The inverse cascade of magnetic helicity in magnetohydrodynamic turbulence

الأصل · EN

The nonlinear dynamics of magnetic helicity, Hᵐ, which is responsible for large-scale magnetic structure formation in electrically conducting turbulent media is investigated in forced and decaying three-dimensional magnetohydrodynamic turbulence. This is done with the help of high resolution direct numerical simulations and statistical closure theory. The numerically observed spectral scaling of Hᵐ is at variance with earlier work using a statistical closure model [Pouquet et al., J. Fluid Mech. 77 321 (1976)]. By revisiting this theory a universal dynamical balance relation is found that includes effects of kinetic helicity, as well as kinetic and magnetic energy on the inverse cascade of Hᵐ and explains the above-mentioned discrepancy. Considering the result in the context of mean-field dynamo theory suggests a nonlinear modification of the α-dynamo effect important in the context of magnetic field excitation in turbulent plasmas.