CERN Large Hadron Collider optics model, measurements, and corrections

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.

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“…Another error source is the beat, which can be corrected to between 10% and 20% in the LHC [22]. If this error is included in Eq.…”

Section: Error Analysis Of the Setup Proceduresmentioning

confidence: 99%

Semiautomatic beam-based LHC collimator alignment

Valentino

Aßmann

Bruce

et al. 2012

Phys. Rev. ST Accel. Beams

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“…A clear signature of the beneficial impact of this optimisation is the actual residual beta and dispersion beating all along the machine, which is well within specification after identification and correction of localised errors found in the insertions [67].…”

Section: Discussionmentioning

confidence: 93%

Dynamic aperture computation for the as-built CERN Large Hadron Collider and impact of main dipoles sorting

Fartoukh

Giovannozzi

2012

Nuclear Instruments and Methods in Physics Research Section A:

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During the design phase of the CERN Large Hadron Collider the dynamic aperture, i.e., the amplitude of the domain in phase space where the particle motion is stable, was used as one of the most important figures-of-merit to specify the field quality of the various types of superconducting magnets and to quantify the machine performance. The programme of magnetic measurements performed during the production and acceptance testing of the magnets generated a large amount of information, which was used to obtain a best estimate of the dynamic aperture of the actual machine. In this paper the results of massive numerical simulations based on the measured field quality of several optical configurations and beam energies, are presented and discussed. The effect of the sorting of the main dipoles on the final value of the dynamic aperture has also been studied and the results are reviewed in detail. AbstractDuring the design phase of the CERN Large Hadron Collider the dynamic aperture, i.e., the amplitude of the domain in phase space where the particle motion is stable, was used as one of the most important figures-of-merit to specify the field quality of the various types of superconducting magnets and to quantify the machine performance. The programme of magnetic measurements performed during the production and acceptance testing of the magnets generated a large amount of information, which was used to obtain a best estimate of the dynamic aperture of the actual machine. In this paper the results of massive numerical simulations based on the measured field quality of several optical configurations and beam energies, are presented and discussed. The effect of the sorting of the main dipoles on the final value of the dynamic aperture has also been studied and the results are reviewed in detail.

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“…This is done using an analysis package developed for the LHC. A description can be found in [3,9]. The action is derived from the measured functions and represents the average of all BPMs in the ring.…”

Section: Data Processing and Analysismentioning

confidence: 99%

“…Linear optics measurements using an ac dipole have been successfully achieved in various machines [1][2][3]. The possibility of using an ac dipole for nonlinear diagnostics was described in [4,5] and a first experimental application measuring the resonance driving terms is described in [6].…”

Section: Introductionmentioning

confidence: 99%

Direct amplitude detuning measurement with ac dipole

White

Maclean

Tomás

2013

Phys. Rev. ST Accel. Beams

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In circular machines, nonlinear dynamics can impact parameters such as beam lifetime and could result in limitations on the performance reach of the accelerator. Assessing and understanding these effects in experiments is essential to confirm the accuracy of the magnetic model and improve the machine performance. A direct measurement of the machine nonlinearities can be obtained by characterizing the dependency of the tune as a function of the amplitude of oscillations (usually defined as amplitude detuning). The conventional technique is to excite the beam to large amplitudes with a single kick and derive the tune from turn-by-turn data acquired with beam position monitors. Although this provides a very precise tune measurement it has the significant disadvantage of being destructive. An alternative, nondestructive way of exciting large amplitude oscillations is to use an ac dipole. The perturbation Hamiltonian in the presence of an ac dipole excitation shows a distinct behavior compared to the free oscillations which should be correctly taken into account in the interpretation of experimental data. The use of an ac dipole for direct amplitude detuning measurement requires careful data processing allowing one to observe the natural tune of the machine; the feasibility of such a measurement is demonstrated using experimental data from the Large Hadron Collider. An experimental proof of the theoretical derivations based on measurements performed at injection energy is provided as well as an application of this technique at top energy using a large number of excitations on the same beam.

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CERN Large Hadron Collider optics model, measurements, and corrections

Cited by 46 publications

References 8 publications

Semiautomatic beam-based LHC collimator alignment

Semiautomatic beam-based LHC collimator alignment

Dynamic aperture computation for the as-built CERN Large Hadron Collider and impact of main dipoles sorting

Direct amplitude detuning measurement with ac dipole

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