Understanding ELM mitigation by resonant magnetic perturbations on MAST

Abstract

Sustained ELM mitigation has been achieved using RMPs with a toroidal mode number of n=4 and n=6 in lower single null and with n=3 in connected double null plasmas on MAST. The ELM frequency increases by up to a factor of eight with a similar reduction in ELM energy loss. A threshold current for ELM mitigation is observed above which the ELM frequency increases approximately linearly with current in the coils. A comparison of the filament structures observed during the ELMs in the natural and mitigated stages shows that the mitigated ELMs have the characteristics of type I ELMs even though their frequency is higher, their energy loss is reduced and the pedestal pressure gradient is decreased. During the ELM mitigated stage clear lobe structures are observed in visible-light imaging of the X-point region. The size of these lobes is correlated with the increase in ELM frequency observed. The RMPs produce a clear 3D distortion to the plasma and it is likely that these distortions explain why ELMs are destabilised and hence why ELM mitigation occurs.

41 pages, 19 figures. arXiv admin note: text overlap with arXiv:1305.3061

References in corpus (5)

• Observation of lobes near the X-point in resonant magnetic perturbation experiments on MAST
• Resonant magnetic perturbations and divertor footprints in poloidally diverted tokamaks
• Effect of resonant magnetic perturbations with toroidal mode numbers of 4 and 6 on ELMs in single null H-mode plasmas in MAST
• Divertor heat fluxes and profiles during mitigated and unmitigated Edge Localised Modes (ELMs) on the Mega Amp Spherical Tokamak (MAST)
• Inter-ELM pedestal evolution on MAST and impact of Resonant Magnetic Perturbations

Cited by in corpus (11)

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• Understanding the effect resonant magnetic perturbations have on ELMs
• Theory of Edge Localized Mode Suppression by Static Resonant Magnetic Perturbations in the DIII-D Tokamak
• ELM mitigation via rotating resonant magnetic perturbations on MAST
• Impact of Resonant Magnetic Perturbations on the L-H Transition on MAST
• Modelling of three dimensional equilibrium and stability of MAST plasmas with magnetic perturbations using VMEC and COBRA
• Nuclear Fusion: Bringing a star down to Earth
• Plasma response to resonant magnetic perturbations near rotation zero-crossing in low torque plasmas
• Improved Particle Confinement with Resonant Magnetic Perturbations in DIII-D Tokamak H-Mode Plasmas