TURBULENCE IN WEAKLY IONIZED PROTOPLANETARY DISKS

We investigate the characteristic properties of self-sustained magneto-rotational instability (MRI) turbulence in low-ionized protoplanetary disks. We study the transition regime between active and dead zones, performing three-dimensional global non-ideal MHD simulations of stratified disks covering a range of magnetic Reynolds numbers between 2700 less than or similar to R-m less than or similar to 6600. We found converged and saturated MRI turbulence for Rm greater than or similar to 5000 with a strength of alpha(SS) similar to 0.01. Below R-m less than or similar to 5000, the MRI starts to decay at the midplane at first because the Elsasser number drops below 1. We find a transition regime between 3300 less than or similar to R-m less than or similar to 5000 where the MRI turbulence is still sustained but damped. At around R-m less than or similar to 3000, the MRI turbulence decays but could be reestablished due to the accumulation of the toroidal magnetic field or the radial transport of the magnetic field from the active region. Below R-m < 3000, the MRI cannot be sustained and is decaying. Here, hydrodynamical motions, like density waves, dominate. We observe anti-cyclonic vortices in the transition between the dead zone and the active zone.