Structure of Alfvén waves at the skin-depth scale

Abstract

This analytical study demonstrates that shear Alfvén waves having transverse scale on the order of the electron skin depth exhibit a collisionless divergence determined by propagation cones that emanate from the edges of the exciting structures. Axial current channels are found to spread radially due to the skin effect up to the cone trajectories and at distances of a few wavelengths from the exciter develop radial diffraction patterns. For values of the collision frequency slightly larger than the wave frequency resistive diffusion allows the axial currents to expand beyond the cone trajectories.

Shear Alfvén waves in a magnetic beach and the roles of electron and ion damping

“…In a pair of theoretical papers beginning in 1994, Morales et al 13,14 studied the radiated azimuthal shear Alfvén wave magnetic field from small perpendicular scale sources in two parameter regimes: v A ӷv e and v A Ӷv e . Here, v A is the Alfvén speed (v A ϭB/ͱ4n i m i , B is the background field strength, n i and m i are the ion density and mass, respectively͒ and v e ϵͱ2T e /m e is the average electron thermal speed, with T e the electron temperature and m e the electron mass.…”

Shear Alfvén Wave Perpendicular Propagation from the Kinetic to the Inertial Regime

“…2 2 Z 0 , where is the ratio of the parallel wave phase speed to the electron thermal speed ( !=k k v e ) and Z 0 is the derivative of the plasma dispersion function [21] with respect to its argument. With these assumptions, k [18,19] for the above assumptions.…”

“…The highly reproducible discharge is repeated once per second which allows for the collection of ensemble data sets. The wave launching antenna is the same design used in other experiments [9,12,17], and the radiation has been modeled theoretically in both the inertial [18] and kinetic [19] regimes. The antenna is simply a 1 cm diameter, circular copper mesh of 50% optical transparency.…”

Real-time physics data-visualization system using Performer

“…Since the waves were excited using structures that had dimension, the collisionless skin depth across the magnetic field, the waves propagated as shear-Alfven-wave cones. 16 Wave vector-magnetic-field data were acquired on 10 planes orthogonal to the background magnetic field, at 400 spatial positions on each plane, and during 2048 time steps at each location. Of interest is the current carried by the wave and its closure in three dimensions.…”