Interlinks between MHD turbulence and dynamos

de Gouveia Dal Pino Elisabete, dalpino@astro.iag.usp.br, IAG-USP, University of Sao Paulo, Brazil

Abstract
The role of MHD turbulence in astrophysical environments is still highly debated. In this lecture, we will discuss this issue in the framework of dynamo processes both, in diffuse media and in stars and accretion disks. In the context of turbulent diffuse media, like the intergalactic (IGM) and intracluster (ICM) media, the so called turbulent dynamo action is generally invoked to explain the amplification of seed magnetic fields as due to their stretching by turbulent eddies. This picture will be reviewed here considering kinetic effects which are particularly important in these collisonless plasmas. These kinetic effects introduce anisotropies in the fluid pressure which oblige to replace the standard MHD treatment of the turbulent fluid by a collisionless-MHD description. We will show the implications of this new approach in the turbulent amplification of magnetic fields in the IGM and ICM. In the context of stars and accretion disks, it is also well known that turbulent motions are a key ingredient for the dynamo operation. A less understood related problem is how the amplified magnetic fields are transported to the surface of these objects. We will discuss currently proposed pumping mechanisms as well as their limitations, and also a new mechanism for diffusive magnetic flux transport which is based on turbulent fast magnetic reconnection. This has been successfully tested in the framework of star formation and found to be rather efficient to decouple and remove the magnetic flux from denser to less dense regions. Numerical simulations of the applicability of this process to the solar and accretion disk dynamos will be also presented.