1. Introduction

Nuclear fusion would have abundant, cheap fuel (deuterium and lithium), excellent safety, and environmental compatibility. A fusion reactor would need to heat the deuterium–tritium fuel to 10 keV (100 Million Kelvin) and confine it long enough for about 1 % of the fuel to “burn”. This can be done by using intense magnetic fields to confine the plasma electrons and ions and to provide thermal insulation between the hot plasma and the walls. Experimental “tokamaks” and “stellarators” are confining plasmas well on a small scale (plasma radius about 1 m), and a larger ITER experiment is under construction. A Demonstration Power Plant (DEMO) to generate electricity would be the next step after ITER. The final challenge will be to produce electricity that is economically competitive with other sources.