arXiv subjects

Amita Das

Publications and source records attributed to Amita Das.

75 records · Page 5Linked to original sources

arXiv2005

Fluid simulation studies of the dynamical behaviour of one dimensional relativistic electromagnetic solitons

A numerical fluid simulation investigation of the temporal evolution of a special class of traveling wave solution of the one dimensional relativistic cold plasma model is reported.The solutions consist of coupled electromagnetic and plasma waves in a solitary pulse shape (Phys. Rev. Lett. 68, 3172(1992); Phys. Plasmas 9, 1820(2002)).Issues pertaining to their stability, mutual collisional interactions and propagation in an inhomogeneous plasma medium are addressed. It is found that solitary pulses that consist of a single light peak trapped in a modulated density structure are long lived whereas structures with multiple peaks of trapped light develop an instability at the trailing edge. The interaction properties of two single peak structures show interesting dependencies on their relative amplitudes and propagation speeds and can be understood in terms of their propagation characteristics in an inhomogeneous plasma medium.

physics.plasm-ph↗

arXiv2004

Nonlinear saturation of magnetic curvature driven Rayleigh Taylor instability in three dimensions

We present three dimensional fluid simulation results on the temporal evolution and nonlinear saturation of the magnetic curvature driven Rayleigh-Taylor (RT) instability. The model set of coupled nonlinear equations evolve the scalar electric field potential $ϕ$, plasma density $n$ and the parallel component of the magnetic vector potential $ψ$. The simulations have been carried out in two limits, (i) a low resistivity case in which RT is the only linearly growing mode, and (ii) a high resistivity case where the drift wave is unstable and for which the magnetic curvature parameter is set to zero to ensure the absence of the RT growth. Our simulations show nonlinear stabilization in both these limits. The stabilization mechanism is similar to that observed in earlier two dimensional simulations, namely the generation of zonal shear flows which decorrelate the radially extended unstable modes. However the nature of the saturated nonlinear state in the 3d case differs from that of 2d in some important ways such as by having significant levels of power in short scales and by the presence of electromagnetic fluctuations. Though, in the linear regime the electromagnetic effects reduce the growth rates, in the nonlinear regime their presence hinders the process of stabilization by inhibiting the process of zonal flow formation. Thus the parameter regime for which nonlinear stabilization takes place is considerably reduced in three dimensions.

physics.plasm-ph↗

arXiv1999

Theory of Two Dimensional Mean Field Electron Magnetohydrodynamics

The theory of mean field electrodynamics for diffusive processes in Electron Magnetohydrodynamic (EMHD) model is presented. In contrast to Magnetohydrodynamics (MHD) the evolution of magnetic field here is governed by a nonlinear equation in the magnetic field variables. A detailed description of diffusive processes in two dimensions are presented in this paper. In particular, it has been shown analytically that the turbulent magnetic field diffusivity is suppressed from naive quasilinear estimates. It is shown that for complete whisterlization of the spectrum, the turbulent diffusivity vanishes. The question of whistlerization of the turbulent spectrum is investigated numerically, and a reasonable tendency towards whisterlization is observed. Numerical studies also show the suppression of magnetic field diffusivity in accordance with the analytical estimates.

physics.plasm-ph↗