Linear Collider: Bold Gamble in Atomic Physics

STANFORD —  Sometime next month, the last switch will be turned on and scientists at the Stanford Linear Collider will learn if they have created an extraordinary device to probe the darkest recesses of the atom or a useless piece of equipment that tries to push the limits of modern technology too far.

If it works, this bold experiment in high-energy physics will rank among the most inventive achievements of modern science, revealing much about the mysterious force that allows one particle to change into another, releasing radioactivity.

But if the machine fails, Nobel laureate Burton Richter and his team of scientists and technicians will have lost an international race that has assumed epic proportions.

“It’s gonna work, but it’s a new machine, and there has never been one like it before,” a confident Richter said.

Optimism Not Universal

That unbridled optimism is not shared universally among the men and women who are adding the finishing touches to the collider, which could go into operation next month, with the first real results coming as early as June.

The design is so revolutionary and success will be so difficult to achieve that even people like Don Getz, the project administrator, wonder if it will indeed work.

“Anybody with any sense would say no,” said Getz, a nuclear physicist who has ramrodded the project for the last five years.

The Stanford Linear Collider is a key player in one of the most esoteric fields of science, the search for understanding of the innermost workings of the atom.

Traditionally, that has also been one of the most expensive fields of science, demanding ever bigger and more costly devices to probe smaller and smaller particles. But the Stanford collider has been built in a bargain basement at a cost of about one-tenth that of its chief rival under construction at Europe’s high-energy physics center near Geneva--called CERN--and it should beat CERN to the starting gate by about two years.

Both colliders--which will pit CERN’s tried-and-proved technology against Stanford’s daring gamble--are designed to do the same thing, so if Richter and his band of revolutionaries are successful, they may already have victory in their grasp by the time their archrival cranks up.

The Stanford project has intrigued scientists at CERN so much that several suggested during interviews a year ago that the United States ought to wait to see if the Stanford collider works before going ahead with a $6-billion accelerator of conventional design, called the super-conducting supercollider. President Reagan recently announced plans to proceed with the supercollider, which would include a circular accelerator with a circumference of more than 52 miles, making it the largest scientific device ever built.

If the Stanford collider is a smashing success, other scientists will undoubtedly question whether the United States is moving down a road toward obsolescence, with a supercollider based on older technology, instead of building on Stanford’s pioneering success.

However, even Richter insists that there are too many uncertainties in the design of the Stanford collider to consider building a giant version on the scale of the supercollider, even if it works perfectly.

The goal of the new accelerator at CERN and the linear collider at Stanford is to capture significant quantities of the Z particle, one of the most exotic habitues of the subatomic world. The Z particle was discovered at CERN in 1983, but it has proven so elusive that only a few dozen have been captured. Physicists believe it may open whole vistas of science if enough can be acquired to permit detailed study.

Z particles are created when electrons collide with a positively charged sister particle, called a positron. They are of profound interest to scientists because they are believed to be the bearers of the so-called “weak force,” one of three forces that govern the subatomic world. The first and best understood of the three is electromagnetism. The second is the “strong force,” the immensely powerful glue that holds atoms together.

The weak force is a force that is so weak it allows atoms to break apart, or decay, in a process that leads to radioactivity.

High-energy physicists believe that a fuller understanding of the weak force could lead to dramatic breakthroughs. The dreamers among them believe that might even include such things as controlling radioactivity through the imposition of a magnetic field.

Any tangible results, however, are many years away. High-energy physicists prefer to describe their work as basic science, meaning no one should expect immediate, tangible rewards. But particle accelerators have changed the course of history through the development of nuclear weapons, and they have even found a place in the everyday world. Television sets, for example, are small particle accelerators, bombarding a screen with electrons to produce a picture.

Thus, any improvement in the understanding of the forces that control the subatomic world could pay rich dividends down the road.

It was none other than Richter who set CERN on the course toward building a bigger accelerator that could capture prodigious quantities of Zs, according to Robert P. Crease and Charles C. Mann, authors of “The Second Creation: Makers of the Revolution in 20th Century Physics.”

Richter, who shared a Nobel Prize in 1976 for the discovery of another subatomic particle, the J/psi, was visiting CERN in 1975 when he set the stage for a drama that would take more than a decade to unfold, according to Crease and Mann. While there, he sketched out the design for what was to become the largest scientific instrument in the world, CERN’s large electron-positron machine, which is under construction.

The machine is a giant nuclear accelerator with a circular “race track” nearly 17 miles long through which electrons and positrons are to be accelerated to nearly the speed of light.

Richter had envisioned that the CERN collider would be a joint U.S.-Europe effort, but the Europeans wanted to go it alone and build the world’s premier high-energy physics center on European soil with European funds, according to Crease and Mann.

Richter, unwilling to be left out of a field he had pioneered, decided to build his own collider at Stanford. But he knew he did not have a prayer of matching the $1-billion cost of CERN’s newest jewel.

Because of the nature of electrons, Richter concluded that it might be possible to build a new kind of collider at a much lower cost. But it would have to function with mind-boggling precision.

Standard accelerators are circular in design, and particles are propelled by an electric field around and around the circle in beams that cross one another. Since the particles continue around the race track at nearly the speed of light as long as the machine is running, the particles have thousands of chances every second to collide with other particles where the beams cross.

That worked fine for most subatomic particles, but it turned out to be very inefficient for electrons. Powerful magnets are used to curve the beams around the race track, but when a beam of electrons is forced to curve, the electrons release most of their energy in a form of radiation. Thus in order to have higher-energy collisions between electrons and positrons, the size of the race track must grow by enormous proportions.

A quarter of a century ago, a young Richter and his mentor at Stanford, Wolfgang Panofsky, had concluded that if accelerators could be built in a straight line rather than in a curved race track, far greater energies could be achieved far more efficiently. In 1962, Panofsky, then head of the program at Stanford, persuaded the university and the scientific community to fund the construction of a linear accelerator.

The accelerator, which from the outside looks like the world’s longest, narrowest barn, runs two miles through the rolling hills west of the Stanford campus and crosses beneath the busy Interstate 280. The purpose of the linear accelerator initially was to fire electrons straight down the course, thus achieving enormous energies, and into a fixed target.

The concept was a radical departure from conventional design, and its success was believed to be one of the factors in Richter’s winning the Nobel Prize several years later.

However, the linear accelerator, like traditional accelerators of that vintage, was limited in that its particles were fired into a fixed target.

Greater Energies in Collisions

Physicists knew that far greater energies could be achieved if particles could be made to collide head-on with other particles, in much the same way as two autos colliding head-on do far more damage than a car striking a brick wall. And indeed, scientists succeeded in getting two particle beams traveling in opposite directions around a conventional accelerator to collide, opening new worlds in nuclear physics.

That revolution, which gave birth to a new generation of particle colliders, turned Stanford’s linear accelerator, with its fixed target, into an antique.

But it turns out that Richter was not ready to abandon the field. After the Europeans decided to build a larger collider, Richter began trying to drum up support for a radical idea.

What if beams of positrons and electrons could be fired down the two-mile accelerator at Stanford and then bent quickly around opposite arms of a circle at the end of the line? Such a design would be extremely efficient, at least rivaling the energies of the collider being built at CERN. But could the beams be compressed so tightly that particles could be made to collide?

Unlike conventional accelerators, where collisions are possible thousands of times every second as the particles whip around and around the race track, the beams emerging from the end of the linear accelerator would cross only once.

To work, the beams would have to be compressed to about one-tenth the thickness of a human hair, and they would have to be focused so closely that they would hit head on.

“The question is, can that be done?” mused Getz, the project administrator.

Getz freely admitted that there is a serious question over whether the device will ever work satisfactorily, since so much of the design is based on the cutting edge of modern technology.

“We are past the state of the art in several areas,” Getz said. “We’ve had problems with all of them.”

The U.S. Department of Energy funded construction of the project at $115.4 million, a paltry sum in high-energy physics. “I think we have about $7.42 left,” Getz said.

Getz, who said the project has been “like a five-year pregnancy,” said he expects to see the collider “doing physics” by June, but he admitted that one of the goals is a little earthier.

“We wanted to beat CERN,” he said.

Nothing would be more satisfying to Richter, except the richness of the moment when he expects to capture the first Zs on detector plates in the large cavern where the beams will collide.

“Our initial goal is 15 per day,” he said. “That will take six days to equal the world’s supply. I’ve told them on the seventh day they can rest.”

“Sometimes, he forgets he isn’t God,” Getz snorted.

If the Stanford collider is a roaring success, why not advance that technology instead of building the supercollider, as scientists at CERN suggested? Why not, as CERN’s technical director, Giorgio Brianti, said in an interview, consider building two huge linear accelerators aimed directly at each other, instead of a conventional accelerator?

Some U.S. physicists agree, although they concede that they are in the minority.

Even Richter said there are too many unknowns to expand the Stanford collider to the scale of the supercollider.

“That would require an extrapolation of our machine by a factor of more than a thousand,” Richter said.

“That’s a long extrapolation,” he added.