AbstractFor diagnostic applications in the Tore Supra/CIEL (TS) upgrade and ITER, sapphire–window assemblies have been developed. Thermo-mechanical analyses, which have been performed for different window–ferrule assemblies and loading cases, show the difficulty of stress evaluation due to uncertainties in the simulation of the bonding joint area. Consequently a prototype of the TS infrared endoscope head has been qualified following a baking and heat flux screening/cycling procedure in the infrared irradiation test facility (IRIFA). For ITER, five sapphire–window assemblies including, for comparison, six polycrystalline ceramic windows have been fabricated and tested, before neutron irradiation, according the ITER test specifications for normal duty events and accumulated normal life.