Plasma response modeling for multivariable tokamak control design

The capabilities of the new DIII-D digital control system have motivated an effort to apply state-of-the-art multivariable techniques to control of the DIII-D tokamak. Tokamak plasma control is inherently multivariable in nature, since many closely coupled equilibrium parameters must be regulated simultaneously during a discharge. The present work describes the determination of dynamic models for plasma response and plasma interaction with conducting structures, necessary for calculation of accurate and robust multivariable control laws. Plasma response matrices and shape prediction matrices are calculated from analytic models and perturbed ideal MHD equilibria. Plasma resistive effects are described by a circuit equation which conserves poloidal flux on time scales shorter than the plasma L/R time. Shape estimation and plasma/conductor eigenmode spectrum results are presented along with experimental data and time-dependent simulations.