Development of 1 m HTS conductor using YBCO on textured metal substrate
Introduction
A high temperature superconducting (HTS) cable using YBa2Cu3O7−x coated conductors (YBCO tapes) has been developed for the increasing demand for electricity in the near future. YBCO tapes maintain higher critical current (Ic) in a high magnetic field and are expected to be applied to various electrical applications, such as power cables, transformers, and current limiters. Recently there has been great progress in the manufacturing of YBCO tapes several 100 m long and high Ic over 300 A. The HTS cable using YBCO tapes is in the advanced stage of development. HTS conductors composed of YBCO tapes using ion-beam assisted deposition (IBAD-type YBCO tapes) were fabricated, and the low AC loss was evaluated [1], [2], [3]. On the other hand, YBCO tapes on a textured metal substrate are often preferred to IBAD-type YBCO tapes in terms of cost reduction [4]. However, textured metal substrates are magnetic, and their magnetic properties can influence the increase in AC loss. The purpose of this paper is to fabricate 1 m HTS conductors and to evaluate the AC loss using YBCO tapes with magnetic substrates.
Section snippets
Specifications of 10 m long YBCO tape
The Ni–5 at.%W substrates were prepared by cold rolling following hot extrusion. Billets 40 mm in diameter were extruded to rods, and then the rods were rolled into tapes with a total reduction of 90% or more. The final tape thickness was 100 μm. Re-crystallization heat treatment was carried out at 1173–1473 K in Ar–3%H2 atmosphere.
The (1 1 1) pole figure of the textured Ni–5 at.%W substrate is shown in Fig. 1a. A textured Ni–5 at.%W substrate has a sharp {0 0 1}〈1 0 0〉 cube texture. The in-plane texturing
Specifications of 50 m long YBCO tape
The basic structure of a 50 m YBCO tape was the same structure as described in Section 2.1. To increase Ic, the thickness of the superconductor layer was 1.6–1.7 μm. For high throughput, the thickness of the intermediate layers was reduced. The (1 1 1) pole figure of the textured Ni–5 at.%W substrate shown in Fig. 1b has the same sharp {0 0 1}〈1 0 0〉 cube texture as Fig. 1a. The thickness of each layer of Ni–5 at.%W, CeO2, YSZ, CeO2, YBCO, and Ag was 100 μm, 100 nm, 100 nm, 100 nm, 1.6–1.7 μm, and 20 μm,
Results and discussion
Fig. 6 shows the V–I plots of C-1, and Ic is 1974 A, which almost corresponds to the sum of Ic of all the YBCO tapes. In other words, Ic degradation did not occur during fabrication.
In Fig. 7, the measured AC loss (50 Hz) in C-1 and C-2 and Norris QNS are plotted against the RMS (root mean square) of the transport current. Here, QNS is defined aswhere It is the amplitude of the transport current; and N is the number of YBCO tapes in the conductor
Conclusion
The 1 m two-layer conductors using YBCO tapes on textured metal substrates were fabricated and evaluated. The Ic of the original tapes was 170 A cm−1 on average. To endure over-current accidents and to reduce AC loss, copper lamination and laser processes were used. There was no degradation of Ic during the fabrication of the conductor, and total Ic was 1976 A. The low AC loss of 0.144 W/m at 1 kArms was achieved even though the conductor had a small outer diameter of 20 mm and was composed of YBCO
Acknowledgement
This work was supported by NEDO as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
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