Self-similar turbulent dynamo.
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.
Schekochihin
Alexander A
AA
Plasma Physics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2BW, United Kingdom. as629@damtp.cam.ac.uk
Cowley
Steven C
SC
Maron
Jason L
JL
McWilliams
James C
JC