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Magnetohydrodynamic (MHD) instabilities in the Wendelstein 7-AS stellarator (W7-AS) [G. Grieger et aL, Phys. Fluids B 4, 2081 (1992)] are characterized experimentally in various plasma parameter regimes and heating scenarios. The observations are compared with theoretical predictions for particular cases. In the high-â range ((â) ? 2%) no clear evidence of a stability â-limit could be found yet. In the lower â regime fast particle driven global Alfven modes are the most important instabilities during neutral beam injection (NBI). Besides of coherent modes with almost no effect on the plasma performance additional Alfven modes appear at higher frequencies up to 400 kHz, which show nonlinear phenomena-like bursting, frequency chirping, and MHD induced energy and fast particle losses. The activity of edge localized modes (ELMs) is investigated in NBI heated discharges. The issue of current driven instabilities and their potential stabilization by a stellarator field has been investigated with regard to the design of compact hybrid stellarator systems.

Additional information

Authors: SPONG D.A, Oak Ridge National Laboratory, Tennessee (US);SALLANDER E, Alfven Laboratory. Royal Institute of Technology, NFR-EURATOM Association, Stockholm (SE);WELLER ET AL, Max-Planck Institut fur Plasmaphysik, IPP-EURATOM Association, Garching (DE)
Bibliographic Reference: An article published in: Physics of Plasmas, vol. 8 no. 3 (2001) pp.931-956
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