SLAC at 50: still very much a going concern

Atom smashing has given over to X-ray investigation, of everything

Click on pictures to enlarge.

By Dave Boyce

Almanac Staff Writer

The SLAC National Accelerator Laboratory on Sand Hill Road in Menlo Park is 50 years old this year. The facility began as a particle smasher -- accelerating electrons to nearly the speed of light inside a two-mile-long underground tunnel and allowing the particles to collide in such a way as to produce meaningful information about the structure of matter.

Over the decades, the mission has changed. Today, the linear accelerator, or linac, continues to generate high-energy particles moving at very high speeds, but they don't collide much. Scientists have expanded and modified the facilities so that they now generate high intensity X-rays. X-rays are a form of light, invisible to the human eye, that is broadly useful for probing deeply into objects. At SLAC, X-rays have probed objects biological and geological, pharmaceutical and atmospheric. A facility that was once a particle smasher is now used to investigate on a scale from the vanishingly small to the impossibly large.

It's been a matter of survival. Wolfgang "Pief" Panofsky, SLAC's first director in the early 1960s, routinely heard the question, "How long will SLAC live," in an account given to the Almanac by SLAC spokesman Andrew Freeberg. Mr. Panofsky's reply: "About 10 to 15 years, unless somebody has a good idea. ... As it turns out, somebody always has had a good idea which was exploited and which has led to a new lease on life for the laboratory."

"That's a tough thing to keep doing, but those 'good ideas' really are what's kept SLAC funded and relevant through 50 years," Mr. Freeberg said.

Some of those good ideas:

■ Sending a beam of energy into a container of superheated liquid (known as a bubble chamber) to elicit behavior from various subatomic particles and learn about their properties based on enigmatic line drawings that the bubble chamber produces. Click here for an example.

■ Sending a beam of energy into a spectrometer, a device for analyzing the properties of light, to capture information on how particles interact with each other. SLAC scientists in the late 1960s and early 1970s used spectrometers to demonstrate the existence of quarks, for example, and received the 1990 Nobel Prize in Physics for their efforts.

■ Sending two beams of energy in opposite directions around a circular accelerator to see what happens when the beams collide. SLAC researchers used these devices to discover the psi and tau particles, which led to Nobel prizes in physics in 1976 and 1995.

There are also projects that have little to do with accelerating small objects. Aaron Roodman is a particle astrophysicist helping to develop a digital camera for the Large Synoptic Survey Telescope (LSST). The camera will have 189 16-Megapixel sensors, each costing about $100,000. "Basically, the best you can get," Mr. Roodman said.

When the $160 million LSST is up and running at the Cerro Tololo Inter-American Observatory in the mountains of Chile, it will scan the sky for gamma rays every night for 10 years, each night capturing 2,000 images encompassing billions of different galaxies. Three or four nights' operation will capture the entire visible sky, then the routine will start over.

Gamma rays could help in understanding dark energy, which scientists say makes up about 70 percent of the universe. The captured images, trillions of them, will be stored in an electronic catalog to allow scientists to compare the same sections of sky as time passes. The catalog will be able to "detect changes within minutes," Mr. Roodman said.

A particle astrophysicist? What can be gained by focusing on the extremely small and the extremely large at the same time? "There's no way to understand the universe without knowing how the particles behave," Mr. Roodman said. "We understand only 4 percent of what's out there."

SLAC researchers could make more money in Silicon Valley, Mr. Roodman said. But at SLAC, "they're part of a team that can work together to discover things about the universe, really hard problems."

Big science

Big tough vehicles used in construction, farming and utility work have powerful engines to carry them down the road and across the field. When the vehicles are standing still, the engines continue to be a source of power if equipped with the right kind of tap. By adding an extra set of gears or clutches to the transmission -- the power take-off, or PTO -- operators can "take off" engine power and use it for other tasks, like pumping water onto a fire, or raising the bed of a dump truck, or lifting an electrician up to a utility line.

It turns out that scientists at SLAC can use power from the accelerator, but it's more complicated than a couple of extra gears. The electron beams, when they're deflected properly, generate X-rays. Parts of the accelerator have had strong magnets added in arrangements that cause the energy beam to wiggle. "The faster the electron is going and the harder you suddenly turn it, the higher the energy of the light or the shorter the X-ray wavelength," SLAC spokesman Andrew Freeberg told the Almanac.

The Stanford Synchrotron Radiation Lightsource (SSRL), a circular tunnel that opened in 1974, generates electrons that become X-rays as they're sent around and around. Scientists at each of 33 stations along the circumference can tap into the X-rays as needed. Each station has its own capabilities. The X-ray beam is millions of times brighter than a medical X-ray, like a laser compared to a gently glowing light bulb, Mr. Freeberg said. But to what end? Imagination comes into play at this point.

Some 1,500 scientists reserve time at the SSRL every year. Among their achievements: designer pharmaceuticals, better fuel cells and better understanding of the relationship of genetic mutations to diabetes. Fossils are not known for the preservation of soft tissue, but the SSRL in 2011 revealed chemical traces of colored feathers in fossilized birds of 100 million and 120 million years old. The discovery that could lead to more accurate depictions of prehistoric birds in dioramas, movies and textbooks, scientists said in a report.

The Almanac published a related story in 2009 in which a team of visiting paleontologists brought with them a 145-million-year-old fossil of archaeopteryx, a proto-bird preserved in limestone and made portable as a thin rectangular slab about two feet on a side. Thinking there might be soft-tissue residues in the limestone, scientists superimposed a pixel map on to the fossil and scanned it pixel-by-pixel with a precision X-ray stylus at the SSRL.

The scan returned indications of phosphorous and sulfur in the feathers, similar to modern birds, according to an SSRL report. "Because the SSRL beam is so bright, we were able to see the teeniest chemical traces that nobody thought were there," physicist Uwe Bergmann said in the report.

It's one thing to observe nature, another to duplicate its ways. One long-term goal at SSRL is to find ways to copy the efficiencies of nature, such as mimicking the way soil bacteria convert nitrogen to plant food. Solving that problem could go a long way toward reducing the huge amounts of energy humans expend to produce nitrogen fertilizer.

This and other projects at SSRL are examples of applied research: research that explores the unknown with the intent of developing new and practical applications.

Basic research, by contrast, explores the unknown in order to answer fundamental questions. Scientists at the Linac Coherent Light Source (LCLS), founded in 2009, are engaged in basic research, also using X-rays but used with more precision than at the SSRL, Mr. Freeberg said. Another contrast: while the SSRL can run many experiments simultaneously, the LCLS can run only one, though a second track is in the works.

The LCLS taps energy from the linac and uses its own magnets called undulators -- to deflect the electrons, creating X-rays that are more than a billion times brighter than SSRL X-rays and shorter in wavelength, meaning that the LCLS can illuminate faster-moving objects than the SSRL.

Climate change is an area of LCLS study. What if scientists could find a way to turn atmospheric carbon dioxide into oxygen as is done by daisies, trees and blades of grass every day? The fundamentals of photosynthesis are under investigation at LCLS. "Because (they're) able to work at a better resolution than anything available before, the (LCLS) researchers are trying to explain how plants convert sunlight and water into energy," Mr. Freeberg told the Almanac.

Big power

The linear accelerator at SLAC draws about 8 billion volts of electricity to accelerate electrons over that two-mile distance. In measurement terms of 9-volt batteries, that would be 888 million batteries in a line that would stretch from Menlo Park to London, SLAC Instrument Scientist Bill Schlotter said in an email. Monthly electric bills of around $1 million are not uncommon.

When all the facilities are operating, not a common occurrence, SLAC uses about 30 megawatts of electricity, Mr. Freeberg said. SLAC has a record of about 70 megawatts from the time when scientists were using the circular accelerators and the entire length of the linear accelerator. "Running all facilities at full power, it's fair to say SLAC can pull about as much power as a small city or use as much as west Menlo Park," he said.

What does a linear accelerator sound like when it's running? "It's really noisy," Mr. Freeberg said, "like an electrical hum coming from a transformer loud enough (so that) you basically have to shout to hear. We offer ear plugs for people visiting and probably close to half of visitors will take them."

SLAC's budget from the U.S. Department of Energy for 2012 fiscal year was $324 million, he said. Other minor sources of income include outside researchers who use the facility and patents.

DOE budgets have a political element, but SLAC has "fairly uniform bipartisan support, SLAC Director Persis Drell said in an email. But in an era of tight budgets, "we have to keep making the case for the importance of basic research to both the White House and Congress, regardless of who is in charge," she said.


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