2018•MPG.PuRe (Max Planck Society)Open access
Impact of the 3D Geometry from Non-axisymmetric Magnetic Perturbations on the Local Edge Stability in ASDEX Upgrade
M. Willensdorfer, M. Griener, E. Strumberger, W. Suttrop, D. Brida, M. Cavedon, S. S. Denk, M. Dunne, R. Fischer, M. Hoelzl, N. Leuthold, M. Maraschek, F. Mink, H. Zohm, T. Cote, C. C. Hegna, D. A. Ryan, Christopher Ham, Andrew G. Kirk, Nengchao Wang, J. Galdón-Quiroga, F. Orain, EUROfusion Mst Team
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Abstract
Mitigation and suppression of edge localised modes (ELMs) at low pedestal collisionality ⌫ ?using externally applied nonaxisymmetric magnetic perturbations (MPs) are closely related with the excitation of ideal stable kink-peeling modes at the edge.The result is a considerable distortion of the axisymmetric tokamak geometry, which is well predicted using single-fluid three-dimensional (3D) magnetohydrodynamic equilibrium codes.The resulting 3D geometry distorts the local edge stability.This is evident by ballooning modes (BMs) that only appear on certain helical positions in the 3D geometry in-between ELMs.The position of these BMs coincidences with the helical position exhibiting the lowest stability against field-line bending.This locally lower stability does not only influence the BMs, but also the following ELM crashes.The initial ELM crashes show the strongest magnetic perturbations and accelerated energetic electrons on these most unstable field-lines.This suggests that the locally lower stability causes a local eruption at the initial ELM crash.1.
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