China's EAST Tokamak achieves stable operation at densities beyond limits

Chinese researchers operating the Experimental Advanced Superconducting Tokamak (EAST) have experimentally demonstrated stable plasma operation at densities significantly beyond the conventional empirical limits, effectively accessing a theorized “density-free regime” for fusion plasmas. By implementing a novel high-density operating scheme that combines control of initial fuel gas pressure with electron cyclotron resonance heating during startup, the team optimized plasma–wall interactions, reduced impurity buildup and energy losses, and pushed plasma density to unprecedented levels without triggering disruptive instabilities. This marks the first experimental verification of the PWSO theoretical density-free regime, where plasma stability is maintained despite exceeding traditional density constraints. These findings suggest a practical and scalable method to extend density limits in tokamaks and future burning plasma fusion devices, offering new physical insights into overcoming a long-standing barrier in fusion research. Since fusion power output scales with the square of fuel density, breaking through the density limit is crucial for achieving fusion ignition and advancing nuclear fusion as a clean, sustainable energy source. The EAST