Machine Protection Challenges for HL-LHC

LHC operation requires the flawless functioning of the machine protection systems. The energy stored in the beam was progressively increased beyond the 140 MJ range at the end of 2012 at 4 TeV/c. The further increase to more than 300 MJ expected for 2015 at 6.5 TeV/c should be possible with the existing protection systems. For HL-LHC additional failure modes need to be considered. The stored beam energy will increase by another factor of two with respect to nominal and a factor of five more than experienced so far. The maximum beta function in the high luminosity insertion regions will increase. It is planned to install crab cavities in the LHC to compensate for the loss in luminosity due to the crossing-angle. With crab cavities, sudden voltage decays within 100 µs after e.g. cavity quenches can lead to large transverse beam oscillations. Tracking simulations predict trajectory distortions of up to 1.5 σ after a sudden drop of the deflecting voltage in a single cavity. Protons in the halo with an energy of several MJ could hit a collimator in case of such event, far above damage level even if the collimator jaws are made of robust material. In this paper we discuss the challenges for machine protection in the HL-LHC era and possible mitigation strategies.