Speaker
Description
A notable recent success of the island-diverted stellarator Wendelstein 7-X is the achievement of stable detached operation. However, central processes involved in detachment access and detached operation of stellarators still need to be fully understood to explain the observed phenomena and improve the design of future machines.
Shedding light on these mechanisms is the aim of the simulation tool Hermes-3, which is based on the BOUT++ framework and is able to use the flux-coordinate independent (FCI) approach. Drift effects for non-axisymmetric domains are currently added to the code, opening the road to never before made investigations. Yet, the neutral dynamics essential for high density operation, high recycling regimes and detachment remain to be verified for stellarator geometries.
This contribution presents the status of the neutral verification effort of the Hermes-3 FCI implementation. We quantitatively compare the diffusion and convection of neutrals resulting from the numerical calculations with and without charge exchange collisions, and match them to analytically expected values in a 3D slab geometry. We check the charge exchange momentum transfer from background ions onto the neutrals for physical consistency.
In a second stage test we plan to further substantiate credibility of the Hermes-3 neutral model by also including field line curvature and surface interaction in a large-aspect-ratio approximated limiter configuration. The resulting neutral fluxes observed in Hermes-3 are then compared to solutions obtained by the well-established EMC3-EIRENE code.