Nonlinear excitation of low-n harmonics in reduced magnetohydrodynamic simulations of edge-localized modes

Journal Article · Thu Aug 15 04:00:00 EDT 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4817953· OSTI ID:22227908

Krebs, I.; Hölzl, M.; Lackner, K.; Günter, S. ^[1]

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1. Max Planck Institute for Plasma Physics, EURATOM Association, Boltzmannstr. 2, 85748 Garching (Germany)

Nonlinear simulations of the early edge-localized mode (ELM) phase based on a typical type-I ELMy ASDEX Upgrade discharge have been carried out using the reduced MHD code JOREK. The analysis is focused on the evolution of the toroidal Fourier spectrum. It is found that during the nonlinear evolution, linearly subdominant low-n Fourier components, in particular the n = 1, grow to energies comparable with linearly dominant harmonics. A simple model is developed, based on the idea that energy is transferred among the toroidal harmonics via second order nonlinear interaction. The simple model reproduces and explains very well the early nonlinear evolution of the toroidal spectrum in the JOREK simulations. Furthermore, it is shown for the n = 1 harmonic, that its spatial structure changes significantly during the transition from linear to nonlinearly driven growth. The rigidly growing structure of the linearly barely unstable n = 1 reaches far into the plasma core. In contrast, the nonlinearly driven n= 1 has a rigidly growing structure localized at the plasma edge, where the dominant toroidal harmonics driving the n = 1 are maximal and in phase. The presented quadratic coupling model might explain the recent experimental observation of strong low-n components in magnetic measurements [Wenninger et al., “Non-linear magnetic perturbations during edge localized modes in TCV dominated by low n mode components,” Nucl. Fusion (submitted)].

• OSTI ID: 22227908
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 8 Vol. 20; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ASDEX TOKAMAK
BOUNDARY LAYERS
COMPARATIVE EVALUATIONS
DISTURBANCES
EDGE LOCALIZED MODES
ELECTRIC DISCHARGES
EXCITATION
HARMONICS
J CODES
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PLASMA
PLASMA SIMULATION
TCV TOKAMAK