Empirical scaling of inter-ELM power widths in ASDEX Upgrade and JET

Abstract The SOL power decay length ( λ q ) deduced from analysis of fully attached divertor heat load profiles from two tokamaks, JET and ASDEX Upgrade with carbon plasma facing components, are presented. Interpretation of the target heat load profiles is performed by using a 1D-fit function which disentangles the upstream λ q and an effective diffusion in the divertor ( S ), the latter essentially acting as a power spreading parameter in the divertor volume. It is shown that the so called integral decay length λ int is approximately given by λ int ≈ λ q + 1.64 × S . An empirical scaling reveals parametric dependency λ q / mm ≃ 0.9 · B T - 0.7 q cyl 1.2 P SOL 0 R geo 0 for type-I ELMy H-modes. Extrapolation to ITER gives λ q ≃ 1 mm. Recent measurements in JET-ILW and from ASDEX Upgrade full-W confirm the results. It is shown that a regression for the divertor power spreading parameter S is not yet possible due to the large effect of different divertor geometries of JET and ASDEX Upgrade Divertor-I and Divertor-IIb.