Features of near and far scrape-off layer heat fluxes on the Wendelstein 7-X inboard limiters

Niemann, H.;Jakubowski, M. W.;Effenberg, F.;Bozhenkov, S. A.;Cannas, B.;Carralero, D.;Langenberg, A.;Pisano, F.;Rahbarnia, K.;Rudischhauser, L.;Stange, T.;Warmer, F.;Wurden, G. A.

2020-01-01

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Abstract

The power fall-off length is used as a characteristic dimension to describe the power exhaust in the scrape-off layer (SOL) in magnetic confinement fusion devices. Measurements from the limiter campaign of the stellarator Wendelstein 7-X with inboard limiters are presented with the first-time characterization of the limiter heat loads. Two fall-off regimes are found with a narrow near SOL with power fall-off length in millimeters and a wider far SOL with fall-off lengths of several centimeters. An attempt is made to describe both regimes with a scaling law for plasma with different heating powers and densities. The results confirm the major geometry effects of the connection length on the heat transport predicted by 3D modeling.