Chapter 5: Collimation system

A variety of processes can cause unavoidable beam losses during normal and abnormal beam operation. Because of the high stored energy of about 700 MJ and the small transverse beam sizes, the HL-LHC beams are highly destructive. Even a local beam loss of a tiny fraction of the full beam in a superconducting magnet could cause a quench, and larger beam losses could cause damage to accelerator components. Therefore, all beam losses must be tightly controlled. For this purpose, a multistage collimation system has been installed, to safely dispose of beam losses. Unlike other high-energy colliders, where the main purpose of collimation is typically to reduce experimental backgrounds, the LHC and the HL-LHC require efficient beam collimation during all stages of operation from injection to top energy. The requirement to operate efficiently and safely with high-intensity hadron beams at small colliding beam sizes provides significant challenges, which drive the key design aspects of the collimation system at the HL-LHC.