• S. Redaelli, O. Aberle, R.W. Assmann, C. Bracco, B. Dehning, M. Jonker, R. Losito, A. Masi, M. Sapinski, Th. Weiler, C. Zamantzas
  CERN, Geneva

A full scale prototype of the Large Hadron Collider (LHC) collimator was installed in 2004 in the CERN Super Proton synchrotron (SPS). During three years of operation the prototype has been used extensively for beam tests, for control tests and also to benchmark LHC simulation tools. This operational experience has been extremely valuable in view of the final LHC implementation as well as for estimating the LHC operational scenarios, most notably to establish procedures for the beam-based alignment of the collimators with respect to the circulating beam. This was made possible by installing in the SPS a first prototype of the LHC beam loss monitoring system. The operational experience gained at the SPS, lessons learnt for the LHC operation and various accelerator physics effects that could limit the efficiency of the collimator alignment procedures are presented.

• W. Scandale, E. Laface, R. Losito
  CERN, Geneva

The UA9 experiment intends to assess the possibility of using bent silicon crystals as primary collimators to direct the beam halo onto a secondary absorber, thus reducing outscattering, beam losses in critical regions and radiation load. The experiment will be performed in the CERN-SPS in storage mode with a low intensity 120 GeV/c proton beam. The beam will be perturbed to create a diffusive halo as in the RD22 experiment. The setup consists of four stations. The crystal station contains two goniometers for crystals. The first tracking station houses silicon strip detectors for single particle tracking. The second tracking station contains the same kind of detectors for tracking. The two stations will allow to measure x-x' densities and collimation efficiencies with high precision. The TAL station, at 90 degrees phase advance,is a 600 mm long tungsten secondary collimator. The observables of the experiment are the collimation efficiencies, the measurement of the phase space and the cleaning efficiency deduced from the losses along the ring. We present here the layout of the experiment and the way we expect to collect data in 2009.

• J.-L. Fernandez-Hernando, D. Angal-Kalinin
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• R. Losito, V. Vlachoudis
  CERN, Geneva

Linac4 is a 160 MeV H^- linac which will replace the existing Linac2, a 50 MeV proton linac, at CERN as a first step of the upgraded LHC proton injector chain. No collimation system is foreseen in the baseline design but it will become mandatory for opreation at highest duty cycle in order to reduce activation of the machine. Such a system will also help to reduce activation at low duty cycle. A review of different collimation options, initial studies on collimator designs capable of intercepting beam power of 10, 25 and 50 Watts at energies between 50 and 160 MeV, the activation of such designs and the downstream elements are shown in this paper.

• M. Petrarca, H.-H. Braun, N. Champault, E. Chevallay, R. Corsini, A.E. Dabrowski, M. Divall Csatari, S. Döbert, K. Elsener, V. Fedosseev, G. Geschonke, R. Losito, A. Masi, O. Mete, L. Rinolfi
  CERN, Geneva
• G. Bienvenu, M. Joré, B.M. Mercier, C. Prevost, R. Roux
  LAL, Orsay
• C. Vicario
  INFN/LNF, Frascati (Roma)

Installation of the new photo-injector for the CTF3 drive beam (PHIN) has been completed on a stand-alone test bench. The photo-injector operates with a 2.5 cell RF gun at 3 GHz, using a Cs2Te photocathode illuminated by a UV laser beam. The test bench is equipped with different beam monitoring devices as well as a 90-degree spectrometer. A grid of 200 micrometer wide slits can be inserted for emittance measurements. The laser used to trigger the photo-emission process is a Nd:YLF system consisting of an oscillator and a preamplifier operating at 1.5 GHz and two powerful amplifier stages. The infrared radiation produced is frequency quadrupled in two stages to obtain the UV. A Pockels cell allows adjusting the length of the pulse train between 50 nanoseconds and 50 microseconds. The nominal train length for CTF3 is 1.272 microseconds (1908 bunches). The first electron beam in PHIN was produced in November 2008. In this paper, results concerning the operation of the laser system and measurements performed to characterize the electron beam are presented.

• S. Redaelli, R.W. Assmann, R. Losito, A. Masi
  CERN, Geneva

The 2008 collimation system of the CERN Large Hadron Collider (LHC) included 80 movable collimators for a total of 316 degrees of freedom. Before beam operation, the final controls implementation was deployed and commissioned. The control system enabled remote control and appropriate diagnostics of the relevant parameters. The collimator motion is driven with time-functions, synchronized with other accelerator systems, which allows controlling the collimator jaw positions with a micrometer accuracy during all machine phases. The machine protection functionality of the system, which also relies on function-based tolerance windows, was also fully validated. The collimator control challenges are reviewed and the final system architecture is presented. The results of the remote system commissioning and the operational experience are discussed. The system tests performed for the 2009 beam operation are also reviewed.