A century of discovery, from the first understanding of how stars burn to the race to build commercial reactors. The essential milestones in humanity's quest for fusion energy.
1920 — British astrophysicist Arthur Eddington proposes that stars are powered by the fusion of hydrogen into helium, following Francis Aston's precise mass measurements showing that four hydrogen atoms weigh more than one helium atom. The 'missing' mass, Eddington suggests, is converted to energy.1
1932 — At the Cavendish Laboratory in Cambridge, Mark Oliphant achieves the first laboratory fusion reaction by accelerating deuterium nuclei into a target, confirming that light nuclei can be fused and that the process releases energy.
1934 — Ernest Rutherford's team demonstrates the deuterium-tritium reaction, which will later become the primary candidate fuel cycle for fusion power.
1942 — The first fission chain reaction (Chicago Pile-1) is achieved. Fusion research begins in parallel, initially in the context of weapons development.
1952 — The United States tests the first thermonuclear weapon (hydrogen bomb), demonstrating uncontrolled fusion on a massive scale. The challenge of controlled fusion for peaceful energy becomes a defining scientific goal.
1958 — At the Atoms for Peace conference in Geneva, previously secret fusion research programs from the US, UK, and Soviet Union are declassified and shared internationally, launching the modern era of open collaboration in fusion science.2
1958 — Soviet physicists Andrei Sakharov and Igor Tamm's tokamak concept — a toroidal magnetic confinement device — begins experimental testing. It will eventually prove far more effective than competing designs.
1968 — The Soviet T-3 tokamak achieves plasma temperatures and confinement times that far exceed anything previously demonstrated, convincing the international community that the tokamak is the most promising path. Laboratories worldwide begin building tokamaks.
1978 — The Princeton Large Torus reaches plasma temperatures of 60 million degrees Celsius, approaching fusion-relevant conditions for the first time.
1983 — The Joint European Torus (JET) begins operation in Culham, England. It will become the world's most successful fusion experiment for nearly four decades.3
1991 — JET achieves the world's first controlled release of fusion power using a deuterium-tritium fuel mix, producing approximately 1.7 megawatts of fusion power.
1994 — Japan's JT-60 tokamak achieves conditions equivalent to scientific breakeven (Q = 1) using deuterium-only plasma, though not with actual D-T fuel.
1997 — JET sets a world record of 16.1 megawatts of fusion power from D-T fuel, a record that will stand for over two decades.4
2006 — Seven international partners (EU, US, Russia, China, Japan, South Korea, India) formally agree to build ITER in Cadarache, France — the most ambitious fusion experiment ever attempted, designed to produce 500 MW of fusion power from 50 MW of input heating.
2021 — MIT and Commonwealth Fusion Systems (CFS) successfully test a 20-tesla high-temperature superconducting (HTS) magnet, the most powerful fusion magnet ever built. HTS technology promises to enable smaller, cheaper, and faster-to-build fusion devices.
2022 (February) — JET sets a new energy record of 59 megajoules of fusion energy sustained over five seconds, demonstrating long-pulse D-T operation before the facility's retirement.
2022 (December) — The U.S. National Ignition Facility achieves scientific ignition for the first time: a laser-driven inertial confinement experiment produces more fusion energy (3.15 MJ) than the laser energy delivered to the target (2.05 MJ).5
2024-2025 — Private fusion companies raise billions in new investment. Over 40 companies worldwide pursue diverse reactor concepts. Multiple teams announce plans for demonstration power plants by the early 2030s.
2025-2026 — Construction advances on ITER in France. China's EAST tokamak and South Korea's KSTAR achieve record-setting long-duration plasma operations. The U.S. Department of Energy launches its Bold Decadal Vision for commercial fusion energy.