Reproduction of anomalously high tungsten transport coefficients in the far-SOL of DIII-D with Flan

The Monte Carlo trace impurity transport code Flan has recently been developed to simulate anomalous, turbulent-driven cross-field impurity transport in the tokamak scrape-off-layer (SOL). Application to tungsten (W) transport in the far-SOL of DIII-D shows Flan reproduces anomalous diffusion coefficients interpreted from experimental data, D_r~10-60 m²/s. Traditionally, edge modeling uses ad-hoc user-defined D_r to approximate turbulent radial transport of impurity ions in the SOL, limiting the predictive capabilities of the model. We address this problem by first simulating the far-SOL of a generic DIII-D L-mode with the turbulent full-f gyrokinetic code Gkeyll in the electrostatic limit. The simulation is constrained against experimental n_e and T_e data from a reciprocating Langmuir probe. The plasma solution is fed into Flan, which tracks impurity ions according to the Lorentz force and uses the Nanbu collision model. Simulations indicate that electric field fluctuations are likely responsible for anomalously high radial impurity transport. The average radial W velocity is v_r ~ 1,000-2,000 m/s. Flan shows that D_r increases from ~10 m²/s at 5 cm from the separatrix up to ~60 m²/s at the outer wall. These agree with previous interpretive modeling estimates from a collector probe inserted during this discharge (v_r ~ 500, D_r~ 5-50 m²/s). This work opens the door to better predictions for W transport into the core of reactor designs.