Conceptual design of a spherical tokamak power plant

The spherical tokamak (ST) has a very low aspect ratio, typically below approximately 1.8, which allows operation at high beta. The ST also offers stability at high elongation which permits operation at high bootstrap current fraction leaving only a modest external current drive requirement. Results from START indicate the ST has resilience to disruptions and low halo currents when disruptions are triggered. In order to explore these potential advantages, a conceptual design of a steady-state ST power plant is being developed for which the thermodynamic, neutronic and mechanical design of the plant have been iterated, together with the plasma parameters, to give a consistent design. The baseline design uses water cooled copper for the centre rod and return limbs of the toroidal field (TF) coils with minimal steel shielding around the rod giving a simple coil design. A helium cooled ceramic pebble bed blanket with beryllium multiplier is used to generate the required tritium and achieve a high thermal efficiency.