3D reconnection due to oblique modes: a simulation of Harris current sheets

Simulations in three dimensions of a Harris current sheet with mass ratio, m(i)/m(e) = 180, and current sheet thickness, p(i)/L = 0.5, suggest the exi stence of a linearly unstable oblique mode, which is independent from eithe r the drift-kink or the tearing instability. The new oblique mode causes re connection independently from the tearing mode. During the initial linear s tage, the system is unstable to the tearing mode and the drift kink mode, w ith growth rates that are accurately described by existing linear theories. However, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibr ium and leads to a change in the growth rates of the tearing and oblique mo des. In the nonlinear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introd uce a helical structure into the magnetic field lines.