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

Knowledge of the critical current of Nb3Sn wires under mechanical loads is increasingly important. In this work, based on an investigation of the bronze Nb3Sn reference wire for the international ITER benchmarking, practical aspects of an Ic(e,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 Ic at zero applied strain can be measured precisely, thus contributing to an improvement in the determination of em, the strain for the maximum of Ic. Further, a new approach for the evaluation of the irreversibility limit, eirr, is proposed by a detailed analysis of logV versus logI characteristics. Finally some recommendations for an eventual future standard are made.