Mechanical analysis of the EC upper launcher with respect to electromagnetic loads

Abstract The design of the EC upper launcher for ITER approaches maturity and thus it needs to be qualified with respect to the critical loads. One major source of critical loads are eddy currents, which are induced in the structure during plasma instabilities, of which the most severe conditions may happen during a vertical displacement event (VDE) followed by a fast current quench. High mechanical loads are then acting on the front end of the cantilevered launcher structure as a consequence of the interaction between the static toroidal field and the eddy currents. The EC upper launcher has a length of about 6 m and the nominal gap to the neighbouring components is 20 mm. The targeted limit for the launcher displacements is 10 mm, when accounting for tolerances in manufacturing, positioning and thermal displacement. The conceptual design of the launcher is at risk to miss this requirement, thus different configurations of the main frame are considered and analysed. Especially, the cross-section of the single wall segment has been varied to identify the most efficient strategy for increasing the stiffness of the structure. For this purpose, the mechanical loads from an upward VDE (linear current decay from 15 to 0 MA within 40 ms) are used as input to a finite element analysis with the ANSYS software tool. The displacement at the free plasma facing end of the launcher is calculated and analyzed. Its main component is in toroidal direction and the effort of mitigation is concentrated primarily on the bottom-wall. The approach satisfies the limitations given by the space requests of the mm-wave system which is to be integrated into the port plug.