• E. Gianfelice-Wendt
  Fermilab, Batavia
• B. Goddard, W. Höfle, V. Kain, M. Meddahi, E.N. Shaposhnikova
  CERN, Geneva
• A. Koschik
  ETH, Zurich

Funding: Work partly supported by Fermilab, operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy

In the Large Hadron Collider –LHC, particles not captured by the RF system at injection or leaking out of the RF bucket may quench the superconducting magnets during beam abort. The problem, common to other superconducting machines, is particularly serious for the LHC due to the very large stored energy in the beam. For the LHC a way of removing the unbunched beam has been studied and it uses the existing damper kickers to excite resonantly the particles travelling along the abort gap. In this paper we describe the results of simulations performed with MAD-X for various LHC optics configurations, including the estimated multipolar errors.

• A.C. Butterworth, M. E. Angoletta, L. Arnaudon, P. Baudrenghien, J. Bento, T. Bohl, O. Brunner, E. Ciapala, F. Dubouchet, G. Hagmann, W. Höfle, T.P.R. Linnecar, P. Maesen, J.C. Molendijk, E. Montesinos, J. Noirjean, A.V. Pashnin, V. Rossi, J. Sanchez-Quesada, M. Schokker, E.N. Shaposhnikova, D. Stellfeld, J. Tuckmantel, D. Valuch, U. Wehrle, F. Weierud
  CERN, Geneva
• R. Sorokoletov
  JINR, Dubna, Moscow Region

Hardware commissioning of the LHC RF system was successfully completed in time for first beams in LHC in September 2008. All cavities ware conditioned to nominal field, power systems tested and all Low level synchronization systems, cavity controllers and beam control electronics were tested and calibrated. Beam was successfully captured in ring 2, cavities phased, and a number of initial measurements made. These results are presented and tests and preparation for colliding beams in 2009 are outlined.

• G. Kotzian, F. Caspers, S. Federmann, W. Höfle
  CERN, Geneva
• R. De Maria
  BNL, Upton, Long Island, New York
• G. Kotzian
  Graz University of Technology (TUG), Signal Processing and Speech Communication Laboratory (SPSC), Graz

In particle accelerators coaxial cables are commonly used to transmit wideband beam signals covering many decades of frequencies over long distances. Those transmission lines often have a corrugated outer and/or inner conductor. This particular construction exhibits a significant amount of frequency dependent group delay variation. A comparison of simulations based on theoretical models and S11 and S21 network analyzer measurements up to 2.5 GHz is presented. It is shown how the non-linear phase response and varying group delay leads to ringing in the pulse response and subsequent distortion of signals transmitted through such coaxial transmission lines.

• E. Métral, G. Arduini, F. Arnold Malandain, W. Höfle, D. Manglunki
  CERN, Geneva

For several years, a large variety of beams have been prepared in the LHC injectors, such as single-bunch and multi-bunch beams, with 25 ns, 50 ns and 75 ns bunch spacings, nominal and intermediate intensities per bunch. As compared to the nominal LHC beam (i.e. with nominal bunch intensity and 25 ns spacing) the other beams can be produced with lower transverse emittances. Beams of low transverse emittances are of interest during the commissioning phase for aperture considerations and because of the reduced long-range beam-beam effects. On the other hand machine protection considerations might lead to prefer nominal transverse emittances for safe machine operations. The purpose of this paper is to present the results of controlled transverse emittance blow-ups using the transverse feedback and octupoles. The procedures tested in the SPS in 2008 allow to tune the transverse emittances up to nominal values at SPS extraction.

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

Funding: Work supported by Department of Energy contract DE–AC03–76SF00515 and the US LARP program.

The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consistent with an Ecloud driven instability. While the SPS has a coupled-bunch transverse feedback system, control of Ecloud-driven motion requires a much wider control bandwidth capable of sensing and controlling motion within each bunched beam. This paper draws beam dynamics data from the measurements and simulations of this SPS instability, and develops initial performance requirements for a feedback system with 2-4 GS/sec sampling rates to damp Ecloud-driven transverse motion in the SPS at intensities desired for high-current LHC operation. Requirements for pickups, kickers and signal processing architectures are presented. Initial lab measurements of proof-of-principle lab model prototypes are presented for the wideband kicker driver signal functions.

• B. Salvant
  EPFL, Lausanne
• G. Arduini, H. Burkhardt, H. Damerau, W. Höfle, E. Métral, G. Papotti, G. Rumolo, B. Salvant, R. Tomás, S.M. White
  CERN, Geneva
• R. Calaga, R. De Maria
  BNL, Upton, Long Island, New York

The upgrade of the CERN Large Hadron Collider (LHC) would require a four- to fivefold increase of the single bunch intensity presently obtained in the Super Proton Synchrotron (SPS). Operating at such high single bunch intensities requires a detailed knowledge of the sources of SPS beam coupling impedance, so that longitudinal and transverse impedance reduction campaigns can be planned and performed effectively if needed. In this paper, the transverse impedance of the SPS is studied by injecting a single long bunch into the SPS, and observing its decay without RF. This particular setup enhances the resolution of the frequency analysis of the longitudinal and transverse bunch signals acquired with strip line couplers connected to a fast data acquisition. It also gives access to the frequency content of the transverse impedance. Results from measurements with short and long bunches in the SPS performed in 2008 are compared with simulations and theoretical predictions.

• J.R. Thompson, J.M. Byrd
  LBNL, Berkeley, California
• W. Höfle, G. Rumolo
  CERN, Geneva

Funding: Supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Single and multi-bunch instabilities on bunch trains driven by electron clouds have been observed in the CERN SPS for some years. In this paper, we present initial results to implement a damping system in a computer simulation of a single bunch vertical instability using the HEADTAIL code. The code simulates the interaction between a proton bunch and a uniform electron cloud that has built up inside of the beam pipe. In all simulations we use typical SPS parameter sets for three different values of the beam momentum : 26 GeV/c, 55 GeV/c and 120 GeV/c. The feedback is implemented as a corrective kick calculated from the vertical centroid of each slice of the electron bunch with a one turn delay. The bandwidth of the feedback is varied by filtering the slice information along the bunch. Initial results indicate that the instability can be damped with a minimum bandwidth of 300 MHz with a relatively high gain.