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Next Steps for the Fusion Science Program

INTRODUCTION

The search for a means to control thermonuclear fusion has led to the development of magnetic and inertial plasma confinement systems and to the study of high-temperature plasma physics in general. Fusion research, carried out in the United States under the sponsorship of the Department of Energy’s (DOE’s) Office of Fusion Energy Sciences (OFES) and referred to herein as “the U.S. fusion program,”1 has made remarkable progress in recent years and has passed several important milestones. A large element in this program is that focused on the science of magnetic fusion, in which hot fusion plasmas are confined by large magnetic fields.

Significant progress has been made in understanding and controlling turbulence and instabilities in high-temperature plasmas; this in turn has led to improved plasma confinement. Theory and modeling are now able to provide useful insights into turbulence and to guide experiments. Experimental diagnostics can extract detailed information about the processes occurring in high-temperature plasmas. It is widely perceived in the plasma physics community that the next

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The committee recognizes that the U.S. fusion program includes substantial efforts in inertial fusion energy. Considering these elements of the program was not part of the committee’s charge. However, no inference should be drawn from the omission of this part of the OFES program from the committee’s discussion.



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Burning Plasma: Bringing a Star to Earth 1 Next Steps for the Fusion Science Program INTRODUCTION The search for a means to control thermonuclear fusion has led to the development of magnetic and inertial plasma confinement systems and to the study of high-temperature plasma physics in general. Fusion research, carried out in the United States under the sponsorship of the Department of Energy’s (DOE’s) Office of Fusion Energy Sciences (OFES) and referred to herein as “the U.S. fusion program,”1 has made remarkable progress in recent years and has passed several important milestones. A large element in this program is that focused on the science of magnetic fusion, in which hot fusion plasmas are confined by large magnetic fields. Significant progress has been made in understanding and controlling turbulence and instabilities in high-temperature plasmas; this in turn has led to improved plasma confinement. Theory and modeling are now able to provide useful insights into turbulence and to guide experiments. Experimental diagnostics can extract detailed information about the processes occurring in high-temperature plasmas. It is widely perceived in the plasma physics community that the next 1   The committee recognizes that the U.S. fusion program includes substantial efforts in inertial fusion energy. Considering these elements of the program was not part of the committee’s charge. However, no inference should be drawn from the omission of this part of the OFES program from the committee’s discussion.

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Burning Plasma: Bringing a Star to Earth large-scale step in magnetic fusion research and high-temperature plasma physics is to create a burning plasma—one in which alpha particles from the fusion reactions provide the dominant heating of the plasma. The objective of doing so is to understand the physics of the confinement, heating, and stability of a burning plasma 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 first mildly burning plasma experiments were achieved in the 1990s at the Tokamak Fusion Test Reactor (TFTR) in the United States and at the Joint European Torus (JET) in the United Kingdom. The plasmas in these experiments generated up to 16 MW of fusion power for about 1 s; 80 percent of this power was in the form of 14 MeV neutrons, which escaped from the plasma, and 20 percent was in the form of 3.5 MeV charged alpha particles (helium nuclei) that were confined within the plasma. These alpha particles heat the plasma through Coulomb collisions with the other particles within the plasma—the fraction of transient alpha-particle heating in TFTR was about 5 percent and in JET about 15 percent. Nevertheless, in both cases alpha-particle-induced heating of electrons near the plasma core was clearly measured. These experiments began the exploration of the burning plasma regime. Several strongly burning plasma experiments have been proposed, including the International Toroidal Reactor (INTOR), the U.S. Compact Ignition Tokamak (CIT), the U.S. Burning Plasma Experiment (BPX), the Italian IGNITOR experiment, the International Thermonuclear Experimental Reactor (ITER), and, most recently, the U.S. Fusion Ignition Research Experiment (FIRE) (see Appendixes C and F for additional information on proposed experiments and fusion reactor concepts). The experimental goal in each of these experiments is to reach a plasma state in which the alpha-particle self-heating is the dominant energy source for the plasma.2 The creation of such plasmas is a necessary but not sufficient condition for the development of a practical energy-producing magnetic fusion power plant. The study of the science and technology of burning plasmas is a critical missing element in the OFES program. The recent report from the National Research Council’s Fusion Science Assessment Committee (FUSAC)3 noted that experi- 2   The fusion-produced alpha-particle heating is considered dominant when it is sufficient to strongly impact the plasma pressure and temperature profiles. This occurs when the alpha heating is comparable to or greater than the external heating source. Thus, the terms “dominant heating source” and “half the energy input” are used interchangeably throughout the text to indicate the required alpha-particle heating contribution for a burning plasma experiment. 3   National Research Council, An Assessment of the Department of Energy’s Office of Fusion Energy Sciences Program, Fusion Science Assessment Committee (FUSAC), Washington, D.C.: National Academy Press, 2001 [hereafter referred to as NRC, FUSAC, An Assessment of the Department of Energy’s Office of Fusion Energy Sciences Program].

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Burning Plasma: Bringing a Star to Earth mental investigation of a burning plasma remains a grand challenge for plasma physics and a necessary step in the development of fusion energy. In light of the need to accomplish that step and in view of the significant advances over the past decade in the understanding of magnetically confined plasmas and in improved designs for burning plasma experiments, the committee recommended in its interim report that the U.S. fusion program participate in a burning plasma experiment.4 During the past decade, the fusion community has achieved notable advances in understanding and predicting plasma performance—particularly in comparing the results of theoretical and numerical calculations with the results of experiments on small and intermediate physics experiments. These advances are documented in detail in the FUSAC report, which noted the “remarkable strides” in fusion science research. Of particular note is the ongoing effort to develop a fundamental understanding of the complex turbulent processes that govern the confinement of hot plasmas in magnetic fields. This effort has resulted in new theoretical models, large-scale computer simulations, new diagnostic techniques, and quantitative comparisons between theory and experiment. The application of these models gives added confidence to projections for the operation of a burning plasma experiment. Progress has also been made in the understanding and control of a new class of large-scale magnetohydrodynamic (MHD) plasma instabilities, the neoclassical tearing mode, which has been a significant concern for the burning plasma regime. Progress in predicting, controlling, and mitigating fast plasma terminations has significantly reduced concerns about unacceptable electromechanical stresses in the proposed experiment. Experiments, both current and planned, and theory are bringing attractive advanced tokamak regimes with high pressure and self-driven currents closer to reality. These tokamak operating regimes may lead to a more economically attractive concept for a fusion reactor. The progress made in fusion science and fusion technology increases confidence in the readiness to proceed with the burning plasma step. The incorporation of advanced design elements from the fusion science and technology community has resulted in more attractive proposals for the burning plasma experiment. These changes have reduced the estimated cost of such an experiment and have allowed the investigation of advanced tokamak features in the burning plasma regime. The designs require less extrapolation from present 4   National Research Council, Letter Report of the Burning Plasma Assessment Committee, Burning Plasma Assessment Committee (BPAC), Washington, D.C.: National Academies Press, 2002. (The text of this interim report is reproduced in Appendix E and is available online at http://books.nap.edu/openbook/NI000487/html/index.html.)

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Burning Plasma: Bringing a Star to Earth experiments, and the operating regime resides safely below established limits in plasma density, pressure, and current, making operational projections much more reliable. However, an additional and important goal of the burning plasma experiment is to explore operational regimes that are not so predictable, where instabilities are expected to arise in the self-heated burning plasma. Undertaking a burning plasma experiment within the U.S. fusion program is a great challenge to the fusion community and to the program itself. It is a step that requires careful strategic planning—a requirement that led to detailed consideration of such a strategy through “the Snowmass process”5 and lengthy deliberations of the DOE’s Fusion Energy Sciences Advisory Committee (FESAC). In addition, DOE charged the Burning Plasma Assessment Committee to conduct an assessment of the importance of a burning plasma experiment, an analysis of the readiness to undertake a burning plasma experiment, and an assessment of DOE’s plan for a burning plasma experimental program. The committee was also asked to make recommendations on the program strategy to maximize the output of such a program for the future development of fusion as an energy source. (See Appendix A for the complete charge to the committee.) The present report answers this charge. Chapter 1 describes the context of the entire discussion and lays out a description of the committee’s reasoning; the chapter concludes with recommendations and guidance. Chapters 2 and 3 then describe in more detail the compelling scientific importance of and readiness for a burning plasma experiment, respectively. Chapter 4 discusses the overall structure of the nation’s fusion program in light of the general comments made in Chapter 1. The issues raised in the later chapters are summarized in the following sections of this chapter as a synopsis of the rationale behind this committee’s findings, which motivated a number of well-defined conclusions. These findings and conclusions are the foundation for the recommendations presented at the end of this chapter. This report focuses on the charge to the committee by assessing the scientific readiness for and benefits from participation in a burning plasma experiment. It is important to note that many additional issues and activities are critical to achieving practical fusion energy through magnetic confinement, but they are outside the purview of this committee. These include issues such as the qualification of 5   The Snowmass process engaged the U.S. fusion community in a technical assessment of the options for U.S. participation in a burning plasma experiment. The process culminated in a 2-week community conference in July 2002. The outcomes of this assessment were provided to the DOE’s Fusion Energy Sciences Advisory Committee (FESAC) for its consideration with respect to the direction of the U.S. fusion program.

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Burning Plasma: Bringing a Star to Earth nuclear materials for long-life operation under high neutron fluences, the development of low-activation materials, the qualification of near-full-scale power technologies such as chamber components, high duty factor testing, and fuel breeding and management. The modeling and testing of the effects of fusion-produced neutrons on materials constitute an area of considerable scientific challenge and interest in itself. The proposed burning plasma experiment will allow some initial examination of several of these fusion technology issues, but their more complete development for practical fusion energy will require consideration at future dedicated facilities beyond ITER. This report focuses on the merits of the proposed experiment to elucidate the scientific and technological issues of a burning plasma. PREPARING FOR A BURNING PLASMA EXPERIMENT Although developing any energy source is a long and difficult task, the international fusion community has concluded that the critical next step toward fusion energy is to build a facility capable of achieving a burning plasma.6 Demonstrating a burning plasma is the experiment necessary for continuing to develop the scientific and technological understanding to proceed toward the development of controlled fusion energy. A number of experiments, ranging from a reactor-scale device using superconducting magnets, to compact, high-field copper-magnet devices, have been considered for implementing a burning plasma experiment (see Appendix C for a discussion of the three currently proposed burning plasma projects—ITER, FIRE, and IGNITOR). On the global scale the greatest effort has been put into realizing the International Thermonuclear Experimental Reactor, an international facility that is designed to demonstrate the scientific feasibility of fusion as an energy source and to develop and test key features of the technology that will be required for a fusion power plant.7 A cutaway figure of the device is shown in Figure 1.1. 6   Several reports have considered this issue (see Appendix D for some fusion community efforts in this regard). The National Research Council has also addressed the subject of burning plasmas, saying, most recently, “(The) experimental investigation of a burning plasma remains a grand challenge for plasma physics and a necessary step in the development of fusion energy” (NRC, FUSAC, An Assessment of the Department of Energy’s Office of Fusion Energy Sciences Program, p. 53). 7   Before its withdrawal in 1998, the United States was a member of the ITER team. Following consecutive budget cuts in the U.S. fusion program (from $365 million in FY 1995 to $225 million in FY 1997) and its restructuring from a schedule-driven development strategy into a science-driven program in 1996, the U.S. Congress mandated withdrawal from the ITER program following the completion of the ITER Engineering Design Activity. Since 1998 the remaining ITER partners have continued with the development of a redesigned and improved ITER machine, and negotiations on the choice of a site and other important decisions are well under way.

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Burning Plasma: Bringing a Star to Earth FIGURE 1.1 Schematic of the International Thermonuclear Experimental Reactor (ITER), which is under development. (A person is shown for scale in the lower-right region near the center.) Courtesy of ITER. The ITER project has benefited greatly from the expertise and scrutiny of fusion-plasma researchers throughout the world. The present design is the result of a decade of effort, which included one major redesign that lowered the anticipated cost by a factor of 2 by reducing the size and eliminating some of the capability to test fusion power components and technologies. The engineering design of ITER is well developed, and prototypes for many of the systems have been built. ITER provides excellent opportunities to address key physics issues. ITER has been designed to accommodate a range of heating and current drive technologies and to have the most complete set of plasma diagnostics of the three currently proposed burning plasma experiments. The long pulse capability, the range and flexibility of heating and current drive technologies, and the extensive diagnostic set provide the capability to explore and evaluate advanced, steady-state operating regimes. In addition, the present ITER design would demonstrate integrated operation of some of the important technologies for fusion power. The U.S. fusion community has asserted that a burning plasma experiment is an essential milestone on the road to practical fusion energy and has identified its

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Burning Plasma: Bringing a Star to Earth readiness to proceed to ITER as the desired platform for investigating burning plasma behavior (see Appendix D regarding recommendations of the fusion community). The community’s near unanimity is based on important advances in understanding the behavior of large-scale hot plasmas. These advances come from experiments on a host of tokamaks around the world, on theory and computer simulations to understand and predict the results of experiments, and on the development of technologies that have made advanced facilities and diagnostics available. With the foregoing assertion of the community in mind, the U.S. fusion program was considering reentering the negotiations on the ITER program when this committee was established. At the committee’s first meeting, on September 17, 2002, Raymond Orbach, director of the DOE Office of Science, asked the committee to report, by December 2002, on two aspects of its charge and to comment on whether the United States should reenter the ITER negotiations. The resulting interim report (see Appendix E) was issued on December 20, 2002, in response to that urgent request. The interim report, expanded upon in the later chapters of this report, makes clear what can be learned from such a burning plasma experiment and why the overall understanding achieved in the past decade makes a burning plasma experiment achievable. These findings are summarized below. Scientific Value and Interest 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. A burning plasma experiment would address for the first time the scientific and technological questions that all magnetic fusion schemes must face. The scientific importance of such an experiment is discussed in Chapter 2 and summarized here. In addition to enabling the next steps in research on plasma confinement and heating, a burning plasma experiment will present new scientific challenges with a plasma that is mainly self-heated by fusion reaction products. The nonlinear behavior of magnetically confined plasmas at high temperature and pressure, a behavior that in turn may be modified by the alpha-particle heating, is of fundamental interest. In addition, burning plasmas used for energy production will be significantly larger in volume than present experiments, affecting the plasma confinement, and they may therefore be expected to show new phenomena and changes in previously studied behavior. An extrapolation from present experiments to the effective size of an energy-producing reactor entails substantial uncertainty, which can, however, be reduced

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Burning Plasma: Bringing a Star to Earth by studying a burning plasma experiment. The increase in effective plasma size at high plasma temperature is predicted to modify many phenomena that can determine the level of fusion power produced in a reactor. Understanding these effects is not feasible in the smaller-scale8 fusion experiments that are available to the scientific community today. In particular, it can be expected that a burning plasma experiment, owing to its unique plasma parameters and its ability to study these issues in the burning state, will make critical contributions to understanding the following: Plasma behavior when self-sustained by fusion (burning), Fusion-plasma turbulence and turbulent transport, Stability limits to plasma pressure, Control of a sustained burning plasma, and Power and particle exhaust. In addition to its scientific importance to fusion energy science, a burning plasma experiment may also make contributions to plasma science and science in general. Basic plasma physics is the study of fundamental processes in the plasma state of matter and is relevant to a variety of fields, including space plasmas, industrial plasmas, astrophysics, and fusion. A burning plasma experiment is designed specifically to investigate the burning plasma state and cannot replace experiments that are purpose-built to directly address the broader set of basic plasma issues. However, a burning plasma experiment and the scientific program that leads to and supports it may make useful contributions to the basic understanding of plasmas on issues such as these: Magnetic field line reconnection, Plasma turbulence, Abrupt plasma behavior, and Energetic particles in plasmas. In considering the potential for even broader impact, the committee notes that progress in plasma physics, and fusion-plasma physics in particular, can lead to progress in other subfields of physical science. A burning plasma experiment will likely lead to progress in new regimes. There will undoubtedly be unexpected discoveries. Only a few examples of such connections are mentioned here. For 8   “Smaller scale,” in the context of this report, should be interpreted as meaning smaller than the ITER scale.

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Burning Plasma: Bringing a Star to Earth instance, burning plasmas will generate the highly energetic ions and large temperature gradients that characterize many astrophysical systems and provide the opportunity to study enhanced transport under these more realistic conditions. In addition, a burning plasma experiment may offer a chance to learn about self-organization of a complex physical system with strong drivers and weak constraints, which occurs in many astrophysical, space, and geophysical settings. Self-organization is characterized by phenomena on small spatial scales acting in concert to produce phenomena on large scales. Technological Value and Interest Depending on its scale, a burning plasma experiment could offer the opportunity for beginning the development of essentially all technologies needed for a fusion reactor. These include components and systems unique to fusion’s energy goal; plasma technologies such as divertors; heating, current drive, and fueling systems; hardened diagnostics; remote handling and maintenance capabilities; and superconducting coils of unprecedented size and energy. A burning plasma experiment will provide an integrated demonstration of the reliability and effectiveness of these technologies. In addition, by operating safely, reliably, and within the structural code requirements used by the nuclear industry, a burning plasma experiment can demonstrate some of the favorable safety characteristics of fusion power. A burning plasma experiment could provide the opportunity to test and evaluate blanket designs—the blanket being the physical system surrounding the hot plasma; it provides shielding and absorbs fast neutrons, converts the energy into heat, and produces tritium. A breeding blanket—that is, a nuclear system that creates tritium via interaction of the fusion-produced 14-MeV neutrons with lithium—is a key fusion nuclear technology. Fusion reactors must operate with more tritium produced and recovered than is burned. A burning plasma experiment provides the first opportunity to evaluate test blanket modules. A burning plasma experiment will contribute to developing the technology for tritium processing. Most of the fuel injected in a fusion reactor will not be burned in a single pass. Unburned fuel will be continuously transported to the plasma edge, where it must be collected, separated from impurities, and then reinjected. The demonstration of an integrated steady-state reprocessing capability in a burning plasma experiment would show that the technology can be extrapolated to the scale needed for a reactor. A related issue is to show that the tritium inventory in a fusion reactor can be kept to an acceptably low level. The behavior and integrity of materials in a fusion system are of great importance to the long-term viability of fusion energy. The high flux of energetic neu-

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Burning Plasma: Bringing a Star to Earth trons poses a serious materials problem that will require substantial testing, some of which may be done on a burning plasma experiment and the rest of which may require a separate materials test facility. Burning plasma experiments will need to develop high-heat-flux components and will serve as testbeds in which to evaluate the performance of the components in a reactor-like fusion environment. The heat loads on components in a burning plasma experiment will be comparable to those expected in a reactor and as a research issue will require the application of state-of-the-art high-heat-flux technology using materials that satisfy requirements of tritium retention, safety, structural integrity, lifetime, and plasma compatibility. While some materials testing may be initiated, an evaluation of material lifetimes under expected fusion reactor neutron fluence will not be possible with the low fluence expected in this first burning plasma experiment. In summary, a burning plasma experiment would be of technological interest particularly with regard to the following issues: Breeding blanket development, Tritium processing, Magnet technology, High-heat-flux component development, and Remote handling technology. Readiness to Pursue a Burning Plasma Experiment Having asserted the scientific and technical interest in a burning plasma experiment, it is prudent to ask if the fusion community is ready to undertake such an experiment. Specifically, the question is whether an experiment designed and constructed with present knowledge can achieve a burning plasma state so that new phenomena present only in such a state can be explored. In assessing readiness, the committee found it useful to define 12 specific scientific and technical criteria—6 in each category—that it judged to be necessary (and sufficient) components of any path to a burning plasma experiment. The committee then assessed the readiness of current science and technology against each criterion. These criteria are discussed in more detail in Chapter 3 and are summarized here. Following are the six criteria for defining scientific readiness: Confinement projections. Reaching the burning plasma regime depends critically on the rate at which energy is lost from the plasma. It is possible to predict accurately the energy-loss rate in existing tokamak experiments through confinement scaling studies; the present level of uncertainty in these projections is acceptable.

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Burning Plasma: Bringing a Star to Earth Operational boundaries—plasma pressure and current. Tokamak operation is constrained by limits on the plasma pressure and current. The present operational boundaries and other constraints, including limits on plasma pressure and current, are sufficiently well understood and amenable to control to proceed. Mitigation of abnormal events. Burning plasma experiments are designed to handle safely abnormal events such as disruptions, should they occur. While there is confidence that these and other abnormal events can be avoided or mitigated, further research is needed to develop operating regimes that present less stringent heat loads to plasma-facing components. Maintenance of plasma purity. Impurities in the plasma—either helium from fusion reactions or from sputtered first-wall materials—can significantly degrade plasma performance. There is confidence that the required plasma purity can be obtained by helium removal and the inhibition of impurity influx from the first wall and divertor. Characterization techniques. Techniques are available to adequately characterize and evaluate most of the important parameters in a burning plasma. Plasma control techniques. Plasma control techniques are needed that are adequate to produce and evaluate burning plasma physics and to explore steady-state advanced operational regimes. Such techniques have been developed. Following are the six criteria that define technical readiness: Fabrication of necessary components. The required techniques for fabricating components have been successfully demonstrated with prototypes. The components for a burning plasma experiment can be manufactured and assembled, including the required magnetic field coils, the vacuum vessel, divertor, and first-wall components. Component lifetime in a nuclear environment. The lifetime of the various parts of a working fusion reactor must be able to minimize the vulnerability to damage from operating in a nuclear environment. There is sufficient assurance that major components can survive in the required nuclear environments. Lifetime of plasma-facing components. Prototype designs of plasma-facing components have been tested for normal heat-flux conditions, and it has been demonstrated that the mechanical designs can accommodate the projected disruption forces. Tritium inventory control. Safety analyses have found that the proposed

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Burning Plasma: Bringing a Star to Earth unconditionally. Under any funding scenario that can be reasonably expected, decisions will need to be made about the relative priority of activities to pursue at any given time. Since the fusion program is a science-based program, these priorities need to be based on a discussion of scientific opportunities and goals. The need for setting priorities is discussed in the subsection below, “Setting Priorities to Strike the Balance.” Implications for the Fusion Community The guiding principle in preparing for U.S. participation in the ITER program is the need to position the U.S. fusion community to optimize the scientific output of its activities in the burning plasma program. This need has been addressed so far in this report by considering a technical level of participation. It is important for participation in the ITER program, and indeed for the entire U.S. fusion program, that the community consider changes in the way that it operates in order to position itself to provide the intellectual leadership of chosen areas of research and to optimize the return on its investment. The choice of major research thrusts will be determined by the government with significant input from the fusion community; examples might include elements of advanced tokamak development, stabilization of large-scale MHD instabilities, turbulence and transport studies, and so on. This approach requires the organization of the community around campaigns that are based more on scientific issues than on the operation of individual facilities. Such an approach appears to be working well in the European program for the operation of JET. A transition to collaborative research based on scientific issues is a model to be considered for the entire U.S. program as it moves forward. Organizing the research efforts on the larger domestic facilities—the advanced tokamaks, spherical torus, stellarator, and reversed-field pinch—in a similar manner will support the transformation of the community to more of a user-group model and will more effectively engage the research community in these efforts. While the nature of fusion science research has its unique features, the community can profitably learn how to coordinate dispersed national and international collaborations from other areas of “big science,” such as the high-energy and astrophysics communities. This will both optimize the large investments needed in the domestic program and provide practical experience for participation in the ITER program. This transformation of the culture of the program will take time and could even be somewhat demographically driven to minimize disruption. However, it is important to start now in making this transformation so that a vibrant domestic

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Burning Plasma: Bringing a Star to Earth research program with a sufficient workforce for fusion-grade facilities is available, and so that the community is intellectually and sociologically positioned to optimize its participation in the ITER program as well as optimally exploiting its domestic faculties. Budget Implications As stated in its interim report, the committee recognizes that pursuing participation in ITER with a balanced program “will eventually require a substantial augmentation in fusion program funding in addition to the direct financial commitment to ITER construction” (see Appendix E, p. 157). However, the incremental funding requirements for the recommended program likely will be relatively small in the initial years, which should minimize the competition for funds within the overall federal research budgets. Since the negotiations on U.S. participation in ITER are just starting, it is not possible to estimate the exact level of funding needed to pursue a viable research program at ITER. The committee is concerned about the pressures on the U.S. fusion program as the United States moves into the ITER program if there is no increase in funding for the OFES. It is important to recognize that the costs of fabricating ITER and its components during the construction phase do not provide any significant support for the science and technology workforce in the fusion research community. While much of the research and development to support ITER has been done, a modest increase in technology and engineering support must be made available to support the negotiations and address some remaining issues, as well as to help mitigate technical risks during ITER construction. Most of the funds for ITER construction will go to those companies that will actually manufacture the components. A flat budget for the OFES will degrade the scientific research support in the fusion program, inevitably leading to decay in facilities and a decline in research opportunities. A constriction of the U.S. fusion program to pay for ITER participation will disproportionately weaken the presence of the fusion program in academia; it will also further erode connections to the wider scientific and engineering community while reducing the career prospects for critically needed new young talent. In a similar vein, reduced effort on all of the large national facilities will reduce the critical activities needed by the U.S. community both to allow significant contributions to the planning of ITER research and to pursue configuration optimization. Such a reduced effort, in turn, will increase the risk that the United States will play a following instead of a leading role in the ITER scientific program. Similar considerations are clearly relevant for theory and simulation and

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Burning Plasma: Bringing a Star to Earth for technology. Overall, this approach weakens the very structures needed to optimize the benefits of the investment in the ITER program. A clear example of this kind of weakening has already been set in motion, as much of the fusion technology program that was focused on developments beyond ITER was eliminated in the FY 2004 budget. Overall, this is precisely the wrong approach and should not be taken. 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 U.S. fusion program. This approach would support the fusion research field as a vibrant and exciting field with opportunities for attracting outstanding 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 project to be leaders in significant fractions of the overall program. Estimates of the funding level needed to maximize the benefit from participation in ITER within the context of a balanced fusion energy program can vary significantly, depending on the areas of U.S. contributions to the ITER program that will be determined in the negotiations. Additional funding for burning-plasma-related support activities and augmentation of the core science program were estimated by FESAC and the DOE Office of Science in briefings to the committee at $50 million to $100 million per year, without elaboration. It is clear that, at a minimum, in order to capture the benefits of a burning plasma experiment, augmenting the U.S. fusion program to cover all of the U.S. ITER construction and operating costs would be required. In addition, for the committee’s recommendations to be implemented, several elements of the resulting program will require increased investment: The U.S. share of ITER fabrication and experimental operation, Investigations on present facilities and diagnostic development that directly support preparation for ITER, Support for university programs and for theory and simulation, An increased technology program, and Increased utilization of programmatically relevant, larger national experimental facilities. These areas of increased investment need to be balanced against currently ongoing and planned activities. The balancing process also could be guided by a multiyear budget-planning path that projects funding growth, within the broad ranges described above.

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Burning Plasma: Bringing a Star to Earth The committee has concluded that a prioritization process is needed to decide on the appropriate programmatic balance, given the science opportunities identified and the budgetary situation of the time. Setting Priorities to Strike the Balance The elements and thrusts of the U.S. fusion program are complementary and intertwined. However, a constrained federal budget environment is likely to continue during the period of ITER implementation, and arguably this will be the greatest influence on the building of a balanced U.S. fusion program that includes participation in the ITER program. Notwithstanding the success of the current portfolio approach to the U.S. fusion program, the budget stress facing the program is real and ongoing. The investment in ITER will be significant and must be accounted for in pursuit of a balanced U.S. fusion program. The OFES and the fusion community will have to make serious judgments with respect to priorities in determining the activities at all stages of the fusion program. The endorsement of the merits of the program activities outlined in this report 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. As the U.S. fusion program rebalances its priorities in light of commencing burning plasma studies, some lean years may be expected. 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. Active planning has been undertaken by the U.S. fusion community in recent years. However, the addition of so major a new element as the ITER program requires that, in order to ensure the continued success and leadership of the U.S. fusion program, the content, scope, and level of U.S. activity in fusion should be defined through a prioritized balancing of the program. A rigorous evaluation of the 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 stated objective of maintaining a balanced program, as discussed in this report. The committee concludes that in order to develop a balanced program that will maximize the yield from participation in a burning plasma project, the prioritization process should be organized with the following program objectives in mind: Advance plasma science in pursuit of national science and technology goals;

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Burning Plasma: Bringing a Star to Earth Develop fusion science, technology, and plasma confinement innovations as the central theme of the domestic program; and Pursue fusion energy science and technology as a partner in the international effort. Through the prioritization process, the fusion community should identify and prioritize the critical scientific and technology questions to address in concentrated, extended campaigns, similar to the planning done for other areas of science such as for high-energy physics. 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 developing clear decision-making processes in the fusion research community. Further discussion of possible models for this process and the types of questions that participants in the process might ask in the making of real priorities are presented in Chapter 4. This prioritization process represents a reasonable form of risk management in the overall planning of a fusion program that stretches over several decades. It requires the identification of those issues that may be most uncertain and/or will have the greatest impact on decisions of future directions and investments. Addressing and resolving such issues will help maintain program focus and will continually improve the case for viable fusion energy. Any future development of larger domestic experiments and any definition of future program needs will be driven by the parallel evolution of related activities in the international community. The international coordination of large science efforts can avoid duplication and exploit opportunities to perform leading-edge research on the best facilities in a cost-effective manner. It is thus important that consideration be given to coordinating with the global fusion program the broad range of fusion activities, including non-ITER-related programs, as appropriate. Finally, the committee is convinced that the implementation of a process of program prioritization will go a long way toward ensuring the best balance of the U.S. fusion program and its continued vitality and leadership. CONCLUSIONS AND RECOMMENDATIONS—ELEMENTS OF A STRATEGICALLY BALANCED FUSION PROGRAM Conclusions Conclusion: Participation in a burning plasma experiment is a critical missing element in the U.S. fusion science program. The committee concludes that the scientific and technological case for adding

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Burning Plasma: Bringing a Star to Earth a burning plasma experiment to the U.S. fusion program is clear. During the past decade, the portfolio of activities within the U.S. fusion program has achieved notable advances in understanding and predicting fusion-plasma performance. Because of the progress made in fusion science and fusion technology, there is now high confidence in the readiness to proceed with the burning plasma step. It is also clear that progress toward the fusion energy goal requires the program to take this step and that the tokamak is the only fusion configuration ready for implementing such an experiment. Conclusion: Participation in the International Thermonuclear Experimental Reactor (ITER) program provides the best opportunity for the United States to engage in a burning plasma experiment. Of the choices proposed for U.S. participation in a burning plasma experiment, ITER, with the United States as a significant partner, is the best choice for a burning plasma experiment. It is the most mature design and, in the committee’s view, is both sound and carefully planned. It is sufficiently conservative in design to provide great confidence in achieving burning plasma conditions, while flexible enough to test critical advanced tokamak operating regimes in steady-state burning plasma conditions. It also allows tests of several fusion-relevant technology issues. Participation in the ITER program also leverages very effectively the U.S. investment in a burning plasma experiment. However, participation in ITER is a major modification to the U.S. fusion program, and the U.S. fusion effort requires a strategically balanced program in the context of meaningful participation in ITER to optimize the scientific output of this investment. Conclusion: The fusion effort requires a strategically balanced program in the context of U.S. participation in ITER in order to optimize the scientific output of this effort and to maintain the readiness to exploit the outcomes of the fusion program as a whole. Conclusion: In developing the U.S. fusion science program with participation in ITER, it will be important to maintain the diversified character of the U.S. program. In particular, the vitality of the U.S. program requires a diverse range of activities in the domestic and the international suite of current and planned tokamak and non-tokamak facilities. When considering the balance of the U.S. fusion program, it is essential to analyze the program as a unified, science-driven effort in pursuit of the fusion energy goal and composed of complementary and diverse efforts. All three ele-

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Burning Plasma: Bringing a Star to Earth ments of the U.S. fusion program, outlined above in the section entitled “Striking the Balance,” are essential. The committee concludes that the strength of the U.S. program is in its science-based foundation. It will, therefore, be essential to maintain a strong program in fusion and plasma science as a companion to a major facility program such as ITER. The outcomes of the negotiations to join ITER are critical to the future development of the U.S. fusion effort. It is therefore vital that the U.S. delegation to the negotiations strive for the best outcome for the program and the nation. As ITER negotiations commence, it will be necessary for the OFES, working with the fusion community, to reexamine all elements of the present and desired fusion program and to work through the difficult, often contentious, but vital process of prioritizing all parts of the program. In the absence of such a process, budget pressures and commitments to ITER could severely unbalance the program. While the ITER process and the outcomes of the negotiations will determine a large part of the U.S. effort, this is not the only determinant when striking a new balance for the U.S. program. For instance, it is clear that 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 ITER. Although not directly related to a burning plasma experiment in a tokamak, some scientific issues of importance to the long-range development of the U.S. fusion program will be best addressed on nonburning facilities in tokamak and non-tokamak machines. The U.S. fusion program must continue an effort parallel to the ITER project focused on developing the scientific base for promising fusion reactor concepts. The internationalization of fusion research is increasing with the development of the ITER project. However, the international effort is not limited to ITER, or indeed to collaborations on the large tokamaks in the global fusion portfolio. International partnerships on developing alternative fusion configurations have been and will continue to be important. Throughout this report, the committee provides analysis of the compelling and key scientific, technical, and programmatic issues that will need to be balanced as the U.S. program progresses. Conclusion: A robust program of theory and simulation, coupled with experimental verification, is required in order to maximize the yield of scientific and technical understanding from a balanced fusion program. Theory and simulation are essential components of understanding large-scale fusion systems and have significantly contributed to progress in understanding the

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Burning Plasma: Bringing a Star to Earth behavior 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. Conclusion: The recruitment, training, and retention of scientific and technical talent are crucial elements of the U.S. fusion science program. The success of the U.S. fusion effort will depend on strong programs in plasma and fusion science. Universities have and will continue to play several critical roles, including those of maintaining the workforce supply and serving as research centers that can generate and nurture new scientific and technological ideas and that can leverage extensively the latest knowledge from other fields of science. The committee concludes that the ramp-up to a burning plasma experiment will pose critical workforce challenges for the U.S. fusion effort. Indeed, the scientific and technical workforce in plasma and fusion science and engineering in the universities and at large fusion facilities is aging, with too few young people entering the field. There is an immediate need for technically trained personnel to build a burning plasma experiment. It is clear, therefore, that the U.S. fusion program will have to take steps to meet these critical needs. There is a related issue regarding the viability and vitality of the university programs. These projects provide many of the new ideas and techniques and the continuing influx of talented personnel that will be needed for a burning plasma experiment and beyond in the quest for useful fusion energy. The specific projects to be pursued in the universities will change as our understanding increases, new ideas are developed, new facilities come online, and strategies involving specific concepts evolve. Nevertheless, the role that university programs play in meeting personnel needs and 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. Recommendations for a Program Strategy The committee offers its conclusions as guiding principles for the Department of Energy as it plans to maintain a strategically balanced fusion program in support of the ITER project, aimed at maximizing the scientific and technical understanding and providing the foundation of fusion as an energy source. It is clear that 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 crystal clear, but this

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Burning Plasma: Bringing a Star to Earth report strives to provide a strategy for the balancing of the program through its elucidation of the key scientific, technical, and programmatic issues that need to be addressed in the coming years. What is clear is that whatever strategy is adopted, it should be flexible, innovative, and inclusive in striking the required balance for success. It is with this objective in mind that the committee offers the following recommendations: The United States should participate in a burning plasma experiment. The United States should participate in the International Thermonuclear Experimental Reactor (ITER). 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 program, 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. 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. 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. 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

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Burning Plasma: Bringing a Star to Earth 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. 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 committee notes that 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 must be cognizant of overall federal budgetary issues and likely spending constraints. With this in mind, the committee offers the following observations on the budget implications of the strategy recommended herein: Undertaking a burning plasma experiment cannot be done on a flat budget. A funding trajectory for the U.S. fusion program should be developed to provide support for capturing the long-term benefits of joining the international ITER collaboration while retaining a strong scientific focus on the long-range goal of the program. A flat budget for the Office of Fusion Energy Sciences (OFES) will degrade the scientific research support in the fusion program, inevitably leading to decay in facilities and a decline in research opportunities. Overall, this approach weakens the very structures needed to optimize the benefits of the investment in the ITER program. At a minimum, in order to capture the benefits of a burning plasma experiment, augmenting the U.S. program to cover all of the U.S. ITER construction and operating costs would be required. The OFES and the fusion community will have to make serious judgments with respect to priorities in determining the activities at all stages of the U.S. fusion program.

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Burning Plasma: Bringing a Star to Earth FINAL COMMENT The committee concludes that the United States is ready to take the next critical step in fusion research and recommends that participation in a burning plasma experiment be implemented through participation in the ITER project as part of a strategically balanced fusion program. As the following chapters show, 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.