1. INTRODUCTION RESULTS OF 3D PHOTOGRAMMETRY ON THE CMS BARREL YOKE.pdf

RESULTS OF 3D PHOTOGRAMMETRY ON THE CMS BARREL YOKE R. GOUDARD, C. HUMBERTCLAUDE *1 , K. NUMMIARO CERN, European Laboratory for Particle Physics, Geneva, Switzerland 1. INTRODUCTION Compact Muon Solenoid (CMS) is one of the four new experiments to operate at the Large Hadron Collider (LHC) at CERN (the European Laboratory for Particles Physics) from 2005. The CMS experiment aims to study very high energy collisions of proton beams with the best precision possible. The detector will be built by many separate pieces of structure from the Central Tracker to the End Caps closing both detector heads. This typical onion layout for detectors is shown in figure 1. This paper focuses on the supporting structures called the Barrel Yoke rings [1] that give a magnet of 15 m diameter and 2.5 m width, and their survey by using photogrammetry and the Kodak DCS 460 camera interfaced to the Rollei CDW (Close-range Digital Workstation) software. Also the results of a real photogrammetric measurement of the first full ring in September 1999 in Deggendorf are shown. Figure 1 - The CMS experiment The precision of the particle tracks reconstruction by a detector like CMS depends on the intrinsic precision of sub-detectors and the precise positioning of those sub-detectors within their supporting structures. At CERN, digital photogrammetry has been taken as a main tool for solving the survey problem of the five Barrel Yokes of the CMS magnet. The precision required for one ring is better than 1 mm. The survey is first done at factory in Deggendorf, Germany (Deggendorfer Werft und Eisenbau GmbH) and afterwards at CERN to determine the * Corresponding author 1 Project Associated at CERN, registered in ETHZ (Swiss Federal Institute of Technology Zurich, CH 8092 Zurich, Switzerland) Diam : 14.60 m Length : 21.60 m Total Weight : ~ 14 600 tonnes 5 Barrel Yoke rings geometrical validation during the construction and transportation. An import