V. I. Molotkov

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.

Mechanism of dust-acoustic instability in a direct current glow discharge plasma

An observation of low frequency waves spontaneously excited in a dc glow discharge dusty plasma is reported. To analyze possible reasons for the instability observed, a linear dispersion relation which takes into account collisions with neutrals, dust grain charge variations, ion drift, and forces acting on dust particles is derived. Numerical analysis of the dispersion relation shows that the observed instability is the result of dust charge variations in the presence of external charge-dependent forces together with the ion drift effect.

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.

Fluid-solid phase transitions in three-dimensional complex plasmas under microgravity conditions

Phase behavior of large three-dimensional (3D) complex plasma systems under microgravity conditions onboard the International Space Station is investigated. The neutral gas pressure is used as a control parameter to trigger phase changes. Detailed analysis of structural properties and evaluation of three different melting-freezing indicators reveal that complex plasmas can exhibit melting by increasing the gas pressure. Theoretical estimates of complex plasma parameters allow us to identify main factors responsible for the observed behavior. The location of phase states of the investigated systems on a relevant equilibrium phase diagram is estimated. Important differences between the melting process of 3D complex plasmas under microgravity conditions and that of flat 2D complex plasma crystals in ground based experiments are discussed.

CRYSTALLINE STRUCTURES OF STRONGLY COUPLED DUSTY PLASMAS IN DC GLOW DISCHARGE STRATA

Abstract 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.

Dynamics of Lane Formation in Driven Binary Complex Plasmas

The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.

Compressional waves in complex (dusty) plasmas under microgravity conditions

Complex plasmas consist of electrons, ions and charged microparticles, with typical charge-to-mass ratios 1:10−5:10−13. The interest in these systems has grown explosively, because they can be investigated at the kinetic level (the microparticles). However, on Earth the supporting forces (against gravity) are of the same order as the electrostatic interparticle forces—and hence only strongly compressed systems can be investigated. Under microgravity conditions these “body forces” are a factor 102 smaller which allows the experimental investigation of weakly compressed three-dimensional complex plasmas. One way to study these systems is by the controlled excitation of low-frequency compressional waves. The first such experiments, conducted with the PKE-Nefedov laboratory on the International Space Station is reported. The waves were excited by modulating the voltage on the rf electrodes. By varying the modulation frequency the dispersion relation was measured. The results are compared with existing theoret...

Liquid- and crystallike structures in strongly coupled dusty plasmas

Dust particle ordering is discussed in various types of low-temperature plasma, such as thermal plasmas at atmospheric pressure, dc glow discharges, UV- and radioactivity induced plasmas. The investigations of UV-induced dusty plasma were made under microgravity conditions. Experimental data are presented. Properties of ordered structures are discussed and the conditions of formation considered.

Crystallization of a dusty plasma in the positive column of a glow discharge

The formation of macroscopic ordered structures in the standing striations of a stationary glow discharge in Ne is observed. A Coulomb quasicrystal is formed by spherical glass particles with diameters of 50–63 μm and charge Zp~7·105e. The interparticle distance is approximately 300 μm. This corresponds to a nonideality parameter Γ~5·104, which leads to crystallization in the Yukawa model. The factors leading to the formation of a quasicrystal in the striations are discussed.

Auto-oscillations in complex plasmas

Experimental results on an auto-oscillatory pattern observed in a complex plasma are presented. The experiments are performed with an argon plasma, which is produced under microgravity conditions using a capacitively coupled rf discharge at low power and gas pressure. The observed intense wave activity in the complex plasma cloud correlates well with the low-frequency modulation of the discharge voltage and current and is initiated by periodic void contractions. Particle migrations forced by the waves are of long-range repulsive and attractive character.