Radiation stability of prototype ITER-type resistive bolometers with improved electrical contacts

We present the results for reactor irradiation of prototype ITER-compatible resistive radiation hardened bolometers up to a total dose of ∼0.01 dpa (thermal/fast [E > 0.1 MeV] neutron fluence of 5.2/0.8 ×10 ¹⁹ n/cm ²). The prototype bolometer has a 100 nm thick Pt meander deposited on an alumina ceramic substrate. Connection of the delicate meander with external wiring is provided via special binding posts placed on the substrate. The binding post consist of a Pt ring attached to the substrate using melted glass, with a laser welded 0.1 mm diameter Pt wire. A vacuum capsule with a special bolometer holder was designed and fabricated to allow reactor irradiation at ∼400 °C in vacuum. The desired temperature was obtained by balancing the radiation heat generation and thermal energy losses via radiation and conductive heat transfer. The resistance of the Pt meander was measured in the course of 19 days irradiation in the BR2 material testing reactor of the SCK·CEN. Immediately after insertion of the bolometer into the reactor a significant decrease of the meander resistance was observed. The resistance then stabilized after several days of irradiation. The meander resistance measurements were stable during the first week of irradiation, but then the electrical contact was lost. Post-irradiation inspection showed that the binding posts remained attached to the substrate while one of the Pt wires detached from the Pt ring most probably due to a bad laser weld.