Nonlinear burn control in tokamaks using in-vessel coils

摘要

The tokamak is a magnetic-confinement device where a plasma is confined with the final purpose of generating power from fusion reactions. Unfortunately, working points with favorable fusion conditions in tokamaks are normally found in a region in which the plasma may be thermally unstable. Therefore, regulation of the plasma temperature and density to produce a certain amount of fusion power while avoiding thermal instabilities, known as burn control, is one of the key issues that need to be solved for the success of burning plasma tokamaks such as ITER. Most previous controllers make use of approximate linearization techniques. In the present work, a model-based control approach using nonlinear techniques is proposed. This nonlinear control approach avoids approximate linearization of the model, is applicable to a greater range of operating conditions, and is stable against a larger set of perturbations. In addition to conventional actuation, like modulation of the auxiliary power and modulation of the fueling rate, the in-vessel coil system is considered as a new actuator. The in-vessel coils have the capability to generate non-axisymmetric magnetic fields that modify the plasma confinement, which influences the plasma energy dynamics. A model is proposed to account for the influence that the in-vessel coil actuation has on the plasma confinement. Finally, the effectiveness of the controller is demonstrated via a simulation study for an ITER-like scenario.