Island divertor investigations on the W7-AS stellarator

The effectiveness of 10 newly installed control coils, which had already be en implemented in preparation for the upcoming divertor experiments, has be en demonstrated in several important areas. Most importantly we have been a ble to show that the control coils can be used to influence the ratio of pa rallel to cross-field transport within an island by nearly a factor 2. High recycling conditions have been attained at the inboard limiters for t(a) = 5/9 but there was no indication of detachment. Excellent data consistency has been achieved during the high density phase of the high recycling disch arges between the saturation current I-sat measured by the target Langmuir probes and the equivalent values derived from the new absolutely calibrated signal of the 2D H-alpha CCD camera. Poloidal as well as toroidal asymmetr ies caused considerable problems when we tried to relate measurements of di fferent edge/target diagnostic signals, taken at equivalent positions aroun d the machine. These asymmetries could with high probability be attributed to toroidally non-symmetrically distributed components like the diamagnetic loop (module 5) or the MINISOX camera (module 3). (C) 2001 Elsevier Scienc e B.V. All rights reserved.