The Heart of the Matter
The mile-long track at the Department of Energy.s Thomas Jefferson National Accelerator Facility in Newport News, Va., may be the world's fastest speedway, with laps clocked at a few millionths of a second.
The loop is an electron accelerator: scientists from around the world use the giant atom smasher for basic research on the structure of the atom. Jefferson is open to the public just once every two years — and Saturday's the day. Visitors to the biennial open house will be able to tour the facility and hear its scientists discuss their work.
"Jefferson Lab is unique," said Emmanuel Paschos, physics professor at the University of Dortmund in Germany, during a recent visit to the lab. "Of the world's dozen or so high-energy accelerators, it is the most powerful built specifically to investigate the structure of everyday matter."
Everyday matter? That's us, and everything around us.
Research at the lab comes down to some pretty simple methods. "I study the nucleus like a five-year old does," says Larry Weinstein, a physics professor at Norfolk's Old Dominion University. "I hit it hard and see what comes out. I'm hitting something really small, a target of some atoms at the end of the accelerator, so I need a really small hammer. And I have to hit the atoms really hard, so I need that hammer moving really fast."
Weinstein's hammer is a single electron, accelerated almost to the speed of light, to vastly increase its mass. He measures what happens to the atomic target during the collision, using the lab's incredibly sensitive instruments, "to learn about the structure of the nucleus, how quarks combine to form protons and neutrons, how protons and neutrons combine to form the nucleus of the atom, and about the forces that hold those building blocks of the nucleus together."
All the major components of the electron accelerator will be on view at the open house. Fired into the accelerator by a laser gun, electrons travel in a tightly focused beam about the diameter of a human hair, enclosed in a pipe 11/2 inches in diameter. The accelerator loop is set in a bored out tunnel 25 feet underground. The business end of the accelerator is three huge experimental halls, spectrometers record the collisions between the electrons and their targets. One magnet alone, used to steer the electrons, weighs 450 tons.
Super-speed, super-collisions, superconductivity. Jefferson has the largest installation of superconducting technology of any accelerator on the planet, used to drive the electrons to higher and higher speeds. Superconductivity. Think cold, very cold. The inside of the electron beam pipe is chilled by liquid helium to 456 degrees below zero Fahrenheit to keep the electrons zipping along. To prevent the electrons from colliding with anything before they hit their target, the pipeline is kept at a nearly perfect vacuum.
The lab's scientists will show visitors some of the 300,000 instruments set up along the accelerator track to speed up the electrons and keep them in tight focus. Jefferson's electron beam is so powerful, and its detectors so precise, that measuring the collisions between the electrons and their atomic targets in the experimental halls gives new insight into the structure of matter. Until recently, for example, scientists could only study the behavior of individual protons and neutrons, though these particles in nature are often paired up.
At the open house, Weinstein will describe how, "just as people behave differently as couples than as individuals, so do protons and neutrons. Just like some human couples, when they get too close they violently repel each other — in this case, whirling around at almost the speed of light, trying to escape. We study what keeps them together: relationship dynamics on a very, very small scale."
Jefferson's open house may be particularly apropos in 2005, the International Year of Physics, which marks the 100th anniversary of Einstein's theory of relativity. After all, explains Department of Energy physicist John Harvey, "What happens at the accelerator is really the application of the theory of relativity."