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

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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

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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

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OHL-modeH-mode

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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)

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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

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LCFS

#105637

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Frequency (kHz)

x probe before puff• probe during puffo GPI during puff

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x reflectometer before puff• reflectometer during puffo GPI during puff

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