A high precision X-ray tomograph for quality control of the ATLAS Muon Monitored Drift Tube chambers

The ATLAS collaboration has recently started the construction of its detector for the LHC at CERN. An essential part of its Muon Spectrometer is based on Monitored Drift Tube (MDT) technology. It consists of about 1200 large muon drift chambers that will be built at 13 institutes spread all over the world. The MDT chambers require an exceptional mechanical construction accuracy of better than 20 μm. The construction quality of the chambers is controlled using X-ray tomography. A dedicated X-ray tomograph has been developed at CERN since 1996. This instrument measures the chamber wire positions with a 2 μm statistical and 2 μm systematic uncertainty over the full tomograph working area of 2.2 × 0.6 m². During the four-year construction phase of the MDT chambers, the X-ray tomograph will be the key tool for ensuring consistent chamber production quality with a sampling rate of ∼15%. To achieve this program efficiently, an effort for complete automation of the tomograph operation is underway. Since mid-2000, first modules from 11 of the construction sites have been measured. Results from this site certification process have demonstrated the essential role of the X-ray tomograph in assessing the validity of the various construction steps.