Stellarator optimization studies in W7-AS

Wendelstein 7-AS is the first large-scale modular stellarator, partially optimized with respect to reduced equilibrium current j||. It therefore plays an important role for the optimized next step stellarator W7-X as a pilot experiment for manufacturing techniques of coils and vessel and for equilibrium and neo-classical transport properties of the Wendelstein stellarator line of IPP. Experimental results from W7-AS of importance for the continuation and optimization of the advanced stellarators are summarized: with respect to magnetic optimization we address improved equilibrium, stability and neo-classical transport and the feasibility of the modular coil system. Regarding operational enhancements we focus on demonstrated high-density operation and the soft edge density limit, improved confinement, verification of the 3D plasma edge topology, stability of island structures for exhaust properties and demonstrated stable divertor high recycling in the island divertor configuration. (author)