[rec.railroad] Warm superconductors

garry@batcomputer.tn.cornell.edu (Garry Wiegand) (11/05/87)

(Cross-posted to rec.railroad)

In article <8710291320.AA08591@bu-cs.BU.EDU> BIOMED@CZHETH5A.BITNET writes:
>Everybody talks about these 'warm superconductors'. ...
>HOW will they change the world ?

The most intriguing idea I've heard so far is to apply them to cheap magnetic
levitation for trains.  I'd guess the trains would travel significantly
faster, use less fuel, and be exceedingly smooth and quieter-riding. The fuel
is probably not significant, but could the other things give trains
a shot at a comeback? I'd *love* to have an alternative to airplanes!

Does anyone have technical knowledge?

(I admit I would *not* love to have trains travelling at 400 mph past
my house.)

garry wiegand   (garry@oak.cadif.cornell.edu - ARPA)
		(garry@crnlthry - BITNET)

neanders@phoenix.Princeton.EDU (Nels Anderson) (11/06/87)

In connection with high-temperature superconductors,
garry@oak.cadif.cornell.edu writes in article

>The most intriguing idea I've heard so far is to apply them to cheap magnetic
>levitation for trains.
>Does anyone have technical knowledge?

Well, I have a little.  Just a bit of the physics.  I don't know anything
about the engineering problems.

According to an article in the IEEE Spectrum about three years ago,
there are two types of magnetic levitation: electromagnetic and
electrodynamic.  In the electromagnetic system both the train and the
track contain electromagnets.  I believe the train's magnets are
actually below the track, in a monorail-type arrangement.  The magnets
are oriented so as to attract each other, with the result that the
train is pulled up.  A control system is required to maintain the
proper separation between the two sets of magnets, reducing the field
if they come to close and increasing it if they get too far apart.

Superconducting electromagnets could be used to eliminate resistive

Electrodynamic suspension is somewhat more elegant.  It is based on
the principle that a changing magnetic field will tend to induce a
current in a conductor (copper, aluminum or a superconductor,
for example).  The induced current will flow in such a way as to
create a magnetic field counter to the original field.  If, for
example, the changing magnetic field is caused by a magnet moving over
the surface of the conductor, the induced currents in the conductor will
repel the magnet in the vertical direction while attracting it
horizontally.  So the magnet is levitated and at the same time held
near the center of the conductor.

The catch here is that in normal conductors the induced currents die
out rapidly.  Constant motion is required to maintain the induced
magnetic field.  In a superconductor, however, the currents continue
to flow indefinitely.  Thus, if you send a magnet skimming over a
block of aluminum at sufficiently high speed, the magnet will be
levitated.  If it slows down, however, the levitation will disappear.
If you do the same thing with a superconductor, you find that the
levitation persists even when the magnet isn't moving.  A New York
Times article on superconductors a few months ago showed a magnet
suspended over a superconductor (or it may have been a superconductor
suspended over a magnet -- the principal is the same).

Without superconducting technology, an electrodynamically suspended
train would contain an ordinary electromagnet and might ride over an
aluminum track.  (The track just has to be a good conductor and must
not be ferromagnetic.  It would start out on wheels.  After reaching
sufficient speed it would lift off the track. The New York Times
article mentioned the possibility of using superconducting technology
for the electromagnet.  If superconductors were really cheap, the
track could be superconducting as well.  Then the train would float as
soon as its magnets were turned on -- there would be no need to get up
to speed.  Superconducting track would also save energy, since the
induced currents in nonsuperconducting track will tend to dissipate.
The energy they dissipate has to come from somewhere, and I believe it
shows up as a retarding force on the train.  This would be quite
substantial; the induced currents holding up a fast-moving train would
be comparable to currents in the train's own magnets.

Magnetic trains have been demonstrated by the British, Germans and, of
course, the Japanese.  As I recall from the IEEE article, the British
system was electromagnetic.  I don't know about the other two, but I
believe that either or both of the German and Japanese experiments
rely on conventional cold (liquid helium) superconductors.

Nothing has been said yet about propulsion, as opposed to levitation.
I presume that it is done by magnetic repulsion or attraction between
electromagnets in the track and the train.

I could go on at greater length about these things, but I suspect that
everybody is bored already.  Unfortunately I know only about the
physical principals involved and nothing about the practical
engineering problems.  (Besides, my thesis advisor would dispute my
claim to understanding ANY physical principals.)


rvk@houdi.UUCP (R.KLINE) (11/06/87)

	one benefit of magnetic levitation would probably be
	significantly lower roadbed wear.  the primary function
	of "tracks" would be to correct lateral excursions.
	fuel savings might be significant because the major source
	of friction would now be wind drag.

						-r. kline

dmc@videovax.Tek.COM (Donald M. Craig) (11/10/87)

Once upon a time the Ontario government had (maybe they still do)
a `Transportation Research Centre' in Kingston, Ontario.
They had a maglev track and a train that ran around on it,
using technology licensed from a German company (Krauss-Maffei ?).

It seemed to work fine, in the summer.  But when the winter blizzards
howled off the Saint Lawrence River the track was buried under ice
and snow, and all the lovely hovering clearances disappeared.
They might still have the train, but they never bought another.

There's a lot of sophistication in old train technology.  When the
Canadian National Railways introduced a United Technologies turbine
powered (jet fuel yet) `Turbo' train on the Toronto - Montreal run
in the early seventies, it took ten years of re-engineering before
the things would run reliably during the winter.  I remember on
several occasions having to transfer to the diesel `Rapido' when
the `Turbo' failed in the thick of a blizzard.

Don Craig
Tektronix Television Systems

robertj@yale-zoo-suned..arpa (Rob Jellinghaus) (11/16/87)

One aspect of the new superconductors that has not been touched on yet
is their applicability to electric motors.  With current technology,
electric cars are not practical, because the motors are too heavy and
too inefficient, as are the batteries.

Warm superconductors could solve both of these problems.  We could
create motors half the size and many times more powerful than the
electric motors of today.  The batteries could also become more
efficient by orders of magnitude.  This could get us out of our current
reliance on petrochemicals, and greatly reduce humanity's destruction
of the biosphere.  Not to mention you never need go to the gas station
again; just plug in your car overnight!

Of course, this leaves out questions of intense electromagnetic fields
inside the car, ability to quickly accelerate, etc.  But GE recently
created a solar-powered car that crossed Australia at an average speed
of over 40 mph (if memory serves).  The thing only drove during the
daylight hours, but that's still an impressive feat.  And that was with
non-superconductor technology.  If that can be done now, imagine what
will be done when the supercoductors come along!

Rob Jellinghaus                | "Lemme graze in your veldt,
jellinghaus@yale.edu.UUCP      |  Lemme trample your albino,
ROBERTJ@{yalecs,yalevm}.BITNET |  Lemme nibble on your buds,
!..!ihnp4!hsi!yale!jellinghaus |  I'm your... Love Rhino" -- Bloom County

djw@beta.UUCP (David Wade, Computer Confuser Group, Chaotic Section, Administrator of illogical "Do Whiles".) (11/22/87)

In article <18946@yale-celray.yale.UUCP> robertj@yale.UUCP writes:
>  Not to mention you never need go to the gas station
>again; just plug in your car overnight!
>Rob Jellinghaus

And your house will burn down as the MEGAWATTS come swiftly into the noload