Fabrication effects on the structural behaviour of large coils for fusion experiments

Field coils for fusion experiments are usually manufactured by winding straight bars to the required contour. The structural behaviour of such coils, especially noncircular coils, due to the winding process is investigated. First, the residual stresses induced by winding of the conductors and the ensuing spring-back are analysed theoretically for the single unconnected turn. The effects of tension forces applied during winding are considered, as well as the effect of rollers. Comparison with experimental value is given. The expressions derived for the single turn are extended to finite element analyses to find the spring-back deformation of the complete coil. Estimates are given for the stresses in the inter-turn insulation layers due to residual stresses from winding. Recommendations are deduced from the analytical results as regards the set-up of bending tests. (Auth.)