Radiation stability of resistive bolometers intended for operation in the ITER environment

We present results of reactor irradiation up to a total dose of ~0.02 dpa [E > 0.1 MeV] of a prototype radiation hard bolometer. The bolometer bridge is formed by a 300 nm thick Pt-meander sputtered on a 1.5 μm-thick Si3N4 membrane made out of a Si wafer by etching the Si in the area dedicated for the meander and absorber. To allow testing at ITER relevant conditions, i.e. high vacuum and ~400 °C, a dedicated irradiation vacuum capsule was designed and fabricated. The desired temperature was obtained by balancing the energy income due to gamma- and nuclear-heating and energy losses via radiation and conductive heat transfer. The resistances of 4 Pt meanders, which form the measurement bridge of one bolometer detector, were measured in situ. Two meander resistances were stable, while for two others resistance perturbations were observed. The bolometer remained operational throughout the irradiation cycle and failed after the end of irradiation, during the unloading operation. Visual post-irradiation examination (PIE) performed in a hot-cell allows to suppose that the reason of the failure is the detachment of a part of the Pt meander from the substrate.