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Intermittent turbulent dynamo at very low and high magnetic Prandtl numbers View all abstracts by submitter

Eric Buchlin   Submitted: 2011-11-09 15:48

Context: Direct numerical simulations have shown that the dynamo is efficienteven at low Prandtl numbers, i.e., the critical magnetic Reynolds number Rm_cnecessary for the dynamo to be efficient becomes smaller than the hydrodynamicReynolds number Re when Re -> infinity. Aims: We test the conjecture (Iskakovet al. 2007) that Rm_c actually tends to a finite value when Re -> infinity,and we study the behavior of the dynamo growth factor gamma at very low andhigh magnetic Prandtl numbers. Methods: We use local and nonlocal shell-modelsof magnetohydrodynamic (MHD) turbulence with parameters covering a much widerrange of Reynolds numbers than direct numerical simulations, but ofastrophysical relevance. Results: We confirm that Rm_c tends to a finite valuewhen Re -> infinity. The limit for Rm -> infinity of the dynamo growth factorgamma in the kinematic regime behaves like Re^eta, and, similarly, thelimit for Re -> infinity of gamma behaves like Rmeta', witheta=eta'=0.4. Conclusion: Comparison with a phenomenology based on anintermittent small-scale turbulent dynamo, together with the differencesbetween the growth rates in the different local and nonlocal models, indicate aweak contribution of nonlocal terms to the dynamo effect.

Authors: E. Buchlin
Projects: None

Publication Status: A&A Letters (published)
Last Modified: 2011-11-10 10:58
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