• R.W. Assmann, G. Bellodi, J.M. Jowett, E. Métral, Th. Weiler
  CERN, Geneva
• L. Keller, T.W. Markiewicz
  SLAC, Menlo Park, California

The LHC collimation system is implemented in phases, in view of the required extrapolation by 2-3 orders of magnitude beyond Tevatron and HERA experience in stored energy. All available simulations predict that the LHC proton beam intensity with the "phase 1" collimation system may be limited by the impedance of the collimators or cleaning efficiency. Maximum efficiency requires collimator materials very close to the beam, generating the dominant resistive impedance in the LHC. Above a certain intensity the beam is unstable. On the other hand, even if collimators are set very close to the beam, the achievable cleaning efficiency is predicted to be inadequate, requiring either beam stability beyond specifications or reduced intensity. The accelerator physics concept for upgrading cleaning efficiency, for both proton and heavy ion beams, and reducing collimator-related impedance is described. Besides the "phase 2" secondary collimators, new collimators are required in a few super-conducting regions.

• R.W. Assmann, G. Bellodi, C. Bracco, V.P. Previtali, S. Redaelli, Th. Weiler
  CERN, Geneva

Collimation and halo cleaning for the LHC beams are performed separately for betatron and momentum losses, requiring two dedicated insertions for collimation. Betatron cleaning is performed in IR7 while momentum cleaning is performed in IR3. A study has been performed to evaluate the performance reach for a combined betatron and momentum cleaning system in IR3. The results are presented.

• B. Mikulec, G. Bellodi, M. Eshraqi, K. Hanke, T. Hermanns, S. Lanzone, A.M. Lombardi, U. Raich
  CERN, Geneva

Construction work for the new CERN linear accelerator, Linac4, started in October 2008. Linac4 will replace the existing Linac2 and provide an H^- beam at 160 MeV (as opposed to the present 50 MeV proton beam) for injection into the CERN PS Booster (PSB). The charge-exchange H^- injection combined with the higher beam energy will allow for an increase in beam brightness required for reaching the ultimate LHC luminosity. Commissioning of Linac4 and of the transfer line to the PSB is planned for the last quarter of 2012. Appropriate beam instrumentation is foreseen to provide transverse and longitudinal beam characterization at the exit of Linac4 and in two dedicated measurement lines located before injection into the PSB. A detailed description of the diagnostics set, especially of spectrometer and emittance meter, and the upgrade of the measurement lines for Linac4 commissioning and operation is presented.