Author: Jimenez, J.M.
Paper Title Page
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.  
 
TUPS017 The LHC Experimental Beam Pipe Neon Venting, Pumping and Conditioning 1557
 
  • V. Baglin, G. Bregliozzi, D. Calegari, J.M. Jimenez, G. Lanza, G. Schneider
    CERN, Geneva, Switzerland
 
  The experimental vacuum chambers of the four LHC experiments (ATLAS, CMS, LHCb and ALICE) are mechanically optimized in order to be transparent to particles. In order to grant their mechanical stability and to avoid any overstress, every time there was a request for detector opening or closing and for working in the vicinity of the vacuum chamber, the experimental beam vacuum chambers have been vented to atmospheric pressure. Since the LHC start up a safety procedure has been applied to mechanically secure the four experimental beam pipes during each long technical stop. Ultra-pure neon was used to preserve at best the NEG pumping efficiency. Up to now more than 15 neon injections and pump down have been performed without detecting any reduction of the NEG efficiency. This paper describes the Gas Injection System performances and the main points of the venting and pumping procedure. Details of the experimental beam pipe vacuum recovery and conditioning are presented for each of the four LHC experiments (ATLAS, CMS, LHCb and ALICE).  
 
TUPS018 Observations of Electron Cloud Effects with the LHC Vacuum System 1560
 
  • V. Baglin, G. Bregliozzi, P. Chiggiato, P. Cruikshank, B. Henrist, J.M. Jimenez, G. Lanza
    CERN, Geneva, Switzerland
 
  In autumn 2010, during the LHC beam commissioning, electron-cloud effects producing pressure rise in common and single vacuum beam pipes, were observed. To understand the potential limitations for future operation, dedicated machine studies were performed with beams of 50 and 75 ns bunch spacing at energy of 450 GeV. In order to push further the LHC performances, a scrubbing run was held in spring 2011. This paper summarizes the vacuum observations made during these periods. The effects of bunch intensity and different filling schemes on the vacuum levels are discussed. Simulations taking into account the effective pumping speed at the location of the vacuum gauge are introduced. As a consequence, the different vacuum levels observed along the LHC ring could be explained. Finally, the results obtained during the scrubbing run are shown together with an estimation of pressure profiles during the 2011 run.  
 
TUPS019 Synchrotron Radiation in the LHC Vacuum System 1563
 
  • V. Baglin, G. Bregliozzi, J.M. Jimenez, G. Lanza
    CERN, Geneva, Switzerland
 
  CERN is currently operating the Large Hadron Collider (LHC) with 3.5 TeV per beam. At this energy level, when the protons trajectory is bent, the protons emit synchrotron radiation (SR) with a critical energy of 5.5 eV. Under operation, SR induced molecular desorption is routinely observed in the LHC arcs, long straight sections and experiments. This contribution recalls the SR parameters over the LHC ring for the present and nominal beam parameters. Vacuum observations during energy ramp, after accumulation of dose and along the LHC ring are discussed. Expected pressure profiles and long term behaviours of vacuum levels will be also addressed.  
 
TUPS022 MedAustron Beam Vacuum System : From sources to Patient Treatment Rooms 1572
 
  • J.M. Jimenez, P. Cruikshank, L. Faisandel, W. Maan
    CERN, Geneva, Switzerland
  • T. Hauser, G. Hulla, P. Landrot, J. Wallner
    EBG MedAustron, Wr. Neustadt, Austria
 
  The MedAustron beam vacuum system is a complex system integrating different technical solutions from the source to the patient treatment rooms. The specified vacuum performances combined with the challenging integration issues require technical compromise which will be presented in this poster. The status of the design of the vacuum system will be reviewed and the pending issues will be explained.  
 
TUPZ015 Electron Cloud Parameterization Studies in the LHC 1834
 
  • C.O. Domínguez, G. Arduini, V. Baglin, G. Bregliozzi, J.M. Jimenez, E. Métral, G. Rumolo, D. Schulte, F. Zimmermann
    CERN, Geneva, Switzerland
 
  During LHC beam commissioning with 150, 75 and 50-ns bunch spacing, important electron-cloud effects, like pressure rise, cryogenic heat load, beam instabilities or emittance growth, were observed. The main strategy to combat the LHC electron cloud relies on the surface conditioning arising from the chamber-surface bombardment with cloud electrons. In a standard model, the conditioning state of the beam-pipe surface is characterized by three parameters: 1. the secondary emission yield; 2. the incident electron energy at which the yield is maximum; and 3. the probability of elastic reflection of low-energy primary electrons hitting the chamber wall. Since at the LHC no in-situ secondary-yield measurements are available, we compare the relative local pressure-rise measurements taken for different beam configurations against simulations in which surface parameters are scanned. This benchmark of measurements and these simulations is used to infer the secondary-emission properties of the beam-pipe at different locations around the ring and at various stages of the surface conditioning. In this paper we present the methodology and first results from applying the technique to the LHC.  
 
THOBA01 Electron Cloud Observations in LHC 2862
 
  • G. Rumolo, G. Arduini, V. Baglin, H. Bartosik, P. Baudrenghien, N. Biancacci, G. Bregliozzi, S.D. Claudet, R. De Maria, J. Esteban Muller, M. Favier, C. Hansen, W. Höfle, J.M. Jimenez, V. Kain, E. Koukovini, G. Lanza, K.S.B. Li, G.H.I. Maury Cuna, E. Métral, G. Papotti, T. Pieloni, F. Roncarolo, B. Salvant, E.N. Shaposhnikova, R.J. Steinhagen, L.J. Tavian, D. Valuch, W. Venturini Delsolaro, F. Zimmermann
    CERN, Geneva, Switzerland
  • C.M. Bhat
    Fermilab, Batavia, USA
  • U. Iriso
    CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
  • N. Mounet, C. Zannini
    EPFL, Lausanne, Switzerland
 
  Operation of LHC with bunch trains different spacings has revealed the formation of an electron cloud inside the machine. The main observations of electron cloud build-up are the pressure rise measured at the vacuum gauges in the warm regions, as well as the increase of the beam screen temperature in the cold regions due to an additional heat load. The effects of the electron cloud were also visible as a strong instability and emittance growth affecting the last bunches of longer trains, which could be improved running with higher chromaticity and/or larger transverse emittances. A summary of the 2010 and 2011 observations and measurements and a comparison with existing models will be presented. The efficiency of scrubbing and scrubbing strategies to improve the machine running performance will be also briefly discussed.  
slides icon Slides THOBA01 [2.911 MB]