Magnetic helicity effects in astrophysical and laboratory dynamos

Magnetic helicity effects are discussed in laboratory and astro-physical settings. Firstly, dynamo action in Taylor–Green flows is discussed for different boundary conditions. However, because of the lack of scale separation with respect to the container, no large-scale field is being produced and there is no resistively slow saturation phase as otherwise expected. Secondly, the build-up of a large-scale field is demonstrated in a simulation where a localized magnetic eddy produces field on a larger scale if the eddy possesses a swirl. Such a set-up might be realizable experimentally through coils. Finally, new emerging issues regarding the connection between magnetic helicity and the solar dynamo are discussed. It is demonstrated that dynamos with a nonlocal (Babcock–Leighton type) α effect can also be catastrophically quenched, unless there are magnetic helicity fluxes.