O. S. Vaulina

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.

Scaling law for the fluid-solid phase transition in Yukawa systems (dusty plasmas)

Yukawa systems serve as models for plasmas and colloidal suspensions of charged particles. The state of these systems is determined by two dimensionless parameters: k = a/λD, which is the ratio of the mean interparticle distance to the Debye length λD, and Γ = Zd2e2/aTd, which is the ratio of the Coulomb potential energy to the particle temperature Td(Zd is the charge of each particle). We propose an empirical scaling law for the critical coupling parameter Γc needed for crystallization in Yukawa systems. The dependence of Γc on k is in good agreement with recent molecular dynamics simulations.

Diffusion and dynamics of macro-particles in a complex plasma

The dynamics of charged macro-particles in a complex “dusty” plasma is investigated for the conditions relevant for laboratory experiments on weakly ionized gas-discharge plasma and modeled by the Brownian dynamics method. The parameters responsible for order and scaling of the particle dynamics in the dissipative system of strongly interacting macro-particles are determined. The expression for the diffusion rate of macro-particles in strongly correlated liquid-type structures is derived and analyzed. The condensation of macro-particles (the growth of clusters) is numerically observed in the transition of the liquid-type Yukawa system to the qualitatively new dynamic state.

Instability of plasma-dust systems with a macroparticle charge gradient

An analysis is made of various self-oscillations which appear in plasma-dust systems with spatially varying macroparticle charges. The conditions of establishment and the nature of the evolution of the two main types of instability of these systems are analyzed. Particular attention is paid to cases of vortex particle motion. Dust systems having parameters similar to those in laboratory experiments are modeled numerically. Calculations were made for charged particles in an external electric field and in the Earth’s gravitational field using a molecular dynamics method.

Analysis of particle sizes, concentration, and refractive index in measurement of light transmittance in the forward-scattering-angle range

A simple method for determining the mean size, the concentration, and the refractive index of the monodispersion and the polydispersion of particles has been presented. The method is based on the empirical inversion of measurements of forward-angle light-scattering transmittance. The effects of particle size distribution and optical constants on forward-angle-scattering transmittance have been considered by using Mie theory. The proposed method has been used successfully for single latex spheres in water and polydispersed weakly absorbing particles of Al(2) O(3) and SiO(2) in the flow of the propane-air flame combustion products.

The dynamics of formation of monolayer dust structures in a confining electric field

The conditions for formation of monolayer dust structures are investigated for dust grains (interacting via isotropic pair potentials) placed in a confining electric field varying linearly with position. The relationships between the grain interaction potential, the number of grains and the gradient of the confining field of the electric trap are established. A criterion for instability of a monolayer dust structure is proposed.

Dynamics of macroparticles in a dusty plasma under microgravity conditions (First experiments on board the ISS)

The results of experimental investigation of macroparticle transport in the dusty plasma of a capacitive high-frequency discharge under microgravity conditions are considered. Experimental data were obtained for monodisperse polymer particles of radius ap=1.7 mm in a wide range of plasma parameters on the International Space Station. Analysis of macroparticle dynamics for a strongly nonideal dusty plasma, including diffusion and dust vortex formation processes, is carried out.

Formation of Vortex Dust Structures in Inhomogeneous Gas-Discharge Plasmas

A generalized analytical model of instabilities in a dusty plasma with a nonzero grain charge gradient in a field of nonelectrostatic forces is considered. A review is given of different experimental observations of the dust self-oscillations that occur in the plasmas of an rf capacitive discharge and a dc glow discharge and whose appearance can be explained in terms of the proposed model. It is shown that the change in the grain charge gives rise to dynamic dust structures in laboratory gas-discharge plasmas. Attention is focused on the analysis of the onset of vortex motion of the dust grains.

Test of the Stokes-Einstein Relation in a Two-Dimensional Yukawa Liquid

The Stokes-Einstein relation, relating the diffusion and viscosity coefficients D and eta, is tested in two dimensions. An equilibrium molecular-dynamics simulation was used with a Yukawa pair potential. Regimes are identified where motion is diffusive and D is meaningful. The Stokes-Einstein relation, Deta proportional k(B)T, was found to be violated near the disordering transition; under these conditions collective particle motion exhibits dynamical heterogeneity. At slightly higher temperatures, however, the Stokes-Einstein relation is valid. These results may be testable in strongly coupled dusty plasma experiments.

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.