Vibration testing of mechanical resilience of bolometer sensors and sensor holders under ITER-relevant conditions

The ITER bolometer diagnostic will provide the measurement of the total radiation emitted from the plasma, a part of the overall energy balance. Up to 550 sensor channels will be installed in ITER in 71 cameras of various sizes and types. The sensor holder is the component inside those cameras to provide attachment and signal connections to the sensor itself. A design of a sensor holder has been proposed previously based on ceramic front and back plates with wire bonded contacts to the sensor and welded signal cables. This concept can provide the reliable electrical connections required for ITER at temperatures up to 350 ° C and had been prototyped and proven to be manufacturable. In order to verify its resilience against mechanical loads as well as that of the sensors, sensor holder assemblies have been subjected to accelerations on a shaking table. The magnitude of the accelerations applied (up to 625 m s 2 in the frequency range from 5 Hz up to 1 kHz) have been deduced based on load definitions from ITER describing the floor response spectra for typical seismic events as well as the ones expected during disruptions due to electro-magnetically induced forces in bolometer cameras and port structures within which they are mounted. A particular focus has been placed on testing whether it is beneficial to cover the bond wires with a ceramic paste to protect them against fatigue breaks due to vibrations. The tests demonstrated that the chosen sensor assembly is well capable of withstanding all applied loads without failures and thus demonstrating its structural integrity during the expected operations. Within the limited number of load cycles no need to apply the ceramic paste could be identified.