Impact of triangularity on edge transport and divertor detachment: a SOLPS-ITER study of TCV L-mode plasmas

TL;DR

This study uses SOLPS-ITER modeling to analyze how magnetic triangularity affects edge plasma behavior and divertor detachment in TCV L-mode plasmas, emphasizing the role of transport properties over geometry.

Contribution

It demonstrates that differences in divertor detachment between negative and positive triangularity are primarily due to transport variations, not magnetic geometry alone.

Findings

Lower particle diffusivity in NT matches experimental profiles.

Neutral pressures differ significantly between NT and PT.

Transport properties, not geometry, drive detachment behavior.

Abstract

Negative triangularity (NT) magnetic configurations have recently gained attention as a promising route to achieve H-mode-like confinement without edge-localized modes (ELMs) and without a power threshold for access. While both core and edge confinement properties of NT have been extensively documented, consistently lower divertor target cooling and increased difficulty in achieving a detached regime have been observed. This work presents a comparative SOLPS-ITER modeling study of two Ohmic L-mode discharges in the TCV tokamak with identical divertor geometry and opposite upper triangularity. We investigate whether magnetic geometry alone can account for the experimentally observed differences in plasma detachment behavior. Simulations with identical transport coefficients reveal no significant differences between NT and positive triangularity (PT) cases, even when including drifts. A parametric scan of radial anomalous transport coefficients shows that reproducing the experimental profiles requires lower particle diffusivity in NT, consistent with reduced turbulent transport and previous findings. Furthermore, the evolution of simulated neutral pressures and recycling fluxes along a density scan reproduces experimental observations of larger neutral divertor pressure in PT, highlighting a distinct neutral dynamics in the two cases. These results support the interpretation that altered cross-field transport, rather than magnetic geometry alone, underlies the observed differences in divertor behavior between NT and PT scenarios.