Kinematic α-effect in isotropic turbulence simulations

Abstract

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 α-effect and a turbulent diffusivity whose values are independent of the magnetic Reynolds number, R_m, provided R_m exceeds unity. These turbulent coefficients are also consistent with expectations from the first-order smoothing approximation. For small values of R_m, α and turbulent diffusivity are proportional to R_m. Over finite time-intervals, meaningful values of α and turbulent diffusivity can be obtained even when there is small-scale dynamo action that produces strong magnetic fluctuations. This suggests that the fields generated by the small-scale dynamo do not make a correlated contribution to the mean electromotive force.