A Bi-2223 Layer-Winding Coil Using 540 m Tape Including a Joint Inside the Winding

Abstract

High Temperature Superconductors (HTS) are now widely used in many applications such as power transmission cables, motors, etc. Recent (Bi,Pb) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (Bi-2223) conductors have been much improved in transport and mechanical properties, and their application as insert coils for high field generation is expected. In order to demonstrate the feasibility and the potential of Bi-2223/Ag tapes for magnet applications, we fabricated a layer-wound coil using Bi-2223/Ag/Cu-alloy tapes. We used two tapes, 330 m- and 210 m-pieces, in order to examine the possibility of extension of conductor length through a lap-joint inside the coil. These two tapes were soldered without removing Cu-alloy laminations. The winding has the dimensions: inner dia. 57.1 mm, outer dia. 88.9 mm, coil height: 153.9 mm, 44 layers (2,355 turns). We tested this coil at 4.2 K in 0 ~ 12 T. The test coil carried 193.3 A (0.1 μV/cm criterion) and generated 3.3 T in the axial direction of the coil in external 12 T (15.3 T in total). The critical current is close to the short sample performance in the perpendicular fields. Splice resistance at the joint stayed about 1 μΩ at 4.2 K, 10 T.