Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions

Cziegler, I.; Hubbard, A. E.; Hughes, J. W.; Terry, J. L.; Tynan, G. R.

doi:10.7910/DVN/WT1XGR

Title: Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions

Abstract

A comprehensive study of fully frequency-resolved nonlinear kinetic energy transfer has been performed for the first time in a diverted tokamak, providing new insight into the parametric dependences of edge turbulence transitions. Measurements using gas puff imaging in the turbulent L-mode state illuminate the source of the long known but as yet unexplained “favorable-unfavorable” geometric asymmetry of the power threshold for transition to the turbulence-suppressed H mode. Results from the recently discovered I mode point to a competition between zonal flow (ZF) and geodesic-acoustic modes (GAM) for turbulent energy, while showing new evidence that the I-to-H transition is still dominated by ZFs. The availability of nonlinear drive for the GAM against net heat flux through the edge corresponds very well to empirical scalings found experimentally for accessing the I mode.

Authors:

Cziegler, I.; Hubbard, A. E.; Hughes, J. W.; Terry, J. L.; Tynan, G. R.

Univ. of York (United Kingdom)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Univ. of California, San Diego, CA (United States)

Publication Date:: 2018-05-17

DOE Contract Number:: FC02-99ER54512; SC0008689

Research Org.:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; Univ. of California, San Diego, CA (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Subject:: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY

OSTI Identifier:: 1878517

DOI:: https://doi.org/10.7910/DVN/WT1XGR

Citation Formats


                    Cziegler, I., Hubbard, A. E., Hughes, J. W., Terry, J. L., and Tynan, G. R. Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions.  United States: N. p., 2018. 
        Web.  doi:10.7910/DVN/WT1XGR.

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                    Cziegler, I., Hubbard, A. E., Hughes, J. W., Terry, J. L., & Tynan, G. R. Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions.  United States.  doi:https://doi.org/10.7910/DVN/WT1XGR

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                    Cziegler, I., Hubbard, A. E., Hughes, J. W., Terry, J. L., and Tynan, G. R. 2018.  
"Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions".  United States.  doi:https://doi.org/10.7910/DVN/WT1XGR.  https://www.osti.gov/servlets/purl/1878517. Pub date:Thu May 17 00:00:00 EDT 2018

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@article{osti_1878517,

  title        = {Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions},

  author       = {Cziegler, I. and Hubbard, A. E. and Hughes, J. W. and Terry, J. L. and Tynan, G. R.},

  abstractNote = {A comprehensive study of fully frequency-resolved nonlinear kinetic energy transfer has been performed for the first time in a diverted tokamak, providing new insight into the parametric dependences of edge turbulence transitions. Measurements using gas puff imaging in the turbulent L-mode state illuminate the source of the long known but as yet unexplained “favorable-unfavorable” geometric asymmetry of the power threshold for transition to the turbulence-suppressed H mode. Results from the recently discovered I mode point to a competition between zonal flow (ZF) and geodesic-acoustic modes (GAM) for turbulent energy, while showing new evidence that the I-to-H transition is still dominated by ZFs. The availability of nonlinear drive for the GAM against net heat flux through the edge corresponds very well to empirical scalings found experimentally for accessing the I mode.},

  doi          = {10.7910/DVN/WT1XGR},

  journal      = {},

  number       = ,

  volume       = ,

  place        = {United States},

  year         = {2018},

  month        = {5}

}

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