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(THP2/33) Instability Threshold of Neoclassical Tearing Mode, Double Tearing Mode and Off-Axis Sawteeth Crash in Tokamaks

D. Li

Dept. of Modern Physics, University of Science and Technology of China, Hefei 230027, Anhui, China

Abstract.  The neoclassical and double tearing modes have been analyzed with related new phenomena in the reversed magnetic shear tokamak plasmas. The instability threshold, and the linear and nonlinear evolution are derived for the neoclassical tearing modes. It is found that the perturbed bootstrap current in the resistive layer has a stabilizing effect while the equilibrium bootstrap current in the outer region can destabilize the modes. The dispersion relation is derived for the double tearing mode. It is found that the onset of ``annular crash'' is due to the fast reconnection of the hot and cold islands, triggered by the interaction of both branches. The onset of ``core crash'' is mainly due to the coalescence between the hot islands, triggered by the explosive growth of the inner branch.

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IAEA 2001