DTT vacuum vessel, in-vessel coils, and out vessel systems: overview of design and procurement.

DTT is one of the largest superconducting tokamak with the mission to get scientific and technological proofs of power exhaust in prospect of the first nuclear fusion power plant. The 5.5MA maximum plasma current, 6T toroidal magnetic field at the plasma center, and 2.19m plasma radius make DTT a flexible and compact facility for testing D-shaped plasmas with different configurations of heat load spreading. The design of vacuum vessel (VV) and in-vessel components is addressed mainly by the disruptions as prevailing loads, whereas the local seismic response results important for the design of all the tokamak systems. Significant stress reductions are obtained in DTT by isolating the base with passive isolation pads to physically decouple the DTT torus complex from the ground motion. Then, low-dissipative structural behaviour of the components is verified thus reducing the maintenance operations after earthquake. This paper deals with the main design solutions analysed: double walled shell of the VV with fluid flow in the inter-shell, supported by 6 gravity supports; permanent supports welded on the inner shell of the VV to sustain the in-vessel components; cryogenic pumping in the divertor region complemented, during pulse-off, by turbomolecular pumps; active thermal control of the in-vessel electrodes for glow discharge cleaning. Among all the foreseen qualification tests, feasibility evaluations are described for: gas puffing in the divertor region tending to reduce gas dispersion in the sub-divertor region and to promote gas pumping by cryopumps; in- vessel forming of coil conductor and on-site joining of the feeders to the already installed in-vessel coils with restoration of fluid and vacuum boundaries. The integrated approach and methodology identifying scope, costs, schedule, and deliverables are applied to the design and procurement of the mechanical systems that include machine cryostat, thermal shield, vessel auxiliary systems, in-vessel coils, and stabilizing plates.