Thermal Strain Exerted on Superconductive Filaments in an ITER Nb₃Sn Strand

Abstract

The Nb₃Sn strands used for the fusion reactor of the ITER are made up of a typical composite material consisting of a brittle superconducting intermetallic compound. Thermally induced strain is inevitably generated in the composite due to different coefficients of thermal expansion and different moduli of elasticity among the constituent components. In order to evaluate the thermal strain exerted on superconductive filaments quantitatively, local strain measurements were carried out during heating and cooling using quantum beams. The stress versus strain curves of the Nb₃Sn strand showed a typical elasto-plastic behavior, which could be numerically evaluated on the basis of the rule of mixture. The local strain exerted on superconductive filaments along the axial direction was compressive at room temperature and tensile at high temperatures. Recently, a numerical method to evaluate temperature dependence was proposed. The present paper reconfirms that the temperature dependence of the thermal strain can be reproduced well using the proposed numerical calculation.