Author: Mounet, N.
Paper Title Page
TUPFI034 Observations of Two-beam Instabilities during the 2012 LHC Physics Run 1418
 
  • T. Pieloni
    EPFL, Lausanne, Switzerland
  • G. Arduini, X. Buffat, R. Giachino, W. Herr, M. Lamont, N. Mounet, E. Métral, G. Papotti, B. Salvant, J. Wenninger
    CERN, Geneva, Switzerland
  • S.M. White
    BNL, Upton, Long Island, New York, USA
  
  Dur­ing the 2012 run co­her­ent beam in­sta­bil­i­ties have been ob­served in the LHC at 4 TeV, dur­ing the be­ta­tron squeeze and in col­li­sion for spe­cial fill­ing pat­terns. Sev­eral stud­ies to char­ac­ter­ize these in­sta­bil­i­ties have been car­ried out dur­ing op­er­a­tion and in spe­cial ded­i­cated ex­per­i­ments. In this paper we sum­ma­rize the ob­ser­va­tions col­lected for dif­fer­ent ma­chine pa­ra­me­ters and the pre­sent un­der­stand­ing of the ori­gin of these in­sta­bil­i­ties.  
 
TUPFI035 Head-on and Long range Beam-beam Interactions in the LHC: Effective Tune Spread and Beam Stability due to Landau Damping 1421
 
  • X. Buffat
    EPFL, Lausanne, Switzerland
  • W. Herr, N. Mounet, E. Métral, T. Pieloni
    CERN, Geneva, Switzerland
  
  We dis­cuss the Lan­dau damp­ing of co­her­ent in­sta­bil­i­ties in the pres­ence of be­ta­tron tune spread. This tune spread can orig­i­nate from ded­i­cated non-lin­ear mag­nets such as oc­tupoles, or through the beam-beam in­ter­ac­tion. In the lat­ter case we have to dis­tin­guish the con­tri­bu­tion from head-on and par­a­sitic beam-beam in­ter­ac­tions and the col­li­sion pat­tern of dif­fer­ent bunches plays an im­por­tant role. The in­ter­play of these sources of tune spread and the re­sult­ing sta­bil­ity is dis­cussed for the case of the LHC.  
 
TUPFI036 Observation of Beam Instabilities with Very Tight Collimation 1424
 
  • H. Burkhardt, N. Mounet, T. Pieloni
    CERN, Geneva, Switzerland
  
  We re­port about the ob­ser­va­tion of in­sta­bil­i­ties in the LHC in spe­cial runs with high β* and very tight col­li­ma­tion down to 2 σ which in­creases the trans­verse im­ped­ance sig­nif­i­cantly. The losses ap­peared pri­mar­ily on the high­est in­ten­sity, non-col­lid­ing bunches which can be in­ter­preted as ev­i­dence for in­suf­fi­cient Lan­dau damp­ing. We de­scribe the beam con­di­tions, ob­ser­va­tions and pos­si­ble ex­pla­na­tions for the ob­served ef­fects.  
 
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.  
 
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.  
 
THOBB102 Beam Coupling Impedance Localization Technique Validation and Measurements in the CERN Machines 3106
 
  • N. Biancacci, G. Arduini, T. Argyropoulos, H. Bartosik, R. Calaga, K. Cornelis, S.S. Gilardoni, N. Mounet, E. Métral, Y. Papaphilippou, S. Persichelli, G. Rumolo, B. Salvant, G. Sterbini, R. Tomás, R. Wasef
    CERN, Geneva, Switzerland
  • M. Migliorati, L. Palumbo
    URLS, Rome, Italy
  
  The beam cou­pling im­ped­ance could lead to lim­i­ta­tions in beam bright­ness and qual­ity, and there­fore it needs ac­cu­rate quan­tifi­ca­tion and con­tin­u­ous mon­i­tor­ing in order to de­tect and mit­i­gate high im­ped­ance sources. In the CERN ma­chines, for ex­am­ple, kick­ers and col­li­ma­tors are ex­pected to be the main con­trib­u­tors to the total imag­i­nary part of the trans­verse im­ped­ance. In order to de­tect the other sources, a beam based mea­sure­ment was de­vel­oped: from the vari­a­tion of be­ta­tron phase beat­ing with in­ten­sity, it is pos­si­ble to de­tect the lo­ca­tions of main im­ped­ance sources. In this work we pre­sent the ap­pli­ca­tion of the method with beam mea­sure­ments in the CERN PS, SPS and LHC.  
slides icon Slides THOBB102 [7.224 MB]  
 
TUPFI031 Effect of Collision Pattern in the LHC on the Beam Stability: Requirements from Experiments and Operational Considerations 1409
 
  • W. Herr, G. Arduini, R. Giachino, E. Métral, G. Papotti, T. Pieloni
    CERN, Geneva, Switzerland
  • X. Buffat, N. Mounet
    EPFL, Lausanne, Switzerland
  • S.M. White
    BNL, Upton, Long Island, New York, USA
  
  Co­her­ent in­sta­bil­i­ties of bunches in the LHC bunch train can be ob­served when the tune spread from beam-beam in­ter­ac­tions be­comes in­suf­fi­cient to en­sure Lan­dau damp­ing. In par­tic­u­lar these ef­fects are seen on bunches with a re­duced num­ber of beam-beam in­ter­ac­tions due to their col­li­sion pat­tern. Fur­ther­more, such a re­duc­tion of the nec­es­sary sta­bil­ity can occur dur­ing the processes when the beams are pre­pared for col­li­sions or dur­ing the op­ti­miza­tion pro­ce­dure. We dis­cuss the ob­ser­va­tions and pos­si­ble coun­ter­mea­sures, in par­tic­u­lar al­ter­na­tives to the ex­ist­ing beam ma­nip­u­la­tion processes where such a sit­u­a­tion can occur.  
 
TUPFI032 Observation of Instabilities in the LHC due to Missing Head-on Beam-beam Interactions 1412
 
  • W. Herr, G. Arduini, R. Giachino, E. Métral, G. Papotti, T. Pieloni
    CERN, Geneva, Switzerland
  • X. Buffat, N. Mounet
    EPFL, Lausanne, Switzerland
  
  We re­port the ob­ser­va­tion of co­her­ent in­sta­bil­i­ties on in­di­vid­ual bunches out of the LHC bunch train. These in­sta­bil­i­ties oc­cured spon­ta­neously after sev­eral hours of sta­ble beam while in other cases they were re­lated to the ap­pli­ca­tion of a small trans­verse beam sep­a­ra­tion dur­ing a lu­mi­nos­ity op­ti­miza­tion. Only few bunches were af­fected, de­pend­ing on there col­li­sion scheme and fol­low­ing var­i­ous tests we in­ter­prete these in­sta­bil­i­ties as a sud­den loss of Lan­dau damp­ing when the tune spread from the beam-beam in­ter­ac­tion be­came in­suf­fi­cient.