Parameter space mapping of the Princeton magnetorotational instability experiment

Area of Science:

• Plasma physics
• Astrophysical fluid dynamics
• Computational physics

Background:

• Magnetorotational Instability (MRI) is crucial for accretion disks and astrophysical phenomena.
• Simulating MRI in laboratory experiments requires precise control of angular velocity and magnetic fields.
• Previous studies have explored MRI in various configurations, but mapping the unstable region is key.

Purpose of the Study:

• To map the Magnetorotational Instability (MRI)-unstable parameter space in the Princeton MRI Experiment.
• To identify key indicators of MRI and propose experimental diagnostics.
• To differentiate MRI from other instabilities like Ekman circulation and Rayleigh instability.

Main Methods:

• Utilized the Spectral/Finite Element code for Maxwell and Navier-Stokes Equations (SFEMaNS) for extensive simulations.
• Performed simulations varying inner cylinder angular velocity and applied vertical magnetic field.
• Analyzed poloidal mode structures and radial magnetic field growth as instability indicators.

Main Results:

• Successfully mapped the MRI-unstable region based on simulations.
• Identified a significant rise in normalized volume-averaged mean-square radial magnetic field within the expected MRI region.
• Demonstrated correlation between local fluid velocity/magnetic field and the volume-averaged indicator.

Conclusions:

• The Magnetorotational Instability (MRI) dominates fluid behavior in the simulated experimental parameter space.
• A diagnostic system measuring radial magnetic field on the inner cylinder is proposed for experimental validation.
• Simulation results provide a strong basis for comparing experimental outcomes with theoretical predictions.