A team led by Prof. XU Guosheng from Hefei Institutes of Physical Science of the Chinese Academy of Sciences for the first time demonstrated a plasma regime in a metal-wall environment that simultaneously achieved partial divertor detachment, an edge-localized-mode (ELM)-free high-confinement mode (H-mode), and high pedestal performance. This integrated regime was sustained on a minute-scale. The study was published in Physical Review Letters.

Controllable nuclear fusion requires managing extreme heat loads on divertor plates while maintaining plasma stability. Impurity gases can reduce divertor heat through detachment, but excessive cooling can damage the plasma edge, and H-mode plasmas are prone to sudden, damaging ELMs. Achieving a steady-state regime that addresses both issues has been a major goal.

In this study, researchers created a new plasma regime on the Experimental Advanced Superconducting Tokamak (EAST) tokamak, called the Detached divertor and Turbulence-dominated Pedestal (DTP) regime, by controlling the injection of light impurity gases. By fine-tuning gas seeding in real time, they achieved partial divertor detachment while maintaining plasma stability.

In this regime, heat flux to divertor plates was greatly reduced, ELMs were completely suppressed, and the pedestal electron temperature increased significantly, improving overall energy confinement. The partial detachment, combined with a closed divertor geometry, trapped and pumped neutral particles, reducing pedestal cooling and enhancing the temperature gradient. This stronger gradient drove micro-turbulence, identified as temperature-gradient-driven trapped electron modes, which naturally transported particles and heat outward. This transport channel limited pedestal pressure buildup, prevented ELMs, and maintained steady, high-performance plasma on a minute-scale.

This study provides a solution to the challenge of balancing divertor heat load management with efficient plasma confinement, representing a major step toward stable, long-pulse fusion operation.