The Short Model Coils working group was set in February 2007 within the context of the Next European Dipole (NED) Joint Research Activity. The aim of the collaborative program is to design, manufacture and test Nb3Sn racetrack subscale coils in dipole configuration. An adapted support structure will be used to perform training studies while investigating pre-stress influence on coil behaviour and quench triggering. It needs to have the ability to apply very high as well as very low pre-stresses on the coil pack, in the three directions. Such a system should help define the mechanical stress limit on different coil pack configurations with innovative insulations. SMC studies will utilise the experience of Berkeley?s SD01 subscale coil, which is pre-stressed by a shell-based structure and is using bladders and keys.
This paper details the initial magnetic optimization of the test structure. It describes the magnetic field specifications and their consequences on the coil parameterization and design. After cross-checking 3D nonlinear models using up to four different finite elements codes (CAST3M, ANSYS, OPERA, ROXIE), the reasons behind the chosen coil parameters are given. The optimization exercise has led to a redesign of the coil, to use iron surrounding parts and to make use of four end spacers to get a peak field higher than 13 T located on conductor, in the centre of the straight section, with high uniformity.