Collisionless reconnection using Alfvén wave radiation resistance

Abstract

Patchy magnetic reconnection involves transient field-aligned current filaments. The spatial localization, transient time-dependence, and orientation of these current filaments means they must radiate torsional Alfvén waves. Radiation of wave energy does not come for free—it must load the current which acts as the radiative source. This loading (radiation resistance) is proposed as the energy sink required for collisionless magnetic reconnection to proceed. Radiation resistance for both inertial and kinetic Alfvén waves is calculated and, for highly collisionless plasmas, is shown to exceed by a substantial factor both Spitzer resistivity and the effective resistance due to the direct acceleration of electrons (inertial loading). The radiation resistivity is shown to provide the magnetic field diffusivity required for magnetic fields to diffuse across the assumed width of the current filament on the time scale of the reconnection. It is also shown that Landau damping of the radiated waves results in the generation of energetic, field-aligned particles: in the β≪me/mi regime the energetic particles are electrons while in the me/mi≪β≪1 regime, the energetic particles are ions.