Nonlinear elastic-plastic analysis of Ignitor TF coils and their support structure

This paper discusses a feasibility study of the Ignitor fusion device conceptual design. Unique features of the design are 1) wedge-shaped sectors to facilitate assembly and maintenance, 2) precompression of entire device using circumferential loading rings to minimize external support, and 3) use of high confinement and elastic-plastic analysis techniques to permit use of low strength oxygen-free high-conductivity (OFHC) copper for toroidal field (TF) coils. This provides an economical and functional advantage over current high strength copper coils. The finite element code, ANSYS, was used with an axisymmetric model in the analysis. The TF coils and support structure were modeled using isoparametric elements with plasticity considered in the case of the coils. Nonlinear, friction resisting, interface elements were used to model the interaction between individual component parts. These same nonlinear spring elements were also used to produce the compressive effects of the circumferential loading rings. To ensure convergence in the plastic range, electromagnetic and thermal loads were applied at steps of varying increments. The values of stress and strain for each element and exaggerated deformation plots for the model were obtained at each load step. The results of this analysis verified the practicality of the loading ring preload concept and the acceptability of low-strength copper coils when adequately confined