Inverse cascades and alpha-effect at low magnetic Prandtl number

Abstract

Dynamo action in a fully helical Beltrami (ABC) flow is studied using both direct numerical simulations and subgrid modeling. Sufficient scale separation is given in order to allow for large-scale magnetic energy build-up. Growth of magnetic energy obtains down to a magnetic Prandtl number PM=RM/RV close to 0.005, where RV and RM are the kinetic and magnetic Reynolds numbers. The critical magnetic Reynolds number for dynamo action RMc seems to saturate at values close to 20. Detailed studies of the dependence of the amplitude of the saturated magnetic energy with PM are presented. In order to decrease PM, numerical experiments are conducted with either RV or RM kept constant. In the former case, the ratio of magnetic to kinetic energy saturates to a value slightly below unity as PM decreases. Examination of energy spectra and structures in real space both reveal that quenching of the velocity by the large-scale magnetic field takes place, with an inverse cascade of magnetic helicity and a force-free field at large scale in the saturated regime.

arXiv comment10 pages, 15 figures

References in corpus (20)

• Astrophysical magnetic fields and nonlinear dynamo theory
• The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence
• Generation of magnetic field by dynamo action in a turbulent flow of liquid sodium
• Shell to shell energy transfer in MHD, Part I: steady state turbulence
• On magnetic field generation in Kolmogorov turbulence
• Numerical study of dynamo action at low magnetic Prandtl numbers
• Numerical demonstration of fluctuation dynamo at low magnetic Prandtl numbers
• The onset of a small-scale turbulent dynamo at low magnetic Prandtl numbers
• Shell to shell energy transfer in MHD, Part II: Kinematic dynamo
• Critical Magnetic Prandtl Number for Small-Scale Dynamo
• On the inverse cascade of magnetic helicity
• Simulation of induction at low magnetic Prandtl number
• Magnetorotational Instability in Liquid Metal Couette Flow
• Averaged Lagrangians and the mean dynamical effects of fluctuations in continuum mechanics
• Observation of a Turbulence-Induced Large Scale Magnetic Field
• Numerical solutions of the three-dimensional magnetohydrodynamic alpha-model
• A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows
• Low magnetic Prandtl number dynamos with helical forcing
• Turbulent magnetic dynamo excitation at low magnetic Prandtl number
• Dynamo action in turbulent flows

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• Transition from large-scale to small-scale dynamo
• A novel type of intermittency in a nonlinear dynamo in a compressible flow
• Large-scale Magnetic Structure Formation in 3D-MHD Turbulence
• Helicity detection of the astrophysical magnetic fields from radio emission statistics
• On the inverse energy transfer in rotating turbulence
• The Lagrangian-averaged model for magnetohydrodynamics turbulence and the absence of bottleneck
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