README.md

2026ADGM

Codex/ChatGPT (July 2026)

Summary

Experiments and global electrostatic gyrokinetic simulations examine why short hydrogen gas puffs improve confinement in ADITYA-U. A puff raises line-averaged density within about $1,\mathrm{ms}$ and electron temperature after $3$--$4,\mathrm{ms}$, while flattening the density profile mainly at normalized radius $0.3<\rho<0.8$. GTC simulations use measured pre- and post-puff profiles, an IPREQ equilibrium, and kinetic passing and trapped electrons. Trapped-electron modes (TEMs) dominate both cases, but after fueling their peak shifts outward from $\psi/\psi_X\approx0.5$ to $0.75$, their poloidal mode number falls from about 160 to 120, and their radial structure retreats from the core. Nonlinear simulations consequently show lower particle and heat transport and curtailed inward turbulence propagation; saturated electron and ion particle diffusivities fall by about 84% and 94%, respectively. The results support profile relaxation, rather than turbulence spreading, as the mechanism linking transient fueling to the rapid core-temperature rise. They establish neutral fueling as an active turbulence-control mechanism in this discharge, although the simulations compare measured states rather than predicting the neutral-plasma profile evolution.

Contributions

1. Connected the post-puff mid-radius density flattening to reduced trapped-electron-mode drive.
2. Reproduced the pre- and post-puff regimes with global GTC simulations using measured profiles and equilibrium geometry.
3. Quantified the outward shift, localization, and reduced mode number of the dominant TEM after fueling.
4. Measured large reductions in saturated particle diffusivities and suppressed inward turbulence propagation.
5. Provided a transport explanation for the observed millisecond-scale core-temperature increase.