August 6, 2004  


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.

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.



The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Wednesday August 04, 2004 by Emily Ball