Abstract
Field-line localized ballooning modes have been observed at the edge of high confinement mode plasmas in ASDEX Upgrade with rotating 3D perturbations induced by an externally applied n=2 error field and during a moderate level of edge localized mode mitigation. The observed ballooning modes are localized to the field lines which experience one of the two zero crossings of the radial flux surface displacement during one rotation period. The localization of the ballooning modes agrees very well with the localization of the largest growth rates from infinite-n ideal ballooning stability calculations using a realistic 3D ideal magnetohydrodynamic equilibrium. This analysis predicts a lower stability with respect to the axisymmetric case. The primary mechanism for the local lower stability is the 3D distortion of the local magnetic shear.
Highlights
Introduction.—In order to mitigate the possible harmful heat load from edge localized modes (ELMs) in the high confinement mode (H mode) in future fusion devices, it is necessary to suppress or to mitigate the ELMs
Field-line localized ballooning modes have been observed at the edge of high confinement mode plasmas in ASDEX Upgrade with rotating 3D perturbations induced by an externally applied n 1⁄4 2 error field and during a moderate level of edge localized mode mitigation
There is growing evidence that stable ideal kink modes can amplify the externally applied magnetic perturbations (MPs) field [2,3], which plays a key role in ELM mitigation [4] and ELM suppression at low ν⋆ [5,6]
Summary
Introduction.—In order to mitigate the possible harmful heat load from edge localized modes (ELMs) in the high confinement mode (H mode) in future fusion devices, it is necessary to suppress or to mitigate the ELMs. Field-Line Localized Destabilization of Ballooning Modes in Three-Dimensional Tokamaks The observed ballooning modes are localized to the field lines which experience one of the two zero crossings of the radial flux surface displacement during one rotation period.
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