A conceptual design of a spherical tokamak power plant

The spherical tokamak (ST) has a very low aspect ratio, typically below ∼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.