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Graduate Student Seminar - 03/12/2010

"Diamagnetism of Rotating Plasma in Shaped Magnetic Fields"

by William Young

Friday, March 12, 2010 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Dr. Adil Hassam

A combination of diamagnetic and magnetic pickup loops external to the Maryland Centrifugal Experiment's (MCX) vacuum vessel measure changes in the local radial magnetic field and the averaged axial magnetic field. The measurements provide an axial profile of the rotating plasma's diamagnetism on a millisecond timescale limited by the L/R time of the vacuum vessel. The results are compared to ideal MHD equilibrium theory. The theory yields 2-D density profiles from parallel dynamics and the magnetic flux function from a solution of the crossfield Grad-Shafranov equation including supersonic rotation. The flux function is obtained by numerically solving for a perturbative (low Alfven Mach number) solution. Combined with density measurements from a midplane and an off-midplane interferometer, the numerical model is compared to the DML and the Br data. There is sufficient data to constrain the model, and this provides an estimate of the plasma temperature and constitutes a test for the efficacy of centrifugal confinement, a central goal of the MCX experiment. The data also provide some insight into various parameter profiles and symmetry. Analysis shows remarkable agreement for the magnitudes and axial profiles of plasma diamagnetism across broad parameter variations. There is a clear signature of the presence of centrifugal confinement in the theory from an exponential Boltzmann factor. This signature is compared directly to the data, and a clear correspondence is demonstrated.

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