Modeling neutral-turbulence interactions in detached scenario with multi-species GBS simulations

We present multi-species simulations of edge plasma turbulence and detachment using the GBS code, benchmarked against experimental TCV results. Designed for validating turbulence models in high-density, dissipative regimes, the TCV scenario we consider, dubbed TCV-X23, features a lower single-null configuration, a long outer divertor leg, both toroidal field directions, and two upstream density levels. The diagnostics include divertor probes, spectroscopy, and gas puff imaging, effectively extending the open-access TCV-X21 database into weakly detached regimes.

GBS employs a three-fluid model (electrons, D⁺, D₂⁺) and two kinetic neutral species (D, D₂), enabling study of turbulence, ionization, and neutral transport. We investigate how divertor geometry and upstream density affect detachment onset, neutral buildup, and ion flux reduction at the target. Simulations show that long-leg, high-density conditions enhance D₂ dissociation and atomic neutral density, suppressing target ion flux and triggering detachment. Turbulence-neutral feedback is captured, including increased divertor fluctuations under high-collisionality conditions.

Simulations reproduce key experimental trends, such as enhanced midplane transport and broader SOL profiles at high density, confirming GBS as a valuable tool for validating and predicting edge plasma behavior.