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T. Sano, J. M. Stone (Univ. of Maryland)
The structure and evolution of accretion disks are largely determined by angular momentum transport processes. One of the most promising processes is MHD turbulence driven by the magnetorotational instability (MRI). The nonlinear regime of the MRI has been well studied in ideal MHD using numerical simulations. However, in some astrophysical systems, accretion disks are expected to be only partially ionized, in which case non-ideal MHD effects must be considered.
In circumstellar (protoplanetary) disks around young stars and in dwarf nova disks in quiescence, the Hall effect and ohmic dissipation are important. Recently, linear analyses of the MRI in the Hall regime has been presented by Wardle (1999) and Balbus & Terquem (2001). The maximum growth rate and characteristic wavelength of the MRI are strongly modified by the Hall effect. Most interesting is that the linear properties of the instability depend on the direction of magnetic field.
We investigate the effect of the Hall term on the nonlinear evolution of the MRI using 3D non-ideal MHD simulations. The local shearing box approximation is used for the calculations. The characteristics of the saturated turbulent state, which determines the accretion rate, are found to depend on the efficiency of the Hall term and ohmic dissipation. We discus the conditions for significant accretion rate in weakly ionized disks and apply the results to the evolutionary scenarios for protoplanetary and dwarf nova disks.