Simulations and measurements of beam loss patterns at the CERN Large Hadron Collider

Abstract

The CERN Large Hadron Collider (LHC) is designed to collide proton beams of\nunprecedented energy, in order to extend the frontiers of high-energy particle\nphysics. During the first very successful running period in 2010--2013, the LHC\nwas routinely storing protons at 3.5--4 TeV with a total beam energy of up to\n146 MJ, and even higher stored energies are foreseen in the future. This puts\nextraordinary demands on the control of beam losses. An un-controlled loss of\neven a tiny fraction of the beam could cause a superconducting magnet to\nundergo a transition into a normal-conducting state, or in the worst case cause\nmaterial damage. Hence a multi-stage collimation system has been installed in\norder to safely intercept high-amplitude beam protons before they are lost\nelsewhere. To guarantee adequate protection from the collimators, a detailed\ntheoretical understanding is needed. This article presents results of numerical\nsimulations of the distribution of beam losses around the LHC that have leaked\nout of the collimation system. The studies include tracking of protons through\nthe fields of more than 5000 magnets in the 27 km LHC ring over hundreds of\nrevolutions, and Monte-Carlo simulations of particle-matter interactions both\nin collimators and machine elements being hit by escaping particles. The\nsimulation results agree typically within a factor 2 with measurements of beam\nloss distributions from the previous LHC run. Considering the complex\nsimulation, which must account for a very large number of unknown\nimperfections, and in view of the total losses around the ring spanning over 7\norders of magnitude, we consider this an excellent agreement. Our results give\nconfidence in the simulation tools, which are used also for the design of\nfuture accelerators.\n