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  On the Existence of Shear-current Effects in Magnetized Burgulence

Käpylä, M. J., Alvarez Vizoso, J., Rheinhardt, M., Brandenburg, A., Käpylä, P., & Singh, N. K. (2020). On the Existence of Shear-current Effects in Magnetized Burgulence. The Astrophysical Journal, 905(2): 179. doi:10.3847/1538-4357/abc1e8.

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 Creators:
Käpylä, Maarit J.1, 2, Author              
Alvarez Vizoso, Javier1, Author              
Rheinhardt, Matthias, Author
Brandenburg, Axel, Author
Käpylä, Petri, Author
Singh, Nishant K.1, Author              
Affiliations:
1Max Planck Research Group and ERC Consolidator Grant: Solar and Stellar Dynamos - SOLSTAR, Max Planck Institute for Solar System Research, Max Planck Society, ou_2265638              
2Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              

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Free keywords: Magnetohydrodynamical simulations ; Astrophysical magnetism
 Abstract: The possibility of explaining shear flow dynamos by a magnetic shear-current (MSC) effect is examined via numerical simulations. Our primary diagnostics is the determination of the turbulent magnetic diffusivity tensor η . In our setup, a negative sign of its component η yx is necessary for coherent dynamo action by the SC effect. To be able to measure turbulent transport coefficients from systems with magnetic background turbulence, we present an extension of the test-field method (TFM) applicable to our setup where the pressure gradient is dropped from the momentum equation: the nonlinear TFM (NLTFM). Our momentum equation is related to Burgers' equation and the resulting flows are referred to as magnetized burgulence. We use both stochastic kinetic and magnetic forcings to mimic cases without and with simultaneous small-scale dynamo action. When we force only kinetically, negative η yx are obtained with exponential growth in both the radial and azimuthal mean magnetic field components. Using magnetokinetic forcing, the field growth is no longer exponential, while NLTFM yields positive η yx . By employing an alternative forcing from which wavevectors whose components correspond to the largest scales are removed, the exponential growth is recovered, but the NLTFM results do not change significantly. Analyzing the dynamo excitation conditions for the coherent SC and incoherent α and SC effects shows that the incoherent effects are the main drivers of the dynamo in the majority of cases. We find no evidence for MSC-effect-driven dynamos in our

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Language(s): eng - English
 Dates: 2020
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: arXiv: 2006.05661
DOI: 10.3847/1538-4357/abc1e8
 Degree: -

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Title: The Astrophysical Journal
Source Genre: Journal
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Publ. Info: Bristol; Vienna : IOP Publishing; IAEA
Pages: - Volume / Issue: 905 (2) Sequence Number: 179 Start / End Page: - Identifier: ISSN: 0004-637X
CoNE: https://pure.mpg.de/cone/journals/resource/954922828215_3