Tolerance evaluation of poloidal shear keys for ITER TF coil

There are 18 ITER Toroidal Field (TF) coils structurally linked by friction sections between the coils, four outer inter-coil structures (OIS) and one inner inter-coil structure (IIS). The IIS consists of poloidal circular keys placed directly between the coil cases and there are high stresses in this section. To confirm the stress when realistic values of geometry variations are included, a series of stress FE analyses considering up to 1 mm geometric deviation of the shear key fit for TF coils has been carried out. Based on the analysis results, the acceptable fit limits of each shear key at which it to loses an unacceptable part of its function are proposed. As the first step in assessment of the possible variations in stresses, a finite element model of one TF coil with 18-fold symmetry, including the detailed structure of the IIS, is used in the analysis. In this first analysis we look at the impact of a single key misfit or misalignment of the keyways (which is optimistic, of course all the keys have a simultaneous fitting error), and still with 18-fold symmetry (which is very conservative). The conclusions proposed here are therefore preliminary only and require further assessment.