First-Principles Model-based Robust Control of the Current Profile Evolution in the DIII-D Tokamak
J. Barton, M.D. Boyer, W. Shi, E. Schuster, T.C. Luce, J.R. Ferron, M.L. Walker, D.A. Humphreys, B.G. Penaflor and R.D. Johnson
American Control Conference
Montreal, Canada, June 27-29, 2012
Abstract
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Setting up a suitable toroidal current profile in a fusion tokamak
reactor is vital to the eventual realization of a commercial nuclear
fusion power plant. Creating the desired current profile during the
ramp-up and early flat-top phases of the plasma discharge and then
actively maintaining this target profile for the remainder of the
discharge is the goal at the DIII- D tokamak. The evolution of the
toroidal current profile in tokamaks is related to the evolution of
the poloidal magnetic flux profile, which is modeled by the magnetic
diffusion equation. A simplified first-principles-driven, nonlinear,
dynamic, control-oriented, partial differential equation model of the
poloidal flux profile evolution is obtained by combining the magnetic
diffusion equation with empirical correlations obtained from
experimental data at DIII-D and is used to synthesize a robust H_inf
feedback controller to track a desired reference trajectory of the
poloidal magnetic flux gradient profile. We employ a singular value
decomposition of the static gain matrix of the plant model to identify
the most relevant channels which we control with the feedback
controller. A framework for real-time feedforward + feedback control
was implemented in the DIII-D Plasma Control System and experimental
results in the DIII-D tokamak are presented to illustrate the
capabilities of the feedback controller. These experiments mark the
first time ever a first-principles-driven model-based magnetic profile
controller was successfully implemented and tested in a tokamak device.