Greifswald 2024 – scientific programme

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P: Fachverband Plasmaphysik

P 17: Magnetic Confinement V/HEPP VI

P 17.1: Invited Talk

Wednesday, February 28, 2024, 16:30–17:00, ELP 6: HS 3

Finite Element Method to Describe Magnetic Measurements of Tearing Modes in ASDEX Upgrade — •Magdalena Bauer, Hartmut Zohm, Marc Maraschek, Anja Gude, Wolfgang Suttrop, Felix Klossek, Bernhard Sieglin, and Louis Giannone — MPI for Plasma Physics, Garching

In large tokamaks a disruption, i.e. a sudden loss of plasma current terminating the discharge, has to be avoided or at least mitigated. Tearing modes (TMs), resistive plasma instabilities, are common precursors to disruptions, particularly TMs with toroidal mode number n=1. Electromagnetic interaction with the vacuum vessel can slow down rotating TMs, which can eventually lock to the wall. Here, toroidal coupling, i.e. the coupling of modes with the same n but different poloidal mode numbers, m, plays an important role. Magnetic perturbations associated with TMs are detected by coils outside the plasma with different orientations and distances to conducting structures. To analyse TMs at all times, the frequency dependence of these measurements has to be described. For this purpose, a three-dimensional model using the finite element method is employed. A TM is introduced as a radially-localized helical current, while the plasma is modelled as vacuum. The vessel and additional conducting structures are integrated in a simplified form. The perturbed magnetic field measured by the coils is calculated taking into account induced currents in the conducting structures. In order to determine the mode composition in all stages of the locking process, agreement between model and measurement is required. The steps performed to achieve this are presented.

Keywords: Tearing modes; Modelling; Finite Element Method; Magnetic measurements; Mirror currents