Monthly Archives: October 2014

Nonthermal Lorentzian wake-field effects on collision processes in complex dusty plasmas

The influence of nonthermal Lorentzian wake-field on the electron-dust grain collision is investigated in complex dusty plasmas. The Eikonal method and the effective interaction potential are applied to obtain the Eikonal scattering phase shift, the differential Eikonal collision cross section, and the total Eikonal collision cross section as functions of the collision energy, the impact parameter, the Mach number, and the spectral index of Lorentzian plasma. It is found that the nonthermal effect enhances the Eikonal scattering phase shift and, however, suppresses the Eikonal collision cross section for the electron-dust grain in Lorentzian complex dusty plasmas. It is also found that the Eikonal scattering phase shift decreases with increasing Mach number and spectral index. In addition, the Eikonal collision cross section increases with an increase of the spectral index and Mach number in Lorentzian complex dusty plasmas.

Dynamics of compressional Mach cones in a strongly coupled complex plasma

Using a Generalised-Hydrodynamic (GH) fluid model, we study the influence of strong coupling induced modification of the fluid compressibility on the dynamics of compressional Mach cones in a dusty plasma medium. A significant structural change of lateral wakes for a given Mach number and Epstein drag force is found in the strongly coupled regime. With the increase of fluid compressibility, the peak amplitude of the normalised perturbed dust density first increases and then decreases monotonically after reaching its maximum value. It is also noticed that the opening angle of the cone structure decreases with the increase of the compressibility of the medium and the arm of the Mach cone breaks up into small structures in the velocity vector profile when the coupling between the dust particles increases.

Spin decoherence in n-type GaAs: The effectiveness of the third-body rejection method for electron-electron scattering

We study the spin decoherence in n-type bulk GaAs for moderate electronic densities at room temperature using the Ensemble Monte Carlo method. We demonstrate that a technique called “third-body rejection method” devised by B. K. Ridley, J. Phys. C: Solid State Phys. 10, 1589 (1977) can be successfully adapted to Ensemble Monte Carlo method and used to tackle the problem of the electron-electron contribution to spin decoherence in the parameter region under study, where the electron-electron interaction can be reasonably described by a Yukawa potential. This scattering technique is employed in a doping region where one can expect that multiple collisions may play a role in carrier dynamics. By this technique, we are able to calculate spin relaxation times which are in very good agreement with the experimental results found by Oertel et al., Appl. Phys. Lett. 93, 13 (2008). Through this method, we show that the electron-electron scattering is overestimated in Born approximation, in agreement with previous results obtained by C. A. Kukkonen and H. Smith, Phys. Rev. B 8, 4601 (1973).

Effective Potential Theory: A Practical Way to Extend Plasma Transport Theory to Strong Coupling. (arXiv:1410.6554v1 [physics.plasm-ph])

The effective potential theory is a physically motivated method for extending traditional plasma transport theories to stronger coupling. It is practical in the sense that it is easily incorporated within the framework of the Chapman-Enskog or Grad methods that are commonly applied in plasma physics and it is computationally efficient to evaluate. The extension is to treat binary scatterers as interacting through the potential of mean force, rather than the bare Coulomb or Debye-screened Coulomb potential. This allows for aspects of many-body correlations to be included in the transport coefficients. Recent work has shown that this method accurately extends plasma theory to orders of magnitude stronger coupling when applied to the classical one-component plasma model. The present work shows that similar accuracy is realized for the Yukawa one-component plasma model and it provides a comparison with other approaches.

Flow of Dusty Plasma Around an Obstacle

Single frame video images of dusty plasmas flowing around a conducting wire are presented in this paper. The images were obtained by laser illumination of the dust suspension with the reflected light recorded using a fast video camera. The images from two different configurations are shown. The first image records the formation of a bow shock formed when a supersonic dust cloud impinges on a thin-wire biased to repel the negatively charged dust. The second image shows the deflection of a thin stream of dust particles around a negatively charged wire.

Imaging of the Dust Acoustic Wave to Explore Synchronization

A self-excited dust acoustic wave is synchronized by sinusoidal modulation of the ion density, and the wave is imaged by planar laser-light scattering. Space-time diagrams based on the images reveal how the nonlinearity of the plasma’s response causes the wave’s frequency to be synchronized to a multiple of 0.5, 1, 2, or 3 of the modulation frequency. Space-time diagrams also reveal wave front merging as is observed for a wide range of modulation frequencies.

Simulation of Three-Dimensional Dusty Plasmas

The structure and dynamics of dust particles in a 3-D dusty plasma is characterized using a Langevin molecular dynamics simulation with a Yukawa potential. Conditions are set appropriate for a liquid-like strongly coupled plasma. The positions of dust particles are shown in an image. The thermal motion of particles is decomposed into the longitudinal wave spectrum, showing a distinctive dispersion relation.

Oscillation Amplitudes in 3-D Dust Density Waves in Dusty Plasmas Under Microgravity Conditions

Large dust clouds in dusty plasmas exhibiting self-excited dust density waves (DDWs) have been investigated in a microgravity environment. With the help of the tracer particle technique [1], 3-D trajectories of single dust particles within the dust cloud have been measured using a stereoscopic camera setup. With the availability of the full phase-space information, 3-D wave properties can be accessed. In this paper, the spatial variation of the oscillation amplitude of single particles participating in a DDW is presented. We find that the amplitude increases in the direction of wave propagation and is nearly homogenous in the plane perpendicular to that direction.

Wave Crest Reconstruction of a Dust Density Wave Using Single Particle Trajectories

Dusty plasmas can feature self-excited longitudinal density waves. These dust density waves have been investigated at the single particle level. From the full 3-D trajectories, it was possible to derive the ensemble wave motion. In this contribution, the reconstructed phase-resolved dust cloud density is shown that visualizes the wave crest evolution in time.

Unstable Plasmoids in Dusty Plasma Experiments

Low-frequency instabilities are easily obtained in dusty plasmas formed using reactive gases or material sputtering. These unstable phenomena can be characterized by complex and impressive features affecting the plasma glow luminosity. In this paper, we report on a particular phase of an instability, where moving bright plasma spots are observed in between the electrodes of a capacitively coupled radio-frequency discharge in krypton. These plasmoids show complex behaviors, such as mutual interactions, consisting in their merging or splitting.