Magnetics Business & Technology - May/June 2024 - 21

RESEARCH & DEVELOPMENT
A scanning electron microscope revealed broken filaments of Nb35n.
Photo courtesy of CERN.
nets were quadrupoles, meaning they were each made from four
separate coils fitted together to form a long and hollow cylinder.
When the magnet is switched on at full current, electromagnetic
forces pull the ends of the four coils with a 100-ton force. This is
usually fine: If the magnet is perfectly symmetrical, then the forces
are equally balanced, and the strong support structure prevents
damage to the delicate conductor. But what if they hadn't been?
The support structures have small alignment gaps to compensate
for the expansion and compression of the material
when the magnets are cooled and warmed. Ambrosio
and his team saw that the alignment gaps
had closed in the broken coil's support structure
but had stayed open in the other three. Could that
have condemned the coil?
A loose wire. An unexpected delay. A broken
symmetry. Ambrosio and his team had gathered
circumstantial evidence against each suspect. But
that wasn't enough. They needed an autopsy.
They quickly realized that the only way to get accurate
results was to do the analysis the old-fashioned
way: inspecting every micron of the samples
visually. Crouvizier and Moros spent several days
hunched over a microscope. " It's not so much the
neck that hurts-it's your back, " Moros says.
After weeks without unearthing any conclusive
evidence, Ambrosio had an idea. " We had been
cutting [the coil] like salami-perpendicular to the
wires-and finding nothing, " Ambrosio says. " But
what if we cut it longitudinally-along the wires? "
" Salami " cuts (pictured above left) are optimized
to look for cracks that travel along the length of
the wires. But more sinister damage-a tear that
rips a delicate filament in half-is usually invisible
to a salami cut. Because longitudinal cuts traverse
the length of the wire, they can reveal very small
tears. But longitudinal cuts are very tricky to do; the
investigating team would have to cut very precisely
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Another clue, but we're not going to give away the ending. Photo
courtesy of CERN.
along sub-millimeter wires without destroying the evidence they
were looking for.
Suffice to say, the mystery was solved with collaboration from
colleagues at other laboratories around the world. Today, subsequent
magnets have a design change and a procedure change.
See the full story at www.symmetrymagazine.org.
Precision Instruments for Professionals
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May/June 2024 * Magnetics Business & Technology 21
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Magnetics Business & Technology - May/June 2024

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