Author: Argyropoulos, T.
Paper Title Page
WEPPR061 Thresholds of Longitudinal Single Bunch Instability in Single and Double RF Systems in the CERN SPS 3066
  • T. Argyropoulos, T. Bohl, J. Esteban Muller, E.N. Shaposhnikova, H. Timko
    CERN, Geneva, Switzerland
  • C.M. Bhat
    Fermilab, Batavia, USA
  A fourth harmonic RF system is used in the SPS as a Landau cavity, in order to stabilize the high intensity LHC proton beam against the longitudinal instabilities. Numerous studies proved that operating the two RF systems, through the whole cycle, in bunch shortening mode is necessary to provide a good quality beam at extraction to the LHC. Furthermore, it was shown that the choice of RF parameters as voltage amplitude ratio and relative phase are critical for the beam stability. This paper presents the results of single bunch measurements performed in single and double RF systems with various RF settings and compares them with the results of macroparticle simulations for the SPS impedance model.  
WEPPR072 Increasing Instability Thresholds in the SPS by Lowering Transition Energy 3096
  • H. Bartosik, G. Arduini, T. Argyropoulos, T. Bohl, S. Cettour-Cave, K. Cornelis, J. Esteban Muller, W. Höfle, Y. Papaphilippou, G. Rumolo, B. Salvant, E.N. Shaposhnikova
    CERN, Geneva, Switzerland
  A new optics for the SPS with lower transition energy was tested experimentally during 2010-2011, showing a significant increase of the single bunch instability thresholds at injection, due to the 3-fold increase of the slip factor. This paper summarizes the series of performed machine studies for different LHC bunch structures and intensities. In particular, the search of the TMCI threshold in the new optics is presented. Observations on the longitudinal multi-bunch stability are compared between the nominal and the low-transition optics. Finally, optics variants with higher vertical tunes are discussed, which can allow to further increase the TMCI and vertical instability thresholds by reducing the vertical beta function.