2019/05/20 by Bhat, Pallavi, Subramanian, Kandaswamy, Brandenburg, Axel
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Plasma Physics (physics.plasm-ph) #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.1905.08278
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.