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 unprecedented energy, in order to extend the frontiers of high-energy particle physics. During the first very successful running period in 2010-2013, the LHC was routinely storing protons at 3.5-4 TeV with a total beam energy of up to 146 MJ, and even higher stored energies are foreseen in the future. This puts extraordinary demands on the control of beam losses. An un-controlled loss of even a tiny fraction of the beam could cause a superconducting magnet to undergo a transition into a normal-conducting state, or in the worst case cause material damage. Hence a multi-stage collimation system has been installed in order to safely intercept high-amplitude beam protons before they are lost elsewhere. To guarantee adequate protection from the collimators, a detailed theoretical understanding is needed. This article presents results of numerical simulations of the distribution of beam losses around the LHC that have leaked out of the collimation system. The studies include tracking of protons through the fields of more than 5000 magnets in the 27 km LHC ring over hundreds of revolutions, and Monte-Carlo simulations of particle-matter interactions both in collimators and machine elements being hit by escaping particles. The simulation results agree typically within a factor 2 with measurements of beam loss distributions from the previous LHC run. Considering the complex simulation, which must account for a very large number of unknown imperfections, and in view of the total losses around the ring spanning over 7 orders of magnitude, we consider this an excellent agreement. Our results give confidence in the simulation tools, which are used also for the design of future accelerators.

The practical Pomeron for high energy proton collimation

“…Experimentally pp and pn cross sections are within less than 2 % at the highestenergy pn data available, √ s = 30 GeV, and theoretically the agreement is expected to be even less than this, as the relevant processes are dominated by Pomeron and f 2 exchange. This approximation has also been used in previous studies of the LHC collimation system ( [4,5] and references therein), which agree with measured losses.…”

Design and implementation of a crystal collimation test stand at the Large Hadron Collider

“…Particular attention has been paid to the impact parameter and the angular spread of particles at the first passage at the crystal. While for standard primary collimators this is not a critical parameter, as results are stable in a wide range of values up to hundreds of µm [35], for crystals the initial distribution affects significantly the channeling efficiency. Impact parameters of the order of tenths of a µm are expected in the real machine [36].…”

Calculations of safe collimator settings andβ*at the CERN Large Hadron Collider

“…The particle trajectories are checked against a detailed aperture model with 10 cm longitudinal precision and the simulation output contains coordinates of all loss locations. SIXTRACK is routinely used to simulate the cleaning performance of the LHC collimation system and the results have been shown to be in very good agreement with beam loss data from the LHC [65].…”

“…Another method to numerically assess the impacts during a SMPF, which accounts for both the true phase advance, the particle-matter interaction inside collimators, the full ring aperture, and all collimators, is to perform a simulation with the SIXTRACK code [61][62][63][64][65]. SIXTRACK does a thin-lens element-by-element tracking through the magnetic lattice, and it has a built-in Monte Carlo code to simulate the particle-matter interaction inside collimators.…”