Resistive wall mode induced disruptions in an advanced tokamak

Abstract

Resistive wall mode is one of the leading causes for tokamak disruptions above the no-wall $β_N$ limit. This paper presents nonlinear three-dimensional resistive MHD simulations of an RWM-induced disruption in a CFETR baseline steady-state equilibrium using the NIMROD code. Linear calculations confirm the dominant presence of the $n=1$ RWM instability, whose growth rate is strongly sensitive to the wall response and becomes weakly dependent on plasma resistivity in the high-$S$ limit, along with a global external-kink-like structure. In the nonlinear phase, the RWM drives rapid flux surface stochastization and a thermal quench, followed by a current quench that is intensified by the post quench increase of Spitzer resistivity. The transient current spike before the current quench is shown to be the outcome of the conservation of poloidal flux and a rapid reduction of internal inductance. During the late current quench stage, closed flux surfaces partially reform from the core region to the edge, relaxing toward the force-free state. Toroidal mode coupling, parallel heat transport, plasma resistivity, and wall conductivity strongly modulate the disruption onset and the quench dynamics. Within the MHD model, these results provide a complete view on the RWM-driven disruption process in advanced tokamak configurations.