Summary

Fusion energy holds the promise of providing a significant part of the world’s long-term, environmentally acceptable energy supply. At the center of all schemes to make fusion energy is a plasma—an ionized gas that, like the center of the Sun, is heated by fusion reactions. The plasma is said to be burning when alpha particles from the fusion reactions provide the dominant heating of the plasma. All fusion reactors require a burning plasma. The key challenge is to confine the hot and dense plasma while it burns.

The search for a means of controlling thermonuclear fusion has been based on the study of high-temperature plasma physics; it has led to the development of both magnetic and inertial confinement systems to contain the plasma. Carried out in the United States under the sponsorship of the Department of Energy’s (DOE’s) Office of Fusion Energy Sciences (OFES), fusion research (referred to herein as the U.S. fusion program) has made remarkable progress in recent years in understanding and controlling turbulence and instabilities in fusion plasmas, which in turn has led to improved plasma confinement. Theory and modeling are now able to provide useful insights into instabilities and thus to guide experiments. Experimental diagnostics can extract useful information about the processes occurring in high-temperature plasmas.

The successes of the U.S. fusion program can be attributed to its science-centered approach, aimed at three goals:



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Burning Plasma: Bringing a Star to Earth Summary Fusion energy holds the promise of providing a significant part of the world’s long-term, environmentally acceptable energy supply. At the center of all schemes to make fusion energy is a plasma—an ionized gas that, like the center of the Sun, is heated by fusion reactions. The plasma is said to be burning when alpha particles from the fusion reactions provide the dominant heating of the plasma. All fusion reactors require a burning plasma. The key challenge is to confine the hot and dense plasma while it burns. The search for a means of controlling thermonuclear fusion has been based on the study of high-temperature plasma physics; it has led to the development of both magnetic and inertial confinement systems to contain the plasma. Carried out in the United States under the sponsorship of the Department of Energy’s (DOE’s) Office of Fusion Energy Sciences (OFES), fusion research (referred to herein as the U.S. fusion program) has made remarkable progress in recent years in understanding and controlling turbulence and instabilities in fusion plasmas, which in turn has led to improved plasma confinement. Theory and modeling are now able to provide useful insights into instabilities and thus to guide experiments. Experimental diagnostics can extract useful information about the processes occurring in high-temperature plasmas. The successes of the U.S. fusion program can be attributed to its science-centered approach, aimed at three goals:

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Burning Plasma: Bringing a Star to Earth To advance plasma science in pursuit of national science and technology goals; To develop fusion science, technology, and plasma confinement innovations as the central theme of the domestic program; and To pursue fusion energy and technology as a partner in the international effort.1 Experiments that have been carried out on the suite of U.S. and foreign tokamaks have been successful in significantly advancing the scientific and technical knowledge base for fusion. Research in innovative and alternate magnetic fusion concepts is contributing to an understanding of how to design, implement, and control future fusion devices. Theory and simulation have contributed significantly to progress in understanding the behavior of fusion plasmas—for example, in the area of turbulence and nonlinear physics. The university-scale efforts within the fusion program have enabled the advances in the fusion effort and provided personnel for the program as a whole. The question now is, What is the next major step for the U.S. fusion effort? It is widely agreed in the plasma physics community that the next large-scale step in the effort to achieve fusion energy is to create a burning plasma—one in which alpha particles from the fusion reactions provide the dominant heating of the plasma necessary to sustain the fusion reaction. The objective of creating a burning plasma is to understand the physics of the confinement, heating, and stability of burning plasmas as well as to explore the technical problems connected with the development of a power-producing fusion reactor. A burning plasma experiment is a key scientific milestone on the road to the development of fusion power. The Burning Plasma Assessment Committee was charged with analyzing and reporting on the following topics: the importance of a burning plasma experiment, the readiness of the U.S. fusion community to undertake a burning plasma experiment, and the DOE’s plan for a burning plasma experimental program. The committee was also asked to make recommendations on the program strategy that would maximize the output of such a program for the future development of fusion as an energy source. Because the committee’s charge was limited to the consideration of magnetically confined burning plasmas, none of the inertial confinement fusion programs are considered in the report. The development of fusion as a source of power is a multidecade enterprise. It 1   U.S. Department of Energy, Strategic Plan for the Restructured U.S. Fusion Energy Sciences Program, DOE/ER-0684, Washington, D.C., August 1996, p. 3.

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Burning Plasma: Bringing a Star to Earth is subject to many unknowns—both technical and societal—that are beyond the scope of this committee’s charge. Indeed, the DOE has not yet established a clear program strategy for fusion (and hence did not present one to the committee), in part because the plans for an international burning plasma experiment have been in flux for the past few years. The committee’s goal is, nevertheless, to define a program approach that will optimize the near-term productivity of the U.S. fusion program and position it for development in the future at levels deemed appropriate at that time. With this task in mind, the committee offers here a short précis of the main elements of this report and then presents its recommendations and their rationale. A burning plasma experiment is critically needed to advance fusion science. The committee is pleased that the U.S. government has rejoined the International Thermonuclear Experimental Reactor (ITER)2 negotiations, which the committee expects will be successful. If the negotiations are not successful, progress toward fusion energy will require moving ahead with some other kind of international burning plasma experiment. Undertaking a burning plasma experiment cannot be done on a flat budget. If the United States is interested in the long-term goal of fusion as a source of economical, sustainable energy and not only in the ITER effort, the nation needs a science program based on some of the existing facilities; a technology program; a computation, simulation, and theory program; and a university program. At a minimum, to capture the benefits of a burning plasma experiment, an augmentation of the U.S. program covering all of the U.S. ITER construction and operating costs would be required in the near term. If negotiations proceed successfully, the fusion science program will move ahead with the ITER endeavor. In doing so, the fusion community should focus on the opportunities that this development will present and accept limitations on the level of activity possible within reasonable budget constraints. It is necessary to recognize that some of today’s facilities will have to be shut down over time and that not all alternate concepts are affordable. Priorities will be set. Although this committee was not tasked to set them, it 2   ITER will be a burning plasma experiment based on the tokamak concept—the leading magnetic-confinement fusion configuration, whose name comes from the Russian word for a toroidally (or doughnut) shaped magnetic field. ITER is expected to be larger than existing tokamaks, with a major radius of 5 to 8 m, and is expected to use superconducting magnets to confine the hot plasma. The negotiations to start the ITER project are being attended by the European Union, Russia, Japan, China, South Korea, Canada, and the United States.

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Burning Plasma: Bringing a Star to Earth does recommend that the community take part in a real prioritization process for the fusion program. The Office of Fusion Energy Sciences must take the lead and bring the community to consensus. On the basis of its own assessments and deliberations, the committee concludes that the progress made in fusion science and fusion technology has increased overall confidence in the readiness to proceed to the burning plasma step, allowed the development of more reliable operational projections, and reduced the estimated cost of such an experiment. An important goal of the burning plasma experiment is to explore operating regimes that are not so predictable and that are likely to give rise to instabilities in the self-heated burning plasma. Such experimentation will make critical contributions to the understanding of how to optimize future directions in fusion research and development. The committee makes the following specific recommendations and observations: The United States should participate in a burning plasma experiment. Participation in a burning plasma experiment is a critical missing element in the U.S. fusion program. The scientific and technological case for adding a burning plasma experiment to the U.S. fusion science program is clear. There is now high confidence in the readiness to proceed to the burning plasma step because of the progress made in fusion science and fusion technology. Progress toward the fusion energy goal requires this step, and the tokomak is the only fusion configuration ready for implementing such an experiment. The United States should participate in the International Thermonuclear Experimental Reactor (ITER) project. If an international agreement to build ITER is reached, fulfilling the U.S. commitment should be the top priority in a balanced U.S. fusion science program. The United States should pursue an appropriate level of involvement in the ITER project, which at a minimum would guarantee access to all data from ITER, the right to propose and carry out experiments, and a role in producing the high-technology components of the facility consistent with the size of the U.S. contribution to the program. If the ITER negotiations fail, the United States should continue, as soon as possible, to pursue the goal of conducting a burning plasma experiment with international partners.

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Burning Plasma: Bringing a Star to Earth Of the alternatives proposed for U.S. participation in a burning plasma experiment, ITER, with the United States as a significant partner, is the best choice. The ITER design is the most mature and is also sufficiently conservative to provide great confidence in achieving burning plasma conditions while being flexible enough to test critical advanced tokamak operating regimes in near-steady-state burning plasma conditions. It also allows tests of several fusion-relevant technologies. Participation by the United States in ITER also very effectively leverages the U.S. investment in its own fusion science program. The pace of the ITER program will be decided by the participants through the negotiating process. The U.S. component will be settled as the negotiations proceed and as procurement packages are assigned and construction preparations commence. These negotiations will determine the U.S. financial contribution to ITER construction as well as the role for and demands on the U.S. program as an ITER partner. Once a U.S. commitment is made to help construct and to participate in ITER, fulfilling this commitment will necessarily become the highest priority in the U.S. fusion science program. It is reasonable to expect that the larger the commitment, the more U.S. participation in the ITER program will be able to meet the nation’s interest in progressing toward fusion energy. A preliminary and successful review of the ITER construction costs has been conducted by DOE.3 This is an important first step in understanding the potential costs of the ITER program for the United States. Furthermore, DOE is carrying out an analysis of the various work packages of primary interest to the U.S. fusion science program, and it has engaged the fusion community in this effort by establishing the Burning Plasma Program Advisory Committee and holding an ITER forum for community input. These, too, are welcome developments. Notwithstanding the goodwill of all of the negotiating parties and the significant progress made to date, the ITER negotiations could conceivably fail. In that case, in order to progress with the development of fusion energy, it would be necessary to look for an alternative approach to a burning plasma experiment, and that most likely would become an international collaboration. In such a scenario, the United States should reassess its options before developing an alternative strategy. Because a burning plasma experiment is a key step on the necessary scientific critical path toward fusion energy, any delays in realizing such an experiment—such as failure in the ITER negotiations—would necessarily delay the domestic program’s ability to address and understand fusion science questions that must be answered before practical fusion power can be developed. 3   Department of Energy Assessment of the ITER Project Cost Estimate, November 2002. Available online at http://fire.pppl.gov/doe_iter_lehman.pdf. Accessed December 12, 2003.

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Burning Plasma: Bringing a Star to Earth A strategically balanced U.S. fusion program should be developed that includes U.S. participation in ITER, a strong domestic fusion science and technology portfolio, an integrated theory and simulation program, and support for plasma science. As the ITER project develops, a substantial augmentation in fusion science program funding will be required in addition to the direct financial commitment to ITER construction. Although the scale of U.S. participation in the ITER program is as yet undetermined, it is clear that the U.S. fusion effort requires a strategically balanced program in the context of participation in ITER. In structuring the U.S. fusion program with participation in ITER, it will be important to maintain the fusion science program as a diversified one that includes science, technology, theory, simulation, and experimentation conducted using the domestic and the international suite of current and planned tokamak and non-tokamak facilities. In this context, the committee has not found particularly useful the common characterization of the U.S. fusion program as a “base program” and a burning plasma program. All of the elements of the U.S. fusion program—advancing plasma science; developing fusion science, technology, and plasma confinement innovations; and pursuing fusion energy science and technology as a partner in the international effort—are essential and coupled. The ITER program should not be the only determinant in the effort to achieve a new balance for the entire U.S. fusion program. For instance, a technology program without a strong science base, or a science program without a strong technology base, will leave the United States unable to build effectively on the developments coming from more advanced programs abroad as well as from the ITER program. In addition, the pursuit of fusion as an attractive energy source requires the investigation of critical plasma physics and stability issues, which are discussed in more detail later in this report (see the section entitled “Scientific Importance of a Burning Plasma for Fusion Energy Science and the Development of Fusion Energy” in Chapter 2). Many of the scientific and technical issues of importance to the long-range development of the fusion program will be best addressed by non-burning-plasma facilities with tokamak and non-tokamak machines. Thus, the U.S. fusion program must continue a domestic effort in parallel with the ITER project focused on developing the scientific base for promising fusion reactor concepts. The committee emphasizes the need for a robust program of theory and simulation, coupled with experimental verification, to maximize the yield of scientific and technical understanding from a balanced fusion program. Theory and simulation are essential components in gaining understanding of large-scale fusion systems and have contributed significantly to progress in understanding the behavior

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Burning Plasma: Bringing a Star to Earth of fusion plasmas—for example, in the area of turbulence and nonlinear physics. Going forward, a program in theory and simulation must rely on a marriage of advances in experimental fusion science, information technology, plasma science, applied mathematics, and future developments in software. The internationalization of fusion research is increasing along with the development of the ITER project. It is important that some of the pre-ITER research and development in the U.S. fusion science program be coordinated with international partners and the ITER process. The U.S. tokamak programs are already loosely integrated with major facilities in the European Union and Japan through the International Tokamak Physics Activity, which identifies and promotes areas of cross-fertilization and comparative experiments. The international effort should not be limited only to ITER activities, or indeed to collaborations on the large tokamaks in the global fusion portfolio. International partnerships for developing alternative fusion configurations have been and will continue to be important. The U.S. fusion science program should make a focused effort to meet the need for personnel who will be required in the era of the burning plasma experiment. This effort should have the following goals: to attract talent to the field; to provide broad scientific and engineering training, specialized training, and training on large devices, as required; and to revitalize the fusion workforce. The recruitment, training, and retention of scientific and technical talent are crucial elements of the U.S. fusion program. The success of the U.S. fusion effort will depend on strong programs in plasma and fusion science. Among the continuing and future roles of universities are those of maintaining the workforce supply and serving as research centers that can generate and nurture new scientific and technological ideas, as well as leverage extensively the latest knowledge from other fields of science. The roles that university programs play in meeting needs for personnel and in providing new ideas and training opportunities can be expected to continue throughout the era of the burning plasma experiment and farther along the path to practical fusion energy. In addition, postdoctoral research programs at the national facilities provide critical advanced training in detailed fusion science issues. The technology component of the U.S. program will be the training ground for the fusion engineers and for those developing the industrial skills needed for the future. Undertaking a burning plasma experiment cannot be done on a flat budget.

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Burning Plasma: Bringing a Star to Earth As with any vibrant research program, the development of a scientifically and programmatically balanced program for fusion energy research and development must be matched with a credible and achievable funding plan. The plan should have a multiyear focus and fit within federal spending constraints. However, a flat budget for the OFES will inevitably lead to decay in facilities and a decline in research opportunities and will virtually guarantee that the United States will not gain the desired benefits from its investment. Such a reduced effort in the critical activities that the U.S. fusion community needs to pursue will increase the risk that the United States will play a following rather than a leading role in the ITER scientific program and the development of fusion energy. A funding trajectory that avoids these risks would provide the support to capture the long-term benefits of joining the international ITER collaboration while retaining a strong scientific focus on the long-range goal of the domestic program. This approach would support fusion research as a vibrant and exciting enterprise with opportunities for attracting the best young talent into the field, as well as increasing the connections of fusion research to the other fields of science and engineering in academia. As important, such an approach will position the U.S. contingent in the ITER program to be leaders in significant fractions of the overall program. Although active planning has been undertaken by the U.S. fusion community in recent years, the addition of so major a new element as ITER requires that, to ensure the continued success and leadership of the U.S. fusion science program, the content, scope, and level of U.S. activity in fusion should be defined through a prioritized balancing of the program. A prioritization process should be initiated by the Office of Fusion Energy Sciences to decide on the appropriate programmatic balance, given the science opportunities identified and the budgetary situation of the time. The balancing process also could be guided by multiyear budget planning that projects funding growth and should involve significant community input. The prioritization process should be organized with three elements of the fusion program in mind: To advance plasma science in pursuit of national science and technology goals; To develop fusion science, technology, and plasma confinement innovations as the central theme of the domestic program; and To pursue fusion energy science and technology as a partner in the international effort.

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Burning Plasma: Bringing a Star to Earth These program elements are indeed the three goals of the U.S. fusion program as outlined by the OFES in 1996. The committee affirms these elements as substantive and appropriate for a strategically balanced program. The merit of any of the U.S. fusion science program activities now under way or envisioned does not mean that every activity can or even should be supported unconditionally. Any funding scenario that can be reasonably expected will necessitate deciding the relative priority of activities to pursue at any given time. The choice of which opportunities to pursue—and which program activities not to pursue—must be determined by the usual federal government process, advised by the fusion community and cognizant of international fusion efforts. A rigorous evaluation of the U.S. fusion program priorities should be undertaken by the OFES with broad-based input from the fusion community. This priority-setting process should be guided by the objective of maintaining a balanced program, as discussed in this report, and it should result in a clear, ordered list of activities to be pursued. Such a list would identify those areas of science and technology that either have the greatest uncertainty or that promise the greatest impact for the future of the fusion program. As with the planning done for other areas of science such as for high-energy physics, the fusion community should identify and prioritize the critical scientific and technology questions to address in concentrated, extended campaigns. A prioritized listing of those campaigns, with a clear and developed rationale for their importance, would be very helpful in generating support for their pursuit, while also requiring the development of a clear decision-making process in the fusion research community. There are many unknowns as the fusion community embarks on this great scientific challenge. The elements required for the long-term health and vitality of this part of the U.S. research enterprise are not entirely clear, but this report strives to provide guidance for balancing the U.S. fusion program through an elucidation of the key scientific, technical, and programmatic issues that need to be addressed in the coming years as it enters the burning plasma era. What is clear is that whatever strategy is adopted, it should be flexible, innovative, and inclusive in achieving the required balance for success. Having concluded that the United States is ready to take the next critical step in fusion research, the committee recommends the implementation of a burning plasma experiment through participation in the ITER program as part of a strategically balanced U.S. fusion program. The opportunity for advancing the science of fusion energy has never been greater or more compelling, and the fusion community has never been so ready to take this step.