Wendelstein 7-X: Fusion research began in Greifswald ten years ago
In December 2015, plasma was ignited for the first time in Wendelstein 7-X. Various records were set in the fusion research facility in Greifswald since then.
Maintenance work in the plasma vessel of Wendelstein 7-X in Greifswald (November 2025)
(Image: Ben Peters/ MPI fĂĽr Plasmaphysik)
There was tense silence in the control room on December 10, 2015. All eyes were on a large monitor in the control center. Thomas Klinger, head of Wendelstein 7-X, called on the scientists, guests, and journalists present to count down for ten seconds – then there was a brief flash on the monitor: the First Plasma in the fusion research facility in Greifswald.
The Wendelstein 7-X is an experimental reactor in which gas is heated to several million degrees so that it transitions into the plasma state. Only in this state is it possible to fuse positively charged atomic nuclei together. Wendelstein 7-X, which heise online visited last year, serves only for plasma research; fusions are not carried out here.
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On that day in December ten years ago, it was possible for the first time to feed one milligram of helium gas into the plasma vessel, which is under vacuum, and heat it to a temperature of one million degrees Celsius using microwave heating with a power of 1.3 megawatts. For a tenth of a second, the helium transitioned into the plasma state.
Merkel starts hydrogen plasma
Two months later, in February 2016, the then Federal Chancellor and physicist Angela Merkel initiated the generation of the first hydrogen plasma, which is hotter than a helium plasma. This allowed scientific operation at the research facility of the Max Planck Institute for Plasma Physics (IPP) to begin.
The first plasma was preceded by a construction period of nine years: In April 2005, work began on the plasma vessel, in May 2014 the outer shell of the facility was closed and preparations for operation began.
Deuterium and tritium fuse into helium
The core of Wendelstein 7-X is a torus, a torus-shaped ring with a diameter of 16 meters, surrounded by 50 superconducting magnetic coils. In this chamber, designated as a stellarator, the conditions are created that cause the hydrogen isotopes deuterium (D) and tritium (T) to fuse into a helium nucleus. This releases neutrons and energy, which are to be used to generate electricity.
Nuclear fusion mimics the process that takes place in the interior of stars, including the sun. The sun releases enough energy that we are supplied with sufficient light and heat at a distance of about 150 million kilometers. However, the conditions in the sun – a pressure of 200 billion bar and a temperature of 15 million degrees Celsius – cannot be replicated on Earth. Because such high pressure cannot be generated here, the ignition temperature must be higher: 100 million degrees and more.
However, no material can withstand such temperatures. The plasma must therefore be held in suspension. This is ensured by 50 magnetic coils whose field encloses the plasma. The field has a complex shape: it is ring-shaped and twisted within itself. To generate such a field, the magnetic coils have special shapes: they resemble crushed rings. However, a supercomputer was required to calculate this shape.
