FAST RECONNECTION OF WEAK MAGNETIC-FIELDS

Fast magnetic reconnection refers to annihilation or topological rearr angement of magnetic fields on a timescale that is independent (or nea rly independent) of the plasma resistivity. The resistivity of astroph ysical plasmas is so low that reconnection is of little practical inte rest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some ext ent if the flow is three dimensional. On the other hand, it is shown t hat in the limited but important case of incompressible stagnation poi nt flows, every flow will amplify most magnetic fields. Although examp les of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent ar guments against the operation of turbulent resistivity in highly condu cting fluids. (C) 1998 American Institute of Physics.