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Overview: Assessment and Historical Context
The quest for fusion energy is one of the greatest scientific and technological challenges ever attempted, driving the development of modern plasma science and of the technology needed to work with one of the most hostile experimental environments on Earth.
The committee, through its three working groups that produced the main chapters of this report, studied the science being carried out in the fusion program, the various past and current plasma confinement configurations, and the interaction of the fusion science program with allied areas of science and technology. This examination of the magnetic confinement plasma research funded by the U.S. fusion program and of the standing of this research in the international fusion community has led to assessments in three areas: scientific progress, the development of plasma confinement configurations, and links to the broader scientific community.
ASSESSMENT OF QUALITY: SCIENTIFIC PROGRESS AND THE DEVELOPMENT OF PREDICTIVE CAPABILITY
The fusion research community has produced a continuing stream of scientific discoveries and technological innovations in pursuit of a practical fusion power source (the fusion energy goal). The research problems central to contemporary magnetic fusion plasma science—turbulence and transport, the limits on the magnetic confinement of plasma energy density, and the physics of reacting, self-heated plasmas—are extraordinarily challenging. The challenge—physical probes cannot survive the intense thermal fluxes in the high-temperature regime of interest to fusion research—is a consequence of the strong nonlinearity of the plasma medium and its resulting complex and rich dynamics. The study of high-temperature plasmas motivated by the fusion goal has become a fundamental branch of physics and one that is of great intrinsic interest. The broader influence of fusion science is clear from its impact on other branches of science, including astrophysics, space plasma physics, nonlinear science, optics, and turbulence.
Fusion research recently passed several important milestones. Weakly burning plasmas were created and confined for the first time, indicating that many of the tools have now been assembled for answering the scientific questions related to the fusion energy goal. The basic understanding of some of
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the dominant instabilities driving turbulence has advanced to the point where the transport produced by this turbulence can be completely suppressed. Even a decade ago, the remote control of small-scale turbulence at the 100-million-degree cores of modern plasma fusion experiments would have been unthinkable. Yet significant inroads are now being made to surmount this critical hurdle of 40 years' standing. Theoretical predictions of fusion plasma behavior have led to the design, optimization, and testing of new plasma confinement approaches and new ways of controlling the macro- and microinstabilities that limit energy containment. The close interaction between theory and experiment represents the new face of the fusion energy sciences program.
A successful scientific enterprise develops state-of-the-art research tools, uses these tools to bring rigorous closure between experiment and theory, and then innovates. The ability to diagnose experiments on high-temperature plasmas and compare the results with theoretical models and numerical simulations has improved markedly over the past two decades and in the committee's view is itself an important achievement of the field of fusion science. The enhanced ability to bring to closure some of the complex problems facing the discipline presages a new period of scientific development and supports a science-based strategy for fusion energy.
Another measure of the quality of a scientific program is the international standing of the discipline supported by the program. The U.S. fusion program has traditionally been an important source of innovation and discovery. A distinguishing feature of the program has been its goal of understanding at a fundamental level the physical processes governing observed plasma behavior. This feature, a strength of the program, was formalized in the 1996 restructuring with the new emphasis on establishing the knowledge base for fusion energy. Over the past several decades, the United States has played a dominant role in plasma theory, which is an essential tool required to unravel the complexities of plasma dynamics. The quantitative detail in which experiments are designed and executed in this country has become a benchmark for the rest of the world. The forte of the U.S. program is, as was mentioned above, the close confrontation between theory and experiment and the development of superior computational physics codes for quantitative exploration of novel physical concepts.
To assess the specific contributions of the DOE's OFES program to the fusion effort in general, one must separate the U.S. effort from the broader international effort. This is not easy, because there has been close interaction between the U.S. and international programs since the beginning, in the 1950s. To be specific, U.S. scientists played a major role internationally in developing the energy principle for describing plasma stability; heating and sustaining currents in plasmas; and understanding and controlling plasma turbulence and transport. (Specific examples of U.S. and foreign contributions can be found throughout the discussion in Chapter 2 and in Chapter 4, in the section devoted to U.S. contributions.)
In short, the quality of the science that has been deployed in pursuit of the fusion energy goal is easily on a par with other leading areas of contemporary physical science. Fusion research has mastered the ability to work flexibly with the super-high-temperature plasma state in the laboratory. It is important to note that the quality of fusion science is not universally appreciated within the broader scientific community, perhaps because fusion has been viewed as a directed energy development project rather than as a scientific enterprise. Isolation of the researchers inside the fusion program from those outside the program is another possible cause for the low opinion of fusion science despite its high quality. Most scientists funded by the program do not actively participate in the wider scientific culture. As a result, the flow of scientific information both out of and into the field has weakened. New ideas and techniques developed in allied fields are slow to percolate into the program.
All in all, a half century of research suggests that the central scientific barriers to the achievement of fusion energy will ultimately be overcome, although it is still not possible to predict when sustained fusion energy production will be realized, and much scientific and engineering work remains to be done.
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PROGRAM DEVELOPMENT: PLASMA CONFINEMENT CONFIGURATIONS
Early in the fusion program a variety of containment approaches were pursued in parallel. However, the constrained fusion budgets of the past two decades were unable to support a diversity of approaches to fusion research, especially in the United States. The basic strategy during that time was to build a series of tokamak configurations of increasing size, until fusion burning became possible. The narrow program focus constrained the range of scientific questions that could be pursued but at least ensured their study in one configuration. Program decisionmaking emphasized empirical machine performance and device-specific science at the expense of results of scientific generality. Although this philosophy complicated attempts to pin down the answers to scientific questions, the ability to produce, confine, diagnose, and understand high-temperature plasmas improved significantly.
In 1985, the G7 countries sponsored an international collaboration to design the International Toroidal Experimental Reactor (ITER), reflecting optimism that continued tokamak scale-up would result in a large experimental reactor in which burning plasma science and fusion engineering issues could be addressed simultaneously. In 1996, Congress reduced OFES program funding significantly. Participation in ITER was discontinued after the ITER Engineering Design Activity was completed in 1998. The remaining international partners are working to reduce the cost of the design before deciding whether to proceed without U.S. participation.
The 1996 congressional action, a roughly $100 million cut in funding (see Appendix B), naturally stimulated reexamination of the U.S. fusion energy program. Consistent with the new science emphasis of the program, the Congress, with support from the community, repositioned the fusion program administratively and budgetarily in the same category (Function 250) as high-energy and nuclear physics and renamed it the Fusion Energy Sciences program. This shift implies that program decisions in Fusion Energy Sciences will ultimately be made using scientific criteria and standards similar to those in high-energy and nuclear physics. The committee believes that it would be harmful to the stability and morale of the program if in the near future its primary focus were to abruptly shift back to energy development.
The present study by the National Research Council is one of several that followed the 1996 congressional action. A report by the Secretary of Energy Advisory Board (SEAB) 1 was especially concerned with the relation between the DOE Office of Energy Research (OER's) magnetic fusion program and the DOE Defense Programs' (DP's) inertial confinement program; the committee has nothing to add to SEAB's conclusions in this area since it did not examine the inertial confinement program. Where the committee and SEAB comment on similar issues, they are in general agreement. Of greater pertinence here is the study by the Fusion Energy Sciences Advisory Committee (FESAC) of DOE. 2 This study, which outlines a detailed program for the next few years, has a function different from that of the present study. Nonetheless, the committee notes that the broad program goals stated in the FESAC plan are generally consistent with a science-based approach to fusion. For example, the FESAC plan recognizes that fusion research will benefit from the deployment of a variety of plasma confinement devices. On the other hand, at a more specific level, the categories of device proposed by FESAC for program planning (concept exploration, proof of principle, performance extension) continue to emphasize the evolution of specific plasma configurations toward a fusion power reactor at the expense of an understanding of the cross-cutting scientific issues. The FESAC decision criteria thus appear not to permit projects of
1 Department of Energy (DOE), Secretary of Energy Advisory Board, Task Force on Fusion Energy. 1999. Realizing the Promise of Fusion Energy: Final Report of the Task Force on Fusion Energy. Washington, D.C.: DOE.
2 Department of Energy (DOE), Fusion Energy Sciences Advisory Committee. 1999. Report of the FESAC Panel on Priorities and Balance. Washington, D.C.: DOE.
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significant scale designed primarily to answer scientific questions. At this level of program detail, scientific goals are still subordinate to directed energy development goals and management conceptions.
The fusion program has undergone a surprisingly large number of reviews, with multiple levels of detail and scope, since the 1995 President's Committee on Science and Technology fusion report, 3 including the present review and the SEAB and FESAC reviews mentioned above. The multiple recommendations at various levels and the drain on program resources motivate primary recommendation 7.
In summary, the U.S. fusion program no longer concentrates solely on achieving a practical tokamak reactor in the shortest time feasible, given budgetary and other limitations, but is turning to a less time-pressured examination of the key scientific issues and technical options surrounding fusion energy. Program planning is moving away from mostly empirical decision criteria and toward scientific decision criteria. This new approach offers the prospect that rigorous fusion science will rapidly advance not only energy goals but science goals as well. However, this prospect will not be realized until identifying and answering key scientific questions become central to program planning, budget formulation, and management philosophy.
INSTITUTIONAL CONSIDERATIONS: INTERACTIONS OF THE FUSION PROGRAM WITH ALLIED AREAS OF SCIENCE AND TECHNOLOGY
There was a clear history of intellectual exchange between the fusion plasma community and the broader scientific community in the early, pioneering years of the fusion program. Much of the basic description of plasma dynamics was being developed, and many of the ideas were of sufficient generality to be widely applicable and accessible. However, in recent years the increasing specialization and technical complexity of fusion research has sharply reduced the accessibility of the work to the broader science community. This trend is evident even though many of the topics being explored could have significance for allied areas of science. The identification of the general nature of many of the more recent scientific results—and, accordingly, their potential significance to other branches of science—has not been adequately encouraged as a programmatic goal. As a consequence, the previously rich interchange between fusion researchers and other scientists has diminished greatly. The present fusion community is relatively isolated from the rest of the scientific community, seriously eroding the university base of plasma and fusion science.
A further contributor to the scientific isolation of the U.S. fusion program is its relatively narrow and static institutional base. Although the relative allocation of DOE funding among national laboratories, universities, and industries arguably is roughly the same in the fusion, nuclear, and high-energy areas, the smaller overall funding of the fusion program does not support an equally diverse community (see Appendix B for representative OFES funding data). The almost negligible funding of fusion science by other U.S. government agencies is a contributing factor, as was the focus during the 1980s on a tokamak-based, directed-energy-development program. Most important, fusion research dollars have flowed from the same agency office to a small group of universities and national and industrial laboratories that has remained relatively stable over several decades. While such long-term and sustained support can often be critical to the successful resolution of important scientific problems, it can also lead to stagnation and lack of competition. Institutional concentration and stasis have narrowed the scientific base of
3 Executive Office of the President, President's Committee of Advisors on Science and Technology, Panel on the U.S. Fusion Energy R&D Program. 1995. The U.S. Program of Fusion Energy Research and Development. Washington, D.C.: White House.
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the fusion energy science program and have acted to reduce the number of knowledgeable scientists from other fields who can contribute to fusion research.
Funding for “general plasma science” is a small fraction of the total of the fusion energy science budget, as shown in Appendix B. Some of these funds appear to have been well used; for example, the National Science Foundation (NSF) and DOE have continued to collaborate on a highly successful but small program to encourage small-scale plasma science experiments. In addition, general plasma science has found support from the National Aeronautics and Space Administration (NASA) and NSF because of its important applications to solar and space science, astrophysics, and geophysics. Industry supports major efforts in the plasma processing of semiconductor chips. Although many of the problems studied in general plasma science do not strictly pertain to the very-high-temperature fusion regime, collaboration with general plasma scientists is one of the main ways in which fusion scientists can interact with the broader scientific community. A firmer institutional commitment to general plasma science on the part of fusion energy science would build stronger links to a vibrant research community that is stimulated by a diversity of research goals.
The proportion of U.S. fusion funding devoted to competitively peer-reviewed grants is relatively small. The peer-review process is a natural way to involve a broader scientific community in the research decisions of a given field; properly administered, it can stimulate a field to evolve a healthy diversity of participants and research approaches.
The committee is concerned that U.S. fusion energy science may have a progressively narrowing demographic base. The replenishment of the fusion community in the future depends on the health of its university programs today. It is very difficult to count fusion and plasma faculty so as to estimate how many students are being trained. There is some information on physics, the discipline that gave birth to plasma and fusion research. Of a total physics faculty of roughly 1300 in 25 leading university research departments, only 3 are assistant professors in plasma physics. This small number suggests that plasma faculty in physics departments are not all being replaced. In addition, the small proportion (roughly 40 percent) of physics departments in leading research universities that have programs in plasma physics is itself a matter of intellectual concern, given plasma's status as the fourth state of matter.
