2D characterization and boundary model validation of radiative divertor regimes with impurity seeding in the DIII-D divertor

Radiative divertor regimes are characterized and modeled in DIII-D H-mode discharges via measurement of divertor radiated power constituents and concentrations of intrinsic and seeded impurities in the divertor and confined plasma. In lower single null H-mode discharges (P_NBI=3-10 MW, I_p=1.3 MA), carbon concentrations f_C in the outer divertor were reduced with density in attached conditions (from ~5 to 2%). In fully detached condition, f_C at the radiation front was further reduced to below 1%. In nitrogen-seeded radiative divertors, no reduction in divertor f_C was observed, with the reduced carbon contribution to radiation driven by a drop in n_e and the total P_rad sustained by a higher total impurity concentration f_Z=f_C+f_N. In fully detached conditions, f_Z scaled with SOL power and inversely with n_e at the radiation front. Multi-fluid UEDGE simulations with inclusion of cross field drifts and charge state resolved C and N impurity species can match measured line-integrated emission and radiated power share while local emissivities and f_Z are higher than those derived experimentally. Recent experiments extended seeded divertor characterization to plasma currents of 0.9-1.5 MA to explore dependence on SOL heat channel width and seeded impurity species N, and Ne.