Magnetorotational instability driven dynamos at low magnetic Prandtl numbers
by
Petri Käpylä
→
Europe/Stockholm
122:026 (House 12)
122:026 (House 12)
Description
Numerical simulations of the magnetorotational instability (MRI) with zero initial net flux in a non-stratified isothermal cubic domain are used to demonstrate the importance of magnetic boundary conditions. In fully periodic systems the level of turbulence generated by the MRI strongly decreases as the magnetic Prandtl number (Pm), which is the ratio of kinematic viscosity and magnetic diffusion, is decreased. No MRI or dynamo action below Pm=1 is found, agreeing with earlier investigations. Using vertical field conditions, which allow magnetic helicity fluxes out of the system, the MRI is found to be excited in the range 0.1 < Pm < 10, and that the saturation level is independent of Pm. The non-vanishing magnetic helicity fluxes alleviate catastrophic quenching and allow strong large-scale magnetic fields to develop. When vertical field conditions are used, the Shakura--Sunyaev viscosity parameter has a value of the order of 0.2.
