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The Role of Magnetic Helicity when It Is Absent on Average
Version 1
: Received: 16 May 2023 / Approved: 17 May 2023 / Online: 17 May 2023 (08:26:02 CEST)
A peer-reviewed article of this Preprint also exists.
Brandenburg, A.; Larsson, G. Turbulence with Magnetic Helicity That Is Absent on Average. Atmosphere 2023, 14, 932. Brandenburg, A.; Larsson, G. Turbulence with Magnetic Helicity That Is Absent on Average. Atmosphere 2023, 14, 932.
Abstract
Magnetic helicity plays a tremendously important role when it is different from zero on average. Most notably, it leads to the phenomenon of an inverse cascade. Here, we consider decaying magnetohydrodynamic turbulence as well as some less common examples of magnetic evolution under the Hall effect and ambipolar diffusion, as well as cases in which the magnetic field evolution is constrained by the presence of an asymmetry in the number density of chiral fermions, whose spin is systematically either aligned or anti-aligned with its momentum. In all those cases, there is a new conserved quantity: the Hosking integral. We present quantitative scaling results for the magnetic integral scale as well as the magnetic energy density and its spectrum. We also compare with cases were also a magnetic version of the Saffman integral is initially finite.
Keywords
decaying turbulence; MHD turbulence; chiral magnetic effect; Hall effect; shell models
Subject
Physical Sciences, Fluids and Plasmas Physics
Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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