Thirty kilometers northeast of Aix-en-Provence, on the edge of the Luberon National Park in southern France, an almost sixty-year-old dream is about to come true.

It is the dream of a clean and safe energy future for mankind.

The aim is to realize it on the site of the Cadarache research center with one of the greatest experiments ever created: the international ITER fusion reactor.

Manfred Lindinger

Editor in the “Nature and Science” section.

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The giant machine, when completed in four years, will tower over twenty stories. Inside, they want to simulate the process that takes place in the sun and has kept our stars burning for more than four billion years - the controlled fusion of hydrogen nuclei to form helium. If the project succeeds, mankind would have an almost inexhaustible source of energy available in a few decades, so the idea. Because just one gram of fuel - the hydrogen isotopes deuterium and tritium - would provide as much energy in a future fusion reactor as would be produced when burning eleven tons of coal, but without polluting the climate through the emission of carbon dioxide.

There is also no need to worry about a shortage of fuel.

After all, deuterium can be obtained from water and tritium via a nuclear reaction from lithium.

Since no long-lived radioactive waste would be produced, the problem of final disposal would be eliminated.

An accident like that of a nuclear power plant would also not have to be feared with a fusion power plant.

So is nuclear fusion the ideal source of energy to satisfy the world's unrestrained hunger for energy in the long term and to keep the global climate from collapsing?

For many, controlled nuclear fusion would come too late to be able to contribute anything to saving the global climate in this century.

Long, rocky and expensive

And indeed: if the fusion fire in Cadarache, France, should really ignite as planned by 2035, it will probably take until the end of the century for nuclear fusion to make a significant contribution to CO₂-free electricity generation. Because ITER is only intended to demonstrate that you can keep the solar fire burning for ten minutes, but not generate any electricity yourself. That will be reserved for the successor DEMO, which could go into operation in 2050 at the earliest. Only then would the way be clear for the first commercial power plants - provided ITER is a success. Because many questions are still open.

The road to controlled nuclear fusion is long, rocky and expensive. While only a few years passed from the discovery of nuclear fission in 1938 by Otto Hahn, Fritz Straßmann and Lise Meitner to the first functioning nuclear reactor, physicists have been working on a fusion reactor since the early 1950s. The task turned out to be more complex than expected, although the principle of nuclear fusion is comparatively simple: Two nuclei of the heavy hydrogen isotopes deuterium and tritium are brought together so closely that they fuse to form a helium nucleus. However, nuclear fusion only takes place under conditions such as those found in the center of the sun, and so many doubt whether what is happening in our star can even be realized on a large scale on earth.Because until now, existing fusion systems always had to use more energy to bring about a fusion of atomic nuclei than what ultimately came out.

The record for controlled nuclear fusion is still held by the largest existing fusion reactor, JET, in Culham, UK. In 1997, the nuclear fusion of deuterium and tritium achieved a yield of sixty percent for the first time. In the fall of this year, they want to rekindle the fusion fire in Culhalm. The experiments serve to prepare the experiments at ITER. However, JET is too small as a reactor to generate energy by fusing atomic nuclei.