Non-linear quenching of diamagnetic and gyroviscous effects in tearing modes

The non-linear behaviour of the drift-tearing instability is investigated within the two-fluid theory. It is shown analytically and verified in numerial computations that diamagnetic effects and ion gyroviscosity, which determine the frequency of the linear mode, are quenched at a magnetic-island size of the order of the resistive-layer width. For finite island width, growth and saturation of the mode depend only on resistivity and current profile, while its frequency is determined by the rotation of the plasma.