Mechanical Validation of the Support Structure of the Magnet FRESCA2

FRESCA2 is a dipole magnet dedicated to upgrade the present CERN cable test station FRESCA to a nominal bore field of 13 Tesla (T) in a 100 mm clear aperture. This paper reports on the assembly process and the three cool-down tests to cryogenic temperature of the support structure of FRESCA2. This structure is based on an aluminum alloy shrinking cylinder pre-loaded through the use of water-pressurized bladders. To verify the assembly and loading processes, this structure was assembled using full block aluminum alloy “dummy coils” standing for the Nb₃Sn coils. Then, the whole assembled structure was cooled-down to 77 K with liquid nitrogen in a dedicated facility at CERN. The mechanical behavior was monitored at all stages by strain gauges located on different components of the structure. Three cryogenic tests were made by increasing the loading gradually up to values corresponding to the ultimate field of 15 T. The expected stresses within the structure after assembly, loading and cool-down were determined from the 3-D finite-element model of the support structure. A comparison of the model predictions with the strain gauge data is presented.