Driven Magnetic Reconnection in Semi-Collisional Parameter Regimes

Recent kinetic simulations of driven magnetic reconnection with boundary conditions relevant to the Magnetic Reconnection eXperiment (MRX) have demonstrated that the electron diffusion layer is significantly thicker in the experiment\footnote{Ji et al., to appear in {\em GRL}, 2008} than in the 2D collisionless simulations.\footnote{Dorfman {\em et al.}, submitted to {\em Physics of Plasmas}, 2008} The two leading possibilities to explain this discrepancy are 3D effects such as current aligned instabilities and Coulomb collisions. In order to address both of these possibilities, we have implemented the new MRX relevant boundary conditions$^2$ within the 3D kinetic simulation code VPIC.\footnote{K. J. Bowers {\em et al.} Phys. Plasmas, v. {\bf 15}, p.~055703, 2008.} Coulomb collisions are treated using a well-known Monte-Carlo technique\footnote{T. Takizuka and H. Abe, J. Comput. Phys., v. {\bf 25}, p. 205, 1977} that models a full collision operator. This approach will allow us to systematically examine the influence of Coulomb collisions and plasma instabilities on the dynamical evolution of the reconnection layer using boundary conditions relevant to the actual experiment. Initial results illustrating the transition between collisionless and semi-collisional regimes are presented.