EFDA EUROPEAN FUSION DEVELOPMENT AGREEMENT Task Force S1 J.Ongena 19th IAEA Fusion Energy...

EFDA EUROPEAN FUSION DEVELOPMENT AGREEMENT

19th IAEA Fusion Energy Conference, Lyon 2002 1

Task Force S1

J.Ongena

Towards the realization on JET of

an integrated H-Mode scenario for ITER

19th IAEA Fusion Energy Conference

14 to 19 October 2002

Lyon, France

J.Ongena and EFDA-JET work programme contributors

Task Force Leader Scenario 1 at JET

Ecole Royale Militaire / Koninklijke Militaire School

Association “EURATOM-Belgian State”

Brussels, Belgium



Task Force S1

J.Ongena

O U T L I N E

• ITER Q=10 ELMy H-Mode operational

requirements for high density, confinement and

beta simultaneously realized in JET discharges

• Towards the realization of acceptable heat loads on

the ITER divertor target plates

• Summary and Outlook



Task Force S1

J.Ongena

High Confinement and high density

in ELMy H-Mode discharges

Obtained in three different ways :

1. Plasma Shaping : High triangularity

2. Impurity seeding : Low and High plasmas

3. High Field Side pellet injection

Peaked density profiles can be seen

Modified confinement scaling taking into account influence of density peaking, triangularity, proximity to Greenwald density



Task Force S1

J.Ongena

1. Plasma Shaping

High Confinement and High Density at High Confinement of high performance high discharges :

• Type I ELMs with indications for Type II ELMs at high density

• Simultaneously for ~ 4 sec (~ 9E) :

• High density n/nGW > 1

• High N,th > 1.8

• High Confinement H98(y,2) = 1



Task Force S1

J.Ongena

JET Confinement depends on and ELM Type• Degradation versus density for all triangularities

• At high : n/nGW, H98(y,2) and N

for ITER obtained simultaneously

• Confinement in lower plasmas improved by increasing Pin/PL-H

• Best points : n/nGW > 1 with H98(y,2) = 1 N ~ 1.9Black diamonds from new HT3 configuration

designed for high current/field operationSee also J.Pamela, OV/1-4



Task Force S1

J.Ongena

2. Impurity Seeding combines

High Confinement and High Density with Radiating Mantle

Result of Ar seeding :

• Increased radiation : Prad/Ptot = 0.65

• Increased density (f p )

• Density up to 1.15 n/nGW (with H98(y,2) = 0.9 and N,th = 2.1)

• Effects on ELMs

Reduction of ELM frequencyHigher D between ELMs

• Moderate increase of Zeff: Zeff ~ 0.2 and CAr(0.2) = 0.05%

• Lack of central heating terminates pulse



Task Force S1

J.Ongena

Radiating Mantle and ITG stabilization with Ar Seeding

• Radiating Mantle in Plasma Edge Reduction of ITG growth rate Improvement of core confinement

For both high and low discharges :

High discharges #53149 #53146

Calculated with Weiland model(I.Voitsekhovitch)

Larger mantle in high discharge

Without Ar

With Ar

#53146 #50473



Task Force S1

J.Ongena

3. High Field Side Pellet Injection • Applied to discharges with medium = 0.32

• Fast Pellet Sequence to raise density• Slow Sequence to keep density and confinement

• Strongly Peaked Density Profiles: n(0)/nped ~ 2



Task Force S1

J.Ongena

Density Peaking

• Obtained with High Field Side Pellet Injection

• But also without Pellet Injection on JET :

Tuning of gas dosing and heating

Impurity seeding in low discharges



Task Force S1

J.Ongena

• New ELM behaviour leading to reduced ELM losses at high n and high (inter ELM losses correlated with MHD, appearance of ELMs similar to Type II ELMs) :

ELM Mitigation StudiesHow to reach acceptable heat loads in the ITER divertor ?

Loss of Power due to ELMs : PELM = fELM WELM

Low n High n

• Determined by edge transport, Psep / edge parameters

• Tools : , D puff, Ar, power

• Beneficial influence of impuritiesSee also A.Loarte, EX/P1-08



Task Force S1

J.Ongena

Reduction of WELM/Wped at high density and high

• With increasing density : Reduction of WELM/Wped Reduction of (Te/Te)ped

Weak decrease of (ne/ne)ped

• ‘Minimum’ Type I ELMs found (at U = 0.5 and reduced L = 0.3) with (Te/Te)ped = 0 and WELM/Wped = 4.5%

See also A.Loarte, EX/P1-08



Task Force S1

J.Ongena

ELM mitigation with impurity seeding

Without Ar

Reduced Target Surface Temperature with Ar seeding

With Ar

During ELMs

in Between ELMs

Unique feature of impurity seeding :

Drop in base line target temperature will allow larger temperature

excursions due to ELMs before reaching ablation limit See also J.Rapp, P.Monier-Garbet, EX/P1-09



Task Force S1

J.Ongena

• Extrapolation to ITER is very different for both scalings• Raises hope for a possibility of Type I ELMs operation on ITER with

an acceptable divertor lifetime• Further work ongoing to determine the correct parameter dependence

//front : char. time for

heat front to reach the

target

Scaling of ELM size and extrapolation to ITER Correlation between ELM size and both

ped and //front

See also A.Loarte, EX/P1-08 and G.Matthews, EX/D1-1



Task Force S1

J.Ongena

Conclusions1. ITER Q=10 ELMy H-Mode Requirements reached on JET with several techniques



Task Force S1

J.Ongena

Conclusions

2. New results on ELM physics and extrapolation to ITER :

• Decrease of ELM size at high density for ITER • Further alleviation of constraints due to

ELM heat load possible with impurity seeding• Hope for a possible window for Type I ELMs operation

with an acceptable ITER divertor lifetime

JET is an excellent testbed to prepare for ITER operation



Task Force S1

J.Ongena

OUTLOOKContinue preparation for ITER Operation using new ‘tools’ at JET

New Pellet TrackITER deep fuelling

New ITER relevant Discharge Shapes

New very long divertor phase (50s) pulses

Near Double NullStudy of Type II ELMs

Plasmas with reduced disruptive forceStudy of High Current Plasmas

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.

Optimisation of pellet fuelling for ITER

Long time plasma and wall constants

NEW!



Task Force S1

J.Ongena



Task Force S1

J.Ongena

Very Long Divertor Phase Pulses On JET

Study of Long time constants in wall and plasma parameters

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.



Task Force S1

J.Ongena

2. Impurity Seeding

Aim :

Realize an integrated operational scenario combining :

• High density and high confinement

• Acceptable power exhaust

In JET : using Ar seeding in low and high discharges

Cautious D and Ar dosing



Task Force S1

J.Ongena

3. Pellet Injection from the High Field Side

• In medium triangularity discharges

• Using an optimised pellet cycle

• High densities reached while keeping high confinement

• Peaked density profiles



Task Force S1

J.Ongena

Spontaneous Density Peaking

Stationary peaked profiles : n(0)/nped ~ 1.3

• Tuning of gas dosing

(flux, position) and

plasma heating

• High and stationary

n/nGW = 1, N,th = 2 and

H98(y,2) = 1



Task Force S1

J.Ongena

Confinement and L-H Threshold

Scaling Studies on JET

• Influence of plasma shaping, density peaking and proximity to the Greenwald limit

H98(y,2),corr = H98(y,2) F

F = 0.46 + 1.35 ln(q95/qcyl) + 0.38(n/nped - 1) - 0.17n/nGW

BENEFICIAL :

Plasma Shape and Density Peaking

DETRIMENTAL :

Proximity to Greenwald limit

Effect on Confinement:

• He plasmas (purity CHe / CD = 85%) show :

Isotope scaling : E M0.19Z-0.59 (from previous H and T data + He database) L-H Power Threshold in He : same Ip Bt and mass dependence as for D

50% higher in absolute value



Task Force S1

J.Ongena

Density Peaking with Impurity Seeding

• Low plasmas ( ~ 0.3)

• High and stationary

n/nGW = 1, N,th = 2 and H98(y,2) = 1

• Peaked density profiles : n(0)/nped ~ 1.3



Task Force S1

J.Ongena

100

1000

100 200 300 400 500

JET

ASDEX-U

JT-60U

IRELM

(μ)s

IIFront(μ )s

Heat pulse delay of ELMs IR

from IR thermographic measurements

Indications for non-determining role of *,ped

)231(

2 *|||| υ +=

scL

€

|| =2L||

cs(1+ 3

2υ*)

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