T. Farid

Low-frequency electrostatic dust-modes in a strongly coupled dusty plasma with dust charge fluctuations

Low-frequency electrostatic dust-modes are theoretically investigated accounting for dust grain charge fluctuation and for equilibrium grain charge inhomogeneity in a strongly coupled dusty plasma. A new stable extremely low-frequency mode, which is due to the inhomogeneity in the equilibrium dust grain charge, is found to exist in such a dusty plasma. It is also found that the dust-acoustic mode becomes unstable due to the effect of this equilibrium dust grain charge inhomogeneity. It is observed here that the influence of strong correlations in the dust fluid significantly modify the dispersion properties of this new mode as well as of the existing dust-acoustic mode. The implications of our results to recent experimental observations and to some space and astrophysical situations are briefly discussed.

Nonlinear electrostatic waves in a magnetized dust-ion plasma

It is shown that the nonlinear equation governing the dynamics of coupled dust-acoustic and dust-cyclotron waves in a magnetized dust-ion plasma can be written in the form of an energy integral. The latter is analyzed analytically as well as numerically to investigate the properties of arbitrary amplitude solitary waves. It is found both analytically as well as numerically that there exist solitary waves only with a negative potential. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring systems and cometary tails, are briefly discussed.

Nonlinear ion-drift waves in a nonuniform plasma with nonzero ion-temperature-gradient effects

It is shown that Grad hydrodynamics can be used for the description of nonlinear ion-drift waves in a low β plasma. The set of nonlinear equations which allows us to describe both the ion polarization drift and the nonzero ion Larmor radius effects is derived. The presence of a nonzero ion temperature gradient induces a corresponding perpendicular thermal flux which in turn substantially modifies the transverse stress tensor. Thus, the description of effects associated with the perpendicular ion polarization drift demands corrections in the magnetic viscosity due to the nonzero thermal flux.

Formation of a tripolar vortex in a contaminated electron-positron magnetoplasma with sheared flows

We derive a system of nonlinear equations governing the dynamics of low-frequency electrostatic waves in a magnetized pair plasma with sheared flows that is contaminated by dust grains. For some specific profiles of the equilibrium sheared flows, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. The implications of our investigation to laboratory and space plasmas are discussed.

Tripolar vortices associated with toroidal ion temperature gradient modes in a magnetoplasma with sheared flows

A system of nonlinear equations for low-frequency toroidal ion-temperature-gradient modes in a nonuniform magnetoplasma with sheared plasma flow is presented. For some specific profiles of the equilibrium density, the ion temperature and sheared plasma flows, the nonlinear equations admit a tripolar vortex. The numerical results show a negative potential vortex core between the lobs of a dipole-like structure which has a positive value of the potential.

Formation of vortex streets due to nonlinearly interacting ion–temperature–gradient modes

Stationary solutions of the nonlinear equations, which govern the dynamics of ion–temperature–gradient (ITG) electrostatic modes, are re-examined without and with magnetic field inhomogeneities. It is shown that for both cases the nonlinear equations admit vortex street solutions in those parameter regimes where spatially bounded double vortex solutions are forbidden. The ITG-driven vortex streets can be associated with coherent nonlinear structures that are observed in laboratory and computer simulation experiments. Furthermore, vortex streets might play a detrimental role in the study of anomalous ion thermal transport in magnetically confined plasmas.

Sheared-flow-driven vortices in a magnetized dusty electron-positron plasma

It is shown that sheared plasma flows can generate nonthermal electrostatic waves in a magnetized dusty electron-positron plasma. Linearly excited modes attain large amplitudes and start interacting among themselves. Nonlinearly coupled modes self-organize in the form of coherent vortices comprising a vortex chain and a double vortex. Conditions under which the latter appear are given. The relevance of our investigation to space, astrophysical, and laboratory plasmas is pointed out.

A class of stationary nonlinear dusty plasma equilibria

It is shown that nonparallel density and temperature gradients can produce magnetic fields in dusty plasmas. Spontaneously created magnetic fields can be maintained if there exists plasma vorticity. In order to understand this phenomena, a self-consistent dusty plasma equilibrium model is constructed by employing a kinetic description and invoking the Hamiltonian approach. Stationary nonlinear dusty plasma equilibria contain specific profiles for the plasma number density, the plasma current, and the magnetic field. The relevance of this investigation to low-temperature laboratory dusty and space plasmas is discussed.

Formation of vortices in the presence of sheared electron flows in the earth's ionosphere

Abstract It is shown that sheared electron flows can generate long as well as short wavelength (in comparison with the ion gyroradius) electrostatic waves in a nonuniform magnetplasma. For this purpose, we derive dispersion relations by employing two-fluid and hybrid models; in the two-fluid model the dynamics of both the electrons and ions are governed by the hydrodynamic equations and the guiding center fluid drifts, whereas the hybrid model assumes kinetic ions and fluid electrons. Explicit expressions for the growth rates and thresholds are presented. Linearly excited waves attain finite amplitudes and start interacting among themselves. The interaction is governed by the nonlinear equations containing the Jacobian nonlinearities. Stationary solutions of the nonlinear mode coupling equations can be represented in the form of a dipolar vortex and a vortex street. Conditions under which the latter arise are given. Numerical results for the growth rates of linearly excited modes as well as for various types of vortices are displayed for the parameters that are relevant for the F-region of the Earths ionosphere. It is suggested that the results of the present investigation are useful in understanding the properties of nonthermal electrostatic waves and associated nonlinear vortex structures in the Earths ionosphere.

The effect of dust charge inhomogeneity on low-frequency modes in a strongly coupled plasma

An analysis of low-frequency modes accounting for dust grain charge fluctuation and equilibrium grain charge inhomogeneity in a strongly coupled dusty plasma is presented. The existence of an extremely low frequency mode, which is due to the inhomogeneity in the equilibrium dust grain charge, is reported. Besides, the equilibrium dust grain charge inhomogeneity makes the dust-acoustic mode unstable. The strong correlations in the dust fluid significantly drive a new mode as well as the existing dust-acoustic mode. The applications of these results to recent experimental and to some space and astrophysical situations are discussed.