NOBODY knows how it got in. In fact, for a long time, nobody even realised
that the problem had four legs. One moment, protons were hurtling round the 6.5
kilometre circumference of the Main Ring accelerator. Next moment, the particle
stream had faltered and died.
Physicists at Fermilab, the world-famous particle physics centre just
west of Chicago, downed tools to search for the cause of the crash. As it turns
out, they didn’t have far to look. The vital clue came from a thin pencil of
light that runs inside the subterranean tunnel housing the Main Ring. The beam
is an essential safety feature: accelerating protons give off powerful
synchrotron radiation, which is not conducive to good health. Anyone entering
the tunnel would interrupt the beam and trip the accelerator.
But, as the physicists discovered to their cost, it’s not just humans who can
break a light beam. Crawling about above the ring was a cat. As its tail dangled
down, it periodically cut the light beam and turned off the ring. It took four
hours to corner the cat. When the physicists finally caught it, they had to send
it away to have it checked for radiation exposure, says Bob Mau, head of
accelerator operations. “There were 30 trillion protons a second flying round
that ring.”
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Nobody can remember the cat’s fate, although it definitely used up at least
one of its nine lives that day. What the incident does show, however, is just
what a nuisance animals can be to Fermilab. And the problems are not usually
caused by domestic animals. Last year, for instance, a raccoon squeezed,
Houdini-like, through a hole in a steel box just 125 millimetres by 50
millimetres. “Unfortunately, the box contained a 13 800 volt cable,” says Mau.
“The raccoon short-circuited the high voltage and fried itself.”
Powerless protons
Naturally, this was a tragedy for the raccoon and its loved ones—and it
didn’t exactly do wonders for the Tevatron, the trillion electronvolt
accelerator that runs alongside the Main Ring. The high-voltage cable carried
power to the superconducting magnets that direct particles into experiments such
as the 5000-tonne CDF detector, which found the top quark.
It took six hours for engineers to restore the supply. But that was not the
end of the trouble. The reckless raccoon had also cut off power to the cryogenic
systems that feed supercold liquid helium to the Tevatron’s superconducting
magnets. “It was days before we could replace all the helium that had boiled off
and get the magnets working again,” says Mau.
The metal box, centrally heated by the high-voltage cable, must have been an
attractive place to shelter out of the wind. Indeed, warmth is one of the main
reasons why wild animals are attracted to Fermilab. The lab sits on 27 square
kilometres of prairie, where the temperature in winter can easily drop to
–20 °C.
Once, when the weather was particularly bad, Mau even saw a sodden raccoon
trying to find a dry place under the insulation on top of a large transformer.
The death-defying animal was caught and sent packing. This was fortunate because
the transformer, which converts 345 000 volts to 13 800 volts, was at Fermilab’s
main electrical substation. “If he’d shorted that out, it would have been the
ultimate wildlife disaster,” says Mau. “We’d have lost power to the experiments
for a week. Simply replacing the boiled-off helium around the 4-mile Tevatron
ring would have cost $80 000.”
Headless snake
There is some dispute over what is the number one problem animal at Fermilab,
but Mau considers mice and snakes to be good candidates. “They get into
accelerator service buildings around the ring and build their nests in
electrical and electronic equipment,” he says. “It’s no fun for the guy who has
to clean out the blackened remains. I’ve seen a snake with its head blown clear
Ǵڴ.”
Mike Becker, who is in charge of roads and grounds at Fermilab, reckons the
biggest problems are Canada geese and sex-starved male deer: “The geese tend to
spend winter at Fermilab rather than going south because the ponds are warmed by
excess heat from the accelerators,” he says. “Last year, a goose turned itself
into a charred cinder by flying between the terminals of a transformer.”
The sex-starved stags are members of a 1000-strong herd of white-tailed deer
which roam freely across the Fermilab site. The problems begin in the rutting
season between October and December, says Becker. When a stag has the doe of his
dreams in his sights, he pays no attention to minor distractions such as
speeding cars. “Most of the collisions with deer occur at night,” says Becker.
“Last year, there were 26 accidents.”
The deer and geese illustrate another reason why Fermilab is irresistible to
wildlife. With a third woodland and the rest open grassland, the site is a
semi-wild island amid a sea of urban development.
Among the wilder residents are muskrats, groundhogs and beavers. “Beavers are
not a big problem,” says Becker. “However, they have been known to put up a dam
and threaten a building or some equipment with the rising waters.” Like beavers,
muskrats undertake serious engineering projects. One such venture involved
digging a hole between two large ponds. The first pond was used for cooling the
Main Ring. All its water poured into the other pond. “It took us a whole day to
repair the damage and refill it,” says Mau. “During the whole of that time we
had to have the accelerator Ǵڴ.”
Part of Becker’s job is to trap any troublesome animals and relocate them to
a wild site far away from Fermilab. He says the struggle against the invaders is
a never-ending one and it is getting worse. “Before Fermilab was built, the land
was used for farming,” says Becker. “Since then, wild animals have moved
back—but without their natural predators.”
Fermilab is also home to a herd of American buffalo. About 40 are kept in a
fenced-off corner of the site. An integral part of Becker’s job is maintaining
the herd. “We’re doing our bit to preserve a bit of the Old West,” says
Becker.
Buffalo stories abound among people who live around the site, and have
spawned some bizarre conspiracy theories. “Some local people have got it into
their heads that buffalo are especially sensitive to radiation,” Mau says. “The
other day an attendant at a gas station near Fermilab asked me whether it was
true we take buffalo down into the tunnels to warn us of high radiation
𱹱.”
And if the idea of using buffaloes as overgrown canaries isn’t strange
enough, there’s also a theory that Fermilab is home to a 4-metre high mutant
buffalo. Mau dismisses this as nonsense. But then he works for FermiLab, so he
would wouldn’t he?