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Torr recently designed, manufactured, tested and supplied four special 1700mm long re-entrant viewports to the Max-Planck Institute.

These are being installed on the Wendelstein 7-X stellarator in Greifswald Germany as part of an ongoing system upgrade. Wendelstein 7-X is the world’s largest stellarator fusion machine. It is demonstrating the suitability of fusion systems of this type for power plants.

Because of the harsh operating conditions inside the stellerator, the viewport bodies were manufactured from low cobalt content 316LN and 316L stainless steel. The optics were made from Infrasil Grade 302, and they were vacuum brazed into a niobium weld ring to produce a part with a very low magentic permeability. As part of the contract, the viewport assemblies were vacuum baked for 24 hours and pre- and post-bake RGA helium leak tested.

Some of the photos below show the viewport assemblies in final test before being packed and shipped to MPI. The other photos show the exterior of Wendelstein 7-X (credit: IPP, Beate Kemnitz) and the station where they will be installed on the machine (credit: IPP, Antara Menzel-Barbara).

The SYSTEM upgrade is intended to further increase the heating energy without overloading the vessel wall. The current graphite plates of the divertor (credit: IPP) are to be replaced by water-cooled elements made of carbon fiber reinforced carbon.

Starting in 2022 they will gradually work their way up to plasmas lasting 30 minutes. Then it can be seen if Wendelstein 7-X can meet its optimization goals even in continuous operation – the main advantage of stellarators.

In order to achieve these goals, it is not necessary to produce an energy-supplying fusion plasma. This is because the properties of an ignited plasma can largely be transferred from the ITER tokamak to stellarators.

Wendelstein 7-X can therefore dispense with the use of the radioactive fusion fuel tritium with great cost savings.

There are more details here: https://www.ipp.mpg.de/9296/einfuehrung