Cusp and Y-type Magnetic Structures and Velocity Fields at the Endpoint of the Reconnection Layer
Authors: Dmitri A. Uzdensky and Russell M. Kulsrud
We study the two-dimensional global scale magnetic field structure for a system of two merging cylindrical plasmas in a steady state. In the limit of very large magnetic Reynolds numbers the reconnection process is slow, and the plasma almost everywhere finds itself in magnetostatic equilibrium. We show that under certain conditions the classical Syrovatskii-type Y-point configuration, with surface current concentrated only in the reconnection layer, is not possible. Instead, a cusp configuration is formed, with finite surface current in the separatrix. The equilibrium condition, together with constraints on the volume per flux, enables us to determine the shape of the separatrix and the magnetic field in the vicinity of the cusp point. Our solution is characterized by a singular power law dependence of current density on the flux coordinate (psi) near the separatrix: j(psi) ~ |psi|-1/2. This solution gives us the boundary conditions that are needed to find the flow in the reconnection and the separatrix regions.