Special Issue

Superconductivity〉〉New ProductsHigh Performance REBCO-HM Wire
1.

INTRODUCTION

Beginning with the control of the global warming, various
technologies have been developed all over the world torealize the carbon neutral society in the midst of a day to
day growing concern over the carbon neutrality. Under
the present circumstance mentioned above, the technology of the fusion is recently in the limelight and energetically developed by research institutions and venture companies in each country. Applying the technology of thefusion, it will be possible to realize a power generation
technology which will never produce the carbon oxide
emission or the long-lived radioactive waste which isinevitably produced in the nuclear power generation. Inaddition, it will continue to be a stable power source into
the future, because resources needed for the fusion phenomenon exist richly in the sea. It is very important tocontrol plasma to realize the very attractive fusion power
generation mentioned above, because it is necessary tokeep the plasma under the state of high density and hightemperature for long time in a power generator. Such afusion power generator has been developed anddesigned all over the world which controls the plasma
based on the high magnetic field technology applied withsuperconducting magnets as a method to control theplasma. The superconducting wire becomes free from its
electric resistance and a high power can flow in it when
its temperature gets lower than a certain temperature (thecritical temperature). An electromagnet which generates ahigh magnetic field can be realized with the use of thesuperconducting wire. Recently, a compact fusion reactor
has attracted a wide attention, which is applied with
REBCO wire, a kind of superconducting wires. TheREBCO wire is the tape-shaped wire which has a superconducting layer made of a compound composed ofrare-earth elements, barium (Ba), copper (Cu), and oxygen (O). The structure of our REBCO wire is shown in
Figure 1. The black layer is the superconducting layer(REBCO layer). Even though its thickness is as thin as
approximately 1.6 μm, a high current of over 100 A canflow in the wire which is only 4 mm wide under the liquid
nitrogen temperature (approximately –196°C). We havecontinued the development of a higher performance
REBCO wire through many years. The characteristics ofour high performance REBCO-HM wire recently developed was approved by our customers and the wire wasadopted in the superconducting magnet of the fusion
reactor 1).
Looking for other applications than the superconducting magnet of the fusion reactor, the development of ahigher magnetic field by magnets is advancing in theapplication of analysis and research in the field of physics
and chemistry and the demand for the high performance
REBCO wire is growing. For example, when a magnet for
Nuclear Magnetic Resonance (NMR) for an analytical
instrument is operated under a higher magnetic field, theintensity of the detectable signal is increased and the resolution of analysis is remarkably improved, which will
enable our more detailed analysis about materials. Our
high-performance REBCO is also adopted in the instrument operated under the high magnetic field mentionedabove.

2.

DESIGN OF HIGH PERFORMANCEREBCO-HM WIRE

The high current performance under the magnetic fieldenvironment is demanded for the REBCO wire, because
either the superconducting magnet for the fusion reactor
or that for producing the high magnetic field is operated

Electroplating

Copper Stabilizer

Sputtering

Silver Overlayer
20 µm

MOCVD

REBCO - HTS (epitaxial)
IBAD/Magnetron Sputtering

2 µm

Buffer Stack< 0.1 mm*～1.6 µm

Electropolishing～0.2 µm

Substrate
50 µm～1.8 µm* not to scale; SCS4050

Figure 1

20 µm

Structure of REBCO wire produced by SuperPower Inc.

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High Performance REBCO-HM Wire

under the magnetic field environment. The movement ofthe magnetic field (flux quantum, technically speaking)which penetrates into the superconducting layer has tobe blocked in order to maintain the high current performance under the magnetic field environment. When themagnetic field is moved, a voltage is generated producing
the electric resistance and the high current performancecannot be maintained. When a part of the normal conductivity is formed in the superconducting layer, the magnetic field is trapped in the part of normal conductivity
and its movement can be blocked. The part of the normal
conductivity is called the artificial pinning center. The artificial pinning center of BaZrO3 is created in our REBCO
wire by adding Zr artificially. We implemented Zr at 7.5%of the material concentration ratio of our traditional
REBCO wire. Under the higher magnetic field environment, more magnetic fields will penetrate into the superconducting layer. We have aimed at the higher density of
the artificial pinning centers by improving the Zr concentration rate by doubling to 15% in order to control themovement of many penetrating magnetic fields efficiently.
In addition, the composition ratio of our REBCO was optimized to create the artificial pinning center effectively.

3.

20 nm

Figure 2Plan view TEM image of REBCO wire with Zr15%
after composition optimization.

CHARACTERISTICS OF HIGHPERFORMANCE REBCO-HM WIRE

Plan view Transmission Electron Microscopy (TEM) images of REBCO wire with Zr15% and REBCO wire with
Zr7.5%, each of these REBCO composition ratio wasalready optimized are shown in Figure 2 and Figure 3. In
Figure 4, a plan view TEM image of REBCO wire with
Zr15% whose REBCO composition ratio was not optimized yet is shown. Parts looking like black circles are
the artificial pinning centers of BaZrO3. We can recognizethat the thinnest artificial pinning centers of BaZrO3 areformed in the highest density of the REBCO wire with
Zr15% whose REBCO composition ratio was alreadyoptimized (see Table 1). In Figure 5 and Figure 6, thecross-section TEM images of the REBCO wire with
Zr15% and the REBCO wire with Zr7.5% are shown. TheBaZrO3 pinning center is formed in a column shape perpendicular to the superconducting layer plane. The artificial pinning centers of BaZrO3 look like thin grey columnsin the vertical direction. We can recognize that the artificial pinning centers of BaZrO3 are continuously linked
together in a column shape all over the superconducting
layer in the REBCO wire with Zr15%. By comparing, weconfirmed that there were discontinuous parts in theareas surrounded by red broken line in the REBCO wirewith Zr7.5% shown in Figure 6. It is when the size of theartificial pinning center is as large as that of the penetrating magnetic field that the artificial pinning center cancatch the magnetic field efficiently. The size of the magnetic field penetrating into the superconducting layer isgenerally reported as to be several nm in radius (reportedas 1.4 nm to 4 nm, 2), 3) ). It is estimated based on the20 nm

Figure 3

Plan view TEM image of REBCO wire with Zr7.5%
after composition optimization.

20 nm

Figure 4

Plan view TEM image of REBCO wire with Zr15%
before composition optimization.

Table 1

Pinning center configuration of each REBCO wire.

Specifications of Wires

Pinning center Pinning center Pinning center
diameterdensityspace(average)(average)(average)2(nm)(rods/cm )(nm)

REBCO wire with Zr15%(after optimizing theREBCO composition)

3.3

7.5 × 1011

7.6

REBCO wire with Zr7.5%(after optimizing theREBCO composition)

5.2

4.7 × 1011

9.8

REBCO wire with Zr15%(before optimizing theREBCO composition)

5.4

4.2 × 1011

12.3

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High Performance REBCO-HM Wire

superconducting layer plane. Ic on the vertical axis shows
the maximum current value which can flow without breaking the superconducting state. We have confirmed thatour developed REBCO wire with Zr15% had the current
performance no lower than double of that of traditional
REBCO wire with Zr7.5% in the temperature range from4.2 K to 30 K (approximately from –270°C to –240°C) andunder the high magnetic field of 10 T or higher.

4.
100 nmFigure 5

Cross-section TEM image of REBCO wire with Zr15%
after composition optimization.

100 nmFigure 6

CONCLUSION

We have developed our high performance REBCO-HM
wire for the superconducting magnet in the fusion reactor
and for the superconducting magnet to produce the highmagnetic field. Improving the concentration rate of Zr
which is a material for the artificial pinning center and further optimizing the composition ratio of the REBCO, wehave accomplished the higher density of the artificial pinning centers in comparison with the traditional REBCO
wire to make tremendous improvement of the in-field performance. Our developed high performance REBCO-HM
wire has satisfied the performance required by various
customers and has been adopted for the superconducting magnet in the fusion reactor and for the superconducting magnet to produce the high magnetic field. We
will drive our development further and supply our higherperformance REBCO wires to support the social infrastructure with our high magnetic field technology.

Cross-section TEM image of REBCO wire withZr7.5% after composition optimization.
REFERENCES

shape and the structure of the pinning center which wereconfirmed by the TEM analysis that our developed
REBCO wire with Zr15% can block the movement of themagnetic field even under the high magnetic field environment and has the required high current performance.
In Figure 7, the measured results of the in-field current
performance of wires with Zr7.5% addition and thosewith Zr15% addition in each magnetic field are shown
when the magnetic field is applied perpendicular to the1400

4.2 K wire with Zr7.5%4.2 K wire with Zr15%
20 K wire with Zr7.5%
20 K wire with Zr15%
30 K wire with Zr7.5%
30 K wire with Zr15%

Ic @ B//c (A/4 mm)

1200
1000
800
600
400200005101520

Magnetic ﬁeld (T)Figure 71) Furukawa Electric HP > News Release > “Tokamak Energy andFurukawa Electric Group Strengthen Relationship to Progress
Commercial Fusion Energy” By Tokamak Energy Ltd., Furukawa
Electric Co., Ltd., and SuperPower Inc.		 released on January 12, 2023 (Referred on February 20, 2024)		https://www.furukawa.co.jp/en/release/2023/kenkai_20230112.
html
2) D.C.Larbalestier, A.Gurevich, D.M.Feldmann and A.Polyanskii:“High-Tc superconducting materials for electric power applications”, Nature 414 (2001), P. 368-377.
3) S.Nawaz, R.Arpaia, T.Bauch and F.Lombardi: “Approaching thetheoretical depairing current in YBa2Cu3O7- δ ”, Physica C 495(2013), 33-38.

For more information, please contact:
Technical Service Section,
Superconducting Products Department,
Research and Development Division
TEL: +81-288-54-0504
Contact form:
https://inquiry-fec-form.spiral-site.com/enrd
Electronics Dept., Electronics & Automotive Div.,FURUKAWA SANGYO KAISHA, LTD.
FAX: +81-3-5405-7615
E-Mail: MO_5403_54030207025100@furukawaelectric.com

In-field performance of REBCO wire with Zr7.5% andZr15%.

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