Investigations of Quench Limits of the LHC Superconducting Magnets

NbTi-based Rutherford cables are used in the coils of the Large Hadron Collider (LHC) magnets. These cables are designed to operate with currents up to 13 kA at temperatures of 1.9 K. Beam losses can locally heat the superconducting cables above the critical temperature and cause a transition to the normal conducting state (quenching). The quench limit, i.e., the energy needed for this transition, is studied to determine the maximum beam intensities and luminosity reach of the LHC. The amount of energy deposited in the coil cannot be measured directly. Therefore, Geant4 simulations are used to correlate the deposited energy with the signal from secondary particles detected outside the magnet cryostat by ionization chambers. An orbital bump technique is used to induce controlled beam losses and provoke a quench. The energy deposition is analyzed in terms of various beam loss patterns and beam energies. The validation of the heat transfer code is presented. The development of the resistive zone is estimated and compared with the voltage measurements over the coils.