alcator c-moditg growth rate profiles 0.00 0.05 0.10 0.15 0.20 0.25 02 15 28 42 55 68 82 rho mrad/s...
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Internal Transport Barriers in Alcator C-ModCatherine Fiore
MIT Plasma Science and Fusion CenterAPS-DPP
November 14, 2007Orlando, Fl
With Contributions from:W. L. Rowan†, A. Dominguez, A. E. Hubbard , A. Ince-Cushman, M. J.
Greenwald, L. Lin, E.S. Marmar , M. Reinke, J. E. Rice, K. Zhurovich£, MIT-PSFC, †FRC-UTA, £Goldman Sachs
Supported by US DoE
C-ModAlcator
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What’s New:• Gyrokinetic stability study at ITB onset• Improved ion temperature profile
measurements• Localization of fluctuation measurements• Ohmic H-mode ITBs
Introduction: ITBs in Alcator C-Mod
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Internal Transport Barriers (ITBs) in C-Mod arise from steady H-mode plasmas lasting 2 or more energy confinement times when the central power input is low: they are seen in both Ohmic and Off-axis heated ICRF plasmas
Features of C-Mod ITBs
t=0.8 st=0.9 s H-mode
t=1.1 st=1.0 s
Transitionto ITB
t=1.3 st=1.2 s
ITBProfiles peak
Major Radius (m)0.65 0.70 0.75 0.80 0.85 0.90
2
4
6
8
10
12
n s
qrt(Z
) (1
0
/m
)e
eff
203
ITb foot position
Divertor
Molytiles
Alcator C-Mod
RFantenna
fci min
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C-Mod plasmas are a unique platform for ITB study:– No particle or momentum input– Monotonic q profiles– Collisionally coupled ions and electrons with Ti ≈Te
Reduction in particle and thermal transport in the barrier region and core allows the Ware pinch to dominate the transport. This results in strongly peaked pressure and density profiles. Ion thermal transport is reduced to neoclassical
Control of particle and impurity accumulation is achieved through application of central ICRF heating: TEM stability plays a role.Ernst, IAEA 2004, 2006
Features of C-Mod ITBs
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Increasing magnetic field moves ICRF resonance off-axis on low field side. ITBs form when Bt > 6.2 T.
R/LTe decreases in the regionnear the ITB foot at the time of
onset.
The region of stability to ITG modes widens with increasing magnetic field.
K. Zhurovich, et al, NP8.00073K. Zhurovich et al 2007 Nucl. Fusion 47 1220-1231
ITBR/L
Te
5.4 5.6 5.8 6.0 6.46.2Toroidal Field (T)
12
0
4
8 R=0.80 m(barrier foot)
ITBR/L
Te
5.4 5.6 5.8 6.0 6.46.2Toroidal Field (T)
0
4
8 R=0.78 m(near barrier foot,inside)
ITG growth rate profiles
0.000.050.100.150.200.25
0.02
0.15
0.28
0.42
0.55
0.68
0.82
rho
Mra
d/s 5.6 T
5.8 T6.0 T6.2 T6.3 T
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Upgraded high resolution x-ray spectrometer measurement of Ti profile shows barrier in temperature during ITB
Excellent agreement is found between Ti from HIREX, central Ti from neutrons, and Te from Thomson Scattering.
•A temperature barrier was found previously with sawtooth heat pulse measurements and inferred from pressure profile increase•Ion temperature profile from HIREX confirms Ti transport barrier.See: Ince-Cushman, P03.00014, this session
Hill, NP8.00080Bitter, NP8.00084
0.70 0.75 0.80 0.85Major radius (m)
0.0
0.5
1.0
1.5
2.0
Ti,T
e (k
ev)
Ti, HIREX
Te, Thomson ScatteringTi, Neutron Inversion
ITB footregion
t=0.71 s, pre ITB
t=0.85, transition to ITB
t=1.09, ITB
Off-Axis ICRF ITB
0.4 0.6 0.8 1.0 1.2 1.4 1.6t (s)
0.0
0.5
1.0
1.5
2.0
T ,T
(k
ev)
Ti, HIREX
Te, Thomson ScatteringTi, Neutron Inversion
Off-axis ICRF ITB
ei
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Normalized temperature gradients (R/LTi) are obtained from high resolution x-ray spectrometer ion
temperature profiles
R/LTi increases from the center, with a drop at larger radius after ITB is established.
R/LTi in outer channels increases with time as ITB grows in the barrier region.
0.0 0.2 0.4 0.6 0.8r/a
0
5
10
15
R/L T
i
t=0.71 H-mode
t=0.85 s, transition to ITB
t=1.09 s. ITB
0.6 0.8 1.0 1.2time (s)
0
5
10
15
R/L
Ti
Normalized T Gradient fromHigh Resolution X-ray Spectrometer
r/a=0.39
r/a=0.58
H-mode
ITB
i
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Fluctuations arising during ITB density peaking have been identified as TEM mode
PCI was configured to preferentially view half of the plasma
The fluctuations in 20-60 kHz propagate in the electron diamagnetic direction
pci Fluctuations
20
40
60
80
100
Freq
(kH
z)
0.00.10.20.30.4
0.9 1.0 1.1 1.2 1.3 1.40.9 1.0 1.1 1.2 1.3 1.4
20
40
60
80
100
1.5
2.0
2.5
2.0
time (s)
density peaking
0.9 1.0 1.1 1.2 1.3 1.40.9 1.0 1.1 1.2 1.3 1.4
ITB
B
PCI:TEM(GS2):QC
TEM-like
-1
shot:1070831021shot:1070831021shot:1070831021t:[1.04,1.10]st:[1.04,1.10]sf:[20,60]kHzf:[20,60]kHz
directione
Aut
o po
wer
[a.u
.]
Wavenumber [cm ]
See Lin, NP8.00076
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Density peaking in an ITB begins shortly after an EDA H-mode develops for both Ohmic and Off-Axis ICRF ITBs
Electron Density, Shot 1070628019
0.8 0.9 1.0 1.1 1.2 1.30.70
0.75
0.80
0.85
0.90
Rm
id, m
0 2•1020 4•1020 6•1020
t (s)
Electron Density, Shot 1070831024
0.2 0.4 0.6 0.8 1.0 1.2 1.4
0.75
0.80
0.85
0.90
Rm
id, m
0 1•1020
2•1020
3•1020
t (s)
0.65 0.70 0.75 0.80 0.85 0.90Major Radius (m)
1
2
3
4
0
Den
sity
(10
/m
)
203
Off-Axis ICRF Heated ITB
t=1.29 s ITB
t=0.79 s L-mode
t=0.89 s H-mode
0.65 0.70 0.75 0.80 0.85 0.90Major Radius (m)
Ohmic H-Mode ITB
1
2
3
4
5
0
Den
sity
(10
/m
)
203
t=1.14 st=1.04 s
} ITB
t=0.79 s L-mode
t=0.89 s H-mode
Density contour plot shows that the peaking time and intensity are similar
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Thermal transport characteristics are similar for off-axis RF induced and Ohmic H-mode ITBs
m
/sec
2
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.6 0.8 1.0 1.2 1.4
χeff
t (s)
L-H transition
ITB
Off-axis ICRF ITB
r/a0.6
0.2
m
/sec
2
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.6 0.8 1.0 1.2 1.4
χeff
t (s)
Ohmic
L-H transition
ITB
Back transition
r/a
0.60.2
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R/LT appears to have different trend in Ohmic H-mode ITB than in off-axis ICRF ITB
0.8 1.0 1.2 1.4
10
5
0time (s)
R/L
Ti
Off-axis ICRF ITB, Transp
0.6
15
0.6 0.8 1.0 1.2 1.4
108
64
2
0
time (s)
R/L
TiOhmic H-mode ITB, Transp
0.8 1.0 1.2 1.4
5
0
time (s)
R/L
Te
Off-axis ICRF ITB, Transp15
0.6
10
ITB
ITB
ITB
H-mode
H-mode
H-mode
0.20.4
0.6
r/a
0.8 1.0 1.2 1.4time (s)
R/L
Te
Ohmic H-mode ITB, Transp
0.6
10
5
0
15ITB
H-mode
0.20.4
0.6
r/a
0.20.4
0.6
r/a
0.2
0.40.6r/a
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ConclusionsNon-linear gyrokinetic modeling shows that broadening of the temperature profile with off-axis ICRF injection increases the size of the core-stable region of the plasma, reducing the outgoing particle flux, allowing Ware pinch to dominate particle transport.
Improved temperature profiles establish that a thermal barrier exists at or near the particle barrier seen in the density profile. These profiles will improve data for stability analysis.
Density fluctuations that arise and strengthen during ITB growthpropagate in the electron direction and are consistent with TEM characteristics.
ITBs arising in Ohmic H-mode plasmas appear identical to those forming in off-axis ICRF heated cases, except for trends in R/LT. Stability analysis is needed.