High Power Heating Experiments On Wendelstein 7-As Stellarator

The upgraded NE heating power on W7-AS allowed extension of the accessible parameter space. In first experiments, a remarkable increase of the ion temperatures was obtained. The results are discussed on the basis of a detailed transport analysis which confirms the neoclassical nature of the ion transport up to the 1mfp regime. The maximum NE heating power was applied to investigate beta limits. Although beta values close to the predicted stability limit could be reached, no clear indication of a limit has been found so far. Several experimental observations on W7-AS point to the necessity of a divertor. The feasibility of a divertor making use of the natural islands in an optimized stellarator was investigated, and a possible solution for an island divertor on W7-AS is outlined.