Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions

Dataset · Thu May 17 04:00:00 EDT 2018

DOI:https://doi.org/10.7910/DVN/WT1XGR· OSTI ID:1878517

Cziegler, I. ^[1]; Hubbard, A. E. ^[2]; Hughes, J. W. ^[2]; Terry, J. L. ^[2]; Tynan, G. R. ^[3]

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

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.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; Univ. of California, San Diego, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• DOE Contract Number: FC02-99ER54512; SC0008689
• OSTI ID: 1878517
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY