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Title: Large-scale dynamo action precedes turbulence in shearing box simulations of the magnetorotational instability

Journal Article · · Monthly Notices of the Royal Astronomical Society
 [1]; ORCiD logo [1];  [2]
  1. Princeton Univ., Princeton, NJ (United States)
  2. Univ. of Rochester, Rochester, NY (United States)
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Here, we study the dynamo generation (exponential growth) of large-scale (planar averaged) fields in unstratified shearing box simulations of the magnetorotational instability (MRI). In contrast to previous studies restricted to horizontal (x–y) averaging, we also demonstrate the presence of large-scale fields when vertical (y–z) averaging is employed instead. By computing space–time planar averaged fields and power spectra, we find large-scale dynamo action in the early MRI growth phase – a previously unidentified feature. Non-axisymmetric linear MRI modes with low horizontal wavenumbers and vertical wavenumbers near that of expected maximal growth, amplify the large-scale fields exponentially before turbulence and high wavenumber fluctuations arise. Thus the large-scale dynamo requires only linear fluctuations but not non-linear turbulence (as defined by mode–mode coupling). Vertical averaging also allows for monitoring the evolution of the large-scale vertical field and we find that a feedback from horizontal low wavenumber MRI modes provides a clue as to why the large-scale vertical field sustains against turbulent diffusion in the non-linear saturation regime. We compute the terms in the mean field equations to identify the individual contributions to large-scale field growth for both types of averaging. The large-scale fields obtained from vertical averaging are found to compare well with global simulations and quasi-linear analytical analysis from a previous study by Ebrahimi & Blackman. We discuss the potential implications of these new results for understanding the large-scale MRI dynamo saturation and turbulence.

Research Organization:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
SC0012467; HST-AR-13916.002; AST1515648
OSTI ID:
1332518
Journal Information:
Monthly Notices of the Royal Astronomical Society, Vol. 462, Issue 1; ISSN 0035-8711
Publisher:
Royal Astronomical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 17 works
Citation information provided by
Web of Science

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Cited By (6)

Derivation and precision of mean field electrodynamics with mesoscale fluctuations journal May 2018
Advances in mean-field dynamo theory and applications to astrophysical turbulence journal August 2018
Dynamo theories journal August 2019
Experimental confirmation of the standard magnetorotational instability mechanism with a spring-mass analogue journal January 2019
The magnetorotational instability prefers three dimensions
  • Oishi, Jeffrey S.; Vasil, Geoffrey M.; Baxter, Morgan
  • Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 476, Issue 2233 https://doi.org/10.1098/rspa.2019.0622
journal January 2020
Advances in mean-field dynamo theory and applications to astrophysical turbulence text January 2018

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79 ASTRONOMY AND ASTROPHYSICS
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