Nuclear fusion and its large potential for the future world energy supply

The energy problem in the world is outlined to show the enormous task of «decarbonizing» the current energy system, with $\sim85\%$ of the primary energy from fossil sources. Currently only two options offer a solution to reduce CO$_2$ emissions: renewable energy (sun, wind, hydro,…) or nuclear fission. Their contributions, $\sim2\%$ for intermittent sun and wind, $\sim6\%$ for hydro power and $\sim5\%$ for fission, must be enormously increased in a relatively short time to meet the targets set by policy makers. In several countries, and in particular in the EU, there is a growing tendency to rule out nuclear fission for energy production. It is therefore questionable if «decarboniztion» is feasible with the currently available techniques, without avoiding difficulties in the energy supply. Additional environmentally friendly options to produce energy will therefore be very welcome. Fusion is such a candidate and a very important one, because of its inherent properties: nearly inexhaustible, no production of greenhouse gases or long term waste and safe. The principles of magnetic confinement are outlined and the two main options for magnetic confinement, tokamak and stellarator, explained. The status of magnetic fusion is summarized and the next steps in fusion research, ITER and DEMO, briefly presented.