"The Fire Next Time" by William J. Hogan, Roger 0.Bangerter, and Charles P. Verdon, in The Sciences (Sept.-Oct. 1996), New York Academy of Sciences, 2 E. 63rd St., New York, N.Y. 10021

Critics of nuclear fusion research joke that Hogan, Bangerter, and Verdon-of the fusion power is only 20 years away-and Lawrence Livermore National Laboratory, always will be. But fusion research scientists the Lawrence Berkeley National Laboratory, and the Laboratory for Laser Energetics at the University of Rochester, respectively- think they will be able, with the aid of a $1.1 billion National Ignition Facility that is in the works, to prove the skeptics wrong.

For fusion researchers, they write, "this is a time of high drama," and morale is high. "The traditional reasons for optimism are as compelling as ever. For one thing, fusion works. An operational fusion reactor, the sun, illuminates the sky every day." A fusion reac- tor scaled down for earthly use would provide a source of energy that, in contrast with nuclear fission, would be safe (no possibility of a sustained chain reaction), clean (no eter- nally radioactive by-products), and virtually inexhaustible. But the physics involved in confining and heating two rarified gases (deuterium and tritium, both hydrogen iso- topes) to the temperature of the sun is a daunting obstacle to scientists.

There are two main approaches. One is magnetic fusion, in which the challenge is to use magnetic fields to keep the fuel confined. International teams in Europe, Japan, the United States, and Russia are currently designing the International Thermonuclear Experimental Reactor, which will be the largest facility of its kind. Hogan and his col- leagues are working on inertial confinement fusion, in which a laser or particle beam is used to heat and compress a fuel capsule until it detonates, with the fuel's own inertia keeping it confined long enough for the reac- tion to take place. "The long-standing hurdle has been ignition," the authors say.

Just a few decades ago, estimates of the energy needed to achieve ignition varied widely-from 10 kilojoules to 10 mega- joules. Now it appears that between one and two megajoules will be needed. This refinement, say the authors, "has made it possible, for the first time, to design equip- ment and set realistic budgets for achieving fusion ignition."

Major programs are under way in the United States and eight other countries. A French inertial confinement research facili- ty, Megajoule, is scheduled to be completed between 2005 and 2010 in Bordeaux. Construction of the U.S. National Ignition Facility, at a site not yet selected, could begin this spring, with late 2002 the target for com- pletion. If that schedule is kept, the authors are confident that "experiments would then lead to ignition by 2005." Two decades after that, they say, commercial fusion power could become a reality.