Poloidal Asymmetries Of The Main Chamber Particle Source In DIII-D

Recent LLAMA (Lyman-α) measurements of DIII-D indicate a one order of magnitude larger ionization rate at the high field side (HFS) main chamber in comparison to the low field side (LFS) when operating with B×∇B directed towards the divertor. In contrast, the ionization at the LFS main chamber is higher by a factor of two with B×∇B drift out of the divertor, while it is lower by a factor of five on the HFS, which eliminates the HFS/LFS imbalance of the main chamber particle source. The LLAMA diagnostic measures the deuterium Lyman-α brightness across the LFS and HFS plasma boundary well below the midplane at the same vertical location. These measurements are of similar order of magnitude as synthetic Lyman-α brightnesses generated by high fidelity EDGE2D-EIRENE simulations with the full set of scrape-off layer (SOL) drifts. However, the model underpredicts the strong HFS/LFS variation when the SOL drift direction is altered and it does not reproduce the steep brightness drop radially from HFS SOL to the separatrix. The presented results highlight the importance of SOL drifts for the HFS particle source above the x-point, which is key for core-edge integrated plasma predictions and edge particle transport studies.