Design and test of the titanium alloy tie rods for the CMS coil suspension system

The Compact Muon Solenoid (CMS) is one of the general-purpose detectors to be provided for the LHC project at CERN. The design field of the CMS superconducting magnet is 4 T, the magnetic length is 12.5 m and the free bore is 6 m. Thirty titanium alloy tie rods are used to support the 225 tonne weight of the cold mass inside its vacuum vessel and react against the forces generated by potential magnetic misalignment. This paper describes the suspension system and its mechanical analysis in different loading cases corresponding to operating conditions of the magnet. Two grades of titanium alloy are foreseen (Ti 6 Al 4 V ELI and Ti 5 Al 2.5 Sn ELI). Based on mechanical tests at room temperature and at 4.2 K, the safety criteria are analyzed for both materials. Before final installation, all tie rods will be tested at 110% of the maximum load with one end at room temperature and the other one at cryogenic temperature. The test system and the test results of the prototype tie rods are also presented.