Generation of Large-Scale Magnetic Fields by Small-Scale Dynamo in Shear Flows

Abstract

We propose a new mechanism for a turbulent mean-field dynamo in which the magnetic fluctuations resulting from a small-scale dynamo drive the generation of large-scale magnetic fields. This is in stark contrast to the common idea that small-scale magnetic fields should be harmful to large-scale dynamo action. These dynamos occur in the presence of a large-scale velocity shear and do not require net helicity, resulting from off-diagonal components of the turbulent resistivity tensor as the magnetic analogue of the "shear-current" effect. Given the inevitable existence of nonhelical small-scale magnetic fields in turbulent plasmas, as well as the generic nature of velocity shear, the suggested mechanism may help explain the generation of large-scale magnetic fields across a wide range of astrophysical objects.

Additional Information

© 2015 American Physical Society. Received 12 June 2015; published 20 October 2015. This work was supported by a Procter Fellowship at Princeton University, and the U.S. Department of Energy Grant No. DE-AC02-09-CH11466. The authors would like to thank A. Schekochihin, J. Krommes, and I. Rogachevskii for enlightening discussion and useful suggestions, as well as G. Lesur for making the snoopy code freely available.

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Submitted - 1506.04109v2.pdf

Published - PhysRevLett.115.175003.pdf

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