Optimal number and position of the magnetic sensors for plasma shape identification in ITER

Position and number of the magnetic sensors affect the accuracy of the plasma shape identification algorithms. These algorithms usually solve an inverse problem based on the solution of the Grad-Shafranov equilibrium equation, and they need as input a certain number of magnetic field and flux measurements in points located around the plasma. The scope of this paper is to investigate on the problem of assessing the minimum number of magnetic sensors that are necessary for thesolution of the plasma shape identification in a tokamak machine. In particular, with reference to the ITER inner vessel magnetic diagnostic system, it is shown that, adopting a heuristic procedure, the available measurements are divided in two subsets, where the measurements in the first subset can be reconstructed by means of suitable linear combinations of measurements in the second subset. In this way, it is possible to evaluate the level of the redundancy of the ITER inner vessel diagnostic system andto outline a suitable fault management system.