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

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.

arXiv comment8 pages, 11 figures. Comments/feedback/discussions are welcome

Cited by in corpus (5)

• Dynamo theories
• Magnetic field amplification in accretion discs around the first stars: implications for the primordial IMF
• Turbulent transport coefficients in galactic dynamo simulations using singular value decomposition
• Saturation of large-scale dynamo in anisotropically forced turbulence
• Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges