Author: Mirarchi, D.
Paper Title Page
MOPWO035 Layouts for Crystal Collimation Tests at the LHC 966
 
  • D. Mirarchi, S. Redaelli, W. Scandale
    CERN, Geneva, Switzerland
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • V. Previtali
    Fermilab, Batavia, USA
 
  Various studies have been carried out in the past years regarding crystal collimation for the LHC. A new extensive campaign of simulations was performed to determine optimum layouts for beam tests at the LHC. The layouts are determined based on semi-analytical models for the dynamics of channeled particles. Detailed SixTrack tracking with all collimators of the ring are then used to validate the different options. An overview of the ongoing studies is given. Comparative studies between the present collimation system, the crystal collimation system, and different crystal collimation layout are presented.  
 
MOPWO038 Cleaning Inefficiency of the LHC Collimation System during the Energy Ramp: Simulations and Measurements 975
 
  • E. Quaranta, R. Bruce, L. Lari, D. Mirarchi, S. Redaelli, A. Rossi, B. Salvachua, G. Valentino
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  The cleaning inefficiency of the LHC collimation system has already been studied in detail at injection and top energy (450 GeV and 4 TeV respectively). In this paper the results are presented for the cleaning inefficiency at intermediate energies, simulated using the SixTrack code. The first comparisons with measured provoked losses are discussed. This study helps in benchmarking the energy dependence of the simulated inefficiency and is thus important for the extrapolation to future operation at higher energies.  
 
MOPWO039 Experience with High-intensity Beam Scraping and Tail Populations at the Large Hadon Collider 978
 
  • S. Redaelli, R. Bruce, F. Burkart, D. Mirarchi, B. Salvachua, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
  • R.W. Aßmann
    DESY, Hamburg, Germany
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  The population of beam tails at the LHC is source of concern because even small fractions of the total beam intensity could represent a potential danger is case of slow or fast losses, e.g. caused by orbit transients or by collimator movements. Different studies have been performed using the technique of collimator scans to probe the beam tail population, for different beam energies and beam intensities. The experience accumulated during the operation at 3.5 TeV and 4 TeV is reviewed and extrapolations to higher energies are considered.  
 
MOPWO048 Cleaning Performance of the LHC Collimation System up to 4 TeV 1002
 
  • B. Salvachua, R.W. Aßmann, R. Bruce, M. Cauchi, D. Deboy, L. Lari, A. Marsili, D. Mirarchi, E. Quaranta, S. Redaelli, A. Rossi, G. Valentino
    CERN, Geneva, Switzerland
  • M. Cauchi
    UoM, Msida, Malta
  • L. Lari
    IFIC, Valencia, Spain
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  Funding: Research supported by EU FP7 HiLumi LHC (Grant agreement 284404)
In this paper we review the performance of the LHC collimation system during 2012 and compare it with previous years. During 2012, the so-called tight settings were deployed for a better cleaning and improved beta-star reach. As a result, a record cleaning efficiency below a few 0.0001 was achieved in the cold regions where the highest beam losses occur. The cleaning in other cold locations is typically a factor of 10 better. No quenches were observed during regular operation with up to 140 MJ stored beam energy. The system stability during the year, monitored regularly to ensure the system functionality for all machine configurations, and the performance of the alignment tools are also reviewed.
 
 
THPFI063 Development and Beam Tests of an Automatic Algorithm for Alignment of LHC Collimators with Embedded BPMs 3439
 
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
  • R.W. Aßmann
    DESY, Hamburg, Germany
  • R. Bruce, M. Gasior, D. Mirarchi, A.A. Nosych, S. Redaelli, B. Salvachua, N.J. Sammut
    CERN, Geneva, Switzerland
 
  Collimators with embedded Beam Position Monitor (BPM) buttons will be installed in the LHC during the upcoming long shutdown period. During the subsequent operation, the BPMs will allow the collimator jaws to be kept centered around the beam trajectory. In this manner, the best possible beam cleaning efficiency and machine protection can be provided at unprecedented higher beam energies and intensities. A collimator alignment algorithm is proposed to center the jaws automatically around the beam. The algorithm is based on successive approximation, as the BPM measurements are affected by non-linearities, which vary with the distance between opposite buttons, as well as the difference between the beam and the jaw centers. The successful test results, as well as some considerations for eventual operation in the LHC are also presented.  
 
THPFI064 Crystal-assisted Collimation Experiment from the SPS to the LHC 3442
 
  • W. Scandale, D. Mirarchi, S. Redaelli
    CERN, Geneva, Switzerland
 
  UA9 was operated in the CERN-SPS for more than six years in view of investigating the feasibility of the halo collimation assisted by bent crystals. Two-millimeter-long silicon crystals, with bending angles of about 150 μrad, are used as primary collimators. The crystal collimation process is obtained consistently through channeling with high efficiency, showing a steady reduction of almost one order of magnitude of the loss rate at the onset of the channeling process. This result holds both for protons and for lead-ions. The corresponding loss map in the accelerator ring is accordingly reduced. These observations strongly support our expectation that the coherent deflection of the beam halo by a bent crystal should enhance the collimation efficiency also in LHC. After a concise description of the results collected in the SPS we propose a scenario to integrate bent crystals in the LHC collimation system for machine experiment.  
 
MOPWO038 Cleaning Inefficiency of the LHC Collimation System during the Energy Ramp: Simulations and Measurements 975
 
  • E. Quaranta, R. Bruce, L. Lari, D. Mirarchi, S. Redaelli, A. Rossi, B. Salvachua, G. Valentino
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  The cleaning inefficiency of the LHC collimation system has already been studied in detail at injection and top energy (450 GeV and 4 TeV respectively). In this paper the results are presented for the cleaning inefficiency at intermediate energies, simulated using the SixTrack code. The first comparisons with measured provoked losses are discussed. This study helps in benchmarking the energy dependence of the simulated inefficiency and is thus important for the extrapolation to future operation at higher energies.  
 
MOPWO048 Cleaning Performance of the LHC Collimation System up to 4 TeV 1002
 
  • B. Salvachua, R.W. Aßmann, R. Bruce, M. Cauchi, D. Deboy, L. Lari, A. Marsili, D. Mirarchi, E. Quaranta, S. Redaelli, A. Rossi, G. Valentino
    CERN, Geneva, Switzerland
  • M. Cauchi
    UoM, Msida, Malta
  • L. Lari
    IFIC, Valencia, Spain
  • D. Mirarchi
    The Imperial College of Science, Technology and Medicine, London, United Kingdom
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  Funding: Research supported by EU FP7 HiLumi LHC (Grant agreement 284404)
In this paper we review the performance of the LHC collimation system during 2012 and compare it with previous years. During 2012, the so-called tight settings were deployed for a better cleaning and improved beta-star reach. As a result, a record cleaning efficiency below a few 0.0001 was achieved in the cold regions where the highest beam losses occur. The cleaning in other cold locations is typically a factor of 10 better. No quenches were observed during regular operation with up to 140 MJ stored beam energy. The system stability during the year, monitored regularly to ensure the system functionality for all machine configurations, and the performance of the alignment tools are also reviewed.