3D modeling of boron transport in DIII-D L-mode wall conditioning experiments

DIII-D L-mode experiments with local boron powder injection for real-time wall conditioning have been interpreted for the first time with the 3D plasma edge transport Monte Carlo code EMC3-EIRENE. Local B sourcing in plasma scenarios with upstream densities 1.5⋅10¹⁹ m⁻³ and 2.2 MW heating results in a non-axisymmetric B distribution in the scrape-off layer (SOL) and on the divertor. The SOL frictional flows at high plasma density cause a strong inboard drag of injected impurities (≈90%), while lower background plasma densities tend to result in a more uniform distribution. The thermal forces prevent B deposition in the near SOL while the frictional force causes B fluxes to cover the divertor plasma-facing components in a region 7–10 cm beyond the strike line. Radiative dissipation occurs for B influxes above 1⋅10²⁰ s⁻¹ and causes a moderate, non-axisymmetric reduction of the far SOL divertor heat fluxes. A comparison of top and midplane B injection shows no substantial difference in inboard vs. outboard asymmetries of the B distribution. On the other hand, erosion or recycling at the strike line may distribute the boron more uniformly in the SOL.