Author: Assmann, R.W.
Paper Title Page
MOPPD062 Aperture Measurements in the LHC Interaction Regions 508
 
  • S. Redaelli, M.C. Alabau Pons, R.W. Assmann, R. Bruce, M. Giovannozzi, G.J. Müller, M. Pojer, J. Wenninger
    CERN, Geneva, Switzerland
 
  The aperture of the LHC interaction regions is crucial for the LHC performance because it determines the smaller β* that can be achieved. The aperture has been measured at a maximum energy of 3.5 TeV and at different β* values, following optimized procedure to allow safe measurements at high energy. In this paper, the results of these aperture measurements, which are used as a reference for β* reach and crossing scheme estimates at the LHC interaction points, are presented.  
 
MOPPD077 Studies for an Alternative LHC Non-Linear Collimation System 544
 
  • L. Lari, R.W. Assmann, V. Boccone, F. Cerutti, A. Mereghetti, R. Versaci, V. Vlachoudis
    CERN, Geneva, Switzerland
  • A. Faus-Golfe, L. Lari, J. Resta-López
    IFIC, Valencia, Spain
 
  Funding: This work has been carried out through of the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program.
A LHC nonlinear Betatron cleaning collimation system would allow larger gap for the mechanical jaws, reducing as a consequence the collimator-induced impedance, which may limit the LHC beam intensity. In this paper, the performance of the proposed system is analyzed in terms of beam losses distribution around the LHC ring and cleaning efficiency in stable physics condition at 7TeV for Beam1. Moreover, the energy deposition distribution on the machine elements is compared to the present LHC Betatron cleaning collimation system in the Point 7 Insertion Region (IR).
 
 
MOPPD078 Accelerator Physics Study on the Effects from an Asynchronous Beam Dump in the LHC Experimental Region Collimators 547
 
  • L. Lari, R.W. Assmann, V. Boccone, R. Bruce, F. Cerutti, A. Mereghetti, A. Rossi, V. Vlachoudis
    CERN, Geneva, Switzerland
  • A. Faus-Golfe, L. Lari
    IFIC, Valencia, Spain
 
  Funding: This work has been carried out through of the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program.
Asynchronous beam aborts at the LHC are to be expected once per year. Accelerator physics studies of asynchronous dumps have been performed at different beam energies and beta-stars. The loss patterns are analyzed in order to identify the losses in particular on the Phase 1 Tertiary Collimators (TCT), since their Tungsten jaw insert has a low damage threshold with respect to the loss load expected. Settings for the tilt angle of the TCTs are discussed with the aim of reducing the thermal loads on the TCT themselves.
 
 
MOPPD079 Preliminary Thermo-Mechanical Analysis of Angular Beam Impact on LHC Collimators 550
 
  • M. Cauchi, R.W. Assmann, A. Bertarelli, F. Carra, A. Dallocchio, D. Deboy, N. Mariani, A. Rossi
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
  • P. Mollicone
    UoM, Msida, Malta
  • N.J. Sammut
    University of Malta, Faculty of Engineering, Msida, Malta
 
  Funding: This work is supported by EuCARD.
The correct functioning of the LHC collimation system is crucial to attain the desired LHC luminosity performance. However, the requirements to handle high intensity beams can be demanding. In this respect, accident scenarios must be well studied in order to assess if the collimator design is robust against likely error scenarios. One of the catastrophic - though not very probable - accident scenarios identified is an asynchronous beam dump coupled with slight angular misalignment errors of the collimator jaw. Previous work presented a preliminary thermal evaluation of the extent of beam-induced damage for such scenarios, where it was shown that in some cases, a tilt of the jaw could actually serve to mitigate the effect of an asynchronous dump on the collimators. This paper will further analyze the response of tertiary collimators in presence of such angular jaw alignments, with the aim to identify optimal operational conditions.
 
 
MOPPD080 Improved Robustness of the LHC Collimation System by Operating with a Jaw-beam Angle 553
 
  • L. Lari, R.W. Assmann, A. Rossi
    CERN, Geneva, Switzerland
  • M. Cauchi
    UoM, Msida, Malta
  • A. Faus-Golfe, L. Lari
    IFIC, Valencia, Spain
 
  Funding: This work has been carried out through of the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program.
The robustness of the Phase I collimation system could be improved playing with the angular orientation of each single jaw. A preliminary study on the asymmetric misalignment of the collimator jaws, scanning through different jaw angles and varying beam sizes and energy, have been carried out, aiming at minimizing the energy deposited on metallic collimators, following an asynchronous dump.
 
 
TUPPR096 Angular Alignment of the LHC Injection Protection Stopper 2056
 
  • C. Bracco, R.W. Assmann, W. Bartmann, B. Goddard, V. Kain, J.A. Uythoven
    CERN, Geneva, Switzerland
 
  Machine safety depends critically on the correct setup of the protection elements. One of the injection protection collimators is constituted by exceptionally long jaws (4 m). For this element, an angular offset of the jaws could affect significantly the measured beam size and, as a consequence, the correct setup with respect to the beam. Dedicated studies and cross-calibrations have been performed to quantify the effect of tilts and offsets on the setup of this collimator and to check the provided passive protection.  
 
TUPPR097 Modeling and Simulation of LHC Beam-Based Collimator Setup 2059
 
  • G. Valentino, N.J. Sammut
    University of Malta, Information and Communication Technology, Msida, Malta
  • R.W. Assmann, F. Burkart, S. Redaelli, A. Rossi, D. Wollmann
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
 
  In the 2011 Large Hadron Collider run, collimators were aligned for proton and heavy ion beams using a semi-automatic setup algorithm. The algorithm provided a reduction in the beam time required for setup, an elimination of beam dumps during setup and higher accuracy with respect to manual alignment. A collimator setup simulator was developed based on a Gaussian model of the beam distribution as well as a parametric model of the beam losses. A time-varying beam loss signal can be simulated for a given collimator movement into the beam. The simulation results and comparison to measurement data obtained during collimator setups and dedicated fills for beam halo scraping are presented. The simulator will then be used to develop a fully automatic collimator alignment algorithm.  
 
TUPPR098 Comparison of LHC Collimator Beam-Based Alignment Centers to BPM-Interpolated Centers 2062
 
  • G. Valentino, N.J. Sammut
    University of Malta, Information and Communication Technology, Msida, Malta
  • R.W. Assmann, R. Bruce, G.J. Müller, S. Redaelli, A. Rossi, G. Valentino
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
 
  The beam centers at the Large Hadron Collider collimators are determined by beam-based alignment, where both jaws of a collimator are moved in separately until a loss spike is detected on a Beam Loss Monitor downstream. Orbit drifts of more than a few hundred micrometers cannot be tolerated, as they would reduce the efficiency of the collimation system. Beam Position Monitors (BPMs) are installed at various locations around the LHC ring, and a linear interpolation of the orbit can be obtained at the collimator positions. In this paper, the results obtained from beam-based alignment are compared with the orbit interpolated from the BPM data throughout the 2011 LHC proton run. The stability of the orbit determined by collimator alignment during the run is evaluated.  
 
THPPP018 Operation of the LHC at High Luminosity and High Stored Energy 3767
 
  • J. Wenninger, R. Alemany-Fernandez, G. Arduini, R.W. Assmann, B.J. Holzer, E.B. Holzer, V. Kain, M. Lamont, A. Macpherson, G. Papotti, M. Pojer, L. Ponce, S. Redaelli, M. Solfaroli Camillocci, J.A. Uythoven, W. Venturini Delsolaro
    CERN, Geneva, Switzerland
 
  In 2011 the operation of the Large Hadron Collider LHC entered its first year of high luminosity production at a beam energy of 3.5 TeV. In the first months of 2011 the number of bunches was progressively increased to 1380, followed by a reduction of the transverse emittance, an increase of the bunch population and a reduction of the betatron function at the collision points. The performance improvements steps that were accumulated in 2011 eventually brought the peak luminosity to 3.6·1033 cm-2s−1. The integrated luminosity delivered to each of the high luminosity experiments amounted to 5.6 fb-1, a factor of 5 above the initial target defined in 2010. The operational experience with high intensity and high luminosity at the LHC will be presented here, together with the issues that had to be tackled on the road to high intensity and luminosity.  
 
THPPR039 Controlled Transverse Blow-Up of High-energy Proton Beams for Aperture Measurements and Loss Maps 4059
 
  • W. Höfle, R.W. Assmann, S. Redaelli, R. Schmidt, D. Valuch, D. Wollmann, M. Zerlauth
    CERN, Geneva, Switzerland
 
  A technique was developed to blow-up transversely in a controlled way high energy proton beams in the LHC. The technique is based on band limited white noise excitation that is injected into the transverse damper feedback loop. The injected signal can be gated to selectively blow-up individual trains of bunches. The speed of transverse blow-up can be precisely controlled. This opens the possibility to perform safely and efficiently aperture measurements and loss maps with high intensity bunch trains well above stored beam energies that are considered to be safe. In particular, lengthy procedures for measurements at top energy, otherwise requiring multiple fills of individual bunches, can be avoided. In this paper, the method is presented and results from beam measurements are discussed and compared with alternative blow-up methods.  
 
THPPR040 First Operational Experience with the LHC Machine Protection System when Operating with Beam Energies Beyond the 100 MJ Range 4062
 
  • M. Zerlauth, R.W. Assmann, B. Dehning, M. Ferro-Luzzi, B. Goddard, M. Lamont, R. Schmidt, A.P. Siemko, J.A. Uythoven, J. Wenninger
    CERN, Geneva, Switzerland
 
  The LHC made a remarkable progress in luminosity production during 2011 operation. This was made possible by a progressive increase of beam intensities by more than 5 orders of magnitude, reaching stored beam energies beyond 100MJ at the end of the year. The correct functioning of the machine protection systems was vital during initial operation and even more when approaching nominal beam parameters, where an uncontrolled loss of a small fraction of the beam is already sufficient to damage accelerator equipment or the large experimental detectors The machine protection system depends on the interplay of many different elements: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. The strategy applied during 2011 to allow for an efficient but yet safe increase of the beam intensities is presented along with the associated risks and drawbacks of a too aggressive approach. The experience gained with the key systems will be discussed along with possibilities to further enhance machine availability whilst maintaining the current level of safety.