Design goals and status of the WENDELSTEIN 7-X project

WENDELSTEIN 7-X (W7-X) is a helical advanced stellarator (HELIAS) which produces the necessary twist of the plasma column only by magnet coils which enable steady state operation. W7-X aims to demonstrate that the HELIAS configuration is a viable alternative for a future power station. Major research and development activities have meanwhile been completed. These include the design of a machine sufficiently well advanced to allow the coil system to be manufactured, the power supplies to be ordered and the cryostat to be specified. The geometry and configuration of the non-planar magnet coils have a considerable impact on the design of the machine, in particular on the shape of the plasma vessel, the positioning of the plasma-facing components and the ports. The requirement for steady state operation has consequences for most of the subsystems of W7-X. The magnet coils are superconducting and must be cooled to 3.8 K by a helium refrigeration plant. The power supply for the magnet coils features a reliable protection system dumping the stored magnet energy in case of a rapid shutdown. The water-cooled divertor must be designed for heat loads of up to 10 MW m-2. ECRH, ICRH and NBI will provide the necessary power to heat the plasma. (author)