Propagation of shear Alfven waves in perturbed plasmas

This dissertation investigates shear Alfvén wave propagation in perturbed plasmas and has applications to the auroral ionosphere, magnetic confinement studies and solar and astrophysical plasmas. The linear and nonlinear plasma response to the interaction between a shear Alfvén wave with large spatial scale transverse to the confining magnetic field and a field-aligned density perturbation with transverse scale on the order of the electron skin-depth is examined. In addition, the effects of large-scale perpendicular drifts on the structure of small-scale Alfvén waves are explored.; The linear plasma response to the interaction between a large-scale shear wave and a small-scale density perturbation is the generation of a small-scale shear mode. The spatial patterns of the small-scale fields are obtained, and the magnitude of the parallel electric field and its effective phase velocity are assessed. An effective cross section that varies with the parallel and transverse scale lengths of the density perturbation summarizes the efficiency of the direct conversion between large and small-scale waves. The nonlinear effects of the interaction are also explored. When the field amplitudes of the small-scale wave are large enough to produce parallel electron velocities on the order of the electron thermal velocity, a streaming instability may develop. However, if the field amplitudes of the small-scale wave are not large enough to trigger the streaming instability, ponderomotive effects become important. In both cases, the largest effects are seen in regions remote from the seed density perturbation leading to the possibility of global density rearrangement and a turbulent medium of embedded density filaments. Estimates of the field amplitude of the large-scale wave necessary to produce small-scale waves that either generate significant ponderomotive effects or that trigger the streaming instability are presented.; The effect of a uniform perpendicular drift on the field patterns of a small-scale shear Alfvén wave and associated parallel currents is investigated. The interplay between the forcing effect of the drifting plasma and the effect of finite electron inertia results in standing wave patterns across the confining magnetic field and further filmentation of the parallel current. The drift-modified fields generate an array of current filaments of alternating polarity which individually have transverse width smaller than the original current channel but which have a collective width that far exceeds the initial width of the channel.