Simulation of boundary plasma turbulence with realistic first wall geometries

Divertor closure is expected to contribute to higher divertor neutral pressures. Higher neutral pressures are associated with facilitated access to a detached regime as well as higher power dissipation along the divertor legs, thereby making the regime attractive for future reactors. Experimentally, the effect of neutral pressure in the divertor has been investigated in devices such as Alcator C-mod, DIII-D, ASDEX Upgrade, MAST-U and TCV. Transport models for boundary plasmas and neutrals dynamics, such as SOLPS-ITER, are typically capable of accounting for realistic first wall geometries. On the other hand, such capabilities remain an active area of development for three-dimensional turbulence models.

We report on progress towards enabling realistic first wall geometry in the GBS code, which provides a self-consistent plasma turbulence solver coupled to a kinetic neutral solver based on numerically discretizing the formal solution based on the method of characteristics. A single-block, non field-aligned, curvilinear, structured, wall conformal mesh is imple­mented in the plasma solver, such that plasma profiles are computed up to the wall across the entire domain, therefore, by not resorting to immersed boundary conditions, the algorithm implemented in GBS allows the use of first-principles boundary conditions. The neutral solver is extended to account for the modified wall geometry. First simulations in a baffled TCV-like configuration are discussed with a focus on neutral compression and its interplay with divertor turbulence, as well as recycling processes in the vicinity of the baffles.