PPPL-5384
The Dimits Shift in a One-Field Fluid Model
Author: D. A. St-Onge
Abstract: The two-dimensional Terry-Horton equation is shown
to exhibit the Dimits shift when suitably modified to capture both
the nonlinear enhancement of zonal/drift-wave interactions and the
existence of residual Rosenbluth-Hinton states. This phenomena
persists through numerous simplifications of the equation, including
a quasilinear approximation as well as a four-mode truncation.
Analytic progress on the truncated system is reported, focused on
determining the growth rates of zonal flows and calculating the upper
bound of the Dimits shift. The results for the truncated system are
then used to estimate the Dimits shift of the fully nonlinear
system. A new understanding is thus developed on the fundamental
nature of the Dimits shift, both on its operation and its eventual
termination.
Submitted to: Journal of Plasma Physics
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