• M.J. Barnes, F. Caspers, T. Kroyer, E. Métral, F. Roncarolo, B. Salvant
  CERN, Geneva

Fast kicker magnets are used to inject beam into and eject beam out of the CERN SPS accelerator ring. These kickers are generally ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. Unless special precautions are taken the impedance of the ferrite yoke can provoke significant beam induced heating, even above the Curie temperature of ferrite. In addition the impedance can contribute to beam instabilities. In this paper different variants of the coaxial wire method, both for measuring longitudinal and transverse impedance, are briefly discussed in a tutorial manner and do's and don'ts are shown on practical examples. In addition we present the results of several impedance measurements for SPS kickers using the wire method and compare those results with theoretical models.

• S. Redaelli, I.V. Agapov, B. Dehning, M. Giovannozzi, F. Roncarolo, R. Tomás
  CERN, Geneva
• R. Calaga
  BNL, Upton, Long Island, New York

Various LHC injection tests were performed in August and early September 2008 in preparation for the circulating beam operation. These tests provided the first opportunity to measure with beam the available mechanical aperture in two LHC sectors (2-3 and 7-8). The aperture was probed by exciting free oscillations and local orbit bumps of the injected beam trajectories. Intensities of a few 10⁹ protons were used to remain safely below the quench limit of superconducting magnets in case of beam losses. In this paper the methods used to measure the mechanical aperture, the available on-line tools, and beam measurements for both sectors are presented. Detailed comparisons with the expected results from the as-built aperture models are also presented. It is shown that the measurements results are in good agreement with the LHC design aperture.

• E. Métral, F. Caspers, A. Grudiev, T. Kroyer
  CERN, Geneva
• F. Roncarolo
  UMAN, Manchester
• B. Salvant
  EPFL, Lausanne
• B. Zotter
  Honorary CERN Staff Member, Grand-Saconnex

The LHC phase 2 collimation project aims at gaining a factor ten in cleaning efficiency, robustness and impedance reduction. From the impedance point of view, several ideas emerged during the last year, such as using dielectric collimators, slots or rods in copper plates, or Litz wires. The purpose of this paper is to discuss the possible choices, showing analytical estimates, electro-magnetic simulations performed using Maxwell, HFSS and GdFidL, and preliminary bench measurements. The corresponding complex tune shifts are computed for the different cases and compared on the stability diagram defined by the settings of the Landau octupoles available in the LHC at 7 TeV.

• B. Salvant
  EPFL, Lausanne
• D. Alesini, M. Migliorati, B. Spataro
  INFN/LNF, Frascati (Roma)
• G. Arduini, C. Boccard, F. Caspers, A. Grudiev, O.R. Jones, E. Métral, G. Rumolo, B. Salvant, C. Zannini
  CERN, Geneva
• R. Calaga
  BNL, Upton, Long Island, New York
• F. Roncarolo
  UMAN, Manchester

A detailed knowledge of the beam coupling impedance of the CERN Super Proton Synchrotron (SPS) is required in order to operate this machine with a higher intensity for the foreseen Large Hadron Collider (LHC) luminosity upgrade. A large number of Beam Position Monitors (BPM) is currently installed in the SPS, and this is why their contribution to the SPS impedance has to be assessed. This paper focuses on electromagnetic simulations and bench measurements of the longitudinal and transverse impedance generated by the horizontal and vertical BPMs installed in the SPS machine.