Influence of the field orientation on the critical current density of Nb/sub 3/Sn strands

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/spl deg/. 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 Nb/sub 3/Sn 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.