For more than two decades, research to harness hydrogen fusion -- the most difficult applied science program ever undertaken -- has been characterized by disappointments and frustrations. But now fusion experts such as John F. Clarke , deputy associate director for fusion at the US Department of Energy, feel elated.
"At last," he says, "we are confident we will have a package we can deliver in 10 years. I'm really excited about it."
This package, he explains, will be a clearly defined concept for a prototype fusion power plant which might well be translated into working hardware by the end of the century.
That may not seem an especially dramatic achievement in a field where the payoff seems always to lie 20 years in the future. But to those struggling with the complexities of managing the "fire of the stars," having such a solid concept will be as welcome as landfall was for the Pilgrims arriving in the New World.
Much hard development work will still be needed to translate the promise of fusion power into reallity. But fusion specialists will at last have firm ground under their feet. They will know where they are, what needs to be done, and whether or not what they are trying to do is economically as well as technologically feasible.
The fact that experts now feel they are within sight of such a "landfall" is reason enough for John Clarke to be excited and for the Congress to give his office a new mandate to step up its research and development program.
Last month, the House voted 365 to 7 to direct the US Department of Energy (DOE) to accelerate the fusion program. It also authorized a substantial increase in funding. The Senate, at this writing, was expected soon to pass similar legislation. Proponents hope, that, by the time Congress adjourns for the year, any differences between the two bills can be resolved and a law enacted to support a substantially increased pace of fusion research.
There are two kinds of basic problems to be solved. First, scientists must learn how to ignite and control a self-sustained fusion process in the laboratory to elucidate the physics involved. Second, and equally important, many difficult engineering problems have to be resolved before such a controlled fusion process can be used commercially to make power.
Study of these engineering problems will require a fusion engineering test facility (ETF) incorporating a fusion reactor dedicated to the purpose.Many experts, including DOE policymakers, had believed that it would be unwise to try to design and build such an ETF until physicists had actually ignited fusion in the laboratory -- a feat expected to be accomplished by the mid-1980s. However, so much progress in understanding the relevant physics has been made in recent years, that it now seems sensible to proceed with an ETF straightaway.
The central question in this research is how to contain the hot fuel and maintain a self-sustained fusion reaction in a controlled manner tha produces power economically and safely. The hydrogen fuel -- typically deuterium and tritium, doubly and triply heavy forms of hydrogen -- will have temperatures on the order of 100 million degrees.
The leading approach in so-called "bottles." One typical shape is the torus, a dough- nut-shaped "bottle" that confines the fuel in a ring. The other main type is a cylinder whose ends are plugged by relatively strong magnetic and electric fields which tend to reflect escaping fuel particles back into the container. This is the magnetic "mirror" concept.
Although bot approaches are promising, the most progress has been made with a version of the torus called a tokamark -- a Russian concept that has become the leading contender for exploring possible fusion reactor designs. Tokamaks at a number of centers, and especially at the Massachusetts Institute of Technology and the Princeton Plasma Physics Laboratory, have achieved fuel temperatures and confinement capabilities that approach those needed in a working reactor.
What is more important to physicists, they have begun to establish certain scaling laws" which predict how a reactor will perform as it is scaled up in size, in fuel density, or in other factors. It is this kind of knowledge that encourages experts to expect fusion to be ignited in the next generation of experimental tokamaks now under construction in Europe, Japan, the USSR, and the United States.
It also is the knowledge that gives experts confidence to proceed with an eTF without waiting for the laboratory demonstration of fusion. "What we need is a program of parallel development," says John Clarke. He explains that all aspects of fusion research now are producing results that are mutually useful. A basic physics program and an engineering development effort can be carried out in tandem with each supplying information that helps the other.
Thus, he says, he expects that, when the ETF is fully operational by 1990, it will be used mainly to confirm and refine knowledge that has already emerged during its development. That is why he thinks fusion experts will be in a position by then to decide how to build a fusion power plant.
Some critics of DOE have urged mounting a fusion effort as intensive as the old Apollo moon-landing project. That would be wasteful now, Dr. Clark says. But, he adds, "By 1990 we should be able to define what can and cannot be done, how much it should cost, and so forth. At that point we could do an Apollo-type program. We would have all the facts. We would, sot to speak, know where the moon is and how to get there."
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