Advertisement

UCLA Team Seeking New Keys to Atoms’ Inner Secrets

TIMES SCIENCE WRITER

Chan Joshi swiftly navigated the labyrinth of Boelter Hall’s classrooms and offices toward his laboratory on the first floor of the UCLA engineering building. The cluttered, windowless room was dominated by a carbon-dioxide laser and the odd gear used to control it.

Off in one corner, away from the skillet-like copper mirrors and the portholes sliced from pure salt crystals, was a stainless steel chamber the size of a vacuum cleaner. Joshi and his graduate-student assistants posed behind it. This was where they taught electrons to surf.

In Texas, workers only recently began constructing the Superconducting Super Collider, and years will pass before the 54-mile-long, $10-billion science device can be switched on to try to answer some fundamental questions about atoms and the universe.

But Joshi and a handful of other scientists already are looking beyond the SSC and asking: What next?

Advertisement

Like superior chess players, these scientists are scrambling to stay several steps ahead of themselves. Their goal is to anticipate the methods and machines that would be needed to solve subatomic riddles no one has yet uncovered--riddles with solutions beyond the reach even of the mighty super collider, the biggest and costliest science device in history.

In his cramped laboratory, Joshi has demonstrated the feasibility of one of these machines, a new kind of particle accelerator. Unlike the super collider, which uses electrical fields to crack open relatively heavy protons, Joshi’s device uses plasma waves to slam together lighter electrons.

His “beat-wave accelerator,” based on a theory by fellow UCLA professor John Dawson, uses exquisitely timed laser pulses a few trillionths of a second long to shove electrons almost to the speed of light in a fraction of the space required by today’s best particle accelerators.

With this technology, better particle accelerators would not necessarily have to be bigger. That is welcome news to policymakers still trying to sell a skeptical Congress on the value of a super collider the size of an entire county.

Advertisement

The laser pulses in Joshi’s device create an electrically agitated gas, or plasma, rippling with very orderly waves. Electrons added at precisely the right instant tend to “surf” these waves, picking up speed the way people do when they ride ocean waves.

It is a delicate and complicated process that relies on notoriously unstable plasmas, Joshi conceded. But the experimental machine in his laboratory, while complex enough to be worthy of Rube Goldberg, shows that the idea works--indeed, he said, “it worked just as advertised.”

And, Joshi added, the beat-wave accelerator has the ability to add speed to electrons more quickly than any other device, so a production model eventually may match the power of some of today’s more powerful accelerators in a fraction of the space.

Whether this technology ever leaves the lab depends on whether Joshi and other researchers--beat-wave accelerators also are being developed in Japan, France and Britain--can increase both the size and power of their machines at a reasonable cost.

But even if they prove unable to do the kind of cutting-edge research expected of the super collider, beat-wave machines still can be useful, Joshi and Dawson said. Since they accelerate particles so much more quickly than conventional designs, powerful beat-wave machines could be relatively compact and easier to fit on more college campuses, making them more accessible.

Instead of one giant machine accommodating a few collaborative experiments--a process that forces many scientists to compromise their work--dozens of machines could be available to let individual researchers pursue their own theories. Accelerator time could be made as accessible as computer time was opened up when personal computers supplanted bulky mainframes.

In addition to benefiting researchers, this would make powerful accelerators accessible to more hospitals, where cell-killing particle beams from a few conventional machines already are used to combat cancer. Beat-wave machines also can be used to generate tiny bursts of light or x-rays that would permit better medical images using only a fraction of the radiation.

These electromagnetic “microbusts” also could allow scientists to make slow-motion movies of chemical reactions, which have never actually been seen before.

Advertisement

None of this occurred to Dawson when he dreamed up the idea of beat-wave particle accelerators while working at Princeton University in the 1970s. At the time, he was trying to use the coherent amplified light in laser beams to trigger temporary nuclear fusion reactions, but was frustrated when the laser created turbulence in the reactor’s plasma fuel.

Once he worked out how the turbulence could be harnessed to accelerate electrons, potential applications were easy to think up, he said.

Accelerator physicist Andrew Sessler of Lawrence Berkeley Laboratory said the demonstration by Joshi was a “significant step forward” in efforts to develop a new generation of machines beyond those available today.

When the super collider eventually uses its unprecedented energy to crack open protons, the debris should tell physicists a lot about atoms: what holds them together, what causes some to decay radioactively and how those processes are related.

But the field of particle physics will not come to an end when the super collider completes its work, even if its discoveries help theorists puzzle out the grand-unification theory--the so-called “theory of everything” that would prove a common basis for all the basic forces in nature. This theory, which stumped Einstein, is the most coveted goal in physics.

Scientists know from history that discoveries made by the SSC are likely to raise a new set of questions.

When the Greeks, for example, first tried 2,400 years ago to divine the most basic building blocks of nature, they suggested matter was made up of indivisible parts called atoms. Nothing could be smaller, they thought.

Savvier scientists later asked what atoms were made of, and then asked the same question of the protons, neutrons and electrons they found inside. This led to the discovery of exotic new particles called leptons and quarks, as well as the bosons, gluons and other particles binding them together.

Advertisement

At each step, the discovery of new “elemental particles” led to a fuller understanding of nature and significant advances in electronics, chemistry and the development of new plastics, metals and other materials.

However, some of the particles described in the “standard model” of atomic structure only exist on paper because no one has a machine powerful enough to thoroughly smash up protons and find them. No one, for example, has confirmed the existence of the “top quark” (an arbitrary name chosen by whimsical physicists) or the Higgs boson (named after a British physicist).

The super collider is designed to discover these missing pieces. But researchers suspect it cannot answer all the questions they want to ask about how these particles interact and it may turn up some unexpected phenomena, such as some particle they didn’t expect, that will require a new device to explore and explain.

To answer such questions, the next generation of physicists would need a new, more powerful generation of accelerators.

A bigger version of the super collider is not an option, scientists agree. The nation could not afford it, they said, and engineers might not even be able to build it.

Moreover, speeding up protons--as the super collider does--needs far more room and energy than accelerating lighter electrons, so scientists around the world have been concentrating on designing electron accelerators. But to reach speeds they desire, a machine using conventional technology would have to be prohibitively big--from 4 to 18.6 miles long--and costly--about $4 billion.

In principle, beat-wave technology may be an alternative. Dawson estimated that a beat-wave accelerator could push particles to 500 billion electron-volts in a little more than three miles--one-sixth the distance needed by some of the more conventional linear colliders under study.

Joshi conceded that no one can yet estimate the cost of a beat-wave machine that size, nor could he say if he or anyone else could create a pencil-thin plasma three miles long. He said much work also is needed to boost the “luminosity,” or density, of the electron beam created by plasma accelerators.

For the record, Joshi stresses he is content to count and clock the electrons streaming out the back of his device, and try to stay a step ahead of friendly competitors at the University of Osaka in Japan, Ecole Polytechnique in France and Rutherford Laboratory in Britain.

Privately, however, he and Dawson let themselves wonder about innovative technologies--the ground-breaking medical diagnostic devices, mind-boggling microscopic movies and world-beating particle accelerators--that may wait just a few experiments down the road.

“We aren’t pretending to be in competition with (traditional) accelerators--yet,” Dawson said. “They’re building on a design developed in the 1930s, so they have a lot of history and experience when it comes to making them bigger and better.

“But if we can continue overcoming technical problems the way Chan has so far, it opens up some real possibilities, oodles of ideas that we are only just now beginning to imagine.”


Advertisement