Resilience of helical fields to turbulent diffusion II: direct numerical simulations

Understand

The recent study of Blackman and Subramanian (Paper I) indicates that large scale helical magnetic fields are resilient to turbulent diffusion in the sense that helical fields stronger than a critical value, decay on slow (~resistively mediated), rather than fast ($\sim$ turbulent) time scales.

• This gives more credence to potential fossil field origin models of the magnetic fields in stars, galaxies and compact objects.
• We analyze a suite of direct numerical simulations (DNS) of decaying large scale helical magnetic fields in the presence of non-helical turbulence to further study the physics of helical field decay.
• We study two separate cases: (1) the initial field is large enough to decay resistively, is tracked until it transitions to decay fast, and the critical large scale helical field at that transition is sought; (2) the case of Paper I, wherein there is a critical initial helical field strength below which the field undergoes fast decay right from the beginning.