The Ionization peak location in the determination of neutral opaqueness in DIII-D plasmas*

An experimental database leveraging Lyman-alpha measurements at the pedestal of DIII-D H-mode plasmas shows a reduced penetration of neutrals as a function of the electron pedestal density as theoretically predicted. This correlation deviates at lower electron pedestal densities, and the neutral penetration can increase if the ionization peak is inside the separatrix. The fueling impact on the pedestal density is poorly understood in current devices and is expected to be reduced in ITER and fusion pilot plants. The database focuses on lower single-null ELMy H-mode discharges with favorable magnetic drift stationary conditions with energy confinement time ~100-200ms, being limited to 80-99% of the ELM cycle. The Thomson Scattering electron density and temperature are fitted using a tanh at each time slice, and the separatrix location is determined using power balance. The neutral density profile is measured by LLAMA diagnostic and fitted with an exponential n₀(r)=n_0,sep Exp((r-rsep)/λ_n0), being λ_n0 the neutral penetration, which is used to compare the opaqueness, △_e,ped/λ_n0 using the pedestal width △_e,ped, with the heuristic opaqueness  a x n, being a the minor radius and n the average of  n_e,sep and n_e,ped.