Wave spectra of a strongly coupled magnetized one-component plasma: quasilocalized charge approximation versus harmonic lattice theory and molecular dynamics

Collective ion dynamics in Coulomb one-component plasmas within the self-consistent relaxation theory

In this paper, we present the theoretical formalism describing the collective ion dynamics of the nonideal Coulomb classical one-component plasmas on the basis of the self-consistent relaxation theory. The theory is adapted to account for correlations between the frequency relaxation parameters that characterize the three- and four-particle dynamics and the parameters associated with the two-particle dynamics. The dynamic structure factor spectra and dispersion characteristics calculated for a wide range of wave numbers are in agreement with the molecular dynamics simulation data and the results obtained with the theory of the frequency moments. The proposed formalism reproduces all the features inherent to the Coulomb one-component plasmas and requires only knowledge of the coupling parameter and the information about the structure.

Dispersion relations of Yukawa fluids at weak and moderate coupling

In this paper we compare different theoretical approaches to describe the dispersion of collective modes in Yukawa fluids when the interparticle coupling is relatively weak, so that the kinetic and potential contributions to the dispersion relation compete with each other. A thorough comparison with the results from molecular dynamics simulation allows us to conclude that, in the investigated regime, the best description is provided by the sum of the generalized excess bulk modulus and the Bohm-Gross kinetic term.

Collective modes in simple melts: Transition from soft spheres to the hard sphere limit

We study collective modes in a classical system of particles with repulsive inverse-power-law (IPL) interactions in the fluid phase, near the fluid-solid coexistence (IPL melts). The IPL exponent is varied from n = 10 to n = 100 to mimic the transition from moderately soft to hard-sphere-like interactions. We compare the longitudinal dispersion relations obtained using molecular dynamic (MD) simulations with those calculated using the quasi-crystalline approximation (QCA) and find that this simple theoretical approach becomes grossly inaccurate for \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$n\,\gtrsim 20$$\end{document}n≳20. Similarly, conventional expressions for high-frequency (instantaneous) elastic moduli, predicting their divergence as n increases, are meaningless in this regime. Relations of the longitudinal and transverse elastic velocities of the QCA model to the adiabatic sound velocity, measured in MD simulations, are discussed for the regime where QCA is applicable. Two potentially useful freezing indicators for classical particle systems with steep repulsive interactions are discussed.

Spontaneous generation of temperature anisotropy in a strongly coupled magnetized plasma

A magnetic field was recently shown to enhance field-parallel heat conduction in a strongly correlated plasma whereas cross-field conduction is reduced. Here we show that in such plasmas, the magnetic field has the additional effect of inhibiting the isotropization process between field-parallel and cross-field temperature components, thus leading to the emergence of strong and long-lived temperature anisotropies when the plasma is locally perturbed. An extended heat equation is shown to describe this process accurately.

Cage correlation and diffusion in strongly coupled three-dimensional Yukawa systems in magnetic fields

The influence of an external homogeneous magnetic field on the quasilocalization of the particles-characterized quantitatively by cage correlation functions-in strongly coupled three-dimensional Yukawa systems is investigated via molecular dynamics computer simulations over a wide domain of the system parameters (coupling and screening strengths, and magnetic field). The caging time is found to be enhanced by the magnetic field B. The anisotropic migration of the particles in the presence of magnetic field is quantified via computing directional correlation functions, which indicate a more significant increase of localization in the direction perpendicular to B, while a moderate increase is also found along the B field lines. Associating the particles' escapes from the cages with jumps of a characteristic length, a connection is found with the diffusion process: the diffusion coefficients derived from the decay time of the directional correlation functions in both the directions perpendicular to and parallel with B are in very good agreement with respective diffusion coefficients values obtained from their usual computation based on the mean-squared displacement of the particles.

Effect of correlations on heat transport in a magnetized strongly coupled plasma

In a classical ideal plasma, a magnetic field is known to reduce the heat conductivity perpendicular to the field, whereas it does not alter the one along the field. Here we show that, in strongly correlated plasmas that are observed at high pressure and/or low temperature, a magnetic field reduces the perpendicular heat transport much less and even enhances the parallel transport. These surprising observations are explained by the competition of kinetic, potential, and collisional contributions to the heat conductivity. Our results are based on first-principle molecular dynamics simulations of a one-component plasma.

Waves in two-dimensional superparamagnetic dusty plasma liquids

Wave dispersion relations in the strongly coupled liquid phase of a two-dimensional system of dust grains interacting via both Yukawa and dipole interactions are investigated. The model system comprises a layer of charged superparamagnetic grains in a plasma in an external, uniform magnetic field B whose magnitude and direction can be varied. Because the induced magnetic dipole moments of the grains lie along B, the interaction between the grains becomes anisotropic as B is tilted with respect to the layer. The theoretical approach uses a reformulated quasilocalized charge approximation that can treat dipole interactions, combined with molecular dynamics simulations. The mode dispersion relations are found to depend on the relative strengths of the Yukawa and dipole interactions and the direction of wave propagation in the plane.

Effect of magnetic field on the velocity autocorrelation and the caging of particles in two-dimensional Yukawa liquids

We investigate the effect of an external magnetic field on the velocity autocorrelation function and the "caging" of the particles in a two-dimensional strongly coupled Yukawa liquid, via numerical simulations. The influence of the coupling strength on the position of the dominant peak in the frequency spectrum of the velocity autocorrelation function confirms the onset of a joint effect of the magnetic field and strong correlations at high coupling. Our molecular dynamics simulations quantify the decorrelation of the particles' surroundings: the magnetic field is found to increase significantly the caging time, which reaches values well beyond the time scale of plasma oscillations. The observation of the increased caging time is in accordance with findings that the magnetic field decreases diffusion in similar systems.

Dynamics of two-dimensional one-component and binary Yukawa systems in a magnetic field

We consider two-dimensional Yukawa systems in a perpendicular magnetic field. Computer simulations of both one-component and binary systems are used to explore the equilibrium particle dynamics in the fluid state. The mobility is found to scale with the inverse of the magnetic field strength (Bohm diffusion), for strong fields (ωc/ωp≳1). For bidisperse mixtures, the magnetic field dependence of the long-time mobility depends on the particle species, providing an external control of their mobility ratio. At large magnetic fields, the highly charged particles are almost immobilized by the magnetic field and form a porous matrix of obstacles for the mobile low-charge particles.