The influence of confinement scaling on spherical tokamak power plant design and performance
Spherical tokamaks show great potential in being the basis for a compact fusion power plant. With a reduced aspect ratio and the benefit of increased plasma performance, spherical tokamaks provide a pathway for tokamak electricity production with reduced capital costs compared to conventional aspect ratio tokamak power plant designs.
The optimal design of a future fusion powerplant is highly sensitive to the plasma energy confinement time. Due to the complexity of the transport physics, scaling relations are developed from existing machines in order to extrapolate the expected performance. This procedure, however, is highly uncertain due to the large extrapolations involved and the relationship with the plasmas they are based on. Not only is there limited data on the highly radiative plasmas that a powerplant will require, there is also very limited data for how spherical tokamaks will behave. This introduces large uncertainty in designs and can lead to different optimisation solutions based on the scaling used.
For the first time, we show using the world-leading fusion power plant systems code PROCESS, the effect different energy confinement time scalings will have on the design and performance of a 1GWe net-electric spherical tokamak power plant. We compare a number of commonly used scalings and show the design impact of using spherical tokamak scalings verses those typically used on conventional aspect ratios, both in terms of size and performance. From this study we can start to quantify the uncertainty this produces and explain the origin of divergent designs presented in the literature.