Chinese scientists shatter fusion energy's density barrier in historic tokamak breakthrough

Scientists in China have made a major advance in fusion energy research by breaking through a long-standing barrier in tokamak operations. The team at the Experimental Advanced Superconducting Tokamak (EAST) confirmed the existence of a 'density-free region', allowing plasma to reach far higher densities than previously possible. Their findings, published in Science Advances, could pave the way for achieving fusion ignition in future reactors.

The breakthrough centres on overcoming the Greenwald density limit, a constraint that typically causes plasma to become unstable at high densities. By carefully controlling the physical conditions of the target plate, researchers reduced tungsten impurity sputtering, enabling the plasma to exceed this limit. Experiments at EAST achieved line-averaged electron densities between 1.3 and 1.65 times the Greenwald threshold.

The team also identified boundary radiation as a key factor in triggering the density limit. Their work was made possible by EAST's all-metal wall platform and an open collaboration system that has hosted Chinese and international scientists since 2006.

In 2025, EAST reached a linear-weighted electron density of 4.4 × 10²¹ m⁻³ s, surpassing its own 2024 record and outperforming other leading tokamaks worldwide. This includes JET in the UK (1.5 × 10²¹ m⁻³ s in 2021), DIII-D in the USA (1.2 × 10²¹ m⁻³ s in 2023), and KSTAR in South Korea (1.8 × 10²¹ m⁻³ s in 2024). Similar progress beyond the Greenwald limit was also reported by WEST in France (2024) and HL-2M in China (2025).

The research involved a collaboration between the Institute of Plasma Physics, Huazhong University of Science and Technology, and Aix-Marseille University.

This discovery provides a clear method for operating tokamaks at higher plasma densities without instability. The results move fusion research closer to achieving the ignition conditions needed for practical energy production. Further experiments will build on these findings to refine the approach.