Calibration and thermal test results of prototype bolometer sensors for ITER fusion reactor

For over 10 years, several bolometer sensors with different properties have been tested in the IBOVAC facility. The aim has been to develop a bolometer sensor that can be operated in ITER and can withstand harsh operating conditions. For this purpose, important physical properties of the sensors, i.e., cooling time constant τ, normalized heat capacity κ, and normalized sensitivity s_n, have been characterized in a vacuum condition and at various temperatures up to 300 °C. The calibration is achieved by ohmic heating of the sensor absorbers by applying a DC voltage and recording exponential current fall during heating. Recently, a Python program was developed to analyze the data and extract the above mentioned parameters including the uncertainties from recorded currents. In the present series of experiments, the latest prototype sensors developed for ITER are tested and evaluated. These include three different sensor types: two with Au absorbers on ZrO₂ membranes (self-supporting substrate sensors) and one with Au absorbers on Si₃N₄ membranes supported by a Si frame (supported membrane sensors). Tests revealed that the sensor with ZrO₂ substrate can only be operated up to 150 °C, while the supported membrane sensors passed the tests up to 300 °C successfully. These results will be used, together with other upcoming tests, such as irradiation testing, to select the most suitable sensors to be employed in ITER.