Twisting together magnetic flux tubes under helical symmetry

This paper investigates nonlinear interaction ofmagnetic flux tubes, as a possible cause of current-sheet formation. We focus attention on Gold–Hoyle tubes because of their simple analytic form, using a frictional magnetic relaxation code to find eventual equilibria. We assume that all fields possess helical symmetry so the problem becomes essentially two-dimensional and high resolution can be more easily achieved. When the tubes are not twisted together current sheets form only if the plasma pressure is zero. Twisting the tubes when the plasma pressure is small but finite results in curved current sheets and line currents. Current singularities are identified by performing calculations at increasing grid resolutions, and observing a regular increase in the maximum current.