From the classified stellarator experiments of Project Matterhorn to the National Ignition Facility's breakthrough and today's booming private sector, the US fusion program has been marked by cycles of ambition, budget cuts, and reinvention.
The United States has been at the forefront of fusion energy research since the field's inception. American scientists have achieved landmark results—from the first controlled thermonuclear reactions to the first demonstration of ignition—yet the program's history is also one of fluctuating political commitment, cancelled flagship projects, and a recent dramatic shift toward private-sector leadership.
The US fusion program began in 1951 when astrophysicist Lyman Spitzer conceived the stellarator at Princeton University. His classified program, codenamed Project Matterhorn, aimed to confine plasma in a twisted magnetic bottle.¹ Simultaneously, other approaches emerged across the national laboratory system: magnetic mirrors at Lawrence Livermore, pinch devices at Los Alamos, and various concepts at Oak Ridge. The 1958 Geneva conference declassified fusion research worldwide, and the US program expanded rapidly. The Model C stellarator at Princeton was the flagship device through the 1960s, but results were disappointing—plasma leaked through the magnetic field far faster than theory predicted.
When the Soviet T-3 tokamak results were confirmed in 1969, the US rapidly pivoted. Princeton converted its Model C stellarator into the Symmetric Tokamak, and soon every major US lab was building tokamaks. The 1970s saw an explosion of devices—Alcator at MIT, Doublet at General Atomics, PLT at Princeton—and increasingly impressive results. PLT achieved 60-million-degree ion temperatures in 1978 using neutral beam injection.² This era culminated in the Tokamak Fusion Test Reactor (TFTR) at Princeton, which operated from 1982 to 1997 and set world records for fusion power output, reaching 10.7 megawatts of deuterium-tritium fusion power in 1994.³
The US was a founding partner in ITER negotiations beginning in 1985 but withdrew in 1998 amid budget pressures. Domestically, the program suffered devastating cuts in the mid-1990s. TFTR was shut down. The proposed BPX (Burning Plasma Experiment) was cancelled. The US rejoined ITER in 2003, but the domestic program shrank to its smallest size in decades, focused on supporting roles rather than leadership.⁴ Meanwhile, the inertial confinement fusion program continued at the National Ignition Facility (NIF) at Lawrence Livermore, primarily as a stockpile stewardship tool.
In December 2022, NIF achieved a historic milestone: the first controlled fusion ignition, producing 3.15 megajoules of fusion energy from 2.05 megajoules of laser energy delivered to the target.⁵ While NIF's approach is not directly applicable to power generation, the scientific achievement was profound. More transformative for the energy mission has been the explosion of private fusion companies—many founded by scientists trained in the national laboratory system. Companies like Commonwealth Fusion Systems, TAE Technologies, Helion Energy, and dozens more have collectively raised over $7 billion. The 2022 White House fusion summit and subsequent DOE milestones-based development program signaled renewed federal commitment. The Milestone-Based Fusion Development Program and the public-private partnership model represent a fundamental shift in how the US approaches fusion energy.
Today the US fusion enterprise is a hybrid of federal and private efforts. The DOE Office of Fusion Energy Sciences funds university and national lab research, while ARPA-E and the Milestone program support private companies. DIII-D at General Atomics remains the largest operating US tokamak. The program's trajectory now depends on whether sustained political and financial commitment can match the scientific opportunity.