Analysis of vertical displacement events in tokamaks removing the evolutionary equilibrium assumption

Abstract

AbstractA key parameter for the vertical stabilisation system of future fusion devices like ITER is themaximum allowable vertical displacementwhich can be recovered by the magnetic control system (Gribov 2015Nucl. Fusion55073021). The computation of this figure of merit is based on MHD evolutionary equilibrium models: the perturbation of the vertical position implicitly considers a perturbation of the external passive currents which guarantees MHD equilibrium. In this paper, we quantify the consequences of considering non-equilibrium perturbations of the vertical position. In this case, one has to specify separately the initial perturbation of the vertical position and of the external currents. We show in particular under which circumstances the evolution of the vertical position, as predicted by the evolutionary equilibrium models, coincides with that obtained considering also plasma inertia.