Princeton University Astroplasmas Seminar

The magnetorotational instability (MRI) is a fundamental process occurring in astrophysical accretion disks. The MRI promotes accretion by driving turbulence on macroscopic scales. In the process, magnetic reconnection and other collective plasma phenomena can accelerate particles to high (possibly nonthermal) energies. The resulting plasma emission may be measurable with observational campaigns.

In radiatively inefficient accretion flows, plasmas are expected to be collisionless. This invokes the use of Particle-in-Cell (PiC) methods to study the dynamics of the MRI in these environments. However, the scale separation between macroscopic and kinetic scales is extremely large for realistic systems. For this reason, only a small number of works have been produced where the MRI is studied with PiC simulations, often with a very limited exploration of the available parameter space and with limited dimensionality.

We are revisiting PiC simulations of the MRI by exploring the parameter space (temporal and spatial scale separation) in detail, and considering different field geometries in the 2D and 3D cases. We find that even in the 2D pair-plasma case, very large simulations are needed to minimize the effect of the limited scale separation; this carries over to the 3D case. Moreover, the field geometry and the dimensionality of the simulation heavily influence the results. Our findings are important in the context of ultimately perform ion-electron 3D simulations of the MRI with PiC, in order to gain insight into the microphysics of observationally targeted RIAFs.