MHD stability studies for high-current scenarios in FAST

In this paper we study some high-current equilibria of the FAST tokamak, in order to analyse potentially dangerous ideal MHD instabilities of such low-q configurations, in view of their passive and active stabilization. Introduction The FAST device is presently under discussion as a possible DEMO and ITER satellite [1]. The main FAST goals are: exploring plasma wall interaction in reactor relevant conditions; testing tools and scenarios for safe and reliable tokamak operation up to the border of stability; studying fusion plasmas with a significant population of fast particles. One of the FAST peculiarities is the capability of addressing all of these items simultaneously in a single, fully integrated scenario with dimensionless physics parameters close to DEMO and ITER. The present paper aims at studying an evolution of the reference scenario, focusing on low-q operation, which allows exploring 10 MA plasmas. In particular, we refer to regions with 2<q95<2.7 that are interesting to push fusion performances, but could be too risky to be tested in ITER. Specifically, we investigate a new FAST scenario at Ip=10 MA, BT=8.5T, with a q95≈2.3 that would correspond to Ip ≈ 20 MA in ITER. The possibility to safely work at q95<3 (q95≈2.6) has been shown recently at JET [2], although with a slight degradation of the energy confinement (H98≈0.9). The key point is to demonstrate the possibility of using in FAST passive conducting structures and active coils to stabilize and control potentially dangerous ideal and resistive MHD modes. To this purpose, FAST will be equipped with a set of feedback controlled active coils located between the first wall and the vacuum vessel and accessible for maintenance with the remote handling system, carrying currents up to 20 kA with AC frequency up to few kHz. 39 EPS Conference & 16 Int. Congress on Plasma Physics P2.079