Open Loop Control Strategies for Plasma Scenarios: Linear and Nonlinear Techniques for Configuration Transitions

This paper deals with the off-line optimization of poloidal field coil currents and voltages to obtain desired plasma scenarios including ramp up, flat top, and ramp down phases. The open loop control problem is solved via a quadratic optimization technique which requires the solution of a certain number of nonlinear plasma equilibrium problems. An alternative approach is based on the use of linearized models. This approach may fail during shape transitions where the effect of control on shape presents significant variations (e.g. limiter-diverted transition or plasma wobbling across a double null equilibrium configuration). To face these situations a novel methodology based on the SVD (singular value decomposition) is proposed, which also opens the way to a linear closed loop control of plasma shape during limiter-diverted configuration transitions. The proposed methodologies are applied to ITER scenarios