IDEAL KINK INSTABILITIES IN LINE-TIED CORONAL LOOPS

We investigate the nonlinear development of ideal kink instabilities i n a line-tied coronal loop, using a three dimensional numerical code. In order to understand how the equilibrium loop properties affect nonl inear evolution, various different initial magnetic equilibria are con sidered. In most cases, a fine-scale magnetic field structure is shown to develop. However, the corresponding electric current structure dep ends sensitively on the initial equilibrium: the initial magnetic twis t profile, the loop length, and the nature of the outer potential regi on. If there are resonant regions at the loop apex where the radial co mponent of the linear perturbed magnetic field vanishes, a current con centration develops there in the subsequent non linear phase. Otherwis e current concentrations may develop as a consequence of the effect of line-tying. The ensuing resistive evolution of the system and the imp act on coronal activity are discussed.