Alpha effect in helically forced turbulence
Résumé
The effect on large-scale dynamics of small-scale helicity injection in three-dimensional resistive mag-netohydrodynamic turbulence is investigated for a weak initial magnetic field. The magnetic configuration of a 2 dynamo prototype flows is such that, generally, the energy concentrates on one large-scale mode. However, we obtain that alpha effect is not limited to the dominant mode and that a non-local equation (in Fourier space) is more appropriate to describe it. It gives some insights into the non-local theory of Pouquet et al. [J. Fluid Mech. 77 (1976) 321] where the inverse cascade results from a competition between the helicity and Alfv e en effects.
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