Diffusion coefficient of a passive contaminant in a local MHD model of a turbulent accretion disc

Augusto Carballido, James McLellan Stone, James E. Pringle

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We calculate the radial diffusion coefficient for a passive contaminant in an accretion disc which is turbulent due to the action of the magnetorotational instability. Numerical magnetohydrodynamic (MHD) simulations are used to follow the evolution of a local patch of the disc using the shearing box formalism. A separate continuity equation for the mass fraction of contaminant is integrated along with the MHD system, and radial profiles of this fraction are obtained as a function of time. Solutions of a linear diffusion equation are fitted to the numerical measured profiles of the contaminant, treating the diffusion coefficient D as the fitting parameter. At early times, the value of D is found to vary; however, once the contaminant is spread over scales comparable to the box size, it saturates at a steady value. The ratio of D to the transport coefficient of angular momentum due to shear stress is small. If D can be used as a proxy for the turbulent magnetic diffusivity, the effective magnetic Prandtl number Peff = v/D (where v is the coefficient of 'effective viscosity' associated with shear stress) would be large.

Original languageEnglish (US)
Pages (from-to)1055-1060
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Apr 11 2005

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Accretion, accretion discs
  • MHD


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