Keyword: collimation
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MOPMF038 Cleaning Performance of the Collimation System with Xe Beams at the Large Hadron Collider simulation, betatron, heavy-ion, proton 176

• N. Fuster-Martínez, R. Bruce, P.D. Hermes, J.M. Jowett, D. Mirarchi, S. Redaelli
CERN, Geneva, Switzerland

The LHC heavy-ion program with Pb ions has delivered substantial physics results since the startup of the LHC. There was a Xe run in 2017 in which collimation losses and cleaning were assessed. These studies give a unique opportunity for very valuable benchmark of simulation models with measurements, which could also be very important to understand limitations for future runs with Pb and other species. In this paper, we present collimation loss maps measured in the first ever operation of the LHC with Xe ions. The measurements are compared with simulations and first conclusions are discussed for possible future operation.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF038
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MOPMF042 Crab Cavity Failures Combined with a Loss of the Beam-Beam Kick in the High Luminosity LHC cavity, beam-losses, luminosity, dumping 192

• B. Lindstrom, H. Burkhardt, V.K.B. Olsen, A. Santamaría García, K.N. Sjobak, M. Valette, D. Wollmann
CERN, Geneva, Switzerland

Crab cavities are an essential component of the High Luminosity LHC (HL-LHC) project. In case of a failure they can create large transverse kicks on the beam within tens of microseconds and, therefore, require a fast extraction of the circulating beam. In this paper, the effects of different crab cavity failures in combination with the missing beam-beam kick following the dump of only one LHC beam are presented and consequences for the interlocking strategy of crab cavities are discussed.
Work supported by the High Luminosity LHC project.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF042
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MOPMF060 Safe Disposal of the LHC Beam without Beam Dump - Method and Experimental Verification experiment, emittance, controls, dumping 253

• M. Valette, B. Lindstrom, A. Mereghetti, R. Schmidt, M. Solfaroli, J.A. Uythoven, D. Valuch, J. Wenninger, D. Wollmann, M. Zerlauth
CERN, Geneva, Switzerland

Funding: Research supported by the HL-LHC project.
In the extremely unlikely event of a non-working beam dumping system in the LHC, the 360 MJ of stored beam energy can be dissipated in the collimation system as a last mitigation measure. In such a situation, it is important to reduce the stored beam energy both quickly and at the same time as smoothly as possible in order to limit the risk of trips of critical systems, to avoid quenches of superconducting magnets (which would lead to changes of the beam trajectory and damage to the accelerator) and ultimately damage to the collimators themselves. Detailed steps and parameters have been developed and validated during two dedicated experiments with beam in the LHC. This paper summarizes the key aspects in view of the preparation of such a procedure for operational use, which will allow for the safe disposal of the full LHC beam by the operation crews.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF060
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MOPMF090 First Studies of Ion Collimation for the LHC Using BDSIM simulation, hadron, heavy-ion, proton 341

• A. Abramov, S.T. Boogert, L.J. Nevay, S.D. Walker
JAI, Egham, Surrey, United Kingdom

At the Large Hadron Collider (LHC) at CERN ion physics runs are performed in addition to proton physics runs. In ion operation the cleaning efficiency of the collimation system is lower than in the case of protons and the ion showering process is more complicated and produces a larger variety of secondary particles. In particular, lighter ion species can be produced as fragmentation products in the collimation system and specialised physics lists are required to simulate their production and propagation in matter. The Geant4 toolkit offers comprehensive physics process lists that extend to the case of arbitrary ion species at high energies. First results from a study of ion collimation for the LHC using the Geant4 physics library in BDSIM are presented here. These include simulations of a full ring loss map and particle spectra for collimator leakage for a Pb beam at injection energy in the LHC.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF090
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MOPML012 Special Collimation System Configuration for the LHC High-Beta Runs background, simulation, detector, experiment 418

• H. Garcia Morales
Royal Holloway, University of London, Surrey, United Kingdom
• R. Bruce, H. Burkhardt, M. Deile, S. Jakobsen, A. Mereghetti, S. Redaelli
CERN, Geneva, Switzerland

Special LHC high-beta optics is required for the forward physics program of TOTEM and ATLAS-ALFA. In this configuration, the beam is de-squeezed (the \beta-function at the collision point is increased) in order to minimize the divergence for measurements at very small scattering angles. In these low beam intensity runs, it is important to place the Roman Pots (RPs) as close as possible to the beam, which demands special collimator settings. During Run I, a significant amount of background was observed in the forward detectors due to particles outscattered from the primary collimator. During Run II, a different collimation configuration was used where a tungsten collimator was used as primary collimator instead of the usual one made of carbon. Using this configuration, a significant reduction of the background at the RPs was observed. In this paper we present a description of the new collimator configuration and the results obtained during the high-beta run carried out in 2016.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML012
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TUPAF043 Testing the Double-Crystal Setup for Physics Beyond Colliders Experiments in the UA9-SPS Experiment experiment, proton, detector, target 790

• S. Montesano
CERN, Geneva, Switzerland

Funding: on behalf of the UA9 Collaboration
The UA9 experiment is installed in the CERN SPS to study how coherent interaction in crystalline materials can be used to steer particles beams. Recently, new experiments requiring complex beam manipulations by means of crystals have been proposed in the framework of the Physics Beyond Colliders study group at CERN. In particular, it was proposed to use a first crystal to direct protons from the LHC beam halo on a target placed in the beam pipe and to use a second crystal to deflect the particles produced in the target (double-crystal setup), allowing to measure their polarization. The layout of the UA9 experiment in the CERN SPS has been modified to study the feasibility of the proposed scenario and its compatibility with the delicate environment of a superconducting collider. A first set of measurements was performed in 2017 proving that the protons deflected by the first crystal can be intercepted and successfully deflected by a second crystal. A further upgrade of the experiment in 2018 will allow measuring more precisely the combined efficiency of the two crystals and the beam-induced background.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF043
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TUPAF046 Conceptual Design of a Collimation System for the CERN Super Proton Synchrotron optics, proton, injection, simulation 802

• M. Patecki, A. Mereghetti, D. Mirarchi, S. Redaelli
CERN, Geneva, Switzerland

The Super Proton Synchrotron (SPS) is the last accelerator in the LHC Injectors Chain. Its performance is constantly being improved in frame of the LHC Injectors Upgrade (LIU) Project in order to prepare it for the future HL-LHC (High Luminosity LHC) operation. One of the LIU goals is to nearly double the intensity extracted from the SPS, up to 2.32×1011 p/bunch. In recent years, nearly 10% of losses are observed for nominal intensity and LHC-type beams; they grow to about 20% for the intensity approaching the HL-LHC target. Beam losses imply activation and aging of the SPS hardware; the possibility to add a collimation system is being considered to mitigate this problem. In this paper we present studies of a collimation system design for the SPS. The concept is based on a primary horizontal collimator located in an available position with high enough dispersion, and a secondary collimator to intercept the particles leaking out from the primary collimator. Performance of the proposed collimation system is evaluated by means of numerical simulations.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF046
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TUPAF059 Design and Evaluation of FCC-hh Injection Protection Schemes injection, kicker, dipole, collider 854

• E. Renner, M.J. Barnes, W. Bartmann, C. Bracco, R. Bruce, F. Burkart, B. Goddard, A. Lechner, L.S. Stoel, F.M. Velotti, C. Wiesner, D. Woog
CERN, Geneva, Switzerland

The Future Circular Collider (FCC) study considers several injector scenarios for FCC-hh, the proposed 100~TeV centre of mass hadron collider located at CERN. The investigated options include amongst others to use the LHC at 3.3~TeV or a superconducting SPS at 1.3~TeV as a High Energy Booster (HEB). Due to the high energy of the injected proton beam and the short time constant of injection failures, a thorough consideration of potential failure cases is of major importance. Further attention has to be given to the fact that the injection is - as in LHC - located upstream of the side experiments. Failure scenarios are identified for both injector options, appropriate designs of injection protection schemes are proposed and first simulations are conducted to validate the protection efficiency.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF059
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TUPAK018 Study on the Collimation Method for a Future Proton-Proton Collider proton, quadrupole, insertion, superconducting-magnet 1004

• J.Q. Yang, Y. Bao, J.Y. Tang, J.Y. Tang, Y. Zou
IHEP, Beijing, People's Republic of China

As the second phase of CEPC-SPPC project, SPPC (Super Proton-Proton Collider) is to explore new physics beyond the standard model in the energy frontier with a center-of-mass energy of 75 TeV. In order to handle extremely-high stored energy in beam, the collimation system of extremely high efficiency is required for safe operation. SPPC has been studying a collimation method which arranges both the transverse and momentum collimations in one long straight section. In this way, the downstream momentum collimation section can clean those particles related to the single diffractive effect in the transverse collimation section thus eliminate beam losses in the arc section. In addition, one more collimation stage is obtained with use of special superconduct-ing quadrupoles in the transverse collimation section. Multiple particle simulations have proven the effectiveness of the methods. This paper presents the study results on the collimation scheme.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAK018
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WEYGBE4 Low-Impedance Collimators for HL-LHC impedance, octupole, operation, luminosity 1794

• S. A. Antipov, N. Biancacci, R. Bruce, A. Mereghetti, D. Mirarchi, E. Métral, S. Redaelli, B. Salvant
CERN, Geneva, Switzerland
• D. Amorim
Université Grenoble Alpes, Grenoble, France

The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will double its beam intensity for the needs of High Energy Physics frontier. This increase requires a reduction of the machine's impedance to ensure the coherent stability of the beams until they are put in collision. A major part of the impedance is the resistive wall contribution of the collimators. To reduce this contribution several coating options have been proposed. We have studied numerically the effect of the novel coatings on the beam stability. The results show that a decrease of up to 30% of the machine impedance and a reduction of up to 120 A in the stabilizing octupole current threshold can be achieved by coating the secondary collimators with Molybdenum. Half of that improvement can be obtained by coating the jaws of a subset of four collimators identified as the highest contributors to machine impedance. The installation of this subset of low-impedance collimators is planned for the Long Shutdown 2 in 2019-2020.
Slides WEYGBE4 [5.719 MB]
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBE4
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WEPAF078 Machine Learning Applied at the LHC for Beam Loss Pattern Classification beam-losses, injection, proton, flattop 2020

• G. Valentino
University of Malta, Information and Communication Technology, Msida, Malta
• B. Salvachua
CERN, Geneva, Switzerland

Beam losses at the LHC are constantly monitored because they can heavily impact the performance of the machine. One of the highest risks is to quench the LHC superconducting magnets in the presence of losses leading to a long machine downtime in order to recover cryogenic conditions. Smaller losses are more likely to occur and have an impact on the machine performance, reducing the luminosity production or reducing the lifetime of accelerator systems due to radiation effects, such as magnets. Understanding the characteristics of the beam loss, such as the beam and the plane, is crucial in order to correct them. Regularly during the year, dedicated loss map measurements are performed in order to validate the beam halo cleaning of the collimation system. These loss maps have the particular advantage that they are performed in well controlled conditions and can therefore be used by a machine learning algorithm to classify the type of losses during the LHC machine cycle. This study shows the result of the beam loss classification and its retrospective application to beam loss data from the 2017 run.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF078
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WEPML076 The Magnetic Measurement of Enhancer-Dipole Magnet for CEPC collider, positron, electron, dipole 2866

• Z. Zhang, H. Wang
IHEP, Beijing, People's Republic of China

The CEPC (Circular Electron Positron Collider) project is in the pre-research stage. When the beam energy of booster is 120 GeV, the magnetic field of deflection magnet is 640 Gs. In order to save funds for scientific research, we also consider the injection energy of 6 GeV, the magnetic field of deflection magnet is 32 Gs. At the different current, the magnetic field value of the enhancer-dipole magnet can reach the beam energy range of 6 Gev-120 GeV. In such a requirements of magnetic field, the stability of the magnetic field value, repeatability, magnet magnetism, has become an important data for the design parameters of enhancer-dipole magnet. The magnet is measured with the Hall-Probe measurement facility by IHEP. In this paper, first written the procedure of motor control and collection by Labview software, then hen the excitation curve（repeat the measurement six times）, transverse field distribution（repeat the measurement three times）, and integral field distribution are measured. Based on the results of the analysis of large amounts of data, the stability and repeatability of the enhance-dipole magnet in different magnetic fields has summarized and analyzed.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML076
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