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Using Edge Magnetic Activity in the HIT-SI Experiment to Explore Internal Magnetic Structure

Author: Jonathan S. Wrobel
Requested Type: Poster Only
Submitted: 2009-12-04 17:29:28

Co-authors: J.S. Wrobel, D.A. Ennis, C.J. Hansen, T.R. Jarboe, G.J. Marklin, B.A. Nelson, R.J. Smith

Contact Info:
University of Washington
AERB Building, Rm. 120, Box 35
Seattle, WA   98195-2

Abstract Text:
An array of surface magnetic probes embedded in the HIT-SI flux conserver has resolved plasma dynamics in the 10 Hz - 200 kHz frequency range. Four separate Amperian loops formed by the surface magnetic array have allowed the local toroidal plasma current to be measured, capturing both injector currents and the spheromak current. While global magnetic field oscillations at the 5.8 kHz injector driving frequency are present, unipolar toroidal currents indicate formation and sustainment of a spheromak. Spheromak current rise times as well as reversal times of 100 μs have been observed. The surface magnetic probe array provides an extensive and non-perturbative set of measurements to compare to numerical models. A new code developed to solve the zero-beta equilibrium equation mu0*J = curl(B) =Lambda*B on a tetrahedral mesh in an arbitrary 3-D geometry has been applied to the full HIT-SI geometry. This allows for non-uniform lambda profiles to be calculated as a superposition of each injector equilibrium and the spheromak equilibrium. Plans are to fit the computed lambda profiles to experimental data by scaling the amplitude of the injector equilibria by the experimentally measured injector parameters, and use a least squares fitting against surface probe data to scale the amplitude of a calculated spheromak equilibrium. Selecting a lambda profile and a magnitude that minimizes the fitting error for each time step will allow the evolution of the internal magnetics to be estimated from surface field measurements. Local deviations of the magnetic profile from a uniform Taylor model may show regions and rates of relaxation. Work supported by USDoE.

Characterization: A1,E3

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Innovative Confinement Concepts Workshop
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