Preload Experiments on Wendelstein 7X Attachment System of the Superconducting Coils

The attachment system of the Wendelstein 7X (W7-X) superconducting coils joins the coil casing support blocks to similar blocks on the main coil support structure using a high strength stud connection. The joint has to withstand the deadweight and the large electromagnetic loads from the coils; it is designed to comply with the large coil deformations during operation and works at 4 K at the allowable load limits. Preloading tests have been performed to determine the behavior of the connection at room and cryogenic temperatures and to define the preloading to be applied during assembly. A full scale mock-up of a single stud connection has been manufactured. During the experiment execution the attachments system had to be improved in order to achieve a high preload, having a limited space for the fitting elements. The paper describes the tests and summarizes the results obtained