Publication Date:
2016-09-08
Description:
The redistribution of angular momentum is a long standing problem in our understanding of protoplanetary disc (PPD) evolution. The magnetorotational instability (MRI) is considered a likely mechanism. We present the results of a study involving multifluid global simulations including Ohmic dissipation, ambipolar diffusion and the Hall effect in a dynamic, self-consistent way. We focus on the turbulence resulting from the non-linear development of the MRI in radially stratified PPDs and compare with ideal magnetohydrodynamics simulations. In the multifluid simulations, the disc is initially set up to transition from a weak Hall-dominated regime, where the Hall effect is the dominant non-ideal effect but approximately the same as or weaker than the inductive term, to a strong Hall-dominated regime, where the Hall effect dominates the inductive term. As the simulations progress, a substantial portion of the disc develops into a weak Hall-dominated disc. We find a transition from turbulent to laminar flow in the inner regions of the disc, but without any corresponding overall density feature. We introduce a dimensionless parameter, α RM , to characterize accretion with α RM 0.1 corresponding to turbulent transport. We calculate the eddy turnover time, t eddy , and compared this with an effective recombination time-scale, t rcb , to determine whether the presence of turbulence necessitates non-equilibrium ionization calculations. We find that t rcb is typically around three orders of magnitude smaller than t eddy . Also, the ionization fraction does not vary appreciably. These two results suggest that these multifluid simulations should be comparable to single-fluid non-ideal simulations.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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