Speaker
Description
Accretion discs require some mechanism to remove angular momentum in order to match observed accretion rates. Turbulence induced by the magneto-rotational instability (MRI) is one leading theory. Most numerical studies of the MRI rely on local shearing box approximations, whereby a small patch of an accretion disc is simulated. However, these artificial boundary conditions necessarily miss the complex dynamics of global discs. We present the results of global, three-dimensional accretion disc simulations of MRI-driven turbulence using the Phantom smoothed particle magnetohydrodynamics (SPMHD) code and the exascale Shamrock code. We show that SPMHD can activate the MRI in global disc simulations, with turbulence sustained over long time integrations with alpha stresses consistent with expectation. We find that the standard SPMHD scheme in Phantom, however, incurs excessive resolution requirements to activate the MRI and correctly evolve MRI-induced turbulence in global discs. We will discuss the origins of this issue, and provide simple, computationally inexpensive changes to the numerical scheme that overcome it. Our results pave the way for the general study of magnetized, global accretion discs using SPMHD.
