Performance of the Large Hadron Collider cleaning system during the squeeze: simulations and measurements

The Large Hadron Collider (LHC) at CERN is a 7 TeV proton synchrotron, with a design stored energy of 362 MJ per beam. The high-luminosity (HL-LHC) upgrade will increase this to 675 MJ per beam. In order to protect the superconducting magnets and other sensitive equipment from quenches and damage due to beam loss, a multilevel collimation system is needed. Detailed simulations are required to understand where particles scattered by the collimators are lost around the ring in a range of machine configurations. merlin++ is a simulation framework that has been extended to include detailed scattering physics, in order to predict local particle loss rates around the LHC ring. We compare merlin++ simulations of losses during the squeeze (the dynamic reduction of the beta function at the interaction points before the beams arc put into collision) with loss maps recorded during beam squeezes for run 1 and 2 configurations. The squeeze is particularly important, as both collimator positions and quadrupole magnet currents are changed. We can then predict, using merlin++, the expected losses for the HL-LHC to ensure adequate protection of the machine.