Nonlinear dynamics of the tearing mode with two-fluid and curvature effects in tokamaks

Curvature and diamagnetic effects are both known to have an influence on tearing mode dynamics. In this paper, we investigate the impact of these effects on the nonlinear stability and saturation of a (2, 1) island using non-linear two-fluid MHD simulations and we apply our results to Tore Supra experiments, where its behavior is not well understood from the single fluid MHD model. Simulations show that a metastable state induced by diamagnetic effect exists for this mode and that it also produces a reduction of the saturated island size, in presence of toroidal curvature. The mode is found to be nonlinearly destabilized by a seed island and it saturates at a macroscopic level causing a significant confinement degradation. The interpretation of dual states, with either no island on q = 2 or a large one, observed on discharges with high non inductive current source on Tore Supra, is revisited.