Toward a standard for critical current versus axial strain measurements of Nb3Sn

Knowledge of the critical current of Nb 3 Sn wires under mechanical loads is increasingly important. In this work, based on an investigation of the bronze Nb 3 Sn reference wire for the international ITER benchmarking, practical aspects of an I c (ε, B ) measurement are discussed and commented on. The use of a helical spring according to Walters et al (1986 Cryogenics 26 406) is favored. It is shown that I c at zero applied strain can be measured precisely, thus contributing to an improvement in the determination of ε m , the strain for the maximum of I c . Further, a new approach for the evaluation of the irreversibility limit, ε irr , is proposed by a detailed analysis of log V versus log I characteristics. Finally some recommendations for an eventual future standard are made.