Core-edge studies with boundary island configurations on the W7-AS stellarator

Core, edge and scrape-off-layer plasma behaviour is studied principally und er conditions of an t(a) = 5/9 boundary island configuration-which is relev ant for the upcoming W7-AS divertor campaign-but for now with ten inboard s ector limiters. The major focus is on compatibility between good core confi nement and attainment of high recycling at the limiter. At low input power P-in less than or equal to 0.4 MW, operation at densities necessary to atta in effective divertor action in the future invariably leads to a transition to the ELM-free H-mode accompanied by lower edge densities and increased c ore radiation until radiation collapse ensues. Thereby, enhancement factors in tau(E) Of nearly two above the international stellarator confinement sc aling are transiently achieved. The threshold density (n) over bar(e)(thr), necessary to attain the H-mode increases with heating power,such that at 2 MW NBI heating power the H-mode is completely suppressed and peak densitie s at the limiter exceeding 1.5 x 10(20) m(-3) are realized. The efficacy of newly-installed control coils designed to manipulate the island geometry i s tested. Their influence on the core plasma is verified. Due to geometrica l effects associated with the mutual shadowing of the inboard limiters, sta tements regarding the influence on island physics must await the divertor c onfiguration.