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Title: The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo

Journal Article · · Journal of Plasma Physics
 [1];  [2]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States); Princeton Univ., Princeton, NJ (United States)
  2. Princeton Univ., Princeton, NJ (United States)
+ Show Author Affiliations

A novel large-scale dynamo mechanism, the magnetic shear-current effect, is discussed and explored. Here, the effect relies on the interaction of magnetic fluctuations with a mean shear flow, meaning the saturated state of the small-scale dynamo can drive a large-scale dynamo – in some sense the inverse of dynamo quenching. The dynamo is non-helical, with the mean field$${\it\alpha}$$coefficient zero, and is caused by the interaction between an off-diagonal component of the turbulent resistivity and the stretching of the large-scale field by shear flow. Following up on previous numerical and analytic work, this paper presents further details of the numerical evidence for the effect, as well as an heuristic description of how magnetic fluctuations can interact with shear flow to produce the required electromotive force. The pressure response of the fluid is fundamental to this mechanism, which helps explain why the magnetic effect is stronger than its kinematic cousin, and the basic idea is related to the well-known lack of turbulent resistivity quenching by magnetic fluctuations. As well as being interesting for its applications to general high Reynolds number astrophysical turbulence, where strong small-scale magnetic fluctuations are expected to be prevalent, the magnetic shear-current effect is a likely candidate for large-scale dynamo in the unstratified regions of ionized accretion disks. Evidence for this is discussed, as well as future research directions and the challenges involved with understanding details of the effect in astrophysically relevant regimes.

Research Organization:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC02-09CH11466
OSTI ID:
1259596
Journal Information:
Journal of Plasma Physics, Vol. 82, Issue 02; ISSN 0022-3778
Publisher:
Cambridge University PressCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 15 works
Citation information provided by
Web of Science

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Cited By (4)

Advances in mean-field dynamo theory and applications to astrophysical turbulence journal August 2018
Dynamo theories journal August 2019
Estimating activity cycles with probabilistic methods: II. The Mount Wilson Ca H&K data journal October 2018
Advances in mean-field dynamo theory and applications to astrophysical turbulence text January 2018

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