Review. The path to fusion power 1103 Figure 4. The ITER project, ready for construction, is designed to produce at least 500 MW of fusion power. It is similar in conﬁguration to JET but twice as large (in each dimension) and it uses superconducting coils. (ii) The International Fusion Materials Irradiation Facility Various materials are known that may be able to remain robust under neutron bombardment characteristic of a fusion reactor. It is, in any case, foreseen that the most strongly affected components will be replaced periodically. However, before a fusion reactor can be licensed and built, it will be necessary to test the materials for many years under power station conditions. The only way to produce neutrons at the same rate and with essentially the same distributions of energies and intensity as those that will be experienced in a fusion power station is by constructing an accelerator-based test facility known as IFMIF (International Fusion Materials Irradiation Facility). IFMIF will operate for 24 h a day, every day. IFMIF, which will cost approximately ¤1B, will consist of two 5 MW accelerators that will accelerate deuterons to 40 MeV (very non-trivial devices). The two beams will hit a liquid lithium target that will produce neutrons, stripped out of the deuterons, with a spread of energies and an intensity close to that Phil. Trans. R. Soc. A (2010)