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P: Fachverband Plasmaphysik

P 9: Poster I

P 9.17: Poster

Tuesday, March 29, 2022, 16:00–17:30, P

Modelling Magnetic Measurements of Tearing Modes in ASDEX Upgrade — •Magdalena Bauer, Marc Maraschek, Hartmut Zohm, Anja Gude, Wolfgang Suttrop, Felix Klossek, Louis Giannone, and the ASDEX Upgrade Team — Max Planck Institute for Plasma Physics, Garching

In future fusion devices, disruptions have to be avoided to prevent damage of the vessel. Locked modes, i.e. tearing modes that are at rest with the vessel due to electromagnetic interaction, are precursors of and significantly involved in disruptions. While rotating modes can be observed by Mirnov coils measuring the poloidal magnetic perturbation field tangential to the wall, locked modes require measuring the radial magnetic field, e.g. by saddle coils on the high-field side. The observed perturbation fields are affected differently by mirror currents induced by rotating modes. In order to model all measurements during a locking process, these mirror currents and their frequency dependence have to be described. Owing to the complexity of the real tokamak, neither the full geometry nor the exact conductivity of all structures can be considered. A recently developed three-dimensional finite element tool modelling the perturbation field for all coils is implemented using an effective conductivity of the wall and - for the saddle coils - an effective distance to the vessel. These two simulation parameters are optimized such that they best describe the ratio of measured mode amplitudes in Mirnov and saddle coils for all frequencies and discharge scenarios. Additional radial field coils are implemented to gain information on the poloidal mode structure of locked modes.