Asymmetry and thermal effects due to parallel motion of electrons in collisionless magnetic reconnection

Fast collisionless reconnection of magnetic flux loops by the macro-particle simulation code shows significant asymmetry of the plasma flow under an ambient toroidal magnetic field. The parallel motion of electrons induced by the reconnection electric field is found to produce large density and toroidal magnetic field inhomogeneities of a quadrupole shape, δn/n0∼0.3, unlike the m=1 mode. The divergence of the plasma flow is locally not identical to zero with each species, ∇⋅V(s)≠0 (s=e,i), due to the electron spatial movement along the magnetic field. This internal structure results in a thick current layer and enhances the reconnection process. A plasmoid that impedes magnetic reconnection is created when the parallel mass diffusivity of electrons arising from their thermal motion is suppressed (the fluid limit). The reconnection rate becomes a smoothly increasing function of the ion mass and an inverse of the toroidal magnetic field, the latter of which being due to the compressional effect. The rate is drastically reduced when the ion Larmor radius far exceeds the ion skin depth.