Particle physics laboratory

SLAC National Accelerator Laboratory • The Nob Hill Gazette

IIt is one of the least aesthetically pleasing buildings imaginable. Painted a blah institutional beige, it stretches on and on and on and on, looking like a long, obsessively straight storage shed. This blight on the peninsula’s bucolic landscape may not exude the romance of the Hanging Gardens of Babylon or the Colossus of Rhodes, but Stanford’s Linear Accelerator is one of the wonders of the world – a monument to the never-ending quest of humanity to understand the universe.

The particle accelerator is the backbone of the SLAC National Accelerator Laboratory, a 426-acre complex on Stanford land off Sand Hill Road near the main university campus. The seeds of what would become SLAC were planted on April 10, 1956, when the Stanford factory Wolfgang “Pief” Panofsky welcomed a group of fellow physicists into his home to come up with a bold project: the world’s largest and most expensive physics research instrument – a $114 million, 2-mile-long linear electron accelerator. Officially called the Stanford Linear Accelerator Center, or SLAC, but affectionately referred to by Stanford scientists as “the monster,” at the time, it would be the largest civilian science project funded by the U.S. government.

Linear accelerators are essentially huge guns that fire electronic bullets – whose velocity is boosted to 99.999% of the speed of light by powerful microwave machines called klystrons – down a long straight barrel on subatomic targets such as protons. When the electrons collide with the target, spectrometers using massive magnets measure the particle debris generated. This allows scientists to study the most basic objects that exist and the forces that hold them together and separate them.

In 1962, construction began on two structures, each 2 miles long – one above ground housing 245 klystrons and one 25 feet below ground housing the accelerator. Precision was required in their construction, with the curvature of the Earth taken into account (a vertical adjustment of 20 inches over 2 miles).

In May 1966, the first electron beam shot down the accelerator and crashed into a target proton. Two years later, the Monster was used to kill a theoretical dragon that had long vexed physicists. A series of proton scattering experiments proved that particles inside protons were not just a mathematical convenience, as previously thought, but actually existed. They were named quarks, after a word in James Joyceit is Finnegans Wake. SLAC physicist Richard E. Taylor and his collaborators at MIT shared the Nobel Prize for this quark research.

Building on the success of the linear accelerator, scientists then began smashing particles directly into each other, using a circular structure called the Stanford Positron Electron Accelerating Ring, or SPEAR. When electrons and anti-electrons (aka positrons) collided in the ring, new particles were revealed: the charmed quark and the tau lepton. These discoveries revolutionized high-energy physics and led to two more Nobel Prizes for SLAC scientists.

The Stanford Linear Accelerator is a monument to mankind’s relentless quest to understand the universe.

SLAC researchers have also creatively repurposed their machines to build new state-of-the-art instruments. A side effect of SPEAR stimulated the former. Scientists knew that the electrons surrounding the ring emitted powerful X-rays, known as synchrotron radiation, which most considered an unnecessary and dangerous nuisance. But a few far-sighted scientists realized that X-rays could be used to do research that no other machine could. Thus was born the Stanford Synchrotron Radiation Project, later called the Stanford Synchrotron Radiation Lightsource, or SSRL. The most powerful X-ray machine in the world, it allows scientists to study the world at the atomic and molecular level.

The second reassignment was even more dramatic. In 2008, with SLAC’s original linear accelerator rendered obsolete, a pivot was made to a new, hitherto untested technology: X-ray lasers. Scientists proposed using the last third of the accelerator to produce a beam of electrons, as before, and to add a revolutionary innovation: using powerful magnets, they would agitate the electrons, producing X-rays which would then turn into laser pulses. This would produce X-rays 10 billion times brighter than those from SSRL, allowing researchers to record images of extremely small objects and processes, in real time. Indeed, it would allow scientists to make movies of chemistry and biology in action.

Many in the field were skeptical. “A huge fraction, maybe half, of the community didn’t believe (this) was going to work,” Dr. Persis Drell, former director of SLAC, in a SLAC documentary. But one night in 2009, she was woken up with the words, “We have a laser. The Linac Coherent Light Source, or LCLS, was operational, initiating a revolutionary new phase of light-based research at SLAC. Scientists have used LCLS lasers to uncover the molecular structure of proteins involved in disease transmission; study the extremely hot and dense matter in the cores of stars; and developing next-generation painkillers.

Since its opening in 1966, SLAC has been one of the most productive scientific projects in the world, bringing to light (literally) fundamental aspects of the universe. That long storage shed under I-280 may be unsightly, but what it has contributed to the realm of human knowledge is as high as the Golden Gate Bridge.