Development of New Conductors of the Cable-in-Conduit Type for HTS Coils with High Performances

A new type cable-in-conduit conductor composed of HTS tapes was proposed as a winding for high performance HTS coils with high current capacities and low ac losses. In the fabrication of the conductor, the twist of stacked tapes around their axes was made before inserting them inside conduits. The twist angle should be changed continuously along the axis to reduce face-on orientated magnetic fields applied to the tape in the winding conductor during coil operation. In order to confirm the high current capacity of this type conductor, two single-layered solenoidal coils wound with sample conductors composed of 5 stacked Bi-2223 tapes with bias angles of 20 and 0 degrees were fabricated and tested in liquid nitrogen. A copper magnet system was used in this experiment to generate the spread magnetic field with a spread angle of 20 degrees from the coil axis to the radial direction, which simulates the profile of magnetic fields near the edge windings of practical coils. A large improvement on critical-currents degradation affected by spread magnetic fields was successfully observed for the test coil wound with the 20-degree bias conductor.