High transportJ_cin magnetic fields up to 28 T of stainless steel/Ag double sheathed Ba122 tapes fabricated by scalable rolling process

Abstract

Abstract:The recently discovered iron-based superconductors with very high upper critical field (H c2 ) and small anisotropy have been regarded as a potential candidate material for high field applications. However, enhancements of superconducting properties are still needed to boost the successful use of iron-based superconductors in such applications. Here, we propose a new sheath architecture of stainless steel (SS)/Ag double sheath and investigate its influence on the microstructures and J c -H property.We found that the transport J c -H curves for rolled and pressed tapes both show extremely small magnetic field dependence and exceed 3×10 4 A/cm 2 under 28 T, which are much higher than those of low-temperature superconductors. More interestingly, 12 cm long rolled tape shows very high homogeneity and sustains J c as high as 7.7×10 4 A/cm 2 at 10 T. These are the highest values reported so far for iron-based superconducting wires fabricated by scalable rolling process. The microstructure investigations indicate that such high J c was achieved by higher density of the core and uniform deformation resulting better texturing. These results indicate that our process is very promising for fabricating long Ba122 wires for high field magnet, i.e. above 20 T.* Author to whom correspondence should be addressed; E-mail: KUMAKURA.Hiroaki@nims.go.jp 2The recently discovered iron-based superconductors have attracted great interest as a subject of both fundamental study and practical applications [1][2][3][4][5][6][7][8][9]. Among the various iron based superconductors, 122-type (AE)Fe 2 As 2 (AE = Sr, Ba) is very attractive for high field applications due to its excellent properties such as very high upper critical field (H c2 ), relatively small anisotropy [10,11], and an advantageous grain-boundary nature [12]. In order to achieve high critical current density (J c ) various processing techniques have been used [13][14][15][16][17][18]. Among these proposed processes, the powder-in-tube (PIT) method seems the most promising technique for practical applications [19][20][21]. Thus, the Ba(Sr)122 PIT wires have been investigated intensively [22][23][24][25][26][27][28][29][30][31], and high J c exceeding the level of 10 4 A/cm 2 at 4.2 K and 10 T has been reported for short samples prepared by applying uniaxial pressing [32][33][34][35].However, unfortunately, pressing processes are usually applicable only for a short sample and it is difficult to attain such high J c values with good reproducibility. For practical applications, it is desirable if high J c values are attained with good reproducibility by rolling, which is easy to scale up to the long length wire production.Although silver looks the most suitable sheath material for 122 phase, there are a number of drawbacks of using pure Ag as the sheathing material: poor mechanical properties after the heat treatment that make the coil winding difficult and limit its ability to support Lorentz forces in high magnetic fields, and high occurrence of sausaging during mechan...

Doping-dependent critical current properties in K, Co, and P-doped BaFe2As2 single crystals

“…Based on the collective pinning model [42], the condition that the above formulas are applicable is H < BSB ~ 5(Jc/Jd)Hc2, where Jd is the depairing current. In the case of K-Ba122 (x = 0.30), BSB is estimated as ~1.5 T using Jc ~ 6 × 10 5 The blue-dashed and the red-dashed curves are the contributions from the Tc pinning and the l pinning, and the black-dashed curves are their sums, respectively. For x = 0.23, the l pinning is larger than the Tc pinning at low T. With increasing T, the Tc pinning increases, and becomes dominant at T > 10 K.…”

“…To evaluate their current carrying ability, various experiments have been carried out so far. In most cases, encouraging results have been obtained, such as a high Jc exceeding 10 5 A/cm 2 even under high-Hs above 10 T [4,5], a moderate anisotropy of Jc in superconducting tapes with respect to the direction of the applied H [6,7], superior inter-grain connectivity [8], etc. It was also demonstrated that the introduction of artificial pinning centers by irradiation with heavy-irons, neutrons, electrons, etc.…”

Enhancement of critical current densities in (Ba,K)Fe2As2wires and tapes using HIP technique

“…Mainly, two pressing methods for the fabrication of IBS wires and tapes have been proven to be effective in enhancing J c , namely, uniaxial pressing for the tape [32][33][34][35][36] and hot isostatic pressing (HIP) for round wires [21,23,39,40]. Although uniaxial-press method has realized the highest J c value, it cannot be used for the fabrication of round wires.…”

Critical current density and microstructure of iron sheathed multifilamentary Sr1−xKxFe2As2/Ag composite conductors

“…Previously, monofilamentary PIT Sr(Ba)-122/Ag composites conductors with iron [19,20], copper [21,22] and stainless steel [23] conductors with large filament number and very fine filaments are needed in order to reduce the AC loss induced by the eddy currents in metallic matrix and the interfilamentary coupling currents [18]. Therefore, in this work, 7-， 19-and 114-filament Sr-122/Ag/Fe composite conductors were prepared.…”