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Jones, O. R.

Paper Title Page
TUPC098 Results of the LHC Prototype Chromaticity Measurement System Studies in the CERN-SPS 1290
 
  • R. J. Steinhagen, A. Boccardi, T. Bohl, M. Gasior, O. R. Jones, J. Wenninger
    CERN, Geneva
  • K. K. Kasinski
    AGH, Cracow
 
  Tune and chromaticity control is an integral part of safe and reliable LHC operation. Tight tolerances on the maximum transverse beam excursions allow oscillation amplitudes of less than 30 um. This leaves only a small margin for transverse beam and momentum excitations required for measuring tune and chromaticity. This contribution discusses the baseline LHC continuous chromaticity measurement with results from tests at the CERN-SPS. The system is based on continuous tracking of the tune using a phase-locked-loop (PLL) while modulating the beam momentum. The high PLL tune resolution achieved ( ~1·10-6 ) made it possible to detect chromaticity changes well below the nominally required 1 unit for relative momentum modulations of only 2·10-5. The sensitive tune measurement front-end employed allowed the PLL excitation and radial amplitudes to be kept below a few tens of micrometers. These results show that this type of measurement can be considered as practically non-perturbative permitting its use even during nominal LHC operation.  
WEPP056 Aperture Restriction Localisation in the LHC Arcs using an RF Mole and the LHC Beam Position Measurement System 2644
 
  • O. R. Jones, J. Albertone, S. Bartolome-Jimenez, C. Boccard, T. Bogey, P. B. Borowiec, E. Calvo, F. Caspers, M. Gasior, J. L. Gonzalez, B. Jenninger, L. K. Jensen, T. Kroyer, S. Weisz
    CERN, Geneva
 
  Ensuring that the two 27km beam pipes of the LHC do not contain aperture restrictions is of utmost importance. Most of the ring is composed of continuous cryostats, so any intervention to remove aperture restrictions when the machine is at its operating temperature of 1.9K will require a substantial amount of time. On warming-up the first cooled sector, several of the sliding contacts which provide electrical continuity for the image current between successive sections of the vacuum chamber were found to have buckled into the beam pipe. This led to a search for a technique to verify the integrity of a complete LHC arc (~3km) before any subsequent cool-down. In this paper the successful results from using a polycarbonate ball fitted with a 40MHz RF transmitter will be presented. Propulsion of the ball is achieved by sucking filtered air through the entire arc, while its progress is traced every 54m via the LHC beam position measurement system which is auto-triggered by the RF transmitter on passage of the ball. Reflectometry at frequencies in the 4-8 GHz range can cover the gaps between beam position monitors and could therefore be used to localise a ball blocked by an obstacle.