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arXiv · 1905.08278

Efficient quasi-kinematic large-scale dynamo as the small-scale dynamo saturates

Pallavi Bhat·Kandaswamy Subramanian·Axel Brandenburg
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Abstract

Large-scale magnetic fields in stars and galaxies are thought to arise by mean-field dynamo action due to the combined influence of both helical turbulence and shear. Those systems are also highly conducting and the turbulence therein leads to a fluctuation (or small-scale) dynamo which more rapidly amplifies magnetic field fluctuations on the eddy scales and smaller. Will this then interfere with and suppress the mean (or large-scale) field growth? Using direct numerical simulations of helical turbulence (with and without shear), we identify a novel quasi-kinematic large-scale dynamo which operates as the small-scale dynamo saturates. Thus both dynamos operate efficiently, one after the other, and lead to the generation of significant large-scale fields.

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Pallavi Bhat, Kandaswamy Subramanian, Axel Brandenburg. 2019-05-20. Efficient quasi-kinematic large-scale dynamo as the small-scale dynamo saturates. https://arxiv.org/abs/1905.08278

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