Dynamo theories

A Magnetic αω Dynamo in Active Galactic Nuclei Disks: II. Magnetic Field Generation, Theories and Simulations

It is shown that a dynamo can operate in an Active Galactic Nuclei (AGN) accretion disk due to the Keplerian shear and due to the helical motions of expanding and twisting plumes of plasma heated by many star passages through the disk. Each plume rotates a fraction of the toroidal flux into poloidal flux, always in the same direction, through a finite angle, and proportional to its diameter. Th...

Dynamo Mechanisms

Dynamo theory is reviewed with particular emphasis on recent developments. There now seems to be a strong case for dynamo eeects that are driven by the magnetic eld itself. This is linked to recent interpretations of the observed stellar cycle periods which suggest that the ratio of cycle frequency to rotational frequency increases, up to some point, with stellar chromospheric activity. This ra...

Accretion-disk dynamo models with dynamo-induced alpha-effect

A nonlinear 1D dynamo model with a heuristic -ansatz for magnetic field-induced turbulence is considered growing for weak fields and suppressed by strong fields. The amplification of initial magnetic fields is regarded in accretion disks like both Kepler disks and galaxies. The solutions for the magnetic field are symmetric with respect to the equator, they are steady for positive -effect and o...

A growing dynamo from a saturated Roberts flow dynamo

Using direct simulations, weakly nonlinear theory and nonlinear mean-field theory, it is shown that the quenched velocity field of a saturated nonlinear dynamo can itself act as a kinematic dynamo. The flow is driven by a forcing function that would produce a Roberts flow in the absence of a magnetic field. This result confirms an analogous finding by F. Cattaneo & S. M. Tobias (arXiv:0809.1801...

Small-Scale-Field Dynamo.