Securing High-beta_N JT-60SA Operational Space by MHD Stability and Active Control Modelling

MHD stability and its active control of reference JT-60SA scenarios is numerically studied with particular attention to high bN plasmas. The qualification of high performance tokamak scenarios is one of the main missions of the JT-60SA device, both in support to ITER and in view of the definition of an optimized DEMO design. Neoclassical Tearing Modes and Resistive Wall Modes will be probably among the most challenging MHD instabilities to be overcome in order to reach this final goal. In the framework of the European-Japanese collaboration on JT-60SA preparation, the main effort presented in this paper is the development and application of some of the main European MHD codes to JT-60SA specific issues. The implementation of these numerical tools is described, taking into account a careful description of the main sources of instability and including the possibility of their active control. Two plasmas, representative in one case of the full current, single null, inductive reference scenario (Scenario2, according to the JT-60SA Research Plan definition) and in the second case of the high bN, fully non inductive reference scenario (Scenario 5), are taken as inputs. For the Scenario 2-like plasma, Neoclassical Tearing Modes are studied as most relevant MHD instabilities and the active stabilization of (m,n)=(2,1) mode provided by electron cyclotron waves is numerically investigated. Resistive Wall Modes are instead considered as the most challenging limiting MHD instability in the Scenario 5-like case and the development of a fully 3D model including closed loop active control by a set of active coils is presented.