THE COALESCENCE INSTABILITY AND THE DEVELOPMENT OF CURRENT SHEETS IN 2-DIMENSIONAL MAGNETOHYDRODYNAMICS

A class of two-dimensional force-free equilibria are shown to be subje ct to an ideal linear instability. This instability is similar to the coalescence instability for chains of magnetic islands. Semianalytic m ethods are used to find second magnetic equilibrium which is accessibl e from the first and has lower magnetic energy. This equilibrium has a discontinuous magnetic field and current sheets at these discontinuit ies. Numerical simulations indicate that the nonlinear evolution of th e instability allows the plasma to relax to this discontinuous equilib rium.