Coherent nonhelical shear dynamos driven by magnetic fluctuations at low Reynolds numbers

Abstract

Nonhelical shear dynamos are studied with a particular focus on the possibility of coherent dynamo action. The primary results -- serving as a follow up to the results of Squire & Bhattacharjee [arXiv:1506.04109 (2015)] -- pertain to the "magnetic shear-current effect" as a viable mechanism to drive large-scale magnetic field generation. This effect raises the interesting possibility that the saturated state of the small-scale dynamo could drive large-scale dynamo action, and is likely to be important in the unstratified regions of accretion disk turbulence. In this paper, the effect is studied at low Reynolds numbers, removing the complications of small-scale dynamo excitation and aiding analysis by enabling the use of quasi-linear statistical simulation methods. In addition to the magnetically driven dynamo, new results on the kinematic nonhelical shear dynamo are presented. These illustrate the relationship between coherent and incoherent driving in such dynamos, demonstrating the importance of rotation in determining the relative dominance of each mechanism.

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Cited by in corpus (15)

• Dynamo theories
• Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence
• The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo
• Motivation and challenge to capture both large scale and local transport in next generation accretion theory
• Compressible test-field method and its application to shear dynamos
• On large-scale dynamos with stable stratification and the application to stellar radiative zones
• On the shear-current effect: toward understanding why theories and simulations have mutually and separately conflicted
• On the existence of shear-current effects in magnetized burgulence
• Moffatt drift driven large scale dynamo due to $\alpha$ fluctuations with nonzero correlation times
• Sustained turbulence and magnetic energy in non-rotating shear flows
• Unified treatment of mean-field dynamo and angular-momentum transport in magnetorotational instability-driven turbulence
• Generation of large-scale magnetic fields due to fluctuating $\alpha$ in shearing systems
• Revisiting Kinematic Fast Dynamo in 3-dimensional magnetohydrodynamic plasmas: Dynamo transition from non-Helical to Helical flows
• Effect of flow shear on the onset of dynamos
• Investigating global convective dynamos with mean-field models: full spectrum of turbulent effects required