IEEE Spectrum September, 2008 - 8

99 mIllIoN

the metric tonnage of greenhouse gas the united States would not emit if it used biogas from
livestock manure to generate electricity, according to researchers at the university of texas at Austin

World's Most Powerful
Magnet Under Construction
one hundred tesla without self-destructing

GK AND ViKKi hArt/Getty iMAGes

ultiply the magnetic
field strength of a
refrigerator magnet
by 2 million and you'll be in
the ballpark of the strength of
the magnet that researchers
at the National High Magnetic
Field Laboratory, based near
Florida State University in
Tallahassee, are trying to
create. When completed later
this year, the pulsed electromagnet, located at the lab's
facility at the Los Alamos
National Laboratory, in New
Mexico, will reach 100 tesla,
the holy grail of magnetic field
strength. And in another first,
if all goes according to plan it
will reach that level-about
67 times as high as a typical
MRI-without blowing itself
to smithereens.
Why would anyone need
a magnet that strong? Greg
Boebinger, director of the
Magnet Lab, says that this
magnetic field strength is the
only way to test the properties
of newly discovered hightemperature superconductors
like iron oxyarsenide, which
may improve the performance
of MRI machines and highvoltage power lines while
lowering their cost. A 100-T
magnet would also let
you conduct certain zerogravity experiments without
traveling into space and
let you develop magnetic
propulsion systems that
could eventually replace
those that burn rocket fuel.
So far, researchers have
reached 90 T, proving that
the Magnet Lab is on the right
track. "We've been running it
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at the hairy edge," Boebinger
says, referring to the tradeoffs
he and his colleagues must
make to get the most out of the
magnet without destroying it
in the process. Researchers
have been able to generate
magnetic fields stronger than
100 T for years but knew that
any such experiment was
a one-and-done situation,
because these magnets would
almost instantly be torn
apart by their own forces.
Boebinger says the Magnet
Lab is close to reaching the
material tensile strength
needed to repeatedly break
the 100-T barrier. That is no
small feat, considering that
the US $10 million magnet
will have to resist enormous
Lorentz forces-the electromagnetic push on electrons
that attempts to force them
in a direction perpendicular
to the flow of current. In a
magnet that strong, says
Boebinger, these forces are
"equivalent to the explosive
force of 200 sticks of dynamite
packed into a volume of
space the size of a marble."
The electromagnet will be
made of two pieces-a thick,
hollow cylinder, called an
outsert, that's 1.5 meters in
diameter by 1.5 meters tall,
and an insert just big enough
to fit inside the outsert's
225-millimeter bore. The
outsert will be powered by
a 1.4-gigawatt generator and
produce fields between 40 T
and 44 T, while the insert
will draw enough current
from a 2-megajoule capacitor
bank to generate fields up

mAgnETIC momEnT: Engineers are readying a supercooled, recordsetting 100-tesla magnet at Los Alamos National Laboratory. The
magnet will have to withstand forces equivalent to 200 sticks of
dynamite. photo: leroy N. sANChez/los AlAMos NAtioNAl lAborAtory

to 60 T. The outsert is never
powered up for more than
2 seconds at a time, during
which the insert can deliver
multiple 20-millisecond
bursts. Enough energy is
transferred during those
2 seconds to raise the
magnet's temperature
from the cryogenic cold of
liquid nitrogen to nearly
200 °C. It takes an hour to
cool the magnet enough
to start another round of
pulses. Boebinger says the
design and composition
will allow researchers to
get roughly 10 000 pulses
out of the $8 million outsert
magnet and about 100 pulses
before a $20 000 insert
magnet is destroyed.
"Simply put, pulse magnets
are applied metal fatigue,"
says Boebinger. "The trick
is to hold off the breakdown
of the bonds between the
molecules due to mechanical
and thermal stresses for

as long as you can."
Several ingredients in
the secret sauce will let this
magnet snap back where
others have simply snapped.
The magnet is made up of
nine nested coils of wire. At
the heart of the two innermost
coils, where Lorentz forces
create pressures 30 times as
great as those at the bottom
of the ocean, researchers
have placed state-of-the-art
nanoparticle wire composed
of 82 percent copper and
threaded through with silver
strands no more than a few
hundred atoms across. The
copper-silver combination
is stronger than either metal
alone by a factor of 100.
From there, things get
a little easier, if only on the
wallet. "The further out you
go, the lesser the forces are,"
says Boebinger, "so you can
afford to use material that is
not as strong and not nearly as
expensive." -Willie D. Jones

September 2008 * Ieee Spectrum * NA

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Table of Contents for the Digital Edition of IEEE Spectrum September, 2008