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Fast failures at the LHC and HL-LHC

During the High-Luminosity LHC (HL-LHC) era, the bunch intensity will be increased to 2.2e11 protons, almost twice the nominal LHC intensity, and the stored energy in each of the two proton beams will in turn increase from 360 MJ to nearly 700 MJ.

Fast failures are defined as failure events leading to uncontrolled beam losses with 10ms or less. Fast failures include, among others, the spurious triggering of magnet protection systems with circulating beams, fault at the level of the crab cavities, symmetric quench of the triplet quadrupoles, etc. These have been analyzed in detail and the criticality of each failure case has been assessed 1.

Additionnally, to cope with such high stored energy and mitigate the detrimental effect of the energy stored in the halo, the HL-LHC will feature beams whose transverse halos are partially depleted through a hollow electron lens. The reduced stored energy in the beam tails will significantly change the development dynamics of beam losses caused by failure originating from magnet protection equipment effect on the circulating beams, active devices, and powering failures.

Dedicated large-scale beam tracking simulations have been performed to evaluate the effect of a partially depleted halo on the criticality and detection of the so-called "fast failures," failures leading to critical loss levels within 10 ms. The time-dependent dynamics of these failures in terms of orbit excursion, beta-beating, and beam losses are presented. The margins between the onset of the failure, its detection, and the time to reach critical loss levels are presented for different levels of halo depletion. The effect of a spurious discharge of the Coupling Loss Induced Quench (CLIQ) magnet protection system on the beam is discussed in detail as it is shown that it constitutes the fastest and most critical failure case discovered so far. The results show that a dedicated ultra-fast interlock is required for machine protection. Finally, interlocking strategies for the different analyzed fast failures are reviewed.

Fast failures beam simulations for LHC and HL-LHC

See also the full list of publications and presentations on the topic.


  1. B Lindstrom, P BĂ©langer, L Bortot, R Denz, M Mentink, E Ravaioli, F Rodriguez Mateos, R Schmidt, J Uythoven, M Valette, A Verweij, C Wiesner, D Wollmann, and M Zerlauth. Fast failures in the LHC and the future high luminosity LHC. Phys. Rev. Accel. Beams, 23(8):81001, aug 2020. URL: