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Generalized universal instability: transient linear amplification and subcritical turbulence

Part of: Focus on Fusion

Published online by Cambridge University Press:  13 July 2015

Matt Landreman ,
Gabriel G. Plunk  and
William Dorland
Matt Landreman*
Affiliation:
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
Gabriel G. Plunk
Affiliation:
Max Planck Institute for Plasma Physics, 17491 Greifswald, Germany
William Dorland
Affiliation:
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742, USA
*
†Email address for correspondence: [email protected]
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Abstract

In this work we numerically demonstrate both significant transient (i.e. non-modal) linear amplification and sustained nonlinear turbulence in a kinetic plasma system with no unstable eigenmodes. The particular system considered is an electrostatic slab with magnetic shear, kinetic electrons and ions, weak collisions and a density gradient, but with no temperature gradient. In contrast to hydrodynamic examples of non-modal growth and subcritical turbulence, here there is no sheared flow in the equilibrium. Significant transient linear amplification is found when the magnetic shear and collisionality are weak. It is also demonstrated that nonlinear turbulence can be sustained if initialized at sufficient amplitude. We prove that these two phenomena are related: when sustained turbulence occurs without unstable eigenmodes, states that are typical of the turbulence must yield transient linear amplification of the gyrokinetic free energy.

Type
Research Article
Information
Journal of Plasma Physics , Volume 81 , Issue 5 , October 2015 , 905810501
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Copyright
© Cambridge University Press 2015 

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