2:00 PM - 2:15 PM
[PEM17-02] Stratified Simulations of Collisionless Accretion Disks by Kinetic MHD with Anisotropic Pressure
Keywords:accretion disk, collisionless plasma, MHD simulation
In this study, we pay attention to the effect of anisotropy of the thermal pressure. Including an anisotropic pressure tensor can modify the nature of the magnetorotational instability (MRI), which has been considered to play an important role for the angular momentum transport in accretion disks. We carried out series of kinetic MHD simulations using a stratified shearing box model, for the purpose of investigating the impact of pressure anisotropy on large scale dynamics of collisionless disks.
In the case of the standard MHD simulations with an isotropic pressure in a stratified domain, it is known that the disk threaded by a weak magnetic field is eventually filled with MRI-driven turbulence, which provides a sufficient rate of the angular momentum transport. This MRI-driven turbulence is considered to be responsible for production of a large-scale toroidal magnetic field observed in the stratified simulations, through some underlying disk dynamo process. We found that, once the effect of the anisotropic pressure is included, the resultant saturation level of the small-scale MRI-driven turbulence reduces to one third of that in the isotropic case with respect to the magnetic energy, due to the anisotropy with P⊥>P|| generated by the MRI itself. On the other hand, the magnetic energy contained in large-scale structure gets much smaller roughly by one order of magnitude, which implies that the dynamo action might not work efficiently in the collisionless disks. In our talk, we will discuss the dynamical behavior in more detail and try to give a theoretical explanation to the reduction of the turbulence and suppression of the disk dynamo.