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Assmann, R.W.

Paper Title Page
TPAP003 Exploring a Nonlinear Collimation System for the LHC 877
 
  • J. Resta, A. Faus-Golfe
    IFIC, Valencia
  • R.W. Assmann, S. Redaelli, G. Robert-Demolaize, D. Schulte, F. Zimmermann
    CERN, Geneva
 
  We explore the adaptation of a nonlinear collimation system, as previously considered for linear colliders, to LHC betatron cleaning. A possible nonlinear system for LHC consists of a horizontal and vertical primary collimator located in between a pair of skew sextupoles. We discuss the modified LHC optics, the need for and optimum placement of secondary absorbers, and the simulated cleaning efficiency.  
TPAP004 Mechanical Design for Robustness of the LHC Collimators 913
 
  • A. Bertarelli, O. Aberle, R.W. Assmann, S. Calatroni, A. Dallocchio, T. Kurtyka, M. Mayer, R. Perret, S. Redaelli, G. Robert-Demolaize
    CERN, Geneva
 
  The functional specification of the LHC Collimators requires, for the start-up of the machine and the initial luminosity runs (Phase 1), a collimation system with maximum robustness against abnormal beam operating conditions. The most severe cases to be considered in the mechanical design are the asynchronous beam dump at 7 TeV and the 450 GeV injection error. To ensure that the collimator jaws survive such accident scenarios, low-Z materials were chosen, driving the design towards Graphite or Carbon/Carbon composites. Furthermore, in-depth thermo-mechanical simulations, both static and dynamic, were necessary.This paper presents the results of the numerical analyses performed for the 450 GeV accident case, along with the experimental results of the tests conducted on a collimator prototype in Cern TT40 transfer line, impacted by a 450 GeV beam of 3.1·1013 protons, with impact parameters from 1 to 5 mm.  
TPAP005 Calculation of Residual Dose Rates and Intervention Scenarios for the LHC Beam Cleaning Insertions–Constraints and Optimization 940
 
  • M. Brugger, O. Aberle, R.W. Assmann, D. Forkel-Wirth, H.G. Menzel, S. Roesler, H. Vincke
    CERN, Geneva
 
  Radiation protection of the personnel who will perform interventions in the LHC Beam Cleaning Insertions is mandatory and includes the design of equipment and the establishment of work procedures. Residual dose rates due to activated equipment are expected to reach significant values such that any maintenance has to be planned and optimized in advance. Three-dimensional maps of dose equivalent rates at different cooling times after operation of the LHC have been calculated with FLUKA. The simulations are based on an explicit calculation of induced radioactivity and of the transport of the radiation from the radioactive decay. The paper summarizes the results for the Beam Cleaning Insertions and discusses the estimation of individual and collective doses received by personnel during critical interventions, such as the exchange of a collimator or the installation of Phase 2. The given examples outline the potential and the need to optimize, in an iterative way, the design of components as well as the layout of the beam cleaning insertions. Furthermore, results of measurements and simulations of residual dose rates for a collimator test recently performed at the SPS are presented.  
TPAP006 Detecting Impacts of Proton Beams on the LHC Collimators with Vibration and Sound Measurements 1018
 
  • S. Redaelli, O. Aberle, R.W. Assmann, A.M. Masi, G. Spiezia
    CERN, Geneva
 
  The 350 MJ stored energy of the 7 TeV LHC beams can seriously damage the beam line elements in case of accidental beam losses. Notably, the LHC collimators, which sit at 6 to 7 σs from the beam centre (1.2-1.4 mm), might be hit and possibly damaged in case of failures, with a consequent degradation of their cleaning performance. The experience from operating machines shows that an a-posteriori identification of the damaged collimators from the observed performance degradation is extremely challenging. Collimator tests with beam at the SPS have proven that the impact of 450 GeV proton beams at intensities from 1010 to 3x1013 can be detected by measuring the collimator vibrations. This was achieved by using high-resolution, radiation hard accelerometers and a microphone to record mechanical and sound vibrations of a LHC-like prototype collimator with impacting beams at different intensities and depth. A similar system could be also used in the LHC to detect collimators damaged by the beam.  
TPAP007 LHC Collimation: Design and Results from Prototyping and Beam Tests 1078
 
  • R.W. Assmann, O. Aberle, G. Arduini, A. Bertarelli, H.-H. Braun, M. Brugger, H. Burkhardt, S. Calatroni, F. Caspers, E. Chiaveri, A. Dallocchio, B. Dehning, A. Ferrari, M. Gasior, A. Grudiev, E.B. Holzer, J.-B. Jeanneret, J.M. Jimenez, Y. Kadi, R. Losito, M. Magistris, A.M. Masi, M. Mayer, E. Métral, R. Perret, C. Rathjen, S. Redaelli, G. Robert-Demolaize, S. Roesler, M. Santana-Leitner, D. Schulte, P. Sievers, E. Tsoulou, H. Vincke, V. Vlachoudis, J. Wenninger
    CERN, Geneva
  • I. Baishev, I.L. Kurochkin
    IHEP Protvino, Protvino, Moscow Region
  • G. Spiezia
    Naples University Federico II, Science and Technology Pole, Napoli
 
  The problem of collimation and beam cleaning concerns one of the most challenging aspects of the LHC project. A collimation system must be designed, built, installed and commissioned with parameters that extend the present state-of-the-art by 2-3 orders of magnitude. Problems include robustness, cleaning efficiency, impedance and operational aspects. A strong design effort has been performed at CERN over the last two years. The system design has now been finalized for the two cleaning insertions. The adopted phased approach is described and the expected collimation performance is discussed. In parallel robust and precisely controllable collimators have been designed. Several LHC prototype collimators have been built and tested with the highest beam intensities that are presently available at CERN. The successful beam tests are presented, including beam-based setup procedures, a 2 MJ robustness test and measurements of the collimator-induced impedance. Finally, an outlook is presented on the challenges that are ahead in the coming years.  
TPAP008 Measurements of the LHC Collimator Impedance with Beam in the SPS 1132
 
  • H. Burkhardt, G. Arduini, R.W. Assmann, F. Caspers, M. Gasior, A. Grudiev, O.R. Jones, T. Kroyer, E. Métral, S. Redaelli, G. Robert-Demolaize, F. Roncarolo, D. Schulte, R.J. Steinhagen, J. Wenninger, F. Zimmermann
    CERN, Geneva
 
  The transverse impedance of the LHC collimators will likely dominate the overall transverse impedance in the LHC at high energies and potentially limit the maximum intensity. A prototype collimator was recently tested in the SPS. Small, but significant tune shifts depending on the collimator position have been observed using different independent high resolution tune measurement methods. In addition trapped modes predicted from numerical simulation at the ends of the collimator jaws have been identified by bench measurement techniques as well as with the beam. We present a description of the measurements and an analysis of the results.  
TPAP014 Energy Deposition Studies for the Betatron Cleaning Insertion (IR7) of LHC 1386
 
  • M. Santana-Leitner, R.W. Assmann, A. Ferrari, M. Magistris, E. Tsoulou, V. Vlachoudis
    CERN, Geneva
 
  Two insertions (IR3, IR7) of the Large Hadron Collider (LHC) are dedicated to beam cleaning with the design goals of absorbing part of the primary beam halo and of the secondary radiation. The tertiary halo which escapes the collimation system in IR7 may heat the cold magnets at unacceptable levels, if no additional absorber is used. In order to assess the energy deposition in sensitive components, extensive simulations were run with the Monte Carlo cascade code FLUKA. The straight section and the dispersion suppressors of IR7 were fully implemented. A modular approach in the geometry definition and an extensive use of user-written programs allowed the implementation of all magnets and collimators with high precision, including flanges, steel supports and magnetic field. This paper provides the number and location of additional absorbers needed to keep the energy deposition in the coils of the magnets below the quenching limit.  
FPAT081 A New Version of SixTrack with Collimation and Aperture Interface 4084
 
  • G. Robert-Demolaize, R.W. Assmann, S. Redaelli, F. Schmidt
    CERN, Geneva
 
  Simulations of collimation and beam cleaning were so far often performed with simplified computer models. However, the increase in available CPU power has opened the possibility for far more realistic simulations. For large accelerators like LHC it is now possible to track millions of particles, element by element over hundreds of turns. The well established SixTrack code treats the full six-dimensional phase space and considers the non-linear magnet components up to very high order. This code is being used for all LHC tracking simulations and has well developed linear and non-linear error models. SixTrack was extended for tracking of large ensembles of halo particles, taking into account halo interaction with arbitrarily placed collimators. An interface to a program for aperture analysis allows obtaining beam loss maps in the machine aperture. A standardized and portable SixTrack version is now available, providing all functionality of the old SixTrack, as well as the newly added support for halo tracking, collimation and aperture loss maps.