Wolf-Christian Müller, Shiva Kumar Malapa, Angela Busse
The nonlinear dynamics of magnetic helicity, $H^M$, 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 $H^M$ is at variance with earlier work using a
statistical closure model [Pouquet et al., J. Fluid Mech. \textbf{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 $H^M$ and explains the
above-mentioned discrepancy. Considering the result in the context of
mean-field dynamo theory suggests a nonlinear modification of the
$\alpha$-dynamo effect important in the context of magnetic field excitation in
turbulent plasmas.
View original:
http://arxiv.org/abs/1201.0717
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