Fabrication and testing of different low resistance HTS tape joints for magnet applications

Technical High temperature superconducting (HTS) tapes are commercially available for various magnet applications. Its higher tensile strength gives rise to strain tolerance and hence can be used for winding of smaller diameter coils. HTS magnets usually consist of a number of spirals/pancakes to be connected in series through low resistance joints for the magnetic field generation. The most crucial component in making an inter-pancake joint is to make with minimum electrical joint resistance. The joining of two HTS tapes is crucial because of their structural design of materials, which are prone to deterioration, if exposed to a higher critical strain and temperature. In the present case, Pb-Sn (60% lead and 40% tin) solder material of melting point around 188°C is used for the fabrication of different joint configurations. Joints are prepared with and without SS sheath by mechanical etching for BSCCO tapes. Resistances of these joints were measured using four probe methods at 77 K and 10 K. The lowest joint resistance of 120 nano Ohm without SS sheath with parallel overlap length of 100 mm achieved at 77 K, and 47 nano Ohm at 10 K, Self-field. In this presentation, various types of joint configurations viz. overlap; parallel overlap, inclined bridge, perpendicular bridge & spiral with Di-BSCCO, BSCCO and YBCO, REBCO tapes and measured joint resistances have been reported. (author)