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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.
