H. A. Shah

Nonlinear Zakharov-Kuznetsov equation for obliquely propagating two-dimensional ion-acoustic solitary waves in a relativistic, rotating magnetized electron-positron-ion plasma

The purpose of this work is to investigate the linear and nonlinear properties of the ion-acoustic waves (IAW), propagating obliquely to an external magnetic field in a weakly relativistic, rotating, and magnetized electron-positron-ion plasma. The Zakharov–Kuznetsov equation is derived by employing the reductive perturbation technique for this wave in the nonlinear regime. This equation admits the solitary wave solution. The amplitude and width of this solitary wave have been discussed with the effects of obliqueness, relativity, ion temperature, positron concentration, magnetic field, and rotation of the plasma and it is observed that for IAW these parameters affect the propagation properties of solitary waves and these plasmas behave differently from the simple electron-ion plasmas. Likewise, the current density and electric field of these waves are investigated for their dependence on the above-mentioned parameters.

Jeans instability in a quantum dusty magnetoplasma

Jeans instability in a homogeneous cold quantum dusty plasma in the presence of the ambient magnetic field and the quantum effect arising through the Bohm potential has been examined using the quantum magnetohydrodynamic model. It is found that the Jeans instability is significantly reduced by the presence of the dust-lower-hybrid wave and the ion quantum effect. The minimum wavenumber for Jeans stability depends clearly on ion quantum effect and the dust-lower-hybrid frequency also.

Effects of positron concentration, ion temperature, and plasma β value on linear and nonlinear two-dimensional magnetosonic waves in electron–positron–ion plasmas

Magnetosonic waves are intensively studied due to their importance in space plasmas and also in fusion plasmas where they are used in particle acceleration and heating experiments. This work considers magnetosonic waves propagating obliquely at an angle θ to an external magnetic field in an electron–positron–ion plasma, using the effective one-fluid magnetohydrodynamic model. Two separate modes (fast and slow) for the waves are discussed in the linear approximation, and the Kadomstev–Petviashvilli soliton equation is derived by using reductive perturbation scheme for these modes in the nonlinear regime. It is observed that for both the modes the angle θ, positron concentration, ion temperature, and plasma β-value affect the propagation properties of solitary waves and behave differently from the simple electron–ion plasmas. Likewise, current density, electric field, and magnetic field for these waves are investigated, for their dependence on the above mentioned parameters.

The parametric decay of dust ion acoustic waves in non-uniform quantum dusty magnetoplasmas

The parametric decay instability of a dust ion acoustic wave into low-frequency electrostatic dust-lower-hybrid and electromagnetic shear Alfven waves has been investigated in detail in an inhomogeneous cold quantum dusty plasma in the presence of external/ambient uniform magnetic field. The quantum magnetohydrodynamic model of plasmas with quantum effect arising through the Bohm potential and Fermi degenerate pressure has been employed in order to find the linear and nonlinear responses of the plasma particles for three-wave nonlinear coupling in a dusty magnetoplasma. A relatively high frequency electrostatic dust ion acoustic wave has been taken as the pump wave. It couples with two other low-frequency internal possible modes of the dusty magnetoplasma, viz., the dust-lower-hybrid and shear Alfven waves. The nonlinear dispersion relation of the dust-lower-hybrid wave has been solved to obtain the growth rate of the parametric decay instability. The growth rate is at a maximum for a small value of the e...

Study of non-Maxwellian trapped electrons by using generalized (r,q) distribution function and their effects on the dynamics of ion acoustic solitary wave

By using the generalized (r,q) distribution function, the effect of particle trapping on the linear and nonlinear evolution of an ion-acoustic wave in an electron-ion plasma has been discussed. The spectral indices q and r contribute to the high-energy tails and flatness on top of the distribution function respectively. The generalized Korteweg–de Vries equations with associated solitary wave solutions for different ranges of parameter r are derived by employing a reductive perturbation technique. It is shown that spectral indices r and q affect the trapping of electrons and subsequently the dynamics of the ion acoustic solitary wave significantly.

Effect of trapping in degenerate quantum plasmas

In the present work we consider the effect of trapping as a microscopic process in a plasma consisting of quantum electrons and nondegenerate ions. The formation of solitary structures is investigated in two cases: first when the electrons are fully degenerate and second when small temperature effects are taken into account. It is seen that not only rarefactive but coupled rarefactive and compressive solitons are obtained under different temperature conditions.

Parallel propagating electromagnetic modes with the generalized (r,q) distribution function

In the present paper, it is argued that non-Maxwellian distribution functions are better suited to model space plasmas. A new model distribution function called the generalized (r,q) distribution function which is the generalized form of the generalized Lorentzian (kappa) distribution function has been employed to carry out theoretical investigation for parallel propagating waves in general and for Alfven waves in particular. New plasma dispersion functions have been derived and their properties investigated. The new linear dispersion relation for Alfven waves is investigated in detail.

Some electrostatic modes based on non-Maxwellian distribution functions

A comparative study of fundamental modes such as Langmuir waves, dust ion acoustic waves, and dust-acoustic waves using non-Maxwellian distribution functions is presented. The real frequency and the growth rate of the modes are calculated by using kappa and generalized (r,q) distribution functions and results are compared with those of Maxwellian distribution. It is noted that in the limit (i) r=0, q→∞ for generalized (r,q) distributions and (ii) κ→∞ for kappa distributions, the non-Maxwellian functions reduce to Maxwellian.

Effects of trapping and finite temperature in a relativistic degenerate plasma

In the present work, we have undertaken, for the first time, investigation on the effect of trapping on the formation of solitary structures in relativistic degenerate plasmas. Such plasmas have been observed in dense astrophysical objects, and in laboratory these may result due to the interaction of intense lasers with matter. We have used the relativistic Fermi-Dirac distribution to describe the dynamics of the degenerate trapped electrons by solving the kinetic equation. The Sagdeev potential approach has been employed to obtain the arbitrary amplitude solitary structures both when the plasma has been considered cold and when small temperature effects have been taken into account. The theoretical results obtained have been analyzed numerically for different parameter values, and the results have been presented graphically.

Drift wave instability in a nonuniform quantum dusty magnetoplasma

Using the quantum hydrodynamic model of plasmas and with quantum effects arising through the Bohm potential and the Fermi degenerate pressure, the possible drift waves and their instabilities have been investigated in considerable detail in a nonuniform dusty magnetoplasma. It is found that in the presence of a nonuniform ambient magnetic field, the drift waves grow in amplitude by taking energy from the streaming ions and density inhomogeneity. The implication of the drift wave instability for nonthermal electrostatic fluctuations to laboratory and astrophysical environments is also pointed out.