Qualification of Sub-Atmospheric Pressure Sensors for the Cryomagnet Bayonet Heat Exchangers of the Large Hadron Collider

The superconducting magnets of the Large Hadron Collider (LHC) will be cooled at 1.9 K by distributed cooling loops working with saturated two‐phase superfluid helium flowing in 107 m long bayonet heat exchangers located in each magnet cold‐mass cell. The temperature of the magnets could be difficult to control because of the large dynamic heat load variations. Therefore, it is foreseen to measure the heat exchangers pressure to feed the regulation loops with the corresponding saturation temperature. The required uncertainty of the sub‐atmospheric saturation pressure measurement shall be of the same order of the one associated to the magnet thermometers, in pressure it translates as ±5 Pa at 1.6 kPa. The transducers shall be radiation hard as they will endure, in the worst case, doses up to 10 kGy and 1015 neutrons⋅cm−2 over 10 years.The sensors under evaluation were installed underground in the dump section of the SPS accelerator with a radiation environment close to the one expected for the LHC. The mon...