Assembly Concept and Technology of the ATLAS Barrel Toroid

The ATLAS detector for the LHC collider at CERN requires a large superconducting Barrel Toroid (BT) with overall dimensions of 25 m length, 22 m diameter which is installed in the ATLAS cavern 100m underground. The Barrel Toroid provides the magnetic field for the muon detector. The toroid is assembled from 8 flat race track coils of dimensions 25m
$times$
5m. Following the on-surface acceptance test of the 8 BT coils, they are successively inserted in the underground cavern and assembled as a full toroid by using 16 supporting rings of struts that link the 8 coils to form a rigid and stable structure. The total mass of the toroid is 850 t. Particular issues are that the axis of the toroid has to be horizontal and the final shape of the toroid cylindrical with a tolerance of
$+/-$
10 mm with respect to an overall system diameter of 22 m. The desired shape of the toroid can only be controlled by installing the 8 coils in calculated positions in space (forming an elliptic shaped structure), and by linking them using bolted struts linking the coils. The final release of the structure is done under its self weight hydraulically. This required very large tooling essentially to support all the 8 coils in space in a nearly stress free condition until the toroid supporting rings have been closed. The theoretical positions are found by performing detailed 3-D Finite Element Calculations that predict the shape of the toroid under its operational load. The assembly of this huge toroid is unique and no experience basis exists. This paper presents the concept and technology required for the assembly of the toroid as well as the cryogenic supply lines, highlights the FEA mechanical calculations performed to predict the shape, summarizes the tooling required and reviews the experience gained during the installation.