DOE Office of Fusion Energy Sciences

Overview

The Office of Fusion Energy Sciences (FES) is the lead federal entity for supporting fundamental research in plasma physics and the development of fusion as a future energy source within the United States. As part of the Department of Energy's (DOE) Office of Science, FES has a dual mission: to expand the fundamental understanding of matter at very high temperatures and densities, and to build the scientific and technological foundations needed to develop a fusion energy system. FES funding supports research at national laboratories, universities, and private companies, encompassing both magnetic confinement fusion (MCF) and, to a lesser extent, aspects of inertial fusion energy (IFE) science and technology. Its strategic importance lies in its role as the steward of the U.S. fusion research portfolio, guiding national priorities, funding major experimental facilities, and representing the U.S. in international collaborations like the ITER project.

Mission and Strategy

The core mission of FES is to develop a predictive understanding of plasmas and to harness this knowledge for the creation of a sustainable, carbon-free energy source. The FES strategic plan is guided by recommendations from the Fusion Energy Sciences Advisory Committee (FESAC), which provides independent advice to the Office of Science Director. A key document shaping recent strategy is the 2020 FESAC long-range plan, "Powering the Future: Fusion & Plasmas," which recommended a pivot towards a strategy focused on closing the science and technology gaps for a commercially viable fusion pilot plant (FPP). This strategy is built on several pillars:

1. Foundational Science: Supporting a broad portfolio of research in general plasma science, high-energy-density physics, and materials science. This includes operating national user facilities and funding individual investigators to advance the knowledge base required for fusion and other plasma applications.
2. Sustaining the Tokamak: Leveraging existing major tokamak facilities, such as DIII-D and the National Spherical Torus Experiment-Upgrade (NSTX-U), to resolve critical physics and technology issues for next-step devices. This research focuses on topics like plasma-materials interaction, heat exhaust management, and achieving stable, high-performance plasma regimes.
3. International Partnerships: Fulfilling U.S. commitments to the international ITER project, which is designed to demonstrate the scientific and technological feasibility of fusion power. The U.S. contribution consists of in-kind hardware components and personnel, managed by the US ITER Project Office at Oak Ridge National Laboratory.
4. Public-Private Partnerships: Fostering a competitive fusion industry through programs like the Milestone-Based Fusion Development Program. This initiative, authorized by the Energy Act of 2020, provides cost-share funding to private companies to achieve specific technical milestones on a path toward a pilot plant design, stimulating innovation and private investment.
5. Exploring Alternatives: Investing in a range of alternative and innovative confinement concepts, including stellarators and other magnetic and inertial approaches, to ensure a robust and diverse national fusion program that can capitalize on scientific breakthroughs beyond the conventional tokamak.

This multi-pronged strategy aims to balance near-term scientific discovery with the long-term goal of demonstrating net energy gain and developing the components for a functional fusion power plant.

Historical Development

The U.S. fusion program, the predecessor to FES, began in 1951 under the Atomic Energy Commission (AEC) as Project Sherwood. Early research was classified and focused on exploring various magnetic confinement concepts like the stellarator (invented by Lyman Spitzer at Princeton) and the magnetic mirror. Following the declassification of fusion research at the 1958 Atoms for Peace conference, the program expanded and became more collaborative internationally.

Throughout the 1970s and 1980s, the tokamak emerged as the leading confinement concept worldwide. The U.S. program achieved significant milestones with devices like the Princeton Large Torus (PLT), which achieved record ion temperatures, and the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory (PPPL). In December 1993, TFTR produced 10.7 MW of fusion power using a deuterium-tritium (D-T) fuel mix, a U.S. record that still stands. This era solidified the scientific basis for the Lawson criterion in tokamaks.

The Office of Fusion Energy Sciences was formally established in its current structure within the DOE Office of Science in 1996. The late 1990s and 2000s saw a focus on advancing the physics basis for a burning plasma experiment, which culminated in the U.S. decision to join the international ITER project in 2003. During this period, FES also supported major domestic facilities like the DIII-D National Fusion Facility at General Atomics and NSTX at PPPL, which explore advanced tokamak and spherical tokamak physics, respectively.

The 2010s were marked by steady scientific progress but also by constrained budgets and debates over the balance between funding the domestic program and the rising costs of the U.S. contribution to ITER. The decade ended with a growing recognition of the rapid emergence of private fusion companies, prompting a strategic re-evaluation that led to the current emphasis on public-private partnerships.

Current Status (as of 2026)

As of 2026, FES operates with an annual budget of approximately $773 million (FY2024 enacted). A significant portion, around $242 million, is allocated to the U.S. contribution to ITER construction. The remaining funds support the domestic research program, including facility operations, university grants, and national laboratory research.

The flagship FES initiative is the Milestone-Based Fusion Development Program. In its first cohort, announced in 2023, FES awarded a total of $46 million to eight companies to advance their fusion power plant designs. This program signals a major strategic shift, formally integrating the private sector into the national fusion development strategy. The companies selected represent a diversity of concepts, including tokamaks, stellarators, and other approaches.

FES continues to operate its major user facilities. DIII-D is focused on developing solutions for plasma-material interactions and advanced operating scenarios for ITER and future FPPs. NSTX-U at PPPL is undergoing recovery efforts after technical challenges but aims to explore the physics of the spherical tokamak at high performance. FES also supports a vibrant research program in stellarators, primarily through university-led experiments and collaborations with international partners like the Wendelstein 7-X device in Germany.

Inertial Fusion Energy (IFE) has also gained renewed attention following the demonstration of ignition at the National Ignition Facility (NIF). While NIF is funded by the National Nuclear Security Administration (NNSA), FES has established a new IFE program, as recommended by the 2022 White House summit on fusion energy, to leverage these advances for energy applications. This includes funding research hubs to tackle IFE-specific challenges like target manufacturing, high-repetition-rate drivers, and chamber design.

Major Programs and Facilities

FES manages a portfolio of programs and facilities that form the backbone of U.S. fusion research:

• DIII-D National Fusion Facility: Operated by General Atomics in San Diego, California. DIII-D is a highly flexible conventional aspect ratio tokamak used by hundreds of researchers annually to study plasma stability, transport, and control.
• National Spherical Torus Experiment-Upgrade (NSTX-U): Located at the Princeton Plasma Physics Laboratory (PPPL) in New Jersey. As a spherical tokamak, it investigates the potential advantages of a compact geometry for a fusion pilot plant.
• US ITER Project: Managed by Oak Ridge National Laboratory (ORNL), this project oversees the design, fabrication, and delivery of all U.S. hardware and personnel contributions to the international ITER experiment in France. This includes large superconducting magnets, microwave heating systems, and diagnostic instruments.
• Milestone-Based Fusion Development Program: A public-private partnership program that co-funds private companies to achieve pre-defined technical milestones. Participants in the first round include Commonwealth Fusion Systems, Xcimer Energy, and Type One Energy Group.
• Theory and Simulation: FES heavily invests in computational plasma physics through its Scientific Discovery through Advanced Computing (SciDAC) program. These efforts develop advanced simulation codes run on DOE supercomputers to model complex plasma behavior, validate experimental results, and design new devices.
• University and Laboratory Research: A significant portion of the FES budget supports research grants at universities and core research programs at national laboratories like PPPL, ORNL, and Lawrence Livermore National Laboratory (LLNL), training the next generation of plasma physicists and fusion engineers.

Strategic Challenges

Despite recent progress, FES faces several strategic and technical challenges:

1. Budgetary Pressure: The FES budget is under constant pressure to balance the large, long-term commitment to ITER with the needs of the domestic research program and new initiatives like the milestone program. Funding levels have often fallen short of the amounts recommended by FESAC to pursue its strategic goals aggressively.
2. Tritium Supply: A viable fusion power plant will require a closed fuel cycle, breeding its own tritium from lithium. The technology for tritium breeding blankets is immature, and the global supply of tritium for near-term D-T experiments is extremely limited. FES must coordinate a national strategy to close this fuel cycle gap.
3. Materials Science: Finding materials that can withstand the extreme environment of a fusion reactor core—high heat fluxes (10s of MW/m²) and intense neutron bombardment—is a critical challenge. Developing and qualifying these plasma-facing and structural materials is a long-lead-time problem that requires dedicated facilities and research programs.
4. Workforce Development: The growth of the private fusion industry and the needs of next-generation public programs require a significant expansion of the skilled workforce, from plasma physicists to specialized engineers and technicians. FES plays a crucial role in funding the university programs that train this workforce.
5. Integrating Public and Private Efforts: Effectively managing the new public-private partnership model is a key challenge. It requires FES to act not just as a grant-making agency for basic science but also as a sophisticated technical program manager, ensuring that taxpayer funds are used effectively to accelerate commercialization while maintaining a strong foundation of public research.

Outlook

Over the next 5-15 years, the FES portfolio is poised for significant evolution. The primary focus will be on executing the strategy outlined in the 2020 FESAC long-range plan: enabling the design and construction of a fusion pilot plant by the 2040s. A key milestone will be the first plasma operation at ITER, which will provide invaluable data on burning plasma physics and test many of the technologies needed for a power plant.

The Milestone-Based Fusion Development Program will likely be expanded, potentially leading to multiple private-sector integrated demonstrations of net energy gain within the next decade. The success of this program will be a critical indicator of the viability of the public-private partnership model for fusion development. Concurrently, FES will need to make critical investment decisions in new facilities to address the major technology gaps, particularly in materials testing and tritium fuel cycle development. A Fusion Prototypic Neutron Source (FPNS) is considered a necessary facility for materials qualification, and its potential construction will be a major decision point. The balance between supporting the large-scale international ITER project and fostering a nimble, competitive domestic ecosystem of public and private players will remain the central strategic challenge for the Office of Fusion Energy Sciences.

References

1. Powering the Future: Fusion & Plasmas — Fusion Energy Sciences Advisory Committee (FESAC) (2020)
2. A New Era for Fusion Energy: The 2023 FES Portfolio — U.S. Department of Energy (2023)
3. DOE Announces $46 Million for Commercial Fusion Energy Development — U.S. Department of Energy (2023)
4. Fusion Energy Sciences (FES) Budget Request — U.S. Department of Energy (2023)
5. Bringing a Star to Earth: The Future of Fusion Energy — The National Academies of Sciences, Engineering, and Medicine (2023)
6. Review of the Fusion Energy Sciences Program of the U.S. Department of Energy — The National Academies of Sciences, Engineering, and Medicine (2004)
7. U.S. Participation in the ITER Project — U.S. Government Accountability Office (GAO) (2023)