Fusion Ignition Research Experiment (FIRE) magnet system structural analyses

The toroidal field coil system of the FIRE tokamak utilizes inertially cooled, copper alloy Bitter plate type magnets which are LN2 cooled between shots. The baseline configuration is wedged. C17510 high strength, high conductivity beryllium copper alloy developed for BPX is proposed for the conductor. These design choices were made after considering a number of alternative structural concepts and a variety of conductor materials. FIRE's high elongation and double null plasma results in high overturning moments. The use of a large compression ring and the large centering forces provides adequate frictional wedging pressures to support the inner leg out-of-plane (OOP) forces. Studies of the pulse length indicate flat top time of 12 sec at peak field and nuclear heat. Non-linear friction simulations have been performed to confirm OOP load support. Structural criteria for the FIRE reactor require demonstration of adequate ductility of the conductor material. Examination of the elastic plastic behavior of the coils for overloaded conditions, 13T, and 14T, has been used to satisfy this criteria, and demonstrate margin. Discussions of primary load paths and evaluation of primary stresses are presented. The contribution of the central tie rod assembly was found to be too small in reducing the inner leg vertical tension stress, and the tie rod has been removed.