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Evolution of the Turbulence Radial Wavenumber Spectrum near the L-H Transition in NSTX Ohmic Discharges

Abstract

Full text: The measurement of radially extended meso-scale structures such as zonal flows and streamers, as well as the underlying microinstabilities driving them, is critical for understanding turbulence-driven transport in plasma devices. In particular, the shape and evolution of the radial wavenumber spectrum indicate details of the nonlinear spectral energy transfer, the spreading of turbulence, as well as the formation of transport barriers. In the National Spherical Torus Experiment (NSTX), the FMCW backscattering diagnostic is used to probe the turbulence radial wavenumber spectrum (k{sub r} = 0 - 22 cm-1 ) across the outboard minor radius near the L- to H-mode transition in Ohmic discharges. During the L-mode phase, a broad spectral component (k{sub r} {approx} 2 - 10 cm{sup -1} ) extends over a significant portion of the edge-core from R = 120 to 155 cm ({rho} = 0.4 - 0.95). At the L-H transition, turbulence is quenched across the measurable k{sub r} range at the ETB location, where the radial correlation length drops from {approx} 1.5 - 0.5 cm. The k{sub r} spectrum away from the ETB location is modified on a time scale of tens of microseconds, indicating that nonlocal turbulence dynamics are playing a strong role.  More>>
Authors:
Kubota, S.; Peebles, W.A., E-mail: skubota@ucla.edu; [1]  Bush, C. E.; Maingi, R.; [2]  Zweben, S. J.; Bell, R.; Crocker, N.; Diallo, A.; Kaye, S.; LeBlanc, B. P.; Park, J. K.; Ren, Y.; [3]  Maqueda, R. J.; [4]  Raman, R. [5] 
  1. UCLA, Los Angeles (United States)
  2. Oak Ridge National Laboratory, Oak Ridge (United States)
  3. Princeton Plasma Physics Laboratory, Princeton University, Princeton (United States)
  4. Nova Photonics, Princeton (United States)
  5. University of Washington, Seattle (United States)
Publication Date:
Sep 15, 2012
Product Type:
Conference
Report Number:
IAEA-CN-197; EX/P7-21
Resource Relation:
Conference: FEC 2012: 24. IAEA Fusion Energy Conference, San Diego, CA (United States), 8-13 Oct 2012; Other Information: 5 refs.; Related Information: In: 24. IAEA Fusion Energy Conference. Programme and Book of Abstracts| 789 p.
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BACKSCATTERING; ELECTRIC DISCHARGES; ENERGY TRANSFER; H-MODE PLASMA CONFINEMENT; L-MODE PLASMA CONFINEMENT; NONLINEAR PROBLEMS; NSTX DEVICE; OSCILLATIONS; PLASMA DENSITY; QUENCHING; SPECTRA; TURBULENCE
OSTI ID:
22109903
Research Organizations:
International Atomic Energy Agency, Vienna (Austria)
Country of Origin:
IAEA
Language:
English
Contract Number:
Contract DE-FG02-99-ER54527; DE-AC02-09CH11466
Other Identifying Numbers:
TRN: XA13S0311067560
Availability:
Available from INIS in electronic form. Also available on-line: http://www-pub.iaea.org/MTCD/Meetings/PDFplus/2012/cn197/cn197_Programme.pdf
Submitting Site:
INIS
Size:
page(s) 249
Announcement Date:
Jul 04, 2013

Citation Formats

Kubota, S., Peebles, W.A., E-mail: skubota@ucla.edu, Bush, C. E., Maingi, R., Zweben, S. J., Bell, R., Crocker, N., Diallo, A., Kaye, S., LeBlanc, B. P., Park, J. K., Ren, Y., Maqueda, R. J., and Raman, R. Evolution of the Turbulence Radial Wavenumber Spectrum near the L-H Transition in NSTX Ohmic Discharges. IAEA: N. p., 2012. Web.
Kubota, S., Peebles, W.A., E-mail: skubota@ucla.edu, Bush, C. E., Maingi, R., Zweben, S. J., Bell, R., Crocker, N., Diallo, A., Kaye, S., LeBlanc, B. P., Park, J. K., Ren, Y., Maqueda, R. J., & Raman, R. Evolution of the Turbulence Radial Wavenumber Spectrum near the L-H Transition in NSTX Ohmic Discharges. IAEA.
Kubota, S., Peebles, W.A., E-mail: skubota@ucla.edu, Bush, C. E., Maingi, R., Zweben, S. J., Bell, R., Crocker, N., Diallo, A., Kaye, S., LeBlanc, B. P., Park, J. K., Ren, Y., Maqueda, R. J., and Raman, R. 2012. "Evolution of the Turbulence Radial Wavenumber Spectrum near the L-H Transition in NSTX Ohmic Discharges." IAEA.
@misc{etde_22109903,
title = {Evolution of the Turbulence Radial Wavenumber Spectrum near the L-H Transition in NSTX Ohmic Discharges}
author = {Kubota, S., Peebles, W.A., E-mail: skubota@ucla.edu, Bush, C. E., Maingi, R., Zweben, S. J., Bell, R., Crocker, N., Diallo, A., Kaye, S., LeBlanc, B. P., Park, J. K., Ren, Y., Maqueda, R. J., and Raman, R.}
abstractNote = {Full text: The measurement of radially extended meso-scale structures such as zonal flows and streamers, as well as the underlying microinstabilities driving them, is critical for understanding turbulence-driven transport in plasma devices. In particular, the shape and evolution of the radial wavenumber spectrum indicate details of the nonlinear spectral energy transfer, the spreading of turbulence, as well as the formation of transport barriers. In the National Spherical Torus Experiment (NSTX), the FMCW backscattering diagnostic is used to probe the turbulence radial wavenumber spectrum (k{sub r} = 0 - 22 cm-1 ) across the outboard minor radius near the L- to H-mode transition in Ohmic discharges. During the L-mode phase, a broad spectral component (k{sub r} {approx} 2 - 10 cm{sup -1} ) extends over a significant portion of the edge-core from R = 120 to 155 cm ({rho} = 0.4 - 0.95). At the L-H transition, turbulence is quenched across the measurable k{sub r} range at the ETB location, where the radial correlation length drops from {approx} 1.5 - 0.5 cm. The k{sub r} spectrum away from the ETB location is modified on a time scale of tens of microseconds, indicating that nonlocal turbulence dynamics are playing a strong role. Close to the L-H transition, oscillations in the density gradient and edge turbulence quenching become highly correlated. These oscillations are also present in Ohmic discharges without an L-H transition, but are far less frequent. Similar behavior is also seen near the L-H transition in NB-heated discharges. (author)}
place = {IAEA}
year = {2012}
month = {Sep}
}