Design and assembly technology for the thermal insulation of the W7-X cryostat

Abstract

The Max-Planck-Institut für Plasmaphysik in Greifswald is building up the stellarator fusion experiment Wendelstein 7-X (W7-X). To operate the superconducting magnet system the vacuum and the cold structures are protected by a thermal insulated cryostat. The plasma vessel forms the inner cryostat wall, the outer wall is realised by a thermal insulated outer vessel. In addition 254 thermal insulated ports are fed through the cryogenic vacuum to allow the access to the plasma vessel for heating systems, supply lines or plasma diagnostics.The thermal insulation is being manufactured and assembled by MAN Diesel & Turbo SE (Germany). It consists of a multi-layer insulation (MLI) made of aluminized Kapton with a silk like fiberglass spacer and a thermal shield covering the inner cryostat surfaces. The shield on the plasma vessel is made of fibreglass reinforced epoxy resin with integrated copper meshes. The outer vessel insulation is made of brass panels with an average size of 3.3 x 2.0 m². Cooling loops made of stainless steel are connected via copper strips to the brass panels. Especially the complex 3 D shape of the plasma vessel, the restricted space inside the cryostat and the consideration of the operational component movements influenced the design work heavily. The manufacturing and the assembly has to fulfil stringent geometrical tolerances e.g. for the outer vessel panels +3/-2mm.

Transition From Construction to Operation Phase of the Wendelstein 7-X Stellarator

“…Also, the extensive pipe work for water cooling of the plasma vessel and ports, and the complex helium pipe work for the cryogenics, i.e. for cooling the superconducting coils, the bus-bars, the current leads, central support structure, and the thermal shields [10] have to be leak checked and tightness has to be confirmed. This latter part of the leak tests has already a time overlap with the first cryogenic tests, since a variation of the helium pressure in the lines is desired.…”

Thermal and mechanical analysis of Wendelstein 7-X thermal shield

“…Correspondingly the machine is divided in 5 modules. The status of the construction and assembly of the thermal insulation is given in reference [1].…”