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?