Characterization of X-point radiation (XPR) operational space and divertor conditions in DIII-D H-mode discharges

X-point radiation (XPR) experiments in the DIII-D tokamak (I_p=0.8-1.3 MA, P_inj= 6-12 MW) explored XPR conditions with ELM mitigation relevant to divertor operation in future devices while collecting detailed measurements of plasma parameters at the radiation front for characterization of access to XPR, its impact on pedestal, and validation of radiation stability models. Stable XPR was accessed from detached conditions via impurity seeding (CD₄, N₂). Similarly to ASDEX Upgrade, access to XPR regimes was accompanied by a reduction in confinement up to 20% compared to detached conditions, with a decrease in pedestal temperatures at nearly unchanged pedestal densities. A narrower operating space was observed with C as the dominant radiator, consistently with theory. Divertor Thomson scattering measurements inside the X-point indicate T_e ~1-2eV with up to a 5-10× reduction in electron pressure with respect to upstream pressure in the confined plasma in the last 1% of ψ_N. Penetration of the radiation front inside the X-point was accompanied by ELM mitigation from ΔW_ELM/W~1.2-1.5% to ΔW_ELM/W~0.3-0.5%. The energy lost per ELM and the peak divertor heat fluxes were largely reduced by 4× and 10× respectively, indicating increased ELM buffering. While at the highest plasma current (I_p) deeper X-point radiation resulted in a back-transition to L-mode maintaining radiation inside the X-point without unstable MARFE evolution, at lower I_p deep X-point radiation resulted in an unstable high field side MARFE.