Author: Biancacci, N.
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MOPOR008 Beam Induced RF Heating in LHC in 2015 602
 
  • B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancacci, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini
    CERN, Geneva, Switzerland
  • M. Bozzo
    INFN Genova, Genova, Italy
  • J.F. Esteban Müller
    EPFL, Lausanne, Switzerland
  • N. Wang
    IHEP, Beijing, People's Republic of China
 
  Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR008  
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MOPOR009 The HL-LHC Impedance Model and Aspects of Beam Stability 606
 
  • N. Biancacci, K.S.B. Li, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
 
  Funding: Research supported by the High Luminosity LHC project
The LHC upgrade to the HLLHC foresees new challenging operational scenarios from the beam dynamics point of view. In order to ensure good machine operation and performance, the machine impedance, among other possible sources of instabilities like beam-beam and electron cloud, needs to be carefully quantified profiting also from the current LHC operation. In this work we present the HLLHC impedance model mainly focusing on the contribution of low-impedance collimators and crab cavities: the first reduces the broad-band impedance baseline thanks to the higher jaw material conductivity, the second increases the machine luminosity at the price of increasing the coupled bunch stabilizing octupole current threshold. Other elements like the injection protection absorber (TDI) will be also discussed.
 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR009  
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MOPOR010 Impedance Measurements and Simulations on the TCTP and TDI LHC Collimators 610
 
  • N. Biancacci, F. Caspers, A. Grudiev, J. Kuczerowski, I. Lamas Garcia, A. Lechner, E. Métral, A. Passarelli, A. Perillo Marcone, B. Salvant, J.A. Uythoven
    CERN, Geneva, Switzerland
  • O. Frasciello, M. Zobov
    INFN/LNF, Frascati (Roma), Italy
  • A. Mostacci
    Rome University La Sapienza, Roma, Italy
  • N. Mounet
    EPFL, Lausanne, Switzerland
 
  The LHC collimation system is a critical element for the safe operation of the LHC machine and is subject to continuous performance monitoring, hardware upgrade and optimization. In this work we will address the impact on impedance of the upgrades performed on the TDI injection protection collimator, where the absorber material has been changed to mitigate the device heating observed in machine operation, and on selected secondary (TCS) and tertiary (TCT) collimators, where beam position monitors (BPM) have been embedded for faster jaw alignment. Concerning the TDI, we will present the RF measurements performed before and after the upgrade, comparing the result to heating and tune shift beam measurements. For the TCTs, we will study how the higher order modes (HOM) introduced by the BPM addition have been cured by means of ferrite placement in the device. The impedance mitigation campaign has been supported by RF measurements whose results are in good agreement with GdfidL and CST simulations. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR010  
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MOPOR011 Impedance Localization Measurements using AC Dipoles in the LHC 614
 
  • N. Biancacci, L.R. Carver, G. Papotti, T. Persson, B. Salvant, R. Tomás
    CERN, Geneva, Switzerland
 
  The knowledge of the LHC impedance is of primary importance to predict the machine performance and allow for the HL-LHC upgrade. The developed impedance model can be benchmarked with beam measurements in order to assess its validity and limit. This is routinely done, for example, moving the LHC collimator jaws and measuring the induced tune shift. In order to localize possible unknown impedance sources, the variation of phase advance with intensity between beam position monitors can be measured. In this work we will present the impedance localization measurements performed at injection in the LHC using AC dipoles as exciter as well as the underlying theory.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR011  
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MOPOR014 Measurements of the CERN PS Longitudinal Resistive Coupling Impedance 626
 
  • M. Migliorati, N. Biancacci, H. Damerau, G. Sterbini
    CERN, Geneva, Switzerland
  • M. Migliorati
    University of Rome "La Sapienza", Rome, Italy
  • M. Migliorati, L. Ventura
    INFN-Roma1, Rome, Italy
  • S. Persichelli
    University of Rome La Sapienza, Rome, Italy
 
  The longitudinal coupling impedance of the CERN PS has been studied in the past years in order to better understand collective effects which could produce beam intensity limitations for the LHC Injectors Upgrade project. By measuring the incoherent quadrupole synchrotron frequency vs beam intensity, the inductive impedance was evaluated and compared with the impedance model obtained by taking into account the contribution of the most important machine devices. In this paper, we present the results of the measurements performed during a dedicated campaign, of the real part of the longitudinal coupling impedance by means of the synchronous phase shift vs beam intensity. The phase shift has been measured by using two different techniques: in one case, we injected in the machine two bunches, one used as a reference with constant intensity, and the second one changing its intensity; in the second case, more conventional, we measured the bunch position with respect to the RF signal of the 40 MHz cavities. The obtained dependence of the synchrotron phase with intensity is then related to the loss factor and the resistive coupling impedance, which is compared to the real part of the PS impedance model.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR014  
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TUPMW011 Current Status of Instability Threshold Measurements in the LHC at 6.5 TeV 1434
 
  • L.R. Carver, J. Barranco, N. Biancacci, X. Buffat, W. Höfle, G. Kotzian, T. Lefèvre, T.E. Levens, E. Métral, T. Pieloni, B. Salvant, C. Tambasco
    CERN, Geneva, Switzerland
  • N. Wang
    IHEP, Beijing, People's Republic of China
  • M. Zobov
    INFN/LNF, Frascati (Roma), Italy
 
  Throughout 2015, many measurements of the minimum stabilizing octupole current required to prevent coherent transverse instabilities have been performed. These measurements allow the LHC impedance model at flat top to be verified and give good indicators of future performance and limitations. The results are summarized here, and compared to predictions from the simulation code DELPHI.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW011  
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TUPOR010 Simulation of Instability at Transition Energy with a New Impedance Model for CERN PS 1674
 
  • N. Wang
    IHEP, Beijing, People's Republic of China
  • S. Aumon, N. Biancacci, M. Migliorati, G. Sterbini, N. Wang
    CERN, Geneva, Switzerland
  • M. Migliorati
    INFN-Roma1, Rome, Italy
  • S. Persichelli
    University of Rome La Sapienza, Rome, Italy
 
  Instabilities driven by the transverse impedance are proven to be one of the limitations for the high intensity reach of the CERN PS. Since several years, fast single bunch vertical instability at transition energy has been observed with the high intensity bunch serving the neu-tron Time-of-Flight facility (n-ToF). In order to better understand the instability mechanism, a dedicated meas-urement campaign took place. The results were compared with macro-particle simulations with PyHEADTAIL based on the new impedance model developed for the PS. Instability threshold and growth rate for different longitu-dinal emittances and beam intensities were studied.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR010  
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WEPMW031 Towards Optimum Material Choices for the HL-LHC Collimator Upgrade 2498
 
  • E. Quaranta, A. Bertarelli, N. Biancacci, R. Bruce, F. Carra, E. Métral, S. Redaelli, A. Rossi, B. Salvant
    CERN, Geneva, Switzerland
  • F. Carra
    Politecnico di Torino, Torino, Italy
 
  The first years of operation at the LHC showed that collimator material-related concerns might limit the performance. In addition, the HL-LHC upgrade will bring the accelerator beyond the nominal performance through more intense and brighter proton beams. A new generation of collimators based on advanced materials is needed to match present and new requirements. After several years of R&D on collimator materials, studying the behaviour of novel composites with properties that address different limitations of the present collimation system, solutions have been found to fulfil various upgrade challenges. This paper describes the proposed staged approach to deploy new materials in the upgraded HL-LHC collimation system. Beam tests at the CERN HiRadMat facility were also performed to benchmark simulation methods and constitutive material models.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW031  
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THPMY019 LHC Injection Protection Devices, Thermo-mechanical Studies through the Design Phase 3698
 
  • I. Lamas Garcia, N. Biancacci, G. Bregliozzi, M. Calviani, M.I. Frankl, L. Gentini, S.S. Gilardoni, A. Lechner, A. Perillo-Marcone, B. Salvant, N.V. Shetty, J.A. Uythoven
    CERN, Geneva, Switzerland
 
  The TDI is a beam intercepting device installed on the two injection lines of the LHC. Its function is to protect the superconducting machine elements during injection in the case of a malfunction of the injection kickers. The TDIS, which will replace the TDI, is foreseen to be installed for high luminosity operation. Due to the higher bunch intensities and smaller beam emittances expected, and following the operational experiences of the TDI, a complete revision of the design of the jaws must be performed, with a main focus on the material selection. Furthermore, the new TDIS will also improve the TDI reliability by means of a robust design of the jaw positioning mechanism, the efficiency of the cooling circuit and by reducing its impedance. A simplified installation procedure and maintenance will also be an important requirement for the new design. This paper introduces the main characteristics of the TDI as LHC injection protection device, showing the needs and requirements for its upgrade. It also discusses the thermo-mechanical simulations that are supporting and guiding the design phase and the material selection, and describes the modifications to be implemented, so far, for this new device.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY019  
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