MHD Closure for Pressure Anisotropy

MHD Closure for Kinetic Pressure Anisotropy Instabilities

Accretion disks around black holes are often simulated as magnetohydrodynamic fluids, a model which is only valid when the plasma that makes up the disk is highly collisional. However, in systems such as radiatively inefficient accretion disks, the collisional mean free path is much larger than the disk’s characteristic length, meaning that a kinetic approach should be more accurate. However, the PIC and hybrid simulations needed to model kinetic effects are much more computationally expensive than simulations that solve the standard MHD equations. Can we somehow modify the MHD equations to accurately capture the relevant kinetic (firehose and mirror) instabilities?

This research was the topic of my undergraduate thesis.