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(OV/2-4) Major Results from Wendelstein 7-AS Stellarator

F. Wagner¹⁾, R. Burhenn¹⁾, F. Gadelmeier¹⁾, J. Geiger¹⁾, M. Hirsch¹⁾, H.P. Laqua¹⁾, A. Weller¹⁾, A. Werner¹⁾, S. Baeumel¹⁾, J. Baldzuhn¹⁾, R. Brakel¹⁾, A. Dinklage¹⁾, P. Grigull¹⁾, M. Endler¹⁾, V. Erckmann¹⁾, H. Ehmler¹⁾, Y. Feng¹⁾, R. Fischer¹⁾, L. Giannone¹⁾, H.-J. Hartfuss¹⁾, D. Hildebrandt¹⁾, E. Holzhauer¹⁾, Y. Igitkhanov¹⁾, R. Jaenicke¹⁾, M. Kick¹⁾, A. Kislyakov²⁾, A. Kreter³⁾, J. Kisslinger¹⁾, T. Klinger¹⁾, S. Klose¹⁾, J.P. Knauer¹⁾, R. Koenig¹⁾, G. Kuehner¹⁾, H. Maassberg¹⁾, K. McCormick¹⁾, D. Naujoks¹⁾, H. Niedermeyer¹⁾, C. Nuehrenberg¹⁾, E. Pasch¹⁾, N. Ramasubramanian¹⁾, N. Rust¹⁾, E. Sallander¹⁾, F. Sardei¹⁾, U. Wenzel¹⁾, H. Wobig¹⁾, E. Wuersching¹⁾, M. Zarnstorff⁴⁾, S. Zoletnik⁵⁾, W7-AS Team^1)
 
1) Max-Planck-Institut für Plasmaphysik, EURATOM Assoc., Garching/Greifswald, Germany
²⁾ IOFFE-Institute, St. Petersburg, Russia
³⁾ Forschungszentrum Jülich, EURATOM Association, Jülich, Germany
⁴⁾ Princeton Plasma Physics Laboratory, Princeton, USA
⁵⁾ KFKI-RMKI, EURATOM Association, Budapest, Hungaria

Abstract.  W7-AS operates with an island divertor, which utilises the natural edge islands of the low-shear stellarator configuration to divert the plasma. High densities (up to 4×10²⁰m^{- 3}) and partly detached divertor conditions have been attained. The details of the divertor operation will be described along with the 3D-efforts to model the divertor observations. At a density beyond 1.5×10²⁰m^{- 3} another confinement bifurcation appears, which allows steady state operation at good energy and low impurity confinement. The transition is possible from a state of normal confinement or from ELMy or quiescent H-modes. Starting with normal confinement, bifurcation is initiated by a broadening of the density profile. This regime can easily be heated above cut-off by ECRH using electron-bernstein-wave mode conversion. The highest beta-values (>3%) are achieved at high density. The relevance of the W7-AS data for Wendelstein 7-X and the Helias-reactor will be discussed.

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