The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo
Abstract
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.
- Authors:
-
- California Inst. of Technology (CalTech), Pasadena, CA (United States); Princeton Univ., Princeton, NJ (United States)
- Princeton Univ., Princeton, NJ (United States)
- Publication Date:
- Research Org.:
- Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1259596
- Grant/Contract Number:
- AC02-09CH11466
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Journal of Plasma Physics
- Additional Journal Information:
- Journal Volume: 82; Journal Issue: 02; Journal ID: ISSN 0022-3778
- Publisher:
- Cambridge University Press
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Citation Formats
Squire, J., and Bhattacharjee, A. The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo. United States: N. p., 2016.
Web. doi:10.1017/s0022377816000258.
Squire, J., & Bhattacharjee, A. The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo. United States. https://doi.org/10.1017/s0022377816000258
Squire, J., and Bhattacharjee, A. Mon .
"The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo". United States. https://doi.org/10.1017/s0022377816000258. https://www.osti.gov/servlets/purl/1259596.
@article{osti_1259596,
title = {The magnetic shear-current effect: Generation of large-scale magnetic fields by the small-scale dynamo},
author = {Squire, J. and Bhattacharjee, A.},
abstractNote = {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.},
doi = {10.1017/s0022377816000258},
journal = {Journal of Plasma Physics},
number = 02,
volume = 82,
place = {United States},
year = {Mon Mar 14 00:00:00 EDT 2016},
month = {Mon Mar 14 00:00:00 EDT 2016}
}
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