Hamid Saleem

Two-stream instabilities in unmagnetized dusty plasmas

Two-stream instabilities in an unmagnetized multi-species dusty plasma are investigated. Four different plasma models are considered. The effect of the dust particles on the instability growth rate and the threshold drift velocity for excitation of the instability are examined.

Ion acoustic vortices in quantum magnetoplasmas

A nonlinear equation for ion acoustic waves in dense quantum plasmas (which is analogous to the classical plasma case) has been obtained in a particular limit. Therefore it is proposed that electrostatic monopolar and dipolar vortices can appear in uniform dense quantum plasmas due to large amplitude acoustic fluctuations. It is noticed that the scale length of these structures will be very short. The main quantum effect appears through Fermi pressure.

Electrostatic Korteweg–de Vries solitons in pure pair-ion and pair-ion–electron plasmas

Linear and nonlinear electrostatic waves are studied in unmagnetized pure pair-ion (PI) and pair-ion–electron (PIE) plasmas. The nonlinear electrostatic potential structures are obtained using the reductive perturbation technique. It is found that potential hump and dip structures are obtained in pure PI plasmas, when there is a slight difference of temperature between positive and negative ions. The electrostatic potential humps are formed when the temperature of the negative ions is greater than that of the positive ions, while the potential dips are obtained in the reverse temperature condition of the plasma species. The electrostatic solitons are also obtained in the presence of electrons in PI plasmas. It is found that only potential dip structures are obtained in the PIE plasma case. The numerical results are also presented for illustration.

Nonlinear structures of drift waves in pair-ion-electron plasmas

The Korteweg–de Vries–Burgers equation is derived for drift waves in a partially ionized nonuniform pair-ion-electron (PIE) plasma. The nonlinearity appears due to electron temperature gradient. The analytical solutions in the form of solitons, monotonic shocks, and oscillatory shocks have been obtained. The numerical calculations have also been presented for PIE plasmas of fullerene and hydrogen for illustration keeping in view the recent experiments. This work can be useful for future experimental investigations.

Streaming instabilities in multicomponent interstellar clouds

Streaming instabilities in interstellar clouds have been investigated. It is pointed out that the motion of a lighter dust species relative to a plasma containing a heavier dust species can give rise to low frequency electrostatic fluctuations. The dust ion acoustic and dust acoustic waves can become unstable in such plasmas. The instability regions are influenced by the presence of background dust. Since interstellar clouds have relative motions in many cases and contain dust species, therefore the present results indicate the presence of an electrostatic dust ion acoustic wave and dust acoustic wave in such systems. The results have been applied to interstellar medium using particular data and comparisons have been made with previous works.

Modified ion-acoustic solitary waves in plasmas with field-aligned shear flows

The nonlinear dynamics of ion-acoustic waves is investigated in a plasma having field-aligned shear flow. A Koeteweg-deVries-type nonlinear equation for a modified ion-acoustic wave is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.

Electron shear-flow-driven instability in magnetized plasmas with magnetic field gradient

It is found that the zero-order current associated with electron shear flow produces a drift wave in magnetized plasmas, which can become unstable under certain conditions. This wave will be particularly important in low density and low temperature plasmas of heavy ions. As an example, numerical estimates are presented for a barium plasma with parameters compatible with experiments.

Nonlinear electrostatic waves in anisotropic ion pressure plasmas

The Korteweg–de Vries electrostatic solitons are studied in the presence of anisotropic ion pressure in a strongly magnetized plasma. The anisotropic ion pressure is defined using double adiabatic Chew–Golberger–Low (CGL) theory. It is found that for the case when perpendicular ion pressure is greater than the parallel pressure, the increase in perpendicular pressure increases the width of the structure, while the amplitude remains the same. However, for the case when ion parallel pressure is larger than the perpendicular pressure, the increase in the parallel pressure decreases the wave amplitude as well as width of the soliton. The effects of obliqueness on the soliton amplitude as well as width are also investigated in anisotropic ion pressure plasmas. The results are found to be quite different from isotropic adiabatic ion pressure magnetized plasmas.

Generation of extraordinary mode radiation by an electrostatic pump

It is shown that an electrostatic wave near the upper‐hybrid resonance frequency can parametrically excite extraordinary (X‐) mode radiation accompanied by a great variety of low‐frequency oscillations. The latter may include the lower‐hybrid, the electron‐acoustic, the ion‐cyclotron, and the shear Alfven waves. Nonlinear dispersion relations and the growth rates are obtained for each case. Comparison of our investigation to an earlier work and its possible application to space plasmas are pointed out.

Kinetic effects on streaming instabilities in electron-positron-ion plasmas

Streaming instabilities in electron-positron-ion plasmas are investigated using kinetic approach in several different limits. The effects of the variation of background temperatures of electrons Teo and positrons Tpo on the growth rates are also presented for the case of ion beam streaming into electron-positron plasmas and positrons beam streaming into electron-ion plasmas. It is noticed that the increase of number density of positrons gives a destabilizing trend to the electrostatic perturbations in the system.