Influence of Current Aligned Instabilities on Magnetic Reconnection in Neutral Sheet Geometry

The influence of current aligned instabilities on collisionless reconnection is studied within neutral sheet geometry using petascale 3D kinetic simulations, which permit ion to electron mass ratios in the range $m_i/m_e =200 - 400$. Open boundary conditions are employed to avoid artificial recirculation effects and better mimic large-scale systems in nature. During the onset and initial evolution, intense lower-hybrid drift activity is observed immediately upstream of the electron diffusion region and along the separatrices, with characteristic wavelength on the electron gyroscale $k_y \rho_e \sim 1$. These fluctuations do not penetrate into the central electron layer, and are gradually weakened as the upstream density gradients relax and a highly elongated electron-scale current layer is formed. At later times, an electromagnetic instability is observed within the elongated electron layer with wavelength $k_y (\rho_i \rho_e)^{1/2} \sim 1$ roughly consistent with previous predictions from Vlasov theory\footnote{Daughton, Phys. Plasmas, {\bf 10}, 3103, 2003}. This instability gives rise to a pronounced kinking or undulation of the electron layer in a manner qualitatively similar to large-scale electron-positron plasmas\footnote{Yin et al, PRL {\bf 101}, 125001, 2008}. The possible influence of these instabilities on the dissipation rate and energy partition is discussed.