ITPA meeting, April (2009)
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L-H power threshold and ELM control L-H power threshold and ELM control techniques: techniques:
experiments on MAST and JETexperiments on MAST and JET
Carlos HidalgoCarlos HidalgoEURATOM-CIEMAT EURATOM-CIEMAT
Acknowledgments to:Acknowledgments to: A. Kirk (MAST) A. Kirk (MAST)
European Fusion Physics Workshop (DEuropean Fusion Physics Workshop (Deecember 2008): cember 2008): Y. Andrew, L. Horton, E. Nardon, W. SuttropY. Andrew, L. Horton, E. Nardon, W. Suttrop
ITPA meeting, April (2009)
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L-H power threshold physics and ITER L-H power threshold physics and ITER plasma scenariosplasma scenarios
Large uncertainties are still present in the empirical description of the L-H power transition with impact in the overall research programme of next step magnetic confinement devices (e.g. ITER).
This fact is reflecting the lack of basic understanding of the physics of sheared flows and edge transport barriers.
ITPA meeting, April (2009)
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• Values of total Pin for Type-III and Type-I ELMy phases are plotted along with measured Pth for L-H transition
Pin > 1.5Pth for H98 = 1.0, Type-I ELMS
R Sartori et al., PPCF 46 (2004) 723 – 750.
• In JET Type-III ELMy H-modes H98 is lower than for Type-I ELMy H-modes over the entire density range.
Pin>1.5Pth is required for H-mode plasma H98=1 access on JET
Y. Andrew et al., EFPW, December 2008.
PPinin = P = Pthth is insufficient for H is insufficient for H9898 = 1 access = 1 access
ITPA meeting, April (2009)
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Type I ELMs must be drastically reduced in ITER
Type-I ELMs are a factor in the order of 10 too large in ITER baseline scenario Development of mechanisms allowing controlling ELM size is a prime target for ITER:
• Vertical kicks
• Pellet pace-making
• Resonant Magnetic Perturbations
A. Loarte et al.,
ITPA meeting, April (2009)
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E. Nardon, EFPW, December 2008
Alternatives to the Type-I ELMy H-mode?
Many regimes observed in different machines
Feasibility at ITER parameters and without loosing confinement?
Alternatives to Type-I ELMy H-mode:No clear solution but some promising paths (e.g. QH) that need to be explored further
ITPA meeting, April (2009)
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Interplay between L-H power threshold and
ELMs control techniques:
an open issue for ITER (Pin≈ 1.5 x Pth)
ITPA meeting, April (2009)
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Ex vessel coils (error field correction coils) in JET
Advantage: External Coils, more relevant for reactor application.
Limitation: low toroidal mode number spectrum of the perturbation
Magnetic perturbation Edge stochastic magnetic field
edge pressure gradient kept below threshold
In-vessel coils in DIII-D and ITER
Advantage: large toroidal mode number spectrum of the perturbation .
Limitation: Internal coils, subject to neutron radiation => reactor relevance?
ELM mitigation with magnetic perturbations
ITPA meeting, April (2009)
8of 12 slides E. Nardon, European Fusion Physics Workshop, Cork,
December 2008
• MAST has new ELM control coils (in-vessel, n=3)– Vacuum modelling predicts σChirikov larger than for DIII-D I-coils
– No ELM suppression so far but experiments are at the beginning.
–On MAST there is already observation of the delay of the L-H transition time if the n=1 coils are applied before the L-H transition.
ELM supression in MAST
ITPA meeting, April (2009)
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A.Kirk et al., (MAST)
n=1 experiments / MAST
L-H transition effected by size of Error field –need to ramp field only after the transition
Increasing error field B
Pin ≈ 2.5 x Pth
ITPA meeting, April (2009)
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n=3 experiments / MAST
L-H transition not effected by size of Elm coil–natural jitter in start of L-H makes conclusions difficult
A.Kirk et al., (MAST)
ITPA meeting, April (2009)
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• ELM frequency increased form 30Hz to
120Hz and ELM energy loss reduced
from 7% to below noise level (~2%).
Reduction in ELM peak heat fluxes and
carbon erosion
• Electron density decreases (pump out)
• Electron and ion temperatures increase
(core and edge)
• Reduction in the thermal energy
confinement but no change compared to
H-mode scaling
Y. Liang PRL, 98, 265004 (2007)
#69564
Ip = 1.5 MA; Bt = 1.78 T; q95 ~ 4.0; U ~ 0.45
Coil current kAt
Density
Temperature keV
Confinement normalisedto H-mode scaling
D emission
• Wide range in q95 (4.8 – 3.0) with n = 1, 2 N up to ~2.9 (no locked mode excited by n=1 field)
• Low collisionality: *e~ 0.09
ELM mitigation with external magnetic perturbation field
ITPA meeting, April (2009)
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Conclusions and actionsConclusions and actionsOn MAST there is already observation of the delay of the L-H transition time if the n=1 coils are applied before the L-H transition (Pin = 2.5 x Pth) but not with n = 3.. Experiments are planned in JET (2009 experimental campaign).
Actions:
•L-H power threshold with ergodic divertor / resonant magnetic perturbations
(RMP) ( e.g. EU: JET / MAST / TEXTOR / AUG-2010,..):
Influence of RMP (different n) on L-H power threshold (Pin ≈ 1.5 x Pth)
•Power minimum at a certain density and Bt dependence (role of RMP)
•L-H power threshold physics: Tokamak vs Stellarators
e.g. Why is it so easy (in terms of heating power) to trigger the L-H transition in low
shear / low q stellarators?;
Role of magnetic shear / q ? Impact of q on zonal flows / GAMs?
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