CERN-ACC-2014-0033 19/02/2014 3PoAF 1 Assembly, Loading, and Cool‐down of the FRESCA2 Support Structure J. E. Muñoz Garcia, C. Giloux, D. T. Ziemianski, F. Rondeaux, G. de Rijk, H. Bajas, J. M. Rifflet, J. C. Perez, M. Durante, M. Charrondiere, M. Bajko, M. Devaux, M. Guinchard, P. Ferracin, P. Fessia, P. Manil Abstract — 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. Index Terms—dipole, EuCARD, magnet, Nb 3 Sn, superconducting accelerator magnet. I. INTRODUCTION he European Coordination for Accelerator Research and Development (EuCARD [1]) aims at new concepts and technologies for upgrading European accelerators: the High Field Magnet task [2] focuses on designing, building and testing a dipole magnet with operational flux density of 13 T in a 100 mm bore. This 1.5 m long dipole called FRESCA2 will be used to upgrade the FRESCA test facility at CERN, fulfilling the need to qualify conductor at higher fields. Following the description in detail about the design of this magnet in [3], the present paper summarizes the status of the mechanical characterization of the FRESCA2 support structure; describing the first assembly and pre-loading with Al dummy coils. Strain gauge data measurements were obtained at all stages then compared with expected stress values issued from Ansys calculations. The whole assembled structure was cooled down to cryogenic temperature. We report on the comparison of the experimental strain gauge measurements with the expected FEM strain values. An overview of the magnet development status is given in [4]. Manuscript received on July 17 TH , 2013. The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579. J. E. Muñoz Garcia, C. Giloux, D. T. Ziemianski, G. de Rijk, H. Bajas, J. C. Perez, M. Charrondiere, M. Bajko, M. Guinchard, P. Ferracin and P. Fessia are with CERN CH-1211 Geneva 23, Switzerland (corresponding author phone +41 2276 62001; e-mail jorge.enrique.munoz.garcia@cern.ch). F. Rondeaux, J. M. Rifflet, M. Durante, M. Devaux and P. Manil are with CEA Saclay, 91191 Gif-sur-Yvette, France II. MECHANICAL DESIGN A. Cross-section The cross-section of FRESCA2 is shown in Fig. 1. The 100 mm aperture is given by the assembly of two inner central posts, without any additional component. Titanium alloy has been chosen in the central region because of its high strength, also in tension, and for its thermal contraction behaviour; the iron post comes from magnetic considerations. The coil is surrounded by pads in the horizontal and vertical directions. These pads transfer forces to the outside split iron yoke through keys mostly in the perpendicular directions. These forces on the iron are contained by a 65 mm thick Al alloy cylinder (shell). Two lateral keys per side are used: in this way, the forces are better aligned with the coil, especially around the ends. Fig. 1. FRESCA2 magnet cross-section The mechanical structure was based on the bladder and key concept, approach developed at LBNL [5] and successfully used in several model magnets. Pre-stress of the coil is provided during cool-down through most of the shrinkage of the shell, and the Lorentz forces will tend to separate the coils during powering. The mechanical design aims at providing adequate pre-stress to the coil, in particular limiting peak stresses at cryogenic temperatures and maintaining the cable under compression along the central posts at the nominal current, providing loading also at full Lorentz forces. The horizontal pad is made of stainless steel; the vertical pad is made of two parts: a stainless steel plate in contact with the coil and an iron insert along the straight section. Ferromagnetic components are shown in Fig. 1: the central post, part of the vertical pad and the yoke. The main effect of the iron in the vertical pad and in the yoke is to increase the field in the aperture for a given current. The mass T