Separating Convective and Diffusive Main Ion Particle Transport in the Tokamak Pedestal with Experimental Ionization Source Measurements

Quantitative edge ionization source measurements and plasma profiles during dynamic events, such as the edge localized mode (ELM) cycle and edge gas puff modulation, allows disentanglement of the relative contributions of diffusion and convection to forming the edge density profile. H-mode density pedestal rebuild after ELMs on the DIII-D tokamak show quantitative evidence of a 5 m/s inward particle pinch and 0.2 m²/s diffusion near the top of the density pedestal. Throughout the density pedestal rebuild and during steady state, inboard and outboard ionization source measurements show a significant asymmetry confirming strong poloidal variation of the ionization source.

Prediction capabilities remain limited for the tokamak edge density profile due to small spatial scales, complex plasma transport and non-negligible effects of neutral particles. Millisecond time resolution of the deuterium ionization source and neutral density from absolutely calibrated Lyman-alpha brightness measurements, allow direct quantitative comparison to the edge density profile. Coupled to advances in inference techniques from the Aurora code, a flux surface average particle transport and radiation forward model, diffusion and convection profiles in the steep density gradient can be calculated. Main ion transport profiles and experimental neutral particle measurements allow quantitative evaluation of the processes forming the density pedestal and constrain modern 2D edge codes, benchmarking their modeling of current devices, thereby, improving their predictive capabilities for future burning plasma devices.