• 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.

• M. Meddahi, S. Bart Pedersen, A. Boccardi, A.C. Butterworth, B. Goddard, G.H. Hemelsoet, W. Höfle, D. Jacquet, M. Jaussi, V. Kain, T. Lefèvre, E.N. Shaposhnikova, J.A. Uythoven, D. Valuch
  CERN, Geneva
• A.S. Fisher
  SLAC, Menlo Park, California
• E. Gianfelice-Wendt
  Fermilab, Batavia

Un­bunched beam is a po­ten­tial­ly se­ri­ous issue in the LHC as it may quench the su­per­con­duct­ing mag­nets dur­ing a beam abort. Un­bunched par­ti­cles, ei­ther not cap­tured by the RF sys­tem at in­jec­tion or leak­ing out of the RF buck­et, will be re­moved by using the ex­ist­ing damper kick­ers to ex­cite res­o­nant­ly the par­ti­cles in the abort gap. Fol­low­ing beam sim­u­la­tions, a strat­e­gy for clean­ing the abort gap at dif­fer­ent en­er­gies was pro­posed. The plans for the com­mis­sion­ing of the beam abort gap clean­ing are de­scribed, and the first re­sults from the beam com­mis­sion­ing are pre­sent­ed.

• 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.