Plasma Reconstruction in Tokamaks with Linearized Approaches

This paper deals with the problem of the equilibrium reconstruction in a tokamak. We firstly describe two approaches for the shape reconstruction: the former based on a nonlinear least square minimization with Finite Element Method modelling taking into account the Grad Shafranov equilibrium equation; the latter based on linear multifilament models accounting for the presence of iron, eddy currents in the passive structures, and plasma. A possible unified treatment for shape and current profile reconstruction using both internal and external measurements is then discussed: the nonlinear least square minimization procedure used for shape identification is modified to account for internal measurements and profile shape fitting. A linearized approach is finally analysed making use of Singular Value Decomposition theory. Some results on the JET tokamak are shown and discussed.