A. M. Lipaev

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.

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.

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.

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.

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al2O3, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles.

Freezing and melting of 3D complex plasma structures under microgravity conditions driven by neutral gas pressure manipulation.

Freezing and melting of large three-dimensional complex plasmas under microgravity conditions is investigated. The neutral gas pressure is used as a control parameter to trigger the phase changes: Complex plasma freezes (melts) by decreasing (increasing) the pressure. The evolution of complex plasma structural properties upon pressure variation is studied. Theoretical estimates allow us to identify the main factors responsible for the observed behavior.

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.

Experimental observation of Coulomb ordered structure in sprays of thermal dusty plasmas

A macroscopic Coulomb-ordered structure of polydisperse CeO2 particles is observed experimentally in a laminar spray of weakly ionized thermal plasma under atmospheric pressure and temperature of about 1700 K. Diagnostic instruments are used to measure plasma parameters. The particles are charged positively and carry about 103 electron charges. The calculated values of Coulomb coupling parameter γp is > 120, corresponding to a strongly coupled plasma.

Direct measurement of the speed of sound in a complex plasma under microgravity conditions

We present a direct measurement of the speed of sound in a three-dimensional complex plasma —a room-temperature plasma that contains micrometer-sized particles as fourth component. In order to obtain an undisturbed system, the setup was placed under microgravity conditions on board the International Space Station. The speed of sound was measured with the help of Mach cones excited by a supersonic probe particle moving through the extended particle cloud at Mach numbers M3. We use the Mach cone relation to infer the particle charge and compare with that predicted by standard theories. In addition, we compare our results with a numerical simulation. In both experiment and simulation, we observe a double Mach cone structure.

Dusty plasma diagnostics methods for charge, electron temperature, and ion density

Diagnostic methods are developed to measure the microparticle charge Q and two plasma parameters, electron temperature Te, and ion density ni, in the main plasma region of a dusty plasma. Using video microscopy to track microparticles yields a resonance frequency, which along with a charging model allows an estimation of Q and Te. Only measurements of microparticle position and velocity are required, unlike other methods that use measurements of Te and plasma parameters as inputs. The resonance frequency measurement can also be used with an ion drag model to estimate ni. These methods are demonstrated using a single-layer dusty plasma suspension under microgravity conditions.