Author: Timko, H.
Paper Title Page
TUP1WA03 Beam Instabilities After Injection to the LHC 163
 
  • H. Timko, T. Argyropoulos, I. Karpov, E.N. Shaposhnikova
    CERN, Geneva, Switzerland
 
  Long-lasting phase oscillations have been observed at injection into the LHC since its first start-up with beam. These oscillations, however, were not leading to noticeable losses or blow-up in operation, and were therefore not studied in detail. In 2017, dedicated measurements with high-intensity bunches revealed that oscillations can lead to losses even slightly below the baseline intensity for the high-luminosity upgrade of the LHC. For the first time, high-resolution bunch profile acquisitions were triggered directly at injection and the formation of large-amplitude non-rigid dipole oscillations was observed on a turn-by-turn basis. First simulations can reproduce this instability via bunch filamentation that takes place after injection, depending on the mismatch between the bunch and bucket size in momentum at injection.  
slides icon Slides TUP1WA03 [2.166 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2018-TUP1WA03  
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TUP2WA03 Studies of Capture and Flat-Bottom Losses in the SPS 180
 
  • M. Schwarz, H. Bartosik, E. Chapochnikova, A. Lasheen, J. Repond, H. Timko
    CERN, Geneva, Switzerland
 
  One of the strong limitations for reaching higher beam intensities in the SPS, the injector of the LHC at CERN, are particle losses at flat bottom that increase with beam intensity. In this paper, different sources of these losses are investigated for two available SPS optics, using both measurements and simulations. Part of the losses originate from the PS-to-SPS bunch-to-bucket transfer, because the PS bunches are rotated in longitudinal phase space before injection and do not completely fit into the SPS RF bucket. The injection losses due to different injected bunch distributions were analyzed. Furthermore, at high intensities the transient beam loading in the SPS has a strong impact, which is (partially) compensated by the LLRF system. The effect of the present and future upgraded one-turn delay feedback system and phase loop on flat-bottom losses was studied using the longitudinal tracking code BLonD. Finally, the total particle losses are also affected by limitations in the SPS momentum aperture, visible for higher RF capture voltages in optics with lower transition energy and higher dispersion.  
slides icon Slides TUP2WA03 [8.038 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2018-TUP2WA03  
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