Role of stable modes in driven shear-flow turbulence

Abstract

A linearly unstable, sinusoidal $E\times B$ shear flow is examined in the gyrokinetic framework in both the linear and nonlinear regimes. In the linear regime, it is shown that the eigenmode spectrum is nearly identical to hydrodynamic shear flows, with a conjugate stable mode found at every unstable wavenumber. In the nonlinear regime, turbulent saturation of the instability is examined with and without the inclusion of a driving term that prevents nonlinear flattening of the mean flow, and a scale-independent radiative damping term that suppresses the excitation of conjugate stable modes. A simple fluid model for how momentum transport and partial flattening of the mean flow scale with the driving term is constructed, from which it is shown that, except at high radiative damping, stable modes play an important role in the turbulent state and yield significantly improved quantitative predictions when compared with corresponding models neglecting stable modes.

arXiv comment34 pages pre-print format, 13 figures, submitted to Physics of Plasmas

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Cited by in corpus (7)

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• Mechanism for Sequestering Magnetic Energy at Large Scales in Shear-Flow Turbulence
• The impact of magnetic fields on momentum transport and saturation of shear-flow instability by stable modes
• Nonlinear mode coupling and energetics of driven magnetized shear-flow turbulence
• Resistive instabilities in sinusoidal shear flows with a streamwise magnetic field