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

Squire, J. and Bhattacharjee, A. (2016) The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo. Journal of Plasma Physics, 82 (2). Art. No. 535820201. ISSN 0022-3778. doi:10.1017/S0022377816000258.

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A novel large-scale dynamo mechanism, the magnetic shear-current effect, is discussed and explored. 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 α 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.

Item Type:Article
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Squire, J.0000-0001-8479-962X
Additional Information:© 2016 Cambridge University Press. Received December 08 2015; Revised February 16 2016; Accepted February 18 2016; Published online: 14 March 2016. Part of a collection on Fundamental Problems of Plasma Astrophysics: New Perspectives. The authors would like to thank J. Krommes, J. Goodman, H. Ji, G. Hammett, and A. Schekochihin for enlightening discussion and useful suggestions, as well as G. Lesur for distribution of the Snoopy code. JS acknowledges the generous support of a Burke Fellowship and the Sherman Fairchild Foundation at Caltech, as well as a Procter Fellowship at Princeton University. This work was funded by U.S. Department of Energy Grant No. DE-AC02-09-CH11466 and computations were carried out on the Dawson cluster at PPPL.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Sherman Fairchild FoundationUNSPECIFIED
Princeton University, Procter FellowshipUNSPECIFIED
Department of Energy (DOE)DE-AC02-09-CH11466
Issue or Number:2
Record Number:CaltechAUTHORS:20160610-085951213
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Official Citation:J. Squire and A. Bhattacharjee (2016). The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo. Journal of Plasma Physics, 82, 535820201 doi:10.1017/S0022377816000258
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67814
Deposited By: Tony Diaz
Deposited On:10 Jun 2016 16:15
Last Modified:11 Nov 2021 03:55

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