Author: Valuch, D.
Paper Title Page
MOPC054 The LHC RF System - Experience with Beam Operation 202
 
  • P. Baudrenghien, M. E. Angoletta, T. Argyropoulos, L. Arnaudon, J. Bento, T. Bohl, O. Brunner, A.C. Butterworth, E. Ciapala, F. Dubouchet, J. Esteban Muller, D.C. Glenat, G. Hagmann, W. Höfle, D. Jacquet, M. Jaussi, S. Kouzue, D. Landre, J. Lollierou, P. Maesen, P. Martinez Yanez, T. Mastoridis, J.C. Molendijk, C. Nicou, J. Noirjean, G. Papotti, A.V. Pashnin, G. Pechaud, J. Pradier, J. Sanchez-Quesada, M. Schokker, E.N. Shaposhnikova, D. Stellfeld, J. Tückmantel, D. Valuch, U. Wehrle, F. Weierud
    CERN, Geneva, Switzerland
  
  The LHC RF sys­tem com­mis­sion­ing with beam and physics op­er­a­tion for 2010 and 2011 are pre­sent­ed. It be­came clear in early 2010 that RF noise was not a life­time lim­it­ing fac­tor: the cross­ing of the much feared 50 Hz line for the syn­chrotron fre­quen­cy did not af­fect the beam. The broad­band LHC RF noise is re­duced to a level that makes its con­tri­bu­tion to beam dif­fu­sion in physics well below that of Intra Beam Scat­ter­ing. Cap­ture loss­es are also under con­trol, at well below 0.5%. Lon­gi­tu­di­nal emit­tance blow-up, need­ed for ramp­ing of the nom­i­nal in­ten­si­ty sin­gle bunch, was rapid­ly com­mis­sioned. In 2011, 3.5 TeV/beam physics has been con­duct­ed with 1380 bunch­es at 50 ns spac­ing, cor­re­spond­ing to 55% of the nom­i­nal cur­rent. The in­ten­si­ty per bunch (1.3 ·1011 p) is sig­nif­i­cant­ly above the nom­i­nal 1.15 ·1011. By Au­gust 2011 the LHC has ac­cu­mu­lat­ed more than 2 fb-1 in­te­grat­ed lu­mi­nos­i­ty, well in ex­cess of the 1 fb-1 tar­get for 2011.  
 
MOPO012 LHC Damper Beam Commissioning in 2010 505
 
  • W. Höfle, G. Kotzian, M. Schokker, D. Valuch
    CERN, Geneva, Switzerland
  
  The LHC trans­verse dampers were com­mis­sioned in 2010 with beam and their use at in­jec­tion en­er­gy of 450 GeV, dur­ing the ramp and in col­li­sions at 3.5 TeV for Physics have be­come part of the stan­dard op­er­a­tions pro­ce­dure. The sys­tem proved im­por­tant to limit emit­tance blow-up at in­jec­tion and main­tain small­er than nom­i­nal emit­tances through­out the ac­cel­er­at­ing cycle. We de­scribe the com­mis­sion­ing of the sys­tem step-by-step as done in 2010 and sum­ma­rize its per­for­mance as achieved for pro­ton as well as ion beams in 2010. Al­though its prin­ci­ple func­tion is to keep trans­verse os­cil­la­tions under con­trol, the sys­tem has also been used as an ex­citer for abort gap clean­ing and tune mea­sure­ment. The ded­i­cat­ed beam po­si­tion mea­sure­ment sys­tem with its low noise prop­er­ties pro­vides ad­di­tion­al pos­si­bil­i­ties for di­ag­nos­tics.  
 
MOPO013 Suppression of Emittance Growth by Excited Magnet Noise with the Transverse Damper in LHC in Simulations and Experiment 508
 
  • W. Höfle, G. Arduini, R. De Maria, G. Kotzian, D. Valuch
    CERN, Geneva, Switzerland
  • V.A. Lebedev
    Fermilab, Batavia, USA
  
  The LHC trans­verse dampers ini­tial­ly build to con­trol trans­verse in­sta­bil­i­ties are also a good rem­e­dy to sup­press the os­cil­la­tions caus­ing emit­tance growth ex­cit­ed by elec­tro-mag­net­ic nois­es at the fre­quen­cies of be­ta­tron side­bands. To pre­vent the emit­tance growth ex­cit­ed by mag­net noise using the damper this sys­tem has to have ex­treme­ly low noise prop­er­ties. The paper dis­cuss­es sim­u­la­tion re­sults on the ef­fec­tive­ness of the trans­verse feed­back sys­tem to sup­press such os­cil­la­tions and the ex­per­i­men­tal re­sults from a damper point of view as they were gained dur­ing the 2010 LHC run. Pos­si­ble im­prove­ments in the damper sys­tem to en­hance its ef­fec­tive­ness with re­spect to the sup­pres­sion of emit­tance blow-up are also dis­cussed.  
 
TUPS072 Performance of the Arc Detectors of LHC High Power RF System 1704
 
  • D. Valuch, O. Brunner, N. Schwerg
    CERN, Geneva, Switzerland
  
  Dur­ing op­er­a­tion, the LHC high power RF equip­ment, such as klystrons, cir­cu­la­tors, waveg­uides and cou­plers have to be pro­tect­ed from dam­age caused by elec­tro­mag­net­ic dis­charges. Once ig­nit­ed these arcs grow over the full height of the waveg­uide and trav­el to­wards the RF source. The burn­ing plas­ma can cause se­ri­ous dam­age to the metal sur­faces or fer­rite ma­te­ri­als. The LHC arc de­tec­tor sys­tem is based on the op­ti­cal de­tec­tion of the dis­charge through small aper­tures in the waveg­uide walls. The light is guid­ed by means of an op­ti­cal fibre from the view port to a photo diode. Ex­pe­ri­ence shows that some of the cur­rent­ly used op­ti­cal fibers suf­fer from x-ray in­duced opac­i­ty. The sen­sors are also ex­posed to the ra­di­a­tion pro­duced by sec­ondary show­ers com­ing from the high in­ten­si­ty beams which, if not treat­ed prop­er­ly, can cause fre­quent spu­ri­ous trips. In the sec­ond half of the paper we pre­sents a num­ber of im­prove­ments to the de­sign. Mea­sure­ments with op­ti­cal pa­ram­e­ters from real arcs and a fiber-less ver­sion of the de­tec­tor with re­dun­dant de­tec­tors for crit­i­cal en­vi­ron­ments.  
 
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]  
 
THPS055 Controlling Beamloss at Injection into the LHC 3553
 
  • B. Goddard, F. Alessio, W. Bartmann, P. Baudrenghien, V. Boccone, C. Bracco, M. Brugger, K. Cornelis, B. Dehning, A. Di Mauro, L.N. Drosdal, E.B. Holzer, W. Höfle, R. Jacobsson, V. Kain, M. Meddahi, V. Mertens, A. Nordt, J.A. Uythoven, D. Valuch, S. Weisz, E.N. del Busto
    CERN, Geneva, Switzerland
  • R. Appleby
    UMAN, Manchester, United Kingdom
  
  Loss­es at in­jec­tion into the su­per­con­duct­ing LHC can ad­verse­ly af­fect the ma­chine per­for­mance in sev­er­al im­por­tant ways. The high in­ject­ed beam in­ten­si­ty and en­er­gy mean that pre­cau­tions must be taken against dam­age and quench­es, in­clud­ing col­li­ma­tors placed close to the beam in the in­jec­tion re­gions. Clean in­jec­tion is es­sen­tial, to avoid spu­ri­ous sig­nals on the sen­si­tive beam loss mon­i­tor­ing sys­tem which will trig­ger beam dumps. In ad­di­tion, the use of the two in­jec­tion in­ser­tions to house down­stream high en­er­gy physics ex­per­i­ments brings con­straints on per­mit­ted beam loss lev­els. In this paper the sources of in­jec­tion beam loss are dis­cussed to­geth­er with the con­tribut­ing fac­tors and var­i­ous is­sues ex­pe­ri­enced in the first full year of LHC op­er­a­tion. Sim­u­la­tions are com­pared with mea­sure­ment, and the im­ple­ment­ed and planned mit­i­ga­tion mea­sures and di­ag­nos­tic im­prove­ments are de­scribed. An out­look for fu­ture LHC op­er­a­tion is given.