Comprehensive understanding of the Greenwald density limit and disruption in tokamak fusion plasmas

The output power of a fusion reactor scales with the square of the plasma density. Achieving high economic performance thus necessitates operation at high plasma density. However, existing devices rarely sustain steady-state operation above the empirical Greenwald density limit—a longstanding puzzle in fusion science. Through our systematical investigation, a critical role of the plasma density and its distribution on the MARFE formation and the consequence of the plasma disruption is discovered. It is found that the Greenwald limit is attributed it to nonlinear interactions among impurity radiation, ballooning modes, and tearing modes. We further demonstrate that the Greenwald limit can be surpassed through the optimization of the density profile. These findings hold significant implications for the design and operation of future fusion reactors.