Wendelstein 7-X produces first hydrogen plasma

On Wednesday, February 3, a hydrogen plasma of 80 million degrees was created in the Wendelstein 7-X stellarator for the first time. The plasma stayed neatly within the magnetic field of the reactor for less than a second, after which it disappeared again.

Chancellor Angela Merkel was allowed to press a button at the Max Planck Institute in Greifswald, Germany to start the process. Her action injected hydrogen into the Wendelstein 7-X to produce a hydrogen plasma that lasted for a split second.

This plasma was formed by heating a very small amount of hydrogen gas with a pulse of two megawatts of microwaves. This formed an extremely hot hydrogen plasma with a very low density. This means that the electrons of the atomic nuclei are split. This process and these extreme temperatures are controlled by magnetic fields. If something with a temperature of 80 million degrees were to hit the wall, it would inevitably lead to major problems.

This is the second phase of the research in Greifswald. The first phase started on December 10, 2015 with testing with helium. A plasma of helium is much less hot, up to about six million degrees. These tests served, among other things, to burn clean the inside of the walls of the plasma chamber. A plasma has already been formed 300 times with the helium plasma, slowly working towards the six million degrees.

The second phase of testing with the hydrogen gas will run until mid-March, after which the plasma chamber will be opened and carbon tiles will be installed to protect the walls of the chamber. After this it should be possible to reach much higher temperatures and to form a plasma for longer, up to ten seconds, explains Thomas Klinger on the site of the institute. In four years, discharges should last up to 30 minutes heated with 20 megawatts of energy, with the plasma reaching a temperature of about 100 million degrees.

Once that happens, there will be no nuclear fusion yet. The nuclear fusion that the researchers want to bring about requires a mixture of heavy and super-heavy hydrogen, namely deuterium and tritium. These reactions also make the reactor radioactive, something the Greifswald experiment was not built for.

Image of first hydrogen plasma in the Wendelstein 7-X

The reactor was built to investigate whether it is actually possible to produce energy with a stellarator reactor. The research should show whether a stellarator is indeed better at balancing the plasma than a more famous tokamak reactor. The latter is a fusion reactor in a donut shape. The problem with a tokamak is that it cannot hold plasma for long periods of time, because the plasma has to be kept in the donut shape with great effort by an enormous amount of power.

In a fusion reactor like a stellarator, the plasma can take on its natural shape, which should make it much easier to keep the plasma in the right place. The magnetic cage, which must contain the plasma, is formed by very strong magnets. The magnets must take intricate shapes in a stellarator; it is therefore very difficult to calculate the correct shape. The Wendelstein 7-X consists of about 20 million parts that all have to fit together with the greatest possible precision.

The aim of the research is to eventually develop a power plant that generates energy with nuclear fusion, just like the sun and stars do. A fusion process only starts at more than 100 million degrees, while the plasma may not come into contact with the walls of the reactor vessel. Those walls are extremely cold because the magnets have to be cooled to near absolute zero of -273.15 degrees Celsius.

A tokamak reactor, ITER, is currently being built in Cadarache, France. This reactor was supposed to start operating in 2016, but that has been postponed until at least 2020. The first experiments will hopefully take place in 2027.