Towards understanding edge localised mode mitigation by resonant magnetic perturbations in MAST

Type-I Edge Localised Modes (ELMs) have been mitigated in MAST through the application of n=3,4, and 6 resonant magnetic perturbations. For each toroidal mode number of the non-axisymmetric applied fields, the frequency of the ELMs has been increased significantly, and the peak heat flux on the dive...

Full description

Saved in:
Bibliographic Details
Published in:Physics of plasmas 2013-05, Vol.20 (5)
Main Authors: Chapman, I. T., Kirk, A., Ham, C. J., Harrison, J. R., Liu, Y. Q., Saarelma, S., Scannell, R., Thornton, A. J., Becoulet, M., Orain, F., Cooper, W. A., Pamela, S., Team, MAST
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AXIAL SYMMETRY
BALLOONING INSTABILITY
Boundaries
BOUNDARY LAYERS
Braking
CHARGED-PARTICLE TRANSPORT
Corrugating
Corrugation
DISTURBANCES
DIVERTORS
EDGE LOCALIZED MODES
Elm
HEAT FLUX
Lobes
MAGNETOHYDRODYNAMICS
MAST TOKAMAK
PLASMA CONFINEMENT
PLASMA PRESSURE
Plasmas
PRESSURE GRADIENTS
Stability
THREE-DIMENSIONAL CALCULATIONS
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Type-I Edge Localised Modes (ELMs) have been mitigated in MAST through the application of n=3,4, and 6 resonant magnetic perturbations. For each toroidal mode number of the non-axisymmetric applied fields, the frequency of the ELMs has been increased significantly, and the peak heat flux on the divertor plates reduced commensurately. This increase in ELM frequency occurs despite a significant drop in the edge pressure gradient, which would be expected to stabilise the peeling-ballooning modes thought to be responsible for type-I ELMs. Various mechanisms which could cause a destabilisation of the peeling-ballooning modes are presented, including pedestal widening, plasma rotation braking, three dimensional corrugation of the plasma boundary, and the existence of radially extended lobe structures near to the X-point. This leads to a model aimed at resolving the apparent dichotomy of ELM control, which is to say ELM suppression occurring due to the pedestal pressure reduction below the peeling-ballooning stability boundary, whilst the reduction in pressure can also lead to ELM mitigation, which is ostensibly a destabilisation of peeling-ballooning modes. In the case of ELM mitigation, the pedestal broadening, 3d corrugation, or lobes near the X-point degrade ballooning stability so much that the pedestal recovers rapidly to cross the new stability boundary at lower pressure more frequently, whilst in the case of suppression, the plasma parameters are such that the particle transport reduces the edge pressure below the stability boundary, which is only mildly affected by negligible rotation braking, small edge corrugation or short, broad lobe structures.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4801743