Precise Thermometry for Next Generation LHC Superconducting Magnet Prototypes

Abstract

Abstract-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 to 5 kV during the quench, dynamic high magnetic field up to 12 T, dynamic temperature range 1.8 K to 300 K in 0.6 sec. 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 crosspropagation 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).

Fast Cycled Magnet Demonstrator Program at CERN: Instrumentation and Measurement Campaign

“…The coil stability was excellent, even with Lorentz forces of 50 % higher than nominal at a current of 7.5 kA. The magnet is supported by eight Invar tie-rods that account for about 60 % of the total thermal load of 5 W [3]. A strain of 20 to 155 μm/m was measured on the rods and no sign of degradation has been observed during the 20000 cycles, see …”

“…The small influence of the exact geometrical position of the coil on the magnetic field quality in the bore makes the co-winding relatively easy. Precise thermometry by Carbon-Ceramic resistive temperature probes is performed to measure the thermal loads on the system [3]. Unfortunately the obtained precision of the enthalpy measurement of the helium was limited by the accuracy of the pressure gauges of ± 0.05 bar, which limited the measurement accuracy of the helium enthalpy.…”

Cryogenic thermometry for refrigerant distribution system of JT-60SA

“…In this work, The accuracies of Cernox and TVO sensors [8] [9] have been experimentally examined simultaneously. TVO stands for initials of Heat resistant Waterproof Volumetric in Russian.…”

Mechanical Validation of the Support Structure of the $\hbox{Nb}_{3}\hbox{Sn}$ Magnet FRESCA2

“…The temperature was monitored by carbon-ceramic sensors mounted at different locations of the support structure. An overview of these sensors is given in [10]. One cool-down operation takes about 2 days and the warm-up process takes 4 to 6 days.…”