MHD Turbulence, Turbulent Dynamo and Applications

Type Conference Paper
Names Andrey Beresnyak, Alex Lazarian
Conference Name Astrophysics and Space Science Library
Place eprint: arXiv:1406.1185
Volume 407
Pages 163
Date 2015
DOI 10.1007/978-3-662-44625-6_8
URL http://adsabs.org/2015ASSL.407.163B
Library Catalog adslabs.org
Abstract MHD Turbulence is common in many space physics and astrophysics environments. We first discuss the properties of incompressible MHD turbulence. A well-conductive fluid amplifies initial magnetic fields in a process called small-scale dynamo. Below equipartition scale for kinetic and magnetic energies the spectrum is steep (Kolmogorov -5/3) and is represented by critically balanced strong MHD turbulence. In this Chapter we report the basic reasoning behind universal nonlinear small-scale dynamo and the inertial range of MHD turbulence. We measured the efficiency of the small-scale dynamo C E = 0. 05, Kolmogorov constant C K = 4. 2 and anisotropy constant C A = 0. 63 for MHD turbulence in high-resolution direct numerical simulations. We also discuss so-called imbalanced or cross-helical MHD turbulence which is relevant for in many objects, most prominently in the solar wind. We show that properties of incompressible MHD turbulence are similar to the properties of Alfvénic part of MHD cascade in compressible turbulence. The other parts of the cascade evolve according to their own dynamics. The slow modes are being cascaded by Alfvénic modes, while fast modes create an independent cascade. We show that different ways of decomposing compressible MHD turbulence into Alfvén, slow and fast modes provide consistent results and are useful in understanding not only turbulent cascade, but its interaction with fast particles.
Tags Physics
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