Criticality of fast failures in the High Luminosity Large Hadron Collider

Abstract: Each of the two Large Hadron Collider (LHC) beams contain 362 MJ of energy. This will be further increased to 678 MJ in the upcoming upgrade to the High Luminosity LHC (HL-LHC). In the event of an uncontrolled beam loss, a significant hazard occurs, that can damage the machine components. This thesis is focused on failures that can lead to a fast increase of beam losses, with a focus on the new optics and equipment in the HL-LHC. The criticality for a number of failure scenarios is studied, under different optics configurations of the machine. Mitigation strategies, involving dedicated interlocking and a reduction of the impact that the failures have on the beam are proposed for the most critical scenarios. For a number of less critical failures it is determined that current interlock strategies are sufficient.Failures involving the magnet protection and the crab cavities constitute the most severe hazards. The former consists of quench heaters and a new system known as coupling loss induced quench (CLIQ). A new connection scheme is proposed for these, in order to limit their effect on the beam. Dedicated interlocks for detecting spurious discharges of these systems are also found to be necessary. The perturbation of the beam orbit caused by the extraction of only one beam is another source of uncontrolled beam losses. A fast hardware linking of the two beams to limit the delay between extracting the two beams of maximum one LHC turn (89 µs) is found to be necessary.Beam-dust interactions have detrimental effects on the machine performance and availability. Advances are made on the understanding of their dynamics through dedicated experiments combined with theoretical work and simulations.              Superconducting magnet quenches are shown capable of causing fast orbit perturbations. The effects of beam-beam compensating wires as well as coherent excitations by the transverse beam damper are also discussed. Finally, realistic combinations of multiple failures is also discussed.