Exploration and Reproducibility of Advanced Plasma Scenarios via Current and Rotation Profile Control in DIII-D

Experimental results in DIII-D successfully demonstrate the potential of physics-model-based control for systematic attainment of desired plasma internal profiles, with the subsequent benefit of enabling exploration and reproducibility. The control scheme is constructed by embedding a nonlinear, controloriented, physics-based model of the plasma dynamics into the control design process. This modeling approach combines first-principles laws with empirical correlations obtained from physical observations, which leads to partial-differential-equation (PDE) control-oriented models capturing the highdimensionality and nonlinearity of the plasma response. Model-based control design includes not only the synthesis of feedback controllers (based on reduced-order models) for robust regulation or tracking, but also the determination of optimal feedforward actuator trajectories (based on higher-order models) for a systematic approach to scenario planning. To steer the plasma to the desired state, model predictive control (MPC) numerically solves successive optimization problems in real time over a receding time horizon by exploiting efficient quadratic programming techniques. A key advantage of this control approach is that it allows for explicit incorporation of state/input constraints to prevent the controller from driving the plasma outside of stability/performance limits and obtain, as closelyas possible, steady state conditions. The enabler of this feedback-control approach is the control-oriented model capturing the dominant physics of the plasma response to the available actuators. Simulations and experiments suggest that control-oriented model-based scenario planning (feedforward control) in combination with MPC (feedback control) can play a crucial role in exploring performance and stability limits of scenarios of interest. Simulated and experimental results will be presented to illustrate DIII-D’s present capabilities for current-profile and rotation-profile control in combination with βN regulation.