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P: Fachverband Plasmaphysik

P 15: Helmholtz Graduate School II

P 15.22: Poster

Dienstag, 14. März 2017, 16:30–18:30, HS Foyer

Investigation of mode coupling during the ELM cycle on ASDEX Upgrade by magnetic bicoherence spectra — •Georg Harrer¹, Elisabeth Wolfrum², Peter Manz², Felician Mink², Friedrich Aumayr¹, and The ASDEX Upgrade Team² — ¹Institut für Angewandte Physik, TU Wien, Wiedner Hauptstr. 8-10/134, 1040 Vienna, Austria — ²Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany

Edge localized modes (ELMs) occur as repetitive bursts of magneto-hydrodynamic activity in high-confinement regimes of tokamak fusion plasmas. ELMs lead to a sudden release of pedestal stored energy and cause high heat fluxes to the first walls. Also, during the inter-ELM phase, mode-like activities can be observed and they can cause additional transport across the separatrix. Simulations suggest that non-linear couplings of these modes might play an important role for the ELM onset. Bicoherence analysis delivers a method to diagnose and display these couplings. In this work an algorithm combining bicoherence and ELM-synchronization has been developed. The algorithm was tested with a non-linear coupling model and improved by dithering and windowing functions. Different phases of the ELM cycle were examined. In most of these phases no coupling was found. Just before some ELMs three wave coupling was found which seems to be connected to the appearance of double peak ELMs.