  The emergence of a large scale magnetic field from randomly forced isotropic
strongly helical flows is discussed in terms of the inverse cascade of magnetic
helicity and the alpha-effect. In simulations of such flows the maximum field
strength exceeds the equipartition field strength for large scale separation.
However, helicity conservation controls the speed at which this final state is
reached. In the presence of open boundaries magnetic helicity fluxes out of the
domain are possible. This reduces the timescales of the field growth, but it
also tends to reduce the maximum attainable field strength.
