The primary U.S. federal agency funding and directing fusion energy research, operating under the Department of Energy's Office of Science with a portfolio spanning plasma physics, materials science, and enabling technologies.
The Office of Fusion Energy Sciences (FES) is the division within the U.S. Department of Energy's Office of Science responsible for the nation's magnetic fusion energy research program. With an annual budget that has grown from approximately $564 million in fiscal year 2022 to over $700 million in recent appropriations, FES supports research at national laboratories, universities, and private-sector partners across the United States.1
Federal investment in fusion research in the United States dates to the 1950s, when early experiments at Los Alamos, Princeton, and Oak Ridge first explored magnetic confinement of high-temperature plasmas. The program was administered under various organizational structures before being consolidated as the Office of Fusion Energy Sciences within the Office of Science. Throughout its history, FES has been the steward of the U.S. contribution to ITER and the primary funder of domestic fusion experiments, including landmark devices such as the Tokamak Fusion Test Reactor (TFTR) at Princeton and the DIII-D tokamak at General Atomics.2
The FES research portfolio is organized around several interconnected thrust areas. Burning Plasma Science supports ITER preparation and the physics of self-heated plasmas. Discovery Plasma Science funds fundamental research into plasma behavior relevant to fusion and other applications. Fusion Nuclear Science addresses the materials and technologies needed to withstand the extreme neutron environment inside a fusion power plant, including structural materials, tritium breeding systems, and plasma-facing components.
FES also supports major computational initiatives through the Scientific Discovery through Advanced Computing (SciDAC) program, funding large-scale simulations of plasma turbulence, magnetohydrodynamic stability, and whole-device modeling that complement experimental campaigns on domestic and international facilities.
In 2021, the National Academies of Sciences, Engineering, and Medicine issued a landmark report, "Bringing Fusion to the U.S. Grid," which called for an aggressive timeline to build a fusion pilot plant by the 2040s. In response, FES launched the Bold Decadal Vision for Commercial Fusion Energy, a strategic framework to align the federal program with the goal of delivering fusion electricity within a generation. Key elements include a Milestone-Based Fusion Development Program to co-fund private-sector pilot plant efforts, expanded materials irradiation testing, and workforce development initiatives.4
Reflecting the maturation of the private fusion industry, FES has increasingly embraced public-private partnership models. The Milestone-Based Fusion Development Program, authorized under the Energy Act of 2020, provides cost-shared awards to private companies pursuing commercially relevant fusion concepts. Initial awardees were announced in 2023, marking a significant shift in how the federal government engages with the fusion sector — moving from a purely research-oriented approach toward one that explicitly supports commercialization pathways.5
As the U.S. fusion landscape evolves with growing private investment and international competition, FES remains the anchor institution for publicly funded fusion science, balancing its historic role in fundamental research with new responsibilities to enable a domestic fusion energy industry.