Kinematic alpha effect in isotropic turbulence simulations

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Sur, Sharanya
Brandenburg, Axel
Subramanian, Kandaswamy
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Abstract
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Using numerical simulations at moderate magnetic Reynolds numbers up to 220 it is shown that in the kinematic regime, isotropic helical turbulence leads to an alpha effect and a turbulent diffusivity whose values are independent of the magnetic Reynolds number, $\Rm$, provided $\Rm$ exceeds unity. These turbulent coefficients are also consistent with expectations from the first order smoothing approximation. For small values of $\Rm$, alpha and turbulent diffusivity are proportional to $\Rm$. Over finite time intervals meaningful values of alpha and turbulent diffusivity can be obtained even when there is small-scale dynamo action that produces strong magnetic fluctuations. This suggests that small-scale dynamo-generated fields do not make a correlated contribution to the mean electromotive force.
Comment: Accepted for publication in MNRAS Letters
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Astrophysics
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