Author: Wenninger, J.
Paper Title Page
TUPZ001 90 m Optics Commissioning 1795
 
  • S. Cavalier
    LAL, Orsay, France
  • H. Burkhardt, M. Fitterer, G.J. Müller, S. Redaelli, R. Tomás, G. Vanbavinckhove, J. Wenninger
    CERN, Geneva, Switzerland
 
  Special β* = 90 m optics have been developed for the two very high luminosity insertions of the LHC, as a first step towards to allow for very low angle precision measurements of the proton-proton collisions in the LHC. These optics were developed to be compatible with the standard LHC injection and ramp optics. The target value of β* = 90 m is reached by an un-squeeze from the injection β* = 11 m. We describe the implementation of this optics in the LHC and the first experience in the commissioning of these optics.  
 
TUPZ006 Aperture Determination in the LHC Based on an Emittance Blowup Technique with Collimator Position Scan 1810
 
  • R.W. Assmann, R. Bruce, M. Giovannozzi, G.J. Müller, S. Redaelli, F. Schmidt, R. Tomás, J. Wenninger, D. Wollmann
    CERN, Geneva, Switzerland
  • M. Alabau
    IFIC, Valencia, Spain
 
  A new method to determine the LHC aperture was proposed. The new component is a collimator scan technique that refers the globally measured aperture limit to the shadow of the primary collimator, expressed in σs of rms beam size. As a by-product the BLM response to beam loss is quantified. The method is described and LHC measurement results are presented.  
 
TUPZ009 LHC Machine Protection against Very Fast Crab Cavity Failures 1816
 
  • T. Baer, R. Tomás, J. Tückmantel, J. Wenninger, F. Zimmermann
    CERN, Geneva, Switzerland
  • T. Baer
    Uni HH, Hamburg, Germany
  • R. Calaga
    BNL, Upton, Long Island, New York, USA
 
  For the high-luminosity LHC upgrade program (HL-LHC), the installation of crab cavities (CCs) is essential to compensate the geometric luminosity loss due to the crossing angle. The baseline is a local scheme with CCs around the ATLAS and CMS experiments. In a failure case (e.g. a CC quench), the voltage and/or phase of a CC can change significantly with a fast time constant of the order of a LHC turn. This can lead to large, global betatron oscillations of the beam. Against the background of machine protection, the influence of a CC failure on the beam dynamics is discussed. The results from dedicated tracking studies, including the LHC upgrade optics, are presented. Necessary countermeasures to limit the impact of CC failures to an acceptable level are proposed.  
 
TUPZ016 First Run of the LHC as a Heavy-ion Collider 1837
 
  • J.M. Jowett, G. Arduini, R.W. Assmann, P. Baudrenghien, C. Carli, M. Lamont, M. Solfaroli Camillocci, J.A. Uythoven, W. Venturini Delsolaro, J. Wenninger
    CERN, Geneva, Switzerland
 
  A year of LHC operation typically consists of an extended run with colliding protons, ending with a month in which the LHC has to switch to its second role as a heavy ion collider and provide a useful integrated luminosity to three experiments. The first such run in November 2010 demonstrated that this is feasible. Commissioning was extremely rapid, with collisions of Pb nuclei achieved within 55 h of first injection. Stable beams for physics data-taking were declared a little over one day later and the final integrated luminosity substantially exceeded expectations.  
 
TUPZ028 Beam Based Optimization of the Squeeze at the LHC 1867
 
  • X. Buffat
    EPFL, Lausanne, Switzerland
  • M. Lamont, S. Redaelli, J. Wenninger
    CERN, Geneva, Switzerland
 
  The betatron squeeze is a critical operational phase for the LHC because it is carried out at top energy, with the maximum stored energy and with reduced aperture margins in the superconducting triplets. A stable operation with minimum beam losses must be achieved in order to ensure a safe and efficient operation. The operational experience at the LHC showed that this is possible. The operation in 2010 is reviewed. In particular, orbit, tune and chromaticity measurements are investigated and correlated to beam losses. Different optimizations are then proposed towards a more efficient and robust operation. The improvements obtained for the operation in 2011 are presented.  
 
MOPS010 Experimental Studies with Low Transition Energy Optics in the SPS 613
 
  • H. Bartosik, T. Argyropoulos, T. Bohl, S. Cettour Cave, K. Cornelis, J. Esteban Muller, Y. Papaphilippou, G. Rumolo, B. Salvant, E.N. Shaposhnikova, J. Wenninger
    CERN, Geneva, Switzerland
 
  The optics of the SPS can be tuned to lower transition energy such that the slippage factor at injection is raised by a factor of almost 3. From theory, an increase of the intensity thresholds for transverse mode coupling, longitudinal coupled bunch and longitudinal instabilities due to the loss of Landau damping can be expected. In this paper, experimental studies in the SPS with single bunches of protons with intensities of up to 3.5·1011 p/b on the flat bottom and at 450 GeV/c are presented. Longitudinal instabilities were studied with LHC-type beams with 50~ns spacing and injected intensities up to 1.8·1011 p/b. The measurements address the increase of intensity thresholds and the achievable transverse emittances in the new low gamma transition optics with respect to the nominal SPS optics. The obtained results are compared with numerical simulations.  
 
TUPC136 Analysis of Fast Losses in the LHC with the BLM System 1344
 
  • E. Nebot Del Busto, T. Baer, B. Dehning, E. Effinger, J. Emery, E.B. Holzer, A. Marsili, A. Nordt, M. Sapinski, R. Schmidt, B. Velghe, J. Wenninger, C. Zamantzas, F. Zimmermann
    CERN, Geneva, Switzerland
  • N. Fuster
    Valencia University, Atomic Molecular and Nuclear Physics Department, Valencia, Spain
  • Z. Yang
    EPFL, Lausanne, Switzerland
 
  About 3600 Ionization Chambers are located around the LHC ring to detect beam losses that could damage the equipment or quench superconducting magnets. The BLMs integrate the losses in 12 different time intervals (from 40 us to 83.8 s) allowing for different abort thresholds depending on the duration of the loss and the beam energy. The signals are also recorded in a database at 1 Hz for offline analysis. During the 2010 run, a limiting factor in the machine availability were sudden losses appearing around the ring on the ms time scale and detected exclusively by the BLM system. It is believed that such losses originate from dust particles falling into the beam, or being attracted by its strong electromagnetic field. This document describes some of the properties of these "Unidentified Falling Objects" (UFOs) putting special emphasis on their dependence on beam parameters (energy, intensity, etc). The subsequent modification of the BLM beam abort thresholds for the 2011 run that were made to avoid unnecessary beam dumps caused by these UFO losses are also discussed.  
 
TUPC137 UFOs in the LHC 1347
 
  • T. Baer, M.J. Barnes, B. Goddard, E.B. Holzer, J.M. Jimenez, A. Lechner, V. Mertens, E. Nebot Del Busto, A. Nordt, J.A. Uythoven, B. Velghe, J. Wenninger, F. Zimmermann
    CERN, Geneva, Switzerland
 
  One of the major known limitations for the performance of the Large Hadron Collider are so called UFOs (”Unidentified Falling Objects”). UFOs were first observed in July 2010 and have since caused numerous protection beam dumps. UFOs are thought to be micrometer sized dust particles which lead to fast beam losses with a duration of about 10 turns when they interact with the beam. In 2011, the diagnostics for such events was significantly improved which allows estimates of the properties, dynamics and production mechanisms of the dust particles. The state of knowledge and mitigation strategies are presented.  
 
TUPS026 Specification of New Vacuum Chambers for the LHC Experimental Interactions 1584
 
  • R. Veness, R.W. Assmann, A. Ball, A. Behrens, C. Bracco, G. Bregliozzi, R. Bruce, H. Burkhardt, G. Corti, M.A. Gallilee, M. Giovannozzi, B. Goddard, D. Mergelkuhl, E. Métral, M. Nessi, W. Riegler, J. Wenninger
    CERN, Geneva, Switzerland
  • N. Mounet, B. Salvant
    EPFL, Lausanne, Switzerland
 
  The apertures for the vacuum chambers at the interaction points inside the LHC experiments are key both to the safe operation of the LHC machine and to obtaining the best physics performance from the experiments. Following the successful startup of the LHC physics programme the ALICE, ATLAS and CMS experiments have launched projects to improve physics performance by adding detector layers closer to the beam. To achieve this they have requested smaller aperture vacuum chambers to be installed. The first periods of LHC operation have yielded much information both on the performance of the LHC and the stability and alignment of the experiments. In this paper, the new information relating to the aperture of these chambers is presented and a summary is made of analysis of parameters required to safely reduce the vacuum chambers apertures for the high-luminosity experiments ATLAS and CMS.  
 
WEPC173 LHC Magnet Quench Test with Beam Loss Generated by Wire Scan 2391
 
  • M. Sapinski, F. Cerutti, K. Dahlerup-Petersen, B. Dehning, J. Emery, A. Ferrari, A. Guerrero, E.B. Holzer, M. Koujili, A. Lechner, E. Nebot Del Busto, M. Scheubel, J. Steckert, A.P. Verweij, J. Wenninger
    CERN, Geneva, Switzerland
 
  Beam losses with millisecond duration have been observed in the LHC in 2010 and 2011. They are expected to be provoked by dust particles falling into the beam. These losses could compromise the LHC availability if they provoke quenches of superconducting magnets. In order to investigate the quench limits for this loss mechanism, a quench test using the wire scanner has been performed, with the wire movement through the beam mimicking a loss with similar spatial and temporal distribution as in the case of dust particles. This paper will show the conclusions reached for millisecond-duration dust-provoked quench limits. It will include details on the maximum energy deposited in the coil as estimated using FLUKA code, showing good agreement with quench limit estimated from the heat transfer code QP3. In addition, information on the damage limit for carbon wires in proton beams will be presented, following electron microscope analysis which revealed strong wire sublimation.  
 
WEPO031 The Magnetic Model of the LHC during Commissioning to Higher Beam Intensities in 2010-2011 2466
 
  • L. Deniau, N. Aquilina, L. Fiscarelli, M. Giovannozzi, P. Hagen, M. Lamont, G. Montenero, R.J. Steinhagen, M. Strzelczyk, E. Todesco, R. Tomás, W. Venturini Delsolaro, J. Wenninger
    CERN, Geneva, Switzerland
 
  The Field Description of the Large Hadron Collider (FiDeL) model is a set of semi-empirical equations linking the magnets behaviours established from magnetic measurements to the magnetic properties of the machine observed through beam measurements. The FiDeL model includes the parameterization of static components such as magnets residual magnetization, persistent currents, hysteresis and saturation as well as the decay and snap-back dynamic components. In the present paper, we outline the relationship between the beam observables (orbit, tune, chromaticity) and the model components during the commissioning to higher beam intensities in 2010-2011, with an energy of 3.5 TeV per beam. The main relevant issues are (i) the operation at 2 A/s and 10 A/s ramp rate and their influence on chromatic correction, (ii) the beta beating and its relation to the knowledge of the resistive quadrupoles transfer functions and (iii) the observed tune decay at injection energy and its possibles origins.  
 
WEPS022 Ions for LHC: Performance of the Injector Chain 2529
 
  • D. Manglunki, M. E. Angoletta, P. Baudrenghien, G. Bellodi, A. Blas, T. Bohl, C. Carli, E. Carlier, S. Cettour Cave, M. Chanel, K. Cornelis, H. Damerau, A. Findlay, S.S. Gilardoni, S. Hancock, J.M. Jowett, D. Kuchler, S. Maury, E. Métral, S. Pasinelli, M. Schokker, G. Tranquille, B. Vandorpe, U. Wehrle, J. Wenninger
    CERN, Geneva, Switzerland
 
  The first LHC Pb ion run took place at 1.38 A TeV/c per beam in autumn 2010. After a short period of running-in, the injector chain was able to fill the collider with up to 137 bunches per ring, with an intensity of 108 Pb ions/bunch, about 50% higher than the design value. This yielded a luminosity of 3E25 Hz/cm2, allowing the experiments to accumulate just under 10 inverse microbarn each during the four week run. We review the performance of the individual links of the injector chain, and address the main issues limiting the LHC luminosity, in view of reaching 1026 Hz/cm2 in 2011, and substantially beyond when the LHC energy increases after the long shutdown in 2013-14.  
 
THPZ025 Stability of the LHC Transfer lines 3741
 
  • V. Kain, W. Bartmann, C. Bracco, L.N. Drosdal, B. Goddard, M. Meddahi, J.A. Uythoven, J. Wenninger
    CERN, Geneva, Switzerland
 
  The LHC is filled from the SPS through two 3 km transfer lines. The injected beam parameters need to be well under control for luminosity performance, machine protection and operational efficiency. Small fractions of beam loss on the transfer line collimation system create showers which can trigger the sensitive LHC beam loss monitor system nearby and cause a beam abort during filling. The stability of the transfer line trajectory through the collimators is particularly critical in this respect. This paper will report on the transfer line trajectory stability during the proton run in 2011, correlations with injection losses, correction frequency and the most likely sources for the observed oscillations.  
 
THPS053 Results from the HiRadMat Primary Beam Line Commissioning 3547
 
  • C. Heßler, M. Arruat, J. Bauche, K. Bestmann, J. Blanco, N. Conan, K. Cornelis, I. Efthymiopoulos, H. Gaillard, B. Goddard, D. Grenier, G.G. Gros, A. Habert, L.K. Jensen, V. Kain, G. Le Godec, M. Meddahi, S. Pelletier, P. Pepinster, B. Puccio, C. Theis, P. Trilhe, G. Vandoni, J. Wenninger
    CERN, Geneva, Switzerland
 
  The High Radiation to Materials facility (HiRadMat) is a new experimental area at CERN, for studies of the impact of high-intensity pulsed beams on accelerator components and materials. The beam is delivered from the SPS by a new primary beam line, which has been constructed during the 2010/11 winter technical stop. The paper summarizes the construction phase and describes the results from the beam line commissioning in spring 2011. Beam parameter and aperture measurements are presented, as well as steering tests. A special emphasis has been put on the handling of the exceptionally flexible beam line optics in the control system.