Extending Modulation Transport Studies to the Pedestal with Edge Particle Source Measurements in DIII-D

Particle transport coefficients are obtained in the pedestal region of DIII-D by utilizing absolutely calibrated source measurements in a time-dependent forward modeling framework, in order to explore transport dependence on factors such as the curvature pinch via normalized safety factor gradient. The diffusion and convection coefficients influence the shape of the density pedestal. We extract the transport coefficients through gas puff modulation. This technique is often employed for core transport, where the modulated and fixed ionization source from the gas puff and wall recycling is negligible [1]. To extend this technique to the pedestal, we require absolute edge particle source measurements from the LLAMA Lyman-alpha diagnostic [2] that are utilized in time-dependent forward modeling with Bayesian inference to optimize a diffusion and convection profile against density profile measurements. This method allows for separation of diffusion and convection terms by exploring the evolution of the density profile through dynamic events such as gas puff modulation or recent work on the inter-ELM rebuild cycle. [3]

[1] S. Mordijck 2020 Nucl. Fusion 60 082006

[2] A.M. Rosenthal et al 2021 Rev. Sci. Instrum. 92 033523

[3] A.M. Rosenthal et al 2023 Nucl. Fusion 63 042002