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Title: Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence

Abstract

The first systematic investigation of core electron thermal transport and the role of local ion temperature gradient/trapped electron mode/electron temperature gradient (ITG/TEM/ETG)-scale core turbulence is performed in high temperature, low collisionality H-mode plasmas in the DIII-D tokamak. Wavenumber spectra of L-mode and H-mode density turbulence are measured by Doppler backscattering. H-mode wavenumber spectra are directly contrasted for the first time with nonlinear gyrokinetic simulation results. Core ITG/TEM-scale turbulence is substantially reduced/suppressed by E × B shear promptly after the L–H transition, resulting in reduced electron thermal transport across the entire minor radius. For small kθρs, both experiment and nonlinear gyrokinetic simulations using the GYRO code show density fluctuation levels increasing with kθρs in H-mode (r/a = 0.6), in contrast to ITG/TEM-dominated L-mode plasmas. GYRO simulations also indicate that a significant portion of the remaining H-mode electron heat flux results directly from residual intermediate/short-scale TEM/ETG turbulence. Electron transport at substantially increased electron-to-ion temperature ratio (Te/Ti ≥ 1, r/a ≤ 0.35) has been investigated in ECH-assisted, quiescent H-mode plasmas. A synergistic increase in core electron and ion thermal diffusivity (normalized to the gyro-Bohm diffusivity) is found with applied ECH. From linear stability analysis, the TEM mode is expected to become the dominantmore » linear instability with ECH due to increased electron-to-ion temperature ratio and a reduction in the ion temperature gradient. This is consistent with increased electron temperature fluctuations and core electron thermal diffusivity observed experimentally. The reduced ion temperature gradient likely results from a reduction in the ITG critical gradient due to increased Te/Ti and reduced E × B shear. These studies are performed at collisonality ( \nu_{\rm e}^\ast \sim 0.05 , r/a ≤ 0.6) and address transport in electron heat-dominated regimes, thought to be important in ITER due to α-particle heating.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); UT-Battelle LLC/ORNL, Oak Ridge, TN (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); General Atomics, San Diego, CA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of California, San Diego, CA (United States); Univ. of California, Los Angeles, CA (United States); Univ. of Wisconsin, Madison, WI (United States); Univ. of Texas, Austin, TX (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1564873
DOE Contract Number:  
AC05-00OR22725; AC52-07NA27344; FC02-04ER54698; FC02-93ER54186; FG02-07ER54917; FG02-08ER54984; FG02-08ER54999; FG02-89ER53296; FG03-97ER54415
Resource Type:
Journal Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 52; Journal Issue: 2; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
Physics

Citation Formats

Schmitz, L., Holland, C., Rhodes, T. L., Wang, G., Zeng, L., White, A. E., Hillesheim, J. C., Peebles, W. A., Smith, S. P., Prater, R., McKee, G. R., Yan, Z., Solomon, W. M., Burrell, K. H., Holcomb, C. T., Doyle, E. J., DeBoo, J. C., Austin, M. E., deGrassie, J. S., and Petty, C. C. Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence. United States: N. p., 2012. Web. doi:10.1088/0029-5515/52/2/023003.
Schmitz, L., Holland, C., Rhodes, T. L., Wang, G., Zeng, L., White, A. E., Hillesheim, J. C., Peebles, W. A., Smith, S. P., Prater, R., McKee, G. R., Yan, Z., Solomon, W. M., Burrell, K. H., Holcomb, C. T., Doyle, E. J., DeBoo, J. C., Austin, M. E., deGrassie, J. S., & Petty, C. C. Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence. United States. https://doi.org/10.1088/0029-5515/52/2/023003
Schmitz, L., Holland, C., Rhodes, T. L., Wang, G., Zeng, L., White, A. E., Hillesheim, J. C., Peebles, W. A., Smith, S. P., Prater, R., McKee, G. R., Yan, Z., Solomon, W. M., Burrell, K. H., Holcomb, C. T., Doyle, E. J., DeBoo, J. C., Austin, M. E., deGrassie, J. S., and Petty, C. C. 2012. "Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence". United States. https://doi.org/10.1088/0029-5515/52/2/023003.
@article{osti_1564873,
title = {Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence},
author = {Schmitz, L. and Holland, C. and Rhodes, T. L. and Wang, G. and Zeng, L. and White, A. E. and Hillesheim, J. C. and Peebles, W. A. and Smith, S. P. and Prater, R. and McKee, G. R. and Yan, Z. and Solomon, W. M. and Burrell, K. H. and Holcomb, C. T. and Doyle, E. J. and DeBoo, J. C. and Austin, M. E. and deGrassie, J. S. and Petty, C. C.},
abstractNote = {The first systematic investigation of core electron thermal transport and the role of local ion temperature gradient/trapped electron mode/electron temperature gradient (ITG/TEM/ETG)-scale core turbulence is performed in high temperature, low collisionality H-mode plasmas in the DIII-D tokamak. Wavenumber spectra of L-mode and H-mode density turbulence are measured by Doppler backscattering. H-mode wavenumber spectra are directly contrasted for the first time with nonlinear gyrokinetic simulation results. Core ITG/TEM-scale turbulence is substantially reduced/suppressed by E × B shear promptly after the L–H transition, resulting in reduced electron thermal transport across the entire minor radius. For small kθρs, both experiment and nonlinear gyrokinetic simulations using the GYRO code show density fluctuation levels increasing with kθρs in H-mode (r/a = 0.6), in contrast to ITG/TEM-dominated L-mode plasmas. GYRO simulations also indicate that a significant portion of the remaining H-mode electron heat flux results directly from residual intermediate/short-scale TEM/ETG turbulence. Electron transport at substantially increased electron-to-ion temperature ratio (Te/Ti ≥ 1, r/a ≤ 0.35) has been investigated in ECH-assisted, quiescent H-mode plasmas. A synergistic increase in core electron and ion thermal diffusivity (normalized to the gyro-Bohm diffusivity) is found with applied ECH. From linear stability analysis, the TEM mode is expected to become the dominant linear instability with ECH due to increased electron-to-ion temperature ratio and a reduction in the ion temperature gradient. This is consistent with increased electron temperature fluctuations and core electron thermal diffusivity observed experimentally. The reduced ion temperature gradient likely results from a reduction in the ITG critical gradient due to increased Te/Ti and reduced E × B shear. These studies are performed at collisonality ( \nu_{\rm e}^\ast \sim 0.05 , r/a ≤ 0.6) and address transport in electron heat-dominated regimes, thought to be important in ITER due to α-particle heating.},
doi = {10.1088/0029-5515/52/2/023003},
url = {https://www.osti.gov/biblio/1564873}, journal = {Nuclear Fusion},
issn = {0029-5515},
number = 2,
volume = 52,
place = {United States},
year = {2012},
month = {1}
}

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