Influence of the field orientation on the critical current densityof Nb3Sn strands

摘要

In many applications using superconducting cables such as tokamaks for fusion, the angle between the strand axis and the applied field can take values different than 90°. Estimating the critical current value for any angles knowing only its value for the well-known perpendicular orientation at a given field, is very useful. A model is presented that could achieve, for a given material, such a result thanks to an intrinsic parameter, called the anisotropy parameter, defined as the ratio of the axial critical current in a perpendicular field to the azimutal critical current In a parallel background field. To check the model for Nb3Sn, this parameter has been measured on Nb3Sn untwisted strands. We used two methods: one based on magnetic measurements and the other on critical current measurements with several field orientations and strengths. Unexpectedly an anisotropy of the critical current density as a function of the field orientation has been pointed out in these measurements