Mean-field dynamo in a turbulence with shear and kinetic helicity fluctuations

Abstract

We study effects of kinetic helicity fluctuations in a turbulence with large-scale shear using two different approaches: the spectral tau-approximation and the second order correlation approximation (or first-order smoothing approximation). These two approaches demonstrate that homogeneous kinetic helicity fluctuations alone with zero mean value in a sheared homogeneous turbulence cannot cause large-scale dynamo. Mean-field dynamo can be possible when kinetic helicity fluctuations are inhomogeneous which cause a nonzero mean alpha effect in a sheared turbulence. On the other hand, shear-current effect can generate large-scale magnetic field even in a homogeneous nonhelical turbulence with large-scale shear. This effect was investigated previously for large hydrodynamic and magnetic Reynolds numbers. In this study we examine the threshold required for the shear-current dynamo versus Reynolds number. We demonstrate that there is no need for a developed inertial range in order to maintain the shear-current dynamo (e.g., the threshold in the Reynolds number is of the order of 1).

12 pages, 3 Figures, small corrections to match the final published version, Physical Review E, in press

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Cited by in corpus (6)

• Generation of Magnetic Field by Combined Action of Turbulence and Shear
• Numerical experiments on dynamo action in sheared and rotating turbulence
• Mean-field dynamos in random Arnold-Beltrami-Childress and Roberts flows
• The dual role of shear in large-scale dynamos
• Galactic dynamo action in presence of stochastic alpha and shear
• Nonhelical mean-field dynamos in a sheared turbulence