Author/Authors :
Erckmann، V. نويسنده , , V. and Gasparino، نويسنده , , U. and Hartfu?، نويسنده , , H. and Kasparek، نويسنده , , W. and Müller، نويسنده , , G.A. and Schüller، نويسنده , , P.G. and Borschegovsky، نويسنده , , A. and Ilʹin، نويسنده , , V.I. and Kurbatov، نويسنده , , V.I. and Malygin، نويسنده , , S. and Malygin، نويسنده , , V.I.، نويسنده ,
Abstract :
Electron cyclotron resonance heating (ECRH) at the W7-AS stellarator is performed 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 × 1020 m−3. 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.
