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V. Erckmann, U. Gasparino, H. P. Laqua,
H. Maassberg, W7-AS Team
Max-Planck-Institut für Plasmaphysik, EURATOM Association, 85748
Garching, Germany
ECRH Group
Institut für Plasmaforschung, Universität Stuttgart, Germany
K. S. Kasilov, N. Marushchenko
Institute of Plasma Physics, NSC-KhPTI, 310108 Kharkov, Ukraine
V. Irkhin, S. Malygin
GYCOM, Nizhny Novgorod, Russia
Abstract. 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'). The experiments confirm, that the electric
field is generated by ECRH driven particle losses in the specific stellarator
magnetic field. ECCD experiments were performed at high input power (1.3 MW)
resulting in EC-driven currents of up to 20 kA. The direction of the EC-driven
current was varied in co- and counter-direction with respect to the
bootstrap current in discharges with zero net-current. Three current
contributions,
i.e. the EC-driven current, the bootstrap current and the inductively driven
current are calculated independently and modify the internal profile of the
rotational transform significantly. A comparison with quasi-linear theory
shows significant deviation in the co-current drive case, which may be
attributed to strong MHD activity and/or violation of the quasilinear
assumptions due to the high power density.
IAEA 2001
