Effect of a Spurious CLIQ Firing on the Circulating Beam in HL-LHC

he High Luminosity LHC (HL-LHC) will reach a nominal, levelled luminosity of 5$\times$10$^{34}$ cm$^{-1}$ s$^{-2}$ and a stored energy of nearly 700 MJ in each of the two proton beams. The new large-aperture final focusing Nb$_3$Sn quadrupole magnets in IR1 and IR5, which are essential to achieve the luminosity target, will be protected using the novel Coupling Loss Induced Quench (CLIQ) system. A spurious discharge of a CLIQ unit will impact the circulating beam through higher order multipolar field components that develop rapidly over a few turns. This paper reports on dedicated beam tracking studies performed to evaluate the criticality of this failure on the HL-LHC beam. Simulations for different machine and optics configurations show that the beam losses reach a critical level after only five machine turns following the spurious CLIQ trigger, which is much faster than assumed in previous simulations that did not consider the higher order multipolar fields. Machine protection requirements using a dedicated interlock to mitigate this failure are discussed.