Ion acceleration in antiparallel collisionless magnetic reconnection: Kinetic and fluid aspects

Using a two-dimensional hybrid simulation code, we study the ion acceleration in the vicinity of the ion decoupling region of collisionless magnetic reconnection. We investigate the fluid consequences of the observed kinetic phenomena and discuss to what extent it could be accounted for in fluid modeling. The initial setup is an antiparallel current sheet in a plasma with homogeneous density. We discuss the different forces acting on the ion bulk and show that the two dominant ones are the Hall electric force and the pressure force acting against each others. A dynamic equilibrium, which might also exist in fluid simulations, is here given by a kinetic effect. We therefore explain this pressure, by an analysis of the ion distribution function and show that these are the result of an electrostatic bounce motion of the particles between the separatrices. This bounce motion is a characteristic of the ion decoupling region and therefore the resulting pattern of the pressure tensor may be considered as an additional observable feature of antiparallel reconnection in satellite data. (c) 2010 Published by Elsevier Masson SAS on behalf of Academie des sciences.