Fabrication of small superconducting coils using (Ba,A)Fe₂As₂ (A: Na, K) round wires with large critical current densities

Abstract

We report the fabrication of small (Ba,A)Fe 2 As 2 (A: Na, K) coils using 10 m-class long round wires, fabricated by powder-in-tube (PIT) method. Coils are sintered using hot-isostatic-press (HIP) technique after glass-fiber insulations are installed. Critical current (I c ) of the whole coil using (Ba,Na)Fe 2 As 2 and (Ba,K)Fe 2 As 2 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)Fe 2 As 2 wires picked up from the coil reach 54 kAcm −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 .

Fabrication of superconducting coils and (Ba,A)Fe2As2 (A:Na, K) long round wires with large superconducting cores

“…In the case of the (Ba,K)Fe 2 As 2 wire, OD and ID of Cu and Ag tubes are 3.0 mm and 2.0 mm, and 4.5 mm and 3.0 mm, respectively. Expected size of superconducting core is the same to that in the previous report [14]. On the other hand, for (Ba,Na)Fe 2 As 2 wire with larger superconducting core, OD and ID of Cu and Ag tubes are 4.0 mm and 3.0 mm, and 6.3 mm and 5.3 mm, respectively.…”

“…As shown in Fig. 3, transport J c under the magnetic field of 10 T of the wires picked up from the (Ba,K)Fe 2 As 2 coil at ~8.5 m reaches 49 kAcm −2 at 4.2 K. This value is slightly larger than the previous largest value of J c of 47 kAcm −2 of the (Ba,K)Fe 2 As 2 round wire [13], although it is smaller than that of 54 kAcm −2 of the (Ba,Na)Fe 2 As 2 round wire [14]. It is demanded that homogeneous long wire with high J c in the whole length of the wire should be fabricated.…”

“…3. Reported highest transport J c of the round wire of both (Ba,K)Fe 2 As 2 and (Ba,Na)Fe 2 As 2 are also plotted [13,14]. As shown in Fig.…”

Critical Current Density and Vortex Dynamics in Pristine and Irradiated KCa2Fe4As4F2

“…As discussed above, suppression of T c and the dose dependence of J c in 2.6-GeV U-ion or 3 MeV protonirradiated KCa 2 Fe 4 As 4 F 2 are different from those in typical IBS of (Ba,K)Fe 2 As 2 , which can be explained by considering the embedded defects in pristine KCa 2 Fe 4 As 4 F 2 . It should be emphasized that maximum J c in KCa 2 Fe 4 As 4 F 2 is larger than that in 122 compounds, which have been extensively studied as raw materials for wires and tapes for future high-field applications [44][45][46]. Fabrications of wires and tapes of KCa 2 Fe 4 As 4 F 2 are demanded.…”

High-Frequency ac Susceptibility of Iron-Based Superconductors

“…Since 2006, when iron-based superconductors (IBSs) were discovered [ 1 ], they raised great interest both from a fundamental point of view and for application-oriented research [ 2 , 3 ]. Throughout the years, new IBS “families” came into play, sharing some common intriguing features [ 4 ], such as their multiband nature [ 5 ], unconventional pairing [ 6 , 7 ], and nontrivial pairing symmetries [ 8 ], and for these reasons they are currently the object of an intense study effort by research groups throughout the world.…”