High Speed Imaging of Edge

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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, NJ 1 Los Alamos
National Lab, Los Alamos, NM 2 West Virginia
University, Morgantown, WV 3 UCSD, San Diego,
CA 4 Oak Ridge National Laboratory, Oak Ridge,
TN 5 Princeton Scientific Instruments Inc,
Monmouth Junction, NJ 6 Hiroshima University,
Hiroshima, Japan TTF Meeting, Madison Apr. 3,
2003
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Outline
Goals Fisheye view of NSTX Gas puff
imaging diagnostic GPI image and time series
analysis Summary Plans
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Goals
Understand edge turbulence by comparing
turbulence measurements 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 ?
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Fisheye View of NSTX
LANL camera, 10 µsec/frame at 1000 frames/sec no
filter (mainly D light)
Magnetic structure of edge plasma
R 85 cm a 68 cm A 1.25 I 1.5 MA B 6
kG 5 MW NBI 6 MW ICRH b? 35
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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
GPI view 16x32 cm
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Typical GPI Image
Use typically 10 µsec exposure time (tac 40
µsec) Average HeI light intensity peaked near
separatrix
PSI camera frame 80 x 160 pixels
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GPI Diagnostic Interpretation

• HeI light emission I visible where 5 eV lt
  Te lt 50 eV
• I ? neaTeb, where a 0.5 and b 0.7 near
  center of cloud,
• with 0.4 lt a lt 1 and 0 lt b lt 2 over most of
  cloud
• Space-time structure of I similar to nea, but
  dI/I a dne/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

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High Speed Imaging of NSTX Edge
CCD camera with 100,000 frames/sec at 10
µsec/frame for 28 frames/shot localized
structures can 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 dI/I and Lpol derived from 28 images
for each shot
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Poloidal Correlation Length and k-spectra
Lpol 4 cm or kpol rs 0.2 (similar to other
experiments) dI/I lower in H-mode than L-mode
(with much variation)
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Time Series of GPI Light Flucutuaions
HeI digitized over 1.5 cm diam. chords through
images Relative fluctuation level larger as R
increases ( images)
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Statistical Analysis of Typical Chords
Autocorrelation times typically 40 20 µsec
Frequency spectra broad over 0.1 - 100 kHz
Autocorrelation function
Frequency spectrum
Probability distribution function
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L-H and H-L Transitions
L -gt H in 100 µsec with obvious precursor
H -gt L in 30 µsec with outward radial pulse
1 ms
100 µs
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Slow Imaging of H-L Transition
Taken with 10 µsec exposures at 1000
frames/sec For this display, outward direction
toward lower right
H-L (105710)
L-H-L (105564)
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Motion of Coherent Structures
Track high intensity blobs over 28 frames of
movies Broad distribution of velocities and
intensities
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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
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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
(DIppolito and Myra) Compare with other
simulations
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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
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(b)
(a)
(3)
(1)
Amplitude (rel.)
(2)
Wavenumber (rel.)
(c)
(3)
(d)
(2)
(1)
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105637
dI/I (rel.)
LCFS
RMP(cm)
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x probe before puff probe during puff o GPI
during puff
Power (rel.)
Frequency (kHz)
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1 0.1 0.01 0.001 0.0001 10-5
x reflectometer before puff reflectometer
during puff o GPI during puff
Power (rel.)
Frequency (kHz)
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?n/n
?T/T
?n/n
?T/T
?n/?n
?T/?T
RMP(cm)
RMP(cm)