Helium Plasma Created In Stellarator Fusion Device

A technician inserts a diamagnetic coil into the plasma vessel of the Wendelstein 7-X reactor.

German researchers have successfully produced a helium plasma in their nuclear fusion device and are looking to produce a hydrogen plasma by the end of January. The Wendelstein 7-X is a stellarator type fusion device at the Max Planck Institute for Plasma Physics (IPP) in Greifswald in north eastern Germany. The core of the stellarator is a ring of 50 superconducting coils, each around 3.5 m tall. They are threaded onto a ring-shaped steel plasma vessel and encased by a steel shell. In the vacuum generated inside the shell, the coils are cooled down to superconduction temperature close to absolute zero using liquid helium. Once switched on, they consume hardly any energy. The magnetic cage they create keeps the 30 cubic metres of ultra-thin plasma – the test object – suspended inside the plasma vessel. As the fusion fire only ignites at temperatures in excess of 100 million degrees, the fuel must not come into contact with cold vessel walls. Confined by magnetic fields, it floats almost entirely contact-free in the interior of a vacuum chamber. “We’re starting with a plasma produced from the noble gas helium. We will not change over to the actual test object, a hydrogen plasma, until next year,” said project leader Thomas Klinger. “This is because it’s easier to achieve the plasma state with helium. Moreover, we can clean the surface of the plasma vessel with helium plasmas.” The first plasma in the machine lasted one tenth of a second and reached a temperature of around one million degrees. The team said everything went according to plan and in the next stages of the experiment, they want to extend the duration of the plasma discharges and to investigate the best method for producing and heating helium plasmas using microwaves. There are two different designs for the magnetic cage in nuclear reactors, the tokamak and the stellarator. An experimental tokamak reactor is currently under construction at Cadarache in southern France, however, the German researchers feel that if they can prove the viability of stellarators, they will have a significant advantage over tokamaks in being able to operate continuously.

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