Bolometer sensor holder suitable for ITER-relevant conditions

Abstract

The ITER bolometer diagnostic shall provide the measurement of the total radiation emitted from the plasma, a part of the overall energy balance. Up to 550 lines-of-sight will be installed in ITER in 71 cameras of various sizes and types. The sensor holder, the component inside those cameras to provide attachment and signal connections to the sensor itself, might vary in shape within each camera. However, concepts for implementing electrical connections and handling of loads are very similar, if not identical. Taking the current design of port-mounted bolometer cameras and the corresponding space restrictions as a basis, a concept for the sensor holder is proposed in line with the requirements on high environmental temperatures of up to 350∘C, mechanical loads and compatibility to operation on vacuum as well as within a nuclear environment. The sensor holder is made of a ceramic with a coefficient of thermal expansion as close as possible to the one of the sensor material to minimise thermal stresses. Wire-bonded connections are used between the sensor and contacting pads deposited on the front plate of the sensor holder. The camera’s internal signal cables are welded to these contacting pads to complete the electrical circuit. The bond wires and the contacting pads may be covered by a ceramic paste for protection against mechanical loads. This concept can be implemented in every port camera and is expected to be easily adaptable to other camera locations as well. Prototypes of this concept have been built to prove the feasibility of manufacturing and assembly as well as to give valuable input for design improvements. Thermal cycling as well as electrical tests have been performed to validate the mechanical stability and functionality under ITER-relevant conditions.