Two 100 m Invar® Transfer Lines at CERN : Design Principles and Operating Experience for Helium Refrigeration

The distribution of helium for the Large Hadron Collider (LHC), at CERN, will require a large variety of transfer lines. At the time of qualification of possible technologies, Invar® was investigated as potential material for internal tubes. Intensive developments were made in industry to qualify the use of Invar® M93 and its associated welding parameters. Although all tests showed good perspective, the risk associated with the lack of proven reference turned out to be dissuasive with respect to the possible cost savings for the LHC cryogenic system. However, since DN100 transfer lines were necessary for the supply and return of a test facility over a distance of 100 m, an Invar® based solution was considered, as repair or exchange would have been less dramatic than in the LHC accelerator tunnel. After recalling the technical requirements, the required material qualification will be presented as well as the design principles and operating features. This equipment has been first cooled-down to 4.5 K and accepted in 2001. More than sixty complete thermal cycles from 300 K to 4.5 K have been performed since then without change of performance including helium leaktightness.