Main chamber fueling asymmetries and their impact on pedestal performance in DIII-D H-mode plasmas

Understanding poloidal asymmetries in main chamber neutral fueling is essential to characterize the balance of particle transport and source in the density pedestal formation. It has been shown on DIII-D that the main chamber ionization rate on the high-field-side (HFS) is typically an order of magnitude larger than on the low-field-side (LFS) with favorable B×∇B drift direction, while fueling is more balanced with unfavorable drift direction [1-3]. In the comparative lower-single-null H-modes investigated, the HFS peak ionization rate (as measured by LLAMA [1, 4]) is reduced by an order of magnitude in the unfavorable drift direction compared to the favorable configuration. This reduction in fueling is not compensated by the ∼30% increase in ionization rate at the LFS. Meanwhile, in the unfavorable drift direction, the pedestal electron density (temperature) is decreased (increased) and overall, the pedestal electron pressure is improved by ∼25%. This observation implies that changes in the magnetic configuration and the resulting effect on main chamber fueling could possibly impact the pedestal performance. This contribution will also report on the effect of main SOL flows [2] on the observed main chamber fueling asymmetries.

[1] Rosenthal RSI 92, 033523 (2021)

[2] Wilkie NF 64 086028 (2024)

[3] Rognlien NME 12 44–50 (2017)

[4] Laggner RSI 92, 033522 (2021)