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
EFDA EUROPEAN FUSION DEVELOPMENT AGREEMENT
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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
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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
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Task Force S1
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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
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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
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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
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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
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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
EFDA EUROPEAN FUSION DEVELOPMENT AGREEMENT
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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
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• 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
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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
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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
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• 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
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Conclusions1. ITER Q=10 ELMy H-Mode Requirements reached on JET with several techniques
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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
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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!
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J.Ongena
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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.
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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
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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
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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
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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
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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
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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
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