In-Field Evaluation of REBCO Superconducting Joint

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 (
R
_j
) was evaluated to be 9.6 × 10
^–15
Ω and 2.3 × 10
^–14
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,
R
_j
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
R
_j
was order of 10
⁻¹¹
Ω. This relatively higher
R
_j
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.