In-Field Evaluation of REBCO Superconducting Joint

Abstract

Joint resistance and current-carrying capacity of the intermediate grown superconducting (iGS) joint were evaluated at temperatures at 4.2 K and 77 K in magnetic fields up to 3 T. The evaluations were done using the joint resistance evaluation system that we have developed. This system utilizes a current decay method. We have improved sensitivity and quantitativeness of the current measurement using a split-core current transformer with a Hall sensor. The joint resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ) was evaluated to be 9.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–15</sup> Ω and 2.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–14</sup> Ω at 4.2 K in self-field and in 3 T, respectively. The residual currents were 306 A in self-field and 296 A in 3 T. This indicates that the iGS joint has sufficiently high current-carrying capacity at 4.2 K in 3 T. In addition, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> of the iGS joint does not show magnetic field dependence up to 3 T at 4.2 K. At 77 K, the injected currents rapidly decreased and evaluated in-field <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> was order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−11</sup> Ω. This relatively higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> is considered to be due to a high load factor of ∼100% at the joint. However, the residual current was observed even in 3 T, which indicates that the iGS joint can be used above 4.2 K in magnetic fields.