The electromagnetic calorimeter of ATLAS and its performances

After a period of testbeam in the beginning of the 1990s, the ATLAS collaboration has begun to build a liquid argon/lead electromagnetic calorimeter. Its engineering is a compromise between technical feasibility and optimization of the response to electrons and photons in the LHC environment (especially the channel H→γγ). Special care is taken for a good uniformity over the whole detector. We will describe the final design of the electromagnetic calorimeter with its expected performances.