Optimization of the FTU toroidal limiter shape

The FTU machine is now operating with an Inconel/stainless steel poloidal limiter. The necessity to withstand a large heat flux in the radio-frequency heating operational phase and to minimize plasma edge asymmetries has induced the feasibility of a toroidal limiter to be assessed. The take into account heat loads due to inevitable misalignments in the radial positioning of the limiter sectors, a 3-D analysis of the problem was carried out. Within this analysis, the shadowing between adjacent sectors has been found to be the most critical factor because of the shortness of energy decay length. In spite of the 3-D optimization of the limiter surface, peak heat load strongly increases with the safety factor at the edge and reaches up to a factor of 4 with respect to the average heat load.