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Abstract. Basic features of the island divertor concepts for low-shear advanced stellarators like W7-AS and W7-X (intrinsic island divertors) and for high-shear heliotrons like CHS and LHD (local island divertors, LID) and first results for both concepts are shortly reviewed. The diverting fields of island divertors are either intrinsic (low-shear case) or externally imposed (high-shear case). The associated field perturbations are very small compared to tokamak poloidal field divertors, which explains the high flexibility of island divertor configurations, but sufficiently large to generate divertor-viable islands. Although the physics of island divertors is expected to be similar to that of tokamak poloidal field divertors, leading geometrical parameters significantly differ from those of comparable-size tokamaks. Furthermore, strong three-dimensional effects arise from toroidally discontinuous target plates. For both the intrinsic and local island divertor configurations, the island structure and the plasma diversion have been verified experimentally. For W7-AS, stable high recycling conditions could be demonstrated in a stellarator for a simple island divertor geometry. In CHS with the LID field switched on, a strong increase of the pumping efficiency was measured, resulting in a 50% reduction of the core density for the same gas-puff rate as in the non-LID case. 3D numerical transport studies with the EMC3/EIRENE code predict, for typical W7-AS values of the upstream density and power into the SOL, partial detachment with 80% power loss by carbon radiation in the SOL and significant momentum losses associated with the island divertor geometry.
IAEA 2001
