Author: Wollmann, D.
Paper Title Page
TUPZ006 Aperture Determination in the LHC Based on an Emittance Blowup Technique with Collimator Position Scan 1810
 
  • R.W. Assmann, R. Bruce, M. Giovannozzi, G.J. Müller, S. Redaelli, F. Schmidt, R. Tomás, J. Wenninger, D. Wollmann
    CERN, Geneva, Switzerland
  • M. Alabau
    IFIC, Valencia, Spain
 
  A new method to determine the LHC aperture was proposed. The new component is a collimator scan technique that refers the globally measured aperture limit to the shadow of the primary collimator, expressed in σs of rms beam size. As a by-product the BLM response to beam loss is quantified. The method is described and LHC measurement results are presented.  
 
TUPZ007 First Ion Collimation Commissioning Results at the LHC 1813
 
  • G. Bellodi, R.W. Assmann, R. Bruce, M. Cauchi, J.M. Jowett, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
 
  First commissioning of the LHC Pb ion beams to 1.38 A TeV energy was successfully achieved in November 2010. Ion collimation has been predicted to be less efficient than for protons at the LHC, because of the complexity of the physical processes involved: nuclear fragmentation and electromagnetic dissociation in the primary collimators creating fragments with a wide range of Z/A ratios, that are not intercepted by the secondary collimators but lost in the dispersion suppressor sections of the ring. In this article we present first comparisons of measured loss maps with theoretical predictions from simulation runs with the ICOSIM code. An extrapolation to define the ultimate intensity limit for Pb beams is attempted. The scope of possible improvements in collimation efficiency coming from the installation of new collimators in the cold dispersion suppressors and combined betatron and momentum cleaning is also explored.  
 
TUPZ013 Calculation Method for Safe Beta* in the LHC 1828
 
  • R. Bruce, R.W. Assmann, W. Herr, D. Wollmann
    CERN, Geneva, Switzerland
 
  One way of increasing the peak luminosity in the LHC is to decrease the beam size at the interaction points by squeezing to smaller values of beta*. The LHC is now in a regime where safety and stability determines the limit in beta*, as opposed to traditional optics limits. In this paper, we derive a calculation model to determine the safe beta*-values based on collimator settings and operational stability of the LHC. This model was used to calculate the settings for the LHC run in 2011. It was found that beta* could be decreased from 3.5 m to 1.5 m, which has now successfully been put into operation.  
 
MOPO011 The First 1 1/2 Years of TOTEM Roman Pot Operation at LHC 502
 
  • M. Deile, G.H. Antchev, R.W. Assmann, I. Atanassov, V. Avati, J. Baechler, R. Bruce, M. Dupont, K. Eggert, B. Farnham, J. Kaspar, F. Lucas Rodríguez, J. Morant, H. Niewiadomski, X. Pons, E. Radermacher, S. Ravat, F. Ravotti, S. Redaelli, G. Ruggiero, H. Sabba, M. Sapinski, W. Snoeys, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
  • R. Appleby
    UMAN, Manchester, United Kingdom
 
  Since the LHC running season 2010, the TOTEM Roman Pots (RPs) are fully operational and serve for collecting elastic and diffractive proton-proton scattering data. Like for other moveable devices approaching the high intensity LHC beams, a reliable and precise control of the RP position is critical to machine protection. After a review of the RP movement control and position interlock system, the crucial task of alignment will be discussed.  
 
THPZ026 Collimation Dependent Beam Lifetime and Loss Rates in the LHC 3744
 
  • D. Wollmann, R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, G. Valentino
    CERN, Geneva, Switzerland
 
  The four primary collimators in each LHC beam define the smallest aperture. Particles with high betatron amplitudes or momentum offset will therefore hit first a primary collimator. The instantaneous particle loss rate at primary collimators is an important measure for the global lifetime of the beams and a major ingredient to identify collimation induced performance limitations in the LHC. These loss rates have been measured during a number of LHC fills, featuring both "good" fills with high luminosity and "bad" fills with beam instabilities. The beam lifetime at the collimators was then calculated from this data for different cases. The results are presented and interpreted within this paper.  
 
THPZ027 First Beam Results for a Collimator with In-jaw Beam Position Monitors 3747
 
  • D. Wollmann, O. Aberle, R.W. Assmann, A. Bertarelli, C.B. Boccard, R. Bruce, F. Burkart, M. Cauchi, A. Dallocchio, D. Deboy, M. Gasior, O.R. Jones, S. Redaelli, A. Rossi, G. Valentino
    CERN, Geneva, Switzerland
 
  With more than 100 collimators the LHC has the most complex collimation system ever installed in an accelerator. The beam-based setup time of the system was a non-negligible factor during the commissioning of the LHC. In addition if the particle orbit at a collimator goes out of tolerance, this collimator needs to be setup again. To reduce the required setup time for the collimation system and to obtain the tight tolerances required for the LHC operation with small beta* and high beam energy, a new collimator design is being developed that integrates a beam position monitor (BPM) into the jaws of the collimator. A prototype of such a phase-II LHC collimator was installed in the SPS at CERN for the 2010 run. In this paper we present the first experimental results from the beam tests performed.  
 
THPZ028 Upgrade Studies for the LHC Collimators 3750
 
  • A. Rossi, R.W. Assmann, D. Wollmann
    CERN, Geneva, Switzerland
 
  The Phase-I LHC Collimation System has to be upgraded to work at high intensity and energy. Theoretical and engineering studies are focusing on different regions of the machine. The IR3 combined momentum and betatron cleaning, initially approved for installation, has presently been kept as fallback solution in case radiation to equipment limits LHC performance. The installation of collimators in the dispersion suppressor section DS3 has been delayed. In this paper we present predictions with matched optics and the effect of machine imperfections on the collimation performance with IR3 combined cleaning, with and without DS3 collimators.  
 
THPZ030 Halo Scrapings with Collimators in the LHC 3756
 
  • F. Burkart, R.W. Assmann, R. Bruce, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
  • L. Lari
    IFIC, Valencia, Spain
 
  The population of the beam halo has been measured in the LHC with beam scraping experiments. Primary collimators of the LHC collimation system were used to scrape the beam halo at different statuses of the machine (injection, top energy, separated and colliding beams). In addition these measurements were used to calibrate the beam loss monitor signals to loss rates at the primary collimators. Within this paper the halo scraping method, the measured halo distribution and the calibration factors are presented and compared to theoretical predictions.  
 
THPZ034 Semi-automatic Beam-based Alignment Algorithm for the LHC Collimation System 3768
 
  • G. Valentino, R.W. Assmann, S. Redaelli, N.J. Sammut, D. Wollmann
    CERN, Geneva, Switzerland
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  Full beam-based alignment of the LHC collimation system was a lengthy procedure as the collimators were set up manually. A yearly alignment campaign has been sufficient for now, although in future this may lead to a decrease in the cleaning efficiency if machine parameters such as the beam orbit drift over time. Automating the collimator setup procedure can allow for more frequent alignments, therefore reducing this risk. This paper describes the design and testing of a semi-automatic algorithm as a first step towards a fully automatic setup. Its implementation in the collimator control software and future plans are described.  
 
THPZ031 Acoustic Measurements in the Collimation Region of the LHC 3759
 
  • D. Deboy, R.W. Assmann, C. Baccigalupi, F. Burkart, M. Cauchi, C.S. Derrez, J. Lendaro, A. Masi, S. Redaelli, G. Spiezia, D. Wollmann
    CERN, Geneva, Switzerland
 
  The LHC accelerator at CERN has the most advanced collimation system ever being installed. The collimators intercept unavoidable particle losses and therefore are essential to avoid beam induced quenches of the superconducting magnets. In addition, they provide passive machine protection against mis-kicked beams. During material robustness tests on a LHC collimator prototype in 2004 and 2006, vibration and acoustic measurements have shown that a beam impact detection system should be feasible using accelerometers and microphones as sensors in the LHC. Recently, such sensors have been installed close to the primary collimators in the LHC tunnel. First analyses of raw data show that the system is sensitive enough to detect beam scraping on collimators. Therefore, the implementation of a sophisticated acoustic monitoring system is under investigation. It may be useful not only to detect beam impacts on primary collimators in case of failure, but also to derive further information on beam losses that occur during regular operation. This paper gives an overview on the recent installation, results of the acoustic measurements made at the LHC, and future plans.  
 
THPZ032 Evaluation of the Combined Betatron and Momentum Cleaning in Point 3 in Terms of Cleaning Efficiency and Energy Deposition for the LHC Collimation Upgrade 3762
 
  • L. Lari, R.W. Assmann, V. Boccone, M. Brugger, F. Cerutti, A. Ferrari, A. Rossi, R. Versaci, V. Vlachoudis, D. Wollmann
    CERN, Geneva, Switzerland
  • A. Faus-Golfe, L. Lari
    IFIC, Valencia, Spain
  • A. Mereghetti
    UMAN, Manchester, United Kingdom
 
  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 Phase I LHC Collimation System Upgrade could include moving part of the Betatron Cleaning from LHC Point 7 to Point 3 to improve both operation flexibility and intensity reach. In addition, the partial relocation of beam losses from the current Betatron cleaning region at Point 7 will mitigate the risks of Single Event Upsets to equipment installed in adjacent and partly not adequate shielded areas. A combined Betatron and Momentum Cleaning scenario at Point 3 implies the installation of new collimators and a new collimator aperture layout. This paper shows the whole LHC Collimator Efficiency variation with the new layout proposed at different beam energies. As part of the evaluation, energy deposition distribution in the IR3 region gives indications about the effect of this new implementation not only on the collimators themselves but also on the other beam line elements.
 
 
THPZ035 Comparison of LHC Collimation Setups with Manual and Semi-automatic Collimator Alignment 3771
 
  • G. Valentino, R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, N.J. Sammut, D. Wollmann
    CERN, Geneva, Switzerland
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  The LHC collimation system beam-based alignment procedure has recently been upgraded to a semi-automatic process in order to increase its efficiency. In this paper, we describe the parameters used to measure the accuracy, stability and performance of the beam-based alignment of the LHC collimation system. This is followed by a comparison of the results at 450 GeV and 3.5 TeV with (1) a manual alignment and (2) with the results for semi-automatic alignment.