Inverse energy transfer in decaying, three-dimensional, non-helical magnetic turbulence due to magnetic reconnection

Journal Article · Wed Dec 16 00:00:00 EST 2020 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/staa3849· OSTI ID:1836118

Bhat, Pallavi ^[1]; Zhou, Muni ^[2]; Loureiro, Nuno F. ^[2]

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1. Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK, International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore 560089, India, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

ABSTRACT It has been recently shown numerically that there exists an inverse transfer of magnetic energy in decaying, non-helical, magnetically dominated, magnetohydrodynamic turbulence in three dimensions (3D). We suggest that magnetic reconnection is the underlying physical mechanism responsible for this inverse transfer. In the two-dimensional (2D) case, the inverse transfer is easily inferred to be due to smaller magnetic islands merging to form larger ones via reconnection. We find that the scaling behaviour is similar between the 2D and 3D cases, i.e. the magnetic energy evolves as t−1, and the magnetic power spectrum follows a slope of k−2. We show that on normalizing time by the magnetic reconnection time-scale, the evolution curves of the magnetic field in systems with different Lundquist numbers collapse on to one another. Furthermore, transfer function plots show signatures of magnetic reconnection driving the inverse transfer. We also discuss the conserved quantities in the system and show that the behaviour of these quantities is similar between the 2D and 3D simulations, thus making the case that the dynamics in 3D could be approximately explained by what we understand in 2D. Lastly, we also conduct simulations where the magnetic field is subdominant to the flow. Here, too, we find an inverse transfer of magnetic energy in 3D. In these simulations, the magnetic energy evolves as t−1.4 and, interestingly, a dynamo effect is observed.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0016215; FG02-91-ER54109; FG02-91ER54109
• OSTI ID: 1836118
• Alternate ID(s): OSTI ID: 1850018
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Vol. 501 Journal Issue: 2; ISSN 0035-8711
• Publisher: Oxford University Press
• Country of Publication: United Kingdom
• Language: English

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