Abstract Details
Abstracts
Author: Anna Grafov
Requested Type: Poster
Submitted: 2019-02-22 14:38:29
Co-authors: W. Dorland
Contact Info:
University of Maryland
Department of Physics
College Park, Maryland 20742
USA
Abstract Text:
Tokamak turbulence can exhibit both sub- and super-critical transitions, neither of which is yet well-understood. High resolution, comprehensive simulations are expensive and time-consuming to run. Here, we focus on severely reduced models, containing a handful of Fourier harmonics and no more than one or two fluctuating fields, such as electrostatic potential and ion temperature. The models are focused on the interactions of streamers [radially extended, poloidally alternating jets of hot (pointing outward) and cold (pointing inward) plasma] and poloidally and toroidally symmetric, radially striated zonal flows. We present results from three coupled-ODE models: the original Lorenz model of thermal convection, an ITG model from Chen, White and Lin, and a similar model of our own. Systems governed by a small set of ODEs are known to exhibit similar dynamics to that of turbulent plasma, with distinctive transitions from a simple oscillatory regime to chaotic behavior. To better understand this transition, we have developed a set of diagnostics, including a Fourier analysis toolkit (that can handle irregularly spaced data), and a separate toolkit to study patterns of successive extrema in time. We use these diagnostics to study data from both the reduced and comprehensive (GS2) models of the turbulence. Our goal is to identify the simplest models that can reproduce the super-critical transition to turbulence (the Dimits shift). The effort to develop dynamical fidelity refinement algorithms for gyrokinetic simulations will benefit from this identification.
Comments:
