H. Saleem

A criterion for pure pair-ion plasmas and the role of quasineutrality in nonlinear dynamics

A criterion is presented to decide whether a produced plasma can be called a pure pair-ion plasma or not. The theory is discussed in the light of recent experiments which claim that a pure pair-ion fullerene (C60±) plasma has been produced. It is also shown that the ion acoustic wave is replaced by the pair ion convective cell (PPCC) mode as the electron density becomes vanishingly small in a magnetized plasma comprised of positive and negative ions. The nonlinear dynamics of pure pair plasmas is described by two coupled equations which have no analog in electron-ion plasmas. In a stationary frame, it becomes similar to the Hasegawa-Mima equation but does not contain drift waves and ion acoustic waves.

Kinetic theory of acoustic wave in pair-ion plasmas

A theoretical analysis of the ion acoustic wave in pair-ion plasmas is presented using a kinetic model. It is shown that a small concentration of electrons in pair-ion plasmas can break down the quasineutrality in perturbed systems because the electron Debye length can become very large. In the limit 1⪡λDe2k2 (where λDe is the electron Debye length), the damping is reduced and hence the acoustic wave can be easily excited. The real frequency of acoustic wave can be larger than the ion plasma oscillation frequency in this case. But the decreasing number density of electrons can increase the Landau damping significantly in the limit λDe2k2⪡1. The results are discussed in comparison with the recent experimental and theoretical findings. It is pointed out that this investigation can be very useful for further research on pair-ion plasmas.

Modulation instability of low-frequency electrostatic ion waves in magnetized electron-positron-ion plasma

The nonlinear amplitude modulation of low-frequency electrostatic ion waves propagating in collisionless magnetized electron-positron-ion plasma are studied. The Krylov–Bogoliubov–Mitropolsky perturbation method is employed to derive the nonlinear Schrodinger equation. Modulation instability of both ion-acoustic and ion-cyclotronlike modes is examined. We found that the ion-acoustic mode, which propagates below the ion-cyclotron frequency, is stable if the strength of the external magnetic field is small. However, as the strength of the magnetic field increases, this mode becomes modulationally unstable for a range of wave numbers and angles of propagation. This range increases as the strength of the magnetic field and/or positron density increases. For the ion-cyclotronlike mode, which propagates above the ion-cyclotron frequency, a number of stability/instability regions appear in the (kc,θ) plane even for a very small value of the magnetic field. It is found that, for both modes, critical wave number k...

Electromagnetic vortices in electron-positron-ion plasmas with shear flow

Two coupled nonlinear equations for a perturbed electromagnetic field in an electron-positron-ion plasma with shear flow, embedded in a nonuniform magnetic field, are derived and solved analytically. The nonlinear solutions of these equations are found in the form of tripolar vortices. The linear instability condition is also discussed. It is found that the presence of ions can play a significant role in nonlinear dynamics, even if the density of ions is of the order of 10−3 as compared to the densities of the lighter species.

Linear and nonlinear drift waves in collisionless and collisional electron-positron-ion plasmas

The linear and nonlinear drift waves in collisional and collisionless electron-positron-ion plasmas are studied in the classical limit. The possibilities of formation of solitons and shocks under different conditions are discussed. To estimate the growth rate of the linear drift dissipative instability in this case is not straightforward. However, in a limiting case it can be calculated exactly. Comparison of the results with the usual electron-ion plasmas is presented and the behavior of linear and nonlinear dynamics is pointed out for applications to laboratory and astrophysical situations.

Unstable drift mode driven by shear plasma flow in solar spicules

Context. The lower solar atmosphere contains at any moment a large number of spicules comprising plasma that moves towards the upper layers with typical axial velocities of 20−30 km s −1 . It is expected that these flows as well as the plasma density are inhomogeneous in the perpendicular direction. The presence of such a density gradient implies the existence of drift waves, while the inhomogeneity of the flow velocity can cause the growth of such modes. Aims. The stability of the drift waves will be discussed within the two-fluid theory taking into account the ion temperature and the stress tensor effects. Methods. An analytical linear normal mode analysis is used within the local approximation. Results. A detailed derivation of the hot ion contribution is performed. A dispersion equation is derived and the stability/instability conditions are discussed in detail for the parameter range appropriate for solar spicules. The drift mode appears to be highly unstable for typical spicule characteristic lengths of the density and the shear flow gradients, i.e. in the range of a few hundred meters up to a few kilometers, yielding wave frequencies of the order of a few Hz. Conclusions. Hence, the waves and the instabilities develop at reasonable time scales regarding the life times of spicules that are measured in minutes.

Solar wind interaction with the stationary dust can produce drift waves to form nonlinear structures

Solar wind electrons and ions penetrating with shear flow into the stationary dust can introduce electrostatic drift wave in plasmas of cometary and planetary environments. The drift wave becomes linearly unstable in the presence of shear flow. The background current also produces shear in the static magnetic field which does not allow the Shukla-VarmaPhys. Fluids B [5, 236 (1993)] mode to exist in such a system. The vortex structures can be formed in nonlinear regime. The relevance of this investigation to space plasmas is pointed out.

Nonlinear dust drift Alfvén waves in rotating planetary magnetospheres

Linear and nonlinear electromagnetic waves are investigated in the dusty magnetospheres of rotating planets. In the presence of heavy dust, the plasma may support very low frequency waves that can be affected by the plasma rotation. It is also shown that Alfven waves can couple with the electrostatic dust drift waves induced by the planetary rotation. A comparison of the results with a previous work has also been made in the electrostatic limit. The electromagnetic vortex structures can be formed in rotating planetary dusty plasmas in the nonlinear regime. An application of this theory to dusty plasmas of the magnetospheres of Saturn and Jupiter is pointed out.

Effects of adiabatic hot dust on arbitrary amplitude electrostatic solitary structures in magnetoplasmas

The effects of dust temperature on arbitrary amplitude dust acoustic solitary waves in a homogeneous magnetized plasma are studied. It is found that the dust temperature is destructive for the formation of solitons in magnetized plasmas. This behavior is similar to the case of unmagnetized hot dusty plasmas. However, the soliton amplitude increases with the increase in the obliqueness of the wave propagation. The numerical results are also shown for illustrative purposes.

Theory of cosmological seed magnetic fields

A theory for the generation of seed magnetic field and plasma flow on cosmological scales driven by externally given baroclinic vectors is presented. The Beltrami-like plasma fields can grow from zero values at initial time t=0 from a nonequilibrium state. Exact analytical solutions of the set of two-fluid equations are obtained that are valid for large plasma β-values as well. Weaknesses of previous models for seed magnetic field generation are also pointed out. The analytical calculations predict the galactic seed magnetic field generated by this mechanism to be of the order of 10−14G, which may be amplified later by the αω dynamo (or by some other mechanism) to the present observed values of the order of ∼(2–10)μG. The theory has been applied to laser-induced plasmas as well and the estimate of the magnetic field’s magnitude is in agreement with the experimentally observed values.