Thermometric chains for ITER superconductive magnets

•CEA develops an electronic board for temperature sensor on cryogenic applications.•Low-level signal can be measured in ITER harsh magnetic surrounding.•PCB technology allows an industrial production for cryogenic integrated thermo-block.•CEA produces 2600 thermo-blocks and 220 electronic for ITER superconducting magnets. High environmental constraints are applied on the ITER magnets and therefore on their cryogenic thermometric chains. Accurate and reliable temperature measurements of the ITER magnets and their cooling circuits is of fundamental importance to make sure they operate under well controlled and reliable conditions. Therefore, thermometric chains shall reach a high operation reliability. In this paper, we present the full thermometric chain installed on the ITER magnets and their helium piping as well as the associated components production. The thermometric chain is described from the signals conditioning electronics, to the sensor and its on-pipe assembly. The thermometric block design is based on the CERN's developed one for the LHC, which has been further optimized thanks to thermal simulations carried out by CEA to reach a high quality level for an industrial production. The ITER specifications are challenging in terms of accuracy and call for severe environmental constraints, in particular regarding irradiation level, electromagnetic immunity and distance between the sensors and the electronic measuring system. A focus will be made on this system, which has been recently developed by CEA. It is based on a lock-in measurement and amplification of small signals, and provides a web interface and a software to monitor and record the temperatures. This measuring device provides a reliable system for resistive temperature sensors between a few ohms and 100 kOhms. During last two years, around 2600 thermo-blocks and nearly 50 crates of five boards, with eight channels each, have been produced and tested at CEA low temperature laboratory. All these developments and tests have been carried out thanks to three test benches built up at CEA Grenoble and in one industrial electronics laboratory. Test benches results on the entire production are presented.