README.md

2025ZSRR

Codex/ChatGPT (July 2026)

Summary

This paper models the first DIII-D divertor-detachment experiments in negative-triangularity plasmas with the two-dimensional multifluid edge code UEDGE, including cross-field particle drifts. Density scans reproduce the observed outer-target ion-saturation-current rollover and compare forward and reverse toroidal-field configurations. The simulations find that forward field requires roughly 40% higher density for detachment onset than reverse field, while reverse field fails to reach deep detachment because $E \times B$ drift drives plasma into the outer far scrape-off layer and prevents density buildup at the outer strike point. In forward field, high-field-side radiation can move above the X-point before outer-target detachment, explaining experimentally observed confinement degradation during density ramps. Comparison with positive-triangularity Ohmic discharges shows that negative triangularity needs much higher separatrix density, near or above the Greenwald limit, to detach. The modeling attributes this difficulty mainly to shorter divertor-leg and connection lengths and weaker cross-field transport.

Contributions

1. Modeled DIII-D negative-triangularity detachment experiments with drift-inclusive UEDGE simulations.
2. Reproduced the field-direction dependence of detachment onset and shallow-detachment behavior.
3. Explained reverse-field detachment saturation through drift-driven outer far-SOL plasma transport.
4. Linked forward-field confinement degradation to high-field-side radiation above the X-point.
5. Compared positive and negative triangularity to isolate geometric and transport limits on detachment.