You could be forgiven for thinking the SLAC National Accelerator Laboratory’s glory days are long over.
The particle accelerator, originally called the Stanford Linear Accelerator Center when built in 1962 next to the prestigious university, extends west from the university’s campus, slipping underneath Interstate 280 into the rolling, oak-dotted hills of Palo Alto, California. Its beam of high-speed electrons led to four Nobel Prizes, mostly for work in the 1960s and 1970s fleshing out the family of elementary particles like quarks that make up the matter in the universe.
But you can only discover charmed quarks once. At SLAC, though, scientists have been able to teach the old dog new tricks.
The latest is a $1 billion upgrade called LCLS-II that’s turning the 2-mile-long accelerator into the world’s most powerful X-ray laser. X-rays this powerful can be used like a super-intense camera flash — bright enough to freeze the motion of molecules midway through chemical reactions. That move follows earlier X-ray developments, 1973’s synchrotron and 2009’s Linac Coherent Light Source (LCLS). On top of that, SLAC has branched out beyond its accelerator into areas like dark matter, cosmology and astronomy.
Not a fan of X-ray crystallography or quantum? You’ll likely appreciate everyday conveniences like satellite navigation, solar panels generating power on your roof or the OLED display on the new iPhone X. Those bits of tech were made possible by many of the sciences explored at SLAC.
Indeed, SLAC is trying to shift more toward work that’s more directly useful for product development, not just understanding what makes the universe tick. Work with X-rays and other photons can have a meaningful impact on your life by inspiring the gadgets and services around you.
“SLAC has been through an incredible transformation,” said Tim Meyer, chief operating officer at Fermilab, a particle accelerator near Chicago that once competed directly with SLAC. That X-ray probing happens to be very helpful for the tech industry. “At the new SLAC, the ivory tower has almost completely crumbled… It turns out photon science allows more external users to stop by and do their work.”
An accelerator uses electromagnetic fields to whip particles up to extraordinarily high speeds — 99.9999999 percent the speed of light, in the case of electrons at SLAC. (Yes, that’s the real measurement. I didn’t just lean on my keyboard’s No. 9 key.) Some accelerators, such as CERN’s vast Large Hadron Collider (LHC) near Geneva, accelerate particles in a circle, but SLAC is linear. That design avoids problems with electromagnetic energy that occur when electrons travel in a curved path.
Massive accelerators with house-size particle detectors can be breathtaking. But thousands of smaller ones are in use around the world, zapping cancer tumors, making radioactive isotopes used in medical tests and even toughening the shrinkwrap on Butterball turkeys.
When you see the inner workings of SLAC’s accelerator — there are public tours if you’re curious — you’ll see the accumulation of decades of scientific work. Older regions show their roots in Cold War-era, analog technology. Black phones with coiled handset cords are placed periodically along concrete walls. But newer areas sport digital displays, fiber-optic and Ethernet cables, and metal gleaming with precision-machined surfaces. In one room, a green robot arm positions a Rayonix mx170 X-ray camera to a position specified in billionths of a meter.
Closer to commerce
SLAC’s X-ray upgrades make it easier to deliver more practical benefits to the country. For example, one area of research is superconductors, materials that transmit electricity without the usual losses in power. Materials don’t usually superconduct until cooled to exceptionally cold temperatures, but high-temperature superconductors could revolutionize everything from computers that aren’t plagued with waste heat to long-distance power transmission that’s dramatically cheaper.
Other projects don’t need SLAC’s big electron beam or X-ray lasers. For example, SLAC is also working on making the US electricity grid more reliable, investigating cheaper sodium-based batteries, working on radio challenges for next-generation super-speedy 5G mobile networks. Another project produced a little black chip that can be used to disinfect water using nothing more than sunlight.
Other SLAC research could improve particle accelerators used to treat cancer.
“We’re trying to build a system that does that whole month of irradiation in less than a second,” said Mike Fazio, leader of SLAC’s effort to extract useful technology. That short pulse could more accurately hit a tumor despite simple organ motion like lungs breathing.
“If you can get that radiation in between heartbeats, you have improved that dramatically,” Fazio said.
But the accelerator remains at the heart of the complex. The LCLS-II upgrade will bring new parts to do the accelerating, supercooled structures built of niobium metal. It’s an engineering challenge to get the components all the way down to minus 456 degrees Fahrenheit — much colder than than the surface of Pluto — but at that temperature niobium becomes a superconductor. That improves electrical properties so SLAC can squeeze much more out of the accelerator.
Specifically, today’s accelerator produces 120 million X-ray pulses per second. LCLS-II will deliver a million per second, and each one can be 10,000 times brighter, SLAC Chief Technology Officer Mark Hartney said.
That’ll permit a lot of exotic research. For example, researchers hope to figure out how the atomic structure of a material translates into properties like brittleness, density or electrical conductivity. That kind of understanding could then help us custom-make materials with just the right behavior for building airplanes, fabric or circuit boards. Another idea: DNA uses genes to process data at the molecular level, but can we come up with our own structures that do the same? SLAC scientists expect to start trying when LCLS-II opens in 2020.
A billion dollars is nothing to sneeze at, but it beats the alternative.
“Often, repurposing is significantly more cost effective than building from scratch,” said John Sarrao, an associate director at Los Alamos National Laboratory (LANL) in New Mexico, another Energy Department-funded facility that has its own linear accelerator. Accelerators “can have a long life and serve many purposes.”
Tucked into various outbuildings at SLAC, there are plenty of other projects, too.
Serious photographers know that in the digital era, a bigger image sensor lets a camera gather more light and take a better photo. That’s particularly important when it’s dim out. A phone sensor is small enough to perch on your fingertip, but a professional-grade SLR camera sensor measures 36x24mm, big enough to fit a few on your palm.
SLAC is working on a different beast altogether in contributing to the Large Synoptic Survey Telescope (LSST), set to begin operations in 2022 atop a peak in Chile. SLAC is assembling a collection of 189 16-pixel image sensors, each a square 42mm on edge. Collectively they form a sensor 640mm across housed within a camera the size of a small car.
With the LSST’s wide field of view, “the goal is to see every spot of the southern-hemisphere in three or four nights,” said Aaron Roodman, a SLAC experimental cosmologist. The imagery should help us understand dark matter better through watching the motion of 20 billion galaxies and 17 billion stars in our own Milky Way galaxy. And by scrutinizing more than 5 million objects in our own solar system, the LSST could help locate potentially dangerous asteroids that could collide with Earth.
You didn’t notice, but in the last second, something like a billion particles probably whooshed through your body. The reason you didn’t notice is that the particles were dark matter — a substance uncovered through gravitational interactions like galaxy formation but that otherwise don’t seem to act with the regular matter we’re made of.
SLAC is among many institutions trying to figure out and even physically detect dark matter. It’s building detectors for a multi-organization project called LUX-ZEPLIN that’ll be buried a mile deep in a South Dakota mine to minimize interference. But SLAC and its allies aren’t the only ones on the prowl for dark matter WIMPs — short for weakly interacting massive particles.
“It’s a race between several experiments,” said SLAC particle physicist Thomas Shutt. “When we turn on LZ, we think we’re going to be in the lead.”
SLAC is also researching dark matter inside a computer with supercomputer simulations of billions of years of the universe’s history, a field called computational cosmology. Reconstructing the universe’s structure shows the wisps of dark matter that thread through the cosmos and produce galaxies where they knot together. Such simulations can help explain our actual universe and guide real-world astronomy, SLAC astrophysicist Risa Wechsler said.
Not many places can accommodate both cosmic curiosity and projects that could make long-range electric cars affordable. That’s the direction SLAC is going, though, LANL’s Sarrao said.
“Accelerator research at SLAC…was central to US leadership in high-energy physics,” he said. “SLAC is having a comparable impact on materials and chemistry research today.”
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