Signal Conditioning for Cryogenic Thermometry in the LHC

Temperature measurement is a key issue in the Large Hadron Collider (LHC), as it will be used to regulate the cooling of the superconducting magnets. The compromise between available cooling power and the coil superconducting characteristics leads to a restricted temperature control band, around 1.9 K. An absolute accuracy of 10 mK below 2.2 K, and 5 K above 25 K, is necessary. For resistive thermometers covering the full temperature range, and having a negative dR/dT sensitivity, this is typically equivalent to a relative accuracy ΔR/R of 3 10-3 over 3 resistance decades. Also, to limit the thermometer’s self-heating, the sensing current must be limited to few μA. Furthermore, the radiation levels next to the accelerator are expected to significantly degrade the performance of conventional analog electronics.