Fabrication of multi-filament(Ba,A)Fe 2 As 2 (A: Na, K) HIP round wires and a small superconducting coil

We report the fabrication and systematic characterizations of multi-filament (Ba, A )Fe 2 As 2 ( A : Na, K) round wires processed under high pressure. The evaluated transport and magnetic critical current density show clear core-number dependence. This trend originates from degradation of the superconducting core during the wire-drawing process, degradation of the concentric texturing of the core, and the enhanced sausaging effect of the core (revealed by x-ray tomography) as the number of cores increases. Details of the characterizations and suggestions for the improvement of the fabrication process are discussed. We constructed a superconducting magnet using seven-filament (Ba,K)Fe 2 As 2 hot-isostatic pressed round wires. The generated magnetic field and critical current ( I c ) of the coils at 4.2 K are 1.0 kOe and 18 A, respectively. Measurements of the I c of short segments picked up from the coil show that there is enough room for improvements.