Author: Lasheen, A.
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MOPOY058 Removing Known SPS Intensity Limitations for High Luminosity LHC Goals 989
  • E.N. Shaposhnikova, T. Argyropoulos, T. Bohl, P. Cruikshank, B. Goddard, T. Kaltenbacher, A. Lasheen, J. Perez Espinos, J. Repond, B. Salvant, C. Vollinger
    CERN, Geneva, Switzerland
  In preparation of the SPS as an LHC injector its impedance was significantly reduced in 1999 - 2000. A new SPS impedance reduction campaign is planned now for the High Luminosity (HL)-LHC project, which requires bunch intensities twice as high as the nominal one. One of the known intensity limitations is a longitudinal multi-bunch instability with a threshold 3 times below this operational intensity. The instability is presently cured using the 4th harmonic RF system and controlled emittance blow-up, but reaching the HL-LHC parameters cannot be assured without improving the machine impedance. Recently the impedance sources responsible for this instability were identified and implementation of their shielding and damping is foreseen during the next long shutdown (2019 - 2020) in synergy with two other important upgrades: amorphous carbon coating of (part of) the vacuum chamber against the e-cloud effect and rearrangement of the 200 MHz RF system. In this paper the strategy of impedance reduction is presented together with beam intensity achievable after its realisation. The potential effect of other proposals on remaining limitations is also considered.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY058  
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TUPOR008 Effect of the Various Impedances on Longitudinal Beam Stability in the CERN SPS 1666
  • A. Lasheen, T. Argyropoulos, J. Repond, E.N. Shaposhnikova
    CERN, Geneva, Switzerland
  The High Luminosity (HL)-LHC project at CERN aims at a luminosity increase by a factor ten and one of the necessary ingredients is doubling the bunch intensity to 2.4x1011 ppb for beams with 25 ns bunch spacing. Many improvements are already foreseen in the frame of the LHC Injector Upgrade (LIU) project, but probably this intensity would still not be reachable in the SPS due to longitudinal instabilities. Recently a lot of effort went into finding the impedance sources of the instabilities. Particle simulations based on the latest SPS impedance model are now able to reproduce the measured instability thresholds and were used to determine the most critical impedance sources by removing them one by one from the model. It was found that impedance of vacuum flanges and of the already damped 630 MHz HOM of the main RF system gave for 72 bunches the comparable intensity thresholds. Possible intensity gains are defined for realistic impedance modifications and for various beam configurations (number of bunches, longitudinal emittances) and RF programs (single and double RF). The results of this study are used as a guideline for planning of a new campaign of the SPS impedance reduction.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR008  
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TUPOR009 Single Bunch Longitudinal Instability in the CERN SPS 1670
SUPSS055   use link to see paper's listing under its alternate paper code  
  • A. Lasheen, T. Bohl, S. Hancock, T. Roggen, E.N. Shaposhnikova
    CERN, Geneva, Switzerland
  • E. Radvilas
    Gediminas Technical University, Vilnius, Lithuania
  The longitudinal single bunch instability observed in the SPS leads to uncontrolled emittance blow-up and limits the quality of high intensity beams required for the High Luminosity LHC and AWAKE projects at CERN. The present SPS impedance model developed from a thorough survey of machine elements was used in macro-particle simulations (with the code BLonD) of the bunch behavior through the acceleration cycle. Comparison of simulations with measurements of the synchrotron frequency shift, performed on the SPS flat bottom to probe the impedance, show a reasonable agreement. During extensive experimental studies various beam and machine parameters (bunch intensity, longitudinal emittance, RF voltage, with single and double RF systems) were scanned in order to further benchmark the SPS impedance model with measurements and to better understand the mechanism behind the instability. It was found that the dependence of instability threshold on longitudinal emittance and beam energy has an unexpected non-monotonic behavior, leading to islands of (in)stability. The results of this study are presented and can be used to define possible parameter settings for the future CERN projects.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR009  
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WEPOY045 Benchmarking the Beam Longitudinal Dynamics Code BLonD 3094
  • H. Timko, J.F. Esteban Müller, A. Lasheen, D. Quartullo
    CERN, Geneva, Switzerland
  The relatively recent Beam Longitudinal Dynamics code BLonD has already been applied to a wide range of studies for all present CERN synchrotrons. Its application area ranges from studies of RF manipulations, over single and multi-bunch interactions with impedance, to the action of feedback loops and RF noise. In this paper, we present benchmarks and comparisons with measurements, theory, or other codes, which have increased greatly the trust in the code. Tests related to bunch-to-bucket transfer, feedback loops, diffusion due to noise injection, as well as collective effects, are presented.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY045  
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