Resistively untangling plasma knots

When a plasma containing highly tangled magnetic field lines is allowed to relax in a high-beta plasma environment, the helicity in the initial configuration gives rise to an ordered self-organizing magnetic configuration. This situation is reminiscent of what happens when the twisted field of a coronal loop is ejected into the high-beta plasma of the solar wind forming a magnetic cloud. We study the resistive evolution of these structures in as simple a geometry as possible; 3D MHD simulations on a fixed Eulerian grid. We briefly describe the equilibrium of the self-organized equilibrium attained: nested toroidal magnetic surfaces, with a minimum of pressure on the magnetic axis. The resistive evolution follows a universal pattern when scaled to resistive time; a Pfirsch-Schlüter like slip allows plasma to flow onto the axis, and the structure slowly expands. The rotational transform becomes nearly constant, and decays according to a power law. The magnetic energy decays faster than resistive time due to expansion perpendicular to the field direction.