This analytic study investigates the interaction between a large-scale shear Alfvén wave propagating through a low-β plasma and a pre-existing density perturbation of small transverse scale. The interaction forms an in situ antenna that self-consistently generates two field-aligned current channels of opposite polarity. The expansion of the current channels across the confining field is bounded by the cone trajectories of small-scale inertial Alfvén waves. The spatial patterns of the radiated 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 process.

This analytic study investigates the nonlinear plasma response when a shear Alfvén wave of large transverse scale interacts with a field-aligned density perturbation whose transverse scale is comparable to the electron skin depth. The interaction between the large-scale wave and the density perturbation produces a small-scale shear mode [T. Drozdenko and G. J. Morales, Phys. Plasmas 7, 823 (2000)], which facilitates the transfer of energy to the plasma particles. The beat of the large-scale wave with the small-scale wave can lead to ponderomotive forces and flows in the plasma, or, if the field amplitudes of the small-scale wave are large enough to produce oscillatory velocities comparable to the electron thermal velocity, a streaming instability may develop. In this study, it is demonstrated that nonlinear effects arise in regions remote from the seed perturbation, and estimates of the amplitude of the large-scale wave necessary to produce significant ponderomotive density changes or trigger significant streaming instabilities are presented.

This analytic study examines the effect of cross-field flow on a microscopic current channel. To illustrate the subtle interplay between finite electron inertia and flows, a simple model of excitation of a microscopic current channel is considered. The model consists of a slab antenna exciter with a transverse width on the order of the electron skin-depth driven at a single frequency. The antenna is fixed in the laboratory frame and embedded within a plasma that has a uniform drift across the confining magnetic field. The combined effects of the plasma flow and the intrinsic, collisionless, cross-field expansion of the current channel lead to standing wave structures across the confining magnetic field. The resulting parallel electric fields generate an array of current filaments of alternating polarity which individually have transverse width smaller than the original channel. These results may help interpret laboratory and spacecraft measurements of Alfvénic turbulence and could lead to the development of a diagnostic tool to map plasma flows.