Magnetic dynamo action in random flows with zero and finite correlation times

Abstract

Hydromagnetic dynamo theory provides the prevailing theoretical description for the origin of magnetic fields in the universe. Here we consider the problem of kinematic, small-scale dynamo action driven by a random, incompressible, non-helical, homogeneous and isotropic flow. In the Kazantsev dynamo model the statistics of the driving flow are assumed to be instantaneously correlated in time. Here we compare the results of the model with the dynamo properties of a simulated flow that has equivalent spatial characteristics as the Kazantsev flow but different temporal statistics. In particular, the simulated flow is a solution of the forced Navier-Stokes equations and hence has a finite correlation time. We find that the Kazantsev model typically predicts a larger magnetic growth rate and a magnetic spectrum that peaks at smaller scales. However, we show that by filtering the diffusivity spectrum at small scales it is possible to bring the growth rates into agreement and simultaneously align the magnetic spectra.

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Cited by in corpus (14)

• Dynamo theories
• Magnetic field amplification in turbulent astrophysical plasmas
• The Turbulent Dynamo in Highly Compressible Supersonic Plasmas
• Fluctuation dynamo at finite correlation times and the Kazantsev spectrum
• Non-Gaussian generalization of the Kazantsev-Kraichnan model
• Magnetic field generation in galactic molecular clouds
• Fluctuation dynamo at finite correlation times using renewing flows
• Suppression of small-scale dynamo in time irreversible turbulence
• Magnetic energy spectrum produced by turbulent dynamo: effect of time irreversibility
• Kazantsev model in nonhelical 2.5D flows
• Growth rate distribution and intermittency in kinematic turbulent dynamos : which moment predicts the dynamo onset?
• Small-scale turbulent dynamo for low-Prandtl number fluid: comparison of the theory with results of numerical simulations
• Small-scale dynamo with finite correlation times
• Large $\mathrm{Pm}$ small-scale kinematic dynamo in protoneutron stars