### Abstract

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 P _{eff} = v/D (where v is the coefficient of 'effective viscosity' associated with shear stress) would be large.

Original language | English (US) |
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Pages (from-to) | 1055-1060 |

Number of pages | 6 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 358 |

Issue number | 3 |

DOIs | |

State | Published - Apr 11 2005 |

### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Keywords

- Accretion, accretion discs
- MHD

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## Cite this

*Monthly Notices of the Royal Astronomical Society*,

*358*(3), 1055-1060. https://doi.org/10.1111/j.1365-2966.2005.08850.x