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Linac Coherent Light Source (LCLS), the world’s first X-ray free-electron laser.

Science’s most brilliant breakthroughs today happen on a scale so small that researchers can study them only with light wavelengths short enough to catch individual atoms in their beam. The international race to build light sources capable of such illumination has begun, and the Linear Accelerator Center operated by Stanford University is in position to reach the finish first.

The Stanford Linear Accelerator Center (SLAC), Menlo Park, Calif., has operated on the frontier of high-energy physics research since 1962. The linear accelerator, or Linac, has been instrumental in discovering evidence of quarks and other subatomic building blocks of matter. Four Nobel Prizes have rewarded researchers’ achievements. Now, SLAC is preparing to refocus on the growing fields of photon science and particle-and-particle astrophysics.

A key tool will be the Linac Coherent Light Source (LCLS), the world’s first X-ray free-electron laser. It will operate like a strobe light for nanoscale photography using an intense, tightly focused beam of X-rays, infrared and ultraviolet radiation 10 billion times brighter than any to date. The fast, bright X-ray pulses will illuminate subatomic dynamics that are invisible using light with longer wavelengths
Before the LCLS, it would take about one second of exposure to X-rays to get a picture or measurement. During that time, the atoms have moved, jiggled or maybe run away, so the pictures are blurred,” says John N. Galayda, LCLS project director. He compares the effect to photographing a hummingbird’s flight with a 1-second exposure. The LCLS X-rays will be “so intense that we can do stop-action photography of atoms as they move,” he says. The LCLS will permit scientists to understand and manipulate matter at the atomic level.

LCLS construction began last fall and is scheduled for completion by June 2008 at a total project cost of $379 million, including line equipment and management, design and construction-related costs, all funded by the U.S Dept. of Energy. It will add a half-mile enclosure and tunnel to the 2-mile-long Linac.

The LCLS will generate the electron beams in the last kilometer of the Linac, bending and focusing them with magnets. The quadrupole undulator, a series of 33 magnets, will make the electrons oscillate right and left, emitting X-radiation and continually bathing them in their own X-rays so they travel in a perfectly straight line, says Galayda.

The LCLS will extend the Linac’s beam on a perfectly straight, flat line running as deep as 110 ft under the Palo Alto Hills. It will connect to the Linac via the 745-ft-long Beam Transport Hall (BTH), crossing the existing Research Yard, a largely open area dotted with buildings. Penetrating a hillside, it will enter the 565-ft-long Undulator Hall tunnel and connect to the 131-ft-long Electron Beam Dump. The beam dump and the 116-ft-long Front End Enclosure both will be built with cut-and-cover methods and connect to the Near Experimental Hall (NEH). This 25,000-sq-ft, two-level concrete structure, to be covered after construction, will house experimental hutches, prep, shop space and a large bay.

From the NEH, the 660-ft-long X-Ray Transport and Diagnostics Tunnel will run to the Far Experimental Hall (FEH), a two-level mined cavern. An access tunnel, on which construction started in early March, is being mined at an acute angle toward the FEH. The bulk of the LCLS—the Undulator Hall and all facilities beyond the Near Experimental Hall—will be completely underground, constructed by tunneling.

On March 29, Insituform Technologies Inc., Chesterfield, Mo., announced its intention to close its tunneling operations and seek a buyer for subsidiary Affholder Inc., the LCLS tunnel subcontractor. With most tunneling still ahead, Galayda is watching the situation closely.

“I would love to know what the most likely disposition of Affholder might be,” he says. “Simple takeover, I hope, but I don’t really know. I recognize that, in situations like this, one might worry that Affholder employees might start looking for jobs [that have] less uncertainty.”

Announcing the decision, Insituform President and CEO Thomas Rooney Jr. said, “We intend to fulfill all contractual obligations and responsibilities associated with our customers, partners and vendors as we wind down this business
Long Time Coming

The status of Affholder was only the latest bump on what has been a long, hard road for the project. Since 1992, it has run the gauntlet of approvals required for costly Energy Dept. research projects. Years of research and development preceded the 2001 approval of LCLS construction. Jacobs Engineering, Pasadena, Calif., began design in 2004, with a target budget for civil construction of $75 million. Turner Construction, New York City, came on board in late 2005. As CM for-fee initially, Turner sought bids from subcontractors that would work under contracts held by Turner.

Design concepts over the years evolved to get maximum yield from the available funds. By 2005, Galayda considered the design locked, and value engineering began. He thought the design should be close to the budget. “We got engineer’s estimates from Jacobs and an independent estimator and market forecasts from Jacobs,” he says. But the bids were surprisingly high.

“Right now, it’s a real busy environment in the Bay Area. It’s not a buyer’s market,” says Michael D. Owens, Turner project manager. “Between 2005 and 2006, there was a substantial market change,” Galayda adds. “We hit the peak of the cost of materials.”

A boom in area construction absorbed much of the labor and construction capacity for which the LCLS competes. And in 2006, the San Francisco Public Utilities Commission launched a $4-billion program to upgrade its water-supply system (ENR 7/17/06 p. 10). In August 2006, Turner received notice to proceed under a firm-fixed-price $88-million contract. Congressional budget limits forced the project to drop a 74,000-sq-ft laboratory and office complex. SLAC will rehabilitate other facilities instead.

Shortly after groundbreaking ceremonies in October 2006 at the site of the Near Experimental Hall, crews began site work for the Beam Transport Hall, which traverses the Research Yard. “The biggest thing was for existing utilities to be rerouted out of the way of the BTH,” says Owens. After more than 40 years of operation, many utilities didn’t show up on the Research Yard’s as-built drawings.

The first concrete was poured on April 5 for the Beam Transport Hall’s 3.5-ft-thick slab-on-grade. This area is the owner’s first priority because it connects directly to the Linac building. Completion will allow installation of LCLS line equipment to begin, says Owens. The Near Experimental Hall’s sub-basement slab was completed April 2, and work will continue with construction of the NEH’s second level, which lies on the beam line. “The goal is to work on all areas at once, and every area is now in progress,” Owens says.

Since March 12, Affholder has advanced 50 ft into the Far Experimental Hall’s access tunnel with a road header, says Patrick Doig, project manager for Hatch Mott MacDonald, which is managing the tunnel work. A second road header arrived the first week of April and is beginning the tunnel from the Research Yard for the Undulator Hall.

The ground throughout the LCLS site is dry, soft sandstone, lying well above the water table. “The sandstone behaves more like soil than rock,” says Doig. “It has a good stand-up time.” He doesn’t anticipate any surprises in the tunneling. “The ground is fairly well known in this area” because SLAC has occupied the site for so long. After the machines cut 4 ft, crews apply 3 in. of gunite to the walls, erect lattice girders and apply 3 in. more gunite before continuing. A final 6 in. of gunite and a concrete floor slab later will finish the tunnel. Progress is 4 to 8 ft per day, says Doig.

The current single shift works 10 hours daily, five days per week, plus nine hours on Saturday, says Owens. Later this month he will start a night shift on the access tunnel, then at the Undulator Hall.

The FEH excavation will begin about mid-May. “The FEH mined cavern is the biggest challenge on the job,” says Doig. The cavern, measuring 212 x 46 x 29 ft high, will be mined in nine cuts on three levels. “It isn’t that often you get to build something this large in soil,” says Doig. FEH mining will take about four months, with additional time required to apply 12 in. of gunite to the walls and roof.

The Undulator Hall mining that just started will take eight to 10 weeks, while the other machine mines the FEH. The Undulator Hall tunnel, 19 ft wide by 14.5 ft high, emerges at the beam dump, one of three cast-in-place concrete structures that includes the Near Experimental Hall. The road header then will move to the Far Experimental Hall. One machine will continue excavating the FEH while the other heads back toward the NEH, mining out the X-Ray Transport and Diagnostics Tunnel. All tunneling is scheduled to be completed by December.

Precise

The electron beam must remain precisely targeted, maintaining a tolerance of 2 microns over 130 meters. “This is a laser and focusing beam on a target more than 2.5 miles away from the electron gun that starts the beam,” says Richard Bambam, project architect in Jacobs’ Cypress, Calif., office. The alignment must remain absolutely flat and straight, actually deflecting 1.5 in. toward the Earth’s center to compensate for the Earth’s curvature before angling back up. Forces that might distort the beam include temperature, vibration and barometric pressure, while some parts of the LCLS require concrete thicknesses of up to 72 in. to shield radiation from within.

Still, Galayda says the job has “pretty standard engineering tolerances.” Structures must be aligned within a couple of millimeters but final alignment of line equipment will be performed by machinery. The concrete floors have no expansion joints. “If it cracks, it cracks,” Galayda says. The equipment can compensate better for shrinkage alone, he says.

Sitting just a mile from the San Andreas Fault, SLAC has site-specific seismic criteria beyond the building code, but seismic events are not a major threat. “Generally, underground structures tend to be pretty safe in an earthquake,” Galayda says. Buildings fall because of differential motion between base and top, he notes. SLAC is designed for a magnitude 7 quake centered a few miles away.

For the equipment, “we need 0.1°C temperature stability,” Galayda says. “HVAC is pretty important to us, particularly the regulation” to maintain a narrow range of equipment temperature. Ambient temperature can fluctuate because the equipment’s mass holds the temperature stable, he notes. Temperature control presented “interesting challenges in the geometry of it,” says Dennis Hickman, manager of engineering at the Portland, Ore., office of Jacobs, which performed the mechanical, electrical and plumbing design. Jacobs designed a system of zone control, in effect separating the tunnels into “segments of the Tootsie Roll,” he says.

Turner is to complete civil construction by June 2008. SLAC then will complete installation of the line equipment. When LCLS operation begins in 2009, the facility is expected to beat its nearest rival, in Hamburg, Germany, by no more than a few months. It will cast the future of science in a whole new light.

In Images:
1.Researchers at the Stanford Linear Accelerator have won four Nobel Prizes.
2.New construction ties in at headwall via Beam Transport Hall, then goes into tunnel.
3.Ultrafast pulses take images of injected molecules. Multiple diffraction patterns yield 3-D images of molecule structures.
4.The Near Experimental Hall is one of three structures in the middle of the beam line being built from the surface instead of tunneled.
1.Excavation of access tunnel just began.

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