Chapter 1

Introduction and

Fusion and plasmas: Powering the future

The US is at a critical moment in the effort to develop fusion as a carbon-neutral, sustainable source of energy. The past decade has seen significant progress in the physics and engineering necessary to confine high-temperature plasmas for fusion. Important technological breakthroughs include high-temperature superconductors that enable the advances in magnet technology required to achieve that confinement. We are on the verge of entering an era of burning plasmas, with the international ITER experiment set to begin operation this decade. At the same time, privately financed fusion research and development (R&D) has experienced rapid growth that has spurred an emerging fusion energy industry. For US fusion research, these developments have created a unique and ambitious path toward a low-capital-cost fusion pilot plant (FPP) that will form the basis for economically attractive fusion electricity.

Fusion energy and plasmas are inextricably linked. A fusion reactor requires a confined, controlled, burning plasma at its core. For that reason, fusion research has historically been an important driver for the development of plasma physics as a fundamental field. The link between the two fields is strong but does not fully define either one. Fusion energy requires R&D into materials resistant to neutron irradiation, into technologies for breeding fusion fuel, and into enabling technologies like magnets. The field of plasma science and engineering is intellectually diverse, is highly interdisciplinary, and has myriad applications beyond fusion energy.

Plasma science and engineering has advanced significantly over the past decade, and future opportunities abound. Extreme states of matter have been produced and studied using the world’s most intense lasers developed from Nobel Prize-winning research in chirped pulse amplification. Understanding of the most energetic events in the universe requires deep knowledge of plasma physics. Such research is essential to interpreting electromagnetic signatures from events like black hole mergers in this era of multimessenger astronomy. Plasmas enable technologies essential to our everyday lives, including plasmaprocessing of semiconductor devices, which is key to the trillion-dollar information technology industry. There is potential to expand these applications with significant societal benefit; for example, plasma-enhanced chemistry could help address energy security and climate change by providing ways to make products from carbon-free electricity, purifying water and developing new medical treatments.

This report details opportunities to accelerate the development of practical fusion energy and to advance the frontiers of plasma science and engineering. Importantly, it outlines a strategy for the Department of Energy (DOE) Fusion Energy Sciences (FES) to act on these opportunities.

Embracing opportunities to form partnerships that accelerate progress in R&D is an important theme of this report. Partnership opportunities exist within the federal government, internationally, and with industry. DOE FES is the primary federal sponsor for fusion research, but other agencies have made important investments, including DOE Advanced Research Project Agency-Energy (ARPA-E), DOE Advanced Scientific Computing Research (ASCR), and the DOE National Nuclear Security Administration (NNSA). Because the field is interdisciplinary in nature and offers a multitude of applications, many federal agencies invest in broader plasma science and engineering, including the National Science Foundation (NSF), NASA, DOE High Energy Physics (DOE HEP), the Office of Naval Research (ONR), and the Air Force Office of Science Research (AFOSR). Better coordination among agencies involved in various aspects of fusion and plasma research could result in more efficient use of federal resources and enable more rapid progress in advancing plasma science and engineering and in developing fusion energy.

Fusion energy and plasma science research are global endeavors. Many nations recognize the promise of fusion energy and have made significant investments in R&D. International collaboration has been critically important to progress. This has been particularly true in the quest to address a top priority for the global fusion research community: Experimental access to a burning plasma, in which energy released by fusion reactions is the dominant heating mechanism. The international community, with the US as a key partner, is collaborating to construct the ITER experiment in France to achieve this goal. At the time of this writing, the ITER project is more than 70% complete toward first plasma. The Burning Plasma Report from the National Academies of Sciences, Engineering, and Medicine (NASEM) highlighted the importance of the ITER project to the US fusion program and stated that it provides the most compelling path to accessing a burning plasma at reactor scale. However, significant R&D is required in addition to ITER to produce electricity from fusion. Additional investment supporting that R&D is needed to advance the science and technology of a fusion pilot plant in a timely manner. While other international parties are considering a reactor scaled directly from ITER, the NASEM report recognized that this approach is too large and expensive to be economically competitive in the US market when compared with other carbon-neutral energy technologies. Consequently, the NASEM report instead set forth a unique US vision for fusion energy using scientific and technological innovations to target the development of a low-capital-cost FPP. That emphasis on developing innovative, world-leading solutions makes the near-term investments in R&D even more critical as other nations continue to invest in new fusion facilities that advance their own approaches to fusion energy development.

Research in fundamental plasma science is also vibrant and growing internationally, with activity spanning scales ranging from the subatomic to the cosmic, from low-temperature atmospheric plasmas to the most extreme conditions in the universe. Over the past few decades, shrewd investments by DOE in worldclass facilities have placed the US at the forefront of pioneering plasma research. However, such scientific leadership requires agility and continuous nurturing. In some instances, the US is losing its leadership position. For example, the 2018 NASEM report Opportunities in Intense Ultrafast Lasers: Reaching for the Brightest Light, highlights how the US has already lost leadership in the highintensity lasers that are essential for high-energy-density science. Although the chirped-pulse laser amplification technology that led to petawatt lasers was developed in the US, the vast majority of high-intensity laser systems are now being built in Europe and Asia. This long-range plan describes a path to regain a leadership position in fundamental plasma science and its applications in the US.

Fusion energy and plasma science research advances fundamental science, but also translates to direct commercial application. The ultimate goal of fusion energy research is the development of commercial fusion power. The fusion energy industry is already taking root, but realizing the ultimate goal of producing power will require additional support to help it become firmly established. The past decade has seen about $2 billion invested worldwide in fusion energy development in the private sector. Internationally, the United Kingdom and China have already established multi-hundred-million-dollar partnership programs to attract private fusion energy companies. Therefore, it is imperative that the US strengthen partnerships in the private sector to accelerate the development of fusion power in the US and maintain a leadership position in the emerging fusion energy industry. For decades, plasma technologies have played a ubiquitous role in manufacturing, crucial for the fabrication of microelectronic circuits, lighting, optics, advanced materials, materials processing, and much more. The future looks even more promising. Recent research suggests that plasmas will influence much of the future economy; they will play a decisive role in technologies that convert electricity from carbon-free sources to the products that drive society, and in future medical treatments, aerospace, particle accelerators, advanced X-ray sources, and agriculture. Countries that can solve the science questions that make these technologies possible and can facilitate technology transfer from academic research to commercial applications will position themselves to lead tomorrow’s economy. This long-range plan outlines ways in which the US can take the lead in both commercial fusion energy and other plasma-based technologies.

This report marks the first time a strategic planning process for DOE FES has been undertaken that addresses both fusion energy and plasma science and that has had a significant community-led portion of the process. The strategic planning process involved two stages: a community-driven stage followed by a stage led by the Fusion Energy Sciences Advisory Committee (FESAC), using input from the community process. The year-long Community Planning Process (CPP), was organized by the American Physical Society’s Division of Plasma Physics. The process was invaluable and resulted in the consensus CPP report that not only enumerates scientific and technological opportunities, but also provides guidance for prioritization. The CPP report formed the basis for this strategic plan and remains an essential companion to this report for those looking for more technical detail on specific initiatives. The technical bases for the considerations in both reports were made based on white papers submitted to CPP and the expert groups that evaluated them. This report presents a strategic plan based on the resulting new program elements and facilities.

Technology and Science Drivers

As acknowledged by the recent burning plasma and plasma decadal reports by NASEM and by the CPP report, fusion science and technology has reached a level of maturity that calls for FES to broaden its focus from the plasma core of a fusion reactor toward a comprehensive energy mission. At the same time, these reports show that plasma science and technology outside the fusion energy mission deepens our understanding of the universe and lays the foundation for creating transformative technologies ranging from microelectronics and medicine to particle accelerators and new materials such as advanced alloys, ceramics, and materials for magnets.

The energy mission is driven by the urgent desire to address climate change and energy security on a time scale that requires activities to resolve the critical challenges of fusion energy in the next two decades. This mission-driven program is founded on the steady progress in plasma science, ITER construction, predictive integrated-modeling capabilities, and a burgeoning investment in private fusion enterprises. However, the least developed domain in the mission portfolio is in fusion materials and technology (FM&T). Fulfilling the energy mission demands a shift in the balance of research toward FM&T, which connects the three science drivers: Sustain a Burning Plasma, Engineer for Extreme Conditions, and Harness Fusion Energy. The program’s renewed attention to economic viability distinguishes it from other ITER partners. It leverages US innovation, leadership, and technology advances to address the key gaps in fusion plasma science, nuclear science, materials science, and the enabling technology that will be required to construct an FPP, anticipated to be the key remaining step to enable commercial fusion energy. Critical gaps in FM&T will have to be closed for any choice of plasma core in an FPP, and without immediate investment those gaps could become pace-limiting. Such a program will create US leadership in a broad range of disciplines through innovation and rigorous scientific inquiry.

A critical need in the quest for fusion energy production is the ability to sustain a burning plasma by controlling and predicting its dynamics. Burning plasmas, in which the heating is primarily due to the energy released from fusion reactions, pose challenges to stability and control that are not fully addressable in current experiments and for which significant uncertainty exists. Addressing those challenges requires establishing scenarios for maintaining high performance in a burning regime and preventing damage associated with transient events through the development of tools to predict, avoid, and mitigate such events. The tokamak approach for the plasma core is the most technically advanced and mature confinement concept. A tokamak FPP will require completing critical research on existing domestic facilities, and significant participation in the ITER research program. ITER participation will increase knowledge in burning plasma physics and in materials science and technology. New collaborations with industry potentially offer pathways to accelerate access to burning plasma conditions. Complementing these priority areas is research into non-tokamak confinement approaches, including stellarators, inertial fusion energy, and other alternate confinement approaches. Investment in the alternate approaches is important both as a risk-mitigation strategy for the tokamak approach and to support innovations that could accelerate progress toward an FPP and commercial fusion energy.

An FPP will produce heat, particle, and neutron fluxes that significantly exceed those in present confinement facilities, and new approaches and materials need to be developed and engineered for the anticipated extreme reactor conditions. Those intense conditions affect all regions of the reactor in distinct ways, including the plasma-facing components (PFCs); structural, functional, magnet, and diagnostic materials; and ex-vessel components. In an FPP, high fluxes of 14 MeV neutrons produce damaging and poorly understood effects in materials. A scientific understanding of how the properties of materials evolve and degrade due to fusion neutron exposure is needed to safely predict the behavior of materials in fusion reactors. Even those components not directly exposed to high fluxes from the plasma still experience a complex multifactor environment that includes high temperatures, tritium migration and trapping, material interfaces, and high stresses. Innovative approaches and new developments will lead to integrated solutions to those harsh conditions.

Interlinked with a burning plasma and materials are the key systems required to harness fusion power, breed fuel, and ensure the safe operation of a reactor. Before an FPP is constructed, materials and components must be qualified and a system design must ensure the compatibility of all components. Just as the plasma and materials in a fusion reactor will need to advance beyond today’s capabilities, the balance of plant equipment, remote handling, tritium breeding, and safety systems will also require significant advances.

The research encompassed by these three technology and science drivers is essential to lowering the risks to an acceptable level for an FPP and will allow the US to pursue a swift, innovative, and economically attractive path to fusion energy production. The societal benefit of establishing a new carbon-neutral power source and developing the industry that supports it cannot be understated. Such a power source would be one of the most transformational technologies in the field of plasma science. On the road to achieving this scientific grand challenge are myriad additional spinoff technologies and fundamental investigations that can reveal new knowledge about the universe.

The field of plasma science and technology is a rich and diverse landscape, from the search for accurate theoretical descriptions of the complex emergent behavior of the plasma state to the production of matter at extreme conditions that exceed even those at the core of giant planets or stars. Low-temperature plasma science can also play a critical role in the development of new technologies. Expanding the fundamental understanding of plasmas and their interactions with their surroundings across wide ranges of temperature and density underpins not only fusion physics but the practical application of plasmas for manufacturing, medicine, and agriculture. The plasma science and technology component of the FES mission is impelled by three main drivers: Strengthen the Foundations, Understand the Plasma Universe, and Create Transformative Technologies. Together these drivers tackle the plasma questions of highest scientific impact and urgency, and they foster innovation by spurring exploration as dynamic as the processes in plasmas themselves. The programs, initiatives, and facilities identified here represent an opportunity to increase US leadership by strengthening investment in research areas of high potential, while moving forward with new capabilities and facilities and tapping the collective wisdom of the scientific community through a series of networks, collaborations, and partnerships.

Strengthening the foundations of plasma science deepens our fundamental understanding of nature. Exciting new experimental capabilities are unlocking unprecedented plasma regimes, while new theories and computational methods provide the insight to decipher them. Extremely intense lasers are making compact particle accelerators possible and may soon reach nonlinear quantum electrodynamic (QED) regimes in which pair plasmas will be created directly from light. Pulsed-power facilities compress matter to such high density that the behavior of the resulting warm dense plasma is fundamentally different from known states of condensed matter or plasmas. Because the plasma has high electrical conductivity, magnetic fields can be compressed to approach strengths only found in astrophysical objects such as white dwarfs. Coupling these drivers with X-ray free electron lasers allows exquisite measurements of these novel states of plasma. At the same time, tabletop-scale experiments create and trap exotic states of antimatter and strongly correlated plasmas, which can be so sensitively diagnosed that they can be used to test fundamental symmetries of nature. Strengthening the foundations of plasma science will require facilities and computational hardware at a range of scales, theoretical research that charts next steps, and a hierarchy of computational techniques that connect the microscopic to the macroscopic.

Understanding the plasma universe is essential to learning about the origins and the evolution of the universe. Nearly every aspect of the cosmos is influenced by plasma, from lightning and aurora in Earth’s atmosphere to stellar winds that fill the space between planets and stars; from accretion disks surrounding supermassive black holes at the centers of the galaxies to the particle jets launched from the most distant and ancient quasars. All these systems are strongly affected by plasma behaviors that are not yet understood, including magnetic reconnection, turbulence, and particle energization. Viewing astrophysics through the lens of plasma physics is crucial, given recent advances in multimessenger astronomy and spacecraft missions. As spacecraft such as the Parker Solar Probe and Solar Orbiter “touch the Sun,” knowledge of plasma mechanisms will play a key role in interpreting this frontier of space exploration. In addition to theoretical and computational studies, exploration of the plasma universe can be conducted through experiments on Earth. The breadth of conditions observed in the plasma universe requires a wide-ranging laboratory approach, from high-energy-density laser experiments to magnetized plasma facilities at multiple scales.

Plasma science and technology lays the foundation for creating transformative technologies unique in implementation and application. The realization of an FPP opens the door to ubiquitous carbon-free electricity. Plasma-based technologies promise unique pathways to bring that electricity to the products that power society. That power could revolutionize the way chemicals are manufactured. Such technologies promise the realization of novel materials that cannot be manufactured by conventional means, such as functionalized nanoparticles for drug delivery and new materials relevant to quantum information systems. The next generation of rockets, powered by fusion, may enable human exploration of the solar system and beyond with faster transit times. The next generation of ultrafast, compact electronic devices, such as cell phones and computers, will rely on plasma science to fuel advances in semiconductor manufacturing. Novel, precise therapies for cancer and for antibiotic-resistant bacterial infections are now within reach, buoyed by advances in atmospheric-pressure plasmas and plasma-based ultracompact accelerators.

Technology and Science Drivers

Programs and facilities to execute the strategic plan

Aligning the program with the six technology and science drivers will require redirection of programs and development of new facilities. Collaborations with international and privately funded research programs are important components of the strategy, and participation in ITER is considered essential for obtaining access to a high-gain burning plasma. Rigorous scientific inquiry is cultivated by leveraging current leadership, partnerships, and priority research areas that advance general plasma science and high-energy-density physics while emphasizing the potential of plasma-based technology for translational research. Success in all of these areas will require robust support for foundational cross-cutting research in theory, modeling, and computation; diagnostic development; and transformative enabling technologies. The multidisciplinary workforce needed for fusion energy and plasma science requires that the community commit to the creation and maintenance of a healthy climate of diversity, equity, and inclusion, which will benefit the community as a whole and the mission of FES.

Research Program Areas

New or expanded research program areas are urgently needed to fulfill the mission of developing our fundamental understanding of plasmas and to move toward a fusion energy source—with FPP readiness by the 2040s. These research program elements are described here at a high level, targeting the specific technology and science drivers identified above, and are not in priority order (prioritization is provided in the budget scenarios in Chapter 2).

FPP System Design and Integration: A central overarching priority is to form a domestic multi-institutional, collaborative FPP mission, design, and study program. This effort will provide the resources and coordination to integrate critical research advances made across the FES portfolio into attractive FPP concepts. It will need to merge advances in the understanding of burning plasma physics with the capabilities of new fusion materials and technologies. Attention also needs to be paid to licensing and safety-related issues (e.g., tritium and activation product transport and stored energy sources including the plasma, magnets, and cryogens). An integrated plant design requires consideration for balance of plant equipment and remote handling capabilities and should address the reliability, availability, maintainability and inspectability (RAMI) of the plant. Participation by private and public stakeholders is essential to ensure economic attractiveness. Innovations made outside the public program are appropriately considered in developing these concepts. An essential component underpinning this effort is a strong theory and computation program, including the advancement of multiscale, multiphysics theory and modeling capabilities necessary to predict the complex interactions between numerous plasma, material, and engineering processes that will occur within an FPP. A vital part of the program is the continued development of validated models at a range of complexities and experimental fidelities, along with the predictive integrated modeling capabilities that utilize them. Creating such models will require continued close partnership between FES and ASCR to fully leverage US investments in highperformance computing, including coming exascale machines. Moreover, accelerated progress and increased readiness of multiple systems are needed to safely design and operate a fusion reactor; those components include advances in diagnostics, instrumentation, data handling, and automated real-time decision making. This design effort should give significant attention to activities contrasting tokamak-based concepts with concept studies for different plasma cores like stellarators, alternates, or inertial confinement fusion energy (IFE). It should also include activities agnostic to the plasma core. Additionally, designs for concept exploration or for devices aiming to extend the performance of successfully tested innovative concepts should be pursued to provide an information basis for the design, decision, and pursuance of new facilities.

Fusion Materials and Technology: Critical developments are needed in fusion materials, magnets, and heating and current drive actuators. Technology advances are needed to handle the extreme conditions expected in future fusion reactors and to harness fusion energy and breed fuel. In addition to advancing key research on existing facilities such as linear plasma devices and in-pile fission irradiation, resource enhancement must allow timely resolution of critical FPP design questions. Because of the significant time scales involved in facility development and subsequent research, immediate action is needed. Increased investment in theory and simulation supporting the research on these facilities is also needed. Focus is given to the development of plasma-facing materials and components, structural and functional materials, and fusion blanket and fuel cycle elements needed for an FPP. Diagnostic advances for fusion materials studies are needed to understand the interaction of materials with the fusion environment. Magnets are an integral feature of magnetic fusion configurations, and it is desirable to develop magnets with higher fields, operating temperatures, and reliability, which are constructed with streamlined manufacturing processes and reduced production costs. All of these factors improve the performance and/or lower the costs of an FPP. Private industry has made significant progress in developing the relevant magnet technology, including high-temperature superconducting magnets, and the federal program should complement and, when possible, collaborate with those activities. Launching structures for radio-frequency plasma heating and current drive actuators must be made of new materials in order to withstand the neutron and plasma environment, have integrated steady-state cooling, and have more acceptable long-pulse reliability. Efficiency improvements in the source, the transmission, and the plasma coupling must be developed to enhance FPP competitiveness. The development of materials and technology appropriate for the nuclear conditions of a fusion reactor is a critical need in the international effort to develop fusion energy. The US is poised for leadership in this area through targeted investments in unique facilities. Collaboration and partnering with the DOE Office of Nuclear Energy in the areas of materials development, generation of qualification-level data, and improved technologies for materials and component irradiation should be cultivated.

Fusion Plasma Core: The tokamak is the most technically advanced approach for use as a fusion reactor power core. The ITER international experiment is the largest single investment by DOE FES, and a US ITER research team needs to be formed to leverage it. That team will make essential contributions to achieving the high gain mission for ITER, exploit unique access to a burning plasma at the reactor scale, and enable US scientists to close the nuclear science and engineering gaps in order to build an FPP. Access to burning plasmas could also be possible in the US-based privately funded SPARC tokamak as early as mid-decade. SPARC will be parallel and complementary to international fusion efforts, including ITER, and to other ongoing private-sector fusion endeavors. The existing DIII-D and NSTX-U national tokamak facilities are key to preparation for the study of burning plasmas in ITER and in other planned and future private devices. Additional research on these facilities, in combination with private and international collaborations, continuing support of existing university tokamak programs, and utilization of US expertise in theory and simulation, is needed to find solutions to remaining technical gaps. These gaps include disruption prediction, avoidance, and mitigation; plasma-facing component integration; and FPPrelevant scenario development. Advances in technology and in our understanding of plasma physics have opened paths to lower capital cost tokamak FPPs, but have also brought scientific and technical challenges that must be overcome. These challenges motivate the construction of a new world-leading domestic tokamak, which would be uniquely situated to develop integrated solutions in a useful time frame. In order to mitigate risks associated with the tokamak approach, alternative pathways to fusion are also pursued, which could lead to more economic fusion power in the longer term by capitalizing on US expertise. Quasi-symmetric stellarators are considered, as are alternate plasma core solutions beyond the tokamak and stellarator. These alternate pathways are supported at three levels, from basic validation of the physics, through development of self-consistent solutions, to demonstration of integrated solutions. A reestablished IFE program takes advantage of US leadership in high-energydensity physics and progress that the NNSA has made toward high yield in inertial confinement fusion.

General Plasma Science Program (GPS): GPS research explores the fundamental behaviors of plasmas. This includes foundational theoretical descriptions of plasma dynamics, numerical methods to model multiscale behavior, and experiments that test whether our understanding of plasmas is accurate. Such foundational research serves as the basis for all areas of plasma science and technology, ranging from the laboratory to astrophysics. Although motivated primarily by the desire to understand nature, many of the physics processes studied have direct relevance to fusion and other technological applications. The GPS program funds research at a range of scales, including operations and construction of the Basic Plasma Science Facility at UCLA, the Wisconsin Plasma Physics Laboratory, the Magnetized Dusty Plasma Experiment at Auburn, and the Facility for Laboratory Reconnection Experiments at Princeton Plasma Physics Laboratory. A major component of the GPS research program is the long-standing NSF–DOE Partnership in Plasma Science and Engineering.

High-Energy-Density Laboratory Plasmas (HEDLP): HEDLP research explores and applies novel regimes resulting from the extraordinary ability to concentrate power—in many cases more power than the world’s total electric generating capacity in an area smaller than the end of a human hair—for a brief fraction of a second. That ability creates new states of matter that include condensed matter, warm and hot dense matter, and plasmas relevant to astrophysical phenomena, stellar properties and processes, and fusion reactors. Self-organized, far-from-equilibrium plasmas are probed and controlled, enabling unique applications such as new accelerators and materials. This program has a successful history of partnering with DOE NNSA, NSF, and DOE HEP to fund research on several midscale laser, pulsed-power, and X-ray free electron (XFEL) facilities.

Plasma-Based Technology Program: Technologies in the plasma science and technology (PST) portfolio include low-temperature plasmas and plasma-based accelerators. These technologies benefit the public by enabling cell phones, computers, advanced drinking water purification, and security and medical methods. They underlie key industries such as semiconductor manufacturing and materials processing, which directly fuel the economy through innovation and maintaining core competence and leadership in those industries. A plasmabased technology program that consolidates and focuses critical efforts will facilitate technology transfer and realize the promise of this area.

Networks: Collaborative networks of researchers and facilities can provide enormous value as a coordinating organization and mechanism for leveraging resources and capabilities. LaserNetUS is a successful model that brings together 10 unique midscale laser facilities and opens up opportunities to a large number of new users. In a similar vein, the establishment of a MagNet centered around basic magnetized plasma and laboratory space/astrophysics, a ZNet for pulsed-power science and technology, and an LTP-Net for low-temperature plasmas could similarly support growth and enable collaborative research in their respective areas. These networks can encourage cross-fertilization as researchers work on multiple facilities and will facilitate the training of students. Coordination and access to computational/theoretical models, diagnostics, and other resources in support of experiments can also be established. These network structures also position the US to be more competitive, because investments, technology development, and future planning can be implemented more strategically by engaging the full community.


New mid- to large-scale facilities are urgently needed to meet the goal of FPP readiness by the early 2040s and to realize the goals of plasma science and technology. The elements of the following list are grouped by topical area and are not in priority order

Fusion Prototypic Neutron Source (FPNS): The science of material exposure to fusion neutron fluxes is a key gap in the international fusion program. No facility exists that can generate the necessary fluence, energy spectrum, and helium production level in the lattice of candidate materials. FPNS concepts that utilize existing facilities like accelerators or commercial units, combined into a costeffective system, can be a fast track forward. FPNS provides leadership opportunities based on existing expertise in nuclear materials in the US program by enabling the fundamental explorations of fusion nuclear material science, which needs to be combined with a reinvigorated neutron theory and computation program. Moreover, accelerated access to fusion neutron exposure is an area of extreme interest to the fusion industry and has significant opportunities for near-term public–private partnerships.

Material Plasma Exposure eXperiment (MPEX): MPEX is under construction and will provide a unique capability to study plasma-material interactions under conditions that are prototypical for a reactor divertor regime as far as the near-wall plasma-material interface is concerned. The ability to expose irradiated materials to these plasma conditions and conduct rapid turnaround in-situ and ex-situ material characterization are the most important project elements that need to be met as key program deliverables toward an FPP.

High-Heat-Flux (HHF) testing facilities: Testing capabilities to explore properties of materials and plasma-facing components, both solid and liquid, under high heat fluxes address a key gap toward FPP material definitions. Experimental capabilities to conduct fundamental testing on coupon levels (centimeter scale) are a necessary testbed for model validation of material properties. The couponlevel testing is a prerequisite for component-level testing (tens of centimeters to meters scale) to qualify components for an FPP. Accordingly, testing facilities for both levels of high-heat-flux materials research are required.

EXhaust and Confinement Integration Tokamak Experiment (EXCITE): High-magneticfield approaches to a tokamak-based FPP raise specific scientific and engineering challenges. High-divertor-power exhaust solutions need to be integrated with sustainment of high-power-density plasma cores, which are needed for generation of significant fusion power. Both the NASEM Burning Plasma Report and the CPP report identify the need to address these challenges in an integrated fashion, rather than at separate facilities. This requirement motivates the need for construction of a new domestic tokamak, previously referred to as NTUF (New Tokamak User Facility) in the CPP report.

Blanket Component Test Facility (BCTF): The CPP report outlines an R&D program on blanket materials and transport phenomena that culminates in the design and fabrication of blanket-section prototypes, which undergo staged testing in a Blanket Component Test Facility (BCTF) and Volumetric Neutron Source (VNS). The CPP report describes a BCTF that integrates all non-nuclear features of a fusion blanket and its ancillary systems (prototypic, at-scale complex structures and coolants) under prototypic conditions of temperature, pressure, magnetic field, and mechanical stress, with surrogate surface and volumetric heating and injected hydrogen or deuterium in place of tritium. Concepts successfully vetted in the BCTF, and fission and/or fusion irradiations, could potentially proceed to full nuclear testing and tritium production in the VNS. Further definition and development of these facilities and research plans should be undertaken by the program and the community.

Midscale Stellarator: A proof of concept experiment is needed to demonstrate improved steady-state plasma confinement in combination with a novel nonresonant divertor. Development of this research line provides risk mitigation for the mainline tokamak approach and could lead to a commercially more attractive fusion system. This stellarator facility would therefore be a discovery-oriented facility that could stimulate a great deal of innovation.

Volumetric Neutron Source (VNS): Recognizing the critical need for integral-effect irradiation testing of components or subcomponents, such as blanket modules, the CPP report recommended pursuit of a VNS for this purpose without specifying particular metrics or a confinement concept that would provide fusion neutrons. Multiple VNS concepts have been proposed and a concept assessment study should evaluate any plasma physics developments required to realize each concept, determine the relevance of these configurations to tokamak/FPP components, and assess them against quantitative metrics (e.g., on neutron flux or fluence) to be achieved in advance of FPP operation. This initial assessment activity should identify either a suitable concept for further development, construction, and operation, or identify an alternate approach (e.g., fission reactor irradiation or early phase testing in FPP) that best meets this mission need.

MEC-Upgrade: An upgrade to the Matter in Extreme Conditions (MEC) end-station at the Linac Coherent Light Source (LCLS) would enable the co-location of a PW-laser operating at 1–10 Hz repetition rate and a multi-kJ long pulse laser with our only domestic XFEL. This would enable us to tackle physical and chemical changes at fundamental time scales and explore new regimes of dense material physics, astrophysics, planetary physics, and short-pulse laser-plasma interactions. The MEC-U proposal has achieved Critical Decision 0 and is currently in preparation for CD-1, also having received line-item status in the FY 2020 Congressional budget.

Solar Wind Facility: How the solar wind is accelerated, heated, and driven turbulent is among the most persistent and important open questions in plasma science. It is an opportune moment to develop, in concert with advanced space missions, a next-generation experimental facility to isolate, control, and diagnose plasma phenomena responsible for the complex solar wind behavior, at relevant scales. This facility would leverage and coordinate existing laboratory space/astrophysics research groups, as the experimental conditions needed to pursue solar-wind-related questions can also benefit research in broader astrophysical contexts. Such a venture would be a prime opportunity to coordinate among interested funding agencies, primarily NSF and NASA, but also ONR and AFOSR.

Multi-Petawatt Laser Facility: Tens-of-petawatt laser systems can produce light pressures in the exapascal regime, copious amounts of radiation, and extremely bright beams of energetic particles, including electrons, ions, neutrons, or antimatter. The novel capabilities enabled by multi-PW lasers open new frontiers in R&D such as particle acceleration and advanced light sources, high-field physics and nonlinear quantum electrodynamics (QED), and laser-driven nuclear physics. As identified in the BLI report, there is a need for the US to develop ultrahigh-intensity technology and build an open-access laser user facility with multiple beamlines at 10–100 PW peak powers.

High-Repetition-Rate Laser Facility: New high-repetition-rate (10 Hz to kHz) laser systems coming online represent a fundamentally new system architecture for high energy density (HED). The greater than 1000 times increase in shot rate over today’s systems, coupled to emerging technologies such as machine learning and additive manufacturing, will result in an enormous acceleration in the rate of knowledge acquisition. Such high-rep-rate high-energy lasers further open the door to unprecedented temporal and spatial resolution of HEDP phenomena, including GeV-class electron beams and precision HED pumps and probes. Recent community reports from NASEM and BLI have clearly outlined the urgent science case and FES mission-relevant needs for a short-pulse, highpeak-power, high-average-power laser system. This may be an area for partnering with DOE HEP, which may take the lead on this facility.

Midscale Z pinch: Extremely strong magnetic fields over macroscopic volumes are only accessible via pulsed-power facilities, which open up the physics of plasmas in a way that other plasma drivers cannot. Current US facilities are either very large and complex (the 26 MA Sandia Z-Machine with < 1 shot/day) or too small (~1 MA or less) to address the breadth of science expressed by the community. There is clear interest in establishing a pulsed-power facility at an intermediate size (up to 10 MA) accessible to the academic community, with a higher shot rate than Z, yet still capable of fielding fusion-relevant and HED experiments. Further, such a facility could explore driver technologies and pulsed-power science for next-generation larger-scale pulsed-power devices such as a 60 MA “Z-Next.” This facility would provide an opportunity for FES to partner with another agency, such as NNSA or NSF, which might take the lead.

Process and Prioritization Criteria

The following criteria express the principles used to prioritize projects and programs discussed in this report. Consensus criteria and guidance for prioritization within program areas were developed by the research community during the CPP process. That guidance is incorporated in the criteria below, which were used for prioritization of the entire portfolio. In applying the criteria and following the charge language, we assume that the ITER construction project will be successful, and we thus focus on the non-ITER portion of the budget.

Alignment: Align projects and programs with the technology and science drivers to achieve the fusion mission, specifically the path to an FPP, and to advance fundamental plasma science and enable societally beneficial plasma applications. Balance technological development with scientific discovery, recognizing the importance of both as the sources of innovations that benefit the entire program.

Urgency: Prioritize the most expeditious path to fusion energy and other plasma technologies that provide compelling solutions to urgent issues such as sustainable, carbon-free power production, advanced medical therapies, and more efficient industrial processes.

Innovation: Embrace innovative research, new developments in technology, and interdisciplinary connections to address key challenges. Reduce the time and cost to develop usable fusion energy and other plasma applications.

Impact: Implement a logical sequence of programs that increases scientific and technological progress relative to investment, reduces the risks associated with the FPP mission and the technology and science objectives, and takes into account time constraints and impacts on the overall program.

Leadership: Establish and maintain US leadership, including world-leading facilities, science, and industries that attract international participation. Recognize federal, industry, and international efforts in fusion and plasma development and form partnerships whenever possible.

Stewardship: As experimental capabilities are developed and program transitions occur, ensure the continued productivity of an essential workforce to maintain scientific and technological progress. Engage all stakeholders in executing the program, including national laboratories, industry, and universities.