  Based on theoretical arguments and quasi-stationary radiative MHD
calculations, a model for an accretion-powered jet is presented. It is argued
that accretion disks around BHs consist of 1) a cold, Keplerian-rotating and
weakly magnetized mediumin the outer part, 2) a highly advective and
turbulent-free plasma inside $r_\mm{tr}=10-20$ Schwarzschild radii, where
magnetic fields are predominantly of large scale topology and in excess of
thermal equipartition, and 3) an ion-dominated torus in the vicinity of the
hole, where magnetic fields undergo a topological change into a monopole
like-configuration. The action of magnetic fields interior to $r_\mm{tr}$ is to
initiate torsional {\Alfven} waves that extract angular momentum from the
disk-plasma and deposit it into the transition layer (-TL) above the disk,
where the plasma is dissipative and tenuous. A significant fraction of the
shear-generated toroidal magnetic field reconnects in the TL, thereby heating
the plasma up to the virial-temperature and forming a super-Keplerian rotating,
and hence centrifugally accelerated outflow. The strong magnetic field in the
TL forces the electrons to cool rapidly yielding thereby an ion-dominated
outflow. The toroidal magnetic field in the TL is in thermal equipartition with
the ions, whereas the poloidal component is in equipartition with the
electrons. Such a strong toroidal magnetic field is essential for increasing
the jet-disk luminosity in the radio regime.

Astrophysics