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(OV2/4) Overview on W7-AS Results with Relevance for WENDELSTEIN 7-X and the Low-Shear Stellarator Line

F. Wagner, M. Anton, J. Baldzuhn, J. Bleuel, R. Brakel, R. Burhenn, G. Cattanei, M. Endler, V. Erckmann, Y. Feng, S. Fiedler, J. Geiger, T. Geist, L. Giannone, P. Grigull, H.-J. Hartfuss, D. Hartmann, G. Herre, M. Hirsch, E. Holzhauer, R. Jänicke, M. Kick, J. Kißlinger, J. Koponen, G. Kühner, H. P. Laqua, H. Maassberg, F. Sardei, U. Stroth, A. Weller, S. Zoletnik, J. H. Chatenet, D. Dorst, A. Elsner, C. Görner, H. Hacker, F. Karger, J. Knauer, R. König, H. Laqua, K. McCormick, Niedermeyer, C. Nührenberg, W. Ott, F. P. Penningsfeld, A. Salat, F. Schneider, C. Theimer, H. Walter, C. Wendland, A. Werner, E. Würsching, P. Zeiler

Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching, Germany

Abstract.  The Wendelstein stellarator programme of Garching has developed low shear stellarators with successively optimised designs to remove the intrinsic deficiencies of this 3D concept. W7-X, presently under construction, is in internal terminology a fully optimised stellarator. W7-AS, the presently operated device, is a partly optimised stellarator. The optimisation of stellarators aims at improved neoclassical confinement in the long mean free path regime and improved equilibrium and stability properties. In this report, we address equilibrium, stability, turbulent and collisional energy confinement aspects (role of magnetic shear, role of the radial electric field, low and improved confinement regimes), particle transport, transport and turbulence at the plasma edge, high density operation, ECRH (OXB scheme) and ICRF heating and the development of the island divertor for exhaust. The maximal parameters achieved in W7-AS (at different discharge types) are: T_e = 5.8 keV, T_i = 1.5 keV, n_e = 3×10²⁰m^{- 3}, $\langle$$\beta$$\rangle$ = 2%, $\tau_{\mathrm{E}}^{}$ = 50 ms.

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