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S. A. Khrapak

Publications and source records attributed to S. A. Khrapak.

28 records · Page 2Linked to original sources
arXiv2014

Ion sphere model for Yukawa systems (dusty plasmas)

Application of the ion sphere model (ISM), well known in the context of the one-component-plasma, to estimate thermodynamic properties of model Yukawa systems is discussed. It is shown that the ISM approximation provides fairly good estimate of the internal energy of the strongly coupled Yukawa systems, in both fluid and solid phases. Simple expressions for the excess pressure and isothermal compressibility are derived, which can be particularly useful in connection to wave phenomena in strongly coupled dusty plasmas. It is also shown that in the regime of strong screening a simple consideration of neighboring particles interactions can be sufficient to obtain quite accurate estimates of thermodynamic properties of Yukawa systems.

physics.plasm-ph↗
arXiv2014

Simple estimation of thermodynamic properties of Yukawa systems

A simple analytical approach to estimate thermodynamic properties of model Yukawa systems is presented. The approach extends the traditional Debye-Hückel theory into the regime of moderate coupling and is able to qualitatively reproduce thermodynamics of Yukawa systems up to the fluid-solid phase transition. The simplistic equation of state (pressure equation) is derived and applied to the hydrodynamic description of the longitudinal waves in Yukawa fluids. The relevance of this study to the topic of complex (dusty) plasmas is discussed.

physics.plasm-ph↗
arXiv2013

Particle flows in a dc discharge in laboratory and microgravity conditions

We describe a series of experiments on dust particles flows in a positive column of a horizontal dc discharge operating in laboratory and microgravity conditions. The main observation is that the particle flow velocities in laboratory experiments are systematically higher than in microgravity experiments, for otherwise identical discharge conditions. The paper provides an explanation for this interesting and unexpected observation. The explanation is based on a physical model, which properly takes into account main plasma-particle interaction mechanisms relevant to the described experimental study. Comparison of experimentally measured particle velocities and those calculated using the proposed model demonstrates reasonable agreement, both in laboratory and microgravity conditions, in the entire range of discharge parameters investigated.

physics.plasm-ph↗
arXiv2013

Three dimensional complex plasma structures in a combined radio frequency and direct current discharge

We report on the first detailed analysis of large three dimensional (3D) complex plasma structures in experiments performed in pure rf and combined rf+dc discharge modes. Inductively coupled plasma (ICP) is generated by an rf coil wrapped around the vertically positioned cylindrical glass tube at a pressure of 0.3 mbar. In addition, dc plasma can be generated by applying voltage to the electrodes at the ends of the tube far from the rf coil. The injected monodisperse particles are levitated in the plasma below the coil. A scanning laser sheet and a high resolution camera are used to determine the 3D positions of about $10^5$ particles. The observed bowl-shaped particle clouds reveal coexistence of various structures, including well-distinguished solid-like, less ordered liquid-like, and pronounced string-like phases. New criteria to identify string-like structures are proposed.

physics.plasm-ph↗
arXiv2012

Fluid-solid phase transitions in 3D complex plasmas under microgravity conditions

Phase behavior of large three-dimensional 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.

cond-mat.soft↗
arXiv2011

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. Evolution of complex plasma structural properties upon pressure variation is studied. Theoretical estimates allow us to identify main factors responsible for the observed behavior.

physics.plasm-ph↗
arXiv2011

Structural properties of dense hard sphere packings

The structural properties of dense random packings of identical hard spheres (HS) are investigated. The bond order parameter method is used to obtain detailed information on the local structural properties of the system for different packing fractions $ϕ$, in the range between $ϕ=0.53$ and $ϕ=0.72$. A new order parameter, based on the cumulative properties of spheres distribution over the rotational invariant $w_6$, is proposed to characterize crystallization of randomly packed HS systems. It is shown that an increase in the packing fraction of the crystallized HS system first results in the transformation of the individual crystalline clusters into the global three-dimensional crystalline structure, which, upon further densification, transforms into alternating planar layers formed by different lattice types.

cond-mat.soft↗
arXiv2010

Effect of ionization/recombination processes on the electrical interactions between positively charged particles in highly collisional plasmas

The effect of ionization and recombination processes on the electrical interactions between a pair of small charged particles in highly collisional plasmas is discussed. In particular, it is shown that these processes suppress the long-range attraction between positively charged particles. The condition corresponding to the vanishing of attraction is derived. The role of the effect for conditions of existing experiments is estimated.

physics.plasm-ph↗
arXiv2004

Measurement of the Ion Drag Force in a Complex DC-Plasma Using the PK-4 Experiment

The force on a microparticle in a complex plasma by streaming ions, the so-called ion drag force, is not well known. However, it is important for the understanding of interesting phenomena in complex plasmas such as the void formation under microgravity conditions. The PK-4 experiment, which is developed for a later use on board of the International Space Station, is ideally suited for investigating this problem. In this experiment a complex DC-plasma is created in a glass tube in which the microparticles flow from the cathode to the anode. Measuring the microparticle velocities, the forces on the particles for different particle sizes, pressures, and DC-currents can be extracted by assuming force balance. Experiments have been performed in the laboratory as well as under microgravity using parabolic flights. The results of these experiments will be presented and compared to theoretical predictions.

physics.plasm-ph↗