Abstract

Magnetised Keplerian disks are subject to the magnetorotational instability (MRI) which is believed to drive their state of turbulence. Isothermal shearing box simulations with a mean magnetic field have shown that the resistivity controls the saturation state of the MRI : low resistivity yields sustained turbulence (active state, hot and magnetised) whereas strong resistivity shuts it off (dead state, cold and unmagnetised). Since the resistivity is generally a (decreasing) function of temperature, the heating due to the dissipation of turbulence provides an interesting backreaction on the system. field) where heating, cooling and the temperature-dependence of the resistivity have been included. These simulations all display strong recurrent or persistent channel flows. I will show how crucial the aspect ratio of the computational box appears to be. I will finally hint at how the parasitic instabilities of the channel flow might be at the heart of the saturation process of mean field simulations.

I will show how a very schematic model can account for the transition between such two states, which can be viewed as a system with two stable phases. I will then report on shearing box simulations (with a mean