Magnetic Jets from Swirling Disks
  A broad swathe of astrophysical phenomena, ranging from tubular planetary nebulae through Herbig-Haro objects, radio-galaxy and quasar emissions to gamma-ray bursts and perhaps high-energy cosmic rays, may be driven by magnetically-dominated jets emanating from accretion disks. We give a self-contained account of the analytic theory of non-relativistic magnetically dominated jets wound up by a swirling disk and making a magnetic cavity in a background medium of any prescribed pressure, p(z). We solve the time-dependent problem for any specified distribution of magnetic flux P(R,0) emerging from the disk at z=0, with any specified disk angular velocity Omega_d(R). The physics required to do this involves only the freezing of the lines of force to the conducting medium and the principle of minimum energy. 
D. Lynden-Bell