High Hopes for a Super Nova

By Natalie Angier

In the lobby of Building No. 391 at Lawrence Livermore Laboratory near San Francisco stands a cast-iron sculpture of Shiva, the multiarmed god whose whirligig dances, according to Hindu tradition, alternately create and destroy all earthly life. Near by is a wood-and-plastic model of Nova, the world's most powerful laser, which is housed in cavernous quarters the size of a football field. The juxtaposition of the two objects is apt, and for several reasons. Like Shiva, the $176 million laser bristles with its equivalent of arms: ten bright blue tubes, each a conduit for an intense laser beam. And like Shiva, Nova will dance to a schizophrenic tune: it could benefit life --and perhaps help to destroy it.

After the giant laser is dedicated in a ceremony at Livermore this week, scientists will employ its intense beam of light in an attempt to weld the nuclei of hydrogen atoms, releasing bursts of energy at temperatures exceeding those at the center of the sun. Should they succeed in harnessing nuclear fusion, they could point the way toward a limitless supply of cheap, clean power. "Once we crack the problem of fusion," says John Emmett, associate director for lasers at Livermore, "we have an assured source of energy for as long as you want to think about it. It will cease to be a reason for war or an influence on foreign affairs."

As the second step in Nova's dance, however, weapons designers will put its powerful beams to a less benign purpose: to improve thermonuclear bombs by mimicking certain reactions in the controlled setting of a laboratory. That will save the Pentagon the expense of having to try out every newly designed bomb at an underground test site in Nevada, a procedure that costs about $10 million per explosion. Eventually, Nova could also be used in research for the Star Wars defense program.

The awesome might of fusion energy can be explained by Albert Einstein's famed equation, E = mc 2. When two nuclei from hydrogen atoms are shoved together to become a single, heavier helium nucleus, a tiny bit of their individual masses is converted into a tremendous amount of energy. In weapons, that energy is uncontrolled and destructive. To channel it into a usable form, scientists must be able to control the fusion reac- tion and confine it to a chamber, which requires surmounting some formidable physical constraints. The hydrogen nuclei must be crushed together with enough force to overcome their mutually repellent positive electric charges. In H-bombs, that force is supplied by the detonation of a fission bomb, or A-bomb.

But A-bombs cannot be exploded in power plants, and when Lawrence Livermore scientists begin their experiments six weeks from now, they will use powerful laser beams instead. In Nova, under the guidance of more than 50 computers, a pulse of light is whipped around a master oscillator until all of its wavelengths are identical and in phase. The pulse of pure laser light is then split into ten parts, each of which races down its own 460-ft.-long tube equipped with amplifiers, spatial filters and isolators. As it emerges, each beam is focused to about the width of three human hairs, yet is a thousand trillion times brighter than the sunlight that falls on the earth. Together they deliver 100 trillion watts of power, about 200 times the present electricity-generating capacity of the U.S., albeit only for a billionth of a second.

The tubes terminate inside an airless 16-ft.-wide aluminum chamber, each entering it from a different direction. Inside, the focusing lenses are arrayed around a pellet of deuterium and tritium, two heavier varieties of hydrogen atoms. Scientists hope that when the beams simultaneously hit the pellet, which is smaller than a grain of sand, the temperature of the pellet's outer surface will be raised to 100 million degrees, causing it to vaporize explosively. Just as a rocket is pushed forward by its tail exhaust, the vaporizing surface would exert a force inward, compressing the pellet to a density 20 times that of lead and forcing the nuclei to fuse. In the fusion power plant of the future, Livermore scientists say, larger pellets will be blasted, one after another, producing successive bursts of energy.

Critics of the laser fusion program contend that it is five to ten years behind magnetic containment fusion, a technique that uses powerful magnetic fields to contain the reaction. But magnetic fusion, too, still has a long way to go. It has not yet even reached the stage at which the energy produced by the machines equals the energy required to run them. Says Livermore's Emmett: "Fusion is one of the most difficult technological undertakings that man has ever engaged in, and probably one of the most important."

With reporting by Christine Gorman/New York and Dick Thompson/San Francisco