China's EAST tokamak achieved a breakthrough in January 2026 reaching what regime in fusion plasma experiments?

In January 2026, China's Experimental Advanced Superconducting Tokamak (EAST), often called the "artificial sun," achieved a significant breakthrough in fusion plasma experiments by reaching a "density-free regime." This accomplishment is a major step forward in the quest for clean and limitless (Review) fusion energy. For decades, fusion reactors known as tokamaks have faced an empirical barrier called the Greenwald density limit, beyond which the superheated plasma inside would become unstable and disrupt, halting the fusion process.

The "density-free regime" refers to a state where the fusion plasma remains stable even at densities significantly higher than this long-standing Greenwald limit. This is crucial because the power output from a fusion reaction increases with the square of the plasma density, meaning that higher densities lead to much greater energy production. Scientists on the EAST project managed to achieve this by carefully controlling the interactions between the plasma and the reactor's inner walls, particularly during the plasma's start-up phase, using techniques like electron cyclotron resonance heating (ECRH) and precise control of initial fuel gas pressure.

This achievement provides new insights into how the density barrier in tokamak operation can be overcome, offering a practical and scalable path for extending density limits in current and future fusion devices. By demonstrating that plasma can be maintained stably at unprecedented densities, the EAST tokamak has moved the scientific community closer to achieving fusion ignition, the point where a fusion reaction becomes self-sustaining and produces more energy than it consumes. This is a vital step toward realizing the dream of clean, reliable energy inspired by the processes that power our sun and stars.