Laser-Induced Phase Transition in a Monolayer of Polymer Particles Levitating in a Low-Pressure Gas-Discharge Plasma

We report on the results of analysis of the mean kinetic energy and the pair correlation function of polymer particles in a plasma–dust structure under the action of laser radiation. We have observed experimentally the crystal–liquid phase transition in the monolayer of particles levitating in the near-electrode layer of a capacitive high-frequency discharge. The coupling parameter of the dust system has been estimated. The results of analysis of the modification of the polymer dust particle surface after holding in the plasma are considered. We propose an explanation of the phase transition taking into account the role of the photophoretic force in the motion of macroparticles. The effect of the photophoretic force is associated with the modification of the dust particle surface in the plasma, as a result of which the particles can effectively absorb laser radiation.     

Dusty plasma induced by solar radiation under microgravitational conditions: An experiment on board the Mir orbiting space station

The dynamics of the formation of ordered structures of macroparticles charged by photoemission under the action of solar radiation under microgravitational conditions without the use of electrostatic traps to confine the particles is studied experimentally and theoretically. The working conditions needed for the formation of structures of charged macroparticles are chosen as a result of a numerical solution of the problem posed, the particle charges and the interparticle interaction parameter are determined, and the characteristic times specifying the dynamics of the formation of an ordered system of macroparticles are calculated. The behavior of an ensemble of macroparticles under the effect of solar radiation is observed experimentally on board the Mir space station. An analysis and comparison of the results of the experimental and theoretical investigations permit drawing a conclusion regarding the possibility of the existences of extended ordered formations of macroparticles charged by photoemission under microgravitational conditions. Zh. éksp. Teor. Fiz. 114, 2004–2021 (December 1998)     

Effect of dust particles on the properties of low-temperature plasmas

Parameters of a low-temperature plasma containing dust particles are calculated numerically with the help of a self-consistent solution of the balance equation for production and recombination of electrons and ions, combined with the molecular dynamics method for direct simulation of processes in the vicinity of macroparticles. The relation between the charges of macroparticles and the neutral gas pressure, as well as the dependence of the low-temperature plasma parameters on the volume concentration of dust particles, is analyzed. It is shown that the plasma characteristics and composition may change noticeably relative to the case unperturbed by dust even for comparatively low concentration of dust particles.     

Dust acoustic waves in a nonequilibrium dusty plasma

With the use of the method of moments applicable for any values of the parameter of the nonideality of a dusty plasma and the hydrodynamic approach applicable only for small nonideality parameters, the theory of waves and oscillations of a complex plasma has been generalized to the case of a two-exponential interaction potential. It has been shown that the hydrodynamic approach and method of moments give the same dispersion relation for small nonideality parameters. It has been demonstrated that the velocity of dust acoustic waves in the long- and short-wavelength regions is determined by the small and large screening constants, respectively. It has been shown that the velocity of dust acoustic waves in nonequilibrium plasma is much higher than that obtained in the Debye screening theory for equilibrium plasma. In the hydrodynamic approach, the importance of the inclusion of the self-consistent mutual effect of the dust, electron, and ion components, and sinks of electrons and ions on dust particles, which lead to a noticeable change in the parameters of the interaction potential of dust particles, has been demonstrated.     

Non-self-sustained discharge in nitrogen with a condensed dispersed phase

A non-self-sustained discharge in nitrogen with a condensed dispersed phase is studied experimentally for the first time under atmospheric pressure at room temperature. It is shown that macroparticles strongly affect the current-voltage characteristics as well as the stability of the discharge process. A numerical simulation of dust particle charging in nitrogen is carried out at room temperature and cryogenic temperatures under continuous medium conditions. It is shown that a considerable charge is accumulated at macroparticles in the nitrogen beam plasma. As the gas temperature decreases, the charge of macroparticles in nitrogen increases, while in argon their charge decreases. For this reason, the Coulomb interaction parameter for dust particles in nitrogen increases strongly upon a transition from room to cryogenic temperature, while in argon this parameter decreases. It is also shown that the characteristic time of dust particle charging is shorter than 1 μs for a beam current density of 90 μA/cm², while the neutralization of the charge takes milliseconds. Possible mechanisms of the influence of the dust component on the characteristics of non-self-sustained discharge are considered.     

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.     

Anomalous kinetic energy of a system of dust particles in a gas discharge plasma

The system of equations of motion of dust particles in a near-electrode layer of a gas discharge has been formulated taking into account fluctuations of the charge of a dust particle and the features of the nearelectrode layer of the discharge. The molecular dynamics simulation of the system of dust particles has been carried out. Performing a theoretical analysis of the simulation results, a mechanism of increasing the average kinetic energy of dust particles in the gas discharge plasma has been proposed. According to this mechanism, the heating of the vertical oscillations of dust particles is initiated by induced oscillations generated by fluctuations of the charge of dust particles, and the energy transfer from vertical to horizontal oscillations can be based on the parametric resonance phenomenon. The combination of the parametric and induced resonances makes it possible to explain an anomalously high kinetic energy of dust particles. The estimate of the frequency, amplitude, and kinetic energy of dust particles are close to the respective experimental values.     

Initiation of dusty structures in chain reactions under the action of gyrotron radiation on a mixture of metal and dielectric powders with an open boundary

A dusty plasma formed in chain exothermal reactions initiated by radiation of a high-power gyrotron in mixtures of metal and dielectric powders has been described. An oscillatory character of such chain reactions, as well as the appearance of dust particles at the first (explosive) stage, has been detected. The tracks, velocities, and sizes of dust particles have been measured. It has been revealed that ensembles of dust particles appear in a reactor after switching-off of the gyrotron against the background of development of chemical reactions. The time of existence of these ensembles is three or four orders of magnitude larger than the duration of a microwave radiation pulse. The quasistationary state of the low-temperature plasma with charged macroparticles appears because of both the chemical heating of the mixture in the reactor and thermophoresis. It has been shown that dust particles are necessary as crystallization nuclei for the creation (or deposition) of complex composites of nano- and micromaterials produced in secondary plasma chemical synthesis.     

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.     

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 of two macroparticles in a nonequilibrium plasma

The interaction of two macroparticles in a nonequilibrium plasma at elevated pressures has been investigated. An asymptotic theory of screening, which leads to a two-exponential dependence of the macroparticle potential on distance with different screening constants, is used to determine the electrostatic energy of the system of charges associated with the two macroparticles. The dependence of the electrostatic energy on interparticle distance has been found to have a minimum, as in an equilibrium plasma. The interaction force between the macroparticles has been determined; it turned out to be asymmetric—for different charges, the forces acting on the first and second macroparticles are not equal. This is the result of an asymmetric charge separation near macroparticles with differing charges and indicates that the interaction force in a nonequilibrium plasma is nonpotential. The forces are equal for identical macroparticles or in an equilibrium plasma and the potential energy of the interaction between the macroparticles has been determined for these cases. Attraction between likely charged particles with different (in magnitude) charges has been found to be possible when they come very close together. Relations to determine the modified coupling parameter for an interaction potential that consists of two exponential terms with different screening constants have been derived.     

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.     

Verifying the reciprocity of interparticle interaction forces in strongly coupled systems

We propose a simple criterion for revealing the breaking of pair interaction symmetry in strongly coupled dissipative systems. The criterion is based on the analysis of correlations between the velocities of strongly interacting particles, which can be measured relatively easily in experiments with macroparticles in various media. We derive analytic relations that make it possible to calculate the derivatives of the interaction force between a pair of particles from the data on the correlations of their velocities and coordinates. The proposed criterion and relations are verified using the results of numerical simulation of the dynamics of dust particles in a plasma.     

On the ultracold plasma evolution

The time evolution of the Coulomb system whose initial total energy is zero is considered. The solution for a system of 2000 particles in the range of 8000 inverse plasma frequencies was obtained by themolecular dynamicsmethod. It is shown that under conditions typical of experiments with ultracold plasma the nonideality parameter of the plasma cannot reach large values due to recombination heating, and the relaxation process itself is not described within the conventional model of three-body recombination.     

The diffusion of macroparticles and criteria of phase transitions for dust structures in weakly ionized plasma

The dynamics of charged particles is investigated under conditions close to those of experiments in a weakly ionized laboratory gas-discharge dust plasma. The existing phenomenological criteria of phase transitions for dust structures in such a plasma are treated, and new criteria are suggested. The parameters responsible for the order and scaling of dynamic processes in Yukawa dissipative systems are determined. The relation for the diffusion coefficient D of macroparticles in strongly correlated liquid structures is derived.     

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.     

Self-similar Solution of a Cylindrical Shock Wave under the Action of Monochromatic Radiation in a Rotational Axisymmetric Dusty Gas

A self-similar flow behind a cylindrical shock wave is studied under the action of monochromatic radiation in a rotational axisymmetric dusty gas. The dusty gas is taken to be a mixture of small solid particles and perfect gas,and solid particles are continuously distributed in the mixture. The similarity solutions are obtained and the effects of the variation of the radiation parameter, the ratio of the density of solid particles to the initial density of the gas, the mass concentration of solid particles in the mixture and the index for the time dependent energy law are investigated.It is observed that an increase in the radiation parameter has decaying effect on the shock waves; whereas the shock strength increases with an increase in the ratio of the density of solid particles to the initial density of the gas or the index for the time dependent energy law. Also, it is found that an increase in the radiation parameter has effect to decrease the flow variables except the density and the azimuthal component of fluid velocity. A comparison is also made between rotating and non-rotating cases.     

Velocity Autocorrelation Functions and Diffusion Coefficient of Dusty Component in Complex Plasmas

The velocity autocorrelation functions of dust particles were calculated by the Langevin dynamics. It was indicated that their oscillations decay more rapidly with increase in the friction parameters. The dependencies of the dust particles diffusion coefficient on the friction coefficient at the different values of various parameters were obtained by the Green‐Kubo relation and mean square displacements. The validity of the Einstein relation at small values of coupling parameter was shown (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of the dynamics of strongly interacting macroparticles in a weakly ionized plasma

The method of molecular dynamics is used to study the dynamic behavior of a nonideal system of particles interacting through screened Coulomb potential. The behavior of the self-diffusion coefficient of particles as a function of the nonideality parameter is investigated. The conditions of the crystallization of such a system are discussed, as well as the possibility of using the crystallization criterion, based on the dynamic characteristics of the system.     

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)