The Inverse Cascade of Magnetic Helicity

The inverse cascade of magnetic helicity in three-dimensional magnetohydrodynamic turbulence is studied by means of high-resolution direct numerical simulations (DNS) of decaying and small-scale-driven turbulent flows. In the decaying case observed self-similar inertial-range behavior of the magnetic helicity spectrum is significantly different from the results of earlier two-dimensional studies based on statistical closure models. The findings are explained by a model based on the statistical eddy-damped quasi-normal Markovian closure theory (EDQNM). It is shown that the inverse cascade of magnetic helicity is governed by the chirality of the turbulent velocity field.