PARIS, July 6 — The long arc of nuclear fusion research, from Cold War laboratories to the sun-like conditions inside a magnetic bottle, now spans more than seven decades. What began as a closely guarded secret in the United States, the Soviet Union, and the United Kingdom in the 1950s has evolved into one of the most ambitious international scientific collaborations ever attempted. Against this backdrop of secrecy and superpower rivalry, the first major turning point came in 1958.
At the Atoms for Peace conference in Geneva, nations took the unprecedented step of declassifying their fusion research. This single act sparked a new era of international scientific cooperation, laying the groundwork for the global projects that would follow.
The Soviet contribution proved decisive. Physicists Igor Tamm and Andrei Sakharov invented the tokamak design in the 1950s, a magnetic confinement concept that would come to dominate the field. The tokamak’s ascendancy was cemented in 1968, when the Soviet T-3 tokamak achieved record plasma temperatures, convincing the international community that this design held the key to controlled fusion.
The 1980s saw a wave of major tokamak construction. The Joint European Torus, known as JET, became operational in the United Kingdom in 1983.
Across the Atlantic, the Tokamak Fusion Test Reactor, or TFTR, ran from 1982 to 1997. Japan built its own machine, JT-60. These three devices became the workhorses of fusion science for a generation.
In 1991, JET produced a milestone that had eluded researchers for decades: the first controlled fusion power, generating 1.7 megawatts. Six years later, in 1997, the same machine pushed further, setting a record of 16 megawatts of fusion power. These were not yet commercial-scale outputs, but they proved the physics was sound.
What is at stake now is far larger. The International Thermonuclear Experimental Reactor, or ITER, was first proposed in 1985 by the United States, the Soviet Union, the European Union, and Japan.
The formal agreement was signed in 2006, and construction is now underway in Cadarache, in the south of France. ITER is designed to produce 500 megawatts of fusion power, a scale that would demonstrate the viability of fusion as a practical energy source. The wider picture shifted dramatically in 2022.
The US National Ignition Facility achieved the first net energy gain from fusion, a landmark moment after decades of effort. In the corridors of fusion laboratories across Europe, the United States, and Japan, the mood is cautiously optimistic.
The science has moved from theory to demonstration, and the engineering challenge of scaling up remains the next great hurdle. The tokamak design born in the Soviet Union half a century ago now finds its ultimate expression in the French countryside. What comes next will depend on whether the world can sustain the collaboration that made this progress possible.
