  A novel model for collimation and transport of electron-positron-ion jets is
presented. Analytical results show that the filamentary structures can be
sustained by self-induced toroidal magnetic fields permeating through the
filaments, whose widths significantly expand in the pair-dominant regimes. The
magnetic field strength reflects a characteristic of equipartition of excess
kinetic energy of the jets. It is also shown that growth of the hoselike
instability is strongly suppressed. Essential features derived from this model
are consistent with recent results observed by using very long baseline
telescopes.
