The spherical Tokamak path to fusion power — Revisited

In their pioneering paper [1] Stambaugh et al developed the Peng-Hicks concept [2] of a fusion reactor based on a solid copper centre-post Spherical Tokamak (ST). Using the promising results from the START experiment [3], they produced a vision for a path to Fusion Power. This path had two elements: the ability to produce high fusion gain from an ST, and equally importantly, the ability to demonstrate this in a small (and therefore low cost) pilot plant device. In this paper we review various attempts to pursue this vision, and try to elucidate why success has not yet been achieved. However we show that the advent of high temperature superconductors (HTS) may overcome some of the problems, and we suggest a revised version of the small, low entry cost route to Fusion Power.