Turbulent diffusion of magnetic fields in astrophysical plasmas

1981 ◽  
Vol 247 ◽  
pp. 293 ◽  
Author(s):  
J. H. Piddington
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion ◽  
Astrophysical Plasmas

scholarly journals The role of magnetic fields for planetary formation

2008 ◽  
Vol 4 (S259) ◽  
pp. 249-258 ◽  
Author(s):  
Anders Johansen
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion ◽  
Planet Formation ◽  
High Pressures ◽  
Mixing Time ◽  
Zonal Flow ◽  
Coherence Time ◽  
Maxwell Stress ◽  
Turbulent Diffusion Coefficient

AbstractThe role of magnetic fields for the formation of planets is reviewed. Protoplanetary disc turbulence driven by the magnetorotational instability has a huge influence on the early stages of planet formation. Small dust grains are transported both vertically and radially in the disc by turbulent diffusion, counteracting sedimentation to the mid-plane and transporting crystalline material from the hot inner disc to the outer parts. The conclusion from recent efforts to measure the turbulent diffusion coefficient of magnetorotational turbulence is that turbulent diffusion of small particles is much stronger than naively thought. Larger particles – pebbles, rocks and boulders – get trapped in long-lived high pressure regions that arise spontaneously at large scales in the turbulent flow. These gas high pressures, in geostrophic balance with a sub-Keplerian/super-Keplerian zonal flow envelope, are excited by radial fluctuations in the Maxwell stress. The coherence time of the Maxwell stress is only a few orbits, where as the correlation time of the pressure bumps is comparable to the turbulent mixing time-scale, many tens or orbits on scales much greater than one scale height. The particle overdensities contract under the combined gravity of all the particles and condense into gravitationally bound clusters of rocks and boulders. These planetesimals have masses comparable to the dwarf planet Ceres. I conclude with thoughts on future priorities in the field of planet formation in turbulent discs.

scholarly journals Developed turbulence and nonlinear amplification of magnetic fields in laboratory and astrophysical plasmas

2015 ◽  
Vol 112 (27) ◽  
pp. 8211-8215 ◽  
Author(s):  
Jena Meinecke ◽  
Petros Tzeferacos ◽  
Anthony Bell ◽  
Robert Bingham ◽  
Robert Clarke ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Galaxy Clusters ◽  
Density Fluctuations ◽  
Line Broadening ◽  
Astrophysical Plasmas ◽  
Developed Turbulence ◽  
Visible Matter ◽  
Merger Event ◽  
The Universe ◽  
The Magnetic Field

The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe.

Turbulent diffusion of magnetic fields

1978 ◽  
Vol 225 ◽  
pp. 1050 ◽  
Author(s):  
E. Knobloch
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion

scholarly journals On Cross-Phase and the Quenching of the Turbulent Diffusion of Magnetic Fields in Two Dimensions

2008 ◽  
Vol 678 (2) ◽  
pp. L137-L140 ◽  
Author(s):  
Shane R. Keating ◽  
L. J. Silvers ◽  
P. H. Diamond
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion ◽  
Two Dimensions

scholarly journals Magnetic field amplification in turbulent astrophysical plasmas

2016 ◽  
Vol 82 (6) ◽  
Author(s):  
Christoph Federrath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Formation Rate ◽  
Density Fluctuations ◽  
Accretion Discs ◽  
Theoretical Modelling ◽  
Dynamo Action ◽  
Astrophysical Plasmas ◽  
Field Amplification ◽  
Prandtl Numbers

Magnetic fields play an important role in astrophysical accretion discs and in the interstellar and intergalactic medium. They drive jets, suppress fragmentation in star-forming clouds and can have a significant impact on the accretion rate of stars. However, the exact amplification mechanisms of cosmic magnetic fields remain relatively poorly understood. Here, I start by reviewing recent advances in the numerical and theoretical modelling of the turbulent dynamo, which may explain the origin of galactic and intergalactic magnetic fields. While dynamo action was previously investigated in great detail for incompressible plasmas, I here place particular emphasis on highly compressible astrophysical plasmas, which are characterised by strong density fluctuations and shocks, such as the interstellar medium. I find that dynamo action works not only in subsonic plasmas, but also in highly supersonic, compressible plasmas, as well as for low and high magnetic Prandtl numbers. I further present new numerical simulations from which I determine the growth of the turbulent (un-ordered) magnetic field component ($B_{turb}$) in the presence of weak and strong guide fields ($B_{0}$). I vary $B_{0}$ over five orders of magnitude and find that the dependence of $B_{turb}$ on $B_{0}$ is relatively weak, and can be explained with a simple theoretical model in which the turbulence provides the energy to amplify $B_{turb}$. Finally, I discuss some important implications of magnetic fields for the structure of accretion discs, the launching of jets and the star-formation rate of interstellar clouds.

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