Experience with silver coated vacuum vessel thermal shield at 80 K in Tore Supra

The thermal shield system at 80 K in Tore Supra provides an optically opaque barrier for thermal loads transferred from warm components to the superconducting toroidal magnetic field coil casing operating at 4 K. The two opposite surfaces (~230 m²) of ¿hot¿ vacuum vessel wall and surrounding ¿cold¿ vacuum vessel thermal shield are silver coated. Remaining cold thermal shield surfaces, including the cryostat thermal shield, which is located between toroidal field coils and cryostat torus (outer vacuum vessel at room temperature), are polished. The knowledge of realistic global surface emissivity values on large assembled components is necessary to estimate correctly the cryo-power consumption. Therefore TS large surface silver coatings have been assessed for ITER concerning the evaluation of surface emissivities from heat transfer measurements during vessel bake-out taking into account the real surface topography of assembled components.