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K. Krieger, B. Sieglin, M. Balden, J. Coenen, B. Göths, F. Laggner, P. de Marné, G. Matthews, D. Nille, V. Rohde, R. Dejarnac, M. Faitsch, L. Giannone, A. Herrmann, J. Horacek, M. Komm, R. Pitts, S. Ratynskaia, E. Thoren, P. Tolias, . ASDEX Upgrade Team, -. EUROfusion MST1 Team:
"Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade";
Physica Scripta, T170 (2017), 0140301 - 0140308.

Repetitive melting of tungsten by power transients originating from edge localized modes
(ELMs) has been studied in the tokamak experiment ASDEX Upgrade. Tungsten samples were
exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II
system. The exposed sample was designed with an elevated sloped surface inclined against the
incident magnetic field to increase the projected parallel power flux to a level were transient
melting by ELMs would occur. Sample exposure was controlled by moving the outer strike point
to the sample location. As extension to previous melt studies in the new experiment both the
current flow from the sample to vessel potential and the local surface temperature were measured
with sufficient time resolution to resolve individual ELMs. The experiment provided for the first
time a direct link of current flow and surface temperature during transient ELM events. This
allows to further constrain the MEMOS melt motion code predictions and to improve the
validation of its underlying model assumptions. Post exposure ex situ analysis of the retrieved
samples confirms the decreased melt motion observed at shallower magnetic field line to surface
angles compared to that at leading edges exposed to the parallel power flux.

plasma-facing components, tungsten, melting, edge-localized modes