Threshold condition for non-linear tearing modes in tokamaks

Abstract

The non-linear evolution of low mode number tearing modes is analysed, emphasizing the need for a threshold condition, to account for observations in tokamaks. The discussion is illustrated by two models recently introduced in the literature. The models can be compared with the available data and/or serve as a basis for planning experiments in order either to test theory (by means of beta -limit scaling laws, as proposed in this paper) or to attempt to control undesirable tearing modes. Introducing a threshold condition in the tearing mode stability analysis is found to reveal some bifurcation points and thus domains of intrinsic stability in the island dynamics operational space