Experience report of the manufacture of the 25 meter long double pancakes for the ATLAS Barrel Toroidal Magnet

The magnet system of the ATLAS detector, which presently is being installed in the LHC accelerator at CERN, consists of four components: the inner Solenoid, two End Cap Toroids and the Barrel Toroid (BT). The Barrel Toroid is composed by 8 separated superconducting coils, race-track shaped, 25 m long and 5 m large, each containing two superconducting windings referred as double pancakes. At the present time all the 8 coils have been completed and independently tested on surface under nominal conditions, and the final assembly of the toroid in the ATLAS cavern is in progress. The construction of double pancakes of unprecedented size has required a great effort in order to match the tight design dimensional tolerances and to obtain a good impregnation quality. In this paper we summarize the most relevant features of the manufacturing process of the double pancakes and the results of the measurements performed to guarantee the geometrical, impregnation and electrical quality. These data can be now considered as the "status of the art" for large size superconducting coils