Fabrication Of Small Superconducting Coils Using (Ba,A)Fe2as2 (A: Na, K) Round Wires With Large Critical Current Densities

We report the fabrication of small (Ba,A)Fe2As2 (A: Na, K) coils using 10 m-class long round wires, fabricated by the powder-in-tube method. Coils are sintered using the hot-isostatic-press technique after glass-fiber insulations are installed. Critical current (I (c)) of the whole coil using (Ba,Na)Fe2As2 and (Ba,K)Fe2As2 are 60 A and 66 A under the self-field, and the generated magnetic fields at the center of the coil reach 2.6 kOe and 2.5 kOe, respectively. Furthermore, the largest transport critical current density (J (c)) and I (c) in (Ba,Na)Fe2As2 wires picked up from the coil reach 54 kA cm(-2) and 51.8 A at T = 4.2 K under a magnetic field of 100 kOe, respectively. This value exceeds transport J (c) of all previous iron-based superconducting round wires. Texturing of grains in the core of the wire due to the improvement of the wire drawing process plays a key role for the enhancement of J (c).