Colliding Heavy Ions in the LHC

The Large Hadron Collider at CERN not only collides protons but also heavier nuclei. So far Pb+Pb, Xe-Xe and p+Pb collisions, at multiple energies, have been provided for what was initially conceived as a distinct physics program on the collective behavior of QCD matter at extreme energy density and temperature. However unexpected phenomena observed in p+Pb and p+p collisions at equivalent energies have blurred the distinction. Intense, low-emittance, ion beams are provided by a dedicated source and injector chain setup. When Pb beams collide, new luminosity limits arise from photon-photon and photonuclear interactions but effective mitigations have allowed luminosities over 3 times design. Asymmetric p+Pb collisions introduce new features and beam-dynamical phenomena into operation of the LHC but have also achieved luminosity far beyond expectations. With experimental requirements for multiple changes in energy and data-taking configurations during very short heavy-ion runs, high operational efficiency and reliability are vital. This invited talk discusses performance, future prospects, and technical challenges for the LHC heavy ion program, including injector performance.