Dec 12, 2014 - mechanism relies on perturbing the magnetic field in the edge plasma region, ... Connected Double Null (CDN) [10] magnetic configurations.
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12/12/14
Effect of resonant magnetic perturbations on low collisionality discharges in MAST and a comparison with ASDEX Upgrade A. Kirk1, W. Suttrop2, Yueqiang Liu1, I.T. Chapman1, P. Cahyna3, T.Eich2, C. Fuchs2, C. Ham1, J.R. Harrison1, MW. Jakubowski4, S. Pamela1, M. Peterka3, D. Ryan1, S. Saarelma1, R. Scannell1, A.J. Thornton1, M. Valovic1, B. Sieglin2, L. Barrera Orte2, M. Willensdorfer2, B. Kurzan2, R. Fischer2 and the MAST, ASDEX Upgrade and EUROfusion MST1 Teams 1
CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK Max-Planck Institut für Plasmaphysik, Garching, Germany 3 Institute of Plasma Physics AS CR v.v.i., IPP.CR, Prague, Czech Republic 4 Max-Planck Institut für Plasmaphysik, Wendelsteinstr, Greifswald, Germany 2
Abstract Sustained ELM mitigation has been achieved on MAST and AUG using RMPs with a range of toroidal mode numbers over a wide region of low to medium collisionality discharges. The ELM energy loss and peak heat loads at the divertor targets have been reduced. The ELM mitigation phase is typically associated with a drop in plasma density and overall stored energy. In one particular scenario on MAST, by carefully adjusting the fuelling it has been possible to counteract the drop in density and to produce plasmas with mitigated ELMs, reduced peak divertor heat flux and with minimal degradation in pedestal height and confined energy. While the applied resonant magnetic perturbation field (brres) can be a good indicator for the onset of ELM mitigation on MAST and AUG there are some cases where this is not the case and which clearly emphasise the need to take into account the plasma response to the applied perturbations. The plasma response calculations show that the increase in ELM frequency is correlated with the size of the edge peelingtearing like response of the plasma and the distortions of the plasma boundary in the Xpoint region. In many cases the RMPs act to increase the frequency of type I ELMs, however, there are examples where the type I ELMs are suppressed and there is a transition to a small or type IV ELM-ing regime.
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Introduction Type I ELMs are explosive events, which can eject large amounts of energy and particles from the confined region [1]. Extrapolation from present measurements suggest that the natural ELM frequency in ITER will vary from ~ 1 Hz for discharges with a plasma current IP = 15MA to
~7Hz for IP = 5MA. Avoidance of both damage to Plasma Facing
Components (PFC) and Tungsten (W) accumulation leads to a requirement that the ELM frequency is increased by a factor of ~3-40 over the natural ELM frequency as IP is increased from 5-15MA (see [2] and references therein).
Hence a mechanism is required
to either increase the ELM frequency or to eliminate ELMs altogether accompanied by sufficient particle transport in order to avoid W accumulation. One such amelioration mechanism relies on perturbing the magnetic field in the edge plasma region, either leading to more frequent smaller ELMs (ELM mitigation) or ELM suppression. This technique of Resonant Magnetic Perturbations (RMPs) has been employed to either mitigate or suppress type I ELMs on DIII-D [3][4], JET [5], ASDEX Upgrade [6], KSTAR [7] and MAST [8]. MAST and AUG are equipped with two rows of in vessel RMP coils (MAST: has 6 in the upper row and 12 in the lower row. AUG: 8 coils in both rows), which allow magnetic perturbations with a range of toroidal mode numbers (MAST: nRMP=2, 3, 4, 6, AUG: nRMP=1, 2, 4) to be applied. In this paper new results from MAST and ASDEX Upgrade at low pedestal top collisionality (*e
