Structure and dynamics of the fast reconnection mechanism in an initially force-free current sheet

The present paper studies the three-dimensional structure and dynamics of the fast reconnection mechanism in an initially force-free current sheet. A large-scale plasmoid (current sheet bulge) is formed ahead of the Alfvenic fast reconnection jet (ux∼VA) generated in a narrow wedgelike region between a pair of slow shocks. The plasmoid structure is divided into the plasmoid reconnection region P and the plasmoid core region C. In the region P, the strongly sheared reconnected field lines are accumulated and the initial (low-beta) plasma pressure is remarkably enhanced to become comparable to the ambient magnetic pressure since the sheared field lines initially embedded in the current sheet are completely swept away by the reconnection jet. On the other hand, in the region C, the magnetized (low-beta) plasma with the sheared (Bz) field lines, initially embedded in the current sheet, is accumulated without reconnection, and the magnitude of the accumulated sheared field becomes much larger than the ambient magnetic field strength. It is demonstrated that the fast reconnection mechanism in an initially force-free current sheet is so powerful to overcome the magnetic tension forces, which result from the large x-directional bent of the sheared field lines, and vitally proceed by effectively extending the fast reconnection jet region in the sheared field (z) direction.