For more than 20 years, the Tevatron reigned as the gold standard in particle accelerators. Under a berm outside Batavia, Illinois, the machine pushed protons and antiprotons to high energies around circular tracks before crashing them into each other. What's the point of that? When high-energy protons and antiprotons collide, they reproduce the conditions at the beginning of the Universe, just after the Big Bang. In the wreckage, you can find particles that don't normally exist, and observe phenomena that humans have never seen before. By rubbernecking at a particle crash, researchers hope to better understand life, the Universe, and everything. It's kind of a big deal.
But on Friday, September 30, the Tevatron smashed its last protons.
Ultimately, the Tevatron was simply the victim of the progress of technology. When it opened in 1983, it replaced older, lower-energy accelerators. And, in turn, the Tevatron has been replaced by the Large Hadron Collider, an accelerator capable of pushing particles to even higher energies. Once that happened, it was only a matter of time before the Tevatron felt the budgetary axe.
The end of the Tevatron doesn't mean the end of research at the Fermi National Accelerator Laboratory, and it doesn't mean the end of particle research in the United States. But it is the end of an era.
William S. Higgins is a radiation safety physicist at Fermilab, and a contributor to Tor.com. He helped build the Tevatron and he was on hand last Friday, recording his thoughts and some photos to share with us. Here, you'll find a sentimental scientific tour of the last day of a great piece of research equipment. Unless otherwise noted, all the captions were written by Higgins.
Meet Bill Higgins: Wistful is a good word to describe the way I felt, as I witnessed the shutdown ceremonies, and joined the crowd at the party—think of it as a wake—afterward.
[In the photo above, Higgins is leaning on a model of the magnets that helped the Tevatron accelerate particles.]
Higgins: Right now I work on shielding analysis to support future operation of Fermilab's multiple accelerators. Over thirty years ago, I was assigned to work on the testing of Tevaron magnets as they came down the production line. In Fermilab's Wilson Hall, one can see a nice cutaway example. A real Tevatron magnet is a steel box 21 feet long, but here the yoke has been removed to display various layers of the cryostat: outer shell, vacuum, liquid nitrogen, more vacuum, two-phase boiling helium, liquid helium, superconducting coil, and, at the center, a two-inch vacuum pipe the [particle] beam passes through.
On the test stands, the magnets would be cooled down, then powered for the first time. We would run the current up and deliberately "quench" them a few times, to measure how much current they could carry before making the abrupt transition from superconducting to non-superconducting state. This invariably involved the boiling of a lot of helium, the opening of a relief valve, and a loud noise something like the bellow of a bull elephant. Quenching was the most fun part of the job. The rest: a collection of precision measurements compiled into a thick three-ring binder describing a magnet's properties. Warm up, pull the magnet off, shelve the binder, and slap another new magnet on the test stand. All 1000 magnets that went into the Tevatron, plus spares, were tested this way.
A Tevatron "gold watch":I was given a pin to commemorate the occasion [of shutting down the Tevatron]. Here it is, resting on the original design report for the Superconducting Accelerator. The cross-shaped Fermilab logo in the center is patterned after the pole tips of dipole magnets in the Main Ring, our original big synchrotron (but it also resembes four copies of a lowercase F). Surrounding it are the superconducting cables of a Tevatron dipole magnet.
Preparing for The End: Reidar Hahn [part of Fermilab's visual media services staff] adjusts track-lighting in the Main Control Room Thursday, 29 September, after setting up TV cameras in preparation for the televised shutdown event. On right, a ridiculously large TV monitor has been brought in so that MCR participants might view the other locations. I do not know why it was needed, but "because the Main Control Room doesn't have enough display screens" cannot have been the reason.
The Obituaries: A cart loaded with Tevatron posters ready to be handed out at the celebration.
Behind the Scenes: Maxwell Monningh, pictured here on Thursday, was Crew Chief presiding over the Tevatron's final shift on Friday. After the officials and camera crews and Tevatron designers had left the Main Control Room for the party, the operators were busy putting the Tevatron into standby, as well as continuing to operate other accelerators.
Machines and experiments operate 24 hours a day. In the Tevatron's early years, Max and I worked together on fixed-target operations, shepherding beams of protons as they emerged from the Tevatron, targeting them to produce secondary particles, and making sure those beams arrived at experiments. In recent years, the machine has been entirely devoted to creating collisions within its own tunnel, rather than extracting external beams.
On Stage: Friday, 1 October, the shutdown ceremony began around 2 PM. Employees and experimenters gathered in the 800-seat Norman Ramsey Auditorium. Fermilab's Director, Pier Oddone, served as host. Others were gathered at the control rooms of the two massive collider experiments, CDF (Collider Detector at Fermilab) and D-Zero, and in the Main Control Room where the accelerator complex is operated.
Here Dr. Oddone is dwarfed by Bob Mau, who served as head of accelerator operations from before the Tevatron started up until December 2010, when he retired. Bob explained what would happen: The CDF and D-Zero experiments would each end their final data-taking run, then the Main Control Room would terminate the "store," the counter-circulating proton and antiproton beams coursing through the vacuum pipe at the heart of the Tevatron.
The Big Buttons: Todd Johnson, an engineer specializing in Tevatron operations, built a special panel that would look good on TV for the shutdown ceremony. The big red button—BEAM—would cause the speeding particles to end up in a metal absorber. The big green button—RAMP—would drain the current from the superconducting magnets, "ramping them down."
A Strong Will To Live:In a somewhat fuzzy view of the auditorium projection screen, Helen Edwards, leader of the Tevatron's design team, pushes the green RAMP button, having already pressed the red button. The display at upper right shows a red trace, the beam intensity, that has dropped to zero, but a green trace indicates that current still flows through the 1000 magnets of the Tevatron.
There was a brief surprise at this moment as the current did not cease—but after Dr. Edwards hit the green button a second time, the Tevatron obediently ramped down for the final time, to thunderous applause.
At the Wake: At this point the party began, in tents outdoors, and in the fifteen-story atrium of Wilson Hall, Fermilab's central laboratory building. Employees were joined by hundreds of university experimenters from the user community and by retirees returning for the occasion. Flags overhead represent some of the nations whose physicists collaborate on experiments here.
Only the Beginning: As I left the party, sunset tinted Wilson Hall pink. The Tevatron was now idle after 28 years of operation. But computers are still churning on the analysis of accumulated data from the Tevatron's experiments. Fermilab staff and users are deeply involved in experiments at the Large Hadron Collider at CERN in Switzerland. And other machines at Fermilab continue to circulate beams through underground tunnels. We'll keep right on doing physics here.
All photos: William S. Higgins, Fermilab.