In this interim report, the Committee on a Strategic Plan for U.S. Burning Plasma Research makes the following assessments of the importance of burning plasma research to the development of fusion energy and of the current status of U.S. burning plasma research, including current and planned participation in international activities.
Assessment 1: Burning plasma research is essential to the development of magnetic fusion energy and contributes to advancements in plasma science, materials science, and the nation’s industrial capacity to deliver high-technology components.
All efforts to make fusion energy require a burning plasma—an ionized gas like the Sun and stars that is heated by fusion reactions. Burning plasma research begins with understanding, measuring, and predicting the complex physical processes of the plasma and of the energetic particles moving within the plasma created by fusion reactions. Next, burning plasma research includes the high-technology tools used to control, confine, and heat the plasma to very high temperature and pressure. Finally, burning plasma research embodies the applied and engineering sciences necessary to design reliable structures that surround the plasma and convert fusion energy into useful heat and power. Burning plasma research is interdisciplinary and results in technological and scientific achievements that touch many aspects of everyday life and lead to new insights in related fields such as optics, fluid mechanics, and astrophysics.
Although significant fusion power has been generated for short periods in the laboratory (4 MW for 4 s and up to 16 MW for shorter periods) and some processes expected in a burning plasma have been studied at the temperatures and pressures required for fusion energy, a burning plasma, which is heated predominately by fusion reactions, has never been created. This requires construction of a burning plasma experiment such as the International Thermonuclear Experimental Reactor (ITER). A burning plasma experiment will allow integrated investigation of the burning plasma with the advanced technology magnetic fusion schemes require. Because of its large size and complexity, constructing a burning plasma experiment leads to advancements in industrial capability, such as for large superconducting magnets, vacuum technologies, complex cryogenic systems, ultra-precise construction, and robotic systems to handle materials.
Assessment 2: The U.S. fusion energy science program has made leading advances in burning plasma science that have substantially improved our confidence that a burning plasma experiment such as ITER will succeed in achieving its scientific mission.
Experiments conducted using research facilities in the United States have been highly productive. New ideas to control and sustain burning plasma have been discovered, and theoretical and computational models developed in the United States have substantially improved the ability to control plasma stability, predict plasma confinement, and enhance fusion energy performance. The understanding of burning plasma science has advanced significantly, including such critical topics as the transport of heat and particles by multi-scale turbulence, the behavior of energetic particles produced by fusion reactions, and the physics of the narrow insulating layer at the plasma edge (or “pedestal”). In addition, new techniques have been developed to avoid and mitigate transient events, which can erode plasma facing materials. Scenarios of burning plasma operation that are expected to simultaneously satisfy the requirements for
stability, confinement, fuel purity, and compatibility with plasma facing components have been developed experimentally and explored with computational models. These scenarios further increase confidence in the burning plasma performance that can be achieved in ITER. While important avenues for further exploration remain, current understanding increases confidence that ITER will achieve its scientific mission. The widely recognized importance of U.S. research contributions to the field also supports the expectation that, if the United States continues to participate in ITER, scientists within the United States will make leading contributions to the study of fusion energy at the power plant scale.
Assessment 3: Construction and operation of a burning plasma experiment is a critical, but not sufficient, next step toward the realization of commercial fusion energy. In addition to a burning plasma experiment, further research is needed to improve and fully enable the fusion power system.
A burning plasma experiment will examine for the first time many of the interconnected scientific and technology issues that must be addressed to produce magnetic fusion energy. Among these are the experimental validation of theoretical predictions related to plasma stability, plasma heating, transport of plasma heat and particles, alpha particle physics from fusion reactions, and disruption avoidance for tokamaks in substantially unexplored regimes of magnetic confinement. Equally important are gains in fusion engineering science including large-scale superconducting magnet technology, progress toward understanding fusion blanket science, tritium science and management, remote handling of materials and components, and large-scale systems integration. As a burning plasma experiment, ITER is a critical step along the path to advance the science and technology of a fusion power source.
Still, ITER is a fusion research facility and a long way from being a system for commercial power. In a commercial system, economics requires the thermal power to increase about seven-fold. Continuous operation requires efficient coupling of radio waves into the plasma to sustain the plasma current. Challenging plasma-wall problems need inventive solutions in order to safely handle the flux of energetic neutrons on the inner wall and the escaping heat from the plasma that is directed onto the plates of a protective divertor. The self-consistent production and safe handling of tritium will not be fully addressed in ITER but must be solved for commercial fusion power. Lastly, the expected gains in engineering and economics that might accrue from technology and materials innovations, like the newly developed rare-earth, high-temperature superconductors, need to be investigated; however, these innovations will only impact fusion facilities built beyond ITER. The overall picture is that a burning plasma experiment, such as ITER, will lead to major gains along the path to fusion energy while other fusion energy experiments will need to address remaining science and technology challenges and demonstrate innovative solutions that lead to a reduced size, lower cost, full-scale power source.
Assessment 4: Although our international partners have national strategic plans leading to a fusion energy demonstration device, the United States does not.
Since the National Research Council’s (NRC’s) study in 2004,1 strategic plans leading to a fusion energy demonstration have been developed by many of our international partners, all with high-level governmental support including, in some cases, accompanying legislation. These strategies all recognize that the burning plasma regime promised by ITER is the most expedient way to demonstrate controlled fusion on commercial scale and, importantly, elucidate the accompanying research and technology programs needed to progress beyond ITER to a commercial fusion reactor. Such strategic planning guides national research and innovation programs, helps to engage industrial partners, and sets the national priorities of our partners, enabling them to develop key areas of unique expertise. The absence of such a
1 National Research Council (NRC), Burning Plasma: Bringing a Star to Earth, The National Academies Press, Washington, D.C., 2004.
nationally endorsed strategic plan for delivery of fusion energy in the United States inhibits the long-term planning of all participants in the fusion endeavor in the United States, from universities, to national laboratories, to industrial partners. Without a long-term plan, the United States risks being overtaken as our partners advance the science and technology required to deliver fusion energy. Conversely, the adoption of such a plan has the potential to support strategic funding decisions and priorities within the national program and help foster innovation towards commercially viable fusion reactor designs.
Assessment 5: Recent closures of domestic experimental facilities without new starts, as well as a reduction of fusion technology efforts, threaten the health of the field in the United States.
As reported by the 2004 NRC report,2 many of the scientific and technical issues of importance to the long-range development of fusion are best addressed by research facilities having size and complexity much smaller than that needed for a burning plasma experiment. A long-term strategy for fusion energy benefits from a domestic effort in parallel with the ITER project focused on developing the scientific base for promising fusion reactor concepts and technologies.
However, during the past decade, various programmatic decisions have closed domestic experimental facilities without opportunities for new starts and without compensating programs internationally. In 2005, the budget for U.S. fusion technology efforts was sharply reduced. In 2013, the Department of Energy’s (DOE’s) Office of Fusion Energy Sciences implemented an overall reduction in the domestic program while making only a modest increase in funding for scientific collaborations on non-U.S. experimental facilities. Currently, only one mid-scale fusion experiment is operating in the United States. Mid-scale experimental facilities can attract talent to the field, provide broad scientific and engineering opportunities, and test innovations that could improve the fusion energy concept and strengthen U.S. expertise in fusion science and technology.
Assessment 6: Any strategy to develop magnetic fusion energy requires study of a burning plasma. The only existing project to create a burning plasma at the scale of a power plant is ITER, which is a major component of the U.S. fusion energy program. As an ITER partner, the United States benefits from the long-recognized value of international cooperation to combine the scientific and engineering expertise, industrial capacity, and financial resources necessary for such an inherently large project. A decision by the United States to withdraw from the ITER project as the primary experimental burning plasma component within a balanced long-term strategic plan for fusion energy could isolate U.S. fusion scientists from the international effort and would require the United States to develop a new approach to study a burning plasma.
Past studies of magnetic fusion energy research recommended U.S. entrance into international partnerships as the most cost-effective approach to undertake large fusion energy experiments. These studies include Cooperation and Competition on the Path to Fusion Energy,3Pacing the U.S. Magnetic Fusion Program,4 the 1995 President’s Committee of Advisors on Science and Technology (PCAST) panel report The U.S. Program of Fusion Research and Development,5 and Realizing the Promise of Fusion Energy.6 After considering various options for a burning plasma experiment, the 2004 NRC
2 NRC, Burning Plasma: Bringing a Star to Earth, The National Academies Press, Washington, D.C., 2004.
3 NRC, Cooperation and Competition on the Path to Fusion Energy: A Report, National Academy Press, Washington, D.C., 1984.
4 NRC, Pacing the U.S. Magnetic Fusion Program, National Academy Press, Washington, D.C., 1989.
5 President’s Committee of Advisors on Science and Technology, The U.S. Program of Fusion Research and Development, Washington, D.C., July 11, 1995.
6 U.S. Department of Energy, Realizing the Promise of Fusion Energy: Final Report of the Task Force on Fusion Energy, Secretary of Energy Advisory Board, Washington, D.C., August 9, 1999.
report7 recommended that the United States should participate in ITER. But, if the United States were not to participate in ITER, that committee also recommended the pursuit of international partnership in an alternate burning plasma experiment. A burning plasma experiment at the scale of a power plant is necessarily a large facility and integrates multiple advanced technologies. At the present time, no country has the combination of scientific and engineering expertise, industrial capacity, and long-term national commitment to undertake this critical task alone.
While previous studies concluded that fusion energy research substantially benefits from international cooperation, they also described a potential for failure if international partners were unable to meet their commitments. The 2009 NRC report A Review of the DOE Plan for U.S. Fusion Community Participation in the ITER Program recommended that steps should be taken to “seek greater U.S. funding stability for the international ITER project to ensure that the United States remains able to influence the developing ITER research program, to capitalize on research at ITER to help achieve U.S. fusion energy goals, to participate in obtaining important scientific results on burning plasmas from ITER, and to be an effective participant in and beneficiary of future international scientific collaborations.”8
The committee has reviewed the recommendations from these past studies in the context of the existing ITER partnership, the assessments of U.S. burning plasma research listed above, and the benefits international partnership brings to large multi-year endeavors at the frontier. Based on this review, the committee concludes that the United States benefits from partnership in ITER as the primary experimental burning plasma component within its own long-term strategic plan for fusion energy. On the other hand, a decision by the United States to withdraw from the ITER project would require a new approach to study a burning plasma. Because there is currently no mature burning plasma experiment as an alternative to ITER, the design, construction, and licensing of such an alternative to ITER would require significant development by the U.S. program, as well as a new approach to avoid isolation from the international fusion energy research effort.
The committee’s final report will provide greater detail and analysis of the options for a long-term strategic plan for a national program of burning plasma science and technology research, including developing various supporting capabilities and participating in international activities. Strategic guidance for scenarios where the United States both is and is not a participant in ITER will be described.
Work for the final report is at an early stage. Nevertheless, based on the input received by the committee and the committee’s assessments, if the United States seeks to continue its pursuit for abundant fusion power, the development of a national strategic plan for fusion energy that spans several decades is necessary. Therefore, the committee makes the following final assessment that will guide the strategies for both scenarios in the final report.
Assessment 7: If the United States wishes to maintain scientific and technical leadership in this field, the committee concludes that the United States needs to develop its own long-term strategic plan for fusion energy.
In the development of the final report, the committee views the following elements as important to its guidance on a long-term strategic plan:
- Continued progress towards the construction and operation of a burning plasma experiment leading to the study of burning plasma,
- Research beyond what is done in a burning plasma experiment to improve and fully enable commercial fusion power,
7 NRC, Burning Plasma: Bringing a Star to Earth, The National Academies Press, Washington, D.C., 2004.
8 NRC, A Review of the DOE Plan for U.S. Fusion Community Participation in the ITER Program, The National Academies Press, Washington, D.C., 2009, pp. 2-3.
- Innovation in fusion science and technology targeted to improve the fusion power system as a commercial energy source, and
- A mission for fusion energy research that engages the participation of universities, national laboratories, and industry in the realization of commercial fusion power for the nation.