M Salahuddin

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...

Planar and cylindrical magnetosonic solitary and shock waves in dissipative, hot electron-positron-ion plasma

Planar and cylindrical magnetosonic solitary and shock structures are studied in a hot and dissipative plasma consisting of electrons, positrons, and ions. By employing the reductive perturbative method, a modified Korteweg-de Vries Burgers (mKdVB) equation is derived in the limit of low frequency and long wavelength by taking into account viscous dissipation of the three species. The effects of variation of various plasma parameters on the profiles of planar and cylindrical solitary and shock structures are discussed. In the limit, when certain terms of the mKdVB equation are small enough to be treated as perturbation, analytical solutions are obtained and compared with the corresponding numerical ones.

Oblique modulation of ion-acoustic waves and envelope solitons in electron-positron-ion plasma

The effect of oblique modulation on the amplitude dynamics of ion-acoustic wave propagating in a collisionless electron-positron-ion plasma is investigated. Using Krylov–Bogoliubov–Mitropolsky (KBM) perturbation method, a nonlinear Schrodinger (NLS) equation is derived which governs the evolution of obliquely modulated ion-acoustic envelope excitations. It is found that the presence of positron component significantly modifies the stability domains for small angles of propagation with the direction of modulation. The stationary solutions of NLS equation, i.e., bright and dark envelope solitons, become narrower as the concentration of positron component increases.

Electrostatic solitary ion waves in dense electron-positron-ion magnetoplasma

The nonlinear coupled ion-acoustic and ion-cyclotron waves propagating obliquely to the external magnetic field in dense collisionless electron-positron-ion magnetoplasma are investigated using Sagdeev potential method. A semiclassical approach is used. Electrons and positrons are treated as degenerate Fermi gases described by Thomas–Fermi density distribution and ions behave as classical gas. It is found that the presence of degenerate positrons in a dense Thomas–Fermi plasma significantly modifies the structure of solitary waves by restricting the electrostatic potential to a certain maximum value which depends upon the concentration of positrons in the system. It is also noted that only subsonic humplike solitary waves can exist and for a given angle of propagation, the presence of degenerate positrons diminishes the amplitude as well as width of the solitary wave.

Perpendicular propagating electromagnetic envelope solitons in electron-positron-ion plasma

The nonlinear amplitude modulation of electromagnetic waves propagating perpendicular to the direction of ambient magnetic field in a uniform collisionless magnetized electron-positron-ion plasma is studied. The Krylov–Bogoliubov–Mitropolsky perturbation method is employed to derive nonlinear Schrodinger equation, which describes the amplitude dynamics of perturbed magnetic field. The modulation instability criterion reveals that the low frequency mode is always stable, whereas the high frequency mode becomes modulationally unstable for certain ranges of wave number and positron-to-electron density ratio. Furthermore, the positron-to-electron density ratio as well as the strength of ambient magnetic field is found to have significant effect on the solitary wave solutions of the nonlinear Schrodinger equation, namely, dark and bright envelope solitons.

Energy levels, transition rates, oscillator strengths and lifetimes in Ne-like, Ni-like, and Cu-like uranium ions

We present the fine-structure energy levels, wavelengths, oscillator strengths, transition energies, and transition rates of optically allowed inner-shell transitions of Ne-, Ni-, and Cu-like uranium ions by using the multiconfiguration Dirac–Fock method with the fully relativistic GRASP2 code (partly improved by us). In order to compare these results, we have performed other independent calculations with a fully relativistic Flexible Atomic Code (FAC). We have determined extensive configuration interaction wavefunctions to calculate the level energies of the inner-shell excited states of these three uranium ionic states. Overall, our calculated energy levels, wavelengths, transition rates, and oscillator strengths within the levels of selected configurations show better agreement with the available experimental and other theoretical results. Furthermore, we report radiative lifetimes of all the excited states of these three uranium ions. We also present many unpublished data about energy values, wavelengths, transitions rates, and oscillator strengths for inner-shell transitions. We believe that our calculated inner shell transition energies are of interest for the analysis of uranium x-ray spectra.

Implosion of two-gas gas-puff Z-θ pinch

An expression for two-gas gas-puff Z-θ pinch compression is derived and the dynamic behavior of the implosion is investigated. It is observed that the compression and the azimuthal magnetic field strengths are critically dependent on the target to driver mass density ratio and on the driver gas shell thickness.

MAGNETIC ELECTRON DRIFT VORTEX IN MAGNETIZED PLASMA

The Magnetic Electron Drift Vortex (MEDV) modes in a homogeneous magnetized plasma are investigated using the Braginskiis fluid model for electrons. It is found that the modes become unstable when the propagation is in both parallel and perpendicular directions with respect to density and temperature gradients. The instability characteristics of the mode are presented by analyzing it analytically as well as numerically. The relevance to wave phenomena in space and laboratory plasmas is pointed out.