Review. The path to fusion power 1107 (with fusion power 5.0 GW) to model D (fusion power 2.5 GW). The cost of fusion- generated electricity is dominated by the capital cost. It therefore depends very sensitively on (i) the cost of borrowing money or discount rate (D) and (ii) the availability of the plant (A), the dependence being approximately D0.6 (for D in the range 5–10%) A−0.6. The cost ﬁgures below assume 6 per cent for D (in real terms) and A = 0.75. The generating costs estimated in the European power plant study (EU Studies 2004) decreased from 9 Eurocents per kW h for an early model A to 5 Eurocents per kW h for an early model D (these costs would decrease as the technology matures). Even the model A result would be competitive with other generating costs if there was a signiﬁcant carbon tax, which now effectively exists in Europe with the Emissions Trading Scheme. If acceptable and necessary, larger plants (with Pe > 1.5 GW) would be more cost effective, as discussed above. These cost ﬁgures should not be taken too seriously in detail. The main point is that the order of magnitude is not unreasonable. The conclusion of the power plant study is that economically acceptable fusion power stations, with major safety and environmental advantages, seem to be accessible through ITER with material testing at IFMIF, and intensive development of fusion technologies. References Becoulet, A. & Hoang, G. T. 2008 The technology and science of steady-state operation in magnetically conﬁned plasmas. Plasma Phys. Control. Fusion 50, 124055. (doi:10.1088/ 0741-3335/50/12/124055) Bickerton, R. J., Connor, J. W. & Taylor, J. B. 1971 Diffusion driven plasma currents and bootstrap tokamak. Nature Phys. Sci. 229, 110. Budny, R. V. 2009 Comparisons of predicted plasma performance in ITER H-mode plasmas with various mixes of external heating. Nucl. Fusion 49, 085008. (doi:10.1088/0029- 5515/49/8/085008) EU Studies 2004 The EU studies of fusion power plant concepts. See http://www.wfda.org/ portal/downloads/efda_rep.htm. Fasel, D. & Tran, M. Q. 2005 Fus. Eng. Des. 75–79, 1163–1168. (doi:10.1016/j.fusengdes. 2005.06.345) Intergovernmental Panel on Climate Change (IPCC) 2007 Climate change: synthesis report. World Meteorological Organization and United Nations. See http://www.ipcc.ch/publications_ and_data/publications_ipcc_fourth_assessment_report_synthesis_report.htm. Ikeda, K. 2007 Progress in the ITER physics basis. Nucl. Fusion 47, 6. (doi:10.1088/ 0029-5515/47/6/E01) Keilhacker, M. et al. 1999 High fusion performance from deuterium–tritium plasmas in JET. Nucl. Fusion 39, 209. (doi:10.1088/0029-5515/39/2/306) Lako, P. et al. 1998 The long term potential of fusion power in Western Europe—MARKAL scenarios until 2100. ECN report No. ECN-C-98-071. McCracken, G. M. & Stott, P. E. 2005 Fusion: the energy of the Universe. Burlington, MA: Elsevier. Moeslang, A. et al. 2006 The IFMIF test facilities design. Fusion Eng. Des. 81, 863–871. (doi:10.1016/j.fusengdes.2005.07.044) Peng, Y.-K. M. et al. 2005 A component test facility based on the spherical tokamak. Plasma Phys. Control. Fusion 47 B263. (doi:10.1088/0741-3335/47/12B/S20) Tobita, K. et al. 2006 Design study of fusion DEMO plant at JAERI. Fusion Eng. Des. 81, 1151– 1158. (doi:10.1016/j.fusengdes.2005.08.058) Phil. Trans. R. Soc. A (2010)