Unlocking the Secrets of Fusion

Ted Taylor was a youthful genius in nuclear weapons circles, a whiz kid who started working at Los Alamos National Laboratory in 1949 and established a reputation for his uncanny ability to divine new and startling methods of building better nuclear bombs.

For almost 20 years, he rode the cutting edge of weapons design, all the while telling himself that it was good for the United States to have a powerful arsenal. The better he could make the weapons, Taylor reasoned, the less likely it was that anyone would be insane enough to actually use them.

But in 1964 Taylor took a job at the Pentagon providing technical advice on the real-world effects of nuclear bombs. Suddenly, instead of theorizing about how to make a bomb smaller, or lighter, he was on the military side, calculating how much destruction different weapons might rain on our enemies. He drew circles on maps of Moscow, to see which of our bombs could wipe out the largest chunk of the city.

He lost his taste for it.
"It was finding out, which I had not known before, how many nukes we had at the time," Taylor recalls. "I thought at most a couple thousand. In fact we had about 35,000 at that time. That's subsequently been declassified, so I can say it.

"I was dumbfounded. I saw no possible reason we should have so many."
Taylor switched sides, and has since devoted his life to lobbying for disarmament and fighting the spread of nuclear technology.

To Taylor, the government's latest foray into nuclear weapons research, the Stockpile Stewardship program, is a disturbing venture. Not only does it promise to sustain the country's addiction to nuclear weaponry, he believes, but it holds the potential for the U.S. to take a huge scientific leap and finally design the weapon that has long eluded our best scientific minds -- the pure fusion bomb.

Understanding Taylor's fear requires some explanation of how nuclear wea-pons work.

When a modern warhead explodes into a fireball, there are actually two nuclear reactions. The first is a fission reaction, in which the atoms in a radioactive material are split apart, unleashing energy.

Each warhead contains a charge of conventional high explosives, like TNT. These high explosives surround a small "pit" of plutonium or enriched uranium. When the explosives go off, they compress the pit, splitting the atoms and starting a fission reaction.

This first reaction, in turn, produces the heat and pressure needed to start the second reaction, a fusion reaction, in which atoms in a thermonuclear fuel like deuterium or tritium are smashed together, releasing even greater amounts of energy.

A fission reaction in and of itself is a powerful beast, capable of producing a respectable fireball. The two bombs dropped on Japan during World War II were both simple fission devices.

But even bigger firepower comes from a fusion reaction, and our arsenal has been significantly more fearsome since U.S. scientists developed the two-step bomb.

No one, however, has yet been able to bypass the first step by figuring out how to trigger a fusion reaction without using a fission reaction to jump-start it. That scientific hurdle has been one of the greatest impediments to anyone -- small nations, terrorist groups, unstable dictators, or whomever -- who might be trying to develop his own nuclear weapons.

Simply put, you need a fission reaction to spark fusion. But to achieve fission, you need either plutonium or enriched uranium, two materials that are very hard to come by. As long as the U.S. and other nuclear nations can keep a tight leash on supplies of these materials, it will be exceedingly difficult for anyone else to make warheads.

The fuels needed for fusion reactions, on the other hand, are plentiful and common elements like lithium and hydrogen. If someone can find a way to spark the fusion reaction without using plutonium or enriched uranium, nuclear weapons will suddenly become much easier to build, and within the scientific grasp of many more would-be nuclear powers.

And that, almost precisely, is what the National Ignition Facility -- the massive new laser being built at Lawrence Livermore National Laboratory -- is designed to do. The NIF, as it is called, will subject tiny pellets of lithium, deuterium, or other fuels to intense pressure and heat, trying to start a small fusion reaction.

"Its function is, for the first time in the history of human beings, to make nuclear explosions without using any fissile material [plutonium or enriched uranium]," Taylor says. "We will be crossing over into a whole new arena."

Many people disagree with Taylor. While his theory may sound plausible, they say, practically speaking there is no way to build a pure fusion bomb. It's a dream, a physicist's chimera, which hasn't proven possible after 50 years of nuclear weapons research.

"I've never seen any even hypothetical analysis of a pure fusion weapon that looked possible," says William Hogan, the senior scientist for the NIF at Lawrence Livermore. "As a weapon, it's not a practical one."

The design of the NIF itself, Hogan says, proves a pure fusion bomb is unlikely ever to be built.

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