INFLUENCE OF THE FIELD ORIENTATION ON THE CRITICAL-CURRENT DENSITY OFNB3SN STRANDS

In many applications using superconducting cables such as tokamaks for fusion, the angle between the strand axis and the applied field can t ake values different than 90 degrees, Estimating the critical current value for any angles knowing only its value for the well-known perpend icular orientation at a given field, is very useful, A model is presen ted that could achieve, for a given material, such a result thanks to an intrinsic parameter, called the anisotropy parameter, defined as th e 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 orientat ions and strengths, Unexpectedly an anisotropy of the critical current density as a function of the field orientation has been pointed out i n these measurements.