Heat Extraction From the LHC Main Dipole, Main Quadrupole, and MQXA Superconducting Cables

The forthcoming operation of the CERN Large Hadron Collider (LHC) at 13-14 TeV requires a deep understanding of the heat transfer mechanisms in the most critical superconducting magnets. This is aimed at determining their steady-state quench limits and constitutes an input to compute the magnets stability in transient conditions as well, to prevent beam induced quenches. Heat extraction capability of the LHC Nb-Ti magnets relies on the significant contribution provided by superfluid helium (He II). Due to lack of knowledge of the He II distribution in the cable and in the compressed insulation, experimental investigations are necessary. In this work we present an experimental study aimed at reproducing the thermal behavior of superconducting coils using short length samples. With respect to previous studies, a new instrumentation technique was developed and an in-situ calibration of the thermocouples was performed. The study was conducted on different types of instrumented cables-stack reproducing the main bending dipole (MB), the main quadrupole (MQ), and the MQXA, which is one of the two low-β interaction region quadrupoles. The heat extraction was determined as a function of the cable temperature, of the bath temperature and of the beam loss scenario.