Vacuum in fusion reactors


The sun as a prototype

The need and demand for clean energy from alternative sources is growing as global warming and climate change continue. Scientists have been trying for many years to replicate the sun here on Earth in order to generate energy according to its example. This would involve hydrogen nuclei being fused to form a helium nucleus – i.e. nuclear fusion would have to take place. The greatest difficulty is replicating the extreme conditions that prevail on the star at the center of our solar system, because the conditions on the sun are completely different to those here on our Earth.

The principle of nuclear fusion
In order to be able to take the principle of nuclear fusion, with which a surface temperature of approximately 6,000 degrees Celsius is reached on the sun, and to use it here on Earth for generating energy, we need to reproduce the reaction of the sun. Vacuum technology plays an important role here, since the sun is surrounded by vacuum.

Large experimental constructions, known as nuclear fusion reactors, are used to recreate solar conditions here on Earth.

The nuclear fusion reactor is a technical plant in which the nuclei of atoms are fused together in a controlled manner in a thermonuclear reaction. The aim of the nuclear fusion process is to generate electricity, since an enormous amount of energy is released when the nuclei of the atoms fuse together.

There are currently two common reactor types: tokamak and stellarator. Both reactor types basically work on the same principle. The differences lie in the shape and arrangement of the coils that generate the magnetic field. Both types involve heating hydrogen or hydrogen isotopes to up to 150 million degrees Celsius. To generate such heat, the plasma needs to float freely in a vacuum, since any contact with other particles or walls allows heat to escape. Therefore, a magnetic field with a strength of up to 10 Tesla is often generated with the help of superconducting electromagnets. The plasma is then heated by means of electric heating or electromagnetic waves to cause, in the best case, nuclear fusion.

Wendelstein 7-X in March 2014, shortly before completion of the main installation phase
Wendelstein 7-X in March 2014, shortly before completion of the main installation phase (image: IPP, Beate Kemnitz)

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