Heating of protostellar accretion discs associated with plasma inhomogeneities

The magnetorotational instability (MRI) is the most promising mechanism in driving angular momentum transport in the radial direction in accretion discs associated to T Tauri stars. However, the fact that this instability requires a minimum ionization fraction, makes it ineffective in the inner regions (i.e. at the midplane of the regions close to the central object) of these discs. In this work, we consider damping of Alfvén waves as a possible source of extra heating in the disc and analyse its effects for the ocurrence of the MRI in these systems. In particular, we focus on how the Kelvin-Helmholtz instability (KHI), associated with the presence of surface Alfvén waves, can develop, enhancing the energy dissipation due to a cascading of the wave energy. We take the Keplerian shear to be the main responsible for the onset of KHI and study how the development of such instability can influence the wave dissipation. Our results confirm that the triggering of this instability can greatly amplify the amount of energy released, as previously stated in the literature, and thus make MRI effective in a larger region of the disc. Finally, we argue that this mechanism, when applied to T Tauri discs, can couple both resonant absorption and turbulent damping of Alfvén waves.