Since the National Research Council (NRC) report in 2004,1 the United States has undertaken an enormous effort in experimental, theoretical, and computational research in support of burning plasma science. The U.S. research program motivated world-leading contributions to science and technology in support of the International Thermonuclear Experimental Reactor (ITER) and other major international fusion experiments. However, the closure of domestic fusion research facilities and the failure either to upgrade or to start new medium-scale experiments, together with substantially decreased funding to fusion nuclear science and technology research, creates concern as to whether the United States will continue to be a scientific leader in the field.
BURNING PLASMA SCIENCE
U.S. fusion scientists and engineers have contributed a substantial number of new, innovative ideas to the study of burning plasma science, including the following examples.
Theory and Simulation to Understand and Predict Burning Plasma Dynamics
The U.S. Department of Energy (DOE) Office of Fusion Energy Sciences (FES) theory and simulation program is organized into a base program, including several Scientific Discovery through Advanced Computation (SciDAC) centers2 focused on developing advanced simulation capabilities. U.S. scientists are recognized internationally as leading the world both in basic theory and in simulation. For example, U.S. researchers led important efforts in understanding multi-scale turbulent transport,3,4,5 energetic particle physics,6 and pedestal physics.7 Many of the most widely employed simulation codes and physics models have been developed within the U.S. theory and simulation program. A recent workshop collaboratively sponsored by the DOE Office of Advanced Scientific Computing Research and
1 National Research Council (NRC), Burning Plasma: Bringing a Star to Earth, The National Academies Press, Washington, D.C., 2004.
3 Ku, Chang, and Diamond, Full-f gyrokinetic particle simulation of centrally heated global ITG turbulence from magnetic axis to edge pedestal top in a realistic tokamak geometry, Nuc Fusion 49:115021, 2009.
4 Howard et al., Multi-scale gyrokinetic simulation of tokamak plasmas: Enhanced heat loss due to cross-scale coupling of plasma turbulence, Nuc Fusion 56:014004, 2015.
5 N.T. Howard et al., Multi-scale gyrokinetic simulations of an alcator C-Mod, ELM-y H-mode plasma, Plasma Phys. Control. Fusion 60:014034, 2018.
6 Fasoli et al., Physics of energetic ions, Nuc Fusion 47:S264-S284, 2007.
7 Ferraro, Jardin, and Snyder, Ideal and resistive edge stability calculations with M3D-C-1, Phys Plasmas 17:102508, 2010.
DOE/FES documented the status, codes, opportunities, and challenges of integrated simulations for magnetic fusion energy sciences.8 In recent years, understanding of key areas such as coupled core/pedestal transport and stability has advanced to the point where detailed predictions can be made in advance of experiments. Indeed, new high-performance regimes of operation have been predicted and later observed in experiments motivated directly by theoretical predictions.9 These same predictive tools have been employed to develop high-performance scenarios for ITER and other planned devices.10 The capability exists to use theoretical understanding to optimize devices and achieve higher performance. While the U.S. theory program is focused primarily on tokamak research, key innovations have also been developed in other areas, such as the idea of quasi-symmetry in stellarators to reduce transport.11
Exascale computing platforms present great opportunities for computational physics.12 The increased computing power should allow researchers to investigate new and previously inaccessible problems in burning plasma science.13 Equally important, exascale computing should greatly improve the community’s ability to understand and predict experiments with validated sophisticated numerical models. Exascale computing can substantially improve our understanding of burning plasma physics and guide experiment planning, but computation will not be a substitute for actually building and carrying out experiments needed to validate models, even at the exascale. Fusion energy simulations14 have been selected as an application area of the new Exascale Computing Project, a collaborative effort of the DOE Office of Science and the National Nuclear Security Administration.
Medium-Scale Fusion Research Facilities
Until the end of fiscal year (FY) 2016, the United States supported three medium-scale experimental facilities: the DIII-D tokamak at General Atomics in San Diego, the National Spherical Torus Experiment-Upgrade (NSTX-U) located at PPPL, and the Alcator C-Mod high-field tokamak at the Massachusetts Institute of Technology (MIT). Descriptions of these three facilities are given, for example, in the DOE FY2016 Congressional Budget Request (pp. 137-138).15 The DIII-D tokamak began operation in 1986. The DIII-D research goal is to “establish the scientific basis to optimize the tokamak approach to magnetic confinement fusion”16 through the exploration of plasma control techniques and conditions scalable to ITER and future fusion reactors. NSTX-U is a low-aspect ratio tokamak designed to assess the spherical tokamak as a possible fusion neutron source, study the plasma-material interface, and advance toroidal confinement physics. NSTX-U is an upgrade of the NSTX experiment that operated from 1999 to 2011. NSTX-U was dedicated in May 2016 but is now undergoing repairs and is not presently operating. The Alcator C-Mod tokamak began operation in 1991. C-Mod is a compact tokamak using strong
8 U.S. Department of Energy (DOE), Integrated Simulations for Magnetic Fusion Energy Sciences, Report from the DOE Workshop held June 2-4, 2015, Washington, D.C.
9 Snyder et al., Super H-mode: Theoretical prediction and initial observations of a new high-performance regime for tokamak operation, Nuc Fusion 55:083026, 2015.
10 Snyder et al., A first-principles predictive model of the pedestal height and width: Development, testing and ITER optimization with the EPED model, Nuc Fusion 51:103016, 2011.
11 Xanthopoulos et al., Controlling turbulence in present and future stellarators, Phys Rev Lett 113:155001, 2014.
12 DOE, Scientific Grand Challenges: Fusion Energy Science and the Role of Computing at the Extreme Scale, Report from the DOE Workshop held March 18-20, 2009, Washington, D.C.
13 DOE, Integrated Simulations for Magnetic Fusion Energy Sciences, Report from the DOE Workshop held June 2-4, 2015, Washington, D.C.
15 DOE, FY2016 Congressional Budget Request for Fusion Energy Sciences, Office of Science, Washington, D.C., 2015, p. 137-138.
magnetic fields to confine high-pressure plasma in a small volume. The compact size and high magnetic field of the Alcator C-Mod tokamak allow operation at and above the ITER design values for magnetic field and plasma density, and it has all-metal walls that experience heat fluxes approaching those projected for ITER. As a consequence of the DOE/FES 2013 decision to reduce domestic fusion research, the operation of the Alcator C-Mod tokamak ended in October 2016,17 immediately following experiments that set the world’s record for volume-averaged plasma pressure contained within a magnetically confined fusion device. Many of the significant accomplishments noted in Chapter 3 resulted from pioneering experiments conducted using these three medium-scale facilities.
In addition to mid-scale research facilities, the U.S. fusion energy sciences program provided about 1.6 percent (approximately $7 million) of the FY2016 budget18 to operate small exploratory experiments, primarily at universities, in support of foundational burning plasma research and long-pulse burning plasma research.
Proposals for new facilities and facility upgrades were recommended by the 2013 Fusion Energy Sciences Advisory Committee (FESAC) Subcommittee on the Prioritization of Proposed Scientific User Facilities19 and by the 2014 FESAC Subcommittee on Strategic Planning.20 These U.S. facility initiatives included major upgrades to the DIII-D and NSTX-U experiments and plans for construction of a Fusion Nuclear Science Facility. Additionally, the Advanced Divertor Experiment was proposed as an upgrade to the Alcator C-Mod facility at MIT.21
A strength of the U.S. program is the close coupling between theoretical and experimental research. Owing to their excellent diagnostics and flexibility, medium-scale facilities are well suited to test and validate experimental models. These validated models are beginning to provide the ability to predict new, and potentially more attractive, operating regimes.
The current U.S. fusion research strategy has an increasing focus on U.S. participation in newer international long-pulse experiments with superconducting magnets including EAST (China),22 KSTAR (Republic of Korea),23 and Wendelstein 7-X (Germany).24 EAST began operation in 2006 and KSTAR began in 2009. The Wendelstein 7-X stellarator began operation in December 2015, requiring €350 million for the stellarator device25 and additional amounts for personnel and materials during construction. The HL-2M tokamak is under construction at the Southwestern Institute of Physics26 as an upgrade to the existing HL-2A27 device. HL-2M will have higher plasma heating power and magnetic field strength to explore higher-pressure, fusion-relevant plasma. The JT-60SA tokamak in Japan is under construction as a Japan-Europe project and is expected to begin operation in 2020.28 Non-U.S. proposals
17MIT News, Alcator C-Mod tokamak nuclear fusion reactor sets world record on final day of operation, October 14, 2016, https://phys.org/news/2016-10-alcator-c-mod-tokamak-nuclear-fusion.html.
18 DOE, FY2016 Congressional Budget Request for Fusion Energy Sciences, Office of Science, 2015, p. 137-138.
19 DOE, Report of the FESAC Subcommittee on the Prioritization of Proposed Scientific User Facilities for the Office of Science, Fusion Energy Sciences Advisory Committee, Washington, D.C., March 21, 2013.
20 DOE, Report on Strategic Planning: Priorities Assessment and Budget Scenarios, Fusion Energy Sciences Advisory Committee, Washington, D.C., December 2014.
21 LaBombard et al., ADX: A high field, high power density, advanced divertor and RF tokamak, Nuc Fusion 55:053020, 2015.
22 Wu, An overview of the EAST project, Fusion Eng and Design 82:463, 2007.
23 Oh et al., Commissioning and initial operation of KSTAR superconducting tokamak, Fusion Eng and Design 84:344, 2009.
24 Bosch et al., Final integration, commissioning and start of the Wendelstein 7-X stellarator operation, Nuc Fusion 57:116015, 2017.
26 Liu et al., Assembly study for HL-2M tokamak, Fusion Eng Design 96-97:298-301, 2015.
27 Duan et al., Overview of recent HL-2A experiments, Nuc Fusion 57:102013, 2017.
28 Shirai, Barabaschi, and Kamada, Progress of JT-60SA Project: EU-JA joint efforts for assembly and fabrication of superconducting tokamak facilities and its research planning, Fusion Eng and Design 109:1701, 2016.
for new facilities include the superconducting Divertor Tokamak Test facility29 that would be built by the Italian National Agency for New Technologies, Energy, and Sustainable Economic Development’s fusion laboratory in Frascati, Italy, and the China Fusion Engineering Test Reactor30 under consideration as a new fusion facility to demonstrate self-sufficient tritium breeding. While researchers in the U.S. fusion community welcome these international opportunities, presentations to the committee31 and during the first fusion community workshop32 did not foresee how international cooperation by itself will allow the U.S. fusion researchers to maintain a world leadership position without new facility starts within the United States.
FUSION TECHNOLOGY AND ENGINEERING SCIENCE
Many of the program contributions to burning plasma science are interrelated to advancements in fusion technology and engineering science. The Virtual Laboratory for Technology (VLT) functions as a “virtual” laboratory with 18 collaborating institutions within the United States, including eight universities, nine national laboratories, and one private company.33 The VLT facilitates fusion technology and engineering science in the United States by (1) developing the enabling technology for existing and next-step experimental devices, (2) exploring and understanding key materials and technology feasibility issues for attractive fusion power sources, and (3) conducting advanced design studies that provide integrated solutions for next-step and future fusion devices and call attention to research opportunities in the field.34
Since the 2004 NRC Burning Plasma Assessment report,35 fusion technology advances have been driven by ITER research needs and by next-step goals to fully enable the fusion energy system. Key contributions from the U.S. fusion technology program are fusion fuel cycle, fusion materials, fusion materials modeling,36 fusion plasma power handling, superconducting magnets, and liquid metals. These contributions have resulted from joint international projects in support of ITER and from tasks directed by U.S. researchers. Examples include vacuum and gas species management,37,38 tritium fusion fuel cycle development,39 pellet injection for fueling and disruption mitigation,40 and the manufacture of the ITER
29 Crisantia et al., The Divertor Tokamak Test facility proposal: Physical requirements and reference design, Nuc Materials and Energy 12:1330, 2017.
30 Song et al., Concept design of CFETR tokamak machine, IEEE Trans Plasma Sci 42:503, 2014.
31 See, for example, Stewart Prager, A reinvigorated US fusion energy program, presented to the Committee for a Strategic Plan for U.S. Burning Plasma Research, August 29, 2017.
32 See, for example, T. Carter, R. Fonck, M. Haynes, D. Maurer, D. Meade, G. Navratil, S. Prager, G. Tynan, D. Whyte, “Perspectives on a Restructured US Fusion Energy Research Program,” presented to the Workshop on U.S. Magnetic Fusion Research Strategic Directions, July 24, 2017.
33 Phil Ferguson, “Response to the NAS Committee for a Strategic Plan for U.S. Burning Plasma Research,” presented to the Committee for a Strategic Plan for U.S. Burning Plasma Research, August 29, 2017. See also http://vlt.ornl.gov/.
34 C.C. Baker, An overview of enabling technology research in the United States, Fusion Engineering and Design 61-62:37-45, 2002.
35 NRC, Burning Plasma: Bringing a Star to Earth, The National Academies Press, Washington, D.C., 2004.
36 Wirth, Hammond, Krasheninnikov, and Maroudas, Challenges and opportunities of modeling plasma’s surface interactions in tungsten using high-performance computing, J Nucl Mater 463:30, 2015.
37 Duckworth et al., Development and demonstration of a supercritical helium-cooled cryogenic viscous compressor prototype for the ITER vacuum system, Adv Cryogenic Eng 57A-B:1234-1242, 2012.
38 Perevezentsev et al., Study of outgassing and removal of tritium from metallic construction materials of ITER vacuum vessel components, Fusion Sci and Technology 72:1-16, 2017.
39 Klein, Poore, and Babineau, Development of fusion fuel cycles: Large deviations from US defense program systems, Fusion Eng Des 1, 2015.
40 Lyttle et al., Tritium challenges and plans for ITER pellet fueling and disruption mitigation systems, Fusion Sci and Tech 71:251, 2017.
central solenoid.41 The United States has made significant advancements in fusion materials studies, including contributing to the qualification of reduced activation ferritic martensitic steels for the European demonstration fusion reactor,42 nanostructured43 and oxide dispersed strengthened steels,44 all aspects of SiC/SiC technology,45 and new understanding of tungsten46 and tungsten composites47 as fusion plasma-facing materials. Linear plasma simulators allow for long-duration study of material evolution under fusion-relevant plasma flux, but they are not useful to test integrated plasma-material effects expected in fusion divertors. In the United States, linear plasma simulators include the PISCES facility at University of California, San Diego,48 the Tritium Plasma Experiment at Idaho National Laboratory (INL),49 and the recently completed Material Plasma Exposure Experiment at Oak Ridge National Laboratory.50 The STAR51 facility, part of the Fusion Safety Program at INL, has unique experimental capabilities that have been used to develop the only fusion safety code accepted by the French authorities for ITER licensing, the INL fusion-modified MELCOR code.52,53
The United States has also made progress in the areas of (1) fusion nuclear systems study, leading to the definition of requirements for a Fusion Nuclear Science Facility54 for integrated testing of fusion components, and (2) experiments and massively parallel simulations to understand magnetohydrodynamic flows of liquid metal, self-cooled, dual-coolant, and helium-cooled lead lithium blanket concepts at the University of California, Los Angeles, Magnetohydrodynamic PbLi Experiment facility.55 This effort is well recognized by the international fusion and magnetohydrodynamics communities for its potential to serve a central role in U.S. and international programs on blankets and plasma-facing components.
41 Libeyre, P., Cormany, C., Dolgetta, N. et al., Starting manufacture of the ITER central solenoid, IEEE Trans on Applied Superc 26:4203305, 2016.
42 Stork et al., Developing structural, high-heat flux and plasma facing materials for a near-term DEMO fusion power plant: The EU assessment, J Nuc Materials 455:277-291, 2014.
43 Parish et al., Helium sequestration at nanoparticle-matrix interfaces in helium plus heavy ion irradiated nanostructured ferritic alloys, J. Nuc. Materials 482:21, 2017.
44 Zinkle et al., Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications, Nuc Fusion 57:092005, 2017.
45 Snead et al., Silicon carbide composites as fusion power reactor structural materials, J Nuc Materials 417:330, 2011.
46 Baldwin and Doerner, Helium induced nanoscopic morphology on tungsten under fusion relevant plasma conditions, Nuc Fusion 48:035001, 2008.
47 Garrison et al., Irradiation effects in tungsten-copper laminate composite, J Nuc Materials 481:134, 2016.
48 Tynan et al., Mixed material plasma-surface interactions in ITER: Recent results from the PISCES Group, in Plasma Interaction in Controlled Fusion Devices (Benkadda, ed.), AIP Conference Proceedings 1237, pp. 78-91, 2010.
49 Shimada et al., Tritium plasma experiment upgrade and improvement of surface diagnostic capabilities at STAR facility for enhancing tritium and nuclear PMI sciences, Fus Sci and Technology 71:310, 2017.
50 Rapp et al., The development of the material plasma exposure experiment, IEEE Trans Plasma Sci 44:3456, 2016.
51 Tynan et al., Mixed material plasma-surface interactions in ITER: Recent results from the PISCES Group, in Plasma Interaction in Controlled Fusion Devices (Benkadda, ed.), AIP Conference Proceedings 1237, pp. 78-91, 2010.
52 Merrill et al., Modifications to the MELCOR code for application in fusion accident analyses Fusion Eng Design 51-52:555-563, 2000.
53 Taylor et al., Updated safety analysis of ITER, Fusion Eng Design 86:619-622, 2011.
54 C.E. Kessel et al., The Fusion Nuclear Science Facility, the critical step in the pathway to fusion energy, Fusion Science and Technology 68:225-236, 2015, doi: 10.13182/FST14-953.
55 Smolentsev et al., Review of recent MHD activities for liquid metal blankets in the US, Magnetohydyamics 53:411, 2017.
Although there have been significant advances in U.S. capabilities since the 2004 NRC report, many research needs for fusion technology and engineering science remain unresolved. These include fusion plasma material interactions, fusion blanket materials, fuel cycle safety, breeding and fueling, and opportunities for advanced materials and manufacturing guided by new high-performance computing tools.
U.S. RESEARCH AND PARTICIPATION IN INTERNATIONAL FUSION ACTIVITIES
Fusion energy research is international. The United States participates actively in Europe and Asia, and international scientists from around the world participate in fusion experiments and research programs within the United States. Many advancements in all key topical areas of fusion research are published collaboratively with international co-authors. The International Tokamak Physics Activity (ITPA) provides an international framework for coordinated fusion research; since 2008, the ITPA operates under the auspices of ITER.56
U.S. Participation in Fusion Activities in Europe
The United States has made and continues to make important contributions to the world’s largest currently operating fusion device, Joint European Tours (JET). This includes involvement in testing important auxiliary systems relevant to ITER (e.g., the ITER-like Shattered Pellet Injector57), plasma diagnostics (e.g., Faraday cups), experimental operating scenarios (e.g., involvement in developing deuterium-tritium scenarios58), and simulation codes (e.g., TRANSP59). Additionally, simulation codes developed by U.S. scientists have been adopted by international partners and are now routinely used for scenario modeling within the JET program and across EUROfusion ITER-related activities. Since 2016, 9 of the 33 articles appearing in the International Atomic Energy Agency (IAEA) journal Nuclear Fusion and reporting results from the JET device involved co-authors from the United States.
For medium-sized tokamaks (ASDEX Upgrade, Germany; TCV, Switzerland; MAST Upgrade, United Kingdom), many bilateral collaborations exist between the United States and EU partners. Prominent recent examples of U.S. contributions include temporarily moving diagnostic devices from U.S. facilities to EU machines and joint experiments on multiple machines to develop understanding and robust demonstration of control schemes and new plasma scenarios. Since 2016, about 10 percent of the articles appearing in Nuclear Fusion describing research with these medium-sized tokamaks involved coauthors from the United States.
Another important U.S. contribution to fusion research in the EU has been the participation in the Wendelstein 7-X stellarator project. This includes the construction and operation of five large auxiliary coils60 (installed on the outside of the device to assist in precise setting of the magnetic fields at the plasma edge) and an X-ray spectrometer, as well as the development of fluctuation diagnostics and a pellet injector. This work is carried out at three U.S. national laboratories (Princeton, Oak Ridge, and Los Alamos) and three U.S. universities (Auburn University, University of Wisconsin, Madison, and MIT),
57 Baylor et al., Disruption-mitigation-technology concepts and implications for ITER, IEEE Trans Plasma Sci 38:419, 2010.
58 Budny et al., Predictions of H-mode performance in ITER, Nuc. Fusion 48:075005, 2008.
59 Budny, Cordey, TFTR Team, and JET Contributors, Core fusion power gain and alpha heating in JET, TFTR, and ITER, Nuc Fusion 56:056002, 2016.
60 Lazerson et al., Error field measurement, correction and heat flux balancing on Wendelstein 7-X, Nuc Fusion 57:046026, 2017.
supporting Wendelstein 7-X with equipment that has been funded, designed, and produced in the United States and with related magnetic field and plasma diagnosis and modeling. Since 2016, more than half of the articles appearing in Nuclear Fusion describing research with the Wendelstein 7-X stellarator involved co-authors from the United States.
U.S. Participation in Fusion Activities in Asia
The United States is actively playing a significant role in developing new fusion programs in Asia. Major contributions have been made to the programs on new Asian devices since the 2004 NRC report, notably in EAST (China), KSTAR (Republic of Korea), HL-2A (China), and J-TEXT (Japan), and a strong relationship continues with smaller spherical tokamaks (QUEST at Q-shu University, Japan; VEST at Seoul National University, Republic of Korea; SUNIST at Tsinghua University, China). One major focus of this international partnership has been in the use of long-pulse superconducting devices to develop steady-state plasma scenarios.61 As an example, collaborations on EAST have made advances in plasma control and wall conditioning techniques developed collaboratively with and initially demonstrated on DIII-D. Novel computer science hardware and software infrastructure has improved data movement, visualization, and communication and allow scientists in the United States to remotely conduct experiments using the EAST facility.62 In July 2017, the Chinese researchers using EAST achieved a stable 101.2-second steady-state high confinement plasma, setting a world record in long-pulse H-mode operation.63
Recent U.S.-Asia cooperation is also seen in the development of HL-2M under construction in China and in the physics design of CFETR burning plasma facility under consideration in China, where the United States provides design expertise and simulation codes.64
U.S. Participation in the International Tokamak Physics Activity
The International Tokamak Physics Activity (ITPA) began operating in 2001 with urging by the United States and under the auspices of the IAEA International Fusion Research Council. Since 2008, ITPA operates under the auspices of ITER. The ITPA provides an international framework for coordinated fusion research useful for all fusion programs and for broad progress toward fusion energy. The United States continues to make significant contributions to the ITPA, which coordinates the international tokamak physics research and development activities and provides the physics basis for the ITER project. Presently, the United States chairs four of the seven ITPA topical working groups. The United States also actively participates in multiple-facility, joint tokamak experimental exercises. Until recently, these joint experiments used the C-Mod, NSTX-U, and DIII-D tokamaks in the United States for dedicated studies and coordinated analysis in support of international joint experiments. For example, joint experiments coordinated among MAST, ASDEX Upgrade, and DIII-D have recently evaluated the use of resonant magnetic field perturbations and pellet injection to suppress edge localized modes (ELMs).65 These joint experiments are in general agreement with plasma response modeling, confirm that
61 See, for example, Garofalo et al., Development of high poloidal beta, steady-state scenario with ITER-like tungsten divertor on EAST, Nuc Fusion 57:076037, 2017.
62 D.P. Schissel et al., Remote third shift EAST operation: A new paradigm, Nucl. Fusion 57:056032, 2017.
64 See, for example, Chen et al., Self-consistent modeling of CFETR baseline scenarios for steady-state operation, Plasma Phys Controlled Fusion 59:075005, 2017.
65 Liu et al., Comparative investigation of ELM control based on toroidal modelling of plasma response to RMP fields, Phys Plasmas 24:056111, 2017.
magnetic perturbations can limit ELMs, and have led to a change in the ITER design to introduce ELM control systems. Since the end of Alcator C-Mod operation, the United States is no longer able to provide scientific support to ITER in the area of tokamak operation and physics in fusion devices with reactor-relevant metallic walls.
International Participation in the U.S. Program
International fusion researchers from the ITER partnership also collaborate in the U.S. research effort. International collaboration with U.S. researchers in burning plasma science involves all parts of the program, including use of experimental facilities and involvement with theory, simulation, and modeling groups. Since 2016, of those articles appearing in the IAEA journal Nuclear Fusion describing research with U.S. medium-sized tokamaks, one-fourth involved co-authors from Europe and one-fourth involved co-authors from Asia. Half of all articles appearing in Nuclear Fusion since 2016 reporting advancements in fusion simulation involved collaborating international co-authors. In the area of fusion technology and engineering science, the EUROfusion Work Package for Plasma Facing Components pays to use the PISCES-B facility at University of California, San Diego, helping to identify first wall materials for ITER and future fusion energy systems. Currently, no other linear plasma facility is capable of performing experiments with beryllium samples. One main goal of this collaboration is to study the interaction between deuterium or helium plasmas with beryllium and tungsten surfaces. Another example is the study of high dose irradiation effects in a U.S.-Japan collaboration in an experiment with more than 8 years of irradiation on the High Flux Isotope Reactor at Oak Ridge National Laboratory.
THE ROLE OF ITER IN TODAY’S U.S. BURNING PLASMA RESEARCH ACTIVITIES
As stated in the DOE Office of Science Ten-Year Perspective (2015) (p. 8), “the global magnetic fusion research community is focused primarily on the commencement of the ‘burning plasma’ era.” This global focus is reflected in the U.S. fusion energy science research program. The three fusion research directions, “burning plasma science: foundations,” “burning plasma science: long pulse,” and “burning plasma science: high power,” advance the plasma science, computational science, and materials science in support of burning plasma research that will be conducted on the ITER device. Research objectives of the DOE Ten-Year Perspective include “urgent scientific questions—such as how to control transient events—required for ITER to meet needs of the ITER project,” validating predictive models for “formulating ITER operational scenarios,” and understanding how to confine and control long-pulse fusion plasmas as “essential expertise for U.S. scientists who may participate in research operations on ITER and future burning plasma experiments.”66
Planning for U.S. participation in the ITER program began in 2006 by the United States Burning Plasma Organization (USBPO) at the request of DOE/FES in response to a requirement of the Energy Policy Act of 2005.67 This plan was endorsed by the 2009 NRC Committee to Review the U.S. ITER Science Participation Planning Process.68 The 2009 NRC report further stated (p. 2), “U.S. involvement in developing the research program for ITER will be crucial to the realization of U.S. fusion research goals.”
66 DOE, The Office of Science’s Fusion Energy Sciences Program: A Ten-Year Perspective, Report to Congress, Washington, D.C., December 2015.
67 U.S. Burning Plasma Organization, Planning for the U.S. Fusion Community Participation in the ITER Program, June 2006, https://www.burningplasma.org/web/ReNeW/EPAct_final_June09.pdf.
68 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.
The USBPO serves the U.S. fusion research community and coordinates burning plasma research through open membership in topical groups. Leaders of each topical group coordinate research to address priority scientific issues and provide contact to the international burning plasma research with the ITPA and with the ITER organization. The director and deputy director of the USBPO explained to the committee69 that burning plasma research in support of the ITER project has resulted in significant progress in many key areas, including transient events, plasma material interactions, integrated simulations, operating scenarios, heating and current drive, diagnostics, plasma control, energetic particles, and transport and confinement, and these advancements “have only increased our readiness to take the burning plasma step.”
Research in support of ITER has facilitated enhanced multi-national collaborative activities (experiments and analysis) through the ITER-sponsored ITPA topical groups. As reported earlier in this chapter, U.S. scientists collaborate with Asian research programs with superconducting tokamaks, EAST and KSTAR. This collaboration targets the development of long-pulse, high-performance operating scenarios with acceptable heat exhaust that are target scenarios for ITER operation.
Additionally, because the vast majority (approximately 80 percent) of U.S. ITER construction funding remains within the U.S. supply chain,70 participation in ITER has resulted in significant advances in U.S. domestic industrial capabilities and capacities that would not have happened without ITER participation. For example,
- The United States has proven its capacity for fabricating superconductor in bulk, producing over four miles of cable-in-conduit superconductor for the toroidal field magnets;
- The United States is fabricating a first-of-a-kind 13 m tall, 13 T central solenoid electromagnet, which is unique worldwide and has required the development of bespoke fabrication and testing infrastructure;
- U.S. industry is developing microwave and radio-frequency transmission lines to provide unprecedented power transfer for heating in ITER;
- High-throughput cryogenic pellet fueling systems and tritium processing systems have been developed by U.S. national laboratories; and
- A wide array of instrumentation for harsh nuclear environments has been developed in the U.S. supply chain.
The United States has also been a key contributor towards the approval of ITER’s license to start construction, by providing a “pedigreed” version of the fusion-modified safety code MELCOR, developed and maintained by the Fusion Safety Program at INL, that has been used extensively for the safety analyses presented to the French Nuclear Regulator (Autorité de Sureté Nucléaire) as part of the Construction Authorization Request.
Of course, in addition to ITER’s role as a focus of both the international and U.S. research programs, the United States has committed to contributing 9.09 percent of ITER’s construction costs. According to the DOE project execution plan for ITER,71 the United States has “made considerable progress in completing its assigned hardware design, R&D, and fabrication work.” Final design of about two-thirds of U.S. hardware is complete, and 2 of 13 in-kind hardware systems have been delivered. A total of $942 million has been obligated by the U.S. ITER project with contracts spread across U.S.
69 Charles Greenfield and Amanda Hubbard, Perspectives on Burning Plasma Research, presented to the Committee for a Strategic Plan for U.S. Burning Plasma Research, June 5, 2017.
70 Ned R. Sauthoff, Perspectives from the US ITER Project, presented to the Committee for a Strategic Plan for U.S. Burning Plasma Research, August 29, 2017.
71 DOE, Project Execution Plan for U.S. ITER Subproject-1, DOE Project No. 14-SC-60, Office of Science, Fusion Energy Sciences, Washington, D.C., January 2017.
industry, universities, and national laboratories, across 44 states.72 The technical leadership and contributions made by the U.S. fusion science team is and will continue to be important to the eventual success of the ITER design, operation, diagnostics, and analyses. In addition, the U.S. financial commitment is highly leveraged by the sharing of costs and technology with its international partners. The performance of the United States in its ITER obligations has been very favorably assessed by the U.S. Government Accountability Office73 and DOE assessments and quality assurance audits conducted in 2015.
As President George W. Bush announced, ITER is “the largest and most technologically sophisticated fusion experiment in the world” and “critical to the development of fusion as a viable energy source.” Because burning plasma research in support of ITER and in preparation for ITER experiments is a primary focus of the international and U.S. research programs, ITER is more than a construction project. ITER plays a central role in today’s U.S. burning plasma research activities, and participation in the ITER project provides formal mechanisms for U.S. scientists to take leading roles in the international effort to develop fusion energy.
72 See slides 56-59 in Ned Sauthoff’s presentation to the committee, August 29, 2017, Ref. 23.
73 U.S. Government Accountability Office, FUSION ENERGY: Actions Needed to Finalize Cost and Schedule Estimates for U.S. Contributions to an International Experimental Reactor, Report to Congress, GAO-14-499, Washington, D.C., June 2014.