arXiv subjects

H. Saleem

Publications and source records attributed to H. Saleem.

5 recordsLinked to original sources

arXiv2023

Reductive Perturbation Method in Magnetized Plasma and Role of Negative Ions

An analysis of reductive perturbation method (RPM) is presented to show that why the solitary structures of nonlinear ion acoustic waves (IAWs) cannot be obtained in magnetized electron ion plasma by employing this technique. In RPM, the nonlinear Korteweg-de Vries (KdV) equation is derived using stretched coordinates in the reference frame of the wave phase speed, considering the dispersion to be a higher-order effect which balances the nonlinearity to produce a solitary structure. The maximum amplitude $\mid Φ_m \mid$ of the nonlinear solitary wave turns out to be larger than one which contradicts the small amplitude approximation. In the presence of negative ions, the maximum amplitude satisfies the condition $\midΦ_m\mid <1$. To elaborate these points, the results have been applied to an experimental plasma consisting of positive ions of xenon $(Xe^{+})$ and negative ions of fluorene $(F^{-})$ along with electrons. The amplitude and width of the solitary structures depend upon the ratio of the electron to positive ion density ($\frac{n_{e0}}{n_{i0}}$). Since the nonlinear coefficient turns out to be negative, rarefied (dip) solitons are formed in the magnetized $Xe^{+}-F^{-}-e$ plasma.

physics.plasm-ph↗

arXiv2012

Self Heating of Corona by Electrostatic Fields Driven by Sheared Flows

A mechanism of self-heating of solar corona is pointed out. It is shown that the free energy available in the form of sheared flows gives rise to unstable electrostatic waves which accelerate the particles and heat them. The electrostatic perturbations take place through two processes (a) by purely growing sheared flow-driven instability and (b) by sheared flow-driven drift waves. These processes occur throughout the corona and hence the self-heating is very important in this plasma. These instabilities can give rise to local electrostatic potentials $φ$ of the order of about 100 volts or less within $3\times10^{-2}$ to a few seconds time if the initial perturbation is assumed to be about one percent that is $\frac{eφ}{T_{e}}\simeq10^{-2}$. The components of wave lengths in the direction perpendicular to external magnetic field $\textbf{B}_{0}$ vary from about 10m to 1m. The purely growing instability creates electrostatic fields by sheared flows even if the density gradient does not exist whereas the density gradient is crucial for the concurrence of drift wave instability. Subject headings: Sun: self-heating of corona, sheared flow-driven instability, drift waves.

physics.plasm-ph↗

arXiv2011

Subtlety in the Use of Maxwell's Equation and a New Electromagnetic Wave in Electron Plasmas

The ambiguity involved in the use of Maxwell's equation particularly in electron plasmas is discussed. It is pointed out that in the slow time scale perturbations the displacement current is ignored but it does not imply that the electron density fluctuations vanish. The contradictions in the assumptions and approximations used in the literature on this subject are discussed. A new low frequency electromagnetic wave is described which is a normal mode of non-uniform magnetized electron plasmas. This wave can couple with plasma hybrid oscillations if ion dynamics is taken into account. It is stressed that the electron magnetohydrodynamics (EMHD) model seems to be simple but in fact its use is subtle and its scope is very limited.

physics.plasm-ph↗

arXiv2005

Gravitomagnetic Effects on Collective Plasma Oscillations in Compact Stars

The effects of gravitomagnetic force on plasma oscillations are investigated using the kinetic theory of homogeneous electrically neutral plasma in the absence of external electric or magnetic field. The random phase assumption is employed neglecting the thermal motion of the electrons with respect to a fixed ion background. It is found that the gravitomagnetic force reduces the characteristic frequency of the plasma thus enhancing the refractive index of the medium. The estimates for the predicted effects are given for a typical white dwarf, pulsar, and neutron star.

astro-ph↗

arXiv2004

Arbitrary amplitude inertial Alfven waves in homogeneous magnetized electron-positron-ion plasmas

Nonlinear set of equations for inertial or slow shear Alfven wave (SSAW) in ideal electron-positron-ion (e-p-i) plasmas are presented. The analytical solution for arbitrary amplitude SSAW in such multi-component plasmas is obtained using Sagdeev potential approach. The numerical solutions for several different cases have also been presented for illustrative purpose. It is found that the electron density dips of SSAW are formed in the super Alfvenic region. The amplitude and the width of the nonlinear shear Alfven wave reduces with the increase in the concentration of positrons in electron-ion (e-i) plasmas. The width of the soliton also depends upon the direction of propagation of the perturbation in both e-i and e-p-i plasmas.

physics.plasm-ph↗