Cool underworld created for Wendelstein 7-X
Water cooling ready / major contract to regional company / channelling of funds to the region
The plasma in Wendelstein 7-X is to have a temperature of 100 million degrees: The objective of fusion research is to derive energy from fusion of atomic nuclei as the sun does. In order to ignite the fusion fire, the hydrogen plasma fuel in a future fusion power plant has to be thermally insulated by confining it in magnetic fields and be heated to extreme temperatures. On completion Wendelstein 7-X will be the world’s largest fusion device of the stellarator type its objective being to investigate this concept’s suitability for a power plant.
In order to attain the high plasma temperatures needed, a microwave heating system will pump ten megawatts of heating power into the plasma for up to 30 minutes twice a day. There will also be other heating systems. Correspondingly high are the requirements for the cooling system, which has to remove these huge quantities of heat from the walls of the plasma vessel – and which is likewise needed for a future fusion power plant. In a power plant not only, as in the Wendelstein 7-X experimental device, has the waste heat to be channelled off, but also the fusion energy produced in the plasma itself has to be transported to a turbine and a power generator.
In the Wendelstein device the heat is absorbed by about a hundred cubic metres of cooling water flowing around the heated components in closed cycles under high pressure. The heat absorbed is transferred by heat exchangers to a second cooling cycle supplied from a subterranean cold-water basin with a capacity of 1200 cubic metres. A regulator circuit mixes in just as much cooling water as is needed to maintain the temperature required by the components of the experiment. The heated cooling water then passes on to a catch basin and is recooled in cooling towers, finally returning to the cold-water basin. During the night it is further cooled here by cryogenic plants to the required start-up temperature.
The water cooling does not have to cater to the 70 more than man-sized magnet coils that produce the magnetic cage for the plasma: The superconducting coils are cooled by their own cryogenic system with liquid helium to a temperature close to absolute zero.
With its numerous cycling pumps, heat exchangers, filters, gauges, temperature sensors, switch cabinets, fittings and more than a thousand metres of piping, the water cooling extends from the technology building for the length of two basement floors of the experimentation hall: From the two subterranean water basins the pipelines traverse a 60 metre long connecting passageway into the lower basement floor of the experimentation hall, where the Wendelstein 7-X research device is now being built. Project head Rüdiger Krampitz states: “Installing the numerous components and large pipes in the tight space available with centimetre precision and without impediment presented a major challenge.” The bunched piping then passes through the basement ceiling into the upper basement floor. Separated into many single lines, they are finally connected – in a second construction phase starting in about three years – in the experimentation hall above to the several hundred supply ports of the fusion device.
After tendering from all over Europe, the 4.8 million euro large-scale contract for planning and constructing the first section of the cooling system was awarded in 2006 to the Anlagen- und Kraftwerksrohrleitungsbau company in Greifswald. More than 600 other companies in the region have already been involved in the construction of IPP’s Greifswald branch and the Wendelstein 7-X large-scale device: Since the year 2000 contracts to the value of more than 40 million euros have been awarded to companies domiciled in Mecklenburg-Vorpommern.