Fusion’s Kept and Broken Promises

Shooting lasers at ping-pong balls

Fusion is weird, and the field is toploaded with expensive gadgets with outlandish names. There are oddball concepts and materials that leave laymen shaking their heads, wondering if they are the products of genius or Star Trek reruns. Take laser fusion: tiny ping-pong balls and spider webs (seriously). In this geek’s fantasia, lasers blast plastic pellets, usually about one millimeter in diameter, that are carefully suspended in real, not figurative, spider webs. To outfit the machines, spiders are bred at the laboratory.

Practitioners of laser fusion have a new Mecca in the National Ignition Facility at Lawrence Livermore National Laboratory in Livermore, Calif. In the high-powered lingo of fusion physicists, “ignition” is achieved when a reaction generates more power than whatever was used to start it. Scientists there hope to achieve ignition by next year. To do so, the plastic pellets are filled with deuterium and tritium gas, then cooled until the gas ices the inside wall. The reactor’s 192 lasers will then fire a torrent of energy at them for a billionth of a second, instantly baking away the surface of the pellets. The force of the material exploding off the surface crunches the ice and gas inside into a super-heated pinpoint of compressed atoms. As the gas and ice compress they heat up to millions of degrees and become 100 times denser than a lead bar. At that density, atoms should fuse and fling particles outward in a stream of energy.

While in other reactors the lasers are fired directly at the pellets, the National Ignition Facility has modified the design. There, the pellets will be suspended within tiny cans lined with gold, uranium and other materials. The lasers will fire from outside the cans and bathe the inner walls, reflecting showers of x-rays that pound the pellet. It will be the biggest laser fusion reactor in the world, poised to demonstrate, arguably for the first time, that a fusion reaction can generate power. If it works.

In Chris Keane’s opinion, it will “explore the basics of fusion energy, building a miniature sun on earth that could supply limitless, safe and carbon-free energy.” Keane, a physicist at the facility, envisions a future laser fusion power plant that generates 1,000 megawatts, about the output of an average coal plant. Others aren’t so sure.

It is too costly and the lasers will break down, says a group of concerned scientists. And then there’s the radiation. Tri-Valley Cares, a conglomeration of citizens and experts in physics and environmental health, have leveled charges against the facility since its plans were announced in 1993. Now, since the release of a new environmental impact statement, “They are forced to admit it will dramatically increase airborne emissions, nuclear waste and worker exposure,” says Marylia Kelley, director of the organization. Officially, however, the Department of Energy has rated it a low-hazard, non-nuclear facility.

Jon Menard, head of Princeton’s fusion laboratory, is not involved with Tri-Valley Cares, but he agreed that the lasers at the facility are unreliable. They will buckle after repeated shots, he says. But the facility’s technological and environmental challenges are just a few of the obstacles laser fusion faces. Some have reservations about the entire concept. Laser fusion is a proxy for weapons testing, they say. “Basically, it’s a device to keep weapons builders employed,” says Charles Seife, science writer and author of a history of fusion, Sun in a Bottle. “It’s billed as an energy project, but it’s a defense project,” he says.

Experts agree: The potential to use laser fusion as a hydrogen bomb test overshadows the quest to develop it into an energy source, according to Johan Frenje, a laser fusion physicist at MIT. “The energy side is sort of hanging on to the weapons research,” he says.

In September 1996 the United States, Russia and 69 other countries agreed to a nuclear weapons test ban, but left their stockpiles intact. The bombs have aged and so have the physicists who have seen them explode. Through laser fusion, weapons testers could study the effects of decaying radioactive elements in their collection of hydrogen bombs (fusion bombs) and young physicists could see fusion reactions occur.

Frenje is a Swede who works in a sunny office at MIT. A whiteboard hung near his desk is tattooed with faded equations scrawled over one another that won’t disappear despite repeated scrubs with the dry eraser. He switched over to laser fusion from magnetic, swayed by the “dark side of the force” as a magnetic researcher once described the other camp. He makes sincere statements — even shocking ones — about his field in a smooth and matter-of-fact tone. For example, he says with a shrug that he doesn’t understand the physics at those high temperatures. He also says he can’t imagine what a laser fusion power plant would look like. A plant, that is, that generates continuous power. It is a far cry from the reactor in California where scientists hope to generate a burst of power for a split second. “It won’t work,” he says. But billions of dollars are spent in pursuit of that dream.

“It’s very off-putting, to be honest with you,” he says. “And maybe I’m ignorant, but they spend tens of millions of dollars and I don’t see any need to spend that money.”

Try to imagine what a laser fusion power plant would look like: a laser shooting range tangled with reams of pellet-studded webs. The pellets are consumed in the reaction and need to be replaced, the reactions are inconceivably brief – there is no continuity for steady energy production. Frenje laughed when asked to consider the possibility. “To me, it’s pie in the sky at this point,” Frenje says. “We’re not there, we’re far from it.” He was speaking about a laser fusion power generator, but he might as well have referred to the whole field of fusion power. There is another way to produce a fusion reaction, however, that many physicists believe is more practical.

Magnetic donuts: our best hope

Andréa Schmidt keeps a gray hardhat embossed with her name on her desk in the control room beside MIT’s tokamak chamber, and ice skates underneath. She is working on a problem in magnetic fusion, one of the many that could block a viable fusion power plant in our lifetimes. To explain her work, something she must do when she ventures to Washington to lobby for congressional funding, she must first explain the tokamak.

If you speak Russian and are familiar with obscure, mid-twentieth century anglicized Russian acronyms, you’ll know that tokamak is a bastardization of Russian words that roughly mean “toroidal [donut-shaped] chamber wrapped with magnetic coils.” Powerful electromagnets line the walls of the inner cavity to guide the plasma around the curved chamber, forcing the particles around the inside of the donut at more than 600 miles per second. If not for the magnets, the plasma would travel in a straight line, smack the tokamak’s wall and cool off. Unfortunately, scientists don’t know how to control the plasma well, and Schmidt is working to add some precision to the effort.