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Electron cyclotron resonance heating (ECRH) at the W7-AS stellarator is performed with two systems of comparable heating power at 70 GHz (0.8 MW, 3 s) and 140 GHz (0.9 MW, 0.4 s). Experiments with 140 GHz open a new parameter window with high density operation up to 1.1 x 1.0 E20/m3. H mode transitions were observed in high density discharges at 2.5 T and at lower density at 1.25 T. The operational window for the stellarator H mode with emphasis on the density and power threshold, and the influence of gas puffing on the H transitions are discussed. Perturbation experiments with modulated ECRH power were performed to determine the heat transport and the power deposition profile. Density control is achieved in combined heating with neutral beam injection (NBI) despite the beam particle fuelling, whereas with NBI alone a steady density rise is observed. The impact of combined heating on the impurity confinement was investigated. Electron cyclotron current drive (ECCD) was studied in different magnetic field configurations and the influence of trapped particles on the ECCD efficiency was examined experimentally and compared with theory.

Additional information

Authors: ERCKMANN V ET AL., Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);KASPAREK W ET AL., University of Stuttgart, Institut für Plasmaforschung (DE);BORSCHEGOVSKY A ET AL., Kurchatov Institute, Moscow (RU);KURBATOV V I, SALUT, Nizhny Novgorod (RU);MALYGIN S, SALUT, Nizhny Novgorod (RU);MALYGIN V I, IAP, Nizhny Novgorod (RU)
Bibliographic Reference: Article: Fusion Engineering and Design, Vol. 26 (1995) pp. 141-152
Record Number: 199510574 / Last updated on: 1995-04-21
Original language: en
Available languages: en