Laboratory Study of Magnetorotational Instability

Abstract

Magnetorotational Instability (MRI) is believed as the main driving mechanism of angular momentum transport in the system of accretion disk. Due to the importance of accretion disk in astrophysical system, myriad computational studies had been done in developing the model of MRI. Yet, in order to be accepted, these models require verifications from real world systems. Observational astronomy results are not enough to investigate the local behavior of MRI. Princeton MRI experiment, a liquid gallium-indium-tin alloy Taylor-Couette experiment, was proposed to recreate the instability in laboratory setting.

This work focused on computational effort to model the experiment through the use of finite element code SFEMaNS. First, underlying method used SFEMaNS was discussed as well as the improvement on simulation procedure which mimics the experimental procedure. Subsequently, main part of this thesis described the numerical mapping of MRI-unstable region on the parameter space of experiment by incorporating the recent change on experiment geometry. The results given by both MRI signal, or the volume averaged radial magnetic field, and jet velocity near the inner cylinder from large number of simulations showed definitive evidence of MRI-unstable region and its numerical threshold. Using the result of parameter space mapping, all three competing effects in the experiments: Ekman circulation, Rayleigh instability and MRI can be systematically isolated. The effect of Reynolds number and other type of configuration were also discussed and compared.

Following the results from numerical simulations, this work will propose new comparison method between diagnostics measurements and simulation results through the use of Hall sensor in addition to UDV measurement. Some modifications related to the high speed runs and new Hall sensor amplifier circuit were also discussed in order to prepare the device for reaching MRI-unstable region. Finally, comparison between simulation result and UDV measurement in low magnetic Reynolds number showed agreement on the behavior in high field limit where the flow is stabilized by magnetic field.