A SIMPLE TYPE OF MAGNETICALLY DRIVEN JETS - AN ASTROPHYSICAL PLASMA GUN

We propose a simple theoretical formulation of the problem of magnetically driven outflows when poloidal magnetic flux surfaces are absent, and the magnetic field has only a toroidal component. The present formulation is the limiting case of the more general Grad-Shafranov one, when B-p/B-phi --> 0. We show that the toroidal magnetic field alone is very efficient in accelerating and collimating outflows (jets) from accretion disks. We therefore suggest that the important physical mechanism which might be responsible for jet production in the inner part of a fully ionized thick accretion disk around an active galactic nucleus is the buildup of the toroidal magnetic field component by the differential rotation of the disk, and its subsequent escape out of the disk. This is qualitatively different from the centrifugal driving mechanism of Blandford and Payne (1982), which might be important only in the partially ionized parts of the accretion disk where B-p similar to B-phi. Our formalism is also applied to describe briefly the time-dependent problem.