Radiation resistant bolometers using platinum on Al2O3 and AlN

Present day JET type bolometers using gold meanders on a mica substrate have been considered for use in ITER. However in-reactor tests at JMTR (Japan) demonstrated that they suffer radiation damage due to transmutation of gold into mercury, and detachment of the meander from the substrate possibly related to this alloy change and/or substrate swelling. The formation of a gold–mercury alloy caused a dose dependent increase in the bolometer meander resistance, and the detachment of the meanders was accompanied by loss of electrical continuity. As a result, work has been undertaken to examine alternative more radiation resistant substrates, together with the substitution of evaporated gold by sputtered platinum. The ionising radiation resistance of prototype bolometers with sputtered platinum on alumina and AlN has been characterized. The results as a function of thermal cycling and radiation dose rate and dose are considered satisfactory.