Author: Aquilina, N.
Paper Title Page
WEEPPB014 The Magnetic Model of the LHC during the 3.5 TeV Run 2194
  • E. Todesco, N. Aquilina, M. Giovannozzi, M. Lamont, F. Schmidt, R.J. Steinhagen, M. Strzelczyk, R. Tomás
    CERN, Geneva, Switzerland
  • N.J. Sammut
    University of Malta, Information and Communication Technology, Msida, Malta
  The magnetic model of the LHC is based on a fit of the magnetic measurements through equations that model the field components (geometric, saturation, persistent) at different currents. In this paper we will review the main results related to the magnetic model during the run of the LHC in 2010-2011: with a top energy of 3.5 TeV, all components of the model but the saturation are visible. We first give an estimate of the reproducibility of the main components and multipolar errors as they can be deduced from beam measurements, i.e. orbit, tune, chromaticity, beta beating and coupling. We then review the main results relative to the decay at injection plateau, dependence on powering history, and snapback at the beginning of the ramp for both tune and chromaticity. We discuss the precision obtained in tracking the magnets during the ramp, where the persistent current components gradually disappear. We conclude by presenting the behaviour of the quadrupoles model during the squeeze. A list of the major changes implemented during the operation together with what are considered as the main open issues is given.  
THPPD025 Expected and Measured Behaviour of the Tune in the LHC Operation at 3.5 TeV 3554
  • N. Aquilina
    CERN, Geneva, Switzerland
  The tune of the Large Hadron Collider depends on the strength of the quadrupole magnets, the b2 component in the main dipoles plus the b3 component in the main dipoles and the sextupolar correctors via feed down in case of systematic misalignment. The magnetic model of the machine, based on a fit of magnetic measurements, has an intrinsic precision which can be estimated in a few units. During the first years of operation of the LHC, tune has been routinely measured and corrected through a feedback system. In this paper we reconstruct from the beam measurements and the settings of the feedback loop the evolution of tune during injection, ramp, and squeeze. This gives the obtained precision of the magnetic model of the machine with respect to quadrupolar and sextupolar components. At the injection plateau there is an unexpected large decay whose origin is not understood: we present the data, with the time constants and the dependence on the previous cycles, and compare to the magnetic measurements. During the ramp the tune drifts by about 0.05: this precision is related to the precision in tracking the quadrupolar field in the machine.