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Carine Giroud 3 21st IAEA Fusion Energy, Chengdu Content Observation of anomalous impurity transport at JET – Reduction of Nickel peaking by electron heating Brief description of recent development in the turbulent transport theory Comparison of experiment with theoretical predictions – A transition of the dominant instability driving the transport could explain the difference in Nickel peaking – Experimental test of Z dependence predicted by turbulent transport theory
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Carine Giroud 1 21st IAEA Fusion Energy, Chengdu 16.10.2006
Carine Giroud 1 IAEA, Chengdu 16.11.2006
Progress in understanding impurity transport at JET
C. Giroud1,
C. Angioni2, G. Bonheure3, I. Coffey4, N. Dubuit5, X. Garbet5, R. Guirlet5, P. Mantica6, V. Naulin7, M.E. Puiatti8, M. Valisa8,
A.D. Whiteford9, K-D. Zastrow1, M.N.A. Beurskens1, M. Brix1,E. de la Luna10, K. Lawson1, L. Lauro-Taroni8, A. Meigs1,
M. O’Mullane9, T. Parisot5, C. Perez von Thun1, O. Zimmermann11 and the JET-EFDA Contributors.
1 2 3 4 5
6 7 108 9 11
Carine Giroud 2 21st IAEA Fusion Energy, Chengdu 16.10.2006
• Within ITB region:Transport can be close to neoclassical predictions
Rest plasma regionInward velocity V~Vneo Impurity D >> DneoIter physics group NF 99
• Inside core region W accumulation observed with peaked density profile without central wave heating in ASDEX
• Global observation:plasma with peaked density are prone to accumulation of highly charged impurities
Picture of impurity transport in present devices
Carine Giroud 3 21st IAEA Fusion Energy, Chengdu 16.10.2006
Content
• Observation of anomalous impurity transport at JET– Reduction of Nickel peaking by electron heating
• Brief description of recent development in the turbulent transport theory
• Comparison of experiment with theoretical predictions– A transition of the dominant instability driving the transport could explain the difference in Nickel peaking– Experimental test of Z dependence predicted by turbulent transport theory
Carine Giroud 4 21st IAEA Fusion Energy, Chengdu 16.10.2006
• Linear relationship assumed between impurity flux and density gradient
• In steady-state conditions and with edge source the local impurity density gradient length:
Experimental determination of transport coefficients
zzzz VnDΓ
rnz
z
z
z
z
DV-
rnn0
z
z
DVR-
Diffusion coefficient
Convection coefficientVz >0 outwards
Peaking factor
R major radius device
Carine Giroud 5 21st IAEA Fusion Energy, Chengdu 16.10.2006
Experimental determination of transport coefficients
• Intrinsic impurities such as C: direct measurement of density profile
– measured density gradient determines –RV/D
• Extrinsic impurities injected by laser ablation (Ni) or gas injection (Ne, Ar).
− D and V determined individually by modelling of time evolution of spectroscopic data
− Ni: soft x-ray and VUV − Ne and Ar: soft x-ray and VUV and also from charge exchange spectroscopy
Carine Giroud 6 21st IAEA Fusion Energy, Chengdu 16.10.2006
Effect of electron heating on Ni transport
#58144, dominant ion#58149, dominant electron
• Two similar ELMy H-modes:
• Two heating schemes:
•Different gradient lengths:
[M-E. Puiatti PoP 13 2006]
q0>10.1 <eff <0.2 (low collisionality) Bt=3.28T, q95=5.9, 3MW ICRH, 12-14MW NBI
ICRH dominant ion heating: 8 % 3HeICRH dominant electron heating: 20% 3He
Density gradient length R/LnTe gradient length R/LTeTemperature ratio Te/Ti Ti gradient length R/LTi
3.94
0.956.6
5.261
6.6
Carine Giroud 7 21st IAEA Fusion Energy, Chengdu 16.10.2006
Two very different Ni profiles
ICRH dominant ion heatingPeaked Ni profile
ICRH dominant electronSlightly hollow Ni profile
[M-E. Puiatti PoP 13 2006]Steady-state profile calculated from D and V
Carine Giroud 8 21st IAEA Fusion Energy, Chengdu 16.10.2006
Due to change in Ni transport
[M-E. Puiatti PoP 13 2006]
– Diffusion increased in centre– Convection reversed at mid-radius
While neoclassical transport unchanged
Reduction in Ni peaking due to anomalous transport
Neoclassical x10
ICRH dominant ion heating
ICRH dominant electron heating
Measurement
Carine Giroud 9 21st IAEA Fusion Energy, Chengdu 16.10.2006
Recent development in turbulent transport theory
• Two main electrostatic micro-instability considered ITG/TEM
Microinstability Ion temperature gradient ITG
Trapped electron mode TEM
Direction of propagation
Ion diamagnetic
Electron diamagnetic
Destabilised by R/LTi R/LTe & R/Ln
Carine Giroud 10 21st IAEA Fusion Energy, Chengdu 16.10.2006
Recent development in turbulent transport theory
• Three main mechanisms have been identified
Curvature pinch1 Compressibility of ExB drift velocity
Independent on Z and A
Thermodiffusion pinch2
Compression of the diamagnetic drift velocity
Dependent of 1/Z
Pinch connected to the parallel dynamics of the impurity3
Compression of parallel velocity fluctuations produced along the field line by the fluctuating electrostatic potential
Dependent on Z/ATzTz
2[X. Garbet PoP 12 2005]2,3[C. Angioni C PRL. 96 2006]
1[J. Weiland NF 29 1989]1[X. Garbet PRL 91 2003]1[M. B. Isichenko PRL 1996]
1[D.R. Baker PoP 5 1998]1[V. Naulin Phys Rev. E 2005]2[M. Frojdh NF 32 1992]
Carine Giroud 11 21st IAEA Fusion Energy, Chengdu 16.10.2006
Pinch mechanisms in theory of turbulent impurity transport
All contribute to the total turbulent pinch
propagation: ITG ion diamagnetic direction TEM electron diamagnetic direction
Carine Giroud 12 21st IAEA Fusion Energy, Chengdu 16.10.2006
Illustration of complex Z dependence of turbulent transport
• D and V calculated with the linear version of the gyrokinetic code GS2: - trace impurity considered.- only the fastest growing mode is taken in the quasi–linear model- no neoclassical transport included.
• Complex trend in Z of turbulent transport
specific calculation needed for studied discharge
GS2 [R/LTi=7, R/LTe=6, Te/Ti=0.88]
[C. Angioni]
Carine Giroud 13 21st IAEA Fusion Energy, Chengdu 16.10.2006
Peaked Ni profileICRH dominant ion
Slightly hollow Ni profile ICRH dominant electron
[M-E. Puiatti PoP 13 2006]
R/Ln=3.9R/LTe=4
Te/Ti=0.95R/LTi=6.6
R/Ln=5.2R/LTe=6.Te/Ti=1.
R/LTi=6.6
Different dominant instability for peaked and flat Ni density
ITG dominated TEM dominatedGS2
Steady-state profile calculated from D and V
Carine Giroud 14 21st IAEA Fusion Energy, Chengdu 16.10.2006
Ni pinch reversal found for a ITG to R/LTe driven TEM transition
[C. Angioni PRL. 96 2006][M-E. Puiatti PoP 13 2006]
• Investigate transition from ITG to R/LTe driven TEM– Stabilised R/Ln driven TEM: R/Ln=2.– gradually decreasing R/LTi towards stabilisation of ITG modes.
• Reproduce a pinch reversal as observed experimentally
Real
freq
uenc
y of
mos
t un
stab
le m
ode
(cs/R
)
ITG
TEM
V<0V>0
Te/Ti=0.95, R/Ln=2
Carine Giroud 15 21st IAEA Fusion Energy, Chengdu 16.10.2006
First results on measured Z dependence of impurity peaking
#66134
Neoclassic
measure-ment
measure-ment
Neoclassic
r/a =0.15
r/a =0.55
Negative C peakingHollow profile
Peaking lower than neoclassical
Stronger Z dependence of peakingin core than at mid-radius
• Ne, Ar and Ni injected in ELMy H-modeq0>1, 0.1 <eff <0.2Bt=2.9T, q95=7, 2MW ICRH, 8.6MW NBI
Carine Giroud 16 21st IAEA Fusion Energy, Chengdu 16.10.2006
GS2 peaking in same range as measurements
GS2
Anomalous part:-R(V-Vneo)/(D-Dneo)
GS2 w/o Thermodiffusion
Discharge ITG dominatedR/LTi~5.8, R/LTe~6.3, R/Ln~0.3 and Te/Ti~1.1, *~0.10
GS2
Measurement
Neoclassic
Carine Giroud 17 21st IAEA Fusion Energy, Chengdu 16.10.2006
Summary
• JET experiments confirm earlier observations that neoclassical transport is not sufficient to describe impurity transport in bulk plasma
• First comparison between turbulent impurity transport theory and experiments show encouraging results:− A transition in the dominant instability driving the transport could explain the observed reversal of Ni convection− Same range of peaking as calculated by linear gyrokinetic calculation are measured : no strong increase of V/D as a function of Z. Turbulent transport could give the means for controlling heavy impurity peaking in ITER
• JET is set out to systematically compare theoretical predictions with experiment in coming campaign using JET upgraded CXRS capability..
Carine Giroud 18 21st IAEA Fusion Energy, Chengdu 16.10.2006
Spare slides
Carine Giroud 19 21st IAEA Fusion Energy, Chengdu 16.10.2006
Reduction of Ni peaking calculated with linear GS2
Condition for discharge with peaked Ni densities
• For increasing R/Ln and R/LTe– reduction of peaking calculated
Condition for discharge with flat Ni densities
Transition from ITG to R/Ln driven TEMReduction of the pinch predicted but
no reversal of the pinch[M-E. Puiatti PoP 2006]
Carine Giroud 20 21st IAEA Fusion Energy, Chengdu 16.10.2006
58143 58149
58142 58144 58141
LBO Data : inverted SXR emissivity profiles.
slower penetration and more peaked profiles
MC
MH
time [s]
Carine Giroud 21 21st IAEA Fusion Energy, Chengdu 16.10.2006
Simulation: line & SXR brightnessess
MH
MCno
rm. b
right
ness
Solid: experimental; dashed:simulation
(core)
(edge)
(core)
(edge)
Carine Giroud 22 21st IAEA Fusion Energy, Chengdu 16.10.2006
Effect of electron heating on Ni transport
Pio
ns (M
W.m
-3)
#58144 #58149 • two similar discharges– q0>1– low collisionality 0.1 <eff <0.2
– 2 ICRH heating schemes were applied
dominant ion heating: 8 % 3He conc. dominant electron heating: 20% 3HeBt=3.28T, q95=?, 3MW ICRH, 12-14MW NBI
• Ni transport probed
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