The saturation of galactic dynamos

We summarize the current state of the long term discussion about the saturation mechanisms associated with rapid growth of small-scale magnetic field, that operate in large-scale galactic dynamos, and related problems with magnetic helicity conservation. Our general conclusion is that, taking into account magnetic helicity fluxes, large-scale magnetic field can be amplified up to about the equipartition level. In contrast, models without helicity fluxes give an initial temporal magnetic field growth, but then decay. In our opinion, it is more appropriate to refer to the situation as a potentially catastrophic scenario rather than as catastrophic alpha-quenching. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim