The Standard - Accretion Disk

We consider the classic MHD turbulent dynamo operating in a thin, Keplerian accretion disk powered by turbulent viscous stress. The character of the turbulence is encapsulated into two constant parameters: the Shakura-Sunyaev dimensionless viscosity, SS , and the Coriolis number, = 2 corr. The dependence of the total electromotive force on SS and is derived and the dynamo-generated magnetic eld is calculated in both ki-nematic and nonlinear regimes for a variety of diierent conditions in the halo. The calculations revealed that the dynamo number, D, increases with , but decreases with SS. The value of the critical dynamo number, D crit , depends on the magnetic diiusivity of the halo. In general, the smaller the halo diiusivity, the easier it is to generate the magnetic eld in the disk. The nonlinear models are calculated without taking into account the back-reaction of magnetic eld on the structure of the disk. Such an approach is consistent providing that the magnetic Mach number, M mag , is smaller than unity. We show that M mag is determined primarily by the value of , and that the consistency condition M mag < 1 requires, in some cases, turbulence with relatively large. In such a regime the dynamo number, the magnitude of the equilibrated large-scale magnetic eld, as well as the ratio of the poloidal and the toroidal magnetic eld strength, depend mostly on the value of SS. The generated eld has a quadrupolar symmetry with respect to the equator, is mostly connned within the disk's density scale-height, and is concentrated in the radially inner part of the disk. The obtained solutions are very regular , they lack any radial reversals, and no oscillatory or chaotic behavior has been found.