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XP-839: Poloidal extent and distribution of edge turbulence and intermittency

XP-839: Poloidal extent and distribution of edge turbulence and intermittency R. J. Maqueda (Nova Photonics) NSTX Edge Team. LFS vs HFS turbulence and blobs: What is the level of turbulence (and intermittency) observed in the HFS compared with the LFS?

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XP-839: Poloidal extent and distribution of edge turbulence and intermittency

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  1. XP-839: Poloidal extent and distribution of edge turbulence and intermittency R. J. Maqueda (Nova Photonics)NSTX Edge Team • LFS vs HFS turbulence and blobs: What is the level of turbulence (and intermittency) observed in the HFS compared with the LFS? • LFS vs Divertor (top view): At what flux surface is the correlation between LFS midplane blobs and divertor blob footprints lost? • LFS vs Divertor (tangential view): What are the characteristics of the turbulence near the X-point and private flux regions? Due to limited run time, scope reduced to points 2 and 3 XP review, PPPL, June 26, 2008

  2. X-point geometry effects • Flux tube stretching near X-point may cause the blob (turbulence) scale length to be less than ion gyro-radius (R. Cohen, D. Ryutov, et al.): • - “x-point disconnection”- possibility of inducing turbulence below the X-point, without degrading midplane (R. Cohen, NF 37, p. 621, 1997). • Is intermittency (i.e. blobs) seen in the divertor region? • Yes • What is the relation to midplane turbulence/blobs? • They are the same… • Then: - Is there “x-point disconnection”? - What are the characteristics of intrinsic X- point and private flux region turbulence (blobs?)

  3. Circular flux tube (3 cm diam.) mapped to bottom divertor target plates. Ro = 1427.2 mm, Zo = 184.7 mm

  4. Circular flux tube (3 cm diam.) mapped to bottom divertor target plates. Ro = 1454.9 mm, Zo = 188.6 mm

  5. Circular flux tube (3 cm diam.) mapped to bottom divertor target plates. Ro = 1494.5 mm, Zo = 194.1 mm

  6. Bottom divertor footprint Bay E Top view of bottom divertor LiI filter • Movement of footprint agrees with that expected for midplane blobs.

  7. Blobs in the divertor region Good correlation between midplane intermittency and divertor intermittency (CGPI-Div ~0.76) • Extended region of good correlation. • Location of best correlation close to where expected. • Movement of footprint agrees with that expected for midplane blobs. 124819 Lower divertor Midplane GPI Correlation to midplane Image intensity (a.u.) Time (s)

  8. Blobs in the divertor region (cont.) Intermittency observed on divertor target plates • Profiles consistent with midplane measurements with GPI. • RMS fluctuation level, skewness and kurtosis increase away from outer strike point. RMS fluctuations Image intensity (a.u.) CHI gap Outer strike point Skewness Kurtosis Shot 124819 124819 R (m) R (m)

  9. Blobs in the divertor region (cont.) Region of “good” correlation seen down to yN ~1.03 Maximum correlation as function of R, mapped to yN 124819 • Caveat: 2007 data available only for extreme k, d shots Shot 124819 Random coincidences New divertor gas puff

  10. XP-839: Run plan(1/2 day) • Reproduce previously developed shots (this year) with different X-point topologies:- 6 different shots- repeat shots 2-3 times • Image lower divertor from top (LiI filter)+Image lower divertor tangentially (HeI filter)(Helium puff in new lower divertor Bay E puffer)+ Gas puff imaging

  11. Shot #1 Shot #2 1 MA, 5.5 kG, 6 MW NBI 1 MA, 5.5 kG, 6 MW NBI Helium puff

  12. Shot #3 Shot #4 1 MA, 5.5 kG, 6 MW NBI 1 MA, 5.5 kG, 6 MW NBI Helium puff

  13. Shot #5 Shot #6 0.8 kA, 4.5 kG, 4 MW NBI 0.9 kA, 4.5 kG, 4 MW NBI Helium puff

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