Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions
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PhysRevLett.118.105003.pdf
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Author(s)
Cziegler, I.
Tynan, G. R.
Hubbard, Amanda E
Hughes Jr, Jerry
Terry, James L
Date Issued
March 2017
Journal
Physical Review Letters
Publisher
American Physical Society
Citation
Cziegler, I. et al. “Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions.” Physical Review Letters 118.10 (2017): n. pag. © 2017 American Physical Society
Version
Final published version
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.
MIT Department
Massachusetts Institute of Technology. Plasma Science and Fusion Center
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DOI of Published Version
https://doi.org/10.1103/PhysRevLett.118.105003
