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P: Fachverband Plasmaphysik

P 5: Poster I

P 5.35: Poster

Dienstag, 31. August 2021, 14:00–16:00, P

Generic Determination of Rotating and Locked MHD Mode Amplitudes on ASDEX Upgrade — •Felix Klossek, Marc Maraschek, Anja Gude, Hartmut Zohm, Louis Giannone, and the ASDEX Upgrade Team — Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany

When approaching a disruption in tokamaks, the plasma typically becomes unstable regarding a tearing mode which locks to the vessel. For the disruption to occur, multiple phase-locked tearing modes with different poloidal mode numbers m are considered necessary for producing a thermal shortcut by stochastisation. For rotating modes it has been possible for a long time to differentiate between different poloidal mode numbers at ASDEX Upgrade. Similar observations for locked modes could not be made until now, as the pick-up coils used for rotating modes rely on induction. The saddle coils used for locked mode detection are located at only one poloidal position on the high field side and therefore cannot resolve the poloidal mode numbers m.

A new method for evaluating magnetic mode signals, in particular the mode amplitude and phase, by projecting the signals on appropriate sine and cosine base vectors with the desired mode number is introduced. With this method, no compute intensive FFT algorithms are needed. For detecting the poloidal mode structure of locked modes for the first time the inactive RMP coils at ASDEX Upgrade are used in addition to the locked mode detector. It is shown that the mode structure is changed during the locking phase prior to the disruption.