  The small-scale magnetic helicity produced as a by-product of the large-scale
dynamo is believed to play a major role in dynamo saturation. In a mean-field
model the generation of small-scale magnetic helicity can be modelled by using
the dynamical quenching formalism. Catastrophic quenching refers to a decrease
of the saturation field strength with increasing Reynolds number. It has been
suggested that catastrophic quenching only affects the region of non-zero
helical turbulence (i.e. where the kinematic alpha operates) and that it is
possible to alleviate catastrophic quenching by separating the region of strong
shear from the alpha layer. We perform a systematic study of a simple
axisymmetric two-layer alpha-omega dynamo in a spherical shell for Reynolds
numbers in the range 1 < Rm < 10^5. In the framework of dynamical quenching we
show that this may not be the case, suggesting that magnetic helicity fluxes
would be necessary.
