The WENDELSTEIN 7-X stellarator will test an optimised magnetic field configuration:
the quality of plasma equilibrium and confinement will be comparable to that of a
tokamak. With discharges lasting up to 30 minutes, WENDELSTEIN 7-X is to demonstrate
the essential property of stellarators, viz. continuous operation. Thus, WENDELSTEIN
7-X will be the first step in demonstrating that fusion devices of the stellarator
type are suitable for power plants.


is being built at the Greifswald Branch  Institute of the Max-Planck-Institut für Plasmaphysik (Germany). When completed, it will be the largest and most advanced stellarator in the world. The assembly will start in spring of 2004. The start of operation is planned for the year 2010.

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The technical core of the device is the coil system comprising 50 specially shaped single coils for producing the magnetic field cage confining the plasma. A further 20 planar coils will serve to vary the magnetic field. The long pulse times involved call for the use of superconductors (niobium-titanium) for the magnets. Manufacture of the stellarator coils is being handled by the German-Italian consortium, Babcock Noell Nuclear GmbH/Ansaldo Superconduttori SpA. Up to date three coils have been completed and more than half of the coils are in production. The acceptance tests for all coils are being conducted at the Low Temperature Institute of CEA Research Centre at Saclay in France. There, each coil is cooled in a cryostat to cryogenic temperature (4 K) and energized up to the rated current. The design margin with respect to quenching, i.e. disappearance of the superconducting properties, is then checked. The first non-planar coil was delivered to Saclay in June. It has successfully passed the functional tests and demonstrated the required operational margin. The first of the 20 planar magnet coils, which are being manufactured by the Tesla company in the United Kingdom, was delivered at the end of October.

The production of the cryostat by the Deggendorfer Werft company in Germany is making good progress. The cryostat is the thermally insulating vessel necessary for the coils operating at cryogenic temperatures. The ring-shaped cryostat with an inner diameter of about 8 m and an outer diameter of about 16 m, encloses the vacuum vessel equipped with about 300 ports affording access to the plasma vessel for heating, cooling and diagnostics to measure relevant parameters. The first segment of the plasma vessel and the ports will be delivered in November for installation of the first half-module. The appropriate two half-shells of the outer vessel will be supplied in spring 2004, but will not be needed for installation till 2006.

Strong support for the project is being given by the Associations of the European Fusion Programme. The Karlsruhe Research Centre (FZK) in Germany has successfully developed and is constructing the high-power (1 MWCW) gyrotrons. A microwave power of 10 megawatts at a frequency of 140 GHz in continuous operation mode will be installed for plasma generation and heating. The “Microwave Heating Project” established for this purpose is coordinating the various contributions from other Associations (CRPP, CEA), laboratories and industry (Thalès). The design and planning of the appropriate transmission lines are being performed by the Institute for Plasma Research (IPF) at the University of Stuttgart (Germany).

The superconducting bus system linking the coils with one another and with the current leads is being designed, manufactured, and installed by Jülich Research Centre (FZJ) in Germany. Tests of prototypes of the electrical connecting elements at cryogenic temperature were successfully completed at CRPP, at PSI in Switzerland and Russia’s Efremov Institute. An engineer from ENEA (Italy) is taking care of system engineering, while CIEMAT (Spain), the University of Vienna (Austria) and UKAEA (UK) are helping to supervise production. Experts from EFDA are also supporting the project in the mechanical structure area.