Magnetic helicity is the scalar product of the magnetic field and the magnetic vector potential. Astrophysical magnetic fields are often helical, which has far reaching implications for their dynamics.
During the magnetic field generation through the dynamo process magnetic helicity impedes the growth of the field, which makes it an undesirable ingredient. How this impeding (quenching) depends on various parameters is studied quantitatively, as well as how fluxes of helicity can reduce the quenching mechanism.
The gauge dependence of magnetic helicity raises questions about its physical relevance. I will show how this issue can be resolved in direct numerical simulations and how the transport of helicity is altered by the gauge choice.
The topological interpretation of magnetic helicity as linking of field lines makes it an intriguing quantity for testing field line topologies. I will show various topologically non-trivial field configurations consisting of linked rings and knots, of which some are helical and others are non-helical. The topology itself does not have any major influence on the relaxation dynamics. The content of magnetic helicity, however, strongly changes the dynamics.
