ELM flushing and impurity transport in the H-mode edge barrier in ASDEX Upgrade

Abstract

Density profiles of He2+, C6+, Ne10+ and Ar16+ are measured at ASDEX Upgrade with high temporal (1.9ms) and radial resolution (>3mm) using CXRS. This allows the transport coefficients at the edge transport barrier to be analyzed in between type-I ELMs during H-mode. All measurements resemble the neoclassical transport coefficients, which means that the diffusion coefficient ranges from 0.15 to 0.35m2/s and the maximum of the inward convection velocity is Z-dependent increasing from 15m/s (He2+) to 90m/s (Ar16+). These results are combined into a simplified transport-erosion model for W which calculates the neoclassical transport coefficients self-consistently while taking several impurity species into account. The model also calculates erosion fluxes at the wall, prompt re-deposition of W and loss terms due to parallel flows in the scrape-off layer. While several free parameters exist in the model, it demonstrates that a quantitative consistency between the measured erosion fluxes of W and the observed W concentration inside the plasma is obtainable.