Monthly Archives: February 2015

Effect of dust-charge fluctuations on dust acoustic solitary waves in an inhomogeneous dusty plasma with nonextensive electrons

The effects of adiabatic dust grain charge fluctuation and inhomogeneity on the nonlinear properties of dust acoustic (DA) solitary waves are studied. The plasma under consideration is a hot magnetized dusty plasma consisting of negatively charged dust particles, Boltzmann ions, and nonextensive electrons. A modified Zakharov-Kusnetsov equation, which admits a solitary wave solution, is derived using the reductive perturbation theory. It is found that the charge fluctuation of the dust grain modifies the nature of DA solitary structures. The numerical results may be useful to understand phenomena in laboratory and astrophysical plasmas.

Turbulence in strongly coupled dusty plasmas using generalized hydrodynamic description

The properties of decaying turbulence have been studied with the help of a Generalized Hydrodynamic (GHD) fluid model in the context of strongly coupled dusty plasma medium in two dimensions. The GHD model treats the strongly coupled dusty plasma system as a visco-elastic medium. The incompressible limit of the GHD model is considered here. The studies carried out here are, however, applicable to a wider class of visco-elastic systems, and are not merely confined to the dusty plasma medium. Our simulations studies show that an initial spectrum that is confined in a limited domain of wave numbers becomes broad, even when the Reynold's number is much less than the critical value required for the onset of turbulence in Newtonian fluids. This is a signature of elastic turbulence, where Weissenberg's number also plays an important role on the onset of turbulence. This feature has been observed in several experiments. It is also shown that the existence of memory relaxation time parameter and the transverse shear wave inhibit the normal process (for 2-D systems) of inverse spectral cascade in this case. A detailed simulation study has been carried out for the understanding of this inhibition.

Practical expressions for the internal energy and pressure of Yukawa fluids

Author(s): Sergey A. Khrapak and Hubertus M. Thomas

Simple practical expressions that allow estimation of thermodynamic properties of Yukawa fluids in a wide range of coupling, up to the fluid-solid phase transition, are presented. These expressions demonstrate excellent agreement with the available results from numerical simulations. The approach pr...

[Phys. Rev. E 91, 023108] Published Wed Feb 25, 2015

Coherent scattering of electromagnetic waves by self-organized dust structures: Degree of coherence

It is demonstrated explicitly that the scattering of electromagnetic waves by dust structures can be strongly enhanced as compared to incoherent scattering by random electrons. If the size of the dust structure is much less than the wavelength of the incident radiation, the scattering is coherent. In this case, the scattering is proportional to the square of the total number of electrons in the structure. In the opposite limit, the scattering is incoherent being proportional to the total number of electrons in the structure. The factor describing the degree of coherency is calculated numerically for several models of self-organized structures. It is demonstrated in general way that for sudden heating of electrons, the factor of coherency in scattering by structures can decrease by several orders of magnitude with subsequent increase after the heating is switched off. In laboratory dusty plasmas, the coherent scattering is proposed for diagnostics of universal structuring instability and as a probe for determining the properties typical for self-organized nature of structures that are observed in recent experiments.

Excitation of Kelvin Helmholtz instability by an ion beam in a plasma with negatively charged dust grains

An ion beam propagating through a magnetized dusty plasma drives Kelvin Helmholtz Instability (KHI) via Cerenkov interaction. The frequency of the unstable wave increases with the relative density of negatively charged dust grains. It is observed that the beam has stabilizing effect on the growth rate of KHI for low shear parameter, but for high shear parameter, the instability is destabilized with relative density of negatively charged dust grains.

Nonthermal and geometric effects on the symmetric and anti-symmetric surface waves in a Lorentzian dusty plasma slab

The nonthermal and geometric effects on the propagation of the surface dust acoustic waves are investigated in a Lorentzian dusty plasma slab. The symmetric and anti-symmetric dispersion modes of the dust acoustic waves are obtained by the plasma dielectric function with the spectral reflection conditions the slab geometry. The variation of the nonthermal and geometric effects on the symmetric and the anti-symmetric modes of the surface plasma waves is also discussed.

Langmuir probe measurements of electron energy probability functions in dusty plasmas

Langmuir probe measurements in dusty plasmas is a challenge because particle and film deposition on the probe leads to contamination and distortion of the current–voltage characteristics. This problem is particularly acute while determining the electron energy probability function (EEPF) from the second derivative of the Langmuir probe current–voltage characteristics. Here, we present reliable EEPF measurements in a capacitively coupled argon–silane dusty plasma using a fast-scanning and shielded Langmuir probe. A solenoid-actuated shield covered the probe and the probe was exposed to the plasma only for short periods of time (less than 6 s) when the current–voltage characteristics were recorded during rapid voltage scans. This approach minimized probe surface contamination. In presence of dust (silicon nanoparticles) the electron density decreased and the electron temperature increased in comparison to a pristine argon plasma. While the population of lower energy electrons decre...

Quantum path integral molecular dynamics simulations on transport properties of dense liquid helium. (arXiv:1502.04554v1 [astro-ph.EP])

Transport properties of dense liquid helium under the conditions of planet's core and cool atmosphere of white dwarfs have been investigated by using the improved centroid path-integral simulations combined with density functional theory. The self-diffusion is largely higher and the shear viscosity is notably lower predicted with the quantum mechanical description of the nuclear motion compared with the description by Newton equation. The results show that nuclear quantum effects (NQEs), which depends on the temperature and density of the matter via the thermal de Broglie wavelength and the ionization of electrons, are essential for the transport properties of dense liquid helium at certain astrophysical conditions. The Stokes-Einstein relation between diffusion and viscosity in strongly coupled regime is also examined to display the influences of NQEs.

Practical expressions for the internal energy and pressure of Yukawa fluids. (arXiv:1502.04060v1 [physics.plasm-ph])

Simple practical expressions are put forward, which allow to estimate thermodynamic properties of Yukawa fluids in a wide range of coupling, up to the fluid-solid phase transition. These expressions demonstrate excellent agreement with the available results from numerical simulations. The approach provides simple and accurate tool to estimate thermodynamic properties of Yukawa fluids and related systems in a broad range of parameters.

Dynamic simulation of sediment films of Yukawa-stabilized particles

Author(s): Damien D. Brewer and Satish Kumar

The fast lubrication dynamics method is applied to simulate the motion and deposition of charge-stabilized 100-nm-diam particles into sediment films from aqueous dispersions. Colloidal interactions are incorporated with a Yukawa potential and the effects of the screened-Coulomb potential strength an...

[Phys. Rev. E 91, 022304] Published Fri Feb 13, 2015