Review. The path to fusion power 1095 D T He He T T + He lithium blanket plasma D + T steam generator turbine generator Figure 1. A conceptual tokamak fusion plant (not to scale) showing the three parts: a fusion burning D–T plasma; a lithium ‘blanket’; and a turbine-driven generator delivering electricity to the grid. Ip magnetic circuit (iron transformer core) inner poloidal field coils (primary transformer circuit) toroidal field coils outer poloidal fields coils (for plasma positioning and shaping) poloidal field toroidal field plasma with plasma current, Ip (secondary transformer circuit) resultant helical magnetic field (exaggerated) Figure 2. In a tokamak, the fusion fuel is held in a toroidal chamber surrounded by magnets. A current is induced in the fuel by transformer action and, together with the toroidal ﬁeld coils, produces a helical magnetic structure that holds the hot fuel away from the wall. produce tritium. The production of additional neutrons can be enhanced, e.g. by adding beryllium or lead. The result is that, on paper at least, it is possible to design fusion reactors that would produce enough tritium for their own use, plus a small surplus to start up new plants. For safety reasons it is desirable to keep the tritium inventory low. Thus, it is important to remove the tritium from the blanket regularly. The neutrons will also slow down and deposit their energy (4/5ths of the fusion power—about 2.8 GW) in the blanket. The blanket will heat up to around 400◦C in the so-called ‘near-term’ power plants that would use relatively ordinary materials. In advanced models that use materials such as silicon carbide it could Phil. Trans. R. Soc. A (2010)