Numerical studies of sawtooth crashes with non-monotonic safety factor profiles

Abstract

The sawtooth crashes with non-monotonic q profiles are numerically investigated by the three-dimensional, toroidal-geometry MHD code (CLT). We find that, when the initial q profiles are non-monotonic, the precursors of the sawtooth crashes are with high n rather than the m/n=1/1 kink mode (where m and n are the poloidal and toroidal mode numbers); and multiple flux tubes form just before sawtooth crashes. The dominant mode transits from higher n to n=1 through mode-mode coupling at the nonlinear stage, and the final pressure crash is still dominated by the 1/1 mode.