Precision emittance measurements in LEP with imaging telescopes, comparison with wire scanner and x-ray detector measurements

Three devices : Synchrotron light Telescopes, Wire Scanners and non imaging X-Ray detectors measure the electron and positron beam emittances in LEP. The particular design features which allow to measure with precision the beam emittance with the Synchrotron Radiation Telescopes are described. The results of comparative measurements with the three instruments and an experimental detector are given, and the importance of the measurement and knowledge of the betatron functions is stressed.