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Eliminating turbulent self-interaction through the parallel boundary condition in local gyrokinetic simulations

Part of: Focus on Fusion

Published online by Cambridge University Press:  20 March 2020

Justin Ball Open the ORCID record for Justin Ball [Opens in a new window] ,
Stephan Brunner  and
Ajay C.J.
Justin Ball*
Affiliation:
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015Lausanne, Switzerland
Stephan Brunner
Affiliation:
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015Lausanne, Switzerland
Ajay C.J.
Affiliation:
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015Lausanne, Switzerland
*
†Email address for correspondence: justin.ball@epfl.ch
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Abstract

In this work, we highlight an issue that may reduce the accuracy of many local nonlinear gyrokinetic simulations – turbulent self-interaction through the parallel boundary condition. Given a sufficiently long parallel correlation length, individual turbulent eddies can span the full domain and ‘bite their own tails’, thereby altering their statistical properties. Such self-interaction is only modelled accurately when the simulation domain corresponds to a full flux surface, otherwise it is artificially strong. For Cyclone Base Case parameters and typical domain sizes, we find that this mechanism modifies the heat flux by approximately 40 % and it can be even more important. The effect is largest when using kinetic electrons, low magnetic shear and strong turbulence drive (i.e. steep background gradients). It is found that parallel self-interaction can be eliminated by increasing the parallel length and/or the binormal width of the simulation domain until convergence is achieved.

Keywords

fusion plasmaplasma nonlinear phenomenaplasma simulation
Type
Research Article
Information
Journal of Plasma Physics , Volume 86 , Issue 2 , April 2020 , 905860207
Copyright
© Cambridge University Press 2020

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