Ideal kink instabilities in line-tied coronal loops

We investigate the nonlinear development of ideal kink instabilities in a line-tied coronal loop, using a three dimensional numerical code. In order to understand how the equilibrium loop properties affect nonlinear evolution, various different initial magnetic equilibria are considered. In most cases, a finescale magnetic field structure is shown to develop. However, the corresponding electric current structure depends sensitively on the initial equilibrium: the initial magnetic twist profile, the loop length, and the nature of the outer potential region. If there are resonant regions at the loop apex where the radial component of the linear perturbed magnetic field vanishes, a current concentration develops there in the subsequent non linear phase. Otherwise current concentrations may develop as a consequence of the effect of line-tying. The ensuing resistive evolution of the system and the impact on coronal activity are discussed.