Design and R&D for MITICA Thermal Sensors

In MITICA, the ITER neutral beam injector prototype, in-vessel components will be instrumented with thermocouples for material thermal measurements and water cooling calorimetry. A subset of MITICA thermal sensors will be installed in ITER Neutral Beam Injectors and it will consist of type N Mineral Insulated (MI) thermocouples with Ultra High Vacuum (UHV) compatible termination. Each sensor will end with a metallic/ceramic transition from MI cable to two pins suitable for direct integration into a Remote Handling (RH) compatible connector. A set of sensor prototypes has been procured and tests demonstrate the measuring capability and UHV compatibility: electrical insulation, conductivity, dielectric, and helium bombing tests passed, thus satisfying the technical requirements. The in-vessel thermal sensor system extends from the sensing junction up to the safety important feedthroughs at the vessel vacuum barrier. The whole cabling has been designed to be RH compatible to perform maintenance and replacement of components. The in-vessel RH compatible connector and the safety important feedthrough have been developed to house sensor cabling in a reliable and compact design, coping with all requirements. The design of different sensing junction types has been integrated with reliable mechanical fastenings, providing good and stable thermal contact. The paper describes the thermal system requirements and design, the qualification procedure undertaken on prototypes and the test results.