• M. Solfaroli Camillocci, G. Arduini, B. Bellesia, J. Coupard, K. Dahlerup-Petersen, M. Koratzinos, M. Pojer, R. Schmidt, A.P. Siemko, H. Thiesen, A. Vergara-Fernández, M. Zanetti, M. Zerlauth
  CERN, Geneva

On 19th Septem­ber 2008 the Large Hadron Col­lid­er (LHC) ex­pe­ri­enced a se­ri­ous in­ci­dent, caused by a bad elec­tri­cal joint, which stopped beam op­er­a­tion just a few days after its be­gin­ning. Dur­ing the fol­low­ing 14 months the dam­age was re­paired, ad­di­tion­al pro­tec­tion sys­tems were in­stalled and the mea­sures to avoid a sim­i­lar in­ci­dent were taken (i.e. new layer of the Mag­net Quench Pro­tec­tion Sys­tem [nQPS], more ef­fi­cient He re­lease valves). As a con­se­quence, a large num­ber of pow­er­ing tests had to be re­peat­ed or car­ried out for the first time. The re-com­mis­sion­ing of the al­ready ex­ist­ing sys­tems as well as the com­mis­sion­ing of the new ones has been care­ful­ly stud­ied, then per­formed tak­ing into ac­count the his­to­ry of each of the eight LHC sec­tors (warm-up, left at float­ing tem­per­a­ture,'). More­over, a cam­paign of mea­sure­ments of the bus-bar splice re­sis­tances has been car­ried out with the nQPS in order to spot out non con­for­mi­ties, thus as­sess­ing the risk of the LHC op­er­a­tion for the ini­tial en­er­gy level. This paper dis­cuss­es how the guide­lines for the LHC 2009 re-com­mis­sion­ing were de­fined, pro­vid­ing a gen­er­al prin­ci­ple to be used for the fu­ture re-com­mis­sion­ing.

• K. Fuchsberger, R. Alemany-Fernandez, G. Arduini, R.W. Assmann, R. Bailey, O.S. Brüning, B. Goddard, V. Kain, M. Lamont, A. Macpherson, M. Meddahi, G. Papotti, M. Pojer, L. Ponce, S. Redaelli, M. Solfaroli Camillocci, W. Venturini Delsolaro, J. Wenninger
  CERN, Geneva

After the in­ci­dent on the 19th Septem­ber 2008 and more than one year with­out beam the com­mis­sion­ing of the LHC start­ed again on Novem­ber 20, 2009. Progress was rapid and col­li­sions under sta­ble beam con­di­tions were es­tab­lished at 1.2 TeV with­in 3 weeks. In 2010 after qual­i­fi­ca­tion of the new quench pro­tec­tion sys­tem the way to 3.5 TeV was open and col­li­sions were de­liv­ered at this en­er­gy after a month of ad­di­tion­al com­mis­sion­ing. This paper de­scribes the ex­pe­ri­ences and is­sues en­coun­tered dur­ing these first pe­ri­ods of com­mis­sion­ing with beam.

• K. Fuchsberger, R. Alemany-Fernandez, G. Arduini, R.W. Assmann, R. Bailey, O.S. Brüning, B. Goddard, V. Kain, M. Lamont, A. Macpherson, M. Meddahi, G. Papotti, M. Pojer, L. Ponce, S. Redaelli, M. Solfaroli Camillocci, W. Venturini Delsolaro, J. Wenninger
  CERN, Geneva

Fol­low­ing the LHC in­jec­tion tests of 2008, two in­jec­tion tests took place in Oc­to­ber and Novem­ber 2009 as prepa­ra­tion for the LHC restart on Novem­ber 20, 2009. Dur­ing these in­jec­tion tests beam was in­ject­ed through the TI2 trans­fer line into sec­tor 23 of ring 1 and through TI8 into the sec­tors 78, 67 and 56 of ring 2. The beam time was ded­i­cat­ed to in­jec­tion steer­ing, op­tics mea­sure­ments and de­bug­ging of all the sys­tems in­volved. Be­cause many po­ten­tial prob­lems were sort­ed out in ad­vance, these tests con­tribut­ed to the rapid progress after the restart. This paper de­scribes the ex­pe­ri­ences and is­sues en­coun­tered dur­ing these tests as well as re­lat­ed mea­sure­ment re­sults.

• 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.

• 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.

• E. Benedetto
  National Technical University of Athens, Zografou
• G. Arduini, S. Cettour Cave, F. Follin, S.S. Gilardoni, M. Giovannozzi, F. Roncarolo
  CERN, Geneva

Dis­per­sion and beam op­tics mea­sure­ments were car­ried out in the trans­fer line be­tween the CERN PS and SPS for the new Mul­ti-Turn Ex­trac­tion beam. Since the ex­trac­tion con­di­tions of the four is­lands and the core are dif­fer­ent and strong­ly de­pen­dent on the non-lin­ear ef­fects used to split the beam in the trans­verse plane, a spe­cial care was taken dur­ing the mea­sure­ment cam­paigns. Fur­ther­more, an ap­pro­pri­ate strat­e­gy was de­vised to min­i­mize the over­all op­ti­cal mis­match at SPS in­jec­tion. All this led to a new op­ti­cal con­fig­u­ra­tion that will be pre­sent­ed in de­tail in the paper.