The aluminization of 600 k WLS fibers for the TileCal/ATLAS/LHC

The TILE CALorimeter, the hadronic sampling calorimeter of ATLAS/LHC/CERN, is made of iron and polystyrene scintillating tiles. The light produced in scintillating tiles is absorbed and guided to the photomultipliers (PMTs) through wave length shifter (WLS) optical fibers. To optimize the detection of jets and muons, the top of the fibers away of the PMTs is coated with an aluminum mirror, that increases the light output in ≃ 75% and enhances the uniformity light output by ≃ 10%. The aluminum mirror is produced by magnetron sputtering, that adds to an excellent reproducibility a minimal thermal aggression important for proper film adhesion to the plastic surface. A dedicated machine for mass production of the ATLAS WLS aluminized fibers has been designed and constructed fulfilling the critical production optical and time requirements. The aluminization of the fibers and their quality control started in August 1999 and went on continuously until May 2002. The quality control results showed a reproducibility over the optical characteristics of the fibers that fully accomplish the ATLAS requirements.