• C. Yin Vallgren, G. Arduini, J. Bauche, S. Calatroni, P. Chiggiato, K. Cornelis, P. Costa Pinto, E. Métral, G. Rumolo, E.N. Shaposhnikova, M. Taborelli, G. Vandoni
  CERN, Geneva

Amor­phous car­bon coat­ings with low sec­ondary elec­tron yield have been ap­plied to the lin­ers in the elec­tron cloud mon­i­tors and to vac­u­um cham­bers of three dipole mag­nets in the SPS. The elec­tron cloud is com­plete­ly sup­pressed for LHC type beams in these mon­i­tors even after 3 months air vent­ing and no per­for­mance de­te­ri­o­ra­tion is ob­served after more than one year of SPS op­er­a­tion. Upon vari­a­tion of the mag­net­ic field in the mon­i­tors the elec­tron cloud cur­rent main­tains its in­ten­si­ty down to weak fields of some 40 Gauss, where fast con­di­tion­ing is ob­served. This is in agree­ment with dark traces ob­served on the RF shields be­tween dipoles. The dy­nam­ic pres­sure rise has been used to mon­i­tor the be­hav­ior of the mag­nets. It is found to be about the same for coat­ed and un­coat­ed mag­nets, apart from a weak im­prove­ment in the car­bon coat­ed ones under con­di­tions of in­tense elec­tron cloud. In­spec­tion of the coat­ed mag­net is fore­seen in order to de­tect po­ten­tial dif­fer­ences with re­spect to the coat­ed mon­i­tors. Mea­sure­ments of the stray fields out­side the dipoles show that they are suf­fi­cient­ly strong to in­duce elec­tron cloud in these re­gions.

• S. Aumon
  EPFL, Lausanne
• S. Aumon, M. Delrieux, P. Freyermuth, S.S. Gilardoni, E. Métral, G. Rumolo, B. Salvant, R.R. Steerenberg
  CERN, Geneva

Tran­si­tion cross­ing in the CERN PS is crit­i­cal for the sta­bil­i­ty of high in­ten­si­ty beams, even with the use of a sec­ond order gamma jump scheme. The in­tense sin­gle bunch beam used for the neu­tron Time-of-Flight fa­cil­i­ty (n-ToF) needs a con­trolled lon­gi­tu­di­nal emit­tance blowup at flat bot­tom to pre­vent a fast sin­gle-bunch ver­ti­cal in­sta­bil­i­ty from de­vel­op­ing near tran­si­tion. This in­sta­bil­i­ty is be­lieved to be of Trans­verse Mode Cou­pling (TMCI) type. A se­ries of mea­sure­ments taken through­out 2008 and 2009 aim at using this TMCI ob­served on the ToF beam at tran­si­tion, as a tool for es­ti­mat­ing the trans­verse glob­al impedance of the PS. For this pur­pose, we com­pare the mea­sure­ment re­sults with the pre­dic­tions of the HEAD­TAIL code and find the match­ing pa­ram­e­ters. This pro­ce­dure also al­lows a bet­ter un­der­stand­ing of the dif­fer­ent mech­a­nisms in­volved and can sug­gest how to im­prove the gamma jump scheme for a pos­si­ble in­ten­si­ty up­grade of the n-ToF beam.

• N. Mounet
  EPFL, Lausanne
• N. Mounet, E. Métral
  CERN, Geneva

Using B. Zot­ter's for­mal­ism, we pre­sent here a novel, ef­fi­cient and exact ma­trix method for the field match­ing de­ter­mi­na­tion of the elec­tro­mag­net­ic field com­po­nents cre­at­ed by an off­set point charge trav­el­ling at any speed in an in­finite­ly long cir­cu­lar mul­ti­lay­er beam pipe. This method im­proves by a fac­tor of more than one hun­dred the com­pu­ta­tion­al time with three lay­ers and al­lows the com­pu­ta­tion for more lay­ers than three. We also gen­er­al­ize our anal­y­sis to any az­imuthal mode and fi­nal­ly per­form the sum­ma­tion on all such modes in the impedance for­mu­lae. In par­tic­u­lar the exact mul­ti­mode di­rect space-charge impedances (both lon­gi­tu­di­nal and trans­verse) are given, as well as the wall impedances to any order of pre­ci­sion.

• N. Mounet
  EPFL, Lausanne
• N. Mounet, E. Métral
  CERN, Geneva

The exact for­mal­ism from B. Zot­ter to com­pute beam cou­pling impedances has been fully de­vel­oped only in the case of an in­finite­ly long cir­cu­lar beam pipe. For other two di­men­sion­al ge­ome­tries, some form fac­tors are known only in the ul­tra­rel­a­tivis­tic case and under cer­tain as­sump­tions of con­duc­tiv­i­ty and fre­quen­cy of the pipe ma­te­ri­al. We pre­sent here a new and exact for­mal­ism to com­pute the beam cou­pling impedances in the case of a col­li­ma­tor-like ge­om­e­try where the jaws are made of two in­fi­nite plates of any lin­ear ma­te­ri­al. It is shown that the impedances can be com­put­ed the­o­ret­i­cal­ly with­out any as­sump­tions on the beam speed, ma­te­ri­al con­duc­tiv­i­ty or fre­quen­cy range. The final for­mu­la in­volves co­ef­fi­cients in the form of in­te­grals that can be cal­cu­lat­ed nu­mer­i­cal­ly. This way we ob­tain new gen­er­al­ized form fac­tors be­tween the cir­cu­lar and the flat cham­ber cases, which even­tu­al­ly re­duce to the so-called Yokoya fac­tors under cer­tain con­di­tions.

• C. Zannini, N. Mounet, E. Métral, G. Rumolo
  CERN, Geneva
• B. Salvant, C. Zannini
  EPFL, Lausanne

The kick­ers are major con­trib­u­tors to the CERN SPS beam cou­pling impedance. As such, they may rep­re­sent a lim­i­ta­tion to in­creas­ing the SPS bunch cur­rent in the frame of an in­ten­si­ty up­grade of the LHC. In this paper, CST Par­ti­cle Stu­dio time do­main elec­tro­mag­net­ic sim­u­la­tions are per­formed to ob­tain the lon­gi­tu­di­nal and trans­verse impedances/wake po­ten­tials of sim­pli­fied mod­els of fer­rite load­ed kick­ers. The sim­u­la­tion re­sults have been suc­cess­ful­ly com­pared with some ex­ist­ing an­a­lyt­i­cal ex­pres­sions. In the trans­verse plane, the dipo­lar and quadrupo­lar con­tri­bu­tions to the wake po­ten­tials have been es­ti­mat­ed from the re­sults of these sim­u­la­tions. For some cases, sim­u­la­tions have also been bench­marked against mea­sure­ments on PS kick­ers. It turns out that the large sim­u­lat­ed quadrupo­lar con­tri­bu­tions of these kick­ers could ex­plain both the neg­a­tive total (dipo­lar+quadrupo­lar) hor­i­zon­tal impedance ob­served in bench mea­sure­ments and the pos­i­tive hor­i­zon­tal tune shift mea­sured with the SPS beam.

• N. Mounet
  EPFL, Lausanne
• N. Mounet, E. Métral
  CERN, Geneva

In this study B. Zot­ter's for­mal­ism is ap­plied to a cir­cu­lar in­finite­ly long beam pipe made of a con­duc­tor of in­fi­nite thick­ness where an off­set point-charge trav­els at any given speed. Sim­ple for­mu­lae are found for the impedances and elec­tro­mag­net­ic fields both at in­ter­me­di­ate fre­quen­cies (re­cov­er­ing Chao's re­sults) and in the low fre­quen­cy regime where the usual clas­sic thick wall impedance for­mu­la does not apply any­more due to the large skin depth com­pared to the pipe ra­dius.

• B. Salvant
  EPFL, Lausanne
• N. Mounet, E. Métral, G. Rumolo, B. Salvant, C. Zannini
  CERN, Geneva

The SPS kick­ers are major con­trib­u­tors to the SPS trans­verse beam cou­pling impedance. The cur­rent "flat cham­ber" impedance model for a kick­er is ob­tained by ap­ply­ing form fac­tors to the the­o­ret­i­cal impedance of an ax­isym­met­ric fer­rite beam pipe. This model was be­lieved to be ac­cept­able for the ver­ti­cal dipo­lar impedance, as two-wire mea­sure­ments on SPS kick­ers re­vealed a sat­is­fac­to­ry agree­ment. How­ev­er, one-wire mea­sure­ments on PS kick­ers sug­gest­ed that this model un­der­es­ti­mates the kick­ers' trans­verse quadrupo­lar (de­tun­ing) impedance. The lon­gi­tu­di­nal and trans­verse dipo­lar impedances of an­oth­er kick­er model that ac­counts for the metal­lic plates on each side of the fer­rite were de­rived in the past by H. Tsut­sui. The same for­mal­ism is used in this paper to de­rive the quadrupo­lar impedance. These for­mu­lae were then suc­cess­ful­ly bench­marked to elec­tro­mag­net­ic sim­u­la­tions. Fi­nal­ly, sim­u­lat­ing the in­ter­ac­tion of an SPS bunch with the im­proved kick­ers' model re­sults in a pos­i­tive hor­i­zon­tal tune shift, which is very close to the tune shift mea­sured with the SPS beam.

• B. Salvant
  EPFL, Lausanne
• G. Arduini, O.E. Berrig, F. Caspers, A. Grudiev, N. Mounet, E. Métral, G. Rumolo, B. Salvant, E.N. Shaposhnikova, C. Zannini
  CERN, Geneva
• M. Migliorati, B. Spataro
  INFN/LNF, Frascati (Roma)
• B. Zotter
  Honorary CERN Staff Member, Grand-Saconnex

The beam cou­pling impedance of the CERN SPS is ex­pect­ed to be one of the lim­i­ta­tions to an in­ten­si­ty up­grade of the LHC com­plex. In order to be able to re­duce the SPS impedance, its main con­trib­u­tors need to be iden­ti­fied. An impedance model for the SPS has been gath­ered from the­o­ret­i­cal cal­cu­la­tions, elec­tro­mag­net­ic sim­u­la­tions and bench mea­sure­ments of sin­gle SPS el­e­ments. The cur­rent model ac­counts for the lon­gi­tu­di­nal and trans­verse impedance of the kick­ers, the hor­i­zon­tal and ver­ti­cal elec­tro­stat­ic beam po­si­tion mon­i­tors, the RF cav­i­ties and the 6.7 km beam pipe. In order to as­sess the va­lid­i­ty of this model, macropar­ti­cle sim­u­la­tions of a bunch in­ter­act­ing with this up­dat­ed SPS impedance model are com­pared to mea­sure­ments per­formed with the SPS beam.

• D. Wollmann, O. Aberle, G. Arnau-Izquierdo, R.W. Assmann, J.-P. Bacher, V. Baglin, G. Bellodi, A. Bertarelli, A.P. Bouzoud, C. Bracco, R. Bruce, M. Brugger, S. Calatroni, F. Caspers, F. Cerutti, R. Chamizo, A. Cherif, E. Chiaveri, P. Chiggiato, A. Dallocchio, R. De Morais Amaral, B. Dehning, M. Donze, A. Ferrari, R. Folch, P. Francon, P. Gander, J.-M. Geisser, A. Grudiev, E.B. Holzer, D. Jacquet, J.B. Jeanneret, J.M. Jimenez, M. Jonker, J.M. Jowett, Y. Kadi, K. Kershaw, L. Lari, J. Lendaro, F. Loprete, R. Losito, M. Magistris, M. Malabaila, A. Marsili, A. Masi, S.J. Mathot, M. Mayer, C.C. Mitifiot, N. Mounet, E. Métral, A. Nordt, R. Perret, S. Perrollaz, C. Rathjen, S. Redaelli, G. Robert-Demolaize, S. Roesler, A. Rossi, B. Salvant, M. Santana-Leitner, I. Sexton, P. Sievers, T. Tardy, M.A. Timmins, E. Tsoulou, E. Veyrunes, H. Vincke, V. Vlachoudis, V. Vuillemin, Th. Weiler, F. Zimmermann
  CERN, Geneva
• I. Baishev, I.A. Kurochkin
  IHEP Protvino, Protvino, Moscow Region
• D. Kaltchev
  TRIUMF, Vancouver

The LHC has two ded­i­cat­ed clean­ing in­ser­tions: IR3 for mo­men­tum clean­ing and IR7 for be­ta­tron clean­ing. The col­li­ma­tion sys­tem has been spec­i­fied and built with tight me­chan­i­cal tol­er­ances (e.g. jaw flat­ness ~ 40 μm) and is de­signed to achieve a high ac­cu­ra­cy and re­pro­ducibil­i­ty of the jaw po­si­tions. The prac­ti­cal­ly achiev­able clean­ing ef­fi­cien­cy of the pre­sent Phase-I sys­tem de­pends on the pre­ci­sion of the jaw cen­ter­ing around the beam, the ac­cu­ra­cy of the gap size and the jaw par­al­lelism against the beam. The re­pro­ducibil­i­ty and sta­bil­i­ty of the sys­tem is im­por­tant to avoid the fre­quent rep­e­ti­tion of beam based align­ment which is cur­rent­ly a lengthy pro­ce­dure. With­in this paper we de­scribe the method used for the beam based align­ment of the LHC col­li­ma­tion sys­tem, its achieved ac­cu­ra­cy and sta­bil­i­ty and its per­for­mance at 450GeV.

Slides

• M. Giovannozzi, E. Benedetto, A. Blas, T. Bohl, S. Cettour Cave, K. Cornelis, D.G. Cotte, H. Damerau, M. Delrieux, J. Fleuret, F. Follin, T. Fowler, P. Freyermuth, H. Genoud, S.S. Gilardoni, S. Hancock, O. Hans, Y. Le Borgne, D. Manglunki, E. Matli, G. Metral, E. Métral, M. Newman, L. Pereira, F.C. Peters, Y. Riva, F. Roncarolo, L. Sermeus, R.R. Steerenberg, B. Vandorpe, J. Wenninger
  CERN, Geneva
• F. Franchi
  ESRF, Grenoble

Fol­low­ing the anal­y­sis of the re­sults ob­tained dur­ing the first year of beam com­mis­sion­ing of the CERN mul­ti-turn ex­trac­tion, a num­ber of changes have been in­tro­duced in the beam ma­nip­u­la­tions per­formed in the CERN Pro­ton Syn­chrotron. This in­cludes a dif­fer­ent con­trol of the lin­ear chro­matic­i­ty, the set­ting of the non-lin­ear mag­nets used to split the beam, and the lon­gi­tu­di­nal struc­ture in the PS. The re­sults ob­tained dur­ing the 2009 run are pre­sent­ed and dis­cussed in de­tail, in­clud­ing the beam per­for­mance in both the PS and the SPS, as well as the op­tics mea­sure­ments in the trans­fer line be­tween the two cir­cu­lar ma­chines.

Slides