Muhammad Fraz Bashir | COMSATS Institute of Information Technology Lahore (original) (raw)

Papers by Muhammad Fraz Bashir

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

It is shown that the universally unstable kinetic drift wave in an electron-ion plasma can very e... more It is shown that the universally unstable kinetic drift wave in an electron-ion plasma can very effectively be suppressed by adding an extra flowing ion (or plasma) population. The effect of the flow of the added ions is essential, their response is of the type (v_{ph}-v_{f0})exp[-(v_{ph}-v_{f0})^{2}], where v_{f0} is the flow speed and v_{ph} is the phase speed parallel to the magnetic field vector. The damping is strong and it is mainly due to this ion exponential term, and this remains so for v_{f0}<v_{ph}.

Physics of Plasmas, 2014

ABSTRACT

Physics of Plasmas

The kinetic instability of the obliquely propagating drift magnetosonic wave for temperature anis... more The kinetic instability of the obliquely propagating drift magnetosonic wave for temperature anisotropic low beta plasmas is studied by using the gyro-kinetic model. The interplay between the temperature anisotropy and the density inhomogeneity free energy sources is discussed in order to provide stabilization of drift instability by the temperature anisotropy effect. It is shown that the anisotropy suppresses the growth rate when the anisotropy ratio Ae,i (=T⊥(e,i)/T∥(e,i)) is greater than unity, whereas it enhances the growth rate for Ae,i<1 . Comparison of kinetic instability with reactive instability [Naim et al., Phys. Plasmas 21, 102112 (2014)] and the scaling of growth time with the diffusion and the anisotropy relaxation times are presented. Additionally, the stability analysis applicable to a wide range of plasma parameters is also performed.

Brazilian Journal of Physics, 2012

Using kinetic theory for homogeneous collisionless magnetized plasmas, we present an extended rev... more Using kinetic theory for homogeneous collisionless magnetized plasmas, we present an extended review of the plasma waves and instabilities and discuss the anisotropic response of generalized relativistic dielectric tensor and Onsager symmetry properties for arbitrary distribution functions. In general, we observe that for such plasmas only those electromagnetic modes whose magnetic-field perturbations are perpendicular to the ambient magnetic field, i.e., B1 ⊥ B0, are effected by the anisotropy. However, in oblique propagation all modes do show such anisotropic effects. Considering the non-relativistic bi-Maxwellian distribution and studying the relevant components of the general dielectric tensor under appropriate conditions, we derive the dispersion relations for various modes and instabilities. We show that only the electromagnetic R-and L-waves, those derived from them (i.e., the whistler mode, pure Alfvén mode, firehose instability, and whistler instability), and the O-mode are affected by thermal anisotropies, since they satisfy the required condition B1⊥B0. By contrast, the perpendicularly propagating X-mode and the modes derived from it ( the pure transverse X-mode and Bernstein mode) show no such effect. In general, we note that the thermal anisotropy modifies the parallel propagating modes via the parallel acoustic effect, while it modifies the perpendicular propagating modes via the Larmor-radius effect. In oblique propagation for kinetic Alfvén waves, the thermal anisotropy affects the kinetic regime more than it affects the inertial regime. The generalized fast mode exhibits two distinct acoustic effects, one in the direction parallel to the ambient magnetic field and the other in the direction perpendicular to it. In the fast-mode instability, the magneto-sonic wave causes suppression of the firehose instability. We discuss all these propagation characteristics and present graphic illustrations. The threshold conditions for different instabilities are also obtained.

Physics of Plasmas, 2012

Using the quantum hydrodynamical model of plasmas, the stability analysis of selfgravitational el... more Using the quantum hydrodynamical model of plasmas, the stability analysis of selfgravitational electrostatic drift waves for a streaming non-uniform quantum dusty magnetoplasma is presented. For two di¤erent frequency domains i.e., 0d << ! < 0i (unmagnetized dust) and ! << 0d < 0i (magnetized dust), we simplify the general dispersion relation for self-gravitational electrostatic drift waves which incorporates the e¤ects of density inhomogeneity rn 0 , streaming velocity v 0 due to magnetic …eld inhomogeneity rB 0 , Bohm potential and the Fermi degenerate pressure. For both frequency domains, the e¤ect of density inhomogeneity gives rise to real oscillations while the ions streaming velocity v 0i as well as the e¤ective electron quantum velocity v 0 F e make these oscillations propagate perpendicular to the ambient magnetic …eld. This oscillatory behavior of self-gravitational drift waves increases with increase in inhomogeneities and quantum e¤ects while it decreases with increase in the gravitational potential. However only for the unmagnetized case, the drift waves may become unstable under appropriate conditions giving rise to Jeans instability. The modi…ed threshold condition is also determined for instability by using the intersection method for solving the cubic equation. We note that the inhomogeneity in magnetic …eld (equilibrium density) through streaming velocity (diamagnetic drift velocity) suppress the Jeans instability depending upon the characteristic scale length of these inhomogeneities. On the other hand, the dust-lower-hybrid wave and the quantum mechanical e¤ects of electrons tend to reduce the growth rate as expected. A number of special cases are also discussed.

Fully relativistic analysis of anomalous skin effects for parallel propagating waves in a weakly ... more Fully relativistic analysis of anomalous skin effects for parallel propagating waves in a weakly magnetized electron plasma is presented and general expressions for longitudinal and transverse permittivites are derived. It is found that the penetration depth for R-& Lwaves increases as we move from non-relativistic to highly relativistic regime. The ambient magnetic field reduces/enhances the skin effects for R-wave/L-wave as the strength of the field is increased. In general, the weak magnetic field effects are pronounced for the weakly relativistic regime as compared with other relativistic cases. The results are also graphically illustrated. On switching off the magnetic field, previous results for field free case are retrieved. 2

The classic Bernstein mode instability driven by a perpendicular momentum ring distribution funct... more The classic Bernstein mode instability driven by a perpendicular momentum ring distribution function is insensitive to the parallel distribution. However, in the relativistic treatment, owing to the inexorable coupling between the parallel and perpendicular momenta through the Lorentz factor, the parallel momentum distribution may affect the instability. This paper discusses such a problem by making use of a model parallel momentum distribution function. It is found that the parallel momentum spread only leads to the modification of the real frequency, but the instability growth rate is largely unaffected.

Physics of Plasmas, Mar 24, 2014

By using the gyrokinetic theory, the kinetic Alfvén waves (KAWs) are discussed to emphasize the d... more By using the gyrokinetic theory, the kinetic Alfvén waves (KAWs) are discussed to emphasize the drift effects through the density inhomogeneity and the temperature anisotropy on their dispersion characteristics. The dependence of stabilization mechanism of the drift-Alfvén wave instability on the temperature anisotropy is highlighted. The estimate of the growth rate and the threshold condition for a wide range of parameters are also discussed.

Employing linearized Vlasov–Maxwell system of equations, the whistler instability is discussed fo... more Employing linearized Vlasov–Maxwell system of equations, the whistler instability is discussed for a semi-relativistic bi-Maxwellian distribution. The dispersion relations are analyzed analytically along with the graphical representation and the estimates of the growth rate and instability threshold condition are also presented in the limiting cases i.e., ξ±=(ω∓Ω)/k∥vt‖⩽1 (resonant case) and ξ±≫1 (non-resonant case). Further for field free case i.e., B0=0, the growth rates for Weibel instability in a semi-relativistic bi-Maxwellian plasma are presented for both the limiting cases.

R.J.F. Sgalla, A.I. Smolyakov, A.G. Elfimov, M.F. Bashir, Jan 2013

We present a fluid model for geodesic acoustic modes including diamagnetic effects due to inhomog... more We present a fluid model for geodesic acoustic modes including diamagnetic effects due to inhomogeneous plasma density and temperature. Effects of ion parallel viscosity (pressure anisotropy), which allows to recover exactly the adiabatic index obtained in kinetic theory are considered. We show that diamagnetic effects lead to the positive up-shift of the GAM frequency and appearance of the second (lower frequency) branch related to the drift frequency. The latter is a result of modification of the degenerate (zero frequency) zonal flow branch which acquires a finite frequency or becomes unstable in regions of high temperature gradients.

Abstract Using kinetic theory for homogeneous collisionless magnetized plasmas, we present an ext... more Abstract Using kinetic theory for homogeneous collisionless magnetized plasmas, we present an extended review of the plasma waves and instabilities and discuss the anisotropic response of generalized relativistic dielectric tensor and Onsager symmetry properties for arbitrary distribution functions. In general, we observe that for such plasmas only those modes whose magnetic-field perturbations are perpendicular to the ambient magnetic field, ie, B 1 B 0, are effected by the anisotropy.

Using the Vlasov-Maxwell system of equations, the dispersion relations for the perpendicular prop... more Using the Vlasov-Maxwell system of equations, the dispersion relations for the perpendicular propagating modes (ie, X-mode, O-mode, and upper hybrid mode) are derived for a weakly magnetized relativistic degenerate electron plasma. By using the density (n0= pF3/3π2ℏ3) and the magnetic field values for different relativistic degenerate environments, the propagation characteristics (ie, cutoff points, resonances, dispersions, and band widths in k-space) of these modes are examined.

Physics of Plasmas, 2010

Employing linearized Vlasov–Maxwell system, we derive a generalized dielectric tensor for a magne... more Employing linearized Vlasov–Maxwell system, we derive a generalized dielectric tensor for a magnetized nonrelativistic bi-Maxwellian electron-ion plasma. Assuming low frequency waves in a low plasma, a new dispersion relation describing oblique propagation of the Alfvenic modes is determined, incorporating the temperature anisotropies of both the electrons and ions and their finite Larmor radii effects. From the resulting dispersion relation for kinetic Alfven waves, analytical expressions are determined for both the kinetic (and) ...