• S.J. Mathot, P. Bourquin, A. Briswalter, Th. Callamand, J. Carosone, N. Favre, J.-M. Geisser, A.M. Lombardi, V. Maire, M. Malabaila, D. Pugnat, Ph. Richerot, B. Riffaud, C. Rossi, M.A. Timmins, A. Vacca, G. Vandoni, M. Vretenar
  CERN, Geneva

The Linac4 RFQ will ac­cel­er­ate the H^- beam from the ion source to the en­er­gy of 3 MeV. The RFQ is com­posed of three sec­tions of 1 meter each, as­sem­bled by means of ultra high vac­u­um flanges and an ad­justable cen­ter­ing ring. The com­plete 3-m long RFQ will be sup­port­ed iso­stat­i­cal­ly over 3 points like a sim­ple beam in order to min­imise the max­i­mum de­flec­tion. The ridge line, used to feed the RF power into the RFQ, will be sup­port­ed via springs and its po­si­tion ad­just­ed in such way that no strain is in­tro­duced into the RFQ at the mo­ment of its con­nec­tion. The me­chan­i­cal de­sign has been done at CERN where the mod­ules are com­plete­ly man­u­fac­tured, heat treat­ed and brazed also. In that way, all of the pro­cess­es are care­ful­ly con­trolled and the in­flu­ence, no­tably of the heat treat­ments, has been un­der­stood in a bet­ter way. Since 2002 sev­er­al four vanes RFQ mod­ules have been brazed at CERN for the TRASCO and IPHI pro­jects. A two-step braz­ing pro­ce­dure has been test­ed. This tech­nique is ac­tu­al­ly used for the as­sem­bly of the CERN Linac4 RFQ. This paper de­scribes the de­sign, the me­chan­i­cal pro­ce­dures adopt­ed for ma­chin­ing and as­sem­bly and the first re­sults ob­tained.

• 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.