Turbulence Spreading into Linearly Stable Zone and Transport Scaling Page: 3 of 18
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Turbulence Spreading into Linearly Stable Zone
and Transport Scaling
T.S. Hahm", P.H. Diamond, Z. Lin', K. Itohd, and S.-I. Itoh'
"Princeton University, Plasma Physics Laboratory, Princeton, NJ 08543, USA
bUniversity of California San Diego, La Jolla, CA 92093-0319, USA
University of California Irvine, Irvine, CA 92697, USA
dNational Institute for Fusion Science, Nagoya 464-01, Japan
'Research Institute for Applied Mechanics, Kyushu University 87, Kasuga 816, Japan
October 9, 2003
We study the simplest problem of turbulence spreading corresponding to the spatio-temporal propagation
of a patch of turbulence from a region where it is locally excited to a region of weaker excitation, or even
local damping. A single model equation for the local turbulence intensity I(x, t) includes the effects of
local linear growth and damping, spatially local nonlinear coupling to dissipation and spatial scattering of
turbulence energy induced by nonlinear coupling. In the absence of dissipation, the front propagation into
the linearly stable zone occurs with the property of rapid progression at small t, followed by slower sub-
diffusive progression at late times. The turbulence radial spreading into the linearly stable zone reduces the
turbulent intensity in the linearly unstable zone, and introduces an additional dependence on the p* - pj/a
to the turbulent intensity and the transport scaling. These are in broad, semi-quantitative agreements with
a number of global gyrokinetic simulation results with zonal flows and without zonal flows. The front
propagation stops when the radial flux of fluctuation energy from the linearly unstable region is balanced by
local dissipation in the linearly stable region.
Achieving understanding of turbulent transport is necessary for the design of an economical advanced
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Hahm, T.S.; Diamond, P.H.; Lin, Z.; Itoh, K. & Itoh, S.-I. Turbulence Spreading into Linearly Stable Zone and Transport Scaling, report, October 20, 2003; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc740443/m1/3/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.