README.md

2026XDZW

Codex/ChatGPT (July 2026)

Summary

Experiments on the full-metal-wall EAST tokamak demonstrate an edge-localized-mode-free high-confinement regime sustained for $50$--$70$ s while the divertor remains partially detached. Feedback-controlled nitrogen seeding lowers target temperature and suppresses tungsten sources without the usual pedestal degradation; a lower-$q_{95}$ discharge raises $H_{98y2}$ from about $0.85$ to $1.2$. The proposed detached, turbulence-dominated-pedestal mechanism begins when power starvation reduces recycling-neutral ionization in the closed divertor. Higher neutral pressure enhances pumping, weakens pedestal cooling, and steepens the electron temperature gradient. High-frequency broadband turbulence then supplies outward particle and heat transport that arrests pedestal growth and prevents ELMs. GENE calculations identify this turbulence as an $\eta_e$-driven trapped-electron mode, consistent with its frequency, wavenumber, gradient dependence, collisional stabilization, and nonlinear fluxes. Independent GENE and CGYRO calculations predict the same mode can overcome $E\times B$ shear in an ITER baseline pedestal. ITER would require a nonreactive seed impurity such as neon rather than nitrogen.

Contributions

1. Demonstrated minute-scale ELM-free H-mode operation with divertor partial detachment and strong confinement.
2. Showed that feedback-controlled seeding reduces divertor heat and metal-impurity sources without cooling the pedestal.
3. Identified high-frequency broadband pedestal turbulence correlated with complete ELM suppression.
4. Matched the measured turbulence to an $\eta_e$-driven trapped-electron mode using linear and nonlinear gyrokinetics.
5. Predicted with two gyrokinetic codes that the mechanism is accessible in the ITER baseline pedestal.