Self-similar turbulent dynamo

Abstract

The amplification of magnetic fields in a highly conducting fluid is studied numerically. During growth, the magnetic field is spatially intermittent: it does not uniformly fill the volume, but is concentrated in long thin folded structures. Contrary to a commonly held view, intermittency of the folded field does not increase indefinitely throughout the growth stage if diffusion is present. Instead, as we show, the probability-density function (PDF) of the field strength becomes self-similar. The normalized moments increase with magnetic Prandtl number in a powerlike fashion. We argue that the self-similarity is to be expected with a finite flow scale and system size. In the nonlinear saturated state, intermittency is reduced and the PDF is exponential. Parallels are noted with self-similar behavior recently observed for passive-scalar mixing and for map dynamos.

revtex, 4 pages, 5 figures; minor changes to match published version

References in corpus (6)

• Small-scale turbulent dynamo
• Structure of Small-Scale Magnetic Fields in the Kinematic Dynamo Theory
• The Decay of Passive Scalars Under the Action of Single Scale Smooth Velocity Fields in Bounded 2D Domains : From non self similar pdf's to self similar eigenmodes
• Chaotic Mixing in a Torus Map
• Universal decay of scalar turbulence
• On geometric properties of passive random advection

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