Laboratory Studies of the Magneto-Rotational Instability in a Plasma

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

AST-0808095 Forest This project will study the MagnetoRotational Instability (MRI), carrying out the first-ever experiments with a newly constructed plasma couette flow device which uses a novel geometry to confine and stir a hot plasma. Accretion is a fundamental process by which virtually all astrophysical bodies form, but for a long time it was unclear what causes the disk matter to lose orbital energy, what it is that transports angular momentum outward and makes the disk material fall onto the central object. The current working hypothesis is that a weak magnetic field leads to a quickly growing magnetic instability, rendering the disk turbulent and tremendously increasing the effective viscosity, and this is supported by numerical simulation. Recent exciting experiments use liquid metals to study the MRI, but a plasma experiment allows larger magnetic Reynolds number and the variation of viscosity independent of conductivity, uses the state of matter most likely to occur in natural accretion, investigates the transition from weakly to strongly magnetized with only modest field strengths, and uses measurement techniques well-developed in plasma physics. Such an experiment has never been performed, but simple extrapolations from existing multi-dipole confinement experiments show it is feasible. This work will characterize the parameters of the ring cusp plasma with electrostatic stirring, search for signs of the MRI to compare to theory, and identify plasma-specific effects beyond the standard magneto-hydro-dynamical model. A central part of research includes the training and mentoring of undergraduate and graduate students, who are involved in all aspects of the project and will be sent regularly to scientific meetings to present their results. Outreach activities will include public lectures and press releases.