Author: Mounet, N.
Paper Title Page
MOPS073 Impedance Calculation for Simple Models of Kickers in the Non-ultrarelativistic Regime 772
 
  • N. Biancacci, N. Mounet, E. Métral, B. Salvant, C. Zannini
    CERN, Geneva, Switzerland
  • N. Biancacci, M. Migliorati, A. Mostacci, L. Palumbo
    Rome University La Sapienza, Roma, Italy
  • Q. Qin, N. Wang
    IHEP Beijing, Beijing, People's Republic of China
  
  Kick­er mag­nets are usu­al­ly sig­nif­i­cant con­trib­u­tors to the beam cou­pling impedance of par­ti­cle ac­cel­er­a­tors. An ac­cu­rate un­der­stand­ing of their impedance is re­quired in order to cor­rect­ly as­sess the ma­chine in­ten­si­ty lim­i­ta­tions. The field match­ing method de­rived by H. Tsut­sui for the lon­gi­tu­di­nal and trans­verse dipo­lar (driv­ing) impedance of sim­ple mod­els of kick­ers in the ul­tra­rel­a­tivis­tic regime was al­ready ex­tend­ed to the non-ul­tra­rel­a­tivis­tic case, and to the quadrupo­lar (de­tun­ing) impedance in the ul­tra­rel­a­tivis­tic case. This con­tri­bu­tion pre­sents the ex­ten­sion to the quadrupo­lar impedance in the non-ul­tra­rel­a­tivis­tic case, as well as bench­marks with other avail­able meth­ods to com­pute the impedance. In par­tic­u­lar, all the com­po­nents of the impedances are bench­marked with Tsut­sui's model, i.e. in the ul­tra­rel­a­tivis­tic limit, with the model for a flat cham­ber impedance re­cent­ly com­put­ed by N. Mounet and E. Métral, in the case of fi­nite rel­a­tivis­tic gamma, and with CST Par­ti­cle Stu­dio sim­u­la­tions.  
 
MOPS075 Simulation of Multibunch Motion with the HEADTAIL Code and Application to the CERN SPS and LHC 778
 
  • N. Mounet
    EPFL, Lausanne, Switzerland
  • N. Mounet, E. Métral, G. Rumolo
    CERN, Geneva, Switzerland
  
  Multi­bunch in­sta­bil­i­ties due to beam-cou­pling impedance can be a crit­i­cal lim­i­ta­tion for syn­chrotrons op­er­at­ing with many bunch­es. It is par­tic­u­lar­ly true for the LHC under nom­i­nal con­di­tions, where ac­cord­ing to the­o­ret­i­cal pre­dic­tions the 2808 bunch­es rely en­tire­ly on the per­for­mance of the trans­verse feed­back sys­tem to re­main sta­ble. To study these in­sta­bil­i­ties, the HEAD­TAIL code has been ex­tend­ed to sim­u­late the mo­tion of many bunch­es under the ac­tion of wake fields. All the fea­tures al­ready pre­sent in the sin­gle-bunch ver­sion of the code, such as syn­chrotron mo­tion, chro­matic­i­ty, am­pli­tude de­tun­ing due to oc­tupoles and the abil­i­ty to load any kind of wake fields through ta­bles, have re­mained avail­able. This new code has been then par­al­lelized in order to track thou­sands of bunch­es in a rea­son­able amount of time. The code was bench­marked against the­o­ry and ex­hib­it­ed a good agree­ment. We also show re­sults for bunch trains in the LHC and com­pare them with beam-based mea­sure­ments.  
 
TUPC050 Impedance Effects in the CLIC Damping Rings 1111
 
  • E. Koukovini, K.S.B. Li, N. Mounet, G. Rumolo, B. Salvant
    CERN, Geneva, Switzerland
  
  Due to the un­prece­dent­ed bril­liance of the beams, the per­for­mance of the Com­pact Lin­ear Col­lid­er (CLIC) damp­ing rings is af­fect­ed by col­lec­tive ef­fects. Sin­gle bunch in­sta­bil­i­ty thresh­olds based on a broad-band res­onator model and the as­so­ci­at­ed co­her­ent tune shifts have been eval­u­at­ed with the HEAD­TAIL code. Sim­u­la­tions per­formed for pos­i­tive and neg­a­tive val­ues of chro­matic­i­ty proved that high­er order bunch modes can be po­ten­tial­ly dan­ger­ous for the beam sta­bil­i­ty. This study also in­cludes the ef­fects of high fre­quen­cy re­sis­tive wall impedance due to dif­fer­ent coat­ings ap­plied on the cham­bers of the wig­glers for e-cloud mit­i­ga­tion and/or ul­tra-low vac­u­um pres­sure. The im­pact of the re­sis­tive-wall wake fields on the trans­verse impedance bud­get is fi­nal­ly dis­cussed.  
 
MOPS074 Stabilization of the LHC Single-bunch Transverse Instability at High-energy by Landau Octupoles 775
 
  • E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  • N. Mounet
    EPFL, Lausanne, Switzerland
  
  When the first ramp was tried on Sat­ur­day 15/05/2010 with a sin­gle bunch of about nom­i­nal in­ten­si­ty (i.e. ~ 1011 p/b), the bunch be­came un­sta­ble in the hor­i­zon­tal plane at ~ 2 TeV. The three main ob­ser­va­tions were: (i) a “Christ­mas tree” in the trans­verse tune mea­sure­ment ap­pli­ca­tion (with many syn­chrotron side­bands ex­cit­ed), (ii) beam loss­es (few tens of per­cents) in IR7, and (iii) an in­crease of the bunch length. This trans­verse co­her­ent in­sta­bil­i­ty has been sta­bi­lized suc­cess­ful­ly with Lan­dau oc­tupoles. Com­par­ing all the mea­sure­ments per­formed dur­ing this first year of LHC com­mis­sion­ing with the the­o­ret­i­cal and sim­u­la­tion pre­dic­tions re­veals a good agree­ment.  
 
MOPS075 Simulation of Multibunch Motion with the HEADTAIL Code and Application to the CERN SPS and LHC 778
 
  • N. Mounet
    EPFL, Lausanne, Switzerland
  • N. Mounet, E. Métral, G. Rumolo
    CERN, Geneva, Switzerland
  
  Multi­bunch in­sta­bil­i­ties due to beam-cou­pling impedance can be a crit­i­cal lim­i­ta­tion for syn­chrotrons op­er­at­ing with many bunch­es. It is par­tic­u­lar­ly true for the LHC under nom­i­nal con­di­tions, where ac­cord­ing to the­o­ret­i­cal pre­dic­tions the 2808 bunch­es rely en­tire­ly on the per­for­mance of the trans­verse feed­back sys­tem to re­main sta­ble. To study these in­sta­bil­i­ties, the HEAD­TAIL code has been ex­tend­ed to sim­u­late the mo­tion of many bunch­es under the ac­tion of wake fields. All the fea­tures al­ready pre­sent in the sin­gle-bunch ver­sion of the code, such as syn­chrotron mo­tion, chro­matic­i­ty, am­pli­tude de­tun­ing due to oc­tupoles and the abil­i­ty to load any kind of wake fields through ta­bles, have re­mained avail­able. This new code has been then par­al­lelized in order to track thou­sands of bunch­es in a rea­son­able amount of time. The code was bench­marked against the­o­ry and ex­hib­it­ed a good agree­ment. We also show re­sults for bunch trains in the LHC and com­pare them with beam-based mea­sure­ments.  
 
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.  
 
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]