Toward coupling flow driven and magnetically driven dynamos

Abstract

Most large-scale dynamo research for astrophysical rotators focuses on interior flow driven helical dynamos (FDHDs), but larger scale coronal fields most directly influence observations. It is thus important to understand the relationship between coronal and interior fields. Coronal field relaxation is actually a type of magnetically dominated helical dynamo (MDHD). MDHDs also occur in fusion plasma devices where they drive a system toward its relaxed state in response to magnetic helicity injection that otherwise drives the system away from this state. Global scale fields of astrophysical rotators and jets are thus plausibly produced by a direct coupling between an interior FDHD and a coronal MDHD, interfaced by magnetic helicity transport through their mutual boundary. Tracking the magnetic helicity also elucidates how both FDHD and MDHDs evolve and saturate. The utility of magnetic helicity is unhampered by its non-gauge invariance since physical fields can always be recovered.