China’s nuclear fusion reactor, nicknamed the “artificial sun,” has crossed a major fusion boundary by firing plasma beyond its usual operational range, furthering humanity’s slow progress toward near-limitless clean energy.
Advanced Experimental Superconducting Tokamak (EAST) conserved plasma – high energy technology fourth state of matter — stable at extreme densities, which was previously considered a major obstacle to the development of nuclear fusion, according to a statement published by the Chinese Academy of Sciences.
Nuclear fusion offers almost unlimited clean energy potential. In other words, energy without too much nuclear waste or global warming greenhouse gas emissions released by the burning of fossil fuels. The new findings, published January 1 in the journal Scientific advancescould bring our species closer to exploiting this energy source, which some researchers say we could exploit in a few decades.
However, nuclear fusion technology has been in development for more than 70 years and still remains a very experimental science, with reactors typically consuming more energy than they can produce. Meanwhile, climate scientists are calling for action reduction of greenhouse gas emissions now that the impacts of climate change are already being felt all over the world. Nuclear fusion is therefore unlikely to represent a practical solution to the current climate crisis, but it could power our world in the future.
Fusion reactors are designed to fuse two light atoms into a single heavy atom via heat and pressure. In doing so, they generate energy in the same way as the sun. However, the sun has much more pressure than Earth’s reactors, so scientists compensate by packing hot plasma at temperatures much higher than those of the sun.
China’s EST is a magnetic confinement reactor, or tokamak, designed to keep plasma burning continuously for extended periods. The reactor heats the plasma and traps it in a donut-shaped chamber using powerful magnetic fields. Tokamak reactors have not yet reached fusion ignition, which is the point at which the fusion process becomes self-sustaining, but the EAST reactor has increased the length of time it can maintain a stable, highly confined plasma loop.
One obstacle for fusion researchers is a density limit called the Greenwald limit, beyond which plasma generally becomes unstable. This limit is problematic because, although higher plasma densities allow more atoms to collide, thereby reducing the energy cost of ignition, the instability also kills the fusion reaction.
To overcome the Greenwald limit, EAST scientists carefully managed the interaction of the plasma with the reactor walls by controlling two key parameters at reactor start-up: the initial pressure of the fuel gas and the electronic cyclotron resonance heatingor the frequency at which plasma electrons absorb microwaves. This kept the plasma stable at extreme densities of 1.3 to 1.65 times beyond the Greenwald limit, much higher than the tokamak’s usual operational range of 0.8 to 1, the study found.
This is not the first time Greenwald’s line has been crossed. For example, the U.S. Department of Energy’s DIII-D National Fusion Facility tokamak in San Diego. crossed the limit in 2022 and 2024, researchers at the University of Wisconsin-Madison in Wisconsin announced that they had maintained stable tokamak plasma at approximately 10 times the Greenwald limit using an experimental device.
However, the breach at EAST allowed researchers to heat plasma for the first time to a previously theorized state called the “density-free regime,” in which the plasma remained stable as density increased. The research is based on a theory called self-organization of the plasma wall (PWSO), which proposes that a density-free regime could be possible when the interaction between plasma and reactor walls is in a carefully balanced state, according to the release.
Progress at EAST and in the United States will inform the development of new reactors. Both China and the United States are part of the International thermonuclear experimental reactor (ITER), which is a collaboration between dozens of countries to build the the largest tokamak in the world In France.
ITER will be another experimental reactor designed to create sustained fusion for research purposes, but could pave the way for fusion power plants. The ITER reactor is expected to begin producing large-scale fusion reactions in 2039.
