The dependence of superconducting properties of Nb3Sn tapes on the mechanical stresses

We have made experiments to decide the optimum winding tension in constructing high field magnets, using Nb3Sn tape of I.G.C. as material. The samples have been stressed uniaxially at room temperature and measured at liquid He temperature. When those tapes are cooled down to liquid He temperature there the thermal stress (or strain) are derived from the difference of the thermal expansion of components materials (Nb, Nb3Sn, Solder, Cu) Nb3Sn layer is under compressional stress for this effect and experimences degradation of T sub(c). The degradation coefficient of T sub(c) (delta T sub(c)/delta p) was found to be -0.16 x 10-3 K/Atm. The degradation of I sub(c) on the tensile stress are observed even in elastic region and it is conjectured that the region of this effect is exsistence of the solder layers and the lower elastic limit of Cu layers compared with that. Guided by the above obtained results we have manufactured a magnet with the low winding tension (-- 60 kg/cm2) and have already achieved field of 11.7 T. (auth.)