Abstract
Full beam-based alignment of the LHC collimation system was a time-consuming procedure (up to 28 hours) as the collimators were set up manually. A yearly alignment campaign has been sufficient for now, although in the future due to tighter tolerances this may lead to a decrease in the cleaning efficiency if machine parameters such as the beam orbit drift over time. Automating the collimator setup procedure can reduce the beam time for collimator setup and allow for more frequent alignments, therefore reducing the risk of performance degradation. This article describes the design and testing of a semiautomatic algorithm as a first step towards a fully automatic setup procedure. The parameters used to measure the accuracy and performance of the alignment are defined and determined from experimental data. A comparison of these measured parameters at 450 GeV and 3.5 TeV with manual and semiautomatic alignment is provided.
Highlights
The CERN Large Hadron Collider (LHC) is built to store and collide two counterrotating 7 TeV beams each with 362 MJ of stored energy with nominal beam parameters [1]
The LHC collimation system advances the state of the art found at the Tevatron [5] and RHIC [6]
The LHC consists of 8 arcs and 8 straight sections, called insertion regions (IRs)
Summary
The CERN Large Hadron Collider (LHC) is built to store and collide two counterrotating 7 TeV beams each with 362 MJ of stored energy with nominal beam parameters [1]. Beam-based alignment of the LHC collimators is necessary to determine the beam center (Áxi) and beam size (iinf) at each collimator i This ensures that a correct collimator hierarchy is established for normal operation. The beam-based alignment procedure relies on feedback from beam loss monitors (BLMs) [13] They consist of ionization chambers placed downstream of the collimators, and intercept secondary particles created by the hadronic and electromagnetic showers caused by beam particles impacting on the collimators. In 2010, the setups were performed ‘‘manually,’’ meaning that human feedback was required to determine when the jaw is aligned to the beam. This was achieved by observing the BLM signal on a screen following a jaw movement. A comparison of the setup results obtained in 2011 with those of 2010 using data from the proton runs is presented
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