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Abstract: We develop a new model of the fluctuation dynamo in which the magnetic fieldis confined to thin flux ropes advected by a multi-scale flow which modelsturbulence. Magnetic dissipation occurs only via reconnections of flux ropes.The model is particularly suitable for rarefied plasma, such as the Solarcorona or galactic halos. We investigate the kinetic energy release into heat,mediated by dynamo action, both in our model and by solving the inductionequation with the same flow. We find that the flux rope dynamo is more than anorder of magnitude more efficient at converting mechanical energy into heat.The probability density of the magnetic energy released during reconnectionshas a power-law form with the slope -3, consistent with the Solar coronaheating by nanoflares. We also present a nonlinear extension of the model. Thisshows that a plausible saturation mechanism of the fluctuation dynamo is thesuppression of turbulent magnetic diffusivity, due to suppression of randomstretching at the location of the flux ropes. We confirm that the probabilitydistribution function of the magnetic line curvature has a power-law formsuggested by Schekochihin et al., 2002. We argue, however, using our resultsthat this does not imply a persistent folded structure of magnetic field, atleast in the nonlinear stage.

Author: Andrew W. Baggaley, Carlo F. Barenghi, Anvar Shukurov, Kandaswamy Subramanian

Source: https://arxiv.org/

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