Barrett H. Ripin, associate executive officer of The American Physical Society, offers this reply:

"Actually, fusion research has made remarkable progress in recent years. There is no longer any question of its scientific feasibility: near breakeven (the state at which the fusion power produced equals the power consumed to sustain the plasma) has been demonstrated with actual fusion fuels in Princeton's nearly 20-year-old Tokamak Fusion Test Reactor (TFTR). Dramatically improved operating regimes have recently been discovered that may form the basis of a practical energy reactor. An alternate approach, known as inertial confinement fusion, has also made substantial progress. Inertial confinement fusion is poised to demonstrate better than break-even gains at the turn of the century. The clear key to this progress has been advances in understanding the scientific underpinnings of plasmas and of fusion science. In the process, several billion-dollar-per-year applications of plasmas have emerged.

"The questions at hand now are really: Will fusion energy become practical and economically feasible? Is society willing to make the necessary investment to find out if the answer is yes?

"When fusion research began in earnest 30 years ago, people simply did not appreciate the complexity and subtlety of the science of plasmas, and the concomitant depth of understanding that would be needed to make controlled fusion work. Scientists also vastly underestimated the engineering requirements and constraints--a result both of naivete and unknown scientific hurdles. And it is natural that the closer one gets to the goal of practical energy, the longer each next step takes. The experimental devices grow larger and more expensive as one approaches a commercially viable fusion reactor.

"Is it worth continuing fusion development? If scientists conclude that the burning of fossil fuels is inducing unacceptable global climate change, then we have a limited number of alternatives to turn to: solar-based sources (photovoltaics, ocean, wind, etc.), nuclear fission and fusion. Solar-based sources will be increasingly important in niches but can not supply humanity's bulk power demands, particularly if worldwide standards of living continue to rise. Nuclear fission could fill the gap, but it has well-known disadvantages.

"So the question really becomes: Can we afford to take the risk not to vigorously pursue fusion? One new power plant costs between $1 billion and $10 billion these days; a new generation of power plants would total about $10 trillion! Is fusion research funding of around a billion dollars per year for even 50 more years a reasonable gamble? It is to me."

Charles C. Baker, associate director for fusion at the School of Engineering at the University of California, San Diego, and the International Thermonuclear Experimental Reactor (ITER) U.S. Home Team Leader, adds his views:

"Thank you for giving me the opportunity to respond to this question. First, let me state that I disagree with the premise of the question. Research in magnetic-confinement fusion has produced excellent results. In the past 15 years, research in the U.S. and other countries has increased by 10,000,000 times the fusion power level produced in experiments, and we have now achieved production of 10 megawatts of fusion power on the Tokamak Fusion Test Reactor at Princeton. (A tokamak is a kind of magnetic donut that has proven to be a particularly stable way to confine the extremely hot plasma needed to achieve fusion.) This dramatic progress has been accomplished through investments made by the U.S., Europe, and Japan during the 1970s on a new, more powerful class of tokamak experiment.

"The next step in power reactor performance levels, at which the plasma is capable of ignition and plasma 'burn' (wherein most of the heating energy comes from the fusion reactions), again requires a new, more powerful experimental device. The U.S. tried to proceed with a next-step burning plasma experiment in the 1980s, but was unable to obtain congressional funding. The U.S., Europe, Japan and Russia are now collaborating on the design and R&D work for a project called the International Thermonuclear Experimental Reactor. ITER is designed to achieve plasma ignition and long-pulse burn. It will also demonstrate the technology required for the core of a fusion power plant and the systems needed for extracting power from the device. This six-year collaboration, called the Engineering Design Activities, began in 1992, and exploratory discussions are now underway concerning cost-shared, international construction of this device. Such an engineering test reactor is required by all parties for progress toward practical fusion energy, so cost sharing for this step is mutually advantageous.

"The combined results from a variety of tokamaks around the world have produced an impressive set of achievements. Neutral beams and a variety of radio-frequency heating methods can provide tens of megawatts of heating power for creating high-temperature plasmas. Experimental devices have produced ion temperatures as high as 45,000 electron volts and densities of approximately 1020 particles per cubic meter, sufficient for fusion reactors. An important overall measure of physics performance is the 'triple product' of the peak ion density, the plasma energy confinement time and the peak ion temperature. A triple-product value of 7 x 1024 electron volt-seconds per cubic meter is required for an ignited, deuterium-tritium reactor. JT-60U, a large Japanese tokamak, has already achieved triple products of 1.3 x 1024 electron volt-seconds per cubic meter.

"The nominal fusion power of ITER is 1,500 megawatts; it represents a framework for a full-size fusion power reactor, though it is not designed to produce electricity. An extrapolation of the present knowledge of tokamaks indicates that commercial fusion reactors will be rather large and expensive. Fortunately, ongoing research programs are revealing ways to improve substantially the performance of tokamak reactors. These promising new directions include higher fusion power densities, and hence smaller reactors; development of 'transport barriers' in the plasma, leading to improved energy confinement and smaller sizes; self-driven plasma currents that permit steady-state operation and low recirculating power; and the development of advanced divertor concepts to provide particle control and heat removal over long reactor lifetimes.

"The rate of progress in the fusion program is consistent with the level of resources being devoted to it. Actual funding has been much less than anticipated during the detailed planning drawn up in the 1970s and 1980s. Present levels of funding in the U.S. ($244 million in fiscal year 1996) are not sufficient to keep pace with the earlier plans. As a result, the U.S. is unfortunately passing its traditional leadership in magnetic fusion to Europe and Japan.

"In August 1996, the U.S. Department of Energy issued a Strategic Plan for the Restructured U.S. Fusion Energy Sciences Program. The nation's previous strategy was a schedule-driven development program to prove fusion to be a technically and economically credible energy source, with the goal of an operating, demonstration power plant by about 2025. In a climate of severe budgetary constraints, however, that strategy became highly unrealistic. In an attempt to stay as close as possible to the goal-oriented schedule, the fusion program has concentrated almost all of its available resources on the tokamak concept, virtually eliminating support for alternative approaches and for basic plasma science. Despite impressive scientific progress, the program continues to receive insufficient resources.

"The new strategy emphasizes an international effort aimed at advancing the scientific knowledge base needed for the development of an economically and environmentally attractive fusion energy source. To be a credible partner in this long-term quest, the U.S. needs a vigorous domestic program in fusion science and technology. At a constant level of funding, the restructured U.S. program will be able to focus on fusion's underlying scientific foundations and will enable the nation to take the lead in selected areas of expertise as part of the international effort to develop fusion energy.

"The restructured U.S. program will strive to remain a credible partner in the international fusion program that includes both ITER and many smaller projects in all areas of fusion science and technology. Given the high projected cost of creating a burning physics experiment and given that the U.S. now funds only about one sixth of the world research effort, a strategy based on international collaboration on fusion energy research and development can be highly cost effective.