Magnetic Collimation in Planetary Nebulae

Recent studies have focused on the the role of initially weak toroidalmagnetic fields embedded in a stellar wind as the agent for collimation inplanetary nebulae. In these models the wind is assumed to be permeated by ahelical magnetic field in which the poloidal component falls off faster thanthe toroidal component. The collimation only occurs after the wind is shockedat large distances from the stellar source. In this paper we re-examineassumptions built into this ``Magnetized Wind Blown Bubble'' (MWBB) model. Weshow that a self-consistent study of the model leads to a large parameterregime where the wind is self-collimated before the shock wave is encountered.We also explore the relation between winds in the MWBB model and those whichare produced via magneto-centrifugal processes. We conclude that a moredetailed examination of the role of self-collimation is needed in the contextof PNe studies