  Investigations of the inverse cascade of magnetic helicity are conducted with
pseudospectral, three-dimensional direct numerical simulations of forced and
decaying incompressible magnetohydrodynamic turbulence. The high-resolution
simulations which allow for the necessary scale-separation show that the
observed self-similar scaling behavior of magnetic helicity and related
quantities can only be understood by taking the full nonlinear interplay of
velocity and magnetic fluctuations into account. With the help of the
eddy-damped quasi-normal Markovian approximation a probably universal relation
between kinetic and magnetic helicities is derived that closely resembles the
extended definition of the prominent dynamo pseudoscalar $\alpha$. This
unexpected similarity suggests an additional nonlinear quenching mechanism of
the current-helicity contribution to $\alpha$.
