If nuclear engineering professor Per Peterson is right, the same energy source that powers the sun may one day generate the electricity that runs your television. In a task that has challenged scientists for decades, Peterson has solved some problems that are key to designing a power plant fueled by fusion, a nearly limitless and clean source of energy.

"Fusion has the potential to be the cleanest of any of the major power sources," says Peterson, who became chair of Berkeley's nuclear engineering department last year. He and other Berkeley engineers are focusing their research on long-term alternatives to current energy systems - efforts that carry renewed significance since California has plunged into an energy crisis,

In a fusion reaction, two hydrogen isotopes— deuterium and tritium — smash together, transforming into a helium atom and a neutron. In the process, enormous amounts of energy are released. As a result, fusion requires minimal fuel. Just six-tenths of a kilogram - a little more than a pound — of hydrogen fuel a day is all it takes to power a thousand-megawatt fusion plant, roughly enough to meet 10 percent of Northern California's electricity demands. Measure this against the seven million kilograms of fuel burned each day in a comparable coal power plant — today supplying 56 percent of this country's electricity needs - and the value of fusion becomes clear.

Hydrogen fuel is also plentiful and easy to obtain. Deuterium exists in water, and tritium can easily be made from lithium. And fusion generates much less waste than either greenhouse-gas-belching coal plants or nuclear power plants, which use fission splitting uranium atoms — to generate energy.

"But reducing radioactive waste requires that the materials close to the fusion reactions are carefully selected," says Peterson.

"Some materials can become highly radioactive when exposed to the neutrons produced by fusion." Peterson and his colleagues have devised an elegant solution to this so-called neutron problem, by reducing the radioactive waste inventory in the power plants to a point so low that even the most alarming release would not require a public evacuation.

Fusion also merits high marks as a power source even when compared to renewable energy sources. The amount of steel and concrete needed to construct a fusion power plant is considerably less than the materials required to build large numbers of solar arrays or windmill farms.

This long list of assets begs the question: why are there no fusion power plants up and running? The enormity of learning how to control fusion, then making it economically competitive, has proven extremely challenging. But by coming up with new ways to simplify a critical piece of the fusion problem, Peterson and his colleagues think they have a solution. "A lot of people believe that fusion is still 50 years away, but by solving the neutron problem, we think we can knock a decade or more off the development path," says Peterson.

His prototype power plant model uses a liquid to protect the fusion chambers walls from energy-producing explosions at its center. The liquid he uses, called flibe - a molten salt composed of fluoride, lithium, and beryllium — is a little more viscous than water, but with twice water's density.

Pumped into the chamber in hundreds of liquid jets, flibe can absorb most of the energetic neutrons streaming out from the fusion explosions. The absorbed neutrons interact with lithium in the flibe to produce tritium, which is later separated from the flibe to supply fuel for the plant.

About half a meter of flibe will absorb nearly all the harmful neutrons in Petersons power plant prototype. "By the time residual neutrons make it out of the liquid, their average energy is so low they have a hard time causing damage," says Peterson. That means that the fusion chamber can be made of simple stainless steel, not exotic materials, thus lowering construction costs. And the stainless steel will last more than 30 years. "Then," say's Peterson, "when we're done with it, it qualifies as low-level waste that can be buried in shallow land because within a few hundred years, everything will have cooled down,"

But, despite the critical breakthroughs, it has been extremely difficult to test various system designs using flibe at the high temperatures (650 degrees Celsius) desired in a fusion plant. Peterson and his colleagues happened upon a seemingly simple solution when they realized they could replace the flibe with water in their experimental tests. "The equations that govern fluid mechanics contain a number of parameters," he says. "If you match those parameters, you can substitute one substance for another and they'll behave in the same way." This has allowed Peterson to use water jets that, for all intents and purposes, behave in exactly lj. the same way as jets of flibe. "That simple approach," says Peterson, "has led to rapid progress."

By experimenting with water jets that move rapidly back and forth, Peterson and.his students have created temporary, liquid-free pockets within the stream of water in the fusion chamber. High-velocity oscillating jets of flibe will behave the same way. This was crucial because the resulting pockets provide the clean vacuum environment required to make inertial confinement fusion work.

In the type of fusion plant Peterson I envisions, a dime-sized cylindrical metal container, called a hohlraum, containing a BB-sized fuel capsule at its center, will be shot into the pocket by a gas gun. As the hohlraum reaches the center of the pocket, highly accelerated beams of heavy ions strike it, heating up its interior to more than three million degrees Celsius. At this temperature, the fuel capsule implodes, compressing a tiny mass of fuel to enormous density, and generating temperatures at its center dose to 100 million degrees Celsius, hot enough to "ignite fusion. Almost half burns before flying apart, releasing energy equal to burning 20 pounds of coal. The resulting explosion destroys the fuel capsule and the liquid carrles the debris away.

"Now we know we can make fresh pockets several times a second," Peterson says. Next were interested in how the pockets respond to the explosion inside.? To test this, Peterson plans to "thump" arrays of water jets by shooting off a series of four blank shotgun cartridges next to them.

Researchers at Lawrence Berkeley National Laboratories, and elsewhere, are working to prove that the fuel capsules will actually ignite and burn and that accelerators can be built that can heat the capsules.

"Over the next 10 years we want to put these pieces in place so that we have high confidence they will work," says Peterson. "A few years later, we could build the first test fusion power plant, generating a few hundred megawatts of power. Then a decade after that, we should be able to build a full-scale demonstrationplant."

All this would fulfill the long-sought quest 'to harness the power of the stars to generate the energy we need on earth.

"Fusion has the potential to be the cleanest of any of the major power sources."