Simulation of magnetic control of the plasma shape on the DEMO tokamak

Abstract

About 85% of the primary energy is currently obtained from fossil sources. In the next future, nuclear fusion can significantly contribute to energy production: the fuel is in principle unlimited and radioactive waste are short lived. Next steps in fusion research are represented by the two tokamaks ITER, which is under construction, and DEMO, which is in its conceptual design phase. In this paper we focus on a specific aspect of DEMO design, that is indeed crucial for tokamak safe operation: plasma vertical and shape control. It is well known that a plasma with elongated cross-section exhibits a vertical instability that needs to be feedback controlled. Typically on operating tokamaks, and in ITER, this task is accomplished using in-vessel actuator coils. Since in the present DEMO design these coils are not foreseen, hereafter we assumed that all the actuator coils, located outside the vessel, are used at the same time to guarantee both vertical stabilization and shape control, resorting to a suitable geometric decoupling. The performance of the controller is shown in simulation using a nonlinear evolution code during a plasma H-L back-transition.