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

Journal Article · Wed May 15 04:00:00 EDT 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4801743· OSTI ID:22228073

Chapman, I. T.; Kirk, A.; Ham, C. J.; Harrison, J. R.; Liu, Y. Q.; Saarelma, S.; Scannell, R.; Thornton, A. J.; Team, MAST ^[1]; Becoulet, M.; Orain, F. ^[2]; Cooper, W. A. ^[3]; Pamela, S. ^[4]

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1. EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom)
2. Association Euratom/CEA, CEA Cadarache, IRFM, F-13108, St. Paul-lez-Durance (France)
3. CRPP, Association EURATOM/Confédération Suisse, EPFL, 1015 Lausanne (Switzerland)
4. IIFS-PIIM. Aix Marseille Université—CNRS, 13397 Marseille Cedex 20 (France)

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.

• OSTI ID: 22228073
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 20; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AXIAL SYMMETRY
BALLOONING INSTABILITY
BOUNDARY LAYERS
CHARGED-PARTICLE TRANSPORT
DISTURBANCES
DIVERTORS
EDGE LOCALIZED MODES
HEAT FLUX
MAGNETOHYDRODYNAMICS
MAST TOKAMAK
PLASMA CONFINEMENT
PLASMA PRESSURE
PRESSURE GRADIENTS
THREE-DIMENSIONAL CALCULATIONS