DESIGN OPTIONS FOR THE NET VACUUM VESSEL AND ITS RESISTIVE ELEMENTS

The vacuum vessel (Fig. 1) acts as vacuumtight containment for the plasma and as shielding for the superconducting coils system and is sectioned in 16 parallel and 16 wedge segments, bolted together to form a rigid toroidal structure. A water cooling system is designed for heat loads up to 100 MW. 16 thinwalled resistive elements bridge the electrically insulated parallel segments to obtain a total toroidal resistance of 10 −4 ω, needed to allow fast penetration of the poloidal field during plasma initiation. The system has to withstand the electromagnetic forces during disruptions, accidental overpressures and thermal stresses caused by the pulsed nuclear and thermal heat radiation. Due to the nuclear activation and contamination all assembly, disassembly and repair must be carried out remotely. The paper reports results of industrial feasibility study contracts showing two different design solutions for the vacuum vessel segments and its cooling system as well as the resistive elements. Points discussed are the manufacturing of the vacuum vessel segments from thick plates by welding, problems for bolts and joints created by thermal transients and the high precision required for assembly. Also a test device for resistive element test panels is shown.