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newsherwood2017-1.pdf2019-04-24 13:02:14Denis St-Onge

Abstracts

Author: Denis A. St-Onge
Requested Type: Poster
Submitted: 2017-04-05 21:18:41

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Contact Info:
Princeton Plasma Physics Lab
P.O. Box 451, M.S. 30
Princeton, NJ   08543
USA

Abstract Text:
The Dimits shift is the nonlinear upshift of the critical temperature gradient that signals the onset of collisionless ion-temperature-gradient-driven turbulence. This phenomenon is caused by the shearing away of turbulent streamers in the radial direction by poloidal zonal flows. While the Dimits shift has been witnessed in both gyrokinetic and gyrofluid simulations, a simple physically-motivated model containing the bare minimum amount of physics needed to capture the shift has remained elusive. In this work, 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 will be presented, focusing on determining the growth rates of zonal flows and a calculation of the upper-bound of the Dimits shift.

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