Magnetorotational instability (MRI) is a crucial mechanism for the amplification of magnetic field in astrophysical accretion disks, characterised by a state of differential rotation around a massive central object, such as neutron stars or black holes. The video shows a particle-in-cell (PIC) simulation of the evolution of the toroidal magnetic field in the meridian plane of a portion of a pair plasma (electron-positron) accretion disk, where the dimensions of the simulation box are small compared to the distance of the simulation from the centre of rotation. During the early time of the simulation, the MRI amplifies the magnetic field on the proper wavelength of the instability. Due to the collisionless nature of PIC simulations, the growth of the magnetic field activates a pressure anisotropy in the plasma. This anisotropy triggers another instability called mirror instability, which modifies the structure of the MRI magnetic field with oblique filaments of the magnetic filed on a smaller scale than the MRI’s one. The magnetic field continues to grow along with the formation of large channel flows (green/blue in the video). On large scale, it is possible to see that these channel flows are modulated in the radial direction by a drift-kink instability. At further time, magnetic reconnection destroy the channel flows and activate a turbulent motion that characterises the saturation regime of the MRI

References
G. Inchingolo, et al., Large scale PIC simulation of high beta magnetorotational instability, P1.413, 44th Conference of Plasma Physics of the European Physical Society (EPS), June 26-30 (2017), Belfast, UK