• M. Meddahi, S. Bart Pedersen, A. Boccardi, A.C. Butterworth, B. Goddard, G.H. Hemelsoet, W. Höfle, D. Jacquet, M. Jaussi, V. Kain, T. Lefèvre, E.N. Shaposhnikova, J.A. Uythoven, D. Valuch
  CERN, Geneva
• A.S. Fisher
  SLAC, Menlo Park, California
• E. Gianfelice-Wendt
  Fermilab, Batavia

Unbunched beam is a potentially serious issue in the LHC as it may quench the superconducting magnets during a beam abort. Unbunched particles, either not captured by the RF system at injection or leaking out of the RF bucket, will be removed by using the existing damper kickers to excite resonantly the particles in the abort gap. Following beam simulations, a strategy for cleaning the abort gap at different energies was proposed. The plans for the commissioning of the beam abort gap cleaning are described, and the first results from the beam commissioning are presented.

• J.D. Fox, A. Bullitt, T. Mastorides, G. Ndabashimiye, C.H. Rivetta, O. Turgut, D. Van Winkle
  SLAC, Menlo Park, California
• J.M. Byrd, M.A. Furman, J.-L. Vay
  LBNL, Berkeley, California
• R. De Maria
  BNL, Upton, Long Island, New York
• W. Höfle, G. Rumolo
  CERN, Geneva

The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consistent with an Ecloud driven instability. We present recent MD data from the SPS, details of the instrument technique and spectral analysis methods which help reveal complex vertical motion that develops within a subset of the injected bunch trains. The beam motion is detected via wide-band exponential taper striplines and delta-σ hybrids. The raw sum and difference data is sampled at 50 GHz with 1.8 GHz bandwidth. Sliding window FFT techniques and RMS motion techniques show the development of large vertical tune shifts on portions of the bunch of nearly 0.025 from the base tune of 0.185. Results are presented via spectrograms and rms bunch slice trajectories to illustrate development of the unstable beam and time scale of development along the injected bunch train. The study shows that the growing unstable motion occupies a very broad frequency band of 1.2 GHz. These measurements are compared to numerical simulation results, and the system parameter implications for an Ecloud feedback system are outlined.

• R. De Maria
  BNL, Upton, Long Island, New York
• C. Boccard, W. Höfle, G. Kotzian, C. Palau Montava, B. Salvant
  CERN, Geneva

The SPS exponential coupler stripline are used to study single bunch instabilities. An accurate description of the response of the pickup is required to obtain high resolution measurements of the bunch vertical motion along the longitudinal axis. In this study we present the results of the comparison between dedicated beam experiments and electromagnetic simulations of a geometrical model of the stripline.