Author: Redaelli, S.
Paper Title Page
MOODB201 Proton-nucleus Collisions in the LHC 49
 
  • J.M. Jowett, R. Alemany-Fernandez, P. Baudrenghien, D. Jacquet, M. Lamont, D. Manglunki, S. Redaelli, M. Sapinski, M. Schaumann, M. Solfaroli Camillocci, R. Tomás, J.A. Uythoven, D. Valuch, R. Versteegen, J. Wenninger
    CERN, Geneva, Switzerland
  
  Following the high integrated luminosity accumulated in the first two Pb-Pb collision runs in 2010 and 2011, the LHC heavy-ion physics community requested a first run with p-Pb collisions. This almost unprecedented mode of collider operation was not foreseen in the baseline design of the LHC whose two-in-one magnet design imposed equal rigidity and, hence, unequal revolution frequencies, during injection and ramp. Nevertheless, after a successful pilot physics fill in 2012, the LHC provided 31 nb-1 of p-Pb luminosity per experiment, at an energy of 5.02 TeV per colliding nucleon pair, with several variations of the operating conditions, in early 2013. Together with a companion p-p run at 2.76 TeV, this was the last physics before the present long shutdown. We summarise the beam physics, operational adaptations and strategy that resulted in extremely rapid commissioning. Finally, we give an account of the progress of the run and provide an analysis of the performance.  
slides icon Slides MOODB201 [6.547 MB]  
 
MOODB202 Simulations and Measurements of Cleaning with 100 MJ Beams in the LHC 52
 
  • R. Bruce, R.W. Aßmann, V. Boccone, C. Bracco, M. Cauchi, F. Cerutti, D. Deboy, A. Ferrari, L. Lari, A. Marsili, A. Mereghetti, E. Quaranta, S. Redaelli, G. Robert-Demolaize, A. Rossi, B. Salvachua, E. Skordis, G. Valentino, V. Vlachoudis, Th. Weiler, D. Wollmann
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
  • E. Quaranta
    Politecnico/Milano, Milano, Italy
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  The CERN Large Hadron Collider is routinely storing proton beam intensities of more than 100 MJ, which puts extraordinary demands on the control of beam losses to avoid quenches of the superconducting magnets. Therefore, a detailed understanding of the LHC beam cleaning is required. We present tracking and shower simulations of the LHC's multi-stage collimation system and compare with measured beam losses, which allow us to conclude on the predictive power of the simulations.  
slides icon Slides MOODB202 [6.343 MB]  
 
MOPWO028 Recent Developments and Future Plans for SixTrack 948
 
  • R. De Maria, R. Bruce, R. Calaga, L. Deniau, M. Fjellstrom, M. Giovannozzi, L. Lari, Y.I. Levinsen, E. McIntosh, A. Mereghetti, D. Pastor Sinuela, S. Redaelli, H. Renshall, A. Rossi, F. Schmidt, R. Tomás, V. Vlachoudis
    CERN, Geneva, Switzerland
  • R. Appleby, D.R. Brett
    UMAN, Manchester, United Kingdom
  • D. Banfi, J. Barranco
    EPFL, Lausanne, Switzerland
  • B. Dalena
    CEA/IRFU, Gif-sur-Yvette, France
  • L. Lari
    IFIC, Valencia, Spain
  • V. Previtali
    Fermilab, Batavia, USA
  • G. Robert-Demolaize
    BNL, Upton, Long Island, New York, USA
  
  Funding: The HiLumi LHC Design Study is included in the HL-LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.
SixTrack is a symplectic 6D tracking code routinely used to simulate single particle trajectories in high energy circular machines like the LHC and RHIC. The paper presents the developments recently implemented and those foreseen for extending the physics models: exact Hamiltonian, different ions and charge states, RF multipoles, non-linear fringe fields, Taylor maps, e-lenses, ion scattering. Moreover new functionalities are also added like variable number of tracked particles, time dependent strengths, GPU computations with a refactoring of the core structure. The developments will benefit studies on the LHC and SPS, for collimation efficiency, ion operations, failure scenarios and HL-LHC design. 		 
 
MOPWO029 Remote Estimate of Collimator Jaw Damages with Sound Measurements during Beam Impacts 951
 
  • D. Deboy, O. Aberle, R.W. Aßmann, F. Carra, M. Cauchi, J. Lendaro, A. Masi, S. Redaelli
    CERN, Geneva, Switzerland
  
  Irregular hits of high-intensity LHC beams on collimators can lead to severe damage of the collimator jaws. The identification of damaged collimator jaws by observation of beam measurements is challenging: online loss measurements at the moment of the impacts can be tricky and degradation of the overall performance from single collimator damage can be difficult to measure. Visual inspections are excluded because collimator jaws are enclosed in vacuum tanks without windows. However, the sound generated during the beam impact can be used to give an estimate of the damage level. In 2012, high-intensity beam comparable to a full nominal LHC bunch at 7 TeV was shot on a tertiary type LHC collimator at the HiRadMat test facility at CERN. The paper presents results from sound recordings of this experiment.  
 
MOPWO031 High Energy Beam Impact Tests on a LHC Tertiary Collimator at CERN HiRadMat Facility 954
 
  • M. Cauchi, O. Aberle, R.W. Aßmann, A. Bertarelli, F. Carra, A. Dallocchio, D. Deboy, L. Lari, S. Redaelli, A. Rossi
    CERN, Geneva, Switzerland
  • M. Cauchi, P. Mollicone
    UoM, Msida, Malta
  • L. Lari
    IFIC, Valencia, Spain
  • N.J. Sammut
    University of Malta, Information and Communication Technology, Msida, Malta
  
  The correct functioning of the collimation system is crucial to safely operate the LHC. The requirements to handle high intensity beams can be demanding. In this respect, investigating the consequences of LHC particle beams hitting tertiary collimators (TCTs) in the experimental regions is a fundamental issue for machine protection. An experimental test was designed to investigate the robustness and effects of beam accidents on a fully assembled collimator, based on accident scenarios in the LHC. This experiment, carried out at the CERN HiRadMat (High Irradiation to Materials) facility, involved 440 GeV beam impacts of different intensities on the jaws of a horizontal TCT. This paper presents the experimental setup and the preliminary results obtained together with some first outcomes from visual inspection.  
 
MOPWO035 Layouts for Crystal Collimation Tests at the LHC 966
 
  • D. Mirarchi, S. Redaelli, W. Scandale
    CERN, Geneva, Switzerland
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • V. Previtali
    Fermilab, Batavia, USA
  
  Various studies have been carried out in the past years regarding crystal collimation for the LHC. A new extensive campaign of simulations was performed to determine optimum layouts for beam tests at the LHC. The layouts are determined based on semi-analytical models for the dynamics of channeled particles. Detailed SixTrack tracking with all collimators of the ring are then used to validate the different options. An overview of the ongoing studies is given. Comparative studies between the present collimation system, the crystal collimation system, and different crystal collimation layout are presented.  
 
MOPWO037 SixTrack Simulation of Off-momentum Cleaning in LHC 972
 
  • E. Quaranta, R. Bruce, S. Redaelli
    CERN, Geneva, Switzerland
  
  In the LHC, high-amplitude particles are cleaned by either betatron collimators or momentum collimators. Previously, betatron losses have been considered more important, but measurements during the first years of operation show high losses also in the off-momentum cleaning insertion. This causes a significant radiation dose to warm magnets downstream of the collimators. Our work in this paper aims at simulating with SixTrack the off-momentum particles, driven into the momentum collimators by radiation damping outside the RF system acceptance. The results are an important ingredient in assessing the effectiveness of new passive absorbers to protect the warm magnets.  
 
MOPWO038 Cleaning Inefficiency of the LHC Collimation System during the Energy Ramp: Simulations and Measurements 975
 
  • E. Quaranta, R. Bruce, L. Lari, D. Mirarchi, S. Redaelli, A. Rossi, B. Salvachua, G. Valentino
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  The cleaning inefficiency of the LHC collimation system has already been studied in detail at injection and top energy (450 GeV and 4 TeV respectively). In this paper the results are presented for the cleaning inefficiency at intermediate energies, simulated using the SixTrack code. The first comparisons with measured provoked losses are discussed. This study helps in benchmarking the energy dependence of the simulated inefficiency and is thus important for the extrapolation to future operation at higher energies.  
 
MOPWO039 Experience with High-intensity Beam Scraping and Tail Populations at the Large Hadon Collider 978
 
  • S. Redaelli, R. Bruce, F. Burkart, D. Mirarchi, B. Salvachua, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
  • R.W. Aßmann
    DESY, Hamburg, Germany
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  The population of beam tails at the LHC is source of concern because even small fractions of the total beam intensity could represent a potential danger is case of slow or fast losses, e.g. caused by orbit transients or by collimator movements. Different studies have been performed using the technique of collimator scans to probe the beam tail population, for different beam energies and beam intensities. The experience accumulated during the operation at 3.5 TeV and 4 TeV is reviewed and extrapolations to higher energies are considered.  
 
MOPWO040 Analysis of Failures of the LHC Collimators during the 2010-2013 Operation 981
 
  • S. Redaelli, A. Masi
    CERN, Geneva, Switzerland
  
  The LHC collimation system must be available in all phases of the machine operation in order to handle the high stored beam energies. The system availability is therefore crucial to achieve an efficient LHC operation. The collimation system has proved to work reliably in the first years of LHC operation, with total stored energies up to 140 MJ. The impact on the machine availability has been limited. The analysis of collimation system availability and the failure rate in the years 2012-2012 is reviewed with the aim to identify possible further improvements for the future.  
 
MOPWO041 Simulations and Measurements of Physics Debris Losses at the 4 TeV LHC 984
 
  • A. Marsili, R. Bruce, F. Cerutti, S. Redaelli
    CERN, Geneva, Switzerland
  
  Funding: The HiLumi LHC Design Study is included in the HL-LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.
Simulations of energy deposition from the physics debris are normally done with shower simulation tools like FLUKA. Tracking tools like SixTrack allow faster simulations that open the possibility to study parametrically and optimize different layouts. In this paper, the results of FLUKA and SixTrack simulations are compared to beam measurements done for different collimator settings at 4 TeV, with p-p luminosities up to 7·1033 cm-2s−1. 		 
 
MOPWO042 Simulations of Collimation Cleaning Performance with HL-LHC Optics 987
 
  • A. Marsili, R. Bruce, R. De Maria, S.D. Fartoukh, S. Redaelli
    CERN, Geneva, Switzerland
  
  Funding: The HiLumi LHC Design Study is included in the HL-LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.
The upgrade of the LHC from the current set-up to high luminosity performances will provide new challenges for the protection of the machine. The different optics considered might create new needs for collimation, and require new collimation locations. In order to evaluate the cleaning performances of the collimation system, different halo cleaning simulations were performed with the particle tracking code SixTrack. This paper presents the cleaning performance simulation results for the high luminosity Achromatic Telescopic Squeeze optics considered as baseline for the HL-LHC. The new limitations observed and possible solutions are discussed. 		 
 
MOPWO043 Hollow Electron Lens Simulation for the SPS 990
 
  • V. Previtali, G. Stancari, A. Valishev
    Fermilab, Batavia, USA
  • S. Redaelli
    CERN, Geneva, Switzerland
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC, Contract No. DE-AC02-07CH11359 with the United States Dep. of Energy. This work was supported by the US LHC Accelerator Research Program (LARP).
The hardware of the Tevatron hollow electron lens, which has been used in the past for collimation purposes, is presently available. Possible applications of similar devices in the LHC are under evaluation, but a realistic date for installation of electron lenses in the LHC would be not earlier than the machine shutdown scheduled for 2018. We investigated the possibility of beam tests with the available hardware in the meantime in the SPS. This article aims to answer this question by presenting the results of dedicated numerical simulations. 		 
 
MOPWO044 Numerical Simulations of a Hollow Electron Lens as a Scraping Device for the LHC 993
 
  • V. Previtali, G. Stancari, A. Valishev
    Fermilab, Batavia, USA
  • S. Redaelli
    CERN, Geneva, Switzerland
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC, Contract No.DE-AC02-07CH11359 with the United States Dep. of Energy. This work was partially supported by US LHC Accelerator Research Program(LARP)
The use of hollow electron beam lens for scraping high energy proton beams has been extensively tested at Fermilab's Tevatron collider. In order to evaluate a possible application of a similar a device in the LHC, a dedicated new routine has been implemented in the standard 6D tracking code used at CERN for the design of the LHC collimation system. The effects of a finite length cylinder of electrons encompassing the main proton beam and traveling in the opposite direction is described in the routine. Realistic electron distributions, including measured radial imperfections, have been included in the model. Various operating modes have been simulated for the 7 TeV machine operation with sextupoles and octupoles included. The loss rate caused by the electron lens has been studied through an extended simulation campaign; the obtained halo removal rates for the different electron lens operating modes are presented. 		 
 
MOPWO046 Simulations and Measurements of Beam Losses on LHC Collimators during Beam Abort Failures 996
 
  • L. Lari, C. Bracco, R. Bruce, B. Goddard, S. Redaelli, B. Salvachua, G. Valentino
    CERN, Geneva, Switzerland
  • A. Faus-Golfe, L. Lari
    IFIC, Valencia, Spain
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  Funding: The HiLumi LHC Design Study is included in the HL-LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.
One of the main purposes of tracking simulations for collimation studies is to produce loss maps along the LHC ring, in order to identify the level of local beam losses during nominal and abnormal operation scenarios. The SixTrack program is the standard tracking tool used at CERN to perform these studies. Recently, it was expanded in order to evaluate the proton load on different collimators in case of fast beam failures. Simulations are compared with beam measurements at 4 TeV. Combined failures are assumed which provide worst-case scenarios of the load on tungsten tertiary collimators. 		 
 
MOPWO048 Cleaning Performance of the LHC Collimation System up to 4 TeV 1002
 
  • B. Salvachua, R.W. Aßmann, R. Bruce, M. Cauchi, D. Deboy, L. Lari, A. Marsili, D. Mirarchi, E. Quaranta, S. Redaelli, A. Rossi, G. Valentino
    CERN, Geneva, Switzerland
  • M. Cauchi
    UoM, Msida, Malta
  • L. Lari
    IFIC, Valencia, Spain
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  Funding: Research supported by EU FP7 HiLumi LHC (Grant agreement 284404)
In this paper we review the performance of the LHC collimation system during 2012 and compare it with previous years. During 2012, the so-called tight settings were deployed for a better cleaning and improved beta-star reach. As a result, a record cleaning efficiency below a few 0.0001 was achieved in the cold regions where the highest beam losses occur. The cleaning in other cold locations is typically a factor of 10 better. No quenches were observed during regular operation with up to 140 MJ stored beam energy. The system stability during the year, monitored regularly to ensure the system functionality for all machine configurations, and the performance of the alignment tools are also reviewed. 		 
 
MOPWO049 Lifetime Analysis at High Intensity Colliders Applied to the LHC 1005
 
  • B. Salvachua, R.W. Aßmann, R. Bruce, F. Burkart, S. Redaelli, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  The beam lifetime is one of the main parameters to define the performance of a collider. In a super-conducting machine like the LHC, the lifetime determines the intensity reach for a given collimation cleaning. The beam lifetime can be calculated from the direct measurement of beam current. However, due to the noise in the beam current signal only an average lifetime over several seconds can be calculated. We propose here an alternative method, which uses the signal of the beam loss monitors in the vicinity of the primary collimators to get the instantaneous beam lifetime at the collimators. In this paper we compare the lifetime from the two methods and investigate the minimum lifetime over the LHC cycle for all the physics fills in 2011 and 2012. These data provide a reference for estimates of performance reach from collimator cleaning.  
 
MOPWO050 Comparison of LHC Beam Loss Maps using the Transverse Damper Blow up and Tune Resonance Crossing Methods 1008
 
  • V. Moens, R. Bruce, S. Redaelli, B. Salvachua, G. Valentino
    CERN, Geneva, Switzerland
  • V. Moens
    EPFL, Lausanne, Switzerland
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  
  The LHC collimator settings are qualified regularly via beam loss maps. In this procedure, the beam is artificially excited to create abnormal loss rates. The transverse damper blow up and tune resonance crossing methods are used to increase the betatron amplitude of particles and verify the efficiency of the collimation cleaning and the collimator hierarchy. This paper presents a quantitative comparison of the methods, based on measurements done at different phases of the LHC machine cycle. The analysis is done using Beam Loss Monitor (BLM) with integration times of 1.3 s and 80 ms. The use of the faster BLM data to study the time evolution of the losses in IR3 and IR7 during off-momentum loss maps is also presented.  
 
MOPWO051 Estimate of Warm Magnets Lifetime in the Betatron and Momentum Cleaning Insertions of the LHC 1011
 
  • B. Salvachua, R. Bruce, M. Brugger, F. Cerutti, S. Redaelli
    CERN, Geneva, Switzerland
  
  The CERN LHC collimation system is designed to perform momentum and betatron cleaning in different insertions, respectively IR3 and IR7. The insertions are not perfectly decoupled because the dispersion in IR7 is not null and the beta function in IR3 is not zero. The detailed sharing of losses between the two insertions depends on the relative collimator settings as observed by the change between 2011 and 2012 LHC operation. In this report, using the beam loss measurements at the primary collimators of IR3 and IR7, the total BLM losses in the two insertions are calculated and compared to each other. These studies are also used to quantify the total dose to warm magnets in those IRs with the aim to understand better their lifetime and the implications of the radiation to electronics. This will be of particular importance in view of LHC operating at nominal performance after several years of operation.  
 
TUPFI033 Colliding During the Squeeze and β* Leveling in the LHC 1415
 
  • X. Buffat
    EPFL, Lausanne, Switzerland
  • W. Herr, M. Lamont, T. Pieloni, S. Redaelli, J. Wenninger
    CERN, Geneva, Switzerland
  
  While more challenging operationally, bringing the beams into collisions during the β squeeze rather than after presents some advantages. The large tune spread arising from the non-linearity of head-on beam-beam interactions can damp impedance-driven instabilities much more efficiently than external non-linearity such as octupoles presently used in operation. Moreover, colliding during the squeeze allows to level the luminosity, optimizing the pile-up in the experiments without changing the longitudinal distribution of collisions. Operational issues are discussed and experimental results from the LHC are presented.  
 
TUPFI037 Collimation Down to 2 Sigma in Special Physics Runs in the LHC 1427
 
  • H. Burkhardt, S. Jakobsen, S. Redaelli, B. Salvachua, G. Valentino
    CERN, Geneva, Switzerland
  
  We report on observations with collimation very close to the beam. Primary collimators were moved in small steps down to 2 σ from the beam axis to allow for measurements of very forward proton scattering in special high-beta runs in the LHC. We studied the reduction in intensity as a function of collimator position which provides information about the halo shape. After scraping at 2 σ, collimators were retracted to 2.5 σ. This allowed for measurements of very forward proton-proton scattering with roman pot detectors at 3 σ from the beam axis at acceptable background levels for about an hour. Good background conditions were restored by another scraping with primary collimators at 2 σ. Beam lifetimes and halo repopulation times were found to be sufficiently long to allow for several hours of data taking between scraping in a single LHC fill.  
 
TUPFI038 Operation of the Betatron Squeeze at the LHC 1430
 
  • S. Redaelli, X. Buffat, M. Lamont, G.J. Müller, M. Solfaroli Camillocci, R. Tomás, J. Wenninger
    CERN, Geneva, Switzerland
  • G.J. Müller
    TU Dresden, Dresden, Germany
  
  The betatron squeeze is one of the most delicate operational phases at the large Hadron collider as it entails changes of optics performed at top energy, with full intensities. Appropriate software was developed to handle the squeeze, which ensured an efficient commissioning down to a β* of 60 cm and a smooth operation. Several optics configurations could be commissioned and put in operation for physics. The operational experience of the LHC runs from 2010 until 2012 is presented and the overall performance reviewed.  
 
TUPFI039 Optics Performance of the LHC During the 2012 Run 1433
 
  • P. Skowroński, T. Bach, M. Giovannozzi, A. Langner, Y.I. Levinsen, E.H. Maclean, T. Persson, S. Redaelli, T. Risselada, M. Solfaroli Camillocci, R. Tomás, G. Vanbavinckhove
    CERN, Geneva, Switzerland
  • M.J. McAteer
    The University of Texas at Austin, Austin, USA
  • R. Miyamoto
    ESS, Lund, Sweden
  • T. Persson
    Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden
  
  During 2012 the LHC was operating at 4TeV with beta star at ATLAS and CMS interaction points of 0.6m. During dedicated machine studies the nominal LHC optics was also setup with beta star of 0.4m. A huge effort was put into the optics commissioning leading to a record low peak beta-beating of around 7%. We describe the correction procedures and discuss the measurement results.  
 
TUPFI041 Operating the LHC Off-momentum for p-Pb Collisions 1439
 
  • R. Versteegen, R. Bruce, J.M. Jowett, A. Langner, Y.I. Levinsen, E.H. Maclean, M.J. McAteer, T. Persson, S. Redaelli, B. Salvachua, P. Skowroński, M. Solfaroli Camillocci, R. Tomás, G. Valentino, J. Wenninger
    CERN, Geneva, Switzerland
  • E.H. Maclean
    JAI, Oxford, United Kingdom
  • M.J. McAteer
    The University of Texas at Austin, Austin, USA
  • T. Persson
    Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  • S.M. White
    BNL, Upton, Long Island, New York, USA
  
  The first high-luminosity p-Pb run at the LHC took place in January-February 2013 at an energy of 4 Z TeV per beam. The RF frequency difference of proton and Pb is about 60 Hz for equal magnetic rigidities, which means that beams move slightly to off-momentum, non-central, orbits during physics when frequencies are locked together. The resulting optical perturbations ("beta-beating") restrict the available aperture and required a special correction. This was also the first operation of the LHC with low beta in all four experiments and required a specific collimation set up. Predictions from offline calculations of beta-beating correction are compared with measurements during the optics commissioning and collimator set up.  
 
TUPME032 Update on Beam Induced RF Heating in the LHC 1646
 
  • B. Salvant, O. Aberle, G. Arduini, R.W. Aßmann, V. Baglin, M.J. Barnes, W. Bartmann, P. Baudrenghien, O.E. Berrig, A. Bertarelli, C. Bracco, E. Bravin, G. Bregliozzi, R. Bruce, F. Carra, F. Caspers, G. Cattenoz, S.D. Claudet, H.A. Day, M. Deile, J.F. Esteban Müller, P. Fassnacht, M. Garlaschè, L. Gentini, B. Goddard, A. Grudiev, B. Henrist, S. Jakobsen, O.R. Jones, O. Kononenko, G. Lanza, L. Lari, T. Mastoridis, V. Mertens, N. Mounet, E. Métral, A.A. Nosych, J.L. Nougaret, S. Persichelli, A.M. Piguiet, S. Redaelli, F. Roncarolo, G. Rumolo, B. Salvachua, M. Sapinski, R. Schmidt, E.N. Shaposhnikova, L.J. Tavian, M.A. Timmins, J.A. Uythoven, A. Vidal, J. Wenninger, D. Wollmann, M. Zerlauth
    CERN, Geneva, Switzerland
  • H.A. Day
    UMAN, Manchester, United Kingdom
  • L. Lari
    IFIC, Valencia, Spain
  
  Since June 2011, the rapid increase of the luminosity performance of the LHC has come at the expense of increased temperature and pressure readings on specific near-beam LHC equipment. In some cases, this beam induced heating has caused delays whilie equipment cools down, beam dumps and even degradation of these devices. This contribution gathers the observations of beam induced heating attributable to beam coupling impedance, their current level of understanding and possible actions that are planned to be implemented during the long shutdown in 2013-2014.  
 
TUPME060 Tune Studies with Beam-Beam Effects in LHC 1703
 
  • S. Paret, J. Qiang
    LBNL, Berkeley, California, USA
  • R. Alemany-Fernandez, X. Buffat, R. Calaga, K. Cornelis, M. Fitterer, R. Giachino, W. Herr, A. Macpherson, G. Papotti, T. Pieloni, S. Redaelli, F. Roncarolo, M. Schaumann, R. Suykerbuyk, G. Trad
    CERN, Geneva, Switzerland
  • R. Miyamoto
    ESS, Lund, Sweden
  
  Funding: This work was partially supported by the U.S. LARP and the NERSC of the U.S. Department of Energy under contract No. DE-AC02-05CH11231.
In high brightness colliders, the tune spread due to the collisions has a significant impact on the quality of the beams. The impact of the working point on emittance growth and beam lifetime has been observed in beam experiments in LHC. Strong-strong beam-beam simulations that were accomplished to better understand such observations are shown. Compared to experiments, wide ranged parameter scans can be done easily. Tune footprints and scans of the emittance growth obtained from simulations are discussed. Three cases are considered: Very high intensity, moderate intensity and collisions with separated beams. 		 
 
TUPWA042 Lessons Learned and Mitigation Measures for the CERN LHC Equipment with RF Fingers 1802
 
  • E. Métral, O. Aberle, R.W. Aßmann, V. Baglin, M.J. Barnes, O.E. Berrig, A. Bertarelli, G. Bregliozzi, S. Calatroni, F. Carra, F. Caspers, H.A. Day, M. Ferro-Luzzi, M.A. Gallilee, C. Garion, M. Garlaschè, A. Grudiev, J.M. Jimenez, O.R. Jones, O. Kononenko, R. Losito, J.L. Nougaret, V. Parma, S. Redaelli, B. Salvant, P.M. Strubin, R. Veness, C. Vollinger, W.J.M. Weterings
    CERN, Geneva, Switzerland
  
  Beam-induced RF heating has been observed in several LHC components when the bunch/beam intensity was increased and/or the bunch length reduced. In particular eight bellows, out of the ten double-bellows modules present in the machine in 2011, were found with the spring, which should keep the RF fingers in good electrical contact with the central insert, broken. Following these observations, the designs of all the components of the LHC equipped with RF fingers have been reviewed. The lessons learnt and mitigation measures are presented in this paper.  
 
TUPWA047 Collimator Impedance Measurements in the LHC 1817
 
  • N. Mounet, R. Bruce, E. Métral, S. Redaelli, B. Salvachua, B. Salvant, G. Valentino
    CERN, Geneva, Switzerland
  
  The collimation system of the LHC is one of the largest impedance contributors of the machine, in particular for its imaginary part. To evaluate the collimator impedance and its evolution with integrated luminosity, several measurement campaigns were performed along the year 2012, in which collimator jaws were moved back-and-forth leading to significant tune shifts for a nominal intensity bunch in the machine. These observations are compared to the results from HEADTAIL simulations with the impedance model in its current state of development.  
 
WEPEA046 Experimental Observations from the LHC Dynamic Aperture Machine Development Study in 2012 2606
 
  • M. Giovannozzi, S. Cettour Cave, R. De Maria, M. Ludwig, A. Macpherson, S. Redaelli, F. Roncarolo, M. Solfaroli Camillocci, W. Venturini Delsolaro
    CERN, Geneva, Switzerland
  
  In view of improving the understanding of the behaviour of the dynamic aperture and to benchmark the numerical simulations performed so far, two experimental sessions have been scheduled at the LHC. The observations of the first sessions have been reported elsewhere[1], while in this paper the latest observations in terms of beam currents, blm losses and beam sizes will be described. The octupolar spool pieces have been used to artificially reduce the dynamic aperture and then induced slow beam losses. Alternating signs have been used in order to probe different configurations. Finally, scans over the strength of the decapolar spool pieces have been performed too.
[1] M. Giovannozzi et al., “First Experimental Observations from the LHC Dynamic Aperture Experiment”, in proceedings of IPAC12, p. 1362 		 
 
THPEA045 Beam Induced Quenches of LHC Magnets 3243
 
  • M. Sapinski, T. Baer, M. Bednarek, G. Bellodi, C. Bracco, R. Bruce, B. Dehning, W. Höfle, A. Lechner, E. Nebot Del Busto, A. Priebe, S. Redaelli, B. Salvachua, R. Schmidt, D. Valuch, A.P. Verweij, J. Wenninger, D. Wollmann, M. Zerlauth
    CERN, Geneva, Switzerland
  
  In the years 2009-2013 LHC was operating with the beam energy of 3.5 and 4 TeV instead of the nominal 7 TeV, with the corresponding currents in the superconducting magnets also half nominal. To date only a small number of beam-induced quenches have occurred, with most being due to specially designed quench tests. During normal collider operation with stored beam there has not been a single beam induced quench. This excellent result is mainly explained by the fact that the cleaning of the beam halo worked very well and, in case of beam losses, the beam was dumped before any significant energy was deposited in the magnets. However, conditions are expected to become much tougher after the long LHC shutdown, when the magnets will be working at near nominal currents in the presence of high energy and intensity beams. This paper summarizes the experience to date with beam-induced quenches. It describes the techniques used to generate controlled quench conditions which were used to study the limitations. Results are discussed along with their implication for LHC operation after the first Long Shutdown.  
 
THPFI046 First Results of an Experiment on Advanced Collimator Materials at CERN HiRadMat Facility 3391
 
  • A. Bertarelli, O. Aberle, R.W. Aßmann, E. Berthomé, V. Boccone, M. Calderón Cueva, F. Carra, F. Cerutti, N. Charitonidis, C. Charrondière, A. Dallocchio, M. Donzé, P. Francon, M. Garlaschè, L. Gentini, M. Guinchard, N. Mariani, A. Masi, P. Moyret, S. Redaelli, A. Rossi, S.D.M. dos Santos
    CERN, Geneva, Switzerland
  • M. Calderón Cueva
    Universidad San Francisco de Quito, Cumbayá, Colombia
  • N. Charitonidis
    EPFL, Lausanne, Switzerland
  • L. Peroni, M. Scapin
    Politecnico di Torino, Torino, Italy
  
  Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579
A comprehensive, first-of-its-kind experiment (HRMT-14) has been recently carried out at CERN HiRadMat facility on six different materials of interest for Beam Intercepting Devices (collimators, targets, dumps). Both traditional materials (Mo, W and Cu alloys) as well as advanced metal/diamond and metal/graphite composites were tested under extreme conditions as to pressure, density and temperature, leading to the development of highly dynamic phenomena as shock-waves, spallation, explosions. Experimental data were acquired, mostly in real time, relying on extensive embarked instrumentation (strain gauges, temperature and vacuum sensors) and on remote acquisition devices (laser Doppler vibrometer and high speed camera). The experiment was a success under all points of view in spite of the technological challenges and harsh environment. First measurements are in good agreement with results of complex simulations, confirming the effectiveness of the acquisition system and the reliability of advanced numerical methods when material constitutive models are completely available. Interesting information has been collected as to thermal shock robustness of tested materials. 		 
 
THPFI063 Development and Beam Tests of an Automatic Algorithm for Alignment of LHC Collimators with Embedded BPMs 3439
 
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  • R.W. Aßmann
    DESY, Hamburg, Germany
  • R. Bruce, M. Gasior, D. Mirarchi, A.A. Nosych, S. Redaelli, B. Salvachua, N.J. Sammut
    CERN, Geneva, Switzerland
  
  Collimators with embedded Beam Position Monitor (BPM) buttons will be installed in the LHC during the upcoming long shutdown period. During the subsequent operation, the BPMs will allow the collimator jaws to be kept centered around the beam trajectory. In this manner, the best possible beam cleaning efficiency and machine protection can be provided at unprecedented higher beam energies and intensities. A collimator alignment algorithm is proposed to center the jaws automatically around the beam. The algorithm is based on successive approximation, as the BPM measurements are affected by non-linearities, which vary with the distance between opposite buttons, as well as the difference between the beam and the jaw centers. The successful test results, as well as some considerations for eventual operation in the LHC are also presented.  
 
THPFI064 Crystal-assisted Collimation Experiment from the SPS to the LHC 3442
 
  • W. Scandale, D. Mirarchi, S. Redaelli
    CERN, Geneva, Switzerland
  
  UA9 was operated in the CERN-SPS for more than six years in view of investigating the feasibility of the halo collimation assisted by bent crystals. Two-millimeter-long silicon crystals, with bending angles of about 150 μrad, are used as primary collimators. The crystal collimation process is obtained consistently through channeling with high efficiency, showing a steady reduction of almost one order of magnitude of the loss rate at the onset of the channeling process. This result holds both for protons and for lead-ions. The corresponding loss map in the accelerator ring is accordingly reduced. These observations strongly support our expectation that the coherent deflection of the beam halo by a bent crystal should enhance the collimation efficiency also in LHC. After a concise description of the results collected in the SPS we propose a scenario to integrate bent crystals in the LHC collimation system for machine experiment.