Physics-model-based Real-time Optimization for the Development of Steady-state Scenarios at DIII-D
W.P. Wehner, A. Pajares, E. Schuster, J.R. Ferron, D.A. Humphreys, R.D. Johnson, B.G. Penaflor, K.E. Thome, M.L. Walker, C.T. Holcomb, B.S. Victor
27th IAEA Fusion Energy Conference
Gandhinagar, India, October 22-27, 2018
Abstract
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In this work, a novel q profile control approach and recent DIII-D
experimental results aimed at reaching stationary plasmas characterized
by a flat loop voltage profile are presented. The control approach
combines commands computed both offline (feedforward) and online
(feedback). Both command components are computed via numerical optimal
control techniques. The key advantage of the numerical computation
approach is that it allows for the explicit incorporation of state and
input constraints to prevent the controller from driving the plasma
outside of stability limits and obtain, as closely as possible, stationary
conditions characterized by a flat loop voltage profile. Using a suitable
control-oriented model, the simulated plasma evolution in response to
the actuators is embedded into a nonlinear optimization problem that
provides a feedforward control policy (set of actuator waveforms) that
under ideal conditions guides the plasma evolution to the desired state.
The time trajectory of the plasma current, gyrotron power, and neutral
beam power are optimized to guide the plasma to stationary state
characterized by a flat loop voltage profile. It is shown in simulations
that an overshoot in the plasma current during ramp-up combined with a
particular timing of the gyrotron and neutral beam injection can improve
the uniformity of the loop voltage profile. The feedback controller
computes updates to the feedforward control law to account for variability
in plasma conditions; optimizing in real-time the model-predicted plasma
evolution in response to the available actuator set.