Results of Magnetic Axis Measurements on a Prototype Main Lattice Quadrupole for the LHC

Abstract

More than 470 twin aperture lattice quadrupoles are needed for the large hadron collider (LHC) under construction at CERN. The lattice quadrupole, assembled with correction magnets in its helium enclosure - the cold mass and integrated in a common cryostat called the short straight section (SSS). All SSS cold mass prototypes have been developed and built by CEA (Saclay) in collaboration with CNRS (Orsay, France). The last SSS prototype (SSS5) was used to investigate the behavior of the magnetic axis through various steps of the installation cycle for the series quadrupoles: including transportation, thermal-cycles, and being lowered into the tunnel. Results of extensive measurements before and after each of these stages are presented here, showing that the effect of transport is weak and within the window of measurement resolution. Also shown is that the long-term stability observed during two years is comparable with the requirements from magnet tolerances. To minimize systematic errors, all tests were performed with two independent measurement systems: single-stretched wire (SSW) and automated scanner. A brief description of these systems is given, concentrating mostly on their accuracies. In addition, establishment of a reliable cold-warm correlation for the magnetic axis position is a very important issue because it can reduce the percentage of cold tests. Though this correlation will be based on proper statistics at the beginning of series production, magnetic axis behavior during thermal-cycle has been investigated for the SSS5 prototype, and these results are also presented.