textfiles/bbs/KEELYNET/GRAVITY/meissner.asc

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|  File Name      : MEISSNER.ASC     |  Online Date     :  07/08/95          |
|  Contributed by : Jerry Decker     |  Dir Category    :  GRAVITY           |
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This is one of the better articles I've seen on superconductivity because it
relates to the field of practical levitation.  Other applications of course
have to do with energy or information storage and transmission.

About a year ago, one of our group had spoken to an inventor named Herb
Wachspress out in California.  He has developed a flying device that he
demonstrates for $5000.  That is because it uses superconducting phenomena to
provide lift AGAINST THE EARTHS' MAGNETIC FIELD and flies off into space each
time.  The patent for his 'Free-Flying Levitator' is listed on KeelyNet as
WACHSPRE.ASC.
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From the New York Times

Dreams of Levitation

A physicist imagines that he is momentarily annoyed by the big conference
table occupying the middle of his office.  He gives it a shove with one hand,
and, in his imagination, it floats away, drifting lazily toward the corner,
until finally it stops with a bump against the wall.

So it might, in a speculative future.  For now, the physicist, Praveen
Chaudbari, vice president for science at the International Business Machines
Corporation, is engaging in a reverie about superconductivity and its most
bizarre by-product:  the phenomenon of levitation, science's answer to the
flying carpet, "You don't even have to make cars," he says.  "You could make
little gizmos, you could put on a pair of special shoes and make little tracks
along which you as a human being could push yourself and keep going.  Nothing
to stop you, right?  I see the whole transportation system being very
different.  At airports, instead of these long conveyor belts we have, you
could get onto one of these platforms that are levitating and just stay on it
while it takes you around."

Levitation is not just the strangest but also one of the most practical
prospects raised by the recent boom in superconducting materials.  Floating
trains, floating furniture, floating toys, floating people - otherwise sober
scientists are talking about applications that used to belong to the realm of
science fiction.  They are amused, but they are serious.  If the new materials
fulfill their early promise, and especially if a room-temperature version can
be made practical, the ability to lift objects off the ground and free them
from mechanical friction could bring suprising rewards.

Levitation comes from a property of superconductors only indirectly related to
the property that gives them their name: the ability to carry electric current
without any loss due to resistance.  With or without electric current, a chunk
of superconductor placed above a magnet settles calmly in midair.  For that
matter, a chunk of magnet placed above a superconductor also hangs in the air
- levitation works either way.  The superconductor has the peculiar property
of pushing out any external magnetic field, so the magnet cannot approach.  It
just hovers, in the soft grip of an invisible hand.

The phenomenon has a certain built-in measure of stability.  "Levitation means
that your piece of metal sits on a magnetic pillow," says Vladimir Z. Kresin
of the Lawrence Berkeley Laboratory in Berkeley, California.  "You can move
right, left, forward, back - because of the configuration of the magnetic
field, you have a real equilibrium position in the center.  It's a system
trying to keep everything in the middle."  Any mechanical device that requires
bearings - any device, for example, in which something must rotate at high
speed, like a generating turbine or a gyroscope - could use levitation to
eliminate friction.  Friction typically sets the limit on the speed of
rotation, and it also produces waste heat that must be drawn away.

Scientists have let themselves fantasize about levitation for decades.
Twenty-two years have passed since a Stanford physicist, William A. Little,
writing in SCIENTIFIC AMERICAN, proposed not only superconducting hovercraft
but also a sort of physicist's theme park, with people "riding on magnetic
skis down superconducting slopes and ski jumps."  To date, the single real-
world anchor for such whimsy is the levitating train, a transportation system
whose feasibility has been demonstrated by a Japanese National Railways
prototype.  The experimental trains carry powerful superconducting magnets,
cooled, expensively, by liquid helium.

Smaller-scale, less expensive technologies await superconductors that require
less cooling, and such superconductors have been found in a series of recent
breakthroughs that have brought superconductivity out of the shadows of
scientific esoterica.  A new class of materials, easy to duplicate and
inexpensive to produce, makes the sudden transition to superconductivity at
record high temperatures, though still several hundred degrees below zero.
Those materials, requiring cooling by liquid nitrogen, are enough to make
possible such non-floating applications as highly efficient long-distance
transmission lines and fast, small supercomputers, applications and vast
commercial promise.

But another class of applications - the kind that would transform a host of
ordinary, visible aspects of everyday life - demands a superconductor that
would require no refrigeration at all.  Physicists have been reporting signs
of this elusive new room-temperature superconductor, seemingly making itself
felt in several different laboratories, though still impossible to isolate and
stabilize.  So scientists are allowing themselves to hope that the room-
temperature superconductor will become a reality, and they are thinking more
seriously than ever about a world in which objects could be made to float.
"If it's going to come into society, you could think of assembly lines,
guiding materials around in this innovative way," says Theodore Geballe of
Stanford University.

Personal transportation could be freed from two dimensions, especially in
cities, "where you get gridlock," he said.  "You could just go into three
dimensions with small, guided transportation, not the big levitated trains."
Metal tracks would have to be built at different levels, floating people
along.  The capital cost would be considerable, and the temptation to slide
through the air at unsafe speeds could be a serious concern.

Propulsion might involve magnets, air jets, or muscle power - in any case,
starting and stopping would be nontrivial engineering problems, as would the
question of air-traffic control.  The consequences of making powerful magnets
a ubiquitious feature of everyday life are far from obvious.  In terms of pure
science, however, the fundamental principles are well understood.

Levitation begins with the fact that a magnetic field creates a current in any
conducting material - the principle at work in electrical generators.  A
current creates its own magnetic field - the principle of work in electric
motors.  But superconductors are special.  If a magnetic field penetrated a
superconductor, it would create a current that would set up exactly the
opposite field.  Wherever the magnet moved and however it was oriented, it
would see its ghostly counterpart below, repelling it.  So the external field
CANNOT penetrate - it is expelled, an effect known as the Meissner field.

Even on the small scale of the laboratory, the results are uncanny.  A piece
of flat iron magnet sits on a table.  A chunk of the new superconducting
material, a dull gray ceramic, is dipped into a Styrofoam cup full of liquid
nitrogen to cool it.  Then the superconductor is put above the magnet, where
it floats.  It can be poked, spun, and nudged from place to place, but it
remains suspended until it warms up.  Then, making the transition from
superconductor to ordinary ceramic, it settles to the ground.

The technology designed for high-speed trains uses a variation of the physics
of levitation, set in motion.  The train is equipped with superconducting
magnets, coils of wire that become magnetic when a current is passed through
them.  Because there is no resistance to electricity, the current does not
need to be maintained with a continuous power supply.  Once it is started, it
continues forever.  The train sits on a track of ordinary metal, such as
aluminum.  As long as it is motionless, it just sits, but when it begins
moving forward, the magnets induce a current in the aluminum, setting up
another repulsive magnetic field.  The effect is instantaneous and short-
lived.

"The magnet in the vehhicle has to think it sees an equal and opposite magnet
down below,"  Dr. Geballe says, "A few milliseconds, that's enough time.  Then
you move on to a virgin piece of aluminum."  The train starts on wheels and
then, at about fifteen miles an hour, lifts off the ground.  For forward
propulsion, the train relies on separate magnets embedded in the track.  In
case of a complete power failure, the train would simply settle gradually down
onto its wheels.

The Department of Transportation investigated levitating trains, among other
futuristic transportation ideas, a decade ago, but interest waned, in part
because the United States, with its spread of urban areas and its love of
private automobiles, seems less than ideally suited for large-scale rail
transport.

Some scientists complain that the federal government has long been too
reluctant to support research into innovative technologies of transport.

The Japanese, however, went ahead with a program of trains using
superconducting magnets, while West Germany sponsored an experimental train
using a different magnetic technology.  As a result, much of the engineering
has already been done.  "It's entirely feasible - the Japanese and the Germans
could implement it right away," says Francis C. Moon, chairman of the
department of theoretical and applied mechanics at Cornell University.  Dr.
Moon conducted research on the stability of levitating trains and observed
tests of the Japanese prototype, flying six to eight inches above its track at
speeds of two hundred to three hundred miles per hour.  Track wear and tear is
not a problem; nor is noise.  "The train goes by in a whisper," he says.
"It's weird to see."

Years of imagination and hard engineering have gone into the levitating train.
The next generation of levitating objects can only be guessed at.  But design
work and engineering calculations have also been applied to the problem of
replacing bearings with superconducting magnets.  In an engine or turbine
where one ring rotates inside another, the principle would be the same as in a
levitating train.

Less industrially, Dr. Chaudhari's floating furniture would be guided by wires
embedded in the floor, he suggested.  To allow a table or chair to rise and
sink, designers could use small electromagnets that could be controlled with a
handy dial.  "It just pops up," he said.

"The strength will determine how high or low it goes."  Others, when they
witness levitation, cannot help but think of toys.  "It's funny by itself,"
said Dr. Kresin of Lawrence Berkeley Laboratory.  "Maybe one application will
be for the toy industry.  You can apply huge fantasy using these principles."
                                                                      >  JG
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