Special Issue

Superconductivity〉〉Contribution

A Logbook Across the Ocean of Electrons
A Story of Material Technology in Furukawa Electric: Now and Then

Toru Fukushima*
We commercialized copper wire cables through the refining of pure copper atthe dawn of the Meiji era. We have been deeply involved in the modernization ofJapan, helping to develop power cable networks, to popularize motors and generators, and to
expand telephone and telegraph networks.
These origins of our founder’s business generated the driving force for the industry development
and became one of the sources for social contributions, which the company should make, whilelighting up the city with safe electric lights, and encouraging interactions among people beyond
time and space. Since then, we have been proposing the world a variety of material, which wasderived from our founder’s business, and have started the beginning of a new information society, for example, by adding optical fibers and semiconductor lasers to material technologies.
On the other hand, the climate warming and its resulting large-scale natural disasters are
becoming a new threat to our planet. In the search for effective and permanent means, attempts
to realize a fusion power generation as soon as possible are increasing. The material that supports this is superconducting wires, which we have cultivated over many years. We will continue
to pursue material technologies to make a new contribution to the society.
In this article, I would like to describe about our “Now and Then”, starting with our exploration ofcopper materials, and aiming to commercialize new materials such as superconductors.

ABSTRACT1.

INTRODUCTION -Furukawa Electric’s
Hydroelectric Power Generation-

The development of the Ashio Copper Mine undertaken
by Furukawa Head Office (later, after being Furukawa
Mining Co,. Ltd., it became Furukawa Co., Ltd.) dates
back to 1877 when the dry mountain was sold to the private sector and purchased by our founder, Ichibei
Furukawa.
On the other hand, in order to transform the crude copper produced into an extremely low-resistance pure copper, i.e. an electric wire, it undergoes a purification process called an electrolytic refining. In other words, theloop of using a lot of electricity to produce transmission
lines must be closed. Incorporating the function of the“power generation” as a part of our business would havebeen a natural progression. From 1906, Furukawa*

General Manager,
Sustainable Energy Succession Project Team and Deputy
General Manager, Research & Development Division

General Partnership sequentially installed hydroelectric
power plants at four locations (Hosoo, Uwanoshiro,
Umamichi, and Setoyama) near Nikko Copper
Electrolyzing Refinery (now our Nikko Works) and began
their operation. The electric energy produced there wastransmitted to the Ashio Copper Mine, and transmission
lines of those days are still in operation today. Today, our
Nikko Works also operates on electricity generated bythese hydroelectric power plants.
The idea of utilizing natural energy called the “hydropower” was an ideal choice, in terms of the natural environment in which our Nikko Works is located and theneed for local community contributions. The desire ofpeople at the time of our founding to take advantage of
the water volume in Lake Chuzenji and to pass it on to
the next generation, combining both the beautiful forest
river and the business, is still being carried on today.
We will contribute to the society based on our material
technologies toward the realization of the next-generationsocial infrastructure and new mobility, and will inherit thespirit of our founder as described above. The environFurukawa Electric Review, No. 55 20242

A Logbook Across the Ocean of Electrons A Story of Material Technology in Furukawa Electric: Now and Then

ment of the earth is changing rapidly these days, and wewould like to add another “contribution to the earth” scenario on top of the material technologies and productbusinesses that we have cultivated so far. This is, so to
speak, the theme of this report.

2.

THE DAWN BROUGHT BY PURE
COPPER WIRES

When impurities are thoroughly removed by the electrolytic refining, the purified copper mass becomes the“ocean of electrons” with a core of uniformly aligned copper atoms surrounded by an abundance of free electrons.
The secret why the copper functions as a “good conductor” is that this “ocean of electrons” transmits energy,
from huge currents to minute voltage amplitudes, like atsunami or a ripple wave, over great distances without
losing its momentum of wave crest. The pure copper
functions as a good conductor of heat as well as an electrical energy. In addition, as it is purified more, it increases
the ductility and becomes easier to process into thin andlong wire rods.
The reason why the copper material broke away fromancient uses of “copper” such as ornaments, precious
metals, or coins and became a basic material that played
a role in industrial development in the early 19th century
must be the overlapping of discovery of the “ocean ofelectrons”, the realization of “wire rod” product, and theneed for electrical applications at the perfect timing.
Although the copper is often seen as a mature field
now, but if we look back at its history, we can trace themagnitude of impact that the pure copper wire has hadon the world. The world’s first transatlantic telegraphcable in 1858 is its best example. The world’s first transatlantic Morse code was transmitted by a central conductor of 7 pure copper wires stranded together, with a total
length of 3,200 km. It was a poignant story that the“ocean of electrons” could be transformed into a communication channel that spanned the oceans of the earth,but this project was difficult to complete and took morethan two years to complete1).
Queen Victoria of the British Empire and President
Buchanan of the United States of America exchanged 98
words telegraphs via an undersea cable that had been
opened. At a time when there was no other means ofcommunication than sending letters by ship, the feat ofsimultaneous communication created a sensation comparable to that of the Apollo moon landing. However, thefirst transatlantic telegraph cable stopped functioning
within a few weeks after the feat. The cause of the malfunction was attributed to the deterioration of the insulation coating material (natural rubber), which allowed thecentral conductor to conduct with seawater. The firstchallenge to the “great ocean of nature” by the “ocean ofelectrons” in the hands of mankind ended in a defeat.
Time moved on to 1884. The Honjyo Copper Smeltery
was established and began businesses, ranging from thepure copper to the electric wire manufacturing. With thisas a starting point, Furukawa Electric was born in 1920. It
has been a long time since it lagged behind Europe andAmerica, and a quarter of a century had already passed
since the successful completion of the transatlantic telegraph cable. Now, we look back the earnest desire of ourpredecessors to bring the dawn of electricity and communications to our country as soon as possible. The gutsof our predecessors, who hurriedly overcame difficultiesof the wire drawing process and the coating material
research in quick succession, based on the refining ofpure copper 2), are immeasurable. They must have poured
their heart and soul into the development of improved
structures and coating insulation technologies, referring
also to the precedent of submarine cables in the US andEuropean teams.

3.

ELECTRIC RESISTANCE AND HORIZON
OF THE OCEAN OF ELECTRONS

Now, copper wire carries the electric power, transmits
the information, and contributes to the industrial development, but needless to say again, its electrical resistanceis not zero. This is also true for other metals such as aluminum, which is a good conductor like copper, but thehigher the temperature, the higher the resistance (Table 1).
Table 1The dependency on the operating temperatures forthe resistivities in Copper and Aluminum.

Metal

Volume resistivity［µΩcm］
–195℃

0℃

100℃

700℃

Aluminum

0.21

2.5

3.55

24.7

1083℃ 1200℃-

32.1

Copper

0.2

1.55

2.23

6.7

21.3

-

This is the limit of the “ocean of electrons,” and thehorizon that will never be reached. The higher the temperature at which it is operating, the more intense the thermal oscillation of the metal atoms becomes. By way of an
example, the surface of the ocean of electrons boils violently, disrupting the wave crests that transmit energy,
and impeding their voyage. At extremely high temperatures, it reaches its melting point and melts down. It canno longer function as an electrical wire to transmit theenergy.
Now, on the contrary, if we thoroughly cool wires madeof copper or aluminum, what will happen? The -195°C
temperature shown in the above table refers to the statein which wires are cooled by immersing them thoroughly
in the liquid nitrogen. Compared to the room temperature
operation, the resistance value is reduced to about onetenth. The thermal energy generated when the same current is applied decreases by a factor of 10 in proportion
to the resistance value. Now, a simple question comes tomind what will happen if cooled down further to an
extremely low temperature, where the ocean of electrons
becomes completely silent. This is exactly the state ofabsolute zero, or –273°C. Since metal atoms stop the
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A Logbook Across the Ocean of Electrons A Story of Material Technology in Furukawa Electric: Now and Thenthermal vibration and electrons around them are free tomove around, the resistance must be extremely close to
zero. If a much larger current is desired, achieving zero
resistance is the ultimate ideal since the calorific energy
generated increases drastically as the square of the current.
However, unfortunately, even when cooled to absolutezero, the electrical resistance of copper wire is neverzero. The insatiable pursuit of “Why is that?” and “Is there
somewhere a dreamlike material that has zero electricalresistance?” will lead to the realization of superconducting wires.

4.

ACROSS THE SUPERCONDUCTIVITY
AND THE OCEAN OF ELECTRONSWhen a pure metal is cooled to absolute zero, the intrinsic quantum-mechanical character of free electronsappears. In other words, electrons are clearly separated
into 2 types (positive and negative spin polarity) that are
spinning clockwise and counterclockwise. And when twoelectrons with the same spin polarity meet, they will hinder each other’s progress on the contrary. This is the limitof the ocean of electrons i.e. the cause of tiny electricalresistance that remains at the end. The search for a way
to break through this limit continued.
On the other hand, the phenomenon that mercury
becomes zero resistance and superconductivity if it iscooed at an extremely low temperature was discoveredby the Dutch scientist Kamerlingh Onnes in 1911, muchearlier than theoretical elucidation. Later, alloys of niobium and titanium, for example, were found to reach a stateof “zero resistance” at a liquid helium temperature(–269°C). The underlying physics of this phenomenon
attracts the keen inquisitiveness of researchers.
What would happen if electrons having two different
spin polarities, positive and negative respectively, could
pair up and behave like a single particle without spin?
And then, wouldn’t one pair be able to move freely without any interference from the other pair, with absolutely
zero resistance? Three scientists (John Bardeen, Leon
Neil Cooper, and John Robert Schrieffer) approachedthese hypotheses and succeeded in explaining the phenomenon of superconductivity quantum mechanically in
1957. And, they showed the possibility that instead ofindividual electrons, a new pair of electrons, the Cooper
pair, could achieve a superconducting state with zero
electrical resistance. This discovery was named the “BCS
theory” after the initials of the three men, and for theirwork on the BCS theory, Bardeen et al. were awarded theNobel Prize in Physics in 1972.
Around the time when the BSC theory of superconductivity was being explained in the world of theoreticalphysics, a series of discoveries of superconductors thatwere not only high in superconducting critical temperature but also resistant to magnetic fields and electric currents were made also in the world of experimental phys-ics. The possibility of practical application of superconducting materials, which had been thought to be difficult
up to that time, was shown. In 1963, basic researches onsuperconducting metal materials began at our Nikko
Works, and we succeeded in commercializing niobium
alloy superconducting wires with no loss of time. Since
then, we have been continuing to supply low-temperature
superconducting wires to customers around the world.
However, low-temperature superconducting filaments
such as niobium-titanium cannot maintain a perfectsuperconducting state unless they are covered with an
oxygen-free copper (ultra-high purity and ultra-low resistance). There is a secret story of struggles and ingenuities
in the development of this high-purity and oxygen-freecopper. This can be said as a good example that thecommercialization of new materials can be achieved byaiming for the ultimate in existing materials. It was in 2003
when we established the ideal oxygen-free copper technology. Efforts to thoroughly eliminate the pathways for
impurities to enter the process, which prevented the highpurification, and to fundamentally improve the process
and facilities have borne fruit. The Residual Resistivity
Ratio (RRR) value, an indicator of ultra-low resistance,
was 500. The improvement was more than three times
greater than that of conventional products, and laid thefoundation for the quality and brand of our low-temperature superconducting wires. We have been also continuing our improvement research and have earned a good
reputation for top-level performance and quality 3).
On the other hand, these alloy-based superconducting
wires will not reach a superconducting state unless they
are cooled to an extremely low temperature (4 K /–269°C)
with liquid helium, which is expensive and difficult to handle. According to the aforementioned BCS theory, there isa limit to the temperature range in which a superconducting state can be achieved, and the search for a more convenient refrigerant, which becomes zero resistance, forexample, using liquid nitrogen (77 K/–196°C), was considered extremely difficult.
However, in the spring of 1986, two IBM researchers(Johannes Georg Bednortz, and Karl Alexander Muller)
found that an oxide combining barium, lanthanum, andcopper could be used to create a superconducting statewith zero electrical resistance at about 35 K/–238°C. It
can be said that its discovery was as close to accidental
as Columbus’ arrival in the Americas.
Taking this opportunity, in the short period from 1986 to
1987, research institutes in Europe, the U.S., and Japan
published their results one after another, and a variety ofhigh-temperature superconducting materials were born.
In addition to the oxide that combines three metals, rareearths such as yttrium, barium, and copper, so called
Rare Earth, Barium, Copper Oxide (REBCO), it has been
revealed that the bismuth-based copper oxide, Bismuth,
Strontium, Calcium, Copper Oxide (BSCCO), etc. havebeen found to show a superconducting state at a liquid
nitrogen temperature with a good reproducibility. What
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A Logbook Across the Ocean of Electrons A Story of Material Technology in Furukawa Electric: Now and Thenthese materials have in common is that the path of superconducting carriers is formed on the crystal plane where
copper and oxygen are bound, and they are collectively
called the “copper oxide-based superconducting materials”.
Incidentally, the perfect theory that can explain thehigh-temperature superconducting state found in theabove oxide materials is still a matter of debate among
many researchers, and several hypotheses have been formulated. At the end of this debate, another material may
be discovered by chance, and a new horizon may suddenly appear beyond the ocean of electrons.

5.

MASS PRODUCTION AND PRACTICALAPPLICATIONS OF REBCO HIGH-TEMPERATURE SUPERCONDUCTING WIRESWe began basic researches in 1986 and worked on the
prototype production and the evaluation of copper oxidebased superconducting materials. The REBCO crystals
are brittle ceramics themselves, and it took many more
years to realize a thin, long, and flexible shape to function
as a superconducting wire.
Current REBCO superconducting wires consist of ametallic tape as the base material, dielectric multilayers
deposited on top of it, and a REBCO crystal thin film (1 to
2 μm thick) that carries the superconducting current.
Even if bending and tensile stresses are applied to theentire structure, as long as the magnitude of stresses isbelow the elastic limit of the metallic tape substrate, eachlayer of thin film is not damaged and functions normally.
And, in 2012, we acquired SuperPower Inc., which had
achieved remarkable results in the deposition process of
Yttrium, Barium, Copper Oxide (YBCO) thin films by introducing Metal Organic Chemical Vapor Deposition(MOCVD), and took a major step toward the mass production of REBCO superconducting wires 4).
When zirconia (Zr) is added during deposition using the
MOCVD method, an effect of pinning a magnetic flux
appears. This improves the critical current density in highmagnetic fields. By combining this technological featureand our manufacturing know-how, they have been improving quality, characteristics, and process capability 5).
In February 2020, a new one floor building was constructed in consideration of a line layout suitable for mass
Table 2

production, and the relocation of existing process lines
was completed. As of 2023, they are continuing toincrease its manufacturing capacity by adding new process facilities to meet the demand for REBCO high-temperature superconducting wires 6).
Now, an important thing as well as the technologicalefforts toward the mass production is finding appropriate
applications. As mentioned at the beginning of this paper,
the lineage of pure copper wires has expanded the use ofelectrical energy and laid the foundation for a consumeroriented economy and industry since the 20th century,
but more than 20 years have passed since the turn of the
century, and social needs have already reached a turning
point. So, what kind of contribution can the advantage of
REBCO wires bring to the global environment both now
and in the future? There are high expectations for thisnew material, which has spanned the ocean of electronsand exceeded the limits of Cooper pairs, and finally materialized after more than 30 years of work. Contributions
with something new uses and new ways of using things
are required.
So, let’s take a look back at the advantages of superconductivity again. First of all, the first advantage that
there is no transmission loss because the heat generated
by electrical resistance is reduced to zero, and that 100%of the input power reaches the other end, is a consumption economic benefit. However, from a different perspective, we should focus on the second advantage that noheat is generated even when extremely large currents are
passed through them. In other words, it is possible towrap a small coil that cannot be achieved using the copper wire, and it is possible to confine an “ultra” strong
magnetic field within it. This is a “thing” that users of thiswire really appreciate. Utilizing the ultra-high magnetic
field generated by superconducting coils, we are contributing to the advancement of technological fields listed inTable 2.
In addition, all of the application fields listed in Table 2
have already been pioneered using a niobium-based
superconducting wire (We manufacture it at our Nikko
Works). For example, in the International Thermonuclear
Experimental Reactor (ITER), the basic concept of condensing and confining deuterium and tritium fuel plasmausing the magnetic field generated by an electromagnet
using niobium tin superconducting wire is becoming a

Examples of applications for superconductors.

The stronger the magnetic field generated, the more complex proteins and macromolecules can
NMR
be identified. This analyzer is indispensable in fields such as advanced medical research, new(Nuclear Magnetic Resonance)
drug development, and food hygiene.
Particle accelerator

Contribution to the advancement of particle physics research (e.g., European Organization for Nuclear
Research (CERN) and medical equipment (heavy particle irradiation equipment for cancer treatment).

Fusion power generation

Research is underway at International Thermonuclear Experimental Reactor (ITER) for practicaluse. Several private projects are being launched because the use of REBCO wire allows for morecompact equipment. The dream of an artificial sun is one step closer to reality.

Magnetic levitation, rotation,and movement

Superconducting coils will be used to levitate heavy objects, enabling them to rotate and move ina straight line with zero frictional resistance. Expected applications in the mobility field, such as
flywheel energy storage, next-generation transportation, and high-performance motors, etc.

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A Logbook Across the Ocean of Electrons A Story of Material Technology in Furukawa Electric: Now and Thenreality. However, this is a gigantic project in which multiple countries are participating in the development by
sharing and constructing a large electromagnet and areactor body. It will take a long time furthermore to complete the project.
On the other hand, when the high-temperature superconducting wire is used, it is possible to create electromagnets that generate an even stronger magnetic field.
This allows the plasma to be condensed more compactly
and densely, making it possible to reduce the size offusion reactors to less than a fraction of its size. It is
expected that the cost and period required for the fusion
reactor construction will be reduced, and realization is
expected to be faster. In the application fields listed inTable 2, systems and equipment are currently becoming
more efficient and more compact due to the switch to
new high-temperature superconducting wires such as
REBCO, or their combination (hybrid configuration). The
achievement of Tokamak Energy Ltd. which showed thepossibility of a compact fusion reactor, producing a prototype superconducting magnet using our REBCO wires
and generating a magnetic field of 20 T, is an example ofsuch efforts (Figure 1).

portation network that floats and moves at high speed iscreated, people and goods will be transported more safely and quickly. It will spin empathy and co-creation, andeliminate the seeds of conflict around the world.
We will continue to improve our mass production technology for high-quality superconducting wires and meetthe expectations of customers who are developing theseapplication fields.

6.

CONCLUSION

A somewhat circuitous voyage from the “ocean of electrons” that begins with pure copper wires, to the “horizonline” drawn by superconductivity was described. Material
technologies form the basis of various fields in which it isapplied, but it takes a tremendous amount of effort andtime to reach that point. The cycle of reincarnation inwhich materials give birth to new technologies, and newtechnologies give birth to the next materials, must continue to be spun in the future. The path from the basic
research to the business is not an easy one, but thesource of the strength to keep going through it is nothing
but a sense of mission to contribute to the health andsecurity for the next generation, and the preservation of
the global environment.
The flow and density of information have been greatly
improved by the optical fiber communication technology,
which was one of the first to break out of the ocean ofelectrons. World events spread far more quickly andwidely than they did during the time of the first transatlantic telegraph cable, and thanks to this, people’s minds
and the ways of thinking have started to change at amore rapid pace than ever before. But something is still
missing. How long will this earth remain calm? Can people really live their lives with peace of mind?
It may still be a dream story for now, but we would liketo connect the Mother Earth and people’s future with newmaterials and new technologies. Furukawa Electric
Review carries the thoughts of so many engineers andwill continue to tick away without stopping its second
hand.

REFERENCES

Figure 1

The HTS magnet for compact fusion reactor
developed by Tokamak Energy Ltd.

The application of superconducting wires can bringwhat was once considered the science fiction world intoa reality world. For example, if we could create an artificial sun on Earth using a fusion reactor, we would no longer need to burn fossil fuels. Or, if the high magnetic field
is used to create new compounds, they could rapidly fix
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Spectrum, Vol. 56 Issue 11 (2019), 60.
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Copper Works of the Furukawa Electric Co., Ltd.”, Journal of the
Mining and Metallurgical Institute of Japan, 84-963(1968), 729-731.
3) Masahiro Sugimoto, et al.: “Development of Cu-Nb Reinforced
Nb 3Sn Wires”, Furukawa Electric Review, 55(2024), nn-nn.
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5) Furukawa Electric: “High Per formance REBCO-HM Wire”,
Furukawa Electric Review, 55(2024), nn-nn.
6) Gene Carota, Tetsu Tateishi, et al.: “Introduction of SuperPowerInc.”, Furukawa Electric Review, 55(2024), nn-nn.

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