Hannover 2020 – scientific programme

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P: Fachverband Plasmaphysik

P 9: Helmholtz Graduate School 2 and Magnetic confinement 2

P 9.1: Invited Talk

Tuesday, March 10, 2020, 14:00–14:30, b305

The Wendelstein 7-X Scrape-Off Layer — •Carsten Killer and W7-X Team — Max-Planck Institut für Plasmaphysik, Greifswald, Germany

The stellarator Wendelstein 7-X employs the island divertor concept, where the intersection of out-flowing plasma by the divertor takes places in a chain of large, intrinsic magnetic islands. The Scrape-Off Layer (SOL) formed by the magnetic islands is inherently three-dimensional and features rather long connections lengths of typically several 100 m. Understanding the transport processes in the SOL is essential for controlled high performance plasma operation since the SOL profiles formed by the relation of parallel and perpendicular transport ultimately govern the heat flux distribution on the targets.
Using a multi-diagnostic approach with a focus on reciprocating probes, we show that the magnetic islands significantly affect the SOL plasma. Most notably, a strong poloidal plasma rotation along the islands’ magnetic flux surfaces is observed, which is accompanied by rather flat or even hollow profiles of electron temperature and density across the islands, resulting in a large SOL width (∼5 cm). Outside the islands, the SOL reveals similarities (e.g. exponentially decaying profiles) and differences to a typical tokamak SOL. A particular focus is laid on blob-filaments, which are found to have much slower radial propagation velocities in W7-X than in tokamaks. The reasons for and implications of this observation will be discussed.