ECRH and ECCD at W7-AS, prospects for W7-X

Abstract

ECRH is the main heating method for both the W7-AS stellarator, which is operational, and W7-X, which is under construction. An overview on physics studies on Electron Cyclotron Resonance Heating (ECRH) and ECCurrent Drive (ECCD) in an extended parameter range at W7-AS is presented. Experiments were performed with an upgraded ECRH power of up to 1.3 MW at 140 GHz. Electron temperatures of up to 5.7 keV were measured, which can only be explained by the beneficial effect of positive radial electric fields (‘electron root’). ECCD experiments at high power density are discussed, where the assumptions of quasi-linear theory are violated. The results from W7-AS establish the experimental and technological basis for W7-X, which aimes at demonstrating the inherent steady state capabality of stellarators at reactor relevant plasma parameters. The status of the design and construction of the ECRH system for W7-X is presented.