Mechanical validation of the support structure of the Nb 3Sn magnet FRESCA2

International audienceFRESCA2 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 ldquodummy coilsrdquo standing for the Nb 3Sn 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

Assembly, Loading, and Cool‐down of the FRESCA2 Support Structure

This paper reports on the assembly process and cool-down to cryogenic temperature of the support structure of FRESCA2, which is a dipole magnet for upgrading the actual CERN cable test facility FRESCA. The structure of the FRESCA2 magnet is designed to provide the adequate pre-stress, through the use of keys, bladders, and an Al alloy shrinking cylinder. In order to qualify the assembly and loading procedures, the structure was assembled with Al blocks (dummy coils) that replaced the brittle Nb$_{3}$Sn coils, and then cooled-down to 77 K with liquid nitrogen. The evolution of the mechanical behaviour was monitored via strain gauges located on different components of the structure (shell, rods, yokes and dummy coils). We focus on the expected stresses within the structure after assembly, loading and cool-down. The expected stresses were determined from the 3D finite element model of the structure. A comparison of the 3D model stress predictions with the strain gauge data measurements is made. The coherence between the predicted stresses with the experimental gauge measurements will validate the FEM model of the structure

Test Set-Up for the Cooling of Heavy Magnets by Controlled Way Down to 77 K

In the scope of the High Field Magnets work package of the European FP7-EuCARD project, the structure of the future dipole magnet RMC and FRESCA2 has been tested at liquid nitrogen temperature replacing the actual Nb$_{3}$Sn-based coils by aluminium dummy coils. Such test aims at measuring during the cooling the evolution of the mechanical stresses and the temperatures via compensated strain gauges and carbon-ceramic sensors placed at various locations on the structure (shell, rods, yokes, dummy coils). These measurements help assess the thermo-mechanical behaviour of the assembly for different applied pre-stresses and validate the finite element simulation of the magnet cooling before including the definitive brittle Nb$_{3}$Sn coils. For this purpose, a specific cool-down/warm-up nitrogen test station has been built up at CERN in order to control the required maximum temperature gradient in the magnet during both cooling and warming. In this paper, we present in detail the test facility, the instrumentation along with the automatic process control system. An analytical approach computing the expected temperature evolution during a thermal cycle is introduced and the temperature measurements related to the magnets cooling down to 77 K and warm up to room temperature are presented