Design and Technical Requirements of the Thermal Shield System for the DTT Facility

The Divertor Tokamak Test (DTT) facility, currently under construction at ENEA Frascati, includes a Thermal Shield System (THS) designed to protect the superconducting magnets from radiative heat loads. The THS comprises the Vacuum Vessel Thermal Shield (VVTS), Port Thermal Shield (PTS), and Cryostat Thermal Shield (CTS), featuring modular helium-cooled panels tailored to their complex geometries. All components are manufactured from AISI 316L stainless steel with restricted content of high-activation impurities. The VVTS and PTS adopt a double-shell design, consisting of a 2 mm actively cooled bottom plate facing the vacuum vessel/ports and a 2 mm passively cooled top plate facing the magnets, whereas the CTS utilizes a single 3 mm cooled shell equipped with Multi-Layer Insulation (MLI) on the cryostat side. The THS is anchored to warm components (Vacuum Vessel, Ports, and Cryostat) via gravity supports designed for plasma operation and baking phases (up to 300 K). The supporting system integrates G-10 epoxy components for thermo-electrical insulation and employs slotted holes on the panels to compensate for thermal contraction, securing the assembly against electromagnetic and thermal loads. The cooling system utilizes fully redundant, continuous seamless pipes intermittently welded to the panels, operating with gaseous helium at 16 bar and 80 K (inlet conditions). The VVTS architecture follows a 40 degrees toroidal periodicity (9 parallel paths inboard/outboard, shared with Port 5 PTS), while PTS ports 1-4 have dedicated parallel paths and the CTS uses 120 degrees periodicity; all configurations are designed to maximize surface coverage. Key design aspects address toroidal sectors of the VVTS, redundant parallel cooling paths, surface roughness less or equal 0.2 microns (VVTS/PTS)/0.8 microns (CTS). A full-scale VVTS prototype will validate welding, distortion management, surface processes, and supports under operational loads. Factory tests will cover mechanical integrity (gravity supports, pipe omegas), inspections (visual, welds, 3D dimensions), magnetic permeability/roughness/emissivity, pressure cycling, helium leaks, flow verification, and instrumentation (temperature/strain/displacement sensors).