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P: Fachverband Plasmaphysik
P 1: Helmholtz Graduate School for Plasma Physices I
P 1.4: Fachvortrag
Montag, 29. Februar 2016, 12:15–12:40, b302
High frequency magnetic fluctuations correlated with the inter-ELM pedestal recovery — •Florian M. Laggner1, Elisabeth Wolfrum2, Felician Mink2, Marco Cavedon2, Mike G. Dunne2, Gregor Birkenmeier2, Friedrich Aumayr1, the ASDEX Upgrade Team2, and the EUROfusion MST1 Team2 — 1Institute of Applied Physics, TU Wien, Fusion@ÖAW, Wiedner Hauptstr. 8-10, 1040 Vienna, Austria — 2Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany
In H-mode plasmas, the maximum achievable pressure gradient at the plasma edge (pedestal) is usually set by an ideal MHD limit (peeling-ballooning), which if exceeded is leading to edge localised modes (ELMs), that relax the pedestal. However, the mechanisms setting the final pedestal shape (height and width) are not fully understood. This contribution focuses on the temporal evolution of the pedestal density and temperature profiles. After the maximum pre-ELM pedestal gradients are established a phase that is accompanied by the sharp onset of radial magnetic fluctuations with frequencies larger than 200 kHz is identified. During their presence the gradients of the edge electron density and temperature are clamped. The observed fluctuation frequencies scale with the minimum E × B velocity at the edge, that is estimated from neoclassical theory, indicating that the underlying modes are located in the steep gradient region. The toroidal mode number (n) of approximately 10 as well as the detection of the fluctuations on the high field side points in the direction of a MHD-type instability with low/high field side symmetric amplitude.