Real-time Optimization of the q Profile Under Constraints for Avoidance of MHD Instability and Achievement of Stationary Conditions
W. Wehner, E. Schuster, J.R. Ferron, C.T. Holcomb, D.A. Humphreys, A.W. Hyatt, K.E. Thome, B.S. Victor
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Portland, OR, USA, November 5-9, 2018
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
feedforward and feedback control commands. Both command components are
computed via numerical optimal control techniques. The key advantage
of the numerical computation approach is that it allows 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 feedback controller
computes updates to the feedforward control law to account for
variability in plasma conditions; optimizing in real-time the plasma
response to the available actuator set over a finite horizon (number
of future control time-steps) while satisfying input and state
constraints.