Cryogenic Thermometer Calibration Facility for the LHC

The “Institut de Physique Nucleaire” (IPN) and the European organization for Particle Research (CERN) collaborate on the design and the construction of a cryogenic thermometer calibration facility for the Large Hadron Collider (LHC). The thermometers are calibrated within the temperature range 1.6 K to 300 K, with an accuracy of ± 5 mK from 1.6 K to 4.2 K and about 1 % for higher temperatures. The calibration system has a capacity of 94 thermometers including 4 RhFe working temperature references. All thermometers are mounted on an isothermal copper block hung in a vacuum vessel and thermally insulated. A circulating helium heat exchanger cools down the copper block. The temperature is stabilized by means of a Proportional Integral regulator which controls a resistive heater mounted near the heat exchanger. For each step of temperature, calibration data are obtained by comparison of the thermometer resistance with the temperature deduced from the working references. The thermometers can be calibrated either in vacuum or immersed in saturated liquid helium. The particularities of this apparatus are its active cooling loop and controlled heating which enable to stabilize the temperature at previously fixed values with good dynamic characteristics. This paper presents the cryogenic thermometer calibration facility and the results of the first calibrations.