Nonlinear growth of marginally unstable tearing modes

In this work, the nonlinear growth of the classical tearing mode is revisited, using reduced magnetohydrodynamic numerical simulations in cylindrical geometry, emphasizing the limiting scenario of a marginally unstable mode, i.e., 0 similar to Delta(')a < 4, where a is the minor radius and Delta(') is the stability parameter [H. Furth, J. Killeen, and M. N. Rosenbluth, Phys. Fluids 6, 459 (1963)]. Conventionally, the mode becomes unstable when Delta(')>0 and, eventually, a steady state island width (saturated island width) is achieved. It is found that, contrary to theoretical predictions, no steady state solution is obtained for typically low temperature plasmas with perpendicular viscosity and magnetic Reynolds number below a certain threshold. Plasma inertial forces are identified as the physical mechanism behind such nonlinear evolution. (C) 2007 American Institute of Physics.