Overview of main-mechanical-components and critical manufacturing aspects of the Wendelstein 7-X Cryostat

Wendelstein 7-X (W7-X) will demonstrate the possibility of a stellarator for a future fusion power plant. This stellarator fusion experiment is at present in the assembly phase at the Max-Planck-Institut für Plasmaphysik (IPP). The main advance of the static plasma is caused by the three dimensional shape of the coils. But inside the Cryostat this extravagant geometry of the coils efforts also a three dimensional contour of the main mechanical components. One of the ambitious challenges is how to build up such complex machine. The manufacturing of these complex devices have been demanded the newest manufacturing methods. At 2014 Wendelstein 7-X will be the world´s largest superconducting helical advanced stellarator. The toroidal plasma vessel geometry follows exactly the three dimensional shape of the plasma. It contains the plasma with a great diameter of 11m and an average plasma diameter of 1.1 m. To control the plasma geometry it is necessary that all the 20 planar and 50 non planar coils are not only extreme narrow positioned to the Plasma Vessel but also within a tolerance of 1.5 mm to each other. To meet this requirement and to withstand the high magnetic forces a complex coil support structure was created. The Central Support Ring have to bear the coils but the different inter coil supports canalize the forces by very stiff connections on one side and sliding areas on the other side. The coils and the support structure are enclosed within the Outer Vessel with its domes and openings. The Outer Vessel, the Plasma Vessel and the ports generate the boundaries for the Cryostat. The vacuum inside provides thermal insulation of the magnet system which is cooled down to 4 K. The 254 ports secure the access to the Plasma Vessel with all the supply lines and the diagnostics. Due to the different thermal movements the Plasma Vessel, Outer Vessel and the Central Support Ring have to be supported separately. The Central Support Ring is held by 10 cryo legs. T- - he Plasma Vessel supporting system is divided into two separate systems, allowing horizontal and vertical adjustments to centre the Plasma Vessel during thermal expansion. Beside an overview about the main components in the cryostat like the plasma vessel, the outer vessel, the ports and the different support systems this paper describes the most demanding manufacturing methods. The author delineates some disparate and special problems during the manufacturing of the components at the companies in the different European countries.