B. A. Klumov

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.

Formation of structures in a dusty ionosphere

An analysis of the evolution of microscopic particles (dust grains) in the Earth’s ionosphere and their effect on ionization in the middle atmosphere is presented. It is shown that summer conditions in the polar ionosphere, which are characterized by an ambient air temperature below 150 K and presence of supersaturated water vapor, facilitate the formation of dust structures in the middle atmosphere, such as noctilucent clouds and polar mesospheric summer echoes. The ionospheric plasma composition can change significantly in the regions occupied by these structures. Depending on photoelectric properties of the grains, their presence may lead to excess, or decrease in, electron concentration and complex behavior of ion concentration. The proposed self-consistent model of the ionosphere allows for grain growth, sedimentation, and charging and can be used to explain the behavior of ionization under summer conditions in the polar ionosphere.

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.

Structural properties of dense hard sphere packings

We numerically study structural properties of mechanically stable packings of hard spheres (HS), in a wide range of packing fractions 0.53 ≤ ϕ ≤ 0.72. Detailed structural information is obtained from the analysis of orientational order parameters, which clearly reveals a disorder–order phase transition at the random close packing (RCP) density, ϕc ≃ 0.64. Above ϕc, the crystalline nuclei form 3D-like clusters, which upon further desification transform into alternating planar-like layers. We also find that particles with icosahedral symmetry survive only in a narrow density range in the vicinity of the RCP transition.

The role of negative ions in experiments with complex plasma

The influence of negative ions on the state of an rf gas-discharge dusty (complex) plasma containing electronegative gaseous impurities was investigated. A simple one-dimensional argon-discharge model allowing for the impurity-induced plasmachemical reactions was taken as an example to show that the addition of even a minor amount of molecular oxygen changes appreciably the plasma composition and plasma transport properties, as well as the microparticle charges. In turn, these changes have a strong effect on the microparticle force balance and on the formation of various dusty structures in the discharge.

Dust particle charging and formation of dust structures in the upper atmosphere

We investigate the dust particle charging process in the Earth’s upper atmosphere. Calculating the spectra of solar radiation, we study the influence of the photoelectric effect on the charging process. We show that both positively and negatively charged dust particles are present in the upper atmosphere. We consider the mechanisms which can be responsible for the formation of dust structures like noctilucent clouds and polar mesosphere summer echoes.

Electrostatic interaction between dust particles in weakly ionized complex plasmas

The electrostatic potential around a dust particle in a complex plasma is calculated, taking into account ion-neutral collisions and collective effects, in a range of plasma parameters relevant for typical laboratory experiments. The existence of attractive wells and dependence of their shape on the main experimental control parameters, neutral gas pressure, and dust number density, is investigated.

Structural properties of 3D complex plasmas: experiments versus simulations

In the paper we discuss recent observations of the three-dimensional plasma crystals created onboard the International Space Station under microgravity conditions. By using the special scanning technique and the image analysis we could retrieve 3D particle positions. We apply the bond-order parameter method to identify the different lattice types of the plasma crystals. It has been shown that observed plasma crystals contain numerous hcp and fcc clusters. Evidence of a small amount of bcc clusters is also reported. Molecular dynamics simulations of crystallization of a simple Yukawa system reproduce remarkably well all peculiarities of the local properties of observed plasma crystals.

Generalized kinetic theory of ensembles with variable charges

A generalized kinetic theory of gaseous ensembles of particles with variable charges is proposed. The evolution of the ensembles due to the mutual particle collisions is investigated. The cases of inhomogeneous and randomly fluctuating charges are studied. It is shown that the particle temperature in such ensembles increases with time, and in some cases can grow by orders of magnitude. The theory is compared with the molecular-dynamics simulations, the relevance to typical experimental conditions is analyzed, and astrophysical implications are discussed.

Features of dusty structures in the upper Earth’s atmosphere

The features of the Earth’s dusty ionosphere are considered using as an example the summer polar mesosphere. The effect of the optical properties of microparticles on their heating and photoelectron emission under the action of solar radiation is analyzed in detail. Certain photochemical consequences of the presence of dust in the upper atmosphere are studied. In particular, it is shown that microparticles can noticeably reduce the concentration of water vapor in the upper atmosphere and this decrease in turn limits the particle sizes. The influence of the effect under consideration on the behavior of the charged component of the upper atmosphere is discussed.