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Some Assembly Required
By
Shawne Neeper
As the summer winds down,
BaBar
scientists are wrapping up a record-making year and
enjoying some well-earned down time. Operations ceased in PEP IR-2
(Bldg. 620) on July 31. But for engineer Jim Krebs (REG) and his team,
the work has just begun.
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The ingenious red press is
being used to curve the brass plates.
(Photo by Diana Rogers) |
Through August and September, Krebs is leading a two-shifts-per-day
engineering effort for the
BaBar
detector upgrade. To reach
BaBar’s
top and bottom sextants, Krebs’ team will move a mountain of concrete,
design and fabricate many new lifting fixtures, and assemble a monster
lifting platform. To prepare, Krebs’ group designed, built and tested an
armament of custom equipment in IR-2’s understudy, IR-12 (Bldg. 720).
The Concrete Temple
In the final days of preparation, the buzz of power equipment overflows
the open warehouse door at IR-12. A 25-foot pyramid of concrete blocks
stretches from the cement floor well towards the overhead bridge crane
spanning the cavernous ceiling. The crane is a duplicate of a crane in
IR-2—a necessity to ensure that the team’s machinations in IR-12 will
work in IR-2. The concrete block tower matches
BaBar’s
dimensions, providing a test bed for equipment that Krebs and colleagues
are inventing for the upgrade.
Welder Scot Johnson (EFD) helped create custom steel I-beams that brace
the concrete tower against earthquakes. He joined SLAC two years ago
after 13 years as a welder for United Airlines. Now he cuts, welds and
hoists steel beams to make the equipment that will access
BaBar’s
detectors.
“If it needs doing, we just figure it out and get it done,” Johnson
said. Accessing and replacing
the detectors will take
some figuring and doing.
To reach the detectors in IR-2, the team must first remove a wall of
more than 30 concrete blocks the size of limousines. Then, using IR-2’s
overhead crane, they will lift
BaBar’s
steel flux return out of the way. To lift parts inside
BaBar
that the crane can’t reach, they will assemble custom-built lifting
fixtures. Starting with the bottom-most of
BaBar’s
hexagonal interior, they will remove the old detectors and install the
new.
The Blue Beast
To access the detector segment, Krebs and team member Les Dittert (BaBar)
designed and commissioned a blue, steel-frame hydraulic lift. The Blue
Beast’s 15-foot base supports a moving upper platform that creeps
upwards at about five inches per minute. The platform can lift the
equivalent of a large car an additional five feet—enough to reach
BaBar’s
top with heavy equipment and parts.
Like all of
BaBar’s
six segments, the top and bottom sections each contain 18 slots. Krebs’
team will install brass plates into six slots, and new detector panels
in the 12 remaining slots above and below each plate. The plates will
absorb background hadron particles, leaving the particles of interest—muons—free
to travel through to the next detectors.
IR-2 engineering coordinator Zorb Vassilian (EFD) will oversee the
installation. A 35-year SLAC veteran who has been with
BaBar
since its start in 1997, Vassilian is the man to see about detector
maintenance.
The Red Press
Inside IR-2, brass plates worth $1,000 apiece are stacked like
plank-shaped bars of gold.
BaBar’s
detector slots will support the 7/8-inch thick plates at their ends. To
prevent sagging at the middle, Krebs dreamed up a scheme to curve, or
‘camber’, the plates. With the curved side down, the plate’s weight is
shifted towards its ends.
Putting a smooth curve into a 5- to 10-foot long brass plate takes
ingenuity. Last year, Krebs applied the weight of a concrete block to
good effect. This year, he designed a press.
To demonstrate, Krebs dons a red construction hat. He’s joined by Mo
Olson (EFD), who works with the team during summer leave from teaching
physics at Saint Norbert College in De Pere, Wisconsin. Krebs operates
IR-2’s huge yellow crane by remote as Olson guides a dangling eight-foot
plate across IR-2 and onto a brightly-painted steel contraption. The red
press emits a whine as its hydraulic foot pushes the plate’s center
downward. The foot rises and the plate springs back, retaining only the
hint of a curve.
“We just put a slight bend in it,” Krebs said, “It’s not much.” This
year, they put that subtle bend into 23.5 tons of brass. The summer 2005
upgrade of
BaBar’s
remaining four segments will require 47 tons.
Next year’s updates will also require adjustments to the Blue Beast.
“We’re going to rebuild it in a different form next year,” Olson said.
He and his colleagues specialize in customization.
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