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High Speed Imaging of Edge Turbulence in NSTX
S.J. Zweben, R. Maqueda1, D.P. Stotler, A. Keesee2, J. Boedo3, C. Bush4, S. Kaye, B. LeBlanc, J. Lowrance5, V. Mastrocola5, R. Maingi4, N. Nishino6,
G. Renda5, D. Swain4, J. Wilgen4 and the NSTX Team
Princeton Plasma Physics Laboratory, Princeton, NJ1 Los Alamos National Lab, Los Alamos, NM2 West Virginia University, Morgantown, WV
3 UCSD, San Diego, CA4 Oak Ridge National Laboratory, Oak Ridge, TN
5 Princeton Scientific Instruments Inc, Monmouth Junction, NJ6 Hiroshima University, Hiroshima, Japan
TTF Meeting, Madison Apr. 3, 2003
Outline
• Goals
• Fisheye view of NSTX
• Gas puff imaging diagnostic
• GPI image and time series analysis
• Summary
• Plans
• Understand edge turbulence by comparing turbulencemeasurements with theory + simulation
• Explain and predict H-mode threshold and pedestal
• Explain and predict transport through SOL to wall
• Explain and predict transport of impurities into plasma
• Explain and predict density limit ?
Goals
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
Fisheye View of NSTX
LANL camera, 10 µsec/frameat 1000 frames/sec
no filter (mainly D light)
Magnetic structure of edge plasma
Gas Puff Imaging Diagnostic
• Look at He1(578.6 nm) from gas puff I none f(ne,Te)
• View along B field line to see 2-D structure B
GPIview
16x32 cm
Typical GPI Image
200
0
100
outsep.
0
40
80
120
142 144 146 148 150 152
0
10
20
30
ne/1011 cm-3
Te(eV)
n(Heo) DEGASHeI
RMP(cm)
GPI HeI
• Use typically 10 µsec exposure time (ac ≈ 40 µsec)
• Average HeI light intensity peaked near separatrix
PSI camera frame80 x 160 pixels
GPI Diagnostic Interpretation
• HeI light emission “I” visible where 5 eV < Te < 50 eV
• I neTe
where≈0.5and≈0.7near center of cloud,with 0.4 < < 1 and 0 < < 2over most of cloud
• Space-time structure of I similar to ne, but I/I ≈ ne/ne
• Fluctuation spectra of I similar to probe and reflectometer
• Fluctuation level of I consistent with TS data ( ≈10-60%)
GPI light gives approximate structure of edge turbulence
High Speed Imaging of NSTX Edge
CCD camera with100,000 frames/sec
at 10 µsec/framefor 28 frames/shot
localized structurescan move outward
at ≈ 105 cm/sec
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Profiles from Typical GPI Images
• HeI profiles narrow from OH to L-mode to H-mode
• I/I and Lpol derived from 28 images for each shot
L(cm) A(k)
I/I kpol(cm-1)0
2
4
6
8
0 0.1 0.2 0.3
OH L-mode H-mode
0.001
0.01
0.1
0.1 1 10
OHL-modeH-mode
~ noise level
Poloidal Correlation Length and k-spectra
• Lpol ≈ 4 cm or kpol s ≈ 0.2 (similar to other experiments)
• I/I lower in H-mode than L-mode (with much variation)
0
2
4
6
8
0 0.1 0.2 0.3
OH L-mode H-mode
0.001
0.01
0.1
0.1 1 10
OHL-modeH-mode
~ noise level
Time (sec)
Time Series of GPI Light Flucutuaions
• HeI digitized over 1.5 cm diam. chords through images• Relative fluctuation level larger as R increases (≈ images)
Statistical Analysis of Typical Chords
• Autocorrelation times typically 40 ± 20 µsec• Frequency spectra broad over ≈ 0.1 - 100 kHz
Autocorrelationfunction
Frequencyspectrum
Probabilitydistribution
function
L-H and H-L Transitions
• L -> H in ≈ 100 µsec with obvious precursor• H -> L in 30 µsec with outward radial pulse
100 µs1 ms
Slow Imaging of H-L Transition
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H-L (#105710)
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L-H-L (#105564)
• Taken with 10 µsec exposures at 1000 frames/sec• For this display, outward direction toward lower right
Motion of Coherent Structures• Track high intensity “blobs” over 28 frames of movies• Broad distribution of velocities and intensities
Summary of Results So Far
• Images consistent with previous measurements- large fluctuation level in edge- broad frequency and k-spectrum- approx. isotropic structure B
• Coherent structures seem to move through edge- “blob- like” look similar to DIII-D IPOs- “wave-like” look similar to EDA, QCM
• H-mode generally more quiescent than L-mode- considerable variation in behavior- transitions can happen very fast
Plans for Comparison with Theory
Using DEGAS-2 or related atomic physics models:
• Compare GPI with BOUT simulations for H- and L-mode (Xu and Nevins)
• Compare motion of GPI “blobs” with blob model (D’Ippolito and Myra)
• Compare with other simulations…
Plans for Additional Measurements
• Capture H-mode transition with high speed camera
• Get better data on zonal flows in images and chords
• Examine turbulence nearer density limit
• Look during RF heating, e.g. co- vs. ctr. current drive
• Make systematic scans of q(a), rotation, Zeff, etc.
• Make quantitative comparisons with other diagnostics
-1
0
1
2
3
4
5
6
142 144 146 148 150 152
RMP(cm)
HeI (rel.)
Alp
ha
0.6
0.8
1
1.2
1.4
1.6
-2 -1 0 1 2 3 4
Cor
rela
tion
len
gth
(re
l.)
Alpha
0
0.2
0.4
0.6
0.8
1
-3 -2 -1 0 1 2 3 4 5
Flu
ctua
tion
leve
l (re
l.)
Alpha
(1)
(2)
(3)
Am
plitu
de (
rel.)
Wavenumber (rel.)
(a) (b)
(c) (d)(3)
(2)
(1)
RMP(cm)
I/I (rel.)
LCFS
#105637
0
0.2
0.4
0.6
0.8
1
136 140 144 148 152
0.2 sec0.165 sec
10-5
0.0001
0.001
0.01
0.1
1
0 20 40 60 80 100
Frequency (kHz)
x probe before puff• probe during puffo GPI during puff
Pow
er (
rel.)
0 20 40 60 80 100
Frequency (kHz)
x reflectometer before puff• reflectometer during puffo GPI during puff
1
0.1
0.01
0.001
0.0001
10-5
Pow
er (
rel.)
0
2
4
6
8
10
142 144 146 148 150 152
0
0.2
0.4
0.6
0.8
10
0.2
0.4
0.6
0.8
1
0
2
4
6
8
10
142 144 146 148 150 152
0
0.2
0.4
0.6
0.8
10
0.2
0.4
0.6
0.8
1
RMP(cm) RMP(cm)
n/n
n/n
n/n
T/T
T/T
T/T