München 2019 – scientific programme

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P: Fachverband Plasmaphysik

P 17: Helmholtz Graduate School VI

P 17.1: Invited Talk

Thursday, March 21, 2019, 14:00–14:30, HS 17

Impurity Transport Investigations at the Wendelstein 7-X Stellarator — •Rainer Burhenn and W7-X Team — Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald, Germany

A critical issue for fusion devices is the plasma contamination by impurities released by interaction of the plasma with plasma-facing components. Depending on impurity concentration they can cause unacceptable dilution of the fusion fuel and substantial radiation cooling in case of highly charged species. The latter might lead to degraded plasma performance or even plasma termination either by an abrupt disruption as in tokamaks or a soft radiative collapse as in devices with small plasma currents such as stellarators. The magnetic field of the superconducting modular stellarator Wendelstein 7-X is optimized to reduce the enhanced particle transport at low collisionality, typically inferred by non-axisymmetric configurations. This allows for long-pulse operation with good energy confinement. For impurities, nevertheless, theory predicts inwards directed fluxes at high densities, potentially causing accumulation and endangering long-pulse operation. However, the latter had not been observed for microwave heated W7-X plasmas so far, indicating the existence of additional transport channels. First modelling of experiments with active impurity tracer injection reveals predominantly anomalous diffusive transport. For clearification of the relevance of turbulence for the observed impurity transport properties a comparison of impurity and bulk plasma confinement with turbulence measurements and gyrokinetic calculations is under investigation.