Nonlinear driven reconnection

Characteristics of driven reconnection are explained with emphasis on the distinction from spontaneous reconnection. Numerical simulations indicate that driven reconnection is almost independent of resistivity but is largely controlled by driving plasma flow, this making a clear contrast with spontaneous reconnection. Four different examples of driven reconnection are studied by 3D MHD simulations. The first one is the case where two identical plasmas with anti-parallel fields are driven to collide in an open system. A typical example is the stretched magnetotail neutral sheet. Simulations indicate that slow mode shocks are formed whereby plasma is explosively accelerated. The second example is the case where a high-beta plasma collides against a low-beta plasma with an arbitrary field angle. The solar wind-magnetosphere interaction is a typical example - Results indicate that no prominent plasma acceleration is observed in this case but the high-beta plasma continuously erodes the low-beta plasma. The fine structure in the vicinity of the reconnection line is disclosed. The third example is the merging process of two spheromaks. It is shown that merging is an energy relaxation process. The final example is the self-reversal process in the reversed field pinch. It is shown that the self reversal is a relaxation process caused by nonlinear driven reconnection