas discharge

The features of the energy distribution function of electrons during their drift in neon are analyzed for typical conditions of experiments with dust structures in plasma. The energy balance of electrons and drift characteristics in an electric field at strengths 13 < E/N < 42 Td were calculated taking into account inelastic collisions and the effect of electron loss on gas-discharge tube walls.

Surface and bulk modification of melamineformaldehyde (MF-R) microparticles suspended in a complex plasma

Changes in the surface layer of melamineformaldehyde (MF-R) microparticles (spheres of the diameter 4.86 ± 0.07 μm) in a direct current glow discharge plasma in neon after their exposure to plasma for 10, 20, and 40 min have been studied experimentally. Microparticles were placed into the composition of ordered plasma-dust structures and were subsequently removed. The results of atomic force and electron microscopy studies of the surface layer profile are presented. An evaluation of the quantitative data on surface layer destruction and the character of its modification are discussed.

The corona discharge in nuclear excited plasma as a way of obtaining ordered dust particle structures

A model of a corona discharge in a nuclear excited dust plasma at the pressures of 1–100 atm is proposed. The distributions of the electric field and current-voltage characteristics of a corona discharge in a nuclear-excited dust plasma are found for a particular cylindrical geometry case at different methods of corona-producing electrode positioning. The conditions for the existence of a stationary corona discharge are obtained. A mathematical model describing the behavior of dust particles in a nuclear plasma that allows taking into account the key physical processes occurring in a nuclear-excited dust plasma is considered. The analyzed plasma properties are as follows: (1) shielding of the Coulomb forces of the interaction between dust particles, (2) the energy exchange and the stochastic character of the dust particle interaction with a buffer gas and ambient plasma, and (3) strong spatial inhomogeneity of the nuclear-excited plasma. The use of a corona discharge in a nuclear-excited plasma will make it possible to ensure stability of plasma-dust structures and more efficient conversion of the nuclear energy into laser radiation.

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.

An experimental complex for studying the operation of beam-plasma reactors for biomedical applications

An experimental complex for studying processes in beam-plasma reactors for biomedical applications has been developed. The complex was tested using plasma-generating media of various atomic and molecular gases and vapors of organic compounds in the pressure range 0.01–100 Torr at temperatures no higher than 50°C. It is shown that plasma-dust structures can be formed via direct condensation of vapors of organic compounds in plasma traps. Technological experiments performed with powders of protein compounds have shown that, in the reactors of the considered type, processes of plasma modification of biomacromolecules and plasma-stimulated deposition can be implemented with the formation of supramolecular complexes. It has been proven that these processes are controlled and the required treatment regimes are ensured by an appropriate choice of the electron-beam power, the pressure of the plasma-forming gas, and the geometry of the reaction volume.