Model-based approach for magnetic reconstruction in axisymmetric nuclear fusion machines

This paper describes an approach for the magnetic reconstruction of large-scale tokamak devices that is suitable for real-time employment in order to provide reference for active control action during the whole plasma evolution. This problem can be seen as a free boundary problem, where the shape features of the plasma are determined by the equilibrium with the external sources, namely, the active circuit currents and the eddy currents flowing in the passive structures. In this respect, a dynamic model is needed to estimate the induced currents and provide a consistent representation of the whole system behavior during the entire plasma discharge. Such a model is then coupled with an iterative optimization procedure to provide a model of the plasma that, superimposed with the external sources, minimizes the error of the reconstructed magnetic map with reference to the available sensor measurements. The analysis and validation of this approach are presented, resulting in a procedure that appears to accurately follow the behavior of the system during both slow varying evolution and strongly dynamic events.