SNF Issue No. 44, April 2018
Record Critical Current Density with Low Anisotropy in Highly-Textured 122 Iron-based Superconducting Tapes
Figure 4. EBSD images for the superconducting core of the HP tape viewed from the ND direction of the tape. (a) The marked neighboring grains with different colors. (b) The inverse pole figure (IPF) image in  direction. (c) The misorientation angle loaded to the grain boundaries. The color codes of this image are posted out on the bottom right corner of this image. (d) The inverse pole figure in  direction for the measured area.
Superior Performance of Iron-based Superconductors
By using a powder-in-tube method combined with hot pressing procedures, Yanwei Ma’s group from the Institute of Electrical Engineering of CAS at Beijing could further increased the transport Jc to 1.5 × 105 A/cm2 (Ic = 437 A) at 4.2 K and 10 T in Ba1-xKxFe2As2 tapes. The transport Jc measured at 4.2 K under a high magnetic field of 27 T is still on the level of 5.5 × 104 A/cm2 and at 20 K and 5 T is as high as 5.4 ×104 A/cm2. These Jc values are the highest ever reported for iron-based superconducting wires and tapes. The reasons of such high transport Jc achieved in the Ba1-xKxFe2As2 tapes are the high degree c-axis texture and the relatively small and uniformly distributed grains of the superconducting cores.
In addition, the Jc values were also measured at different magnetic field directions, the anisotropy of tapes at 4.2 K and 10 T is 1.37, a value which is much smaller than that of the Bi-2223 and YBCO tapes. These results further strengthen the position of iron-based superconductors as a competitor to other superconductors in high field applications.
Robust High Je RE-Ba-Cu-O Symmetric Tape Round (STAR) Wire for Accelerator Magnets
Soumen Kar, Wenbo Luo, Anis Ben Yahia, Xiaofen Li, Goran Majkic, Venkat Selvamanickam
AMPeers and University of Houston have jointly developed an innovative approach to fabricate round REBCO wires with high Je and good bend strain tolerance . These wires are only 1.6 to 1.9 mm in diameter and are made by winding narrow REBCO tapes on an AWG 18 (1 mm diameter) copper wire former. Such small diameter wires are possible by the use of symmetric tapes where the REBCO film is positioned at the geometric center, close to the neutral axis as shown in figure 1. Such a symmetric tape architecture is achieved by a strategic selection of the thickness of the copper stabilizer to match the thickness of the Hastelloy substrate. The substrate itself is made thin, about 22 µm, so as to enable good tolerance to bend strain. The overall thickness of the REBCO tape is about 45 – 60 μm including the copper stabilizer. Symmetric Tape Round (STAR) wires have been fabricated with six to eight of these REBCO tapes, each about 2-3 mm in width, wound on AWG 18 copper wire former. The optimized STAR wires are found to be mechanically robust and retain 97% of its critical current of over 500 A at 77 K, self-field even when bent to a small radius of 15 mm as shown in figure 2 (photo top left of article).
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