Magnetic Shearing Instability and Magneto-Hydrodynamic Turbulence in Accretion disks

Physics

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Scientific paper

In previous work magnetic shearing instability (MSI) with vertical magnetic field was shown to induce strong magneto-hydrodynamic (MHD) turbulence in thin, Keplarian accretion disks. Despite the fact that the linear growth rate of MSI maximizes at small scales where k ~ Omega /VA_0, the angular momentum transport is dominated by the magnetic Reynolds stress on large scales where k ~ H(-1) . It was also shown by a simple quasilinear analysis that a mean azimuthal magnetic field B_theta can be generated by an alpha -omega dynamo-like process. In the present work, the physics of accretion disks with azimuthal magnetic field is investigated. The discussion includes three major parts: First, the properties of the azimuthal-magnetic-field-induced MSI turbulence, especially the saturation of the fluctuation fields, the angular momentum flux (due to B_theta ), and the energy dissipation processes, are analyzed in detail. The second part is to evaluate the amplitude of B_theta as a function of B_z, which is the dipole magnetic field originating from the central object and penetrating the accretion disk. In this part, both nonlinear back-reaction and magnetic buoyancy effects are considered. The coupling of MSI to Parker instability is also discussed. Finally, we analyze the interaction between internal waves and MSI turbulence, and its implication on the angular momentun transport in accretion disks.
Work supported by NASA grant NAGW 2418.
W. Z. Liang, P. H. Diamomd, and E. T. Vishniac, submitted to Ap.J. (1992).

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