Hyperdiffusion in non-linear, large and small-scale turbulent dynamos

Abstract

The generation of large-scale magnetic fields is generically accompanied by the more rapid growth of small-scale fields. The growing Lorentz force due to these fields back reacts on the turbulence to saturate the mean-field and small-scale dynamos. For the mean-field dynamo, in a quasi-linear treatment of this saturation, it is generally thought that, while the alpha-effect gets renormalised and suppressed by non-linear effects, the turbulent diffusion is left unchanged. We show here that this is not true and the effect of the Lorentz forces, is also to generate additional non-linear hyperdiffusion of the mean field. A combination of such non-linear hyperdiffusion with diffusion at small scales, also arises in a similar treatment of small-scale dynamos, and is crucial to understand its saturation.

4 pages, accepted in Physical Review Letters, small changes to match accepted version

References in corpus (4)

• Dynamic nonlinearity in large scale dynamos with shear
• A model of nonlinear evolution and saturation of the turbulent MHD dynamo
• Structure of Small-Scale Magnetic Fields in the Kinematic Dynamo Theory
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