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Plasma 2018, 1(1), 126-143; https://doi.org/10.3390/plasma1010012

Investigation of a Multiple-Timescale Turbulence-Transport Coupling Method in the Presence of Random Fluctuations

Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
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Received: 28 May 2018 / Revised: 5 July 2018 / Accepted: 10 July 2018 / Published: 12 July 2018
(This article belongs to the Special Issue Multiscale Methods in Plasma Physics)
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Abstract

One route to improved predictive modeling of magnetically confined fusion reactors is to couple transport solvers with direct numerical simulations (DNS) of turbulence, rather than with surrogate models. An additional challenge presented by coupling directly with DNS is the inherent fluctuations in the turbulence, which limit the convergence achievable in the transport solver. In this article, we investigate the performance of one numerical coupling method in the presence of turbulent fluctuations. To test a particular numerical coupling method for the transport solver, we use an autoregressive-moving-average model to generate stochastic fluctuations efficiently with statistical properties resembling those of a gyrokinetic simulation. These fluctuations are then added to a simple, solvable problem, and we examine the behavior of the coupling method. We find that monitoring the residual as a proxy for the error can be misleading. From a pragmatic point of view, this study aids us in the full problem of transport coupled to DNS by predicting the amount of averaging required to reduce the fluctuation error and obtain a specific level of accuracy. View Full-Text
Keywords: multiple-timescale; transport; turbulence multiple-timescale; transport; turbulence
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Parker, J.B.; LoDestro, L.L.; Campos, A. Investigation of a Multiple-Timescale Turbulence-Transport Coupling Method in the Presence of Random Fluctuations. Plasma 2018, 1, 126-143.

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