Three types of pressure crash in the low magnetic shear tokamaks

Abstract

Numerical investigations on the pressure crash with a low magnetic shear profile in Tokamaks are carried out through the three-dimensional, toroidal, and nonlinear MHD code CLT. We find that there exist at least three different kinds of pressure crashes. The first type is that one cold bubble forms and merges into the hot core, which is the standard case for the nonlinear evolution of the quasi-interchange mode. The second type is two cold bubbles forming and squeezing the hot core, leading to fast pressure crashes. The third one is similar to that caused by the resistive-kink mode, i.e., an m/n =  1/1 magnetic island grows up and fills up the whole central region. The thresholds for these kinds of pressure crashes are systematically discussed.