1
C2C David W. Croft
Maj. Kline
Engr 310
4 December 1988
Superconductors
ABSTRACT
Superconductivity allows current to pass through a
material with no resistive losses at near absolute zero
temperatures. It also exhibits the Meissner effect which
causes the superconducting material to repel magnetic
fields. The application of this technology has been
extremely limited due to the prohibitive costs of using
Helium to cool the material to the critical temperatures.
Recently, however, new ceramic materials were
discovered which exhibit superconductive properties at
higher temperatures which can be reached using cheaper
liquid Nitrogen cooling. Applications have immediately
expanded and are expected to become amazing in the near
future as scientists search for a room temperature
superconductor.
ORIGINS
Superconductivity is the passing of electricity through
conductors with no loss of power (Graham 17). The
resistance of a superconductor is zero.
P = I*I*R = 0
where the power P lost in the conductor is equal to the
current I squared times the resistance R (which is zero).
Superconductivity was first discovered in 1911 when Dutch
physicist H. Kamerlingh Onnes was experimenting with
materials at near absolute zero temperatures. He was
measuring the resistance of a mercury crystal as he lowered
the temperature and getting the expected curve of decreasing
resistance. Unexplicably, however, at four degrees Kelvin,
2
the resistance suddenly went to zero (Schedter 74).
Superconductivity was discovered although a suitable theory
was not to be developed for another half century.
Progress was slow. In 1973, a niobium and germanium
alloy was found to become superconductive at the record high
temperature of 23 degrees K. There were few advances beyond
this until 1986 even though the benefits of a higher
temperature were thought to be enormous. Superconducting
technology needed liquid Helium to achieve the low
temperatures which was expensive to purchase and maintain as
it rapidly evaporated (Graham 18).
PHYSICS
The most popular theory explaining superconductivity,
the BCS theory (named after its authors), is that electrons
move through the superconductors in pairs at low
temperatures and thus avoid most of the collisions in the
conductor which generate unwanted heat (Graham 20). This
theory was put forth in 1957, when physicists Bardeen,
Coopers, and Schrieffer explained current resistance as a
stream of flowing electrons smashing into the fixed crystal
lattice of the metal conductor which converts the power into
disorganized energy. In superconductivity, they proposed,
the electrons attract each other and travel in pairs --
mirror imaging each others actions. When one bangs into the
lattice, its partner ricochets, thus regaining the lost
energy; the net effect is that no energy is lost in the
transmission (Schedter 74).
3
An interesting side effect of superconductivity, the
Meissner effect or "magnetic exclusion," is the prevention
of magnetic field penetration into the superconducting
material. Superconductive materials repel magnetic fields
and thus will levitate above magnets (see Fig. 1) (Graham
19). In addition, new discoveries have shown that some
materials will hang below a magnet (see Fig. 2). The
proposed reason for this is that the magnetic field is
pinned in place by impurities in the material and thus the
superconductive properties will work to keep the magnetic
field unchanging. As with all experiments on the leading
edge of the superconductive field, success is limited and
not thoroughly understood -- scientists have only been able
to produce four samples which exhibit this property
(Fitzgerald).
CERAMICS
In January of 1986, two scientists at IBM's Zurich
Research Center developed a new class of ceramic compounds
which would become superconductive at a much higher
temperature -- high enough to cool with liquid Nitrogen (see
Fig. 3). Liquid Nitrogen is extremely cheap and easier to
maintain as it boils into gas at a much slower rate (Graham
18). The whole process of cooling with Nitrogen,
considering all the technology and materials, is about 1000
times cheaper than Helium -- Nitrogen is cheaper than beer
and can be kept overnight in a picnic cooler (Schedter 76).
4
In 1988, Dr. C. W. Chu of the University of Houston
discovered a new, cheaper class of ceramic compounds that
produced results at 110 degrees Kelvin. Scientists are
predicting and desperately looking for a material that will
exhibit superconductive properties at room temperature (295
degrees Kelvin) (Graham 18). Some have reported that they
have created materials which do so briefly and unpredictably
(as long as 3 hours). Many feel that room temperature
superconductivity can be achieved reliably in two to four
years ("Getting" 42 - 43). One major obstacle which they
have to overcome is electron current capability. Present
high temperature superconductors are only capable of small
currents -- about 1000 times lower than what is desired
("Seeking" 67).
APPLICATIONS
The desperate chase for high temperature
superconductivity is due to the remarkable possible
applications. Supercollider technology could benefit as it
uses many powerful magnets -- superconductors generate
magnetic fields much more efficiently than current
technology. These magnetic fields could also be used to
contain the reaction in a fusion generator at a cost that
would be many times cheaper than that which current
experimental fusion reactors experience (Graham 16 - 17).
Medical image scanning, which use the penetrating power of
magnetic fields over the older technology of x-rays, would
5
also benefit in costs with the switch from Helium to
Nitrogen ("Getting" 42).
Using room temperature superconduction, power lost in
transmission lines could be reduced by 20%. Computers would
no longer require bulky fans as their smaller, zero
resistance chips would not heat up. This would also mean
that they would be faster and use a minimal of power; all
this would lead to a very small, fast computer that uses
little power (Graham 19 - 20). Because of this zero
resistance in superconducting wires, all electric motors
could be improved in efficiency (Graham 16 - 17).
Communications using electromagnetic waves would get a
boost as a high temperature superconductivity coating on the
inside of resonators, high-frequency generators,
surveillance satellites, television, lasers, particle
accelerators, and radio astronomy products improves
performance by reducing power loss. This power loss is
inhibitive at higher frequencies, but now, using
superconductivity, the "wireless" transmission bandwidth
increases 167 times as operating frequencies will eventually
move from 30 GHz to five TeraHz (5000 GHz) (Cambridge 44 -
45).
Electric generators, made more efficient by using
superconducting wires, could store their energy in
superconducting coils during the night to be used in peak
hours during the day. These storage coils would have a
6
current flow without any resistance or voltage source --
energy that can be stored and tapped anytime, forever.
V = I * R = 0 (Ohm's Law)
where the voltage V is zero, the resistance R is zero, and
the current I is limited by the properties of the material.
These storage coils could be used in electric autos, thus
freeing us from the costs and hazards of petroleum energy
("Seeking" 66 - 67). Deserts might be covered with huge
solar collectors which feed these coils (Schedter 74).
The Meissner effect could be used to levitate trains
over their tracks allowing them to reach speeds of 300 mph.
In the 21st century, this principle could also be applied to
cars for those who commute frequently ("Getting" 42). Heavy
objects could be more efficiently moved down assembly lines
in factories using superconducting levitation ("Seeking" 66
- 67). Frictionless bearings could also be a result of the
newly discovered effect which "holds" a magnetic field
(Fitzgerald).
Defense applications are also abundant.
Superconducting sensors in the cold of space could be used
to detect missile launches. Submarines could be tracked
using tiny magnetic detectors scattered throughout the seas.
And to counter acoustical detection, a submarine could
propel itself through the water with no moving parts using
superconductivity to generate magnetic fields which would
force water through a pipe ("Seeking" 66 - 67). Strategic
Defense Initiative laser technology could get its required
7
megawatt energy burst from superconduction storage units
instead of proposed nuclear detonations (Graham 16-17).
The benefits of the applications of high temperature
superconductivity are enormous -- and extremely profitable
to the scientists who develop this new technology. Thus, we
will probably see breakthroughs in the near future as
scientists put all of their efforts into research. Until
then, we can only imagine the possibilities.
Works Cited
Cambridge Report on Superconductivity, The. "MIT Finds New
Use for Superconductivity." High Technology Business.
________________________
Vol. 8, pp. 44 - 45, August 1988.
Fitzgerald, Karen. "Ceramic Superconductors Defy Gravity
Anew." Electrical Engineering 443 Course Handout,
Fall, 1988.
"Getting Warmer . . . ." Newsweek. Vol. 110, pp 42-3,
________
6 July 1987.
Graham, Charles. "Superconductor Speed-Up." Electronics
___________
Handbook. Pp. 16 - 22, 93, Fall 1988.
________
Schedter, Bruce. "How to make your own superconductors."
Omni. Vol. 10, pp 72-4+, November 1987.
____
"Seeking the Perfect Wire." U.S. News & World Report.
________________________
Vol. 102, pp 66 - 71, 11 May 1987.