History and Archives

On September 15, the Main Ring shut down after 25 years in the forefront of particle physics research.

Videocameras rolled, Nikons flashed, and onlookers cheered. On September 15, with a ceremonious push of a giant gold lever fitted with royal-blue grips, beam in the historic Main Ring was switched off in Fermilab’s Main Control Room, ending a stunning era of particle physics.

When it was completed in 1972, the Main Ring was the most powerful accelerator of its time, and in the years to come, as Director John Peoples said, it would put Fermilab “on the map.” Despite its balky dipole magnets, the Main Ring enabled physicists to collect reams of data confirming the Standard Model and to find the bottom quark, the first quark in the third generation of matter’s elementary particles. In its last 14 years, the aging accelerator still served as an injector, thrusting protons into the still-more-powerful Tevatron and spurring the discovery of the top quark.

But who might have predicted such an illustrious part in the history of particle physics from the Main Ring’s fitful beginnings?

Bob Mau, chief of Accelerator Operations, who was here at Fermilab when the Main Ring was first commissioned, said that turning off the Main Ring at the Monday morning ceremony was a lot easier than turning it on 25 years ago.

Then, said Rich Orr, another Main Ring veteran who spoke at the ceremony, “there were floods, there were famines, there were frogs.... The machine had every flaw imaginable.... We were the laughingstock of the world.”

Design

“The old 200-GeV project [with the Main Ring as its centerpiece] was easily the biggest thing [the U.S. Department of Energy] ever attempted,” said Peoples. Its $250 million pricetag is equivalent to $1 billion today.

The design of the Main Ring was born in 1967 on an empty stretch of tile flooring in unfinished rented office space in Oak Brook, Illinois, when Robert Wilson, Fermilab’s founding director, promised Congress he would build the machine by June 1972.

He would, indeed, but he would do it his way, according to Catherine Westfall and Lillian Hoddeson, historians of science who have chronicled this period. He had no experience in building large proton synchrotrons, but he shunned the experts, dismissed the engineers, lauded creativity and extolled risk-taking. His detractors called him irresponsible; his supporters, a genius.

“Money and effort that would go into an overly conservative design might better be used elsewhere...,” he told Westfall and Hoddeson, explaining his unconventional approach. “A major component that works reliably right off the bat is, in one sense, a failure—it is over-designed.”

Wilson’s goal was to build the highest-energy machine at the least possible cost. And since the bending magnets absorb at least a quarter of the total cost of an accelerator, attention focused there. To save money, Wilson opted for compact bending magnets with simplified methods for inserting and fabricating the coils. Never mind, according to Westfall and Hoddeson, that “the use of pared-down magnets was inherently risky, since larger magnets produce higher fields more reliably...[:] the simplification bought considerable savings.” Later modifications decreased the magnets’ weight and improved magnetic properties.

Westfall and Hoddeson quote Norman Ramsey, then president of the Universities Research Association, Inc., as saying that Wilson “took risks on about 20 aspects of the design, saving about $5 million per risk. ‘We knew something would fail,’ he noted, ‘but we figured it would be much less expensive to fix the failure than to play it safe with all 20 items.’”

Construction

In October 1969, Wilson broke ground for the Main Ring’s tunnel (Fermilab physicist Ernest Malamud, who served on Wilson’s management team, still has the shovel).

Those were heady times, when Wilson spurred Herculean efforts, but Malamud also remembers the pressure, as Wilson advanced deadlines and drove his staff toward ambitious goals.

The director insisted, for example, that a magnet be set in the tunnel as soon as it was dug, not for technical reasons, but just to let the construction workers know that the scientists were “on their tails,” according to Westfall and Hoddeson.

And money for machine parts was doled out to two contractors at a time. Each contractor would receive a third of the money; whichever one finished first got the remaining third.

Installation of the magnets proceeded at a feverish pace. In April 1970, the first magnet was placed in the tunnel, and a year later, the last.

Summer of 1971

But in the summer of 1971, tensions were wound as tight as a copper coil. Because of the hurried schedule—by now, Wilson had promised to get the Main Ring done a year early—the magnets had been installed in the middle of winter, making them very cold. When spring arrived, it brought in warm air. Water, as much as a quart, condensed on the magnets, and they short-circuited. As Westfall and Hoddeson noted, “Unless the magnet problems were solved, the entire project would fail,” and no one was sure what the causes were.

Other problems surfaced, according to Westfall and Hoddeson: magnets were misaligned, ion pumps failed, pieces of copper were found lying in the beam pipe, a plastic cap was stuck in a quadrupole.

Shards of stainless steel, left over from the process of cutting magnets, lay in the Main Ring’s vacuum tube. Researchers tried training a ferret, named Felicia, to collect the debris by dragging a harness through the tube, but Felicia refused to cooperate.

Rumors spread of a campaign to oust Wilson.

But by winter, the troublesome magnets had been reconditioned or replaced, and the project was finally back on track.

Success

In January 1972, researchers produced a stable beam of 20 GeV, and Wilson could claim that the project had come in on time and under budget. By February, the beam reached 100 GeV, breaking the world’s record for proton energy. Malamud and Soviet colleagues launched the first fixed-target experiment, attempting to determine whether the size of the proton varied with the energy of a collision.

The beam ramped up to 300 GeV in July 1972, and to 400 GeV by the end of the year.

According to Westfall and Hoddeson, a full-scale research program was under way by 1975, with the beam routinely operating at 400 GeV and an intensity of 1.84 X 10¹³, and unscheduled downtime totaling only 28 percent. In May 1976, the Main Ring produced a beam of 500 GeV.

By then, according to Westfall and Hoddeson, people were jokingly proposing Wilson for sainthood. Yet those dipole magnets remained a problem, to the very end.

On to the Main Injector

With the shutdown of beam on September 15, crews began dismantling the Main Ring. Parts of the historic machine will be recycled, though not the troublesome dipoles. Eighteen of the Main Ring’s radiofrequency cavities, which accelerate the beam, and 120 quadrupole magnets, which focus the beam, will find their way into the new Main Injector, scheduled for launching in 1999. The Main Injector promises a much greater number of collisions, and better chances of finding elusive particles at high energies.

Thus the Main Ring, or pieces of it at least, will witness a new era of particle physics, perhaps the discovery of supersymmetric particles, maybe even the Higgs boson, helping explain still deeper reaches of matter and its distant beginnings.

But officially, the next beam projected into the Tevatron will be from the Main Injector, not the Main Ring. That’s why Steve Holmes, project manager for the new injector, told the September 15 gathering he was not contemplating the end of one era and the beginning of another. With all the work yet to do next year, he was thinking only: “Gulp!”