Hannover 2020 – scientific programme

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P: Fachverband Plasmaphysik

P 15: Helmholtz Graduate School 3 and Magnetic confinement 3

P 15.3: Talk

Wednesday, March 11, 2020, 14:55–15:20, b305

Carbon distribution and transport in ECRH and NBI heated plasmas with Charge Exchange Spectroscopy on W7-X — •Lilla Vanó, Oliver P. Ford, and Robert C. Wolf — Max-Planck-Institute for Plasma Physics, Greifswald, Germany

Impurity transport plays a crucial role in the optimization of fusion plasmas, as impurities affect the plasma radiation and can cause power losses. If neoclassical effects dominate the transport, strong impurity accumulation is predicted in the plasma core. According to simulations, neoclassically dominated impurity transport is a possibility in the optimized stellarator Wendelstein 7-X (W7-X) plasma.

To quantify impurity confinement in W7-X, carbon concentration profiles are investigated and used with the impurity transport modeling code STRAHL to determine the transport coefficients (diffusivity and radial convective velocity). The results are compared with neoclassical predictions in order to assess the anomalous contribution.

The profiles are derived from the Charge Exchange Recombination Spectroscopy (CXRS) diagnostic that observes the Neutral Beam Injection (NBI) which is well-suited for determining spatially resolved profiles of fully-stripped low-Z impurities. This work concentrates on carbon, the main intrinsic impurity in W7-X.

Different configurations, densities and heating scenarios with different NBI and ECRH power ratios are explored. Of particular interest are discharges with pure NBI heating phases or with very low ECRH power, where indications of unusually high impurity confinement times have been observed.