NONLINEAR EVOLUTION OF NEOCLASSICAL DOUBLE TEARING MODE

A theory for the nonlinear neoclassical double tearing mode is present ed. The equations governing the nonlinear evolution of the mode are ob tained for both the locked islands and the islands with different rota tion frequencies. The coupling of the two islands plays a destabilizin g role in the island growth, especially when the phase between the two islands is locked. The perturbed bootstrap current has a strong stabi lizing effect on the inner island but a weak destabilizing effect on t he outer island. The inner island width is decreased when there is a r elative rotation between the two islands, while the outer island is le ss affected by plasma rotation. The outer island width is found be an important parameter in determining the inner island width and the stab ility of the nonmonotonic q-profile. (C) 1997 American Institute of Ph ysics.