The Barrel Toroid Magnet is part of the Magnet System of the ATLAS Detector for the LHC. It consists of eight flat superconducting coils and will extend over a length of 26 meters with an inner bore of 9 meters and an outer diameter of 20 meters. The whole magnet structure is made of aluminium or aluminium alloys, and is subjected to a high level of strain induced by the Lorenz forces. In order to ensure the reliability of the magnet an innovative process for the prestressing of the windings in the coil casing has been develloped at DAPNIA/STCM Saclay. The paper explains this process and reviews the developments undertaken at Saclay to qualify the materials and predict the remaining level of stress at the operating temperature (4.8 K).
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