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How eigenmode self-interaction affects zonal flows and convergence of tokamak core turbulence with toroidal system size

Part of: Focus on Fusion

Published online by Cambridge University Press:  28 September 2020

Ajay C. J. Open the ORCID record for Ajay C. J. [Opens in a new window] ,
Stephan Brunner Open the ORCID record for Stephan Brunner [Opens in a new window] ,
Ben McMillan Open the ORCID record for Ben McMillan [Opens in a new window] ,
Justin Ball Open the ORCID record for Justin Ball [Opens in a new window] ,
Julien Dominski Open the ORCID record for Julien Dominski [Opens in a new window]  and
Gabriele Merlo
Ajay C. J.*
Affiliation:
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center, CH-1015Lausanne, Switzerland
Stephan Brunner
Affiliation:
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center, CH-1015Lausanne, Switzerland
Ben McMillan
Affiliation:
Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, CV4 7ALCoventry, UK
Justin Ball
Affiliation:
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center, CH-1015Lausanne, Switzerland
Julien Dominski
Affiliation:
Princeton Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, NJ08543-0451, USA
Gabriele Merlo
Affiliation:
The University of Texas at Austin, Austin, TX78712, USA
*
†Email address for correspondence: ajay.chandrarajanjayalekshmi@epfl.ch
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Abstract

Self-interaction is the process by which a microinstability eigenmode that is extended along the direction parallel to the magnetic field interacts non-linearly with itself. This effect is particularly significant in gyrokinetic simulations accounting for kinetic passing electron dynamics and is known to generate stationary $E\times B$ zonal flow shear layers at radial locations near low-order mode rational surfaces (Weikl et al. Phys. Plasmas, vol. 25, 2018, 072305). We find that self-interaction, in fact, plays a very significant role in also generating fluctuating zonal flows, which is critical to regulating turbulent transport throughout the radial extent. Unlike the usual picture of zonal flow drive in which microinstability eigenmodes coherently amplify the flow via modulational instabilities, the self-interaction drive of zonal flows from these eigenmodes are uncorrelated with each other. It is shown that the associated shearing rate of the fluctuating zonal flows therefore reduces as more toroidal modes are resolved in the simulation. In simulations accounting for the full toroidal domain, such an increase in the density of toroidal modes corresponds to an increase in the toroidal system size, leading to a finite system size effect that is distinct from the well-known profile shearing effect.

Keywords

fusion plasmaplasma simulationplasma non-linear phenomena
Type
Research Article
Information
Journal of Plasma Physics , Volume 86 , Issue 5 , October 2020 , 905860504
Copyright
Copyright © The Author(s), 2020. Published by Cambridge University Press

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