The long and strange lives of Enrico Fermi’s accelerator building at UChicago

‘Really a surprise’

The Accelerator Building’s original inhabitants were two ‘atom smashers,’ as they were popularly called at the time. One was a betatron, which generated gamma rays and other particles for physics research. The other was much more powerful. Known as a cyclotron, when it was completed in 1951, for a period it was the world's most powerful particle accelerator.

Designed by Fermi and fellow Manhattan Project veteran Prof. Herbert L. Anderson, the cyclotron used a 2,500-ton magnet to accelerate particles such as protons and nuclei to energies of up to 450 million electron-volts.

“One of the most striking things they did was to discover that the proton has structure to it, and that structure can be excited just like an atom can be excited—and that revealed there was something more inside the proton,” said Pilcher. “That was one of the very first pieces of evidence for an internal structure. It was really a surprise.” (Later experiments at Fermilab and others would finally catalogue the pieces rattling around inside the proton—the top and bottom quarks.)

Scientists also used the cyclotron to make several other fundamental measurements and discoveries, such as studying the properties of a “heavy electron” called the muon.

More powerful accelerators were eventually built elsewhere, however, and the betatron was decommissioned in 1965 and the cyclotron in 1972. But that wasn’t the end of the story.

First, the cyclotron’s gigantic magnet was shipped off to become part of other experiments at what would later become Fermi National Accelerator Laboratory. (It took 22 truckloads, each carrying a 90-ton segment of the magnet.)

Then, in the coming decades, the building would shelter dozens of scientific experiments in their infancies, as scientists used the now-freed space to build large pieces of detectors and instruments that couldn’t fit in any other space.

The search for cosmic rays

Parts of the newly empty building were immediately colonized. Pioneering cosmic ray scientist John A. Simpson stashed the data acquired from his NASA missions in the old proton-counting room, which extended underground beneath Ellis Avenue. The university’s Central Shop acquired the south end of the building for gigantic lathes and milling machines, which produced specialized scientific equipment for the university.

But the Accelerator Building’s second life began in earnest when the director of the Enrico Fermi Institute, Prof. Robert Sachs, saw the potential for hosting experiment construction. As physics advanced through the 20th century, its experiments were getting larger and more logistically complex, and they often had to be built and then taken to other locations. “It would be like building a submarine in a basement: you could do it, but then you wouldn’t be able to get it out,” said the late Prof. Dietrich Müller in 2021.

So the Accelerator Building, with its sturdy engineering, crane, and large doors that backed straight out onto the street for easy removal once the experiment was ready to be moved, was a godsend to scientists.

The first experiment housed was an instrument called CRN, affectionately known as the “Chicago Egg” for its shape. It was built for NASA by Profs. Müller and Peter Meyer in order to study cosmic rays—rare, high-energy particles that occasionally zip by on their way from exploding stars and other phenomena in faraway galaxies. Each one has a story to tell about where it came from and what it encountered along the way—if scientists can catch it, which is easier to do above the Earth’s atmosphere.

The Chicago Egg had a successful flight aboard the Challenger space shuttle in 1985. “It was a very pioneering experiment. It measured cosmic ray particles up to very high energies which nobody had done before, using techniques that no one had used before—we had developed them here,” said Müller.

In the decades that followed, the University of Chicago became a leading institution in building instruments for these cosmic ray expeditions.

From the late 1980s to the present day, a dozen of these pioneering experiments took shape inside the Accelerator Building high bay. They launched aboard balloons from Canada, New Mexico and Antarctica, or sat in Utah deserts, piecing together what kinds of cosmic rays were hitting the Earth and where they likely came from—and what they told us about the Milky Way and beyond.

The last instrument to begin its life in the Accelerator Building was Prof. Scott Wakely’s HELIX project, specially built to catch light cosmic rays to reveal insights into how cosmic rays are accelerated and other scientific mysteries. HELIX launched aboard a balloon from Sweden in May 2024.

The leading edge of particle physics

Meanwhile, the experiments used to discover what makes up the smallest parts of an atom were also getting larger and larger.

Through the late 1980s and 1990s, a team of University of Chicago scientists, including Profs. Ed Blucher, Roland Winston, Yau Wah and Bruce Winstein, used the Accelerator Building to construct components of experiments that went into experiments at nearby Fermilab’s large particle accelerators. These helped illuminate the path to discovering several missing quarks, the last sub-atomic particles, and explored the question of “CP violation”—why there is more matter than antimatter in the universe.

More recently, Wah also built components for two experiments in Japan, J-PARC and KEK, which studied particles called kaons to further narrow down the rates at which CP violation occurs.

And Prof. Jim Pilcher’s team built pieces that went into the Large Hadron Collider at CERN in Europe—the world’s largest particle physics accelerator. Then, when data came back from the detectors, some of it was analyzed at a powerful computer system housed in the high bay. News rippled around the world when the Large Hadron Collider at last discovered the Higgs boson in 2012—an achievement that was honored with the Nobel Prize in Physics in 2013.

Meanwhile, scientists wondered if CP violation could be explored through a different particle—the mysterious, ghostly particles called neutrinos. Prof. Ed Blucher built pieces for an experiment in France called Double Chooz, which began in 2011, looking for oscillations as neutrinos traveled from a nearby nuclear reactor. For this, they had to create 130 modules, each about five by 13 feet across. “We actually had to occupy the entire high bay and parts of the next-door building; we could not have done it without having a space like that on campus,” said Blucher. “That’s also what made it possible for us have undergrads working on the project. They took leading roles in how we did a lot of the work.”

Closer to home, Assoc. Prof. David Schmitz led a team to build parts of a neutrino experiment called MicroBOONE at Fermilab, which began in 2015.

Today, Blucher leads construction for a segment of a massive experiment that will further that work, called DUNE, which will send neutrinos from Fermilab 800 miles underground to a detector located in a mine in South Dakota in order to study oscillations of those ghostly neutrinos. Blucher’s team already constructed parts of an initial test facility called proto-DUNE, and major parts of the detector are among the first occupants of the new high bay to the west.  

“Having this space allows us at the university to take a leading role in many experiments that we couldn’t otherwise,” said Blucher. “It’s a very unique resource that not only lets us build things, but allows faculty to take leading roles in these experiments, to develop new hardware tech, and for both undergraduate and graduate students to get first-hand experience on the leading edge of experimental physics.”

Gamma rays, Big Bang light, and crocodiles

Other instruments were built to look to the universe from the ground.

The high bay played host to the infancy of the South Pole Telescope, which today sits in Antarctica surveying the sky for the remnant light left over from the Big Bang, known as the cosmic microwave background.

Profs. Simon Swordy and Scott Wakely used the space to build components for VERITAS, a collection of four large telescopes that now sits in southern Arizona to observe high-energy gamma rays from the sky. And Prof. Henry Frisch used the space to experiment with R&D for new technology for detectors for many kinds of experiments.

Perhaps the space’s most surprising occupants weren’t instruments, though; those would be the dinosaurs.

More than 20 tons of fossils from the Sahara Desert by Prof. Paul Sereno spent time in the high bay, carefully wrapped in preparation for painstaking further excavation by a team of scientists and students.

Sereno’s lab was located in the high bay for two decades, starting in the early 2000s when Prof. Riccardo Levi-Setti, a professor of physics who loved trilobite fossils, issued an invite to Sereno as university officials were pondering how to house the enormous tonnage of fossils he had found.

“The high bay let us unload specimens by the ton, and we could take smaller pieces over to the facilities next door at UChicago Medicine for X-rays and scans to reconstruct the skin, bone, and muscle,” Sereno said.

Once, Sereno was pondering how crocodilians swim in order to reconstruct the movements of their ancient relatives, including the meat-eating Spinosaurus and a 40-foot-long monster nicknamed “SuperCroc.” He wanted to get high-speed footage of modern crocodilians swimming, so his team cleared a space on the high bay floor and took extensive measurements as an alligator on loan from the Herpetological Society of Chicago swam in a temporarily constructed pool.

“Yes, the high bay has seen some amazing things,” Sereno said.

A legacy in students

Dozens of students worked on these experiments, exposing them to the joys and frustrations of large-scale scientific endeavors.

“There’s no substitute for understanding an instrument and an experiment better than getting in there and getting your hands dirty working on it, and that’s what students did for decades in the high bay,” said Müller. (For example, one of the high bay’s famous alumni is NASA astronaut John Grunsfeld, famous for fixing the Hubble Space Telescope as it orbited the Earth.)

As this chapter in the Accelerator Building’s life comes to a close, the scientists and engineers who worked there are enjoying the conveniences of their new building (for example, air conditioning). But many expressed a fondness for the old building despite its drawbacks. From the hand-painted numbers on the electrical panels to the file cabinets filled with spare parts for experiments dating back 50 years, the building’s legacy permeated the space.

“It’s impossible to work in that space without thinking of the history of the building,” said Blucher. “I think everyone there knew the connections to Fermi and the discoveries that had been made there, and that was exciting. It was always a real treat to do the work there.”

Editor’s Note: Prof. Emeritus Dietrich Müller provided information and quotes for this article in early 2021. Sadly, he passed away late that year.