Plasma vertical stabilization in ITER-FEAT

In this paper, we address the key issues related to the design of the plasma vertical position controller in ITER-FEAT. Some preliminary studies showed that—due to the use of ex-vessel control coils to stabilize the plasma vertical position—the closed-loop system has limited phase margin. As a consequence, its dynamic response deteriorates rapidly if delays (as due, for example, to the diagnostic system) increase above a certain threshold. To improve this situation, we investigate different control strategies and compare their robustness properties with respect to some specific plant perturbations.