Alternative structural concepts for the fusion ignition research experiment (FIRE)

The baseline toroidal field coil system of the FIRE tokamak utilizes inertially cooled, copper alloy Bitter plate type magnets which are LN₂ cooled between shots. The TF configuration is wedged and uses C17510 high strength, high conductivity beryllium copper alloy which was developed for BPX in the inner leg, where the stress is highest. In FY 01, a slightly larger design was adopted (R=2.14 m. compared to the previous 2.0 m.) which affords better physics performance with lower TF field, and thus lower TF stresses. Bucked and wedged (B&W) TF designs have also been considered. The B&W design results in lower coil stresses in the inner leg that may be used to increase field or design margin, or alternatively could allow the use of high conductivity OFHC copper which would allow longer pulse lengths. B&W designs require good fit-up, and effects of fit-up uncertainties, friction factor variations, and methods of evaluating primary load paths are presented. The effects of the size change and possible change in structural concept are summarized.