Fusion Experiment Sets 5.6-Million Watt Record : Science: The nuclear reaction is hailed by scientists who say it realizes the potential of a cheap source of electricity with little environmental damage.

Researchers at Princeton University hit an “eagerly anticipated milestone” by producing the strongest controlled nuclear fusion reaction on record, scientists said Friday.

They generated a burst of 3 million watts of energy--nearly twice the previous world record--in a test Thursday night before 500 invited scientists and guests. An experiment Friday nearly doubled the fusion reaction to 5.6 million watts, said Dale M. Meade, deputy director of Princeton Plasma Physics Laboratory.

The reaction was created in an experimental reactor at the lab financed by the U.S. Department of Energy. In the next nine months, the scientists said, they hope to increase the output to 10 million watts, enough to power about 3,000 homes in the United States.

The new record was set by supplementing the reactor’s deuterium fuel with radioactive tritium, a gas used to enhance hydrogen-bomb explosions. Deuterium and tritium are isotopes of hydrogen--chemically identical to the simple element but with significant differences in atomic nuclei.

“We always knew that once we added this high-performance fuel--nitroglycerine, really--we would have high-performance output,” said Michael Brown, a senior research associate at the California Institute of Technology in Pasadena. “From a scientific perspective, it was interesting but something we would have predicted.

“But from a public relations perspective,” Brown added, “it is very important because it makes it easy for us to connect with the general public, policy makers and funding agencies.”

Federally funded fusion-energy programs have come under congressional scrutiny recently as deficit-conscious budget analysts have skeptically reviewed decades of unrealized promises about fusion’s potential to supply large amounts of cheap electricity with little environmental damage.

Practical fusion energy, which would use the process that fuels the sun to create virtually limitless energy from the constituents of ordinary seawater, is still decades away from being practical, scientists acknowledged Friday.

But by demonstrating the increased efficiency afforded by tritium, scientists believe they have re-energized fusion research after spending decades learning how to control a nuclear reaction inside a magnetic field.

Fusion reaction works by forcing the nuclei of hydrogen isotopes to merge, or fuse, into helium. The theory is simple, but the practice is extremely difficult because atomic nuclei naturally tend to repel one another.

To overcome this tendency, fusion reactors must strip atoms of their electrons and heat the stripped nuclei to millions of degrees Fahrenheit, causing them to move very rapidly. Applying a strong magnetic force steers these speeding nuclei toward one another, where their inertia can overcome their natural distaste for one another.

When the single-proton deuterium and tritium nuclei get close enough, an atomic phenomenon called the strong force--the force that binds protons and neutrons together in the nucleus of an atom--lets them fuse into twin-proton helium atoms. The process sends neutrons hurtling off into space, releasing the energy that formerly bound it in the atom.