Experiments and Modeling on the Influence of Main Ion Mass in the Pedestal and Scrape-Off Layer of DIII-D

The pedestal and divertor of H-mode hydrogen (H) plasmas have been characterized and compared to similar deuterium (D) plasmas under a range of conditions in order to assess the impact of ion mass on these regions. In H, higher electron densities are measured at the outer target despite having similar outer target temperatures as the D references. Upstream density at detachment onset is increased only 5% for H over D. Heat flux to the target is consistently measured to be 2 times higher in H with no significant reduction in peak values associated with detachment, suggesting a change in SOL energy transport mechanisms. H pedestal profiles show evidence of an increased particle source inside the confined region with the pedestal top density increasing independently of core density. Higher neutral pressure throughout the chamber in H is identified as a driving factor in this change, with divertor detachment greatly exacerbating this effect. In interpretive SOLPS-ITER modeling, H+C simulations reach detached conditions at a 10% higher upstream density than D+C, consistent with experiment. However, the experimentally observed changes to parallel heat flux are not captured. Higher neutral ionization rates are found within the LCFS in the H+C simulations.