Scientists Announce Fusion Breakthrough At Princeton U. Lab

THERE'S good news coupled with a sobering challenge for American physicists trying to tame hydrogen fusion - the power source of the stars.

The Princeton Plasma Physics Laboratory in Princeton, N.J., expects to announce a new world record today. In an experimental run last Wednesday, its Tokamak Fusion Test Reactor reached 10.7 megawatts of pure fusion power. That exceeds the project's original 10-megawatt target. Furthermore, the reactor team managed to do it for $400 million less than the project's authorized $1.8-billion budget.

``That's good,'' says deputy laboratory director Dale Meade as he notes that the machine is performing beyond its design requirements. But he adds that his elation is tempered by the realization that political constraints and funding restrictions will make it hard to maintain this research momentum.

Fusion power, which is decades away from commercial viability, would open up a virtually unlimited source of energy. Fusion is also expected to be cleaner, without any of the waste associated with fission, the current nuclear technology.

Having exceeded its target, the Princeton machine was due to shut down this fall. An extension of funding, however, will allow an extra year for researchers to round out their investigations.

Concern for 1996 budget

But to move on to the next level of research, scientists need the laboratory's proposed new $700-million Tokamak Physics Experiment. Even though they have money for design studies of the new Tokamak, the future of that machine is uncertain. Congress has so far failed to provide funds for construction. The laboratory is ``in good shape for 1995, but there's great apprehension about the 1996 budget,'' Dr. Meade says.

Congress and the Department of Energy, which funds the research, want to focus less on basic science and more on moving toward a practical fusion power plant. But many of the researchers believe that they need more basic knowledge, as Massachusetts Institute of Technology fusion physicist Richard Petrasso explained last week during a Council for the Advancement of Science Writing conference in Madison, Wis.

Professor Petrasso pointed out some of the subtleties involved. The Princeton machine is the first to work with a roughly 50-50 mixture of deuterium and tritium - two heavy types of hydrogen, the kind of fuel a fusion power plant would use. Earlier machines used pure deuterium. Physicists need to know if they can control this fuel with magnetic forces at temperatures of 100 million degrees C and hold it stable long enough to produce useful power.

Also, the fusion of deuterium and tritium produces the nuclei of helium atoms, called alpha particles. These particles need to deposit their energy in the gas where fusion takes place and thus help to heat it. Then they should be removed. If alpha particles carry away too much energy or accumulate in the fuel, they can cool down the gas and choke off the fusion process.

Generating power

Princeton's Meade says that his laboratory's latest results both hint at alpha heating and show the particles are removed as expected in this experiment. They also show the hot gas was held stable for a so-called energy confinement time of 0.27 seconds - long enough to generate substantial power.

``The deuterium-tritium physics is working, the alpha physics is working,'' Meade says.

Petrasso explained that while the work at Princeton over the past year has been encouraging, more basic research with new machines is needed to see if the fusion physics and alpha physics continue to work as the research is scaled up.

The next step is to ignite a self-sustained fusion process. The Princeton machine cannot do this. Injectors supplied 39.5 megawatts of power to keep the reaction going while fusion itself contributed 10.7 megawatts. The United States has no authorized project to achieve ignition. It is a partner with Europe, Japan, and Russia in the International Thermonuclear Experimental Reactor (ITER) program that aims at building a machine to achieve ignition. But if the Princeton laboratory's proposed next generation reactor is not funded for construction, the US will not have a major facility of its own to explore the subtleties of magnetic-confinement fusion before ITER.

There would still be several smaller university projects. Yet even these may be pinched if the Energy Department and Congress continue to deemphasize basic fusion research.