CURRENT SHEET FORMATION IN UNIFORMLY TWISTED MAGNETIC-FLUX TUBES

This paper considers force-free equilibria in twisted magnetic Bur tub es with helical symmetry. Such symmetry simplifies the force-free fiel d condition to a pair of equations which are generalisations of the Gr ad-Shafranov equations. A simple linear solution is given analytically in terms of a Heun function, which exhibits several important aspects of twisted flux tubes. The equilibrium equations impose a functional relation between the axial field component and the flux function for t he other two components, which can be used to establish current-sheer formation when certain classes of flux tubes are twisted together. Imp lications for magnetic energy release in the solar corona are discusse d.