Optimal Estimation of Vessel Currents for Equilibrium Reconstruction Enhancement at DIII-D
Y. Ou, E. Schuster, J.R. Ferron and M.L. Walker
IEEE Conference on Decision and Control
San Diego, California, December 13-15, 2006
Abstract
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A tokamak discharge requires accurate feedback
control of many of the discharge parameters, including plasma
shape. Real-time estimation of the plasma boundary, which
is not directly measurable, is critical for shape control. One
of the available methods for plasma boundary estimation is
based on the equilibrium reconstruction. Equilibrium codes
calculate the distributions of flux and toroidal current density
over the plasma and surrounding vacuum region that best fit
the external magnetic measurements in a least square sense,
and that simultaneously satisfy the MHD equilibrium equation
(Grad-Shafranov equation). Although these codes use direct
measurements of the currents in the plasma and poloidal
coils, they usually neglect the current induced in the vessel
of the tokamak due to the simple fact that they cannot be
directly measured. Kalman filtering theory is employed in this
work to optimally estimate the current in the tokamak vessel.
The real-time version of the EFIT code is modified to accept
the estimated vessel currents with the goal of improving the
equilibrium reconstruction for the DIII-D tokamak.