Role of neutral particles on pedestal structure for H-mode experiments in DIII-D

We present a database study investigating the role of fueling versus plasma parameters in determining the separatrix and pedestal electron density for DIII-D H-mode plasmas.

The database consists of multiple equilibrium (100-200ms stationary) lower single null ELMy H-mode discharges with engineering parameters ranging over toroidal magnetic field $B_{T}$ in [1.2, 2.2] (T), plasma current $I_{P}$ in [1.0, 1.8] (MA), Neutral Beam power $P_{NBI}$ in [1.0,13.0] (MW), safety factor $q_{95}$ in [3.0, 6.5]. Data in 50-98% of the ELM cycle are included. In our analysis, we will be able to infer neutral density profiles from the LLAMA diagnostic. The profiles of neutral density are fitted with an exponential function which allows us to link the neutral density at the separatrix and neutral penetration directly to the pressure in the divertor, gas fueling rate as well as plasma and operational parameters. The preliminary results indicate a correlation between the decrease of the neutral density in the separatrix (LFS) and the increase of the total power injected but this correlation is reversed, increasing of neutral separatrix density (LFS) with total power injected, if the toroidal magnetic field is reversed. It was also observed that the neutral density on the separatrix decays to a minimum value and less scattered for separatrix temperatures greater than 100 eV.