Dissipative magnetic structures and scales in small-scale dynamos

Abstract

Small-scale dynamos play important roles in modern astrophysics, especially on Galactic and extragalactic scales. Owing to dynamo action, purely hydrodynamic Kolmogorov turbulence hardly exists and is often replaced by hydromagnetic turbulence. Understanding the size of dissipative magnetic structures is important in estimating the time scale of Galactic scintillation and other observational and theoretical aspects of interstellar and intergalactic small-scale dynamos. Here we show that, during the kinematic phase of the small-scale dynamo, the cutoff wavenumber of the magnetic energy spectra scales as expected for large magnetic Prandtl numbers, but continues in the same way also for moderately small values - contrary to what is expected. For a critical magnetic Prandtl number of about 0.3, the dissipative and resistive cutoffs are found to occur at the same wavenumber. In the nonlinearly saturated regime, the critical magnetic Prandtl number becomes unity. The cutoff scale now has a shallower scaling with magnetic Prandtl number below a value of about three, and a steeper one otherwise compared to the kinematic regime.

9 pages, 12 figures, 4 tables, submitted to MNRAS, revised version

References in corpus (10)

• Simulations of nonhelical hydromagnetic turbulence
• On magnetic field generation in Kolmogorov turbulence
• Is nonhelical hydromagnetic turbulence peaked at small scales?
• Magnetic Prandtl number dependence of kinetic to magnetic dissipation ratio
• Scatter broadening of pulsars and implications on the interstellar medium turbulence
• Magnetic structures produced by the small-scale dynamo
• Traces of large-scale dynamo action in the kinematic stage
• Fundamental scales in the kinematic phase of the turbulent dynamo
• Dynamo effect in the Kraichnan magnetohydrodynamic turbulence
• Batchelor, Saffman, and Kazantsev spectra in galactic small-scale dynamos

Cited by in corpus (8)

• Numerical viscosity and resistivity in MHD turbulence simulations
• Fundamental MHD scales -- II: the kinematic phase of the supersonic small-scale dynamo
• The effect of pressure-anisotropy-driven kinetic instabilities on magnetic field amplification in galaxy clusters
• Inflationary and phase-transitional primordial magnetic fields in galaxy clusters
• Taking control of compressible modes: bulk viscosity and the turbulent dynamo
• Magnetically assisted vorticity production in decaying acoustic turbulence
• Small-scale dynamo with finite correlation times
• Small-scale turbulent dynamo for low-Prandtl number fluid: comparison of the theory with results of numerical simulations