Monthly Archives: March 2015

Molecular dynamics simulations of soliton-like structures in a dusty plasma medium

The existence and evolution of soliton-like structures in a dusty plasma medium are investigated in a first principles approach using molecular dynamic (MD) simulations of particles interacting via a Yukawa potential. These localized structures are found to exist in both weakly and strongly coupled regimes with their structures becoming sharper as the correlation effects between the dust particles get stronger. A surprising result, compared to fluid simulations, is the existence of rarefactive soliton-like structures in our non-dissipative system, a feature that arises from the charge conjugation symmetry property of the Yukawa fluid. Our simulation findings closely resemble many diverse experimental results reported in the past.

Orbital-motion-limited theory of dust charging and plasma response. (arXiv:1503.07820v1 [physics.plasm-ph])

The foundational theory for dusty plasmas is the dust charging theory that provides the dust potential and charge arising from the dust interaction with a plasma. The most widely used dust charging theory for negatively charged dust particles is the so-called orbital motion limited (OML) theory, which predicts the dust potential and heat collection accurately for a variety of applications, but was previously found to be incapable of evaluating the dust charge and plasma response in any situation. Here we report a revised OML formulation that is able to predict the plasma response and hence the dust charge. Numerical solutions of the new OML model show that the widely-used Whipple approximation of dust charge-potential relationship agrees with OML theory in the limit of small dust radius compared with plasma Debye length, but incurs large (order-unity) deviation from the OML prediction when the dust size becomes comparable with or larger than plasma Debye length. This latter case is expected for the important application of dust particles in a tokamak plasma.

Solution of the inverse Langevin problem for open dissipative systems with anisotropic interparticle interaction

Solution of the inverse Langevin problem is presented for open dissipative systems with anisotropic interparticle interaction. Possibility of applying this solution for experimental determining the anisotropic interaction forces between dust particles in complex plasmas with ion flow is considered. For this purpose, we have tested the method on the results of numerical simulation of chain structures of particles with quasidipole-dipole interaction, similar to the one occurring due to effects of ion focusing in gas discharges. Influence of charge spatial inhomogeneity and fluctuations on the results of recovery is also discussed.

Stabilization of Rayleigh-Taylor instability in a non-Newtonian incompressible complex plasma

The stabilization of Rayleigh-Taylor (RT) instability is investigated in a non-Newtonian unmagnetized dusty plasma with an experimentally verified model of shear flow rate dependent viscosity. It has been found that non-Newtonian property has also a significant role in stabilization of RT instability along with velocity shear stabilization in the short wavelength regime. The effect of the non-Newtonian parameters is more profound in the higher velocity shear rate regime. A detailed study is reported on the role of non-Newtonian effect on RT instability with conventional dust fluid equations using standard numerical eigenvalue analysis.

Fluid approach to evaluate sound velocity in Yukawa systems and complex plasmas

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

The conventional fluid description of multicomponent plasma, supplemented by an appropriate equation of state for the macroparticle component, is used to evaluate the longitudinal sound velocity of Yukawa fluids. The obtained results are in very good agreement with those obtained earlier employing t...

[Phys. Rev. E 91, 033110] Published Fri Mar 20, 2015

Dust-acoustic solitary waves and shocks in strongly coupled quantum plasmas. (arXiv:1409.1982v2 [physics.plasm-ph] UPDATED)

We investigate the propagation characteristics of electrostatic dust-acoustic (DA) solitary waves and shocks in a strongly coupled dusty plasma consisting of intertialess electrons and ions, and strongly coupled inertial charged dust particles. A generalized viscoelastic hydrodynamic model with the effects of electrostatic dust pressure associated with the strong coupling of dust particles, and a quantum hydrodynamic model with the effects of quantum forces associated with the Bohm potential and the exchange-correlation potential for electrons and ions are considered. Both the linear and weakly nonlinear theory of DA waves are studied by the derivation and analysis of dispersion relations as well as Korteweg-de Vries (KdV) and KdV-Burgers (KdVB)-like equations. It is shown that in the kinetic regime ($\omega\tau_m\gg1$, where $\omega$ is the wave frequency and $\tau_m$ is the viscoelastic relaxtation time), the amplitude of the DA solitary waves decays slowly with time with the effect of a small amount of dust viscosity. However, the DA shock-like perturbations can be excited in the hydrodynamic regime with $\omega\tau_ml1$. The analytical and numerical solutions of the KdV and KdVB equations are also presented and analyzed with the system parameters.

Exclusive Window onto Higgs Yukawa Couplings

Author(s): Alexander L. Kagan, Gilad Perez, Frank Petriello, Yotam Soreq, Stoyan Stoynev, and Jure Zupan

Creative Commons We show that both flavor-conserving and flavor-violating Yukawa couplings of the Higgs boson to first- and second-generation quarks can be probed by measuring rare decays of the form h→MV, where M denotes a vector meson and V indicates either γ, W or Z. We calculate the branching ratios for these pr...

[Phys. Rev. Lett. 114, 101802] Published Tue Mar 10, 2015

Ion acoustic and dust acoustic waves at finite size of plasma particles

We consider the influence of the finite size of ions on the properties of classic plasmas. We focus our attention at the ion acoustic waves for electron-ion plasmas. We also consider the dusty plasmas where we account the finite size of ions and particles of dust and consider the dispersion of dust acoustic waves. The finite size of particles is a classical effect as well as the Coulomb interaction. The finite size of particles considerably contributes to the properties of the dense plasmas in the small wavelength limit. Low temperature dense plasmas, revealing the quantum effects, are also affected by the finite size of plasma particles. Consequently, it is important to consider the finite size of ions in the quantum plasmas as well.

Observations of imposed ordered structures in a dusty plasma at high magnetic field

Dusty plasmas have been studied in argon, rf glow discharge plasmas at magnetic fields up to 2 T, where the electrons and ions are strongly magnetized. In this experiment, plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper, electrically floating electrode supports a semi-transparent, titanium mesh. We report on the formation of an ordered dusty plasma, where the dust particles form a spatial structure that is aligned to the mesh. We discuss possible mechanisms that may lead to the formation of the “dust grid” and point out potential implications and applications of these observations.

Theory of correlation effects in dusty plasmas

A theory of correlation effects in dusty plasmas based on a suitably augmented Debye Huckel approximation is proposed. A model which takes into account the confinement of the dust within the plasma (by external fields) is considered. The dispersion relation of compressional modes with correlation effects is obtained. Results show that strong coupling effects may be subdominant even when Г ≫ 1. Thus, in the limit Γ → 0 and/or κ → ∞, one obtains the weakly coupled dust thermal mode. In the range of values of Г ≫ 1, the strong coupling effects scale with κ instead of Г; increasing Г increases the dust acoustic waves phase velocity C D A W in this regime. In the limit Γ ≫ 1 , κ ≪ 1 , one obtains the weakly coupled dust acoustic wave. Only in the limit Γ ≫ 1 , κ ≥ 1 , one obtains strong coupling effects, e.g., the dust lattice waves ( κ = a / λ d , a is the mean particle distance and λ d is the Debye length). Observations from a number of experiments are explained.