Author: Bregliozzi, G.
Paper Title Page
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.  
 
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.  
 
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]