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Title: Gyrokinetic predictions of multiscale transport in a DIII-D ITER baseline discharge

New multiscale gyrokinetic simulations predict that electron energy transport in a DIII-D ITER baseline discharge with dominant electron heating and low input torque is multiscale in nature, with roughly equal amounts of the electron energy flux Q e coming from long wavelength ion-scale (k yρ s < 1) and short wavelength electron-scale (k yρ s > 1) fluctuations when the gyrokinetic results match independent power balance calculations. Corresponding conventional ion-scale simulations are able to match the power balance ion energy flux Q i, but systematically underpredict Q e when doing so. We observe significant nonlinear cross-scale couplings in the multiscale simulations, but the exact simulation predictions are found to be extremely sensitive to variations of model input parameters within experimental uncertainties. Most notably, depending upon the exact value of the equilibrium E x B shearing rate γ E x B used, either enhancement or suppression of the long-wavelength turbulence and transport levels in the multiscale simulations is observed relative to what is predicted by ion-scale simulations. And while the enhancement of the long wavelength fluctuations by inclusion of the short wavelength turbulence was previously observed in similar multiscale simulations of an Alcator C-Mod L-mode discharge, these new results show formore » the first time a complete suppression of long-wavelength turbulence in a multiscale simulation, for parameters at which conventional ion-scale simulation predicts small but finite levels of low-k turbulence and transport consistent with the power balance Q i. Though computational resource limitations prevent a fully rigorous validation assessment of these new results, they provide significant new evidence that electron energy transport in burning plasmas is likely to have a strong multiscale character, with significant nonlinear cross-scale couplings that must be fully understood to predict the performance of those plasmas with confidence.« less
Authors:
 [1] ;  [2] ; ORCiD logo [3]
  1. Univ. of California, San Diego, CA (United States). Center for Energy Research
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Grant/Contract Number:
AC02-09CH11466; SC0006957; FG02-06ER54871; FC02-99ER54512; FC02-04ER54698
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 6; Related Information: DIII-D data shown in this paper can be obtained in digital format by following the links at https://fusion.gat.com/global/D3D_DMP.; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma turbulence; gyrokinetics; multiscale; electron transport; electron-temperature-gradient; d tokamak; turbulence; plasma; confinement
OSTI Identifier:
1361163

Holland, C., Howard, N. T., and Grierson, B. A.. Gyrokinetic predictions of multiscale transport in a DIII-D ITER baseline discharge. United States: N. p., Web. doi:10.1088/1741-4326/aa6c16.
Holland, C., Howard, N. T., & Grierson, B. A.. Gyrokinetic predictions of multiscale transport in a DIII-D ITER baseline discharge. United States. doi:10.1088/1741-4326/aa6c16.
Holland, C., Howard, N. T., and Grierson, B. A.. 2017. "Gyrokinetic predictions of multiscale transport in a DIII-D ITER baseline discharge". United States. doi:10.1088/1741-4326/aa6c16. https://www.osti.gov/servlets/purl/1361163.
@article{osti_1361163,
title = {Gyrokinetic predictions of multiscale transport in a DIII-D ITER baseline discharge},
author = {Holland, C. and Howard, N. T. and Grierson, B. A.},
abstractNote = {New multiscale gyrokinetic simulations predict that electron energy transport in a DIII-D ITER baseline discharge with dominant electron heating and low input torque is multiscale in nature, with roughly equal amounts of the electron energy flux Qe coming from long wavelength ion-scale (kyρs < 1) and short wavelength electron-scale (kyρs > 1) fluctuations when the gyrokinetic results match independent power balance calculations. Corresponding conventional ion-scale simulations are able to match the power balance ion energy flux Qi, but systematically underpredict Qe when doing so. We observe significant nonlinear cross-scale couplings in the multiscale simulations, but the exact simulation predictions are found to be extremely sensitive to variations of model input parameters within experimental uncertainties. Most notably, depending upon the exact value of the equilibrium E x B shearing rate γ E x B used, either enhancement or suppression of the long-wavelength turbulence and transport levels in the multiscale simulations is observed relative to what is predicted by ion-scale simulations. And while the enhancement of the long wavelength fluctuations by inclusion of the short wavelength turbulence was previously observed in similar multiscale simulations of an Alcator C-Mod L-mode discharge, these new results show for the first time a complete suppression of long-wavelength turbulence in a multiscale simulation, for parameters at which conventional ion-scale simulation predicts small but finite levels of low-k turbulence and transport consistent with the power balance Qi. Though computational resource limitations prevent a fully rigorous validation assessment of these new results, they provide significant new evidence that electron energy transport in burning plasmas is likely to have a strong multiscale character, with significant nonlinear cross-scale couplings that must be fully understood to predict the performance of those plasmas with confidence.},
doi = {10.1088/1741-4326/aa6c16},
journal = {Nuclear Fusion},
number = 6,
volume = 57,
place = {United States},
year = {2017},
month = {5}
}