Double Layers, Electron Scattering and Anomalous Resistivity in 3-D Magnetic Reconnection

In the case of a simple reversed magnetic field, simulations in three dimensions have revealed that collisionless magnetic reconnection remains nearly two-dimensional. The strong current layers which form near the x-line in 2-D simulations remain completely stable in 3-D while the slow shocks which bound the outflow region downstream of the x-line exhibit weak lower-hybrid-drift turbulence which does not significantly impact the rates of reconnection. Reconnection in the presence of a guide field is much more dynamic. The guide field slows the convection of electrons away from the x-line, which enables the reconnection electric field to accelerate electrons in this region to very high velocity. The resulting magnetic-field-aligned electron beams are two-stream unstable. The instability nonlinearly develops into distinct double layers, in which regions of locally intense electric fields form on spatical scales of 10's of Debye lengths. These intense electric fields scatter the electron beams, causing strong electron heating and a large effective resistivity. The nonlinear development of the system is being explored with full particle simulations using up to one billion particles to understand the conditions under which these structures develop and their impact on electron energization and the rates of reconnection in magnetospheric and astrophysical systems.