Measurement and analysis of thermal performance of LHC prototype cryostats

The heat inleaks into the cryostats represent a significant fraction of the total heat loads to the Large Hadron Collider (LHC). In view of the large size of this machine and the high thermodynamic cost of low-temperature refrigeration, it is essential to maintain the heat inleaks within budgeted values. Following experimental validation of thermal design of critical components (e.g. multilayer reflective insulation, support posts, cold valves), thermal performance assessment of complete cryomagnets has been undertaken. Thermo-mechanical and cryogenic behavior was measured on full-scale prototype units. The heat loads in nominal steady-state conditions at the three temperature levels: 1.9 K, 4.5-20 K, 50-75 K have been analyzed. The variation of temperature of cryostat components has allowed a thorough investigation of the total heat inleak sensitivity to temperature. The effect of vacuum degradation on heat inleaks (from 10-3 Pa to 10-1 Pa) has also been measured. Measured values have been compared to calculated values and to budgeted heat loads