On the Inverse Cascade of Magnetic Helicity

We study the inverse cascade of magnetic helicity in conducting fluids byinvestigating the detailed transfer of helicity between different sphericalshells in Fourier space in direct numerical simulations of three-dimensionalmagnetohydrodynamics (MHD). Two different numerical simulations are used, onewhere the system is forced with an electromotive force in the inductionequation, and one in which the system is forced mechanically with an ABC flowand the magnetic field is solely sustained by a dynamo action. The magnetichelicity cascade at the initial stages of both simulations is observed to beinverse and local (in scale space) in the large scales, and direct and local inthe small scales. When saturation is approached most of the helicity isconcentrated in the large scales and the cascade is non-local. Helicity istransfered directly from the forced scales to the largest scales. At the sametime, a smaller in amplitude direct cascade is observed from the largest scaleto small scales.Comment: Submitted to PR