Experiments close to the beta-limit in W7-AS

Weller, A.; Geiger, J.; Werner, A.; Zarnstorff, M. C.; Nührenberg, C.; Sallander, E.; Baldzuhn, J.; Brakel, R.; Burhenn, R.; Dinklage, A.; Fredrickson, E.; Gadelmeier, F.; Giannone, L.; Grigull, P.; Hartmann, D.; Jaenicke, R.; Klose, S.; Knauer, J. P.; Könies, A.; Kolesnichenko, Ya. I.; Laqua, H. P.; Lutsenko, V. V.; McCormick, K.; Monticello, D.; Osakabe, M.; Pasch, E.; Reiman, A.; Rust, N.; Spong, D. A.; Wagner, F.; Yakovenko, Yu. V.; W7-AS Team; NBI-Group

doi:10.1088/0741-3335/45/12A/019

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Experiments close to the beta-limit in W7-AS

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Weller, A.
Stellarator Scenario Development (E5), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109156

Geiger, J.
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons110781

Werner, A.
W7-X: Physics (PH), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons110071

Nührenberg, C.
Stellarator Theory (ST), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons110310

Sallander, E.
Stellarator Scenario Development (E5), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons108767

Brakel, R.
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons108825

Burhenn, R.
VINETA, Max Planck Institute for Plasma Physics, Max Planck Society;
W7-AS, Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons108944

Dinklage, A.
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109170

Giannone, L.
Experimental Plasma Physics 1 (E1), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109226

Grigull, P.
W7-X: Physics (PH), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109312

Hartmann, D.
Technology (TE), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109491

Jaenicke, R.
W7-AS, Max Planck Institute for Plasma Physics, Max Planck Society;
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109629

Klose, S.
Plasma Diagnostics Group (HUB), Max Planck Institute for Plasma Physics, Max Planck Society;
Experimental Plasma Physics 2 (E2), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109652

Könies, A.
Stellarator Theory (ST), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons109914

McCormick, K.
Stellarator Scenario Development (E5), Max Planck Institute for Plasma Physics, Max Planck Society;
W7-AS, Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons110111

Pasch, E.
Stellarator Optimisation (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons110298

Rust, N.
W7-X: Heating (HT), Max Planck Institute for Plasma Physics, Max Planck Society;

/persons/resource/persons110725

Wagner, F.
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

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Citation

Weller, A., Geiger, J., Werner, A., Zarnstorff, M. C., Nührenberg, C., Sallander, E., et al. (2003). Experiments close to the beta-limit in W7-AS. Invited papers from the 30th European Physical Society Conference on Controlled Fusion and Plasma Physics, A285-A308. doi:10.1088/0741-3335/45/12A/019.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0027-3DED-6

Abstract

A major objective of the experimental program in the last phase of the W7-AS stellarator was to explore and demonstrate the high-β performance of advanced stellarators. MHD-quiescent discharges at low impurity radiation levels with volume averaged β-values of up to ‹β›= 3.4% have been achieved. A very important prerequisite was the attainment of the high density H-Mode (HDH) regime. This was made possible by the installation of extensive graphite plasma facing components designed for island divertor operation. The co-directed neutral beam injection provided increased absorbed heating power of up to 3.2 MW in high-β plasmas with B ≤ 1.25 T. The anticipated improved features concerning equilibrium and stability at high plasma β could be verified experimentally by the comparison of x-ray data with free boundary equilibrium calculations. The maximum β found in configurations with a rotational transform around ι= 0.5 is determined by the available heating power. No evidence of a stability limit has been found in the accessible configuration space, and the discharges are remarkably quiescent at maximum β, most likely due the increase of the magnetic well depth. An increase in low m/n MHD activity is typically observed during the transition towards high β. The beneficial stability properties of net-current-free configurations could be demonstrated by comparison with configurations where a significant inductive current drive was involved. Current driven instabilities such as tearing modes and soft disruptions can prevent access to β-values as high as in the currentless case. The experimental results indicate that optimized stellarators such as W7-X can be considered as a viable option for an attractive stellarator fusion reactor.