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During its Run 2 (2015-2018), the Large Hadron Collider (LHC) operated atalmost twice higher energy, and provided Pb-Pb collisions with an order ofmagnitude higher luminosity, than in the previous Run 1. In consequence, thepower of the secondary beams emitted from the interaction points by thebound-free pair production (BFPP) process increased by a factor ~20, while thepropensity of the bending magnets to quench increased with the higher magneticfield. This beam power is about 35 times greater than that contained in theluminosity debris from hadronic interactions and is focused on specificlocations that fall naturally inside superconducting magnets. The risk ofquenching these magnets has long been recognized as severe and there areoperational limitations due to the dynamic heat load that must be evacuated bythe cryogenic system. High-luminosity operation was nevertheless possiblethanks to orbit bumps that were introduced in the dispersion suppressors aroundthe ATLAS and CMS experiments to prevent quenches by displacing and spreadingout these beam losses. Further, in 2015, the BFPP beams were manipulated toinduce a controlled quench, thus providing the first direct measurement of thesteady-state quench level of an LHC dipole magnet. The same experimentdemonstrated the need for new collimators that are being installed around theALICE experiment to intercept the secondary beams in the future. This paperdiscusses the experience with BFPP at luminosities very close to the futureHigh Luminosity LHC (HL-LHC) target, gives results on the risk reduction byorbit bumps and presents a detailed analysis of the controlled quenchexperiment.

Bound-free pair production from nuclear collisions and the steady-state quench limit of the main dipole magnets of the CERN Large Hadron Collider