Angle-Dependent U(I) Measurements of HTS Coated Conductors

Abstract

Increasing magnetic fields generated by pure superconducting high field magnets to greater than 25 T is not possible with the LTS NbTi and NbSn conductors that are currently used. Therefore, the next step is to use the HTS REBCO-CC, which has a greater critical current density, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , at higher magnetic fields. Because of the anisotropy of this type of superconductor, its critical properties change according to its orientation with respect to an external magnetic field and therefore further analysis is necessary before these REBCO conductors can be used for a high field insert coil within the experimental facility HOMER II. To study the effect of orientation and magnetic field strength, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> ) measurements of several commercial CCs were carried out in our JUMBO facility in a free bore of 100 mm and magnetic field up to 10 T at 4.2 K and 77 K. The angle between the applied field and the normal vector to the tape can be adjusted between 0 and 180°. The resulting <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> ) curves were approximated by various mathematical models using Matlab software, and from these the parameters describing the angular dependence of the critical current, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , were determined. Three-dimensional surface plots of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> as a function of angle and field strength were produced and a suitable fit found. The fitted function was then extrapolated up to 30 T to enable the determination of the behavior of the superconductor in the high field region.