Precise Thermometry for Next Generation LHC Superconducting Magnet Prototypes

The next generation of LHC superconducting magnets is very challenging and must operate in harsh conditions: high radiation doses in a range between 10 and 50 MGy, high voltage environment of 1-5 kV during the quench, dynamic high magnetic field up to 12 T, dynamic temperature range 1.8-300 K in 0.6 s. For magnet performance and long-term reliability, it is important to study dynamic thermal effects, such as the heat flux through the magnet structure, or measuring hot spot in conductors during a magnet quench with high sampling rates above 200 Hz. Available on the market, cryogenic temperature sensors comparison is given. An analytical model for special electrically insulating thermal anchor (Kapton pad) with high voltage insulation is described. A set of instrumentation is proposed for fast monitoring of thermal processes during normal operation, quenches, and failure situations. This paper presents the technology applicable for mounting temperature sensors on high voltage superconducting (SC) cables. The temperature measurements of fast heat cross propagation in MQXC SC cable and FCM dynamic tests are also presented. Novel thermometry has been successfully applied to a few CERN magnet prototypes (MQXC, FCM, and FRESCA2).