Joint resistances between two parallel high Tc superconducting tapes

Eight different types of joining between two parallel high Tc superconducting (HTS) tapes were prepared and current-voltage (I-V) characteristic curves were investigated at 77 K, liquid nitrogen temperature. Contact resistances of joint parts with 25 mm in length were estimated from I-V curves. Lowest contact resistance among eight samples having different types of joining was 0.497 μΩ. The best joining method is to do crossly joining with HTS tapes on two parallel HTS tapes after filling solder paste into their gap. In this case, lowest joint resistance was 0.15 μΩ at 77 K and 0.05 μΩ at 28 K. Joule heat of a joint sample generated at 30 K and at 100 A was calculated 0.492 mW. Also, in I-V curve of samples crossly joined with HTS tapes, it was found that joint resistance does not depend on variation of magnetic fields (0∼7000 G) at 77 K. From consideration of Joule heat generation, such joining method is available for fabricating the field winding of superconducting rotating machine.