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  Generation of large-scale magnetic fields due to fluctuating α in shearing systems

Jingade, N., Singh, N. K., & Sridhar, S. (2018). Generation of large-scale magnetic fields due to fluctuating α in shearing systems. Journal of Plasma Physics, 84(6): 735840601. doi:10.1017/S0022377818001174.

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Jingade, Naveen, Author
Singh, Nishant K.1, Author           
Sridhar , S., Author
Affiliations:
1Max Planck Research Group in Solar and Stellar Magnetic Activity, Max Planck Institute for Solar System Research, Max Planck Society, ou_2265638              

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 Abstract: We explore the growth of large-scale magnetic fields in a shear flow, due to helicity fluctuations with a finite correlation time, through a study of the Kraichnan-Moffatt model of zero-mean stochastic fluctuations of the α parameter of dynamo theory. We derive a linear integro-differential equation for the evolution of the large-scale magnetic field, using the first-order smoothing approximation and the Galilean invariance of the α-statistics. This enables construction of a model that is nonperturbative in the shearing rate S and the α-correlation time τα. After a brief review of the salient features of the exactly solvable white-noise limit, we consider the case of small but non-zero τα. When the large-scale magnetic field varies slowly, the evolution is governed by a partial differential equation. We present modal solutions and conditions for the exponential growth rate of the large-scale magnetic field, whose drivers are the Kraichnan diffusivity, Moffatt drift, shear and a non-zero correlation time. Of particular interest is dynamo action when the α-fluctuations are weak; i.e. when the Kraichnan diffusivity is positive. We show that in the absence of Moffatt drift, shear does not give rise to growing solutions. But shear and Moffatt drift acting together can drive large-scale dynamo action with growth rate γ α |S|.

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Language(s): eng - English
 Dates: 2018
 Publication Status: Issued
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1017/S0022377818001174
 Degree: -

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Title: Journal of Plasma Physics
Source Genre: Journal
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Publ. Info: London : Cambridge University Press
Pages: - Volume / Issue: 84 (6) Sequence Number: 735840601 Start / End Page: - Identifier: ISSN: 0022-3778
CoNE: https://pure.mpg.de/cone/journals/resource/954925334694