  A unified, three-scale system of equations accommodating nonlinear velocity
driven helical dynamos, as well as time-dependent relaxation of magnetically
dominated unihelical or bihelical systems is derived and solved herein. When
opposite magnetic helicities of equal magnitude are injected on the
intermediate and small scales, the large scale magnetic helicity grows
kinematically (independent of the magnetic Reynolds number) to equal that on
the intermediate scale. For both free and driven relaxation large scale fields
are rapidly produced. Subsequently, a dissipation-limited dynamo, driven by
growth of small scale kinetic helicity, further amplifies the large scale
field. The results are important for astrophysical coronae fed with bihelical
structures by dynamos in their host rotators. The large scale for the rotator
corresponds to the intermediate scale for the corona. That bihelical magnetic
relaxation can produce global scale fields may help to explain the formation of
astrophysical coronal holes and magnetohydrodynamic outflows.
