Electron cyclotron resonance heating and EC-current drive experiments at W7-AS, status at W7-X

Electron Cyclotron Resonance Heating (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 ECRH and EC-current drive ( ECCD) in an extended parameter range at W7-AS is presented. Current drive w as investigated with an ECRH power of up to 1.3 MW at 140 GHz in a wide ran ge of plasma density and launch angle. The experimental results are compare d to predictions from quasilinear theory. Electron temperatures of up to 5. 7 keV were measured at low to intermediate densities, which can only be exp lained by the beneficial effect of positive radial electric fields ('electr on root feature'). The results from W7-AS establish the experimental and te chnological basis for W7-X, which aims at demonstrating the inherent steady state capabality of stellarators at reactor relevant plasma parameters. Th e status of the design and construction of the ECRH system for W7-X is pres ented. (C) 2001 Elsevier Science B.V. All rights reserved.