SELF-GENERATED TURBULENCE IN MAGNETIC RECONNECTION

Classical Sweet-Parker models of reconnection predict that reconnection rates depend inversely on the resistivity, usually parameterized using the dimensionless Lundquist number (S). We describe magnetohydrodynamic (MHD) simulations using a static, nested grid that show the development of a three-dimensional (3D) instability in the plane of a current sheet between reversing field lines without a guide field. The instability leads to rapid reconnection of magnetic field lines at a rate independent of S over at least the range 3.2 x 10(3) less than or similar to S less than or similar to 3.2 x 10(5) resolved by the simulations. We find that this instability occurs even for cases with S less than or similar to 10(4) that in our models appear stable to the recently described, two-dimensional, plasmoid instability. Our results suggest that 3D, MHD processes alone produce fast (resistivity independent) reconnection without recourse to kinetic effects or external turbulence. The unstable reconnection layers provide a self-consistent environment in which the extensively studied turbulent reconnection process can occur.