Implementation of model-based multivariable control on DIII–D

A model-based multivariable controller for plasma shape control has been successfully tested on the DIII–D tokamak. Good steady-state control of plasma boundary shape and X-point position was demonstrated in lower single-null ohmic plasmas. Quality of control for rapid plasma shape variation was mixed, but was robustly stable for all degrees of freedom explored. The control design was based on a linear plasma response model derived from fundamental physics assumptions, which was extensively validated against DIII–D experimental data. A linear controller produced with robust control design methods was tested and improved using results of closed loop simulations prior to experimental tests. A modification of the linear controller which addressed one of several practical DIII–D nonlinear constraints was tested during the experimental discharges.