Development of an LHC model in BDSIM to study collimation cleaning and beam-induced backgrounds at ATLAS

Stuart Walker

Research output: ThesisDoctoral Thesis

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The Large Hadron Collider (LHC) is at the frontier of high energy physics. At 27 km in circumference and operating at the highest achieved energy to date at 6.5 TeV, it is reliant on cold superconducting magnets throughout the machine to steer and control the beam. These cold superconducting magnets are extremely sensitive to heating from the beams that they steer. Even a billionth of a beam deposited on a single magnet can cause it to quench and lose its superconductivity, resulting in lengthy downtime or even component damage. For this reason the LHC features a number of systems to protect the machine from itself. For example, around 3600 beam loss monitors (BLMs) are placed around the ring, and if they detect losses above some threshold, the beam is dumped safely. Also aiding the machine's protection is its collimation system that is used to remove halo beam particles safely from circulation. Simulating the collimation system is vital to optimising its function, and in this thesis it is simulated using the novel accelerator code, Beam Delivery Simulation (BDSIM), and compared with existing comparable simulations. Additionally, individual BLMs are placed in the model, the BLM dose is simulated and compared one-to-one with measured BLM data from a dedicated qualification run.

The general purpose experiments are vulnerable to beam-induced backgrounds, which originate from upstream proton losses that generate secondary showers that can reach the detectors. This is particularly problematic due to the propensity for such backgrounds to mimic signals in the search for novel physics. They must be understood and mitigated in the physics analysis. In this thesis such background sources are simulated by building a detailed model of the beam line upstream of the ATLAS detector, which has been used to simulate various scenarios and the results are compared with existing simulations at an interface plane with the detector. They are then passed into a dedicated ATLAS simulation where they are compared with real data from recent runs in which the beam-induced background rate was deliberately increased by raising the gas pressure in upstream sections of the beam pipe.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Gibson, Stephen, Supervisor
Publication statusUnpublished - 2020


  • beam-induced backgrounds
  • LHC
  • collimation
  • beam-gas
  • interface plane
  • Accelerator modelling
  • energy deposition studies
  • loss map

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