• A. Dallocchio, G. Arnau-Izquierdo, K. Artoos, A. Bertarelli
  CERN, Geneva

Phase I collimators, equipped with Carbon-Carbon jaws, effectively met specifications for the early phase of LHC operation. However, the choice of carbon-based materials is expected to limit the nominal beam intensity mainly because of the high RF impedance and limited efficiency of the collimators. Moreover, C/C may be degraded by high radiation doses. To overcome these limitations, new Phase II secondary collimators will complement the existing system. Their extremely challenging requirements impose a thorough material investigation effort aiming at identifying novel materials combining very diverse properties. Relevant figures of merit have been identified to classify materials: Metal-diamonds composites look a promising choice as they combine good thermal, structural and stability properties. Molybdenum is interesting for its good thermal stability. Ceramics with non-conventional RF performances are also being evaluated. The challenges posed by the development and industrialization of these materials are addressed in a collaboration program, involving academic and industrial partners and complementing material research with an innovative design.

• K. Artoos, O. Capatina, C.G.R.L. Collette, M. Guinchard, C. Hauviller, F. Lackner, J. Pfingstner, H. Schmickler, M.V. Sylte
  CERN, Geneva
• B. Bolzon, L. Brunetti, G. Deleglise, N. Geffroy, A. Jeremie
  IN2P3-LAPP, Annecy-le-Vieux
• P.A. Coe, D. Urner
  OXFORDphysics, Oxford, Oxon
• M. Fontaine
  CEA, Gif-sur-Yvette

To reach the design luminosity of CLIC, the movements of the quadrupoles should be limited to the nanometer level in order to limit the beam size and emittance growth. Below 1 Hz, the movements of the main beam quadrupoles will be corrected by a beam-based feedback. But above 1 Hz, the quadrupoles should be mechanically stabilized. A collaboration effort is ongoing between several institutes to study the feasibility of the “nano-stabilization” of the CLIC quadrupoles. The study described in this paper covers the characterization of independent measuring techniques including optical methods to detect nanometer sized displacements and analyze the vibrations. Actuators and feedback algorithms for sub-nanometer movements of magnets with a mass of more than 400 kg are being developed and tested. Input is given to the design of the quadrupole magnets, the supports and alignment system in order to limit the amplification of the vibration sources at resonant frequencies. A full scale mock-up integrating all these features is presently under design. Finally, a series of experiments in accelerator environments should demonstrate the feasibility of the nanometer stabilization.

• K. Artoos, O. Capatina, C.G.R.L. Collette, M. Guinchard, C. Hauviller, M.V. Sylte
  CERN, Geneva
• B. Bolzon, A. Jeremie
  IN2P3-LAPP, Annecy-le-Vieux

The demanding nanometer transverse beam sizes and emittances in future linear accelerators results in stringent alignment and nanometer vibration stability requirements. For more than two decades, ground vibration measurements were made by different teams for feasibility studies of linear accelerators. Recent measurements were performed in the LHC tunnel and at different CERN sites on the surface. The devices to measure nanometer sized vibrations, the analysis techniques and the results are critically discussed and compared with former measurement campaigns. The implications of the measured integrated R.M.S. displacements and coherence length for the CLIC stabilization system are mentioned.