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.     

Self-Organization Phenomena in a Cryogenic Gas Discharge Plasma: Formation of a Nanoparticle Cloud and Dust–Acoustic Waves

The dusty plasma structures in a glow discharge of helium in a tube cooled by superfluid helium at a temperature of 1.6 K and higher have been studied experimentally. The bimodal dust plasma formed by clouds of polydisperse cerium dioxide particles and polymer nanoparticles has been analyzed. We have observed wave oscillations in the cloud of polymer nanoparticles (with a size up to 100 nm), which existed in a narrow temperature range from 1.6 to 2.17 K. Vortices have been observed in the dusty plasma structures at helium temperatures.     

Charge and structures of dust particles in a gas discharge at cryogenic temperatures

A dusty plasma in a dc gas discharge is considered at low (cryogenic) temperatures of the gas. The formation of dusty plasma structures consisting of monodisperse poly(styrene) particles (d = 5.44 μm) in a dc glow discharge is experimentally investigated at cryogenic temperatures in the range from 4.2 to 77 K, and the results obtained are presented. The ion velocity distribution function and the charging of dust particles at cryogenic temperatures are calculated using the molecular dynamics method. The primary attention is focused on the correct inclusion of ion-atom collisions in the analysis. This is essential to the understanding of the main mechanisms of the experimentally observed increase in the density of dust particles with decreasing temperature of the gas in the discharge.     

Large-Scale Transport of Charged Macroparticles Induced by Dust–Acoustic Solitons

We have studied experimentally the oscillatory process in the dusty plasma in the glow discharge stratum. It is shown that the oscillations are induced by the dust–acoustic instability, as a result of which dust–acoustic solitons are excited. The motion of dust particles in the electric field of solitons has been analyzed. It has been established that a soliton leads to a large-scale unidirectional transport of charged particles in the direction of its motion. The experimental results have been interpreted theoretically using the MHD model of the plasma.     

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.     

Dust charging and levitating in a sheath of plasma containing energetic particles

The structure of the sheath in the presence of energetic particles is investigated in the multi-fluid framework. Based on the orbital motion limited(OML) theory, the dust grain charging inside the sheath of plasma containing energetic particles is examined for the carbon wall, and then the effect of the energetic particles on the stationary dust particle inside the sheath is discussed through the trapping potential energy. It is found that with the increase of energetic ion concentration or energy,the size of dust staying in levitation equilibrium decreases and the levitating position is much closer to the wall. In the case of deuterium ions as energetic ions, the bigger dust particle can be trapped by the sheath than in the case of hydrogen ions as energetic ions. When the energetic electron component is present, the levitating position of dust particle in the sheath depends strongly on the energetic electron. The levitating dust particle is closer to the wall as the energetic electron energy or concentration is increased. In addition, with the increase of temperature of thermal background ion, the size of dust particle trapped by the sheath decreases and the levitating positions of dust particles with the same size radius inside the sheath move toward the wall. Our results can be helpful in investigating the property of the sheath where the energetic particle component is present.     

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.     

Formation of liquidlike and crystalline structures in dusty plasmas

Under certain conditions in a dusty plasma, which is a low-temperature plasma with dust grains, the strong interaction between grains can give rise to gas-liquid-solid-state phase transitions. A study is made of ordered (liquidlike and crystalline) grain structures in various kinds of dusty plasmas: a thermal plasma at atmospheric pressure, a plasma of a dc glow discharge, and a UV radiation-driven plasma. The results of experimental observations of ordered dust structures are reported, and the characteristic features of the dust structures and the conditions for their appearance are discussed.     

Ion Heating in Dusty Plasma of Noble Gas Mixtures

Ion heating in dusty plasma of noble gas mixtures is studied by the observation of dust particles in stratified glow discharge. The particles and their formations can be used as a “contact‐free” probe of the ion flows. It is shown that under condition of experiments transition of dust particles into crystalline state in pure gases occur at much lower pressures in comparison to the case of gas mixtures. This observation is also supported by the evaluation of “effective” kinetic temperature of dust particles as defined from the velocity distribution function at the same set of discharge parameters. Absolute value of temperature of dust component in the mixture of helium and argon indicates important role of argon ionization process (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Collective Phenomena in Strongly Coupled Dissipative Systems of Charged Dust: from Ground to Microgravity Experiments

In present work the formation of dusty plasma structures in cryogenic glow dc discharge was investigated. The ordered structures from large number (～10⁴) of charged diamagnetic dust particles in a cusp magnetic trap have been also studied in microgravity conditions. The super high charging (up to 5·10⁷e) of dust macroparticles under direct stimulation by an electron beam is experimentally performed and investigated. The results of the investigation of Brownian motion for strongly coupled dust particles in plasma are presented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of Harmonic Modulation of Current in Glow Discharge Dusty Plasma with Ordered Structures

New method of disturbance by imposing harmonic signals on discharge current in DC glow discharge with ordered structures is studied at low values of disturbing amplitudes in molecular nitrogen. Influence of disturbing signals with frequencies from 10 Hz to 100 kHz is observed. New effects of changing vertical size and position of dusty structures in discharge space observed. Forced oscillations of dust particles and self‐oscillating crystals stabilizing effect under different conditions registered. Studied dusty structure's vertical size change dependencies on frequency and amplitude of disturbing signal (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dust acoustic waves in a dc glow-discharge plasma

The spontaneous excitation of low-frequency oscillations of the macroparticle density in ordered dust structures levitating in standing striations of a dc glow discharge is discovered. It is concluded on the basis of a simplified linear model of an ideal collisionless plasma that the observed instability is caused by the drift motion of ions relative to the dust, which leads to the excitation of dust acoustic oscillations of the plasma. Zh. éksp. Teor. Fiz. 116, 902–907 (September 1999)     

Measurement of temperature of a dusty plasma from its configuration

A new concept called “configurational temperature” is introduced in the context of dusty plasma, where the temperature of the dust particles submerged in the plasma can be measured directly from the positional information of the individual dust particles and the interaction potential between the dust grains. This method does not require the velocity information of individual particles, which is a key parameter to measure the dust temperature in the conventional method. The technique is initially tested using two-dimensional (2D) OpenMP parallel molecular dynamics and Monte Carlo simulation and then compared with the temperature evaluated from experimental data. The experiment have been carried out in the Dusty Plasma Experimental (DPEx) device, where a 2D stationary plasma crystal of melamine formaldehyde particles is formed in the cathode sheath of a DC glow discharge argon plasma. The kinetic temperature of the dust is calculated using the standard particle image velocimetry technique at different pressures. An extended simulation result for the three-dimensional case is also presented, which can be employed for the temperature measurement of a three-dimensional dust crystal in laboratory devices.     

Crystalline structures of strongly coupled dusty plasmas in dc glow discharge strata

Strongly coupled dusty plasmas are formed by suspending micron-sized dust particles in strata of a dc glow neon discharge. We have observed for the first time an ordered structure of the negatively charged particles trapped in the strata region. Image analysis reveals the crystalline structure, which is consistent with a large value of the Coulomb coupling parameter.     

Anomalous heating of a system of dust particles in a gas-discharge plasma

The coexistence of regions of negatively charged macroparticles with substantially different kinetic temperatures in a highly nonideal dusty plasma in a dc glow discharge has been observed experimentally. An explanation of the observed anomalous heating of the system of dust particles in a gas-discharge plasma is proposed on the basis of a molecular-dynamics model. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 392–397 (25 September 1997)     

Dusty plasma structures in magnetic fields in a dc discharge

The formation of dusty plasma structures has been experimentally investigated in a cylindrical dc discharge in axial magnetic fields up to 2500 G. The rotation of the dusty plasma structures about the discharge symmetry axis with a frequency depending on the magnetic field has been observed. When the field increases to 700 G, the displacement of dust particles from the axial region of the discharge to the periphery, along with the continuation of the rotation, has been observed. The kinetic temperatures of the dust particles, the diffusion coefficients, and the effective nonideality parameter have been determined for various magnetic fields. The explanation of the features in the behavior of the dust particles in the discharge in the magnetic field has been proposed on the basis of the analysis of ambipolar diffusion in the magnetized plasma. The maximum magnetic field at which the levitation of the dust particles in the discharge is possible has been estimated.     

Analysis of macroparticle charging in the near-electrode layer of a high-frequency capacitive discharge

Spatial variation of dust particle charges are estimated numerically for typical laboratory experiment conditions in a radio-frequency (rf) capacitive discharge. The surface potentials of macroparticles levitating in the upper part of the near-electrode layer of the rf discharge are measured. A model is proposed for the formation of irregular dust oscillations due to stochastic motion of dust in the bulk of a spatially inhomogeneous plasma (in the presence of a dust charge gradient). This mechanism is used for analyzing the results of measurements of the amplitude of vertical vibrations of dust particles in the near-electrode layer of the rf discharge. It is found that the dust charge gradient may be responsible for the development of such vibrations.     

Dusty plasma system in the surface layer of the illuminated part of the moon

The dusty plasma system in the surface layer of the illuminated part of the Moon has been considered. The maximum height of the dust rise has been determined. It has been shown that a dead zone, where dust particles cannot rise over the surface of the Moon, is absent near a lunar latitude of 80°. The size and height distributions of dust have been determined.     

Investigation an Effective Interaction Potential of Dust Particles in Nonideal Dusty Plasma

Interaction between dusty particles remains to be an interesting issue that still requires deeper theoretical and experimental investigations. In the present paper we formulate a theoretical approach to the calculation of effective interaction potential of dust particles on the basis of Poisson equation and experimentally measured pair correlation functions. By application of our model to the data from the liquid phase of dust formations in stratified dc glow discharge, it is shown that there is an attractive component in the interaction of dust particle (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)