CAN A DISC DYNAMO GENERATE LARGE-SCALE MAGNETIC-FIELDS

A dynamo process of some kind is widely believed to be able to operate in accretion discs and simple physical considerations suggest that fi elds generated in this way would have a canonical length-scale of the order of the disc thickness, H. However, in order to drive a hydromagn etic wind from a radius, R, it seems likely that the disc must be thre aded by poloidal magnetic fields with length-scales of order R or grea ter. We investigate how an inverse cascade process, involving reconnec tion of magnetic loops above and below the disc, might, in principle, lead to large-scale fields being generated by the dynamo.