Spontaneous fast reconnection model in three dimensions

Abstract

The spontaneous fast reconnection model is studied in a three-dimensional (3D) situation for different plasma parameter values. In any case, once a current-driven anomalous resistivity is ignited, magnetic reconnection explosively evolves as a nonlinear instability, and the 3D fast reconnection mechanism involving large-scale standing slow shocks is realized as an eventual solution on the nonlinear saturation phase. For the smaller plasma β, the reconnection evolution is more drastic, and the resulting fast reconnection mechanism becomes more powerful. In the fast reconnection configuration, the central 3D diffusion region becomes unstable against resistive tearing and is bifurcated into a pair of diffusion regions, which move away from each other. In the moving diffusion region, the locally enhanced anomalous resistivity is self-consistently sustained by the reconnection flow, and the slow shock stands between the 3D diffusion region and a large-scale 3D plasmoid. Since the plasmoid moves much more rapidly than the diffusion region, the 3D slow shock rapidly extends in the x direction in a finite extent in the z direction to occupy the overall system. In the wide range of plasma β, the reconnection outflow jet ux attains the Alfvén velocity, measured in the ambient magnetic field region. Hence, the 3D fast reconnection mechanism established in the center of the system, which is consistent with the well-known 2D one, is sustained steadily and extends outwards to drastically collapse the field system at large.